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Fabricação de novas heteroestruturas a partir de estruturas SOI obtidas pela técnica 'smart-cut'.; New semiconductor heterostructures based on SOI structures obtained by "smart-cut" process.

Escobar Forhan, Neisy Amparo
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 17/03/2006 PT
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Esta pesquisa engloba o estudo e desenvolvimento de novas heteroestruturas semicondutoras, tomando como base as estruturas SOI (Silicon-On-Insulator - silício sobre isolante) obtidas pela técnica Smart Cut, estudadas nestes últimos anos no Departamento de Engenharia de Sistemas Eletrônicos da Escola Politécnica da Universidade de São Paulo (EPUSP). Esta técnica combina a solda direta para a união de lâminas e a implantação iônica (I/I) de íons leves para a separação de camadas especificadas. São essenciais na preparação destas estruturas SOI, processos de I/I, limpeza e ativação das superfícies das lâminas e recozimentos em fornos a temperaturas moderadas. Estudamos também, diferentes métodos para a obtenção de novas heteroestruturas, basicamente combinando as técnicas de fabricação da estrutura SOI e os métodos de formação do carbeto de silício (SiC), que chamaremos de heteroestruturas SiCOI (Silicon Carbide-On-Insulator). O método usado para a formação do SiC depende, em cada caso, das características desejadas para o filme que, ao mesmo tempo, estão relacionadas com a aplicação à qual estará destinado. Analisamos três métodos de obtenção do material SiC com características específicas diferentes. A metodologia proposta aborda as seguintes tarefas: Tarefa 1: Obtenção de estruturas SOI pelo método convencional utilizado em trabalhos anteriores e melhoramento das características superficiais da estrutura resultante. Tarefa 2: partindo de uma lâmina de Si previamente coberta por uma camada isolante...

Propriedades eletrônicas de hetero-estruturas de semicondutores zincblende.; Electronic properties of zincbled semiconductor heterostructures.

Chitta, Valmir Antonio
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 27/10/1987 PT
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Utilizou-se um Hamiltoniano KP (6x6) do tipo Kane para, se estudar a estrutura de bandas e níveis de Landau para heteroestruturas de semicondutores zincblende dos grupos III-V e II-VI. Os efeitos do acoplamento entre as bandas de condução e valência, da mistura dos estados da banda de valência, da não-parabolicidade dos níveis, da total degenerescência dos níveis, do warping e das descontinuidades das massas efetivas nas heterointerfaces são levados em conta. Mostrou-se que a interação entre as bandas de condução e valência não pode ser desprezada, mesmo para semicondutores de gap largo, como citado em trabalhos existentes na literatura. Para um estudo sistemático do modelo, utilizou-se um poço quântico de GaAs Ga(Al)As e então aplicou-se o modelo a um sistema de semicondutores semi-magnéticos (poço quântico de CdTe Cd(Mn)Te).; A Kane-like (6x6) KP Hamiltonian is used to study the subband structure and Landau levels for group III-V and group II-VI zincblende semiconductor heterostructures. The effects of conduction-valence band coupling, valence band states mixing, nonparabolicity of the levels, the full degeneracy of the levels, warping and effective masses discontinuities at the heterointerfaces are taken into account. It is shown that the interaction between conduction-valence bands cannot be neglected...

Propriedades eletrônicas de heteroestruturas semicondutoras magnéticas diluídas.; Electronic properties of diluted magnetic semiconductor heterostructures

Marin, Ivan Silvestre Paganini
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 28/02/2007 PT
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Neste trabalho e apresentado um estudo, via teoria de massa efetiva multibanda autoconsistente de heteroestruturas de semicondutores magnéticos diluídos, generalizada para incluir parâmetros de diferentes materiais. A interacao magnética e descrita por um modelo de campo médio baseado no mecanismo de troca indireta, com a possibilidade de inclusão de diferentes íons magnéticos. As equacoes de massa efetiva são resolvidas de forma autoconsistente com o auxílio da equacao de Poisson. As interacoes de spin-órbita e de troca-correlacao, na aproximacao de densidade local, são incluídas no cálculo. O método e aplicado para o estudo das estruturas de bandas e densidades de carga com separacao por spin do portador de heteroestruturas com dopagem tipo-n e tipo-p, variando a geometria dos pocos magnéticos e também o período da super-rede, as densidades de portadores e as concentracoes de íons magnéticos. Solucoes autoconsistentes da equacao de massa efetiva são encontradas para o oxido semicondutor (Zn,Co)O. Será mostrada a separacao de portadores por spin em funcao dos parâmetros variados, simulando diversas concentracoes possíveis, utilizadas em sistemas descritos na literatura, e será analisado o comportamento dos perfis de potencial. Usando os dados obtidos...

Contribuições á física das propriedades eletrônicas das heteroestruturas semicondutoras; Contributions to the physics of the electronic properties of the semiconductor heterostructures

Silva, Erasmo Assumpção de Andrada e
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 13/12/1990 PT
Relevância na Pesquisa
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Esta tese compõe-se de contribuições à física das propriedades eletrônicas das heteroestruturas semicondutoras. São investigadas propriedades eletrônicas das duas hetero­estruturas básicas: o poço quântico e a super-rede. Considera-se o poço quântico dopado com impurezas rasas e estudam-se as suas propriedades eletrônicas nos regimes de poço fraca e altamente dopado. No caso de baixa densidade de impurezas é feita uma simulação Monte Carlo. É utilizado um modelo semi-clássico de band de impureza. A interação elétron-elétron é incluída de forma exata e são calculadas as seguintes propriedades do estado fundamental à temperatura zero: densidade de estados de uma partícula, distribuição de carga, energia de Fermi e distribuição do campo elétrico sobre os doadores neutros, todas em função do grau de compensação, da densidade de impurezas e da largura do poço. É observada uma. grande dependência com a compensação. Os resultados são explicados à luz da competição entre os efeitos de desordem e confinamento. É observada a ocorrência de Coulomb Gap característico de sistemas bidimensionais. Mostra-se que a. distribuição de carga possui largura e constante de decaimento determinados independentemente pela compensação e pela concentração de impurezas...

Crescimento e caracterização de heteroestruturas tensionadas de InxGa1-x-As/GaAs; Growth and characterization of stressed heterostructures of InxGa1-x-As/GaAs

Ceschin, Artemis Marti
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 17/12/1992 PT
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Utilizando a técnica de epitaxia por feixe molecular (MBE), crescemos heteroestruturas tensionadas de InxGa1-xAs sobre substratos de GaAs (100). A composição de In, a espessura para a transição 2D-3D e a espessura crítica (hc) foram determinadas através da análise "in situ" pelo RHEED. Os valores da hc e da espessura para a transição 2D- 3D foram observadas ser funções da composição do In e da temperatura do substrato. Um estudo do efeito da desorientação do substrato de GaAs (100) de alguns graus sobre as qualidades ópticas (PL) de poços quânticos simples e múltiplos de InxGa1-xAs/GaAs também foi realizado. Microscopia eletrônica por transmissão (TEM) foi utilizada para a verificação da qualidade das interfaces dos poços quânticos de InxGa1-x/GaAs. Algumas estruturas de dupla barreira (AlGaAs/GaAs/InAs/GaAs/AlGaAs) foram crescidas e caracterizadas opticamente (PL); InxGa1-xAs strained heterostructures were grown on GaAs (100) by Molecular Beam Epitaxy (MBE). Indium concentration (x), 2D-3D growth mode transition thickness and critical thickness (hc) were determined by "in situ" RHEED analysis. Hc and 2D-3D growth mode transition thickness values were verified to depend on In concentration and substrate temperature. The dependence of the InxGa1-xAs /GaAs simple and multiple quantum wells (SQW and MQW) PL optical quality on the GaAs (100) substrate misorientation was also studied. The SQW interfaces were investigated by Transmission Eletronic Microscopy (TEM). Some double-barrier structures (AlGaAs/GaAs/InAs/GaAs/AlGaAs was also grown and optically characterized

Estrutura de bandas de heteroestruturas semicondutoras dopadas tipo-p; Band structure of semiconductor heterostructures doped p-type.

Rodrigues, Sara Cristina Pinto
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 28/06/2001 PT
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Neste trabalho iremos apresentar a teoria autoconsistente k. p aplicada a heteroestruturas dopadas tipo-p que resolve a Hamiltoniana 6 x 6 de Luttinger-Kohn, generalizada para tratar diferentes materiais, juntamente com a equação de Poisson na representação de ondas planas. A generalização do termo de energia cinética é inserido explicitamente na Hamiltoniana de Luttinger-Kohn levando em conta os efeitos de diferentes materiais, através da inclusão de conjuntos distintos de parâmetros de Luttinger e considerando os elementos adicionais na matriz, da Hamiltoniana de Luttinger-Kohn e que não aparecem naquela para homoestruturas. O método é aplicado ao estudo pioneiro da estrutura de sub-bandas e minibandas de valência de heteroestruturas com dopagem tipo-p envolvendo semicondutores nitretos do grupo-III cúbicos. Heteroestruturas de compostos III-V derivados do GaAs também são estudadas, com o objetivo principal de testar o método generalizado e sua implementação no programa. Especificamente, iremos obter soluções auto consistentes da equação da massa efetiva de multibandas e da equação de Poisson para poços quânticos e super-redes de AlxGa1-xN/GaN e GaN/InxGal-xN na fase cúbica, bem como para heteroestruturas de GaAs/lnxGal-xAs e AlxGa1-xAs/GaAs...

Quantum well to quantum wire crossover in AlAs/GaAs/AlAs heterostructures induced by interface roughness increase

Dargam,T. G.; Capaz,R. B.; Koiller,Belita
Fonte: Sociedade Brasileira de Física Publicador: Sociedade Brasileira de Física
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/1999 EN
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Adopting a real-space tight-binding supercell approach, we investigate interface roughness effects in semiconductor heterostructures. AlAs/GaAs/AlAs (001) QWs of average width W are considered, in which one of the interfaces is planar and the other has a shape defined by periodic steps with amplitude A and wavelength lambda. The oscillator strength f of the fundamental transition in the well describes the optical nature of the heterostructures. By investigating the wavefunctions as a function of the interface parameter A, we conclude that the f behavior with A is an optical signature of the quantum well to quantum wire crossover in the heterostructures. Recently, photoluminescence experiments showed that hydrostatic pressure produces an increase in the optical eficiency of heterostructures in which the interfaces present a high degree of roughness. In order to investigate this optical behavior, we discuss hydrostatic pressure effects on rough-interface heterostructures.

Heterostructures based on inorganic and organic van der Waals systems

Lee, Gwan-Hyoung; Lee, Chul-Ho; van der Zande, Arend M.; Han, Minyong; Cui, Xu; Arefe, Ghidewon; Nuckolls, Colin; Heinz, Tony F.; Hone, James; Kim, Philip
Fonte: AIP Publishing Publicador: AIP Publishing
Tipo: Artigo de Revista Científica
EN_US
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The two-dimensional limit of layered materials has recently been realized through the use of van der Waals (vdW) heterostructures composed of weakly interacting layers. In this paper, we describe two different classes of vdW heterostructures: inorganic vdW heterostructures prepared by co-lamination and restacking; and organicinorganic hetero-epitaxy created by physical vapor deposition of organic molecule crystals on an inorganic vdW substrate. Both types of heterostructures exhibit atomically clean vdW interfaces. Employing such vdW heterostructures, we have demonstrated various novel devices, including graphene/hexagonal boron nitride (hBN) and MoS2 heterostructures for memory devices; graphene/MoS2/WSe2/graphene vertical p-n junctions for photovoltaic devices, and organic crystals on hBN with graphene electrodes for high-performance transistors; Physics

Recent advances in semiconductor nanowire heterostructures

Jackson, H. E.; Smith, L. M.; Jagadish, Chennupati
Fonte: Electrochemical Society Publicador: Electrochemical Society
Tipo: Artigo de Revista Científica Formato: 5 pages
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We review a selection of recent optical experiments which provide unique characterizations of the energy landscape in semiconductor nanowires, both simple nanowires and more complex semiconductor heterostructures. The optical experiments include the techniques of photoluminescence, time-resolved photoluminescence, photoluminescence excitation spectroscopy, photocurrent spectroscopy, and Raman scattering brought to bear on structures from simple core-shell structures, to axial heterostructures, to core-multiple-shell heterostructures. The physics that is illuminated ranges from localization of excitons in GaAs quantum well tubes, to strain in GaAs/GaP axial heterostructures, to carrier relaxation dynamics in GaAs/AlGaAs core-shell NWs probed by the new technique of transient Rayleigh scattering.

Structural and optical properties of ZnS/MgNb2O6 heterostructures

Santos, L. P. S.; Cavalcante, L. S.; Fabbro, M. T.; Beltran Mir, H.; Cordoncillo, E.; Andres, J.; Longo, E.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 180-192
ENG
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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Processo FAPESP: CEPID-CDMF2013/07296-2; In this letter, we report a simple and efficient synthetic procedure where the first step is a coprecipitation/calcination method used to obtain magnesium niobate MgNb2O6 (MN) nanoctystals and in the second stage a microwave assisted hydrothermal method (MAR) is employed to synthesize zinc sulfide (ZnS) nanocrystals and ZnS/MN heterostructures. These heterostructures were characterized by X-ray diffraction (XRD), micro-Raman (MR) spectroscopy, field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high-esolution TEM (HR-TEM), selected area electron diffraction (SAED), energy dispersive X-ray spectrometry (EDX). XRD patterns and MR spectra indicate that MN and ZnS nanocrystals have an orthorhombic and cubic structure, respectively. FE-SEM, TEM and HR-TEM images proved the presence of aggregated MN nanocrystals, ZnS nanocrystals and the presence of ZnS nanocrystals on the surface of MN nanocrystals. Their optical properties were investigated by ultraviolet visible spectroscopy (UV vis) and photoluminescence (PL) measurements at room temperature. ZnS/MN heterostructures show a decrease in the values for the optical band gap with respect to both components. The presence of the ZnS nanocrystals in this heterostructure promotes a high intense PL emission.

Growth Studies of Organic Heterostructures for Photovoltaic Applications; Wachstumsuntersuchungen an organischen Heterostrukturen für photovoltaische Anwendungen

Hinderhofer, Alexander
Fonte: Universität Tübingen Publicador: Universität Tübingen
Tipo: Dissertation; info:eu-repo/semantics/doctoralThesis
EN
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The aim of this work was the characterization of organic heterostructures with different geometries and material combinations relevant for organic photovoltaic. The studied geometries include planar heterostructures, i.e. one material is deposited on top of the other, and mixed heterostructures (two materials are deposited at same time to form a mixed heterostructure). The organic heterostructures were prepared by thermal evaporation in ultra high vacuum and characterized by X-ray scattering. For planar heterostructures it was shown that for controlled deposition a detailed knowledge of the properties of the first layer is essential to predict the growth behavior of top layer. For one material combination it was shown that the molecular orientation and crystal quality in terms of the in-plane coherent island size of the top layer vary significantly with the molecular orientation and crystal quality of the bottom layer. In addition, the deposition of an organic compound onto the surface of a thin film of another compound may lead to smoothing at the interface. The observed smoothing for crystalline organic heterostructures follows a fundamentally different mechanism than the smoothing observed in growth of anorganic materials. The key question for growth of organic mixed heterostructures is if both compounds intermix on a molecular level or phase separate. Based on results from X-ray scattering the following conclusions on mixed heterostructure growth can be drawn: The strong interaction between hydrocarbons and similar perfluorinated compounds leads to the formation of equimolar molecular mixed complexes both for structurally nearly equivalent compounds as well as for structurally different compounds. In films with a molar mixing ratio deviating from 1:1...

Photodiode-Like Behavior and Excellent Photoresponse of Vertical Si/Monolayer MoS2 Heterostructures

Li, Yang; Xu, Cheng-Yan; Wang, Jia-Ying; Zhen, Liang
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em 26/11/2014 EN
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Monolayer transition metal dichalcogenides (TMDs) and their van der Waals heterostructures have been experimentally and theoretically demonstrated as potential candidates for photovoltaic and optoelectronic devices due to the suitable bandgap and excellent light absorption. In this work, we report the observation of photodiode behavior in (both n- and p- type) silicon/monolayer MoS2 vertical heterostructures. The photocurrent and photoresponsivity of heterostructures photodiodes were dependent both on the incident light wavelength and power density, and the highest photoresponsivity of 7.2 A/W was achieved in n-Si/monolayer MoS2 vertical heterostructures photodiodes. Compared with n-Si/MoS2 heterostructures, the photoresponsivity of p-Si/MoS2 heterostructure was much lower. Kelvin probe microscope (KFM) results demonstrated the more efficient separation of photogenerated excitons in n-Si/MoS2 than that in p-Si/MoS2. Coupling KFM results with band alignments of (p-, n-) Si/MoS2 heterostructures, the origins of photodiode-like phenomena of p-Si/MoS2 and n-Si/MoS2 have been unveiled, that is intrinsic built-in electric field in p-n junction, and modulated barrier height and width at the interface in n-n junction. Our work may benefit to the deep understanding of the integration of two-dimensional materials with more conventional three-dimensional semiconductors...

Silica/clay organo-heterostructures to promote polyethylene–clay nanocomposites by in situ polymerization

Belver, Carolina; Ruiz Hitzky, Eduardo; Aranda, Pilar; Quijada, Raúl; Zapata, Paula A.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo de revista
EN
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Artículo de publicación ISI; Two clay organo-heterostructures have been prepared and employed as fillers and catalyst supports for the development of polyethylene–clay nanocomposites. The new silica–clay organo-heterostructures have been obtained from two organoclays modified with tetramethoxysilane. In contrast to related heterostructures reported previously the organic moieties are not removed by heating and their presence intends to confer hydrophobicity to the interlayer region of the clay, even after delamination by hydrolysis-polymerization of the alkoxysilane takes place. These organo-heterostructures were used for preparing clay–polyethylene nanocomposites by in situ polymerizations in which the organoheterostructures were added together with the metallocene catalyst, and by using the silica–clay as support for the metallocene catalysts. The polymers formed when the organo-heterostructures were used as support for the catalyst have higher molecular weights than the standard polyethylene formed under homogeneous conditions. Moreover, the presence of the inorganic silica network developed in the interlayer region of the organoclay favours the existence of a larger organophilic region in which it is possible to accommodate both the catalyst and the monomer...

Novel growth phenomena observed in axial InAs/GaAs nanowire heterostructures

Paladugu, Mohanchand; Zou, Jin; Guo, Yi N; Auchterlonie, Graeme J; Joyce, Hannah J; Gao, Qiang; Tan, Hoe Hark; Jagadish, Chennupati; Kim, Yong
Fonte: Wiley-VCH Verlag GMBH Publicador: Wiley-VCH Verlag GMBH
Tipo: Artigo de Revista Científica
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Growth behavior in Axial InAs/GaAs nanowire heterostructures was observed as they have important applications in optoelectronics. The physical phenomena, which resulted in the failure of axial InAs nanowire growth on GaAs nanowires, was demonstrated. The

Prediction of high zT in thermoelectric silicon nanowires with axial germanium heterostructures

Shelley, Matthew; Mostofi, Arash A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 06/05/2011
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We calculate the thermoelectric figure of merit, zT=S^2GT/(\kappa_l+\kappa_e), for p-type Si nanowires with axial Ge heterostructures using a combination of first-principles density-functional theory, interatomic potentials, and Landauer-Buttiker transport theory. We consider nanowires with up to 8400 atoms and twelve Ge axial heterostructures along their length. We find that introducing heterostructures always reduces S^2G, and that our calculated increases in zT are predominantly driven by associated decreases in \kappa_l. Of the systems considered, <111> nanowires with a regular distribution of Ge heterostructures have the highest figure-of-merit: zT=3, an order of magnitude larger than the equivalent pristine nanowire. Even in the presence of realistic structural disorder, in the form of small variations in length of the heterostructures, zT remains several times larger than that of the pristine case, suggesting that axial heterostructuring is a promising route to high-zT thermoelectric nanowires.; Comment: In print with Europhysics Letters (2011)

Observation of an intrinsic bandgap and Landau level renormalization in graphene/boron-nitride heterostructures

Chen, Zhi-Guo; Shi, Zhiwen; Yang, Wei; Lu, Xiaobo; Lai, You; Yan, Hugen; Wang, Feng; Zhang, Guangyu; Li, Zhiqiang
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 20/06/2014
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Van der Waals heterostructures formed by assembling different two-dimensional atomic crystals into stacks can lead to many new phenomena and device functionalities. In particular, graphene/boron-nitride heterostructures have emerged as a very promising system for band engineering of graphene. However, the intrinsic value and origin of the bandgap in such heterostructures remain unresolved. Here we report the observation of an intrinsic bandgap in epitaxial graphene/boron-nitride heterostructures with zero crystallographic alignment angle. Magneto-optical spectroscopy provides a direct probe of the Landau level transitions in this system and reveals a bandgap of ~ 38 meV (440 K). Moreover, the Landau level transitions are characterized by effective Fermi velocities with a critical dependence on specific transitions and magnetic field. These findings highlight the important role of many body interactions in determining the fundamental properties of graphene heterostructures.; Comment: To appear in Nature Communications

Efficient Interlayer Relaxation and Transition of Excitons in Epitaxial and Non-epitaxial MoS2/WS2 Heterostructures

Yu, Yifei; Hu, Shi; Su, Liqin; Huang, Lujun; Liu, Yi; Jin, Zhenghe; Purezky, Alexander A.; Geohegan, David B.; Kim, Ki Wook; Zhang, Yong; Cao, Linyou
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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Semiconductor heterostructures provide a powerful platform for the engineering of excitons. Here we report the excitonic properties of two-dimensional (2D) heterostructures that consist of monolayer MoS2 and WS2 stacked epitaxially or non-epitaxially in the vertical direction. We find similarly efficient interlayer relaxation and transition of excitons in both the epitaxial and nonepitaxial heterostructures. This is manifested by a two orders of magnitude decrease in the photoluminescence and the appearance of an extra absorption peak at low energy region. The MoS2/WS2 heterostructures show weak interlayer coupling and can essentially act as atomicscale heterojunctions with the intrinsic bandstructures of the two monolayers largely preserved. They are particularly promising for the applications that request efficient dissociation of excitons and strong light absorption, including photovoltaics, solar fuels, photodetectors, and optical modulators. Our results also indicate that 2D heterostructures promise unprecedented capabilities to engineer excitons from the atomic level without concerns of interfacial imperfection.

GaAs/GaSb nanowire heterostructures grown by MOVPE

Jeppsson, Mattias; Dick, Kimberley A.; Wagner, Jakob B; Caroff, Philippe; Deppert, Knut; Samuelson, Lars; Wernersson, Lars-Erik
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
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We report Au-assisted growth of GaAs/GaSb nanowire heterostructures on GaAs(1 1 1)B-substrates by metal-organic vapor phase epitaxy. The growth is studied at various precursor molar fractions and temperatures, in order to optimize the growth conditions for the GaSb nanowire segment. In contrast to most other III-V nanowire systems, the GaSb nanowire growth is Group V-limited under most conditions. We found that depending on the TMSb molar fraction, the seed particle is either supersaturated AuGa or AuGa2 during GaSb growth. The high Ga content in the particle gives a characteristic diameter increase between the GaAs and GaSb segment. From TEM and XEDS measurements we conclude that the GaSb nanowire growth occurs along either the AuGa-GaSb or AuGa2-GaSb pseudo-binaries of the Au-Ga-Sb ternary phase diagram. Finally, the GaSb nanowires exhibit untapered radial growth on the {1 1̄ 0} side facets.

Defects Formed During 1 MeV Si Ion-Irradiation of GeSi/Si Strained Layer Heterostructures at Elevated Temperature

Glasko, J; Elliman, Robert; Zou, Jin; Cockayne, David John Hugh; Fitz Gerald, John
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
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The strain relief observed in GeSi/Si strained-layer heterostructures irradiated with MeV ions at elevated temperature (253°C) is shown to be consistent with the accumulation of excess vacancies in the alloy layer. Partial recovery of the asgrown strain

Synthesis and photocatalytic activity of Zn xCd1-xS/TiO2 heterostructures nanofibre prepared by combining electrospinning and hydrothermal method

Changa,Wei; Ren,Xiaosai; Yang,Guorui; Yan,Wei; Guo,Yanrong
Fonte: South African Journal of Chemistry Publicador: South African Journal of Chemistry
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2015 EN
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The Zn xCd1-xS/TiO2 hierarchical heterostructures were successfully fabricated by combining electrospinning technology and hydrothermal methods. The morphology, crystallinity, composition and band gap of Zn xCd1-xS/TiO2 were characterized by SEM, XRD, EDS, and UV-vis diffuse reflectance spectroscopy. The results indicated the sulphur concentration had a significant influence on the composition and morphology of the products. The values of the band gap energy for Zn xCd1-xS/TiO2 varied from 2.33 to 2.66 eV with the change of sulphur concentration. When the molar ratio of S/Ti was 0.96, the Zn xCd1xS/TiO2 hierarchical heterostructures exhibited enhanced visible light photocatalytic behaviour for the decomposition of Rhodamine B (RhB) under visible light irradiation. The photocatalytic degradation of RhB followed first-order reaction kinetics.