Synthesis and physical properties of 3D hybrid halide perovskites and their low-dimensional 0D, 1D, and 2D counterparts

Jose Antonio Souza

Universidade Federal do ABC (CCNH)

Hybrid organic-inorganic halide perovskites have been attracting considerable attention due to their excellent optoelectronic properties. Tuning electronic, crystal structures, and photoelectric conductivity for enhanced efficiency is very important for the discovery of new materials with novel functionalities in optoelectronic devices. Key physical properties such as adjustable band gaps, low exciton binding energy, large optical absorption coefficients, long hole-electron diffusion length are crucial for efficient charge separation and collection. In contrast to conventional 3D perovskites, low-dimensional perovskites demonstrate improved environmental stability and offer more diverse compositions, electronic structures, and crystal structures. In this talk, we will show some contributions of our research group on synthesis and physical properties of 3D and their low dimensional 0D, 1D, and 2D organic-inorganic halide perovskites. For 3D system, a long thermal annealing causes a significant shift in the structural phase transition, stabilizing the high-efficiency cubic structure at room temperature. We propose a new phase diagram for this important system combining different structural phases as a function of temperature with annealing time for MAPbI3. We have also growth low dimensional perovskites by using a recrystallization process starting from their 3D counterparts and studied the optical properties. We have also introduced magnetism into the semiconducting structure. The variation of dimensionality bringing about strong quantum confinement effect leads to change in physical/chemical properties which in turn offer a broad exploration research field for optoelectronic applications including light emitting and solar conversion devices.

Spectroscopic studies under extreme thermodynamic conditions

The non-destructive nature, speed, and versatility in data acquisition make Raman spectroscopy one of the most widely used techniques for characterizing materials and in the study of physical and chemical effects. Based on inelastic light scattering processes, this technique enables us to take direct measurements of the energies of the vibrational modes, which are determined by the interactions between the constituent atoms. Hence, the Raman spectrum is a characteristic signature of each material, which can be significantly modified as a result of compositional and structural changes, such as atomic interdiffusion, phase transitions, stress/strain, and quantum confinement, turning the Raman spectroscopy a powerful tool in the study of such properties. In this talk, we will discuss how Raman data can be interpreted and how they can be combined with results from other techniques to provide information about the physical characteristics of materials. Examples of the use of such techniques available at the Department of Physics at UFSCar will be presented, highlighting the possibilities of performing in situ analyses as a function of temperature and pressure, which are essential in the study of phase transitions and other properties of matter under extreme thermodynamic conditions.

Two Dimensional Materials for optoeletronics and spintronics

Yara Galvão Gobato

Physics Department- Federal University of São Carlos

São Carlos-SP-Brazil

    Two-dimensional (2D) transition metal dichalcogenide (TMDs) materials are attractive systems for fundamental physics and also for possible applications in optoeletronics and spintronics. These materials can be vertically stacked to form van der Waals (vdW) heterostructures with unique physical properties. They exhibit periodic variations, leading to a new type of in-plane superlattice known as moiré superlattice/pattern which has important impact on optical and magneto-optical properties of excitons in vdW heterostructures. Among the interesting properties of such heterostructures, we highlight the type-II band alignment that induces the formation of interlayer excitons (IEs) with electrons and holes located in adjacent layers. Furthermore, there are also vdW heterostructures where the carrier wavefunctions are distributed over both layers and these excitons are referred to as hybrid excitons. More recently, it has also been demonstrated that 2D magnetic materials are promising platforms for effective building blocks for the next generation of spintronics devices. Interestingly, those materials can also be stacked with 2D TMDs to form magnetic vdW heterostructures. In this talk, we will present our latest research focusing on the interplay of smooth/local strain, doping, moiré patterns, and magnetic proximity effects on the valley and exciton physics of van der Waals heterostructures. Our studies not only contribute to the fundamental understanding of TMD-based heterostructures but also open avenues for engineering their physical properties for novel device applications.

"O mega-experimento DUNE: decifrando as partículas-fantasmas"

Dra. Laura Paulucci 

Universidade Federal do ABC - Santo André -SP

Dedicado ao estudo dos misteriosos neutrinos, o Deep Underground Neutrino Experiment, DUNE, busca responder questões fundamentais sobre essas partículas, se estabelecendo como uma das maiores colaborações de física de partículas atuais. O experimento terá o mais intenso feixe de neutrinos do mundo e contará com enormes tanques de argônio líquido (a -196oC!) cerca de 1,5 km abaixo do solo nos EUA. Os neutrinos são partículas fundamentais com carga elétrica nula e que podem ser detectados em três tipos: neutrino do elétron, do múon e do tau. Experimentos mostram que os neutrinos têm uma pequena massa e que seus três tipos são capazes de se transformar uns nos outros, fenômeno batizado de oscilação de neutrinos. O DUNE será capaz de medir independentemente todos os parâmetros necessários para descrever as oscilações devido ao seu grande volume, faixa de energia e intensidade do feixe. Além disso, testará se neutrinos e suas antipartículas se comportam de maneira semelhante ou não, o que pode ser a chave para a explicação da assimetria matéria-antimatéria no Universo primordial. Nesta palestra, veremos como funciona este experimento, qual a física que irá abordar e mais detalhes da participação brasileira no mesmo.

O Co3O4 como matriz de fontes alternativas de energia

Dr. Márcio P. F de Godoy - UFSCar

Atualmente, fontes alternativas de energia são uma demanda essencial para a sociedade, pois o acesso às novas tecnologias depende de sua manutenção, disponibilidade e custos de produção. Assim, a investigação de materiais e o desenvolvimento de rotas de síntese, fabricação e processamento de novos dispositivos são um campo de pesquisa que não se evanesce em abordagens de física fundamental e aplicada e é crítico nacional e internacionalmente.

Nesta palestra, apresentaremos um panorama de nossas investigações no óxido de cobalto (Co3O4) em funcionalidades que podem ser aplicadas nesta área, como a fotocondutividade e a termoeletricidade. O Co3O4 é um sistema que apresenta propriedades interessantes relacionadas à presença de duas valências do Co (+2 e +3) em sua estrutura cristalina como, por exemplo, a presença de duas bordas de absorção óptica. Além disso, como grande maioria de óxidos binários, o Co3O4 não é estequiométrico, e possui uma deficiência de átomos de oxigênio à qual é atribuída a responsabilidade por alguns efeitos. Discutiremos, em linguagem acessível, o papel de alguns tipos de defeitos no perfil de fotorresposta considerando a sintonização da excitação óptica em comprimentos de onda específicos. Além disso, mostraremos como a adição de sódio (Na), formando  filmes finos policristalinos de NaxCoO2, contribui na resposta termoelétrica. Nossos dados mostram um coeficiente Seebeck competitivo para filmes finos policristalinos, evidenciando uma estratégia para produção em larga escala de camadas termoelétricas do tipo-p.

             EPITAXIA POR FEIXE MOLECULAR: um método de preparo de filmes cristalinos

Dr. Paulo. H. de O. Rappl - INPE

 Os métodos epitaxiais surgiram para atender a demanda da indústria eletrônica na fabricação de dispositivos semicondutores e pesquisa básica. A Epitaxia por Feixe Molecular, também conhecida como MBE, é um desses métodos usados na deposição de filmes finos ordenados (cristalinos). Na oportunidade, em nível básico, o assunto abordará aspectos essenciais para a compreensão do método. Também, imagens do sistema de MBE, modelo Riber 32 P, instalado no Instituto Nacional de Pesquisas Espaciais – INPE, em São José dos Campos, SP, ilustrarão a apresentação.

The Connection Between Phonon Chirality and Electronic Topology

The mirror symmetries of crystals play a particular role in the properties of phonons. When they are broken, the lattice ions can display circular motion with finite angular momentum. These modes are called chiral phonons, and recently they have been the subject of intense research because, unlike regular phonons, they respond to magnetic fields. Notably, from the fundamental perspective, giant magnetic moments are predicted to result from electronic contributions to the magnetism of phonons. In this talk, I will present measurements of time-domain terahertz spectroscopy in a set of Pb(1-x}Sn(x)Te films, which is a topological crystalline insulator for x > 0.32 and has a ferroelectric transition at an x-dependent critical temperature. The results strongly indicate the existence of interplay between the magnetic properties of chiral phonons and the topology of the electronic band structure. Our work opens up new avenues for topology-based devices and applications through magnetic field-based phonon control of electronic states.

Diodos Emissores de Luz Orgânicos (OLEDs): Propriedades moleculares que

influenciam a eficiência da eletroluminescência

A estatística de spin dirige a eficiência dos emissores puramente fluorescentes, que utilizam apenas estados excitados singletos para eletroluminescência, limitada a 25% dos estados pela formação estatística. Amplamente utilizados, os átomos pesados que buscam ativar as propriedades fosforescentes dos emissores, fazem com que os materiais sejam híbridos. Há  ainda mecanismos para os sistemas puramente orgânicos, que buscam meios para a conversão de estados tripletos não emissivos em estados singletos emissivos, como a Aniquilação Tripleto-Tripleto (TTA) e a Fluorescência Atrasada Ativada Termicamente (TADF). Será apresentado uma breve introdução teórica sobre esses mecanismos e discutidos os resultados dos OLEDs que apresentam o mecanismo de TADF.

