Three-dimensional quantum-size effect in chemically deposited cadmium selenide films

A low cost chemical bath deposition (CBD) technique has been used for the preparation of Cu 2-x Se thin films on glass substrates. Structural, electrical and optical properties of these films were investigated. X-ray diffraction (XRD) study of the Cu 2-x Se films annealed at 523K suggests a cubic structