Highlights
We are looking for excellent and highly motivated candidates for several PhD, Postdoc and engineer positions in the SALD team. Check regularly here (link) for details. If you are interested in joining our team, send an email with CV and cover letter to this address
2024-04-01. We welcome Vijaya Shanti PAUL RAJ, new postdoc in the team!!
2024-03-21. Gaining understanding on recombination junctions for tandem solar cells. Congratulations to Pía!
Optical, electrical and chemical characterization of inorganic hole-transporting materials for the recombination junction in two-terminal perovskite / silicon heterojunction solar cells
Solar Energy, accepted
The properties of inorganic thin films (20 nm) featuring indium-free junctions between bottom and top cell of two-terminal perovskite/silicon heterojunction tandem structures have been investigated, namely p-doped hydrogenated nanocrystalline silicon, molybdenum and tungsten oxide, and cuprous oxide. Systematic characterization of the optical, structural and electrical properties of these materials deposited on SHJ substrates, compared to those of glass- and crystalline silicon reference samples is carried out and the validity of fast, reference characterization versus more complex, complete solar cell stack characterization is assessed. Spin coating deposition of wide bandgap (Eg = 1.73 eV) perovskite formulation in all substrates was chemically characterized. Results indicate that deposition of all HTL materials do not impact SHJ substrate passivation, or its optical properties. At a chemical level, high surface energy of (p+)nc-Si:H and MoOx, WOx surfaces allow proper perovskite deposition without need of surface treatment, evidenced by X-Ray diffraction and photoluminiscence spectroscopy measurements. Energy bandgaps of perovskite were measured around the nominal value of 1.75 eV, and PbI2/ PK ratios lower than 0.2, with the expected cubic phase and preferred crystalline orientations in the [0 1 1] family of planes. Perovskite crystallization on Cu2O surface shows prevailing PbI2 phases with a blueshifted Eg, therefore, the as-deposited thin film does not favor perovskite nucleation and needs further investigation.
2024-03-19. We welcome Tongwei Zhu, master 1 internship student, in the team in colaboration with G-SCOP!!
2024-02-19. ITO-free transparent electrode for electrochromic applications. Congratulations to Ambreen!
Silver Nanowires-based Transparent Electrodes for V2O5 Thin Films with Electrochromic Properties
ACS Applied Materials and Interfaces, 2024, 16, 8, 10439–10449
The development of electrochromic systems, known for the modulation of their optical properties under an applied voltage, depends on the replacement of the state-of-the-art ITO (In2O3:Sn) transparent electrode (TE) as well as the improvement of electrochromic films. This study presents an innovative ITO-free electrochromic film architecture utilizing oxide-coated silver nanowire (AgNW) networks as a TE and V2O5 as an electrochromic oxide layer. The TE was prepared by simple spray deposition of AgNWs that allowed for tuning different densities of the network and hence the resistance and transparency of the film. The conformal oxide coating (SnO2 or ZnO) on AgNWs was deposited by atmospheric-pressure spatial atomic layer deposition, an open-air fast and scalable process yielding a highly stable electrode. V2O5 thin films were then deposited by radio frequency magnetron sputtering on the AgNW-based TE. Independent of the oxide’s nature, a 20 nm protective layer thickness was insufficient to prevent the deterioration of the AgNW network during V2O5 deposition. On the contrary, crystalline V2O5 films were grown on 30 nm thick ZnO or SnO2-coated AgNWs, exhibiting a typical orange color. Electrochromic characterization demonstrated that only V2O5 films deposited on 30 nm thick SnO2-coated AgNW showed characteristic oxidation–reduction peaks in the Li+-based liquid electrolyte associated with a reversible orange-to-blue color switch for at least 500 cycles. The electrochromic key properties of AgNW/SnO2 (30 nm)/V2O5 films are discussed in terms of structural and morphological changes due to the AgNW network and the nature and thickness of the two protective oxide coatings.
2024-01-01. We welcome Pía Vasquez-Rivera as new postdoc in the team!!
2023-11-28. Congratulations to Pía for passing his PhD viva!!! Great job!!!
2023-11-24 Congratulations to Hayri for getting the prize to the best oral presentation in the Rafald Workshop 2023 in Lille!
2023-11-21. Probing the structural evolution of AgNW networks. Congratulations to Laetitia and Masoud!
Exploring the Degradation of Silver Nanowire Networks under Thermal Stress by Coupling In Situ X-Ray Diffraction and Electrical Resistance Measurements
Nanoscale, Accepted
The thermal instability of silver nanowires (AgNWs) leads to a significant increase of the electrical resistance of AgNW networks. A better understanding of the relationship between the structural evolution of the wires during thermal stress and the resulting electrical properties of AgNW networks is primordial for their efficient integration as transparent electrodes (TEs) for the next generation of In-free and flexible optoelectronics. In this work we present a combined in situ study of the evolution of the structural and electrical properties of AgNWs netwroks when subjected to thermal stress. In particular, the evolution of several important crystallographic parameters (i.e. integrated intensity, interplanar spacing and peak broadening) of two Ag-specific Bragg peaks, (111) and (200), during a thermal ramp up to 400 °C has been evaluated through in situ X-ray diffraction (XRD) measurements, coupled with in situ electrical resistance measurements on the same AgNW network. First, we assign the (111) and (200) peaks of χ-scans to each ive crystallites within AgNWs thanks to rotation matrices model. Then, we show that the thermal transition of bare AgNW networks occurs within a temperature range of about 25 °C for the electrical properties, while for the structural properties the transition spans over 200 °C. The effect of a protective tin oxide coating (Sn02) on AgNW networks is also investigated through this original in situ coupling approach. For Sn02-coated AgNW networks, the key XRD signatures from AgNWs remain constant, since the SnO2 coating prevents Ag atomic surface diffusion, and thus AgNW spheroidization. Moreover, the SnO2 coating does not affect the strain of both (111) and (200) planes. The thermal expansion for bare and Sn02-coated AgNW networks appears very similar to the thermal expansion of bulk Ag. Our findings provide insights into the underlying failure mechanisms of AgNW networks subjected to thermal stress, helping researchers to develop more robust and durable nanomaterials.
2023-11-15. Review on the ALD of Pd. Congratulations to Matthieu and Clement!
Atomic layer deposition (ALD) of palladium: from processes to applications
Critical Reviews in Solid State and Materials Sciences , Accepted
Atomic layer deposition (ALD) has been successfully used for the deposition of palladium (Pd) thin films and nanostructures, with a wide range of applications in fields such as microelectronics, energy conversion, sensors, catalysis, membranes, and sensing devices. Thanks to the self-saturating and surface-selective nature of ALD, it allows for precise control of the amount of Pd deposited on challenging surfaces with different precursor chemistries and customizable processing conditions. This technique can produce low-dimensional nanostructures such as single atoms, nanoclusters, core/shell nanoparticles, and ultrathin continuous films. This article provides an overview of the Pd ALD processes and studies reported to date, highlighting the various precursor chemistries used and the intended applications of the prepared nanostructures. This review opens up prospects and demonstrates the potential of using Pd nanomaterials produced through ALD in real devices.
2023-10-11. We welcome PHD student Stefano D'Ercole to the team!!
onlinelibrary.wiley.com/doi/10.1002/admt.202301143 2023-10-10. MgO coating by SALD to stabilize AgNW networks. Congratulations to Abdou and Dorina!
Highly Transparent and Stable Flexible Electrodes based on MgO/AgNW nanocomposites for transparent heating applications
Advanced Materials Technologies, accepted.
Transparent electrodes (TE) based on silver nanowire (AgNW) exhibit good physical properties and constitute a promising alternative to transparent conductive oxides due to their low cost, flexibility, and low toxicity. Nevertheless, they suffer from stability issues over harsh conditions, and encapsulation allows to overcome these limitations. Herein, we report the low-cost, scalable fabrication and study of transparent electrodes based on sprayed AgNW networks coated with MgO thin films deposited by atmospheric pressure spatial atomic layer deposition (AP-SALD) at mild deposition temperature (≤220 °C). Fabrication of MgO thin films by AP-SALD is reported here for the first time, and their deposition on different substrates have been optimized. MgO exhibits a pure phase and conformal growth with a preferential (220) crystalline orientation and a higher growth rate as compared to conventional atomic layer deposition (ALD). Furthermore, thanks to the conformal coating of MgO on AgNW, the obtained nanocomposites exhibit great optical transparency of ~ 85% and flexibility while maintaining high stability under thermal and electrical stress. Indeed, this study shows a clear enhancement of the stability of AgNW networks for thin MgO coatings of only few nanometers thick. Finally, a proof-of-concept transparent heater has been fabricated to melt a piece of cheese.
2023-10-01. We welcome Keerati Meporn as visiting postdoc to the team!!
2023-09-23. Congratulations to Masoud for passing his PhD viva!!! Great job!!!
2023-09-21. SALD is greener than ALD. Congratulations to Farooq and Matthieu!!
Comparative study of the environmental impact of depositing Al2O3 by Atomic Layer Deposition and Spatial Atomic Layer Deposition.
ACS Sustainable Chemistry & Engineering, accepted.
With increasing concerns about the environmental impacts of human activities, novel nanotechnologies and nanomaterials are being explored as key solutions to tackle pollution and pave the way for a more sustainable future. One such technology that has gained attention is Atomic Layer Deposition (ALD), which can be used to prepare thin films with precise control over thickness and composition. Spatial ALD (SALD), in particular, presents high deposition rates and can be performed at high pressure, and has emerged as a promising alternative to conventional ALD. However, to the best of our knowledge, there is no literature reporting on its environmental performance compared to that of ALD. Herein, we present a comparative life cycle assessment (LCA) study between conventional ALD and SALD to quantify and compare their environmental impacts. The study focuses on the deposition of a 20 nm alumina thin film from TMA (trimethylaluminum) and water at 200 °C as the functional unit, considering the use of typical lab-scale reactors, the SALD being based on the close-proximity approach. Different region-based scenarios were evaluated, considering the film production in Europe, in France and in Taiwan. The assessments obtained revealed that electricity consumption was the primary contributor to most impact categories for both ALD and SALD processes, followed by the TMA precursor. The results indicated that, for the alumina process and the assumptions considered, SALD had a notably better environmental performance than ALD for the majority of assessed impact categories, in all three regions considered.
2023-08-21. Better PV HET modules with less indium. Congratulations to Tristan!
Feasibility test of drastic indium cut down in SHJ solar cells and modules using ultra-thin ITO layers
In this work, we investigate the possibility to drastically decrease the indium (In) consumption in silicon heterojunction (SHJ) solar cells, using ultrathin (<15 nm) ITO layers on both cell sides, in combination with SiN:H capping dielectric layers. The best ITO/dielectric combinations were assessed using optical simulations. The optimal stacks were integrated on front, rear, and both sides of complete SHJ cells. Two types of nanocrystalline layers (nc-Si:H and nc-SiOx:H) were implemented as selective layers on the front side, and proved to relax the constraints on the front ITO conductivity. Among all conditions including 100 nm references, the highest module efficiencies were obtained with 15 nm front ITO (22.4%), while modules with ITO layers below 10 nm on nc-Si:H showed very low efficiency losses compared to the reference. Integration of such ultrathin ITO layers on the rear side proved to be non-optimal since the Fill Factor (FF) losses are not counterbalanced with current gains (contrary to what is observed on the front side with ultra-thin ITO). Finally, UV reliability tests were performed and showed an enhanced reliability for modules with thinner ITO layers. After 60 kW h.m−2 of UV exposure, modules with 5 nm ITO on nc-Si:H showed the best efficiencies among all tested conditions. Subsequent damp heat tests were also performed and did not show a clear warning against using ultrathin ITOs on the front side, and in the end, modules with nc-Si:H layers feature the highest efficiencies at the end of the reliability sequence.
2023-07-31. SALD and laser for fast and cheap colouring. A nice collaborative work with INMA in Saragosa, Spain, with the participation of our visitors Alejandro Frechilla (INMA) and Francesca lo Presti (University of Catania)!
Generating colours through a novel approach based on spatial ALD and laser processing
This work studies the combination of direct femtosecond laser structuring of metal surfaces and Spatial Atomic Layer Deposition (SALD) of metal oxides as a novel approach to generate colours on different types of day-to-day metallic objects. In particular, a stainless-steel knife and an outdated 25 ct Dutch florin coin have been selected for the study. Our results show that it is possible both, to preserve the iridescence properties produced by laser processing and to tune the final metal surface colour by controlling the thickness of the ZnO coating. At the same time, this oxide coating could act as a protecting layer for the original material. We thus explore two different strategies to generate colour, namely, iridescence and interference, which can be even developed selectively. This novel methodology to colour metallic surfaces is a promising route to achieve cheap, scalable, and high-throughput processing methods and opens up a new avenue of possibilities and applications related to colour.
2023-07-31. Congratulation to Hayri, whose design has been chosen for the LMGP presentation template!
2023-07-22. Modeling the behaviour of bare and coated AgNW networks. Congratulations to Laeti and Masoud!
SnO2-Coated Silver Nanowire Networks as a Physical Model Describing their Reversible Domain under Electrical Stress for Stable Transparent Electrode Applications
Thermal, electrical, and chemical instabilities affect the efficient integration of silver nanowire (AgNW) networks as transparent electrodes for energy and wearable electronics. By coupling experimental data and a simple physical model, we deduce the electrical areal power density ranges that AgNW networks can withstand, to observe either reversible modifications (i.e., electron–phonon interaction) or irreversible modifications (i.e., electrical sintering or degradation). This approach also allows us to predict the associated Joule heating temperature in the reversible domain for any applied voltage and initial resistance. It constitutes an efficient guide to design any device incorporating AgNW networks in which electrical current is applied. To improve AgNW stability, tin oxide (SnO2) coating has been deposited by atmospheric-pressure spatial atomic layer deposition at 200 °C. For a similar initial resistance, the observed maximum areal power density increases from 1.6 to 3.3 W cm–2 for bare AgNWs and 40 nm-SnO2/AgNW networks, respectively, and their associated Joule heating temperatures are 220 and 410 °C, respectively. In addition to the high electrical stability of SnO2/AgNW nanocomposites, we demonstrate their enhanced stability when exposed to either thermal stress up to 400 °C, or environmental stress with 80% of relative humidity at 70 °C for 2 weeks.
2023-06-20 Our recent paper on the environmental impact of ALD highlighted in the CNRS INC site!
https://www.inc.cnrs.fr/fr/cnrsinfo/diminuer-lempreinte-carbone-des-nanotechnologies
2023-06-15 Congratulations to LIam and Ambreen for getting the best 1st year PhD student presentation and best 2nd year PhD student poster during the LMGP scientific days!!!
2023-06-15 The SALD team, during the LMGP scientific Days!
2023-06-12 New approach to control texture and other thin film properties. Congratulations to Chiara!
Tuning the Texture and Polarity of ZnO Thin Films deposited by Spatial Atomic Layer Deposition with a Volatile Shape-Directing Agent
Materialia, accepted.
