JCR Articles

Peak-fitting of Cu 2p photoemission spectra in Cu0, Cu1+, and Cu2+ oxides: A method for discriminating Cu0 from Cu1+ 

Jorge Alejandro Torres-Ochoa, Dagoberto Cabrera-German, Orlando Cortazar-Martinez, Mariela Bravo-Sanchez, Gustavo Gomez-Sosa, Alberto Herrera-Gomez.  

The photoemission spectra of Cu 2p are one of the most studied. Its analysis is especially challenging because, among others, the peaks for Cu0 and Cu1+ overlap, and Cu1+ and Cu2+ coexist under many conditions. The chemical state determination of metallic copper and the initial oxidation mechanism of copper require state-of-the-art peak fitting analysis and background modeling. This work presents a detailed and quantitative analysis of the Cu 2p photoemission spectra for a metallic ultra-thin film and the initial oxidation stages. Additionally, annealed films at 200 °C for up to 5 min were analyzed to assess the full oxidation of the copper oxides and assert the validity of the proposed peak-fitting procedures. For the initial oxidation, it was possible to accurately identify Cu1+ and Cu2+ states and, alongside, quantify the corresponding O 1s species, resulting in compositions close to stoichiometric values. Using the active background, it was possible to achieve close reproduction of all the photoemission spectra; three coexisting copper species were resolved during the fitting procedure. An accurate peak-fitting analysis allowed for quantifying the relative proportion of Cu1+ to Cu0 states despite their strong overlap.

March 2023, Applied Surface Science. (View PDF) 

Detailed peak fitting analysis of the Ni 2p photoemission spectrum for metallic nickel and an initial oxidation

Dulce María Guzman-Bucio, Gustavo Gomez-Sosa, Dagoberto Cabrera-German, Jorge Alejandro Torres-Ochoa, Mariela Bravo-Sanchez, Orlando Cortazar-Martinez, Abraham Jorge Carmona-Carmona, Alberto Herrera-Gomez.  

A quantitative study of the surface composition of clean metallic and partially oxidized nickel exposed to oxygen was carried out employing X-ray photoelectron spectroscopy (XPS). By fitting both branches of the metallic Ni 2p spectrum, it was possible to resolve two previously unreported satellite peaks in the Ni 2p1/2 portion of the spectrum. For the partial oxidation of the nickel surface, we analyzed the Ni 2p, O 1s, and C 1s angle-resolved XPS spectra. Using state- of-the-art peak fitting (including the block approach) and background modeling methods (including the active approach) it was possible to discriminate the peaks of Ni2O3 from those of metallic nickel for both branches of the Ni 2p spectra from partially oxidized nickel. The oxidation of metallic nickel is through the formation of a Ni+3 oxide layer together with deep protrusions. The uncertainties are calculated with the covariance matrix method. The strong overlap and shape similarity of the Ni0 L3M45M45 Auger structure with that of the Ni+3 strongly suggests that the modified Auger Parameter does not provide direct additional insight about the chemical state to that provided by the photoemission spectra.

January 2023, Journal of electron spectroscopy and related phenomena. (View PDF)

Structural, chemical, and MIR response of covellite CuS films via SILAR as opaque Low-E coatings 

Zeuz Montiel-González, Obed Yamín Ramírez-Esquivel, Dagoberto Cabrera-German, Jorge Alejandro Torres-Ochoa, Axel Agustín Ortíz-Atondo, Dalia Alejandra Mazón-Montijo

Studying materials to control solar radiation is a current topic, where covellite CuS (CuS-cov) looks for an opportunity as partially opaque Low-E coating. This work explores the relationship between structural and chemical properties of SILAR deposited CuS-cov films, assessing the impact on the Mid Infrared (MIR) response. Rietveld refinement, together with the compositional analysis, evidence the high control of the synthesis and stability of a nanocrystalline single phase of stoichiometric CuS-cov. The optical behavior in the MIR revealed the impact of the CuS-cov growth, evaluated through the thickness, crystallinity, and composition, as an increasing reflectivity, reaching 80% in the Thermal Infrared for deposition cycles ≥75 (110 nm). With these results, we demonstrate that when the reflectivity of the films is maximized in the Thermal Infrared, these opaque CuS-cov Low-E coatings have emissivities between 0.1 and 0.2, among the lowest reported for commercial transparent conductive oxides.

April 2022, Optical Materials 126:112208 (view PDF)

Oxidation mechanims of metallic chromium at room temperature 

Orlando Cortazar-Martinez, Jorge Alejandro Torres-Ochoa, Joaquin Gerardo Raboño-Borbolla, Alberto Herrera-Gomez. 