Aplicação de Filmes Finos de Dióxido de Titânio na Fotodegradação Ambiental 

Adhimar F Oliveira, João Henrique Pinton, Felipe Sievert da Costa Portes, Maria Elena Leyva González e Caroliny Fernandes de Carvalho 

Universidade Federal de Itajubá

Apresentamos a pesquisa em curso no Laboratório de Caracterização Magnética e Óptica (LMCO) focada na preparação de filmes finos de dióxido de titânio (TiO2) destinados à aplicação na fotodegradação. O trabalho envolve a exploração de diversas abordagens de preparação, incluindo o método sol-gel por miscelas reversas [1], síntese verde [2], e uma síntese combinada com a esfoliação eletroquímica do óxido de grafeno (GO) [3]. Para a preparação dos filmes finos, desenvolvemos um sistema automatizado de spray com componentes de baixo custo, permitindo o controle da espessura e uniformidade do filme Nossos resultados iniciais incluem a bem-sucedida preparação e caracterização de filmes finos. Utilizando o método sol-gel. Além disso, obtivemos nanopartículas de TiO2 na fase anatase por meio da síntese verde, confirmada por técnicas de difração de raios-X (DRX) e espectroscopia de infravermelho por transformada de Fourier (FTIR). Para avaliar a eficácia dos filmes, construímos uma câmara de radiação abrangendo uma ampla faixa do espectro eletromagnético, incluindo UVB e UVC, a fim de conduzir testes de fotodegradação em diferentes corantes. Já realizamos testes bem-sucedidos de fotodegradação nos filmes finos preparados pelo método sol-gel. Atualmente, estamos em fase de avaliação dos resultados de algumas sínteses que combinam a esfoliação de GO, com planos de futuras publicações dos resultados.

 [1] OLIVEIRA,  A. F. et al. Preparation and characterization of palladium-doped titanium dioxide for solar cell applications. Materials Science and Engineering: B, v. 280, p. 115702, 2022. 

[2] SUTRADHAR, Prasanta; SAHA, Mitali. Green synthesis of zinc oxide nanoparticles using tomato (Lycopersicon esculentum) extract and its photovoltaic application. Journal of Experimental Nanoscience, v. 11, n. 5, p. 314-327, 2016. 

[3] WILLIAMS, Graeme; SEGER, Brian; KAMAT, Prashant V. TiO2-graphene nanocomposites. UV-assisted photocatalytic reduction of graphene oxide. ACS nano, 2008, 2.7: 1487-1491. 

Agradecimentos: Os autores gostariam de agradecer às agências brasileiras CAPES, CNPq e Fapemig (Código de Financiamento APQ-02676-16 e APQ-00010-18) pelo apoio financeiro. 

The fermiology of Quantum Materials unveiled by quantum oscillation measurements

Steffen Wiedmann

High Field Magnet Laboratory, HFML-FELIX, Radboud University

Toernooiveld 7, 6525 ED Nijmegen, Netherlands

steffen.wiedmann@ru.nl

Quantum mechanics serves as the basis for explaining the properties of all materials, including how atoms bond and electrons interact at a fundamental level. Although classical descriptions can approximate these effects at the macroscopic level in many cases, there is growing interest in exploring material systems that exhibit quantum effects across a broader range of energy and length scales.

These materials, known as quantum materials, include graphene, topological insulators, Dirac, Weyl and nodal-line semimetals, and superconductors, among others. Many of these materials exhibit unique properties due to their reduced dimensionality, particularly the confinement of electrons to two-dimensional sheets.

In my presentation, I will introduce the electronic properties of quantum materials in which, for instance, topological and correlated phases play a fundamental role. I will demonstrate how quantum oscillation measurements, using different experimental techniques under extreme conditions like high magnetic fields, are crucial in the determination of their Fermi surface thereby providing access to  the unique quasi-particle properties of these materials.

Micro e Nano Eletrônica como Tecnologias Habilitadoras

Ricardo Cotrin Teixeira, Ph.D.

Após 50 anos da Lei de Moore, a microeletrônica evoluiu a tal ponto que as suas tecnologias se tornaram uma ciência por si só e permitem a fabricação de dispositivos que vão muito além do seleto grupo de memórias e microprocessadores. Durante a apresentação, vamos fazer um breve histórico da Lei de Moore e suas consequências para a indústria eletrônica e como as tecnologias envolvidas migraram para outras áreas de aplicação. Entre as observações do ITRS e sua evolução para o IRDS / HIR faremos a apresentação de como isso se reflete no território nacional através do INCT – NAMITEC e das tecnologias disponibilizadas pela DIMES/CTI.

Siglas:

ITRS – International Technology Roadmap for Semiconductors

IRDS – International Roadmap for Devices and Systems

HIR – Heterogenous Integration Roadmap

INCT – Institutos Nacionais de Ciência e Tecnologia

INCT - NAMITEC – INCT Nano e Microeletrônica para tecnologias habilitadoras

DIMES – Divisão de Montagem, Empacotamento eletrônico e integração de Sistemas

CTI – Centro de Tecnologia da Informação Renato Archer, Unidade de Pesquisa do MCTI

MCTI – Ministério da Ciência Tecnologia e Inovação

Porous silicon photonic crystals: Fabrication and Application as chemosensors

Danilo Roque Huanca

Laboratório de Dispositivos e Sistemas Micro e Nanoestruturados - LADISmNE.

Instituto de Física e Química – Universidade Federal de Itajubá

Photonic crystals (PCs) are periodic structures characterized by stratified dielectric media. They are categorized into one-dimensional, two-dimensional, and three-dimensional structures based on the variation in their dielectric constants throughout the structure. The defining feature of PCs is the presence of a photonic band gap (PBG) within the optical spectrum, where photonic states are forbidden. The width and spectral position of this PBG are contingent upon the dielectric properties and geometric attributes of the unit cell. Due to their vast potential applications in various scientific and technological fields, numerous materials and fabrication methods have been proposed for its fabrication. Among these, silicon-based PCs have aroused significant interest within the optoelectronic field, particularly for applications such as silicon-based lasers and integration with existing complementary metal-oxide-semiconductor (CMOS) technology. For this aim, notably, porous silicon has emerged as a cost-effective and easily manageable approach, particularly for the creation of one-dimensional photonic crystals (1D-PSPCs). This kind of devices consist of a stack comprising a high-porosity (pH) single layer with a thickness, denoted as dH, followed by a thinner single layer with low porosity (pL) and a thickness dL. These parameters, under a given substrate and electrolyte features, can be finely controlled during the electrochemical anodization by managing the applied current densities (JH and JL) and etching times (tH and tL). However, despite the widespread demonstration of 1D-PSPC fabrication, certain challenges persist. These difficulties stem from the consumption of HF (hydrofluoric acid) during pore formation and difficulties associated with HF diffusion towards the etch-front. To address these issues, a suggested approach involves introducing pauses between the formation of two adjacent layers with thicknesses dH and dL. Nevertheless, it is observed that as the duration of the pause increases, the thicknesses of dH and dL also proportionally increase, accompanied by a decrease in porosities pH and pL.

Conversely, in the context of 1D-PSPCs, their porous nature enables the introduction of liquids or gases within the pores, rendering them valuable as optical sensors for the detection of chemical and/or biological analytes. The presence of these analytes induces a linear redshift in response to changes in the analyte's refractive index. Nonetheless, it has been observed that the sensitivity of non-passivated devices surpasses the theoretical projections. Upon an examination of the reflectance spectra, this sharp sensitivity is attributed to the contraction-expansion phenomenon within the dL and dH layers, respectively. This phenomenon arises from the interaction of the porous structure with the analytes, possibly associated with capillarity effects. In order to address this issue, it becomes necessary to passivate 1D-PSPCs before employing them as sensors. However, it is noteworthy that this passivation process can lead to a degradation in device sensitivity. Investigation into the choice of passivating materials, specifically SiO2 and TiO2, has indicated that the optimal performance of 1D-PSPCs as chemosensors is achieved when TiO2 is utilized as the passivating layer.

Quantum Sensing Applications Using Macroscopic-Scale Elements

Dr. Francisco Paulo Marques Rouxinol

UNICAMP

In this presentation, we will provide an overview of the utilization of hybrid systems to establish quantum-coherent interactions between superconducting qubits and resonant nanomechanical structures. Our primary focus will be on our ongoing efforts at UNICAMP, where we are developing an electromechanical circuit designed to achieve a strong coupling between a nanomechanical resonator, a superconducting qubit, and a microwave cavity. Our goal is to create hybrid systems with the potential to generate and measure various non-classical states in nanoscale structures. These hybrid systems are expected to serve as a significant platform for enabling the production and measurement of diverse non-classical states in nanoscale structures. This positions them as potentially crucial components for quantum processing architectures and for exploring quantum behavior in novel contexts. The topics covered will encompass the fundamental physics of mechanical systems, including nanomechanical and micromechanical technologies, the quantum constraints inherent in the measurement of mechanical systems, the integration of other quantum systems (e.g., superconducting circuits and qubits) with mechanical structures for the manipulation and measurement of quantum properties of motion. We will also delve into the discussion of the experimental challenges and unresolved questions currently confronting researchers in this field.