Many functional devices are nowadays based on thin films deposited by physical or chemical vapour deposition methods. Being able to control the texture of the films is very important to tune their functional properties. Texture is commonly tuned by either using single crystalline substrates or seed layers, or by modifying the deposition parameters (gas flows, precursor concentration, temperature, etc.). In this study a volatile shape-directing agent (VSDA), namely 4-(5)-Methylimidazole (4-(5)-MeIM), is used during the deposition of ZnO thin films by Atmospheric-Pressure Spatial Atomic Layer Deposition (AP-SALD) to control the texture and growth rate of the films. In particular, ZnO thin films can be grown preferentially along (002), resulting in an enhanced piezoelectric coefficient. In addition, the polarity of the ZnO films also depends on the amount of VSDA used. An innovative industry-compatible approach to control texture and polarity of ZnO thin films is presented, having a clear potential for other functional materials and applications.
2023-05-09 We welcome Terence COHEN to the SALD team for his M1 internship!
2023-05-02 We welcome Xinyi JAW to the SALD team for his PHELMA Prepa internship!
2023-04-27 Mapping CVD vs ALD regime in SALD.
Can we rationally design and operate spatial atomic layer deposition systems for steering the growth regime of thin films?
J. Phys. Chem. C, Accepted
Fine control over the growth of materials is required to precisely tailor their properties. Spatial atomic layer deposition (SALD) is a thin-film deposition technique that has recently attracted attention because it allows producing thin films with a precise number of deposited layers, while being vacuum-free and much faster than conventional atomic layer deposition. SALD can be used to grow films in the atomic layer deposition or chemical vapor deposition regimes, depending on the extent of precursor intermixing. Precursor intermixing is strongly influenced by the SALD head design and operating conditions, both of which affect film growth in complex ways, making it difficult to predict the growth regime prior to depositions. Here, we used numerical simulation to systematically study how to rationally design and operate SALD systems for growing thin films in different growth regimes. We developed design maps and a predictive equation allowing us to predict the growth regime as a function of the design parameters and operation conditions. The predicted growth regimes match those observed in depositions performed for various conditions. The developed design maps and predictive equation empower researchers in designing, operating, and optimizing SALD systems, while offering a convenient way to screen deposition parameters, prior to experimentation.
2023-03-28 Looking into how green ALD is. Congrats to Matthieu!
Assessing the environmental impact of Atomic Layer Deposition (ALD) processes and pathways to lower it.
ACS Materials Au, Accepted
Due to concerns on resources depletion, climate change and overall pollution, the quest toward more sustainable processes is becoming crucial. ALD is a versatile technology, allowing for the precise coating of challenging substrates with a nanometer control over thickness. Due to its unique ability to nanoengineer interfaces and surfaces, ALD is widely used in many applications. Although the ALD technique offers the potential to tackle environmental challenges, in particular, renewable energy devices sustainability considerations urge for greater efficiency and lower carbon footprint. Indeed, the process itself has currently a consequent impact on the environment, which should ideally be reduced as the technique is implemented in a wider range of products and applications. This paper reviews the studies carried out on the assessment of the environmental impact of ALD and summarizes the main results reported in the literature. Next, the principles of green chemistry are discussed, considering the specificities of the ALD process. This work also suggests future pathways to reduce the ALD environmental impact, in particular, the optimization of the reactor and processing parameters, the use of high throughput processes such as spatial ALD (SALD), and the chemical design of greener precursors are proposed as efficient routes to improve ALD sustainability.
2023-02-02 Controling the oxidation state of Cu in thin films deposited in the open air. Congrats to Abdou!
Selective spatial atomic layer deposition of Cu, Cu2O and CuO thin films in the open air: reality or fiction?
Materials Today Chemistry, Accepted
Copper and binary copper oxide thin films are key materials for microelectronic, optoelectronic, and sensing devices. Herein, we report innovative atmospheric-pressure spatial atomic layer deposition (AP-SALD) processes enabling the facile control over the copper oxidation state. The selective deposition of Cu, Cu2O, and CuO thin films at low temperatures (160 -260 °C) has been achieved by using Cu(I)(hfac)(tmvs) as copper source and nitrogen, water, or ozone as co-reactants, respectively. The three obtained materials are pure and crystalline, as revealed by X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). The deposition mechanism of the Cu, Cu2O, and CuO phases is based on disproportionation, hydrolysis, and oxidation reactions. Interestingly, metallic copper films with resistivity as low as ~3.7x10-6 Ω.cm have been obtained, and resistivity values of 100 Ω.cm and 0.2 Ω.cm have been measured for the Cu2O and CuO semiconductor layers, respectively. Although working in an open-air environment, the oxidation state of copper-based thin films can be controlled using the same precursor, thus reducing cross-contamination and allowing for a faster and more reliable process. This demonstrates the versatility of AP-SALD, and open prospects for the manufacturing of novel devices such as wearables, sensors, or flexible electronics.
2023-02-16 We welcome Samuel Porcar García, visiting PhD from University Jaume I (Castellón, Spain), who's going to be in the team till mid April
2023-01-30 We welcome Farooq NIAZI to the SALD team for his M2 research internship!
2022-12-16 Our last results in collaboration with CENIMAT have been highlighted in the press:
https://thenextbigidea.pt/vidros-do-carro-congelados-no-inverno-ha-forma-de-nao-voltar-a-acontecer/
2022-11-21 Transparent electrodes from solution. Congratulations Dornia!
Fully solution-based AgNW/AlOx nanocomposites for stable transparent heaters
ACS Applied Electronic Materials, Accepted
Transparent heaters (TH) have a lot of potential in flexible and wearable applications. Consequently, interest in using nanomaterials, such as metallic networks, grids, and meshes, has expanded as alternative to conventional transparent conductive oxides like indium tin oxide. In particular, silver nanowire (AgNW) networks are very promising transparent and flexible electrodes thanks to their optimum physical properties and the possibility to obtain them by low-cost fabrication techniques. However, AgNW networks suffer from instabilities that affect their electrical performance at high operating voltages or over time and thus require a protective layer, often deposited by vacuum-based techniques. In this work, we implemented a low-cost solution-based aluminum oxide (AlOx) coating produced by combustion synthesis to encapsulate spray-coated AgNW networks. The TH with an AlOx coating obtained from a 0.4 M precursor solution concentration presents the best compromise between optical transmittance and electrical resistance. Besides this, such coating provides a robust protection against corrosion under accelerated environmental stress (relative humidity = 80%; temperature = 70 °C) up to 7 days. As a proof-of-concept, a 50×50 mm2 TH was fabricated and tested as defroster (down to – 21 °C) showing a highly reproducible heating performance (up to 90 °C at 6 V) and stability for 12 hours. In addition, different morphologies of the AlOx thin film, namely smooth or porous, can be obtained when either conventional thermal annealing or Joule heating of AgNWs is used, respectively, to carry out the combustion reaction. This offers a promising tunability for different final applications.
2022-11-17 Efficient and Low-Cost Transparent all-oxide Diodes.
n-ZnO/Out-of-Stoichiometry p-CuCrO2 Diodes for Efficient and Low-Cost Transparent Electronic Applications
ACS Applied Electronic Materials, Accepted
In this work, we present the synthesis of high-performance transparent diodes based on p-type out-of-stoichiometry CuCrO2 and n-type ZnO thin films. The oxides were fabricated by scalable chemical deposition methods at low temperature and ambient pressure, without any further postdeposition annealing treatment. We report the optimization of the devices through the fine-tuning of the deposition parameters of the two layers, namely, the composition of the p-type semiconductor and the deposition temperature of the n-type counterpart, and their thorough characterization. UV–vis spectroscopy measurements highlighted the antireflection function of the ZnO layer, resulting in an optical transmittance of the junction above 75% in the visible range. In-depth XPS profile studies confirmed the absence of atomic diffusion between the different layers. The optimized junction between a nanocomposite Cu2O+CuCrO2 coupled with polycrystalline ZnO presents the highest rectification ratio reported in the literature for similar devices, with values greater than 105 between −2.5 and +2.5 V. These extremely high performances are attributed to the formation of intraband levels, due to the stoichiometry variation of the CuCrO2 phase and the low crystallinity of n-type ZnO. These results open many prospects for optoelectronics and are particularly promising for the transparent oxide electronics industry..
22-11-04 Part of the SALD team in the RAFALD SALAD school last week
2022-11-04 We welcome PhD Hayri Okcu to the SALD team!!
2022-11-01 Our recent paper in ACS SC&E featured as a supplementary cover!
2022-10-18 SALD is moving beyond planar substrates! Congratulations to Fidel!
Custom 3D Printed Spatial Atomic Layer Deposition Manifold for the Coating of Tubular Membranes.
ACS Sustainable Chemistry & Engineering, Accepted
The development of highly efficient membranes represents a great opportunity to significantly reduce the environmental impacts of human activities through gas separation and water filtration, and are also very attractive for process intensification when coupled to existing industrial processes. Tubular membranes have higher modularity, better pressure resistance, and they offer easier sealing than their flat counterparts. The ability to deposit thin films on their surface is crucial to optimize their chemical and physical properties. However, the deposition of thin films on tubular membrane supports with conventional vacuum-based deposition techniques is relatively complex, slow and costly. In this work the versatility of spatial atomic layer deposition (SALD) and 3D printing technologies has been combined to design and fabricate a custom SALD manifold for coating tubular substrates. SALD is a scalable deposition technique, offering high-throughput at atmospheric pressure and thus can be advantageously employed to coat tubular membranes, enabling high quality thin films to be deposited at the nanoscale considerably faster than with other conventional techniques. Computational fluid dynamics (CFD) calculations by means of COMSOL Multiphysics have been used to optimize this innovative SALD gas manifold. The proof-of-concept of the new SALD manifold has been validated through successful ZnO thin film depositions performed on tubular Cu foils and porous Al2O3 tubular membrane supports, demonstrating the capability of SALD to achieve high-throughput depositions on non-planar, complex substrates. These results open prospects for the interface engineering of membranes or electrolyzers, where precise coatings of tubular surfaces are needed.
2022-10-03 We welcome postdoc Antoine DUHAIN to the SALD team to work in the EPISTORE project in collaboration with the Nanoionics team.
2022-10-03 We welcome PhD student Liam JOHNSTON to the SALD team to work in the ANRI REACTIVE project.
2022-09-12 We welcome Francesca Lo Presti, visiting PhD from University of Catania (Italy), who's going to be in the team till the end of December
2022-09-09 AP-SALD Cu2O thin films show record conductivity, thanks to some extra oxygen during deposition. Congratulations to Abdou!!
Chemical deposition of Cu2O films with ultra-low resistivity: Correlation with the defect landscape.
Nature Communications. Accepted
Cuprous oxide (Cu2O) is a promising p-type semiconductor material for many applications. So far, the lowest resistivity values are obtained for films deposited by physical methods and/or at high temperatures (~1000 °C), limiting their mass integration. Here, Cu2O thin films with ultra-low resistivity values of 0.4 Ω.cm were deposited at only 260 °C by atmospheric pressure spatial atomic layer deposition, a scalable chemical approach. The carrier concentration (7.1014-2.1018 cm-3), mobility (1- 86 cm2/V.s), and optical bandgap (2.2-2.48 eV) are easily tuned by adjusting the fraction of oxygen used during deposition. The properties of the films are correlated to the defect landscape, as revealed by a combination of techniques (positron annihilation spectroscopy (PAS), Raman spectroscopy and photoluminescence). Our results reveal the existence of large complex defects and the decrease of the overall defect concentration in the films with increasing oxygen fraction used during deposition.
2022-07-21 End of season lunch with the SALD team. And our farewell to Abdou, Octavio, Ambre, Soline, Thomas, Dorina and Ozden who are moving on towards new scientific adventures! All the best for them!
2022-7-2 Microfluidic chips with cheap customizable heating for in situ studies. Congratulations to Dorina!!
Stable flexible transparent electrodes for localized heating of lab-on-a-chip devices
In situ biological observations require stable, accurate and local temperature control of specimen. Several heating elements are coupled with microfluidic systems, but few of them are transparent to visible light and therefore compatible with microscopic observation. Traditional transparent electrodes such as indium tin oxide, still suffer from high fabrication cost and brittleness, which is not fully compatible to emerging microfluidic devices. Here, we propose a lightweight, low-cost, flexible transparent heater based on percolating silver nanowire networks, protected with a transparent zinc oxide film, for the in situ monitoring of biological experiments. Using the fluorescence of dyes bound to double-stranded DNA to monitor its temperature in situ, we demonstrate that such nanocomposites allow rapid and reproducible heating under low applied voltage. Furthermore, selective heating is achieved in different zones of the same microchannel or for adjacent microchannels of the chip heating at different temperatures, with a single transparent heater and bias.
2022-06-23 Congratulations to Abdou Sekkat for winning a best thesis prize from the French Chemical Society, Solid State Chemistry Division!!!
2022-6-7 New SALD process for the deposition of SnO2 thin films!.
Atmospheric atomic layer deposition of SnO2 thin films with tin(ii) acetylacetonate and water
Dalton Transactions. Accepted
Due to its unique optical, electrical, and chemical properties, tin dioxide (SnO2) thin films attract enormous attention as a potential material for gas sensors, catalysis, low-emissivity coatings for smart windows, transparent electrodes for low-cost solar cells, etc. However, the low-cost and high-throughput fabrication of SnO2 thin films without producing corrosive or toxic by-products remains challenging. One appealing deposition technique, particularly well-adapted to films presenting nanometric thickness is atomic layer deposition (ALD). In this work, several metalorganic tin-based complexes, namely, tin(IV) tert-butoxide, bis[bis(trimethylsilyl)amino] tin(II), dibutyltin diacetate, tin(II) acetylacetonate, tetrakis(dimethylamino) tin(IV), and dibutyltin bis(acetylacetonate), were explored thanks to DFT calculations. Our theoretical calculations suggest that the three last precursors are very appealing for ALD of SnO2 thin films. The potential use of these precursors for atmospheric-pressure spatial atomic layer deposition (AP-SALD) is also discussed. For the first time, we experimentally demonstrate the AP-SALD growth of SnO2 thin films using tin(II) acetylacetonate (Sn(acac)2) and water. We observe that Sn(acac)2 exhibits efficient ALD activity with a relatively large ALD temperature window (140–200 °C), resulting in a growth rate of 0.85 ± 0.03 Å per cyc. XPS analyses show a single Sn 3d5/2 characteristic peak for Sn4+ at 486.8 ± 0.3 eV, indicating that a pure SnO2 phase is obtained within the ALD temperature window. The as-deposited SnO2 thin films are in all cases amorphous, and film conductivity increases with the deposition temperature. Hall effect measurements confirm the n-type nature of SnO2 with a free electron density of about 8 × 1019 cm−3, electron mobility up to 11.2 cm2 V−1 s−1, and resistivity of 7 × 10−3 Ω cm for samples deposited at 270 °C.
2022-05-25 Our recent review on TCM based on metallic nanostructures has made the inside front cover of Small!
2022-05-25 Congratulations to Abdou Sekkat for winning one of the 7 UGA thesis prizes!
2022-05-24 Our recent simulation results on Cu2O/ZnO solar cells have made the cover of ACS Applied Energy Materials!
2022-05-23 We welcome Ambre DECILAP to the SALD team for her GIANT research internship!
2022-05-02 We welcome Soline BEITONE to the SALD team for her M1 research internship!
2022-04-04 We welcome Thomas GHEORGHIN to the SALD team to work in a joint project with the IMBM team at LMGP
2022-3-3 Open-air fabrication of self-standing oxide cantilever sensors. Great collaboration with K. Musselman's team at U. Waterloo.
Highly Sensitive Self-Actuated Zinc Oxide Resonant Microcantilever Humidity Sensor,
Nano Letters. Accepted
A resonant microcantilever sensor is fabricated from a zinc oxide (ZnO) thin film, which serves as both the structural and sensing layers. An open-air spatial atomic layer deposition technique is used to deposit the ZnO layer to achieve a ∼200 nm thickness, an order of magnitude lower than the thicknesses of conventional microcantilever sensors. The reduction in the number of layers, in the cantilever dimensions, and its overall lower mass lead to an ultrahigh sensitivity, demonstrated by detection of low humidity levels. A maximum sensitivity of 23649 ppm/% RH at 5.8% RH is observed, which is several orders of magnitude larger than those reported for other resonant humidity sensors. Furthermore, the ZnO cantilever sensor is self-actuated in air, an advantageous detection mode that enables simpler and lower-power-consumption sensors.
2022-3-2 Book Chapter on the use of ALD for 3D printing.
Nanometric 3D printing of functinoal materials by Atomic Layer Deposition, in Advanced Additive Manufacturing, Edited by Prof. Igor Shishkovsky , IntechOpen
Atomic layer deposition (ALD) is a chemical vapour deposition (CVD) method that allows the layer-by-layer growth of functional materials by exposing a surface to different precursors in an alternative fashion. Thus, thanks to gas-solid reactions that are substrate-limited and self-terminating, precise control over thickness below the nanometer level can be achieved. While ALD was originally developed to deposit uniform coatings over large areas and on high-aspect-ratio features, in recent years the possibility to perform ALD in a selective fashion has gained much attention, in what is known as area-selective deposition (ASD). ASD is indeed a novel 3D printing approach allowing the deposition of functional materials (for example metals to oxides, nitrides or sulfides) with nanometric resolution in Z. The chapter will present an introduction to ALD, which will be followed by the description of the different approaches currently being developed for the ASD of functional materials (including initial approaches such as surface pre-patterning or activation, and newer concepts based on spatial CVD/ALD). The chapter will also include a brief overview of recent works involving the use of ALD to tune the properties of 3D printed parts.
2022-02-25 Congratulations to Chiara for passing her PhD viva!!! Excellent job and great thesis!!!
2022-3-3 Understanding why ZnO/Cu2O all oxide solar cells are not still that good. Congratullations to Abdou!!
Unveiling Key Limitations of ZnO/Cu2O All-Oxide Solar Cells through Numerical Simulations,
ACS Applied Energy Materials. Accepted
ZnO/Cu2O solar cells emerge as one of the most promising technologies with significant potential when considering the Schockley–Queisser limit (SQL) and taking into consideration other important factors such as materials abundance, low-cost fabrication, suitable band alignment, and the possibility of having semitransparent devices. However, the actual efficiency values obtained are still far from the expected theoretical values. The reasons behind this are mainly attributed to the low control over the properties of the oxides and the lack of knowledge on how the final device performance is affected by both materials properties and cell architecture. To close this gap, we explore the working mechanism of ZnO/Cu2O junctions thanks to numerical simulations based on the SCAPS-1D software. In particular, the present study aims at investigating the limiting factors and key parameters that affect the behavior of the ZnO/Cu2O junctions. The impacts of altering the absorber and collector film thickness, the diffusion length, side illumination, and the concentration of defects at the junction interface are explored. The data indicate that the thickness of Cu2O is critical for the output results when correlated with the diffusion length, which in turn is strongly affected by the oxide deposition technique and conditions. Bifacial illumination demonstrates a significant enhancement of the power conversion efficiency, while defects at the interface inhibit the charge generation drastically and enhance recombination at the subcell level. This study provides an overarching view of cell behavior and different routes toward the improvement of ZnO/Cu2O devices.
2021-01-09 Masoud Akbari's galactic picture (Nanogalaxy) has been awarded the 2ndt prize in the 2021 edition of the CMTC photo contest. Congratulations Masoud!
2022-1-25 Predicting the failure of AgNW networks under electric and thermal stresses. Congratullations to Dorina and Joao!!
Time of Failure of Metallic Nanowire Networks under Coupled Electrical and Thermal Stress: Implications for Transparent Electrodes Lifetime.
ACS Applied Nano Materials. Accepted
Silver nanowire networks are extensively studied due to their excellent optical and electrical properties and exceptional flexibility. These networks constitute a promising candidate for transparent and flexible electrodes applications. However, they can degrade under electrical or thermal stresses, so the understanding of the degradation mechanism is crucial for the integration of these metallic nanostructures in devices. In the present work, the electrical resistance of about 200 silver nanowire networks was monitored in situ to study the failure mechanisms under constant electrical current and temperature, to assess the prevailing stress in the failure process. For both origins of failure, electrical and thermal, the temperature-induced instabilities appear to be the prevailing phenomena at the origin of the network degradation. A semi-empirical physical model is proposed considering the generated Joule heating and the effect of the imposed temperature. This model allows to calculate the time of failure of silver nanowire networks for different electrical and thermal applied conditions and network densities, showing a good agreement with experimental data. The proposed model provides a deeper insight and constitutes a quantitative prediction tool for stability assessment, thus contributing to propel the integration of nanowire networks into devices as transparent electrodes, thanks to their robustness and reliability.
2021-02-01 We welcome Alejandro Frechilla Zabal, visiting PhD from INMA (Zaragoza, Spain), who's going to be in the team till the end of April!
2022-1-15 New Review. Nanometals make great transparent electrodes! Congratulations to Viet, and the AgNW and SALD teams!
Advances in flexible metallic transparent electrodes .
Small. Accepted
Transparent electrodes (TEs) are pivotal components in many modern devices such as solar cells, light-emitting diodes, touch screens, wearable electronic devices, smart windows, or transparent heaters. Recently, the high demand for flexibility and low cost in TEs requires a new class of transparent conductive materials (TCMs) as substitutes for conventional indium tin oxide (ITO), which is so far the most used TCM but exhibits brittleness and high cost. Among the different emerging alternative materials to ITO, metallic nanomaterials have received much interest due to their remarkable optical-electrical properties, low cost, ease of manufacturingproduction facility, flexibility, and widespread applicability. These involve metal grids, thin oxide/metal/oxide multilayers, metal nanowire percolating networks, or nanocomposites based on metallic nanostructures. In this review, a comparison between TCMs based on metallic nanomaterials and other TCM technologies is discussed. Next, the different types of metal-based TCMs developed so far and the fabrication technologies used are presented. Then, the challenges that these TCMs face towards integration in functional devices are discussed. Finally, the various fields in which metal-based TCMs have been successfully applied as well as emerging and potential applications are summarized.
2021-12-17 Congratulations to Abdou for passing his PhD viva!!! Excellent job and great thesis!!!
2021-12-16 Protecting conductive polymers with oxide layers. The precursor chemistry matters. Congratulations to Abdou!
High performance encapsulation of transparent conductive polymers by spatial atomic layer deposition.
Synthetic Metals. Accepted
Poly(3,4-ethylenedioxythiophene) (PEDOT) is a transparent conductive polymer widely used in flexible photonic and optoelectronic devices because of its excellent electrical and optical properties. However, its current range of applications is limited by its poor stability under high humidity and solar radiations. Encapsulation is an attractive solution to this problem and the development of a low-temperature and scalable deposition method is highly desirable. In this study, we report the use of spatial atomic layer deposition (SALD) to deposit ultrathin layers of ZnO, TiO2, and Al2O3. These nanolayers maintain the electrical performance of the conductive polymer and its high optical transmittance. The use of SALD ensures low-cost and flexible processing with pinhole-free high-quality coatings at atmospheric pressure and high-throughput. The present study is the first to investigate the effect of various multilayer metal oxide encapsulations on the long-term stability of PEDOT-based transparent conductive materials under solar radiations. We demonstrate finally that bilayer TiO2/Al2O3 and TiO2/ZnO coatings preserve the optoelectronic properties of three different PEDOT-based films, namely PEDOT:OTf (OTf = triflate), PEDOT:Sulf (Sulf = sulfate)and PEDOT:PSS (PSS = PolyStyreneSulfonate) films.
2021-11-01 We welcome PhD student Tristan GAGEOT to the SALD team in collaboration with INES
2021-11-01 We welcome Clément Lausecker to the SALD team to work in the ALD4MEM project improving hydrogen separation membranes with SALD
2021-10-18 Congratulations to Dorina Papanastasiou for wining a second prize to the best thesis, this time from C'Nano AURA!!
2021-10-18 Making AgNW networks more stable! Nice collaboration between the SALD and the AgNW teams.
Silver Nanowire Networks: Ways to Enhance Their Physical Properties and Stability.
Nanomaterials. Accepted
Silver nanowire (AgNW) networks have been intensively investigated in recent years. Thanks to their attractive physical properties in terms of optical transparency and electrical conductivity, as well as their mechanical performance, AgNW networks are promising transparent electrodes (TE) for several devices, such as solar cells, transparent heaters, touch screens or light-emitting devices. However, morphological instabilities, low adhesion to the substrate, surface roughness and ageing issues may limit their broader use and need to be tackled for a successful performance and long working lifetime. The aim of the present work is to highlight efficient strategies to optimize the physical properties of AgNW networks. In order to situate our work in relation to existing literature, we briefly reported recent studies which investigated physical properties of AgNW networks. First, we investigated the optimization of optical transparency and electrical conductivity by comparing two types of AgNWs with different morphologies, including PVP layer and AgNW dimensions. In addition, their response to thermal treatment was deeply investigated. Then, zinc oxide (ZnO) and tin oxide (SnO2) protective films deposited by Atmospheric Pressure Spatial Atomic Layer Deposition (AP-SALD) were compared for one type of AgNW. We clearly demonstrated that coating AgNW networks with these thin oxide layers is an efficient approach to enhance the morphological stability of AgNWs when subjected to thermal stress. Finally, we discussed the main future challenges linked with AgNW networks optimization processes.
2021-9-01 We welcome Marco DIBENEDETTO, Master student from the University of Turin to work in the SPRINT project
2021-8-31 Exploring the effect of precursor choice on the deposition of TiO2 by SALD
Tuning the band gap and carrier concentration of titania films grown by spatial atomic layer deposition: a precursor comparison.
Nanoscale Advances. Accepted
Spatial atomic layer deposition retains the advantages of conventional atomic layer deposition: conformal, pinhole-free films and excellent control over thickness. Additionally, it allows higher deposition rates and is well-adapted to depositing metal oxide nanofilms for photovoltaic cells and other devices. This study compares the morphological, electrical and optical properties of titania thin films deposited by spatial atomic layer deposition from titanium isopropoxide (TTIP) and titanium tetrachloride (TiCl4) over the temperature range 100–300 °C, using the oxidant H2O. Amorphous films were deposited at temperatures as low as 100 °C from both precursors: the approach is suitable for applying films to temperature-sensitive devices. An amorphous-to-crystalline transition temperature was observed for both precursors resulting in surface roughening, and agglomerates for TiCl4. Both precursors formed conformal anatase films at 300 °C, with growth rates of 0.233 and 0.153 nm s−1 for TiCl4 and TTIP. A drawback of TiCl4 use is the HCl by-product, which was blamed for agglomeration in the films. Cl contamination was the likely cause of band gap narrowing and higher defect densities compared to TTIP-grown films. The carrier concentration of the nanofilms was found to increase with deposition temperature. The films were tested in hybrid bilayer solar cells to demonstrate their appropriateness for photovoltaic devices.
2021-7-13 Non-homogenous AGNW networks help gain insight into network failure mechanisms. Congratulations Dorina and Abdou!
Effects of non-homogeneity and oxide coating on silver nanowire networks under electrical stress: comparison between experiment and modeling.
Nanotechnology. Accepted
Silver nanowire (AgNW) networks are among the most promising indium-free, flexible transparent electrodes for energy, lighting and heating devices. However, the lack of stability of such networks is a key factor that limits their industrial application. While applications require homogeneous networks, non-homogeneous AgNW networks are intentionally prepared in the present work to probe the mechanisms leading to failure under electrical stress. We show that induced non-homogeneities have a strong impact both on the spatial distribution of temperature (measured by IR imaging) and the current density throughout the electrode (as deduced from modeling). Regions with higher current density under elevated electrical stress are correlated to the origin of degradation. Furthermore, the influence of a zinc oxide (ZnO) layer on electrical performances of non-homogeneous specimens is studied. Thanks to ZnO coating, the tortuosity of electrical potential lines measured by the one-probe mapping technique is much lower than for bare networks. Additionally, coated network electrical failure occurs at 40 % higher voltage compared to bare network, over 18 V, while reaching superior power-induced heating of 360 °C. The results presented here will contribute to the design and fabrication of more robust nanowire networks, particularly for application in transparent heaters.
2021-6-30 Cu2O thin films with record mobility deposited via SALD. Congratulations Abdou!
Open-Air Printing of Cu2O Thin Films with High Hole Mobility for Semitransparent Solar Harvesters
Coms. Mat. (Nature) Accepted.
Cu2O is a promising p-type semiconductor for low-cost photovoltaics and transparent optoelectronics. However, low-cost and low-temperature fabrication of Cu2O films with good transport properties remains very challenging, thus limiting their widespread adoption in devices. Here, we demonstrate the possibility to obtain thin Cu2O films (20-80 nm) with excellent hole mobility up to 92 cm2V-1s-1 using atmospheric-pressure spatial atomic layer deposition (AP-SALD) at low temperatures (< 260 °C). Particularly, Copper (I) Hexafluoro-2,4-Pentanedionate Cyclooctadiene (CuhfacCOD) has been used for the first time as a thermally stable solid precursor for copper. Raman spectroscopy indicates the presence of copper split vacancies, VCu,split, and shows that the superior hole mobility can be correlated to the low concentration of shallow acceptor defects. The optical bandgap of deposited films can be tuned between 2.08 eV and 2.5 eV, depending on the deposition temperature. All-oxide semitransparent Cu2O/ZnO solar harvesters have been fabricated by AP-SALD showing efficiency values comparable to devices that incorporate much thicker Cu2O layers. Our work provides a promising approach towards cost-efficient, all-oxide solar harvesters, and other (opto)electronic devices.
2021-6-28 Showing the potential of SALD and Cu2O for large-area Si heterojunction solar cells. Congratulations Abdou!
Open-air, low-teperature deposition of phase pure Cu2O thin films as efficient hole-transporting layers for silicon heterojunction solar cells
J. Mater. Chem. A. Accepted
Recent research focuses on finding alternative materials and fabrication techniques to replace traditional (p) and (n) doped hydrogenated amorphous silicon (a-Si:H) to reduce cost and boost the efficiency of Silicon Heterojunction (SHJ) solar cells. In this work, low-cost p-type Cu2O thin films have been investigated and integrated as a hole-transporting layer (HTL) in SHJ solar cells, using Atmospheric-Pressure Spatial Atomic Layer Deposition (AP-SALD), an open-air, scalable ALD approach. Phase pure Cu2O thin films have been deposited at temperatures below the degradation limit of the SHJ, thus maintaining the passivation effect of the a-Si:H layer. The effect of deposition temperatures and HTL thicknesses on the performance of the devices has been evaluated. The fabricated Cu2O HTL-based SHJ cells, having an area of 9 cm², reach a power conversion efficiency (PCE) of 13.7%, which is the highest reported efficiency for silicon-based solar cells incorporating a Cu2O HTL.
2021-6-25 Congratulations to Dorina Papanastasiou for wining the prize to the best thesis from the IMEP-2 Doctorate school!!
2021-5-28 We welcome Ozden CELIKBILEK to the SALD team to work in the EPISTORE project in collaboration with the Nanoionics team.
2021-5-28 Our recent results on the Resistive Switching of AgNW/TiO2 hybrid networks have made the inside back cover of Small
2021-5-18 Our recent perspective on LALD is featured in the front Cover of issue 19/2021 of Dalton Tansactions
2021-5-17 We welcome Richard NTI, Master 1 student from Phelma who's going to beworking with us during the next months!
2021-5-10 Taking advantage of custom 3D printed SALD heads for the desposition of non-homogenousnes thin films towards combinatorial studies, in collaboration with Prof. Musselman from the University of Waterloo.
Nanoscale film thickness gradients printed in open air by spatially varying chemical vapor deposition
Adv. Func. Mater. Accepted.
Nanoscale films are integral to all modern electronics. To optimize device performance, researchers vary the film thickness by making batches of devices, which is time-consuming and produces experimental artifacts. We present thin films with nanoscale thickness gradients that are rapidly deposited in open air for combinatorial and high-throughput (CHT) studies. Atmospheric pressure spatial atomic layer deposition reactor heads are used to produce spatially varying chemical vapor deposition rates on the order of angstroms per second. We printed ZnO and Al2O3 films with nm-scale thickness gradients in as little as 45 seconds and performed CHT analysis of a MIM diode and perovskite solar cell. By testing 360 Pt/Al2O3/Al diodes with 18 different Al2O3 thicknesses on one wafer, we identified a thicker insulator layer (~7.0 nm) for optimal diode performance than reported previously. Al2O3 thin film encapsulation was deposited by atmospheric pressure chemical vapor deposition (AP-CVD) on a perovskite solar cell stack for the first time and a convolutional neural network was developed to analyze the perovskite stability. The rapid nature of AP-CVD enables thicker films to be deposited at a higher temperature than is practical with conventional methods. The CHT analysis showed enhanced stability for 70 nm encapsulation films.
2021-5-10 We welcome Alice Le Paih, Master 1 student from Phelma who's going to be driving the SALD during the next months!
2021-04-29 Our new approach to selective ALD and 3D printing of functional materials highlighted in the G-INP, UGA and Carnot Energies du Futur Sites:
https://www.grenoble-inp.fr/fr/recherche-valorisation/le-depot-de-couches-atomiques-reinvente
2021-04-27 Composite films of AgNWs and Al2O3 prove to be an efficient low-emissivity coating. Congratulations Chiara!
Transparent and Mechanically Resistant Silver Nanowire based Low-Emissivity Coatings
This article reports on the fabrication and investigation of low-emissivity (low-E) coatings based on random networks of silver nanowires (AgNWs). The transparent layers based on AgNWs do exhibit low emissivity while being still transparent: an overall emissivity as low as 0.21 at 78% total transmittance was obtained. A simple physical model allows to rationalize the emissivity-transparency dependence and a good agreement with experimental data is observed. This model demonstrates the role played by AgNWs which partially reflect IR photons emitted by the substrate, exacerbating then the presence of AgNWs and lowering the total emissivity. The potential use of such layers in functional devices is hampered by the poor intrinsic surface adhesion of the AgNWs, which renders the coating fragile and prone to mechanical damaging. Two very efficient encapsulation processes based on the deposition of a conformal alumina thin film using the Spatial Atomic Layer Deposition technique and the solution processed layer deposition of a polysiloxane varnish have been developed to thwart this weakness. Both coatings combine sturdy mechanical resistance relying on a strong interfacial adhesion and excellent optical transmittance properties. The performances for the mechanically resistant low E coatings achieve an overall emissivity as low as 0.34 at 74% total transparency. The set of optical properties and mechanical resistance of the reported AgNWs based low E coatings combined with the ease of fabrication and the cost-effective production process make it an excellent candidate for a wide set of applications, including smart windows for energy-saving buildings.
2021-03-09 Rationalising the different approaches to atomic layer deposition in liquid phase. Congratulations Octavio!
Perspective: Liquid atomic layer deposition as an emergent technology for the fabrication of thin films
Dalton Transactions, accepted. To be part of the spotlight collection on ALD/MLD
Atomic layer deposition (ALD) is widely recognized as a unique chemical vapor deposition technique for the fabrication of thin films with a high conformality and precise thickness control down to the Ångstrom level, therefore allowing surface and interface nanoengineering. However, several challenges such as the availability of chemical precursors for ALD and the use of vacuum conditions have hampered its widespread adoption and scalability for mass production. In recent years, the liquid phase homologue of ALD, liquid atomic layer deposition (LALD), has emerged as a much simpler and versatile strategy to overcome some of the current constraints of ALD. This perspective describes the different strategies that have been explored to achieve conformality and sub-nanometer thickness control with LALD, as well as the current challenges it faces to become part of the thin-film community toolbox, in particular its automation and compatibility with different types of substrates. In this regard, the important role of LALD as a complimentary technology to ALD is emphasized by comparing the different pathways to deposit a same material and the precursors used to do so.
2021-03-09 A new example that failure does not always mean loosing. Congratulations to Joao and Abdou!
Planar and Transparent Memristive devices based on Titanium Oxide coated Silver Nanowire Networks with Tunable Switching Voltage
Small, accepted
Threshold Switching devices are fundamental active elements in More than Moore approaches, integrating the new generation of non-volatile memory devices. Here, we report an in-plane threshold resistive switching device with an on/off ratio above 106, a Low Resistance State of 10 to 100 kΩ and a High Resistance State of 10 to 100 GΩ. Our devices are based on nanocomposites of silver nanowire networks and titanium oxide, where volatile unipolar threshold switching takes place across the gap left by partially spheroidized nanowires. Device reversibility depends on the titanium oxide thickness, while nanowire network density determines the threshold voltage, which can reach as low as 0.16 V. The switching mechanism is explained through percolation between metal-semiconductor islands, in a combined tunneling conduction mechanism, followed by a Schottky emission generated via Joule heating. The devices are prepared by low-cost, atmospheric pressure, and scalable techniques, enabling their application in printable, flexible and transparent electronics.
2021-02-26 See our latest results and developments, featured in a MIDI MINATEC (https://www.minatec.org/fr/vie-de-campus/les-midis-minatec/)
2021-02-01 We welcom Dr. Matthieu Weber, who has joined the LMGP as Research Engineer!
2021-01-09 Abderrahime Sekkat's rough picture (The Pyramids of Science) has been awarded the 1st prize in the 2020 edition of the CMTC photo contest. Congratullations Abdou!
2020-12-09 Congratulations to Dorina for passing his PhD viva!!! Great job!!! And Welcome to the SALD TEAM as new joint-postdoc with Daniel's Bellet AgNW NETWORKS TEAM
2020-12-09 Our recent work is featured in the inside back cover of the December issue of Adv. Mat. Technologies
2020-11-30 Gaining insight in how Ag nanowire networks fail thanks to simulation. Congratullations to Dorina and Joao!
Dynamic degradation of metallic nanowire networks under electrical stress: a comparison between experiments and simulations
Metallic nanowire networks represent a promising solution for a new generation of transparent and flexible devices, including touch screens, solar cells or transparent heaters. They however lack of stability under thermal and electrical stresses, often leading to the degradation of nanowires, which results in the loss of electrical percolation paths. We propose a comprehensive description of the degradation mechanism in a metallic nanowire network subjected to electrical stresses. The nanowire network degradation is ascribed at a very local scale, to the hot-spot formation and the subsequent propagation of a spatially correlated disruptive crack. We compare the behaviour of actual networks under electrical and thermal stresses to dynamic simulations of randomly deposited sticks on a 2D surface, and thermal phenomenon simulated in a metal thin film. On one hand, such comparison allows to deduce an average junction resistance between nanowires. On the other hand, we observed that initial flaws in a discrete network results in a local current density increase in the surrounding area, further leading to an amplified Joule effect. This phenomenon promotes the spatial correlation in the damage of the percolating network. Such non-reversible failure on the transparent electrode are in good agreement with experimental observations.
2020-11-05 Congratulations to Abdou Sekkat for wining a best PhD presentation prize during RAFALD2020.
2020-10-01 We welcome PhD student Pia VASQUEZ RIVERA to the SALD team, in collaboration with INES
2020-10-01 Congratulations to Abdou Sekkat for wining the prize to the best 2nd year PhD presentation during the LMGP 2020 Scientific Day.
2020-09-28 Short Review on recent in situ and operando approaches to probe solid oxide fuel cells.
In situ and operando characterisation techniques for solid oxide electrochemical cells: Recent advances
Journal of Physics: Energy. Accepted.
Oxygen activity and surface stability are two key parameters in the search for advanced materials for intermediate temperature solid oxide electrochemical cells, as overall device performance depends critically on them. In particular in situ and operando characterisation techniques have accelerated the understanding of degradation processes and the identification of active sites, motivating the design and synthesis of improved, nanoengineered materials. In this short topical review we report on the latest developments of various sophisticated in situ and operando characterization techniques, including Transmission and Scanning Electron Microscopy (TEM and SEM), surface-enhanced Raman spectroscopy (SERS), Electrochemical Impedance Spectroscopy (EIS), X-ray Diffraction (XRD) and synchrotron based X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS), among others. We focus on their use in three emerging topics, namely: (i) the analysis of general electrochemical reactions and the surface defect chemistry of electrode materials; (ii) the evolution of electrode surfaces achieved by nanoparticle exsolution for enhanced oxygen activity and (iii) the study of surface degradation caused by Sr segregation, leading to reduced durability. For each of these topics we highlight the most remarkable examples recently published. We anticipate that ongoing improvements in the characterisation techniques and especially a complementary use of them by multimodal approaches will lead to improved knowledge of operando processes, hence allowing a significant advancement in cell performance in the near future.
2020-09-16 Open-air, fast pattering and 3D printing of functional materials! Do you fancy a ZnO doughnut? Congratulations to the current and former members of the SALD team that contributed to this long work.
Gas-phase 3D printing of functional materials
Advanced Materials Technologies. Accepted.
Spatial Atomic Layer Deposition (SALD) is a recent approach 100 times faster than conventional ALD, even at atmospheric pressure. Previous works exploited these assets focusing on high-rate, large-area deposition for scaling-up into mass production. Conversely, this work shows that SALD indeed represents an ideal platform for area-selective deposition of functional materials by proper design and miniaturization of close-proximity SALD heads. In particular, the potential offered by 3D printing is used to fabricate low-cost customized close-proximity heads, which can be easily designed and modified to obtain different deposition areas, free-form patterns, and even complex multimaterial structures. Finally, by designing a miniaturized head with circular concentric gas channels, 3D printing of functional materials can be performed with nanometric resolution in Z. This constitutes a new gas-phase 3D printing approach. Because the process is based on ALD reactions, conformal and continuous thin films of functional materials can be printed at low temperatures and with high deposition rate in the open air. Our approach represents a new versatile way of printing functional materials and devices with spatial and topological control, thus extending the potential of SALD and ALD in general, and opening a new avenue in the field of area-selective deposition of functional materials.
2020-08-10 Setting the path towards Metal-Organic Framework thin films. Minireview by Chiara and Octavio in collaboration with ETH Zurich and the UB. Congratulations to both!
Advanced Technologies for the Fabrication of MOF Thin Films
Materials Horizons. Accepted.
Metal-organic framework (MOF) thin films represent a milestone in the development of future technological breakthroughs. The processability of MOFs as films on surfaces together with their major features (i.e. tunable porosity, large internal surface area, and high crystallinity) is broadening their range of applications to areas such as gas sensing, microelectronics, photovoltaics, and membrane-based separation technologies. Despite the recent attention that MOF thin films have received, many challenges still need to be addressed for their manufacturing and integrability, especially when an industrial scale-up perspective is envisioned. In this brief review we introduce several appealing approaches that have been developed in the last few years. First, a summary of liquid phase strategies that comprise microfluidic methods and supersaturation-driven crystallization processes are described. Second, gas phase approaches based on atomic layer deposition (ALD) will be also presented.
2020-07-08 Our study on the effect of the different parameters of the SALD growth and film properties has been accepted in Chemical Engineering Journal. Bravo Viet and Abdou!
Impact of Precursor Exposure in Spatial Atomic Layer Deposition on Process Efficiency and Film Properties
Chemical Engineering Journal. Acccepted
Being able to control the exposure of precursors to the substrate surface is essential towards an optimum Atomic Layer Deposition (ALD) process. Conventional ALD usually requires large excesses of precursors and expensive vacuum chamber in which the precursor exposure can be controlled via the injection pulse duration followed by a delay time. A version of ALD, namely Spatial ALD (SALD), which has the same unique assets as conventional ALD but being faster, vacuum-free, and easier to scale up, has recently attracted much attention. In SALD, precursors are continuously exposed to a moving surface, and thus it is more complicated to tune precursor exposure than with conventional ALD. Here, we present a study on how to control this critical parameter in for the deposition of ZnO films using a close-proximity, open-air SALD. Our results are based on both simulations and experiments. A simple physical model supported by Comsol Multiphysics simulations has been developed to study the effect of the substrate velocity as well as the precursor concentration in the carrier gas on film growth rate. We found that the precursor entrainment by the moving substrate induces an asymmetric precursor concentration profile that affects the obtained GPC. Also, we show that the mass density and structural properties of the deposited films depend closely on the film growth rate. For instance, fast growth does not always produce dense films. Indeed, a compromise between the growth rate and the precursor consumption should be considered to obtain both good process efficiency and high-quality films. Our findings are particularly relevant for using SALD in large-scale coating applications, in which high deposition rate and good coating density should be obtained with a minimal ALD precursor consumption.
2020-05-15 Our recent works have been featured as Supplementary Covers in Crystal Growth and Design and Chemistry of Materials.
2020-05-5 SiO2 printed at low temperature, in the open air- Congratulations to Viet. Abdou and Chiara!
Atmospheric Plasma-Enhanced Spatial Chemical Vapor Deposition of SiO2 Using Trivinylmethoxysilane and Oxygen Plasma
Chemistry of Materials, Accepted.
SiO2 constitutes one of the most widely used dielectric materials in the microelectronics, packaging, and optical industries. Therefore, the development of new processes to deposit SiO2 at low temperature and in an affordable and scalable way are desirable. In this work, we present a low-temperature, open-air process based on spatial atomic layer deposition (SALD) that yields high purity SiO2 films at temperatures down to room temperature. The films were obtained by operating our SALD system in CVD mode (i.e., allowing precursor crosstalk), using an oxygen plasma in combination with trivinylmethoxysilane (TVMS). TVMS is an appealing precursor since it is highly volatile, is affordable, and does not contain halogen elements, thus being very suitable for application in atmospheric-pressure spatial deposition systems. Conversely, water, oxygen, hydrogen peroxide, or ozone did not show any reactivity with TVMS at temperatures up to 260 °C. Thus, when operating our system in ALD mode, no film could be obtained due to the lack of reactivity of the precursor with OH* surface groups. 3D printing was employed to fabricate custom heads integrating both the precursor injector and the atmospheric plasma generator. Our results show that conformal SiO2 thin films can be deposited by our atmospheric plasma-enhanced spatial chemical vapor deposition (APE-SCVD) approach at low temperatures (RT–180 °C) on different substrates, including silicon wafers, microglass slides, or even polymeric substrates with a high growth rate up to 2–5 nm/min. The deposition rate increased when increasing the power applied to the plasma reactor but decreased when increasing the deposition temperature due to the faster decay of the metastable oxygen radical species. FTIR results showed no differences for films deposited with different plasma powers. Conversely, temperature had an effect on the ratio between the AS1 and the AS2 bands. Even though the deposition of SiO was carried out at low temperatures in the open air using a metalorganic precursor, no contamination from SiNx or SiCx was observed by FTIR and XPS measurements. Our results open the door to the low-temperature, fast printing of Si-based devices.
2020-05-1 Gaining insight in the formation mechanism of AgCuO2. Congratulations to Hongjun and Abdou!
Reaction pathway of the hydrothermal synthesis of AgCuO2 from in situ time-resolved X-ray diffraction
Crystal Growth and Design, Accepted.
AgCuO2 is an interesting semiconductor oxide with appealing optical and electronic properties. While the oxide has been synthesized in bulk by different approaches, no study on the formation mechanism has been carried out to date. We present an in situ time-resolved X-ray diffraction study of the hydrothermal synthesis of AgCuO2 from AgO and CuO. The effects of reaction pH and temperature on the reaction pathways and products have been studied. While pH is a key parameter for the successful synthesis of AgCuO2, temperature affects mainly the reaction kinetics. A reaction pathway is proposed that involves a series of dissolution-precipitation reactions, mediated by Cu and Ag hydroxy complexes. Finally, we have compared different approaches to obtain the reaction activation energy, which was calculated to be 70.6±5.1 kJ/mol. Nevertheless, our results show that new models need to be developed for the type of reaction presented here.
2020-04-24 Guest editor with Prof. Bellet of an Special Issue on Transparent Conductive Materials in the Journal Nanomaterials.
Follow the link for more information and for submitting you contribution!
https://www.mdpi.com/journal/nanomaterials/special_issues/Transparent_Conductive_Nanomaterials
2020-2-15 We welcome Thomas Pelletier, M2 from Phelma who is going to be working with us in a collaboration between the SALD and the IMBM teams
2020-02-12 Review on Transparent Heaters accepted in Adv. Func. Mater. Congratulations to Dorina!
Transparent heaters (TH) have attracted intense attention from both scientific and industrial actors due to the key role they play in many technologies, including smart windows, deicers, defoggers, displays, actuators and sensors. While transparent conductive oxides have dominated the field for the past five decades, a new generation of THs based on nanomaterials has led to new paradigms in terms of applications and prospects in the past years. Here we will review the most recent developments and strategies to improve the properties, stability and integration of these new THs.
2020-02-10 Abderrahime Sekkat's interstellar picture (Across the Universe) awarded the 3rd prize in the 2019 edition of the CMTC photo contest. Congratullations Abdou!
2019-12-2 Our ALD/CVD symposium at the MRS. Congratulations to the winners of the symposium best poster awards!
2019-11-26 Congratulations to César Masse for passing his PhD viva!!! Excellent job!!!
2019-11-25 We welcome Masoud Akbari, new PhD student in the SALD team!
2019-11-1 We welcome Octavio Graniel Tamayo, new postdoc in the SALD team!
2019-9-18 Making AgNW networks more stable and more transparent with bilayers deposited by SALD. Congratulations to Sara!
Versatility of bilayer metal oxide coatings on silver nanowire networks for enhanced stability with minimal transparency loss
Silver nanowire (AgNW) networks have been lately much investigated thanks to their physical properties and are therefore foreseen to play a key role in many industrial devices as transparent electrodes, but their stability can be an issue. Although it has been shown that thin metal oxide coatings enhance the stability of AgNW networks, such stabilization is achieved at the expenses of transparency. We demonstrate that by depositing a second oxide coating, which acts as an antireflective layer, it is possible to obtain highly stable and transparent composite electrodes. AgNW networks were deposited by the airbrush method, and zinc oxide (ZnO) and aluminum oxide (Al2O3) coatings were deposited, by Atmospheric Pressure Spatial Atomic Layer Deposition (AP-SALD), using both glass and plastic substrates: therefore the proposed fabrication method is low-cost and compatible with high-throughput scalable fabrication. The mechanical stability of bare, ZnO and ZnO/Al2O3-coated AgNWs upon bending is also presented. The obtained nanocomposites exhibit highly homogeneous and conformal oxide coatings with average thicknesses of a few tens of nanometers. Samples with bilayer coating of 70 nm ZnO/70 nm Al2O3 still exhibit very good stability after annealing in air up to 450 °C for 6 repetitive cycles.
2019-9-16 Viet H. Nguyen has won the prize to the best PhD thesis, awarded by the French Chemical Society, Solid state Chemistry division. Congratulations to Viet!
2019-9-1 We welcome Fidel Toldrà Reig, new postdoc in the SALD team!
tailoring of the properties of highly demanded fluorine doped tin oxide (FTO) films.
2019-6-27 Our recent work on nanocomposite transparent electrodes featured in the inside cover of Nanoscale, issue 25, 2019
2019-7-31 New paper on the effect of Al doping on SnO2 thin films. Congratulations to Getnet!
SnO2 Films Deposited by Ultrasonic Spray Pyrolysis: Influence of Al Incorporation on the Properties
Molecules, 2019, 24(15), 2797
Aluminum-doped tin oxide (SnO2:Al) thin films were produced by an ultrasonic spray
pyrolysis method. The effect of aluminum doping on structural, optical, and electrical properties
of tin oxide thin films synthesized at 420 ◦C was investigated. Al doping induced a change in the
morphology of tin oxide films and yielded films with smaller grain size. SnO2 thin films undergo a
structural reordering and have a texture transition from (301) to (101), and then to (002) preferred
cristallographic orientation upon Al doping. The lattice parameters (a and c) decreases with Al
doping, following in a first approximation Vegard’s law. The optical transmission does not change in
the visible region with an average transmittance value of 72–81%. Conversely, in the near infrared
(NIR) region, the plasmon frequency shifts towards the IR region upon increasing Al concentration
in the grown films. Nominally undoped SnO2 have a conductivity of ∼1120 S/cm, which is at
least two orders of magnitude larger than what is reported in literature. This higher conductivity
is attributed to the Cl− ions in the SnCl4.5(H2O) precursor, which would act as donor dopants.
The introduction of Al into the SnO2 lattice showed a decrease of the electrical conductivity of SnO2
due to compensating hole generation. These findings will be useful for further studied tackling the
2019-6-19 SALD coatings yield more stable and better FETs. Congratulations to Fanny!
Al2O3, Al doped ZnO and SnO2 encapsulation of randomly oriented ZnO nanowire networks for high performance and stable electrical devices
Nanotechnology, accepted 2019
Two-dimensional (2D) randomly oriented nanowire networks, also called nanonets, have remarkable advantages including low-cost integration, good reproducibility and high sensitivity, which make them a promising material for electrical devices. With this work, we focus on the study of ZnO nanonet as channel materials in field effect transistors (FETs). In our process, ZnO nanowires were assembled in NNs by the liquid filtration method and were integrated in transistors, with the bottom-gate configuration, using simple technological steps. Non-encapsulated devices exhibited state of the art performances but their stability toward air exposure was poor. Using a proper encapsulation of the nanonets, with cheap abundant and non-toxic oxides, we demonstrate our ability not only to stabilize their electrical properties, but also to enhance performance to values never reach before for ZnO nanowire-based transistors. Our best FETs exhibit a low off-current while maintaining very good on current, which results in a Ion/Ioff ratio exceeding 106 for a drain voltage of 5 V. The behavior of these ZnO NN-based FETs was studied for three different encapsulation materials, alumina (Al2O3), tin oxide (SnO2) and Al-doped ZnO (AZO). These results prove that ZnO NNs are highly promising materials for an easy and low-cost integration into FETs.
2019-6-14 Our rcent work in collaboration with J. Puigmartí featured as Backcover in Adv. Mater. Tech.
2019-6-7 We welcome Punam Murkute, new postdoc in the SALD group!
2019-5-20 New paper on composite transparent electrodes based on Ag nanowires and oxides. Congratullations to Viet and Joao!
Low-cost fabrication of flexible transparent electrodes based on Al doped ZnO and silver nanowire nanocomposites: impact of the network density.
Nanoscale, accepted 2019.
We report the study of nanocomposite transparent electrodes based on Aluminium doped Zinc Oxide (ZnO:Al) thin films and silver nanowire (AgNW) networks. The electrodes are fully fabricated by low-cost, open-air techniques, namely, atmospheric pressure spatial atomic layer deposition and spray coating. We show that the transparency and the electrical conductivity of the ZnO:Al/AgNW nanocomposites can be tuned by controlling the AgNW network density. We also demonstrate that the thermal, electrical and mechanical stabilities of the nanocomposites are drastically enhanced compared to those of AgNW networks or ZnO:Al thin films separately. Interestingly, we report a clear continuous decrease of the electrical resistance of the nanocomposites for network densities even below the percolation threshold. We propose a model to explain the relationship between the conductivity of the nanocomposites and the AgNW network density. Our physical model is based on the non-negligible contribution of percolating clusters of AgNWs for network densities below the percolation threshold. Our results provide a means to predicting the physical properties of such nanocomposites for applications in solar cells and other optoelectronic devices. Finally, the deposition methods used open the way towards stable, low-cost and flexible transparent electrodes for industrial applications.
2019-5-03 New paper on ZnO nanowire based gas sensors in collaboration with C. Ternon (LMGP). Congratullations to Fanny and Viet!
ZnO based nanowire network for gas sensing applications. Marterials Research Express
This work reports on the transfer of randomly oriented nanowire networks based on ZnO and Al-doped zinc oxide (AZO) encapsulated ZnO nanowires onto a complementary metal oxide semiconductor (CMOS) micro electro mechanical system (MEMS) platform. The substrate consists of an embedded tungsten micro-heater with gold interdigitated electrodes on top of the membrane. The presence of the micro-heater allows to control the operating temperature of the metal oxide material whilst the electrodes are used to measure the resistance across the sensing layer. These networks, also called nanonets, are prepared using simple technological steps: (i) nanowire growth, (ii) nanowire dispersion and (iii) nanowire filtration. The characterization of the resulting devices demonstrated for the first time that the transfer of the nanonets on the suspended membrane devices is feasible and does not cause any mechanical failure. Bench testing showed that the resistance of the nanonets respond to the modulation of the operational temperature in line with the semiconductor behaviour of the film. An operational temperature of 370 °C was chosen thus to tune to the resistance in the range of the MΩ and carry out further gas testing which demonstrated that the sensor resistance changed upon exposure to 1.5 ppm of acetone. These tests showed that ZnO and AZO-passivated ZnO nanonets have sensitivity of [1.2-1.3] and [1.1-1.2], respectively, as measured by the ratio between the resistance in air and gas. It was also observed that the sensitivity of the devices prepared using the encapsuled nanonets is more stable than the bare ZnO nanonets.
2019-5-2 We welcome Omar Hassan, M1 from Phelma who is going to be working 3 months with us in the SALD team
2019-4-01 New paper on the role of oxide ultrathin coatings on the performace of ZnO-based resistive switching in collaboration with K. Musselman at Univ. Waterloo
Ultrathin metal-oxide interface mediated ZnO nanowire memristive devices emulating synaptic behaviors. Advanced Electronic Materials, 2019
One-dimensional semiconductor nanowires have been widely used as important building blocks in different device. However, the performance of semiconductor nanowire devices is strongly affected or hindered by the surface states/defects on the nanowires. Mitigation of effects of surface defects of nanowires is a great concern to realize reliable and predictable performance. In this paper, we demonstrate the introduction of an ultrathin metal oxide layer between Au electrodes and ZnO nanowire can minimize the surface effects of the ZnO nanowire, leading to reliable symmetrical threshold switching performance. Study of the conduction mechanism demonstrated that the TiOx interfacial layer functions as a barrier between the metal electrode and the nanowire, wherein the oxygen defects provide localized trap sites for electron hopping at low electric field as well as assisting the electron tunneling at high electric field. Several key synaptic functions including excitatory current response, facilitation
and depression, short-term plasticity are realized for the modified ZnO nanowire device, which are promising for neuromorphic computing applications. This bidirectional memristive device demonstrates that interface engineering between a metal electrode and a semiconductor nanowire can provide an important step in realizing reliable memristive devices, opening new approaches to assembling
neuromorphic systems with nanometer-sized features.
2019-2-15 We welcome Miguel Granados. He'll be doing an internship in the group until the summer working on our SALD system.
2019-2-14 Easy patterning of MOF films on reactive surfaces thanks to microfluidics, a collabotarion with J. Puigmartí-Luis from ETH Zurich
In‐Flow MOF Lithography. Adv. Mater. Technologies.
Continuous‐flow microfluidic systems are widely recognized as advanced and robust tools for materials synthesis. Indeed, the exquisite spatiotemporal control over reagent concentrations in a microfluidic channel has enabled the formation of composite materials and structures with unique features. Herein, we show for the first time that by combining reactive substrates with continuous‐flow microfluidic devices, material growth can be spatiotemporally driven and modulated on a surface. We demonstrate such unprecedented control by crystallizing and patterning compositional gradients of HKUST‐1 (a widely investigated metal‐organic framework (MOF)) on a reactive surface. We believe that this novel approach will engender new possibilities for incorporating MOFs on reactive surfaces, and thus for developing new advanced technological architectures and devices.
2019-2-13 Our work in colaboration with K. Musselman featured as Frontispice in Adv. Func. Mater.
2019-2-06 Our work has been featured as Inside Cover in Adv. Mater. Interfaces
2019-2-04 Co-organiser of a symposium dedicated to ALD and CVD at the 2019 MRS Fall meeting.
See the call for abstracts here
2019-1-10 Book Chapter on Spatial Atomic Layer Deposition
in, Chemical Vapor Deposition for Nanotechnology, Edited by Pietro Mandracci, IntechOpen
In conventional atomic layer deposition (ALD), precursors are exposed sequentially to a substrate through short pulses while kept physically separated by intermediate purge steps. Spatial ALD (SALD) is a variation of ALD in which precursors are continuously supplied in different locations and kept apart by an inert gas region or zone. Film growth is achieved by exposing the substrate to the locations containing the different precursors. Because the purge step is eliminated, the process becomes faster, being indeed compatible with fast-throughput techniques such as roll-to-roll (R2R), and much more versatile and easier and cheap to scale up. In addition, one of the main assets of SALD is that it can be performed at ambient pressure and even in the open air (i.e., without using any deposition chamber at all), while not compromising the deposition rate. In the present chapter, the fundamentals of SALD and its historical development are presented. Then, a succinct description of the different engineering approaches to SALD developed to date is provided. This is followed by the description of the particular fluid dynamics aspects and the engineering challenges associated with SALD. Finally, some of the applications in which the unique assets of SALD can be exploited are described.
The chapter features a table with all materials synthesized (an published) via SALD at the time of publication (Sorry if I forgot any!).
2018-12-19 Exploiting the CVD mode in close proximity AP SALD for making area selective deposition
Influence of the geometric parameters on the deposition mode in spatial atomic layer deposition: a novel approach to area-selective deposition
Coatings, 2018, 9(5), 5. Congratulations to César!
Within the materials deposition techniques, Spatial Atomic Layer Deposition (SALD) is gaining momentum since it is a high throughput and low-cost alternative to conventional ALD. SALD relies on a physical separation (rather than temporal separation, as is the case in conventional ALD) of gas-diluted reactants over the surface of the substrate by a region containing an inert gas. Thus, fluid dynamics play a role in SALD since precursor intermixing must be avoided in order to have surface-limited reactions leading to ALD growth, as opposed to chemical vapor deposition growth (CVD). Fluid dynamics in SALD mainly depends on the geometry of the reactor and its components. To quantify and understand the parameters that may influence the deposition of films in SALD, the present contribution describes a Computational Fluid Dynamics simulation that was coupled, using Comsol Multiphysics®, with concentration diffusion and temperature-based surface chemical reactions to evaluate how different parameters influence precursor spatial separation. In particular, we have used the simulation of a close-proximity SALD reactor based on an injector manifold head. We show the effect of certain parameters in our system on the efficiency of the gas separation. Our results show that the injector head-substrate distance (also called deposition gap) needs to be carefully adjusted to prevent precursor intermixing and thus CVD growth. We also demonstrate that hindered flow due to a non-efficient evacuation of the flows through the head leads to precursor intermixing. Finally, we show that precursor intermixing can be used to perform area-selective deposition.
2018-11-30 Review on fast approaches to ALD
Speeding up the unique assets of atomic layer deposition
Materials Today Chemistry, accepted.
Atomic Layer Deposition (ALD) has been traditionally regarded as an extremely powerful but slow thin-film deposition technique. The (perceived) limitation in terms of deposition rate has resulted in a slow penetration of the technology into mass manufacturing beyond established applications in the semiconductor industry until recently. At present, several developments have resulted in a significant increase in the use of ALD in a number of mass manufacturing applications. On the one hand, there is an increasing demand from the device makers side to incorporate nanotechnology in their products that relies on the unique advantages of ALD. On the other hand, a number of technical improvements have been implemented in the ALD method allowing it to be much faster. In this paper, we provide an overview of different High Throughput (HT) ALD approaches, putting them in perspective with other common HT deposition techniques already used in the industry. As an example, the use of HT ALD for Organic Light-Emitting Diodes (OLED) thin-film encapsulation is discussed.
2018-11-29 Cu2O thin films grow differently depending on the weather!
The role of humidity in tuning the texture and electrical properties of Cu2O thin films deposited via Aerosol Assisted CVD
Advanced Materials Interfaces, accepted. Congratulations to Hongjun!
This work reports a study on the effect of carrier gas (CG) humidity on the texture and the resulting electronic properties of Cu2O thin films deposited using Aerosol Assisted Chemical Vapor Deposition (AA-CVD) at low temperatures (< 365 °C). By increasing the CG humidity, the preferred orientation of the films can be tuned from [110] to [111]. By studying the initial stages of film deposition, a different growth mode is found for dry and humid conditions, which in turn directs the final texture of the films. The analysis of the electric properties of the thin films by Hall-effect shows that while carrier concentration remains in the order of 1015 cm-3 when using both in dry and humid conditions, Cu2O samples deposited with humid CG generally present a higher mobility, up to 17 cm2 V-1s-1. [111] Textured Cu2O films with high mobility were used to fabricate a diode by depositing a ZnO layer on top using Atmospheric Pressure Spatial Atomic Layer Deposition (AP-SALD). The diode shows an excellent rectifying behavior with a high asymmetry close to 104 between -1 V and +1 V.
2018-11-28 MIM diodes made fast and in the open air! in collaboration with K. Musselman from Univ. Waterloo
Quantum-tunneling metal-insulator-metal diodes made by rapid atmospheric pressure chemical vapor deposition
Advanced Functional Materials, accepted. Congratulations to Viet!
A quantum-tunneling metal-insulator-metal (MIM) diode is fabricated by atmospheric pressure chemical vapor deposition (AP-CVD) for the first time. This scalable method is used to produce MIM diodes with high-quality, pinhole-free Al2O3 films more rapidly than by conventional vacuum-based approaches. This work demonstrates that clean room fabrication is not a prerequisite for quantum-enabled devices. In fact, the MIM diodes fabricated by AP-CVD show a lower effective barrier height (2.20 eV) at the electrode-insulator interface than those fabricated by conventional plasma-enhanced atomic layer deposition (2.80 eV), resulting in a lower turn on voltage of 1.4 V, lower zero-bias resistance and better asymmetry of 107.
2018-11-28 using UV radiation under soft conditions to improve the mobility of air-processed ZnO:Al thin films
Increasing the Electron Mobility of ZnO-Based Transparent Conductive Films Deposited by Open-Air Methods for Enhanced Sensing Performance
ACS Applied Nano Materials, accepted. Congratulations to Viet!!
The development of open-air, high-throughput, low-cost thin film fabrication techniques has immense potential and interest in optoelectronics. However, the oxygen-rich atmosphere associated with such processes can have detrimental effects on the electrical properties of the deposited films. An example of this is found in materials based on ZnO, for which atmospheric processing results in low mobility values. This stems mainly from adsorbed oxygen species at the grain boundaries, which limit carrier transport. This paper describes the effect of a low-temperature UV treatment on the electrical properties of ZnO and aluminum doped zinc oxide (ZnO:Al) films deposited by Atmospheric Pressure Spatial Atomic Layer Deposition (AP-SALD). Thanks to the mild UV treatment, a significant decrease in the amount of oxygen traps at the grain boundaries has been observed. This results in a large improvement of the carrier mobility, up to 47 times for undoped ZnO and 16 times for ZnO:Al. The effect of temperature (RT to 220 °C) during the UV treatment on the conductivity of undoped ZnO and ZnO:Al films is discussed. The study of the time-dependent conductivity of ZnO and ZnO:Al films using tunneling emission based models provides a simple means for extracting the grain boundary trap density, a critical parameter in semiconductors that is usually not easy to estimate. We show that the high conductivity of the UV-treated films can be preserved when exposed to oxygen at high temperature thanks to a very thin alumina (Al2O3) barrier layer. Finally, we demonstrate that the effect of UV illumination of thin ZnO films deposited in oxidizing atmospheres can be used to design improved UV or oxygen sensors.
2018-10-08 Congratulations to Viet Nguyen for passing his PhD viva!!! Excellent thesis and excellent Viva!!!
2018-10-01 We welcome Chiara Crivello and Abderrahime Sekkat, new PhD students in the SALD group.
2018-09-20 Very happy about the many positive feedback on our ALD symposium at the E-MRS.
Congratulations to Eun Gyo Jeong for the best poster award, sponsored by Wiley Advanced Materials Interfaces (Thanks Dr. A. Troeger, Wiley Editor, for giving the award to Prof. Riedl in representation of Eun Gyo Jeong).
Congratulations to Sandra Haschke for the best graduate student presentation, sponsored by Picosun (Thanks to C. Hossbach for giving the award)
Below a picture of the nice dinner between most of the invited speakers, the scientific and the organising committee. Thanks to Prof. Marek Godlewski for taking us to such a nice place!
2018-09-11 Nice Surprise! Viet's image has been chosen for the cover of the June issue of Nanotoday
Congratulations to Viet!
2018-08-16 CuO spotted within Cu2O thin films. In collaboration with E. Fortunato from CENIMAT.
Visualization of nanocrystalline CuO in the grain boundaries of Cu2O thin films and effect on band bending and film resistivity
APL Materials, 2018. Congratulations to Hongjun!!
Direct evidence for the presence of a CuO structure in the grain boundaries of Cu2O thin films is provided by high resolution automated phase and orientation mapping (ASTAR), which was not detectable by classical transmission electron microscopy techniques. Conductive atomic force microscopy (C-AFM) revealed that the CuO causes a local loss of current recti.cation at the Schottky barrier between the C-AFM tip and Cu2O. The suppression of CuO formation at the Cu2O grain boundaries is identifi.ed as the key strategy for future device optimization.
2018-08-8 Photodectors with fast response deposited processed at low temperature and atmospheric pressure.
ZnO / CuCrO2 Core-Shell Nanowire Heterostructures for Self-Powered UV Photodetectors with Fast Response
Advanced Functional Materials, 28, 1803142, 2018. Congratulations to Thomas and Joao!!
An original self-powered UV photodetector integrating ZnO / CuCrO2 core-shell nanowire heterostructures is fabricated using low-cost and scalable chemical deposition techniques operating at moderate temperatures. A 35 nm-thick delafossite phase CuCrO2 shell is formed with high uniformity by aerosol-assisted chemical vapor deposition over an array of vertically aligned ZnO nanowires grown by chemical bath deposition. The CuCrO2 shell consists of columnar grains at the top of ZnO nanowires as well as nano-grains with some preferential orientations on their vertical sidewalls. The ZnO / CuCrO2 core-shell nanowire heterostructures exhibit significant diode behavior, with a rectification ratio approaching 1.2 x 104 at ±1 V, as well as a high optical absorptance above 85% in the UV part of the electromagnetic spectrum. A high UV responsivity at zero bias under low-power illumination of up to 3.43 mA/W under a 365 nm UV lamp, and up to 5.87 mA/W at 395 nm from spectrally-resolved measurements, alongside a high selectivity with a UV-to-visible (395-550 nm) rejection ratio of 106 are measured. The short rise and decay times of 32 and 35 µs, respectively, both measured at zero bias, further establish these devices as promising candidates for cost-efficient, all-oxide self-powered UV photodetectors.
2018-07-31 Invited talk at the AVS ALD conference.
you can see my presentation at the following site (AVS membership required): https://www.pathlms.com/avstechnicallibrary/events/1220/video_presentations/113727
2018-06-16 Rationalisation of nanocomposite hazy transparent conductive oxides
Hazy Al2O3-FTO Nanocomposites: A Comparative Study with FTO-Based Nanocomposites Integrating ZnO and S:TiO2 Nanostructures
Nanomaterials, 2018. Congratulations Shan-Ting!!
We report the use of Al2O3 nanoparticles in combination with fluorine doped tin oxide (F:SnO2, aka FTO) thin films to form hazy Al2O3-FTO nanocomposites. In comparison to previously reported FTO-based nanocomposites integrating ZnO and sulfur doped TiO2 (S:TiO2) nanoparticles (i.e., ZnO-FTO and S:TiO2-FTO nanocomposites), the newly developed Al2O3-FTO nanocomposites show medium haze factor HT of about 30%, while they exhibit the least loss in total transmittance Ttot. In addition, Al2O3-FTO nanocomposites present a low fraction of large-sized nanoparticle agglomerates with equivalent radius req > 1 μm; effectively 90% of the nanoparticle agglomerates show req < 750 nm. The smaller feature size in Al2O3-FTO nanocomposites, as compared to ZnO-FTO and S:TiO2-FTO nanocomposites, makes them more suitable for applications that are sensitive to roughness and large-sized features. With the help of a simple optical model developed in this work, we have simulated the optical scattering by a single nanoparticle agglomerate characterized by bottom radius r0, top radius r1, and height h. It is found that r0 is the main factor affecting the HT(λ), which indicates that the haze factor of Al2O3-FTO and related FTO nanocomposites is mainly determined by the total surface coverage of all the nanoparticle agglomerates present.
2018-05-31 Guest Editor of the Frontiers Research Topic: Window Electrodes for Emerging Thin Film Photovoltaics
2018-05-23 Deadline approaching! 28th May: Symposium dedicated to ALD in the coming E-MRS meeting in Warsaw
2018-05-17 A new model for highly doped semiconducting polycrystalline thin films.
Electron tunneling through grain boundaries in transparent conductive oxides and implications for electrical conductivity
Materials Horizons, accepted. Congratullations Viet!
In this work, we have applied the Airy Function Transfer-Matrix Method to provide a numerical description of the charge scattering mechanisms taking place at the grain boundaries in polycrystalline, degenerately Al-doped ZnO (ZnO:Al) films, one of the most studied Transparent Conductive Oxides (TCOs). By discretizing the potential barrier at the grain boundary into linear segments, an accurate calculation of the electron tunneling probability through the grain boundaries have been obtained. Conversely to analytical models based on the Wentzel–Kramers–Brillouin (WKB) approximation, our new approach is valid for any doping level. We thus provide a complete model that allows a comprehensive explanation for carrier transport in highly doped semiconductors, for which charge tunneling across grain boundaries cannot be neglected. We have tested our model with ZnO:Al thin films prepared by different physical and chemical deposition techniques, namely, sputtering, atomic layer deposition and atmospheric pressure spatial atomic layer deposition. A linear relationship between trap density at the grain boundaries and carrier density has been extracted by fitting our model to Hall mobility data for the different samples. Our results provide a guidance on how to adapt the deposition conditions to obtain high-quality materials, with an optimum ratio between optical and electrical properties as required for specific applications.
2018-05-10 Making AgNWs transparent electrodes more stable with oxide coatings deposited by AP-SALD.
Stability enhancement of silver nanowire networks with conformal ZnO coatings deposited by atmospheric pressure spatial atomic layer deposition
ACS Advanced Materials & Intercaces. Congratullations Viet!
Silver nanowire (AgNW) networks offer excellent electrical and optical properties and have emerged as one of the most attractive alternatives to transparent conductive oxides to be used in flexible optoelectronic applications. However, AgNW networks still suffer from chemical, thermal and electrical instabilities which in some cases can hinder their efficient integration as transparent electrodes in devices such as solar cells, transparent heaters, touch screens or organic light emitting diodes (OLEDs). We have used atmospheric pressure spatial atomic layer deposition (AP-SALD) to fabricate hybrid transparent electrode materials in which the AgNW network is protected by a conformal thin zinc oxide layer. The choice of AP-SALD allows to maintain the low-cost and scalable processing of AgNW based transparent electrodes. The effects of the ZnO coating thickness on the physical properties of AgNW networks are presented. The composite electrodes show a drastic enhancement of both thermal and electrical stabilities. We found that bare AgNWs were stable only up to 300 °C when subjected to thermal ramps while the ZnO coating improved stability up to 500 °C. Similarly, ZnO coated AgNWs exhibited an increase of a 100 % in electrical stability with respect to bare networks, withstanding up to 18 V. A simple physical model shows that the origin of the stability improvement is the result of hindered silver atomic diffusion thanks to the presence of the thin oxide layer and the quality of the interfaces of hybrid electrodes. The effects of ZnO coating on both the network adhesion and optical transparency are also discussed. Finally, we show that the AP-SALD ZnO-coated AgNW networks can be effectively used as very stable transparent heaters.
2018-05-03 Seeing how good silver nanowire networks are, and how they fail.
Electrical Mapping of Silver Nanowire Networks: A Versatile Tool for Imaging Network Homogeneity and Degradation Dynamics during Failure
ACS Nano. Congratullations Thomas!
Electrical stability and homogeneity of silver nanowire (AgNW) networks are critical assets for increasing their robustness and reliability when integrated as transparent electrodes in devices. Our ability to distinguish defects, inhomogeneities, or inactive areas at the scale of the entire network is therefore a critical issue. We propose one-probe electrical mapping (1P-mapping) as a specific simple tool to study the electrical distribution in these discrete structures. 1P-mapping has allowed us to show that the tortuosity of the voltage equipotential lines of AgNW networks under bias decreases with increasing network density, leading to a better electrical homogeneity. The impact of the network fabrication technique on the electrical homogeneity of the resulting electrode has also been investigated. Then, by combining 1P-mapping with electrical resistance measurements and IR thermography, we propose a comprehensive analysis of the evolution of the electrical distribution in AgNW networks when subjected to increasing voltage stresses. We show that AgNW networks experience three distinctive stages: optimization, degradation, and breakdown. We also demonstrate that the failure dynamics of AgNW networks at high voltages occurs through a highly correlated and spatially localized mechanism. In particular the in situ formation of cracks could be clearly visualized. It consists of two steps: creation of a crack followed by propagation nearly parallel to the equipotential lines. Finally, we show that current can dynamically redistribute during failure, by following partially damaged secondary pathways through the crack.
2018-05-2 Seminar in METU, Ankara, for a crowded auditorium! Thanks a lot to Dr. Emrah Unlanan for organising it. Superb research and fantastic team!
2018-04-6 With Viet and Thomas at the MRS spring meeting, in Phoenix.
2018-04-1 We welcome Lukas Fusek. He'll be doing an internship in the group until the summer working on our SALD system.
2018-03-18 Congratulations to Viet Nguyen, winner of the Nanoart Contest (February 2018), awarded by the Nanosciences Fondation.
2018-03 Organization of a symposium dedicated to ALD in the coming E-MRS meeting in Warsaw
2017-12-23 Trasparent electrodes based on Cu Nanowire Networks become more stable thanks to plastic and SALD encapsultaion. In collaboration with J-P. Simonato from LETI
Oxidation of Copper Nanowires based Transparent Electrodes in Ambient Conditions and their Stabilization by Encapsulation. Application to Transparent Film Heaters
Whereas the integration of silver nanowires in functional devices has reached a fair level ofmaturity, the integration of copper nanowires still remains difficult, mainly due to the intrinsic
instability of copper nanowires in ambient conditions. In this paper, copper nanowire based
transparent electrodes with good performances (33 Ω sq−1 associated with 88% transparency)
were obtained, and their degradation in different conditions was monitored, in particular by
electrical measurements, transmission electron microscopy, x-ray photoelectron spectrometry
and Auger electron spectroscopy. Several routes to stabilize the random networks of copper
nanowires were evaluated. Encapsulation through laminated barrier film with optical clear
adhesive and atmospheric pressure spatial atomic layer deposition were found to be efficient and
were used for the fabrication of transparent film heaters.
2017-12-13 Farewell lunch with Hongjun. Good luck for the future!!
This is one of the best things when doing research: 8 people, 8 nationalities!!! From left to right: César (México), Hongjun (China), Me (Spain), Viet (Vietnam), Thomas (Fance), Getnet (Ethiopia), Sara (Iran), Evgenii (Russia). And even the one missing (my fault), Dorina (Greece).
2017-12-05 Building bridges thanks to ALD and new materials.
2017-11-27 We welcome Pedro Veiga. He'll be doing an internship in the group until the summer working on our SALD system.
2017-11-06 Invited lecturer and speaker at the 2017 edition of the INT MINATEC SCHOOL and IWNA conference, Vietnam.
2017-10-31 Congratulations to Hongjun Liu for passing his PhD viva!!! Great job!!!
At the LMGP stand in the French Science Week 2017
We welcome DorinaPapanastasiou, new PhD student in the group, who'll be working on Silver nanowire networks.
Invited paper in CRAS just published
Spatial Atomic Layer Deposition (SALD), an emerging tool for energy materials. Application to new-generation photovoltaic devices and transparent conductive materials
Materials properties are the keystone of functional devices for energy including energy conversion, harvesting or storage. But to market new energy materials, the development of suitable processing methods allowing affordable prices is needed. Recently, a new approach to atomic layer deposition (ALD) has gained much momentum. This alternative approach is based on separating the precursors in space rather than in time, and has therefore been called Spatial ALD (SALD). With SALD, the purge steps typical of ALD are not needed and thus deposition rates a hundred times faster are achievable. Additionally, SALD can be easily performed at ambient atmosphere, thus it is easier and cheaper to scale up than conventional ALD. This opens the door to widespread industrial application of ALD for the deposition of energy materials for applications including solar energy, energy storage, or smart windows. SALD is presented here and examples of application to photovoltaics and transparent conductive materials are given. We show that SALD is capable of producing high-quality films fully suited for device integration.
Probing the nature of TiO2 blocing layers for photovolatic applications
Polymorphism of the Blocking TiO2 Layer Deposited on F:SnO2 (FTO) and Its Influence on the Interfacial Energetic Alignment
Journal of Physical Chemistry C, accepted. Congratulations to Shan-Ting Zhan!!
As widely employed in dye-sensitized, perovskite, and quantum-dot solar cells, the interface between F-doped SnO2 (FTO) and blocking TiO2 (b-TiO2) is essential in understanding the working principles of these types of solar cells. In this work, we have deposited b-TiO2 layers using a simple sol-gel method. While the b-TiO2 layers deposited on Si (100) wafers form pure anatase polymorph, we have found that the rutile structure of the FTO substrates consistently induces the b-TiO2 layers to crystallize into mixed anatase and rutile polymorphs - the same is observed on rutile RuO2 substrates. This indicates that the rutile structural similarity favors the formation of rutile polymorph in b-TiO2 layers; due to the coexistence of both anatase and rutile polymorphs, the interface of FTO/b-TiO2 is essentially inhomogeneous. We also show that the amount of rutile polymorph present in the b-TiO2 layer is a function of layer thickness, with rutile polymorph dominating in thin b-TiO2 layers. As a result, the energetic alignment at the FTO/b-TiO2interface in general still favors the charge transport. This is confirmed by directly probing an ultra-thin (<10 nm) b-TiO2 layer using X-ray photoelectron spectroscopy (XPS). We emphasize that the rutile structure of FTO substrate plays a significant role in determining the polymorph of successively deposited b-TiO2 layer, which in turn affects the energetic alignment with FTO electrodes and mesoporous nanocrystalline TiO2, and ultimately the performance of solar devices.
New paper on the deposition of FTO epitaxial films using low-cost spray pyrolysis
High quality epitaxial fluorine-doped SnO2 films by ultrasonic spray pyrolysis: in-depth structural and physical property investigation
Materials and Design, 2017, 132, 518-525. Congratulations to Shan-Ting Zhan!!
Despite its wide use in the display and photovoltaic industries, fluorine-doped tin oxide (F:SnO2, FTO) has been studied only in its polycrystalline form. In this work, we report on the first growth of epitaxial FTO thin film by ultrasonic spray pyrolysis – a simple chemical deposition method – and we reveal the structure-property interplay by investigating in details its growth, morphology and strain/defects. Epitaxial FTO films are successfully grown on (110) rutile TiO2 single crystals and form mosaic domains with an out-of-plane distribution smaller than 0.5°, showing high structural quality comparable to epitaxial films prepared by molecular beam epitaxy and pulsed-laser deposition. Owing to the large lattice mismatch with rutile TiO2, the FTO film develops significant structural defects to release the epitaxial strain and is consequently nearly fully relaxed with a slight residual strain of 0.1-0.2%. With the help of an innovative nano-beam precession electron diffraction technique, the strain distribution is mapped at the TiO2/FTO interface, from which we could identify the interfacial and secondary strain relaxation taking place mainly in the first 22 nm in the FTO film. The Hall-mobility of the epitaxial FTO films is close to the state-of-the-art and expected to improve further at lower carrier concentrations.
New paper on the deposition of Ag coating by Aerosol Assisted MOCVD using two new Ag metalorganic precursors
http://pubs.rsc.org/en/content/articlelanding/2014/dt/c7dt01647f#!divAbstract Congratulations to Hongjun Liu!!
This work reports two new silver metalorganic precursors for the chemical vapor deposition of Ag metallic coatings. Both precursors are based on β-diketonate adducts, namely, Ag(hfac)(L) (H-hfac= 1,1,1,5,5,5-hexafluoro-2,4-pentanedione), where L is 1,10-phenanthroline (phen) or 2,5,8,11-tetraoxadodecane (triglyme). Using these ligands, the designed precursors have better solubility in alcoholic solvents and are less toxic and costly than previously reported ones. The new precursors have been characterized and their crystallographic structure solved. With the new triglyme precursor, [Ag(triglyme)2]+[Ag(hfac)2]- , pure metallic Ag coatings made of Ag nanoparticles about 20 nm in diameter were succesfully deposited on glass and Si substrates using Aerosol Assisted Metalorganic CVD (AA-CVD).
A very nice initiative, worth supporting
https://www.indiegogo.com/projects/my-super-science-heroes-marie-curie-series#/
We welcome Kissan Mistry, PhD student in the University of Waterloo, Canada, who'll be visiting during three months to work on the deposition of ZnO based devices using our SALD system within the framework of our ongoing collaboration with Prof. Musselman's group.
We welcome Théodulf Rousseau, who has joined the group as Postdoc (funded by CEMAM) for the development of solar cells with innovative architectures
New paper on AgNWs based transparent conductive materials
Transparent electrodes based on silver nanowire networks: from physical considerations towards device integration
Materials,special issue: http://www.mdpi.com/journal/materials/special_issues/advances_transparent_conducting_materials
Materials 2017, 10(6), 570; doi:10.3390/ma10060570
The past few years have seen a considerable amount of research devoted to nanostructured transparent conducting materials (TCM), which play a pivotal role in many modern devices such as solar cells, flexible light-emitting devices, touch screens, electromagnetic devices, and flexible transparent thin film heaters. Currently, the most commonly used TCM for such applications (ITO: Indium Tin oxide) suffers from two major drawbacks: brittleness and indium scarcity. Among emerging transparent electrodes, silver nanowire (AgNW) networks appear to be a promising substitute to ITO since such electrically percolating networks exhibit excellent properties with sheet resistance lower than 10 Ω/sq and optical transparency of 90%, fulfilling the requirements of most applications. In addition, AgNW networks also exhibit very good mechanical flexibility. The fabrication of these electrodes involves low-temperature processing steps and scalable methods, thus making them appropriate for future use as low-cost transparent electrodes in flexible electronic devices. This contribution aims to briefly present the main properties of AgNW based transparent electrodes as well as some considerations relating to their efficient integration in devices. The influence of network density, nanowire sizes, and post treatments on the properties of AgNW networks will also be evaluated. In addition to a general overview of AgNW networks, we focus on two important aspects: (i) network instabilities as well as an efficient Atomic Layer Deposition (ALD) coating which clearly enhances AgNW network stability and (ii) modelling to better understand the physical properties of these networks. View Full-Text
Congratulations to Shan-ting Zhang for passing her PhD viva!!! Excellent job!!!
New paper on ZnO based thin films deposited by SALD as components in solar cells
Deposition of ZnO based thin films by Atmospheric Pressure Spatial Atomic Layer Deposition (AP-SALD) for application in solar cells
Journal of Renewable and Sustainable Energy, 2017, 9, 021203. Congratulations to Viet Nguyen!!
The use of Atmospheric Pressure Spatial Atomic Layer Deposition (AP-SALD) has gained popularity in the last decade. The success of this technique relies on the possibility to deposit thin films in a fast, vacuum-free, low-cost, low-damage and high throughput way. In this work, we present ZnO and Aluminium doped ZnO (AZO) films deposited by AP-SALD at low temperature (<220 ºC) with high uniformity and conformity. The ZnO films present a high transparency of 80 % – 90 % in the visible range, with a tuneable band-gap, between 3.30 eV and 3.55 eV, controlled by the deposition temperature. Carrier density reaches values greater than 3 x 1019 cm-3, while the electron mobility of the films is as high as 5,5 cm2V-1s-1, resulting in an optimum resistivity of 5x 10-2 Ohm.cm. By doping ZnO with aluminium, the resistivity decreases down to 5,57 x 10-3 Ohm.cm, as a result of a significant increase in carrier density up to 4,25x 1020 cm-3. The combination of ZnO thin films with p-type cuprous oxide (Cu2O), deposited by Aerosol Assisted Metal Organic Chemical Vapor deposition (AA-MOCVD) allowed the formation of oxide-based pn junctions. The dark I-V characteristic curve confirms a rectifying behaviour, opening the window for the production of all-oxide solar cells completely by chemical vapour deposition methods. We also show the potential of AP-SALD to deposit AZO as transparent conductive oxide (TCO) layer for silicon heterojunction solar cells.
Highlighted in Twitter by Bald Engineering while presenting in the ALD4INDUSTRY workshop 2017, Dresde, Germany
Beautiful TiO2 microflowers with hierarchical structure.
Structural study of TiO2 hierarchical microflowers grown by aerosol assisted MOCVD.
CrystEngComm, 2017, 19, 1535-1544. Congratulations to Sayari Biswas!!
TiO2 is a promising n-type semiconductor for optoelectronic devices, in particular dye sensitized and hybrid solar cells, andmore recently for hybrid perovskite-based solar cells,as well as for lithium batteries. For these applications, TiO2 structuresoffering a high mesoporosity and surface area are especially interesting as it increases the efficiency of phenomena takingplace at the interfaces. We have used aerosol assisted metalorganic chemical vapor deposition (AA-MOCVD) to depositTiO2 films containing hierharchical TiO2 microflowers. Both the film and the microflowers crystallize with the anatasestrucrture. The microflowers have diameters of around 2-3 microns while the petals are only several nanometers thick.The density of microflowers and of petals in each flower can be controlled by adjusting the deposition parameters. Thesemicrostructures are stable to high temperature annealing (950 °C). In this communication, we describe the synthesis of themicroflowers and present the detailed study of their structural and morphological properties.
Close proximity AP-SALD: Fast deposition of functional films on 3D devices shown
Rapid open-air deposition of uniform, nanoscale, functional coatings on nanorod arrays
Coating of high-aspect-ratio nanostructures has previously been achieved using batch processes poorly suited for high-throughput manufacturing. It is demonstrated that uniform, nanoscale coatings can be rapidly deposited on zinc oxide nanorod arrays in open-air using an atmospheric pressure spatial deposition system. The morphology of the metal oxide coatings is examined and good electrical contact with the underlying nanorods is observed. The functionality of the coatings is demonstrated in colloidal quantum dot and hybrid solar cells.
HDR (habilitation à diriger des recherches) obtained!
New member of the Ag-Cu mixed oxides family: (in collaboration with N. Casañ-Pastor from ICMAB-CSIC)
Ag2Cu3Cr2O8(OH)4:A new bidimensional silver-copper mixed -oxyhydroxide with in-plane ferromagnetic coupling
Dalton Transactions, 2017,46, 1093-1104.
Ag2Cu3Cr2
O8(OH)4, a new Ag-Cu-Cr-O layered mixed oxide, prepared by soft hydrothermal heterogeneous reactions, is reported. The new phase is an oxohydroxide and presents a structure with alternating brucite-like Cu-O and Ag-O layers and connected by individual chromate groups. The crystallographic structure has been solved and refined from high resolution powder X-ray diffraction data and is supported by density functional theory calculations, yielding a triclinic, space group P-1, a = 5.3329(1) Å, b = 5.3871(1) Å, c = 10.0735(1) Å, α = 80.476(1) °, β = 87.020(1) °, γ = 62.383(1)°. Bond valence sums suggest the formulation Ag+2Cu2+3Cr6+2O8(OH)4, an electronic state fully supported by X-ray photoelectron spectroscopy (XPS) and Cr K-edge X-ray absorption near edge structure (XANES) measurements. Ag2Cu3Cr2O8(OH)4 exhibits bidimensional Cu-O-Cu ferromagnetic correlations that are apparent at much higher temperatures than in other similar Cu-O layered structures, without coupling between Cu-O layers, which represents a unique case in the recent family of silver copper oxides. The role of Ag inducing bidimensionality in copper oxides is therefore expanded further with the presence of chromate anions. Ab initio calculations using density functional theory show that the electronic states involved originate mainly from Cu and OH orbitals, with minor contributions from Cr and the O atoms linking the Cr tetrahedra to the brucitic Cu-O layer, and almost no contribution from Ag. Further modeling of the in-plane magnetic interactions between Cu atoms suggests that coupled magnetized stripes are responsible for the observed behavior. The results are discussed in relation with previous Ag-Cu mixed oxide phases where metallic behavior or ferro-antiferro transitions had been observed. The structure of this new Ag-Cu-O phase as compared with previous silver copper oxides supports the conclusion that Ag-Cu layered ordering is favored in oxidizing conditions.
Congratulations to César Masse, selected for the eit Innoenergy doctorate program!!!
New paper: Enhancing the stability of transparent heaters based on silver nanowire networks with ALD TiO2 coatings.
Understanding the mechanisms leading to failure in metallic nanowire-based transparent heaters, and solution for stability enhancement
Nanotechnology, 2017, 28, 055709. Congratulations to Mélanie Lagrange!!
Silver nanowire (AgNW) networks are emerging as one of the most promising alternative to indium tin oxide (ITO) for transparent electrodes in flexible electronic devices. They can be used in several optoelectronic applications such as solar cells, touch panels and organic light emitting diodes. Recently they have also proven to be very efficient when used as transparent heaters (TH). In addition to the study of AgNW networks as TH in regular use, i.e. at low voltage and moderate temperature, their stability and physical behavior at higher voltages and for longer durations should be studied in view of integration into real devices. The properties of AgNW networks deposited by spray coating on glass or flexible transparent substrates are thoroughly studied via in situ measurements. The AgNW networks’ behavior at different voltages for different durations and under different atmospheric conditions, both in air and under vacuum, has been examined. At low voltage, a reversible electrical response is observed while irreversibility and even failure are observed at higher voltages. In order to gain a deeper insight into the behavior of AgNW networks used as transparent heaters, simple but realistic physical models are proposed and found to be in fair agreement with experimental data. Finally, as the stability of AgNW networks is a key issue, we demonstrate that coating AgNW networks with a very thin layer of TiO2 using atomic layer deposition improves the material resistance against electrical and thermal instabilities without altering optical transmittance. We show that the critical annealing temperature associated to network breakdown increases from 270 °C for as deposited AgNW networks to 420 °C for AgNW networks coated with TiO2. Similarly, the electrical failure which occurs at 7 V for as deposited networks has been increased to 13 V for TiO2 coated networks. TiO2 also proved to stabilize AgNW networks during long duration operation and at high voltage. Temperature higher than 235 °C was achieved at 7 V without failure.
New paper on highly conductive TiO2-FTO composite transparent electrodes with tunable properties:
Tuning the properties of F:SnO2 (FTO) nanocomposites with S:TiO2 nanoparticles as promising hazy transparent electrodes for photovoltaics applications.
J. Mater. Chem. C, 2017,5, 91-102. Congratulations to Shan-Ting Zhan!!
The proper choice of nanoparticles is proved to be essential in tuning the properties of F:SnO2 (FTO) nanocomposites. With the use of more conductive sulphur-doped TiO2 (S:TiO2) nanoparticles, the sheet resistance of S:TiO2-FTO nanocomposites is successfully reduced down to 38% as compared to standard flat FTO (11.7 Ω/sq), while the haze factor of the S:TiO2-FTO nanocomposites can be varied from almost zero (reference flat FTO) up to 60%; in the meantime the majority of <110> oriented S:TiO2 nanoparticles leads to a strong (110) texture of resulting S:TiO2-FTO nanocomposites by local epitaxy. Careful morphology analyses and angle-resolved measurements reveal that the haze factor is proportional to the total surface coverage of the S:TiO2 nanoparticle agglomerates while the feature size of the agglomerates determines the angular distribution of the scattered light – this is confirmed by an angle-resolved Mueller matrix polarimeter which allows to obtain the optical microscopic and angle-resolved images of the exact same textured region. Our work establishes the guidelines to fabricate FTO and other transparent conductive oxide (TCO) nanocomposites as promising electrodes in solar cells with tunable structural, electrical, and optical properties.
New paper on the deposition of epitaxial fluoride films by MOCVD: (in collaboration with G. Malandrino, from Univ. Catania)
The quest towards epitaxial BaMgF4 thin films: exploring MOCVD as a chemical scalable approach for the deposition of complex metal fluoride films.
Dalton Transactions, 2016,45, 17833-17842. Congratualations to Sergio Battiato!
Conventional and Pulsed Liquid Injection MOCVD processes (C-MOCVD and PLI-MOCVD) have been explored as synthetic routes for the growth of BaMgF4 on Si (100) and single crystalline SrTiO3 (100) substrates. For the two applied approaches, the volatile, thermally stable b-diketonate complexes Ba(hfa)2tetraglyme and Mg(hfa)2(diglyme)2(H2O)2 have been used as single precursors (C-MOCVD) or as a solution multimetal source (PLI-MOCVD). Structural characterization through X-ray diffraction (XRD) measurements and transmission electron microscopy (TEM) analyses confirmed the formation of epitaxial BaMgF4 films on SrTiO3 substrates. Energy dispersive X-ray (EDX) analyses have been used to confirm composition and purity of deposited films. The impact of process parameters on film properties has been addressed, highlighting the strong influence of precursor ratio, deposition temperature and oxygen partial pressure on composition, microstructure and morphology of the films. Both methods appear well suited for the growth of the BaMgF4 phase, but while PLI-MOCVD yields a more straightforward control of the precursor composition that reflects on film stoichiometry, C-MOCVD provides an easier control of the degree of texturing as a function of temperature.
New paper showing the application of IR thermography for the live imaging of the formation of electronic percolation pathways in Ag nanowire networks:
Nano Letters, accepted 2016. Congratulations to Thomas Sannicolo!
Advancement in the science and technology of random metallic nanowire (MNW) networks is crucial for their appropriate integration in many applications, including transparent electrodes for optoelectronics and transparent film heaters. We have recently highlighted the discontinuous activation of efficient percolating pathways (EPPs) for networks having densities slightly above the percolation threshold. Such networks exhibit abrupt drops of electrical resistance when thermal or electrical annealing is performed, giving rise to a “geometrically quantized percolation”. In this letter, Lock-in Thermography (LiT) is used to provide visual evidence of geometrical quantized percolation: when low voltage is applied to the network, individual “illuminated pathways” can be detected and new branches get highlighted as the voltage is incrementally increased. This experimental approach has allowed us to validate our original model and map the electrical and thermal distributions in silver nanowire (AgNW) networks. We also study the effects of electrode morphology and wire dimensions on quantized percolation. Furthermore we demonstrate that the network failure at high temperature can also be governed by a quantized increase of the electrical resistance, corresponding to the discontinuous destruction of individual pathways (anti-percolation). More generally, we demonstrate that LiT is as a promising tool for the detection of conductive sub-clusters, as well as hot spots in AgNW networks.
NEW SALD system developed and Book on Materials For Energy are featured in MINANEWS
We welcome Cesar Masse de la Huerta, who will join us soon as a PhD student, funded by CONACYT, to work on the development of SALD for the fabrication of innovative solar cells.
Congratulations to Viet Nguyen for the "Best Poster Award" in the RAMSES School, Milan, Italy.
We welcome Salvatore Sanzaro, from the University of Catania, who will join the group during 3 months to grow TiO2 nanostructures and TCOs by CVD and Spray Pyrolysis for application in solar cells.
We welcome Stéphane Brochen, who has joined the group as Postdoc (funded by CEMAM) for the development of solar cells with innovative architectures
New book coedited with Prof. Moya on Materials for Energy
Member of the organizing committee of RAFALD2016
Congratulations to Sayari Biswas for the 3rd prize to the best 2015 Nanoart image contest.
Congratulations to Viet Nguyen who has rated 1 out of 82 in his Materials Science and Engineering undergrad program. INSA Lyon
New paper on the application of AP-SALD to the fundamental study of new generation PV devices:
The Influence of an Inorganic Interlayer on Exciton Separation in Hybrid Solar Cells.
ACS Nano, accepted 2015. Congratulations to Claire Armstrong!
"It has been shown that in hybrid polymer-inorganic photovoltaic devices, not all the photo-generated excitons dissociate at the interface immediately, but can instead exist temporarily as bound charge pairs (BCPs). Many of these BCPs do not contribute to the photocurrent as their long lifetime as a bound species promotes various charge carrier recombination channels. Fast and efficient dissociation of BCPs is therefore considered a key challenge in improving the performance of polymer-inorganic cells. Here we investigate the influence of an inorganic energy cascading Nb2O5 interlayer on the charge carrier recombination channels in poly(3-hexylthiophene-2,5-diyl) (P3HT)-TiO2 and PbSe colloidal quantum dot-TiO2 photovoltaic devices. We demonstrate that the additional Nb2O5 film leads to a suppression of BCP-formation at the heterojunction of the P3HT cells and also a reduction in the non-geminate recombination mechanisms in both types of cells. Furthermore we provide evidence that the reduction in non-geminate recombination in the P3HT-TiO2 devices is due in part to the passivation of deep mid-gap trap states in the TiO2, which prevents trap assisted Shockley-Read-Hall recombination. Consequently a significant increase in both the open-circuit voltage and the short-circuit current was achieved, in particular for P3HT-based solar cells where the power conversion efficiency increased by 39%."
Congratulations to Sayari Biswas, Exchange PhD student (ERASMUS), winner of the Nanoart Contest (Agust 2015), awarded by the Nanosciences Fondation.
Congratulations to Shanting Zhang for the "Best student presentation award", sponsored by the Royal Society of Chemistry, E-MRS Fall meeting, symposium G!!!
Congratulations to Sayari Biswas, Exchange PhD student (ERASMUS) for the best oral presentation award in EuroCVD!!!!
Plenary lecture at the Thep-Center annual meeting, Krabi, Thailand, 21/05/2015
Member of the Scientific Committee, symposium G, E-MRS 2015 Fall Meeting:
“Transparent conductive materials: from fundamental understanding to applications”
at the E-MRS 2015 Fall Meeting (15-18 September 2015, Tuesday-Friday) in Warsaw, Poland.
http://www.emrs-strasbourg.com/index.php?option=com_content&task=view&Itemid=1662&id=876
Congratulations to Hongjun Liu, selected for the Kic Innoenergy doctorate program!!!
Co-organizer of RAFALD
Participation in a Marie Curie EJD project :
http://euromat2015.fems.org/scientific-programme/detailed-programme/
Warsaw, Poland 20-24 September 2015.
Call for abstract open: http://euromat2015.fems.org/scientific-programme/call-for-abstracts/
International workshop on materials for energy
Synthesis and modeling of uniform complex metal oxides by close-proximity atmospheric pressure chemical vapor deposition
ACS Appl. Mater. Interfaces, Just Accepted Manuscript
ACS Appl. Mater. Interfaces, 2015, 7 (20), pp 10684–10694
Research update on ZnO deposited by Atmospheric Pressure Spatial Atomic Layer Deposition
"Atmospheric pressure spatial atomic layer deposition (AP-SALD) has recently emerged as an appealing technique for rapidly producing high quality oxides. Here, we focus on the use of APSALD
to deposit functional ZnO thin films, particularly on the reactors used, the film properties and the dopants that have been studied. We highlight how these films are advantageous for the
performance of solar cells, organometal halide perovskite LEDs and thin-film transistors. Future AP-SALD technology will enable the commercial processing of thin films over large areas on a
sheet-to-sheet and roll-to-roll basis, with new reactor designs emerging for flexible plastic and paper electronics."
APL Materials, 3, 040701, 2015.
Co-organizer of symposium A1.1 Materials for Energy Harvesting, EUROMAT2015
MARIE CURIE "CAREER INTEGRATION GRANT" (CIG) Awarded to Dr. Muñoz-Rojas to carry out his research at the LMGP.
Minireview on novel spatial ALD for low-cost photovoltaics accepted in Materials Horizons
"Recently, a new approach to atomic layer deposition (ALD) has been developed that doesn't require vacuum and is much faster than conventional ALD. This is achieved by separating the precursors in space rather than in time. This approach is most commonly called Spatial ALD (SALD). In our lab we have been using/developing a novel atmospheric SALD system to fabricate active components for new generation solar cells, showing the potential of this novel technique for the fabrication of high quality materials that can be integrated into devices. In this minireview we will introduce the basics of SALD and illustrate its great potential by highlighting recent results in the field of photovoltaics. "