A quantitative study of the surface composition of clean metallic and oxidized chromium exposed to atmospheric conditions was carried out employing X-ray photoelectron spectroscopy (XPS). Advanced tools were used for the fitting process and surface composition analysis. We found that, in contrast with most metals, the oxidation does not come about through the formation of an oxide layer. State of the art analysis showed that, even at long exposures, a fraction of the chromium surface retains its metallic nature even at the top layers. Depth profile of XPS spectra shows no shape modulation from angle to angle which strongly suggest both Cr3+ and Cr6+ species coexist with the metallic species throughout the probing depth of XPS. The oxidation mechanism of metallic chromium exposed to ambient is through the partial oxidation of surface regions.

December 2020. Applied Surface Science. Vol 542 (view PDF)

PVP-SiO2 and PVP-TiO2 hybrid films for dielectric gate applications in CdS-bases thin films transistors

M.S. de Urquijo-Ventura, M.G. Syamala Rao, S. Meraz-Davila, J.A. Torres-Ochoa, M.A. Quevedo-Lopez, R. Ramirez-Bon.

We report a simple solution process to deposit organic-inorganic poly (vinyl phenol) (PVP)–SiO2 and PVP-TiO2 hybrid films. The spin dropped hybrid films were prepared at low-temperature and their main properties were studied by TGA, FE-SEM, AFM, FTIR, XPS and contact angle measurements. The results show that the surface of the PVP-SiO2 and PVP-TiO2 hybrid films is smooth with very low surface roughness of 0.25 and 0.51 nm, and surface energy of 48.4 and 40.1 mJ/m2, respectively. The electrical properties of the hybrid films, measured on MIM devices, show low leakage current density under 10−7 A/cm2 and dielectric constant of 5 and 4.6 at 1 kHz, respectively. The hybrid films were used as gate dielectric in solution-processed CdS thin film transistors (TFTs), showing diverse performance. The CdS/PVP-SiO2 devices showed high mobility of 18 cm2/Vs, on/off current ratio of 104, low threshold voltage of 0.6 V and subthreshold swing of 0.25 V/dec. Whereas, the corresponding values for the CdS/PVP-TiO2 ones were 0.45 cm2/Vs, 104, 1.9 V and 1.25 V/dec, respectively. The lower electrical performance of the CdS/PVP-TiO2 devices was attributed to the mismatching surface energies between the surfaces of the dielectric and semiconductor layers, and to the influence of a large number of trapped charges at this interface.

March (2020). Polymer. 191. (view PDF)

Low-Temperature Deposition of Inorganic-Organic HfO2-PMMA hybrid Gate Dielectric Layers for High-Mobility ZnO Thin-Film Transistors

Gouri Syamala Rao Mullapudi, Gonzalo Alonso Velazques-Nevarez, Carlos Avila-Avendano, Jorge Alejandro Torres-Ochoa, Manuel Angel Quevedo-López, Rafael Ramírez-Bon.

present work, we developed a novel inorganic–organic HfO2–PMMA hybrid dielectric material by an efficient eco-friendly sol–gel method, deposited by spin-coating technique and converted into dielectric thin films at a very low thermal annealing temperature of 185 °C. The HfO2–PMMA hybrid thin-film formation was systematically investigated by FTIR and XPS techniques. Subsequently, a very low surface roughness of 0.8 nm and high uniformity of hybrid thin films were observed by tapping-mode AFM. Also, the thin films showed a hydrophilic nature with a high surface energy of 59.9 mJ/m2 as observed by the contact angle technique. The insulating properties of this hybrid film, studied by C–V and I–V measurements, showed very low leakage current density under 1 nA/cm2 at −5 V, high gate capacitance of 106 nF/cm2, and high dielectric constant of 11.3 at 1 kHz. With such dielectric properties, the hybrid thin films were tried as dielectric gate layers in room-temperature-sputtered ZnO thin-film transistors (TFTs). As-fabricated devices achieved low operating voltage, less than 5 V, with high saturation field effect mobility of 15.5 cm2 V–1 s–1, very low threshold voltage of 0.5 V, high on/off current ratio of 106, and low subthreshold slope of 0.37 V/dec. These results reveal the promising application of the HfO2–PMMA hybrid material as the gate dielectric for the fabrication of ZnO-based TFTs at low temperature.

May (2019). ACS Applied Electronic Materials. No. 1 vol. 6. pp 1003-1011. ISSN 2637-6113. https://doi.org/10.1021/acsaelm.9b00175

Synthesis of a geopolymer and use of response surface methodology to optimize the bond strength to red brick for improving the internal coating in burners kilns 

J.A. Torres-Ochoa, N.R. Osornio-Rubio, H. Jiménez-Islas, J.L. Navarrete-Bolaños, G.M. Martínez-González. 

In Mexico, fixed kilns made of red brick after several burn cycles at 1000 °C, may expand, crack and open. In light of that, we worked to obtain a geopolymer using clays (Caolín, Tepozán and Bauwer), that attaches to red brick. The clays were characterized using energy dispersive X-ray spectroscopy (EDS), atomic absorption spectroscopy (AAS), UV-VIS spectrophotometry and powder X-ray diffraction (PXRD), finding that the clays have refractory properties. The response surface methodology was used to optimize the adherence of the geopolymer on red brick, keeping the sodium silicate concentration constant. The optimal formulation of the geopolymer contains 50% commercial sodium silicate, 21% Caolín, 23% Tepozán, and 6% Bauwer, where the curing time was 7 days and the burning cycle was 8 h at 1000 °C. The best fit was achieved with a quadratic model that predicts an adherence of 3.2 MPa, comparable to the experimental value of 2.8 MPa. The geopolymer can be used as an internal coating in brick kilns to increase its useful life. In addition, the geopolymer has potential use as a coating for materials for refractory use.

November. (2018). Revista Mexicana de Ingeniería Química. Vol. 18. No. 1, pp. 361–373.  (view PDF)

Dielectric constant measurement using atomic force microscopy of dielectric films: a system theory approach

E. Cruz-Valeriano, D.E. Guzmán-Caballero, T. Escamilla-Díaz, A. Guitierres-Peralta, Susana Meraz-Davila, J.A, Torres-Ochoa, J.J. Gervacio-Arciniega, E.A. Murillo-Bracamontes, C.I. Enriquez-Flores, R. Ramírez-Bon, Joel Moreno Palmerin, J.M. Yañez-Limón. 

A technique was developed to measure dielectric constant at microscale based on the system theory approach using an atomic force microscopy (AFM), this makes possible the electrical characterization of dielectric materials using an optimized instrumentation. This technique is capable of measuring capacitance on either metallic contact–insulator–metallic contact or metallic contact–insulator with the AFM tip as the upper contact, the dielectric constant can be calculated from these results. The technique compares the frequency response between the input voltage and the output voltage of an equivalent RC-circuit (resistance–capacitance) in the frequency range 1 Hz–60 kHz. This comparison is analyzed using a transfer function model and a least-squares process to get the time constant involved in this kind of circuit, facilitating the implementation of this technique with any atomic force microscopy equipment. Additionally, the measurements can be carried out in a single point or in a mapping. The measurements were carried out on two hybrid films, PMMA–TiO2–SiO2 and PMMA–TiO2–BT, which were prepared by sol–gel technique and deposited on indium tin oxide (ITO)-coated glass substrates. The results obtained with this technique agreed with conventional measurements that use commercial capacitance–voltage analyzer, and indicated that dielectric constant is 11.31 for PMMA–TiO2–SiO2 , and 15.41 for PMMA–TiO2–BT.

(2018). Applied Physics A. 124:667. https://doi.org/10.1007/s00339-018-2093-4 

Low-temperature sol-gel ZrHfO2-PMMA hybrid dielectric thin films for metal oxide TFT’s

M.G. Syamala Rao, M.A.Pacheco-Zuñiga, L.A.Garcia-Cerda, G.Gutiérrez-Heredia, J.A.Torres Ochoa, M.A.Quevedo López, R.Ramírez-Bon. 

In this work, we developed a novel inorganic-organic hybrid gate dielectric by combining zirconium and hafnium components to form zirconium hafnium oxide strongly linked with polymethyl methacrylate (ZrHfO2- PMMA) and deposited at low temperature (200 °C) by sol-gel method. The obtained 108 nm thick, high-quality hybrid gate dielectric showed an exceptionally low surface roughness (0.9-nm), a low leakage current density (7.7×10−6 A/cm2) and reasonable dielectric properties such as gate capacitance along with dielectric constant (77 nF/cm2 & 9.4 @1 kHz) respectively. To examine the ZrHfO2-PMMA hybrid dielectric electrical properties we constructed thin-film transistors (TFTs) with room temperature r.f sputtered n-type metal oxide semiconductors, a-IGZO and ZnO, as active channels. The bottom gate fabricated a-IGZO TFTs driving at as low as below 6 V, with extracted field effect mobility of 2.45 cm2/V. s, a low threshold voltage of 1.2 V with large ON/OFF current ratio 107 respectively. On the other hand, for comparison we employed ZnO TFTs by applying same hybrid dielectric system, the obtained parameters of bottom gate ZnO TFTs were good field effect saturation mobility of 12.8 cm2/V. s, threshold voltage of 1.8 V and ON/OFF current ratio of 103.

(2018).. Journal of Non-Crystalline Solids. Vol. 502, pp 152-158, /doi.org/10.1016/j.jnoncrysol.2018.08.014

Accelerated weathering study of extruded polyethylene /poly (lactic acid)/chitosan films

L.L.Lizárraga-Laborín, J.M.Quiroz-Castillo, J.C.Encinas-Encinas, M.M.Castillo-Ortega, S.E.Burruel-Ibarra, J.Romero-García, J.A.Torres-Ochoa, D.Cabrera-Germán, D.E.Rodríguez-Félix.

Polyethylene/poly (lactic acid)/chitosan films, with and without poly (ethylene-g-maleic anhydride) (PEgMA) as compatibilizer, were prepared by extrusion and the degradation behavior under different times of standard weathering conditions was analyzed. The materials were characterized by means of infrared spectroscopy, scanning electron microscopy, tensile strength, differential scanning calorimetry and thermogravimetric analysis. It was demonstrated that blends of synthetic and natural polymers have a higher susceptibility to degradation in comparison to neat polyethylene and poly (lactic acid) films. Additionally, it is found that the incorporation of PEgMA into the extruded films apparently favored the polymer degradation, as it deduced from the fall of the mechanical properties when the films are exposed to accelerated weathering simulation.

(2018). Polymer Degradation and Stability. vol. 155. pp. 43-51. 2018. doi.org/10.1016/j.polymdegradstab.2018.06.007 (view PDF)

Intensity modulation of the Shirley background of the Cr 3p spectra with photon energies around the Cr 2p edge

Alberto Herrera-Gomez, Dagoberto Cabrera-German, Anthony D. Dutoi, Milton Vazquez‑Lepe, Servando Aguirre-Tostado, Piero Pianetta, Dennis Nordlund, Orlando Cortazar-Martinez, Alejandro Torres-Ochoa, Oscar Ceballos-Sanchez, Lizeth Gomez‑Muñoz, 

The background in X‐ray photoelectron spectroscopy data originates, partially, from inelastically scattered photoelectrons. In fact, the current theoretical methods for calculating the background intensity are based on electron energy losses. However, a critical part of the experimental signal, which is known as the Shirley background, cannot be described within the current formalisms. This suggests that the Shirley electrons are not associated with energy losses of photoelectrons and must originate from a different photoexcitation phenomenon with a cross section of its own. We propose a mechanism based on core channeling as the physical origin of the Shirley signal.

(2018) , Surface and Interface Analysis, vol. 50, issue. 2, pp. 246-252, 2018.  doi.org/10.1002/sia.6364, ISSN 1096-9918

Study of the dehydroxylation of kaolinite and alunite from a Mexican clay with DRIFTS-MS

N. R. Osornio-Rubio, J. A. Torres-Ochoa, M. L. Palma-Tirado, H. Jiménez-Islas, R. Rosas-Cedillo, J. C. Fierro-González, and G. M. Martínez-González, 

Few reports exist on the use of Diffuse Reflectance Infrared Fourier Transform Spectrometry coupled with Mass Spectrometry (DRIFTS-MS) in situ to monitor the dehydroxylation of kaolinitic clays. The use of DRIFTS-MS in situ allows study of the effect of heat treatment on the dehydroxylation, identifying intensities and temperatures at which the hydroxyl groups are released, forming metakaolinite and meta-alunite. The effluent gases from the infrared cell were analysed by mass spectrometry. The decrease in intensity of the bands at 3694, 3669, 3650 and 3621 cm−1 associated with the −OH stretching vibration modes of AlVI−OH−AlVI of kaolinite began at 450°C. Two additional bands at 3513 and 3485 cm−1 are associated with the vibration of AlVI−OH of alunite that also began to disappear during thermal treatment. Monitoring of the fractions m/e 17 and 18 using a mass spectrometer revealed that the intensity of these fractions increased starting at 450°C. Therefore, it is possible to study the dehydroxylation process of clays during thermal treatment.Chemical and mineralogical characterization of a kaolinitic clay (KN) fromMexico showed that the clay consists of 64.8% kaolinite, 11.0% alunite and 24.4% quartz based on PXRD, EDS, TG/DTA, TEM and FTIR results, and suggested that the material might have potential for use in the manufacture of ceramics, refractory bricks or geopolymers. 

(2016), Clay Minerals, vol. 51, No. 1, pp. 1–14.  (View PDF)

Estudio de la remoción de cromo hexavalente mediante arcillas funcionalizadas con H3PO4, HNO3, C3H6O2 y C4H8O2

Jorge Alejandro Torres Ochoa, Gloria María Martínez González, Hugo Jiménez Islas, Ma. Lourdes Palma Tirado, Enrique Barrera Calva, Nadia Renata Osornio Rubio. Retos de la Ingeniería Química en la Globalización, Memorias del XXXVI Encuentro Nacional de la AMIDIQ. Cancún, Q. Roo. 5 al 8 de mayo del 2015. Pág. 2556-2559. ISBN: 978-607-95593-3-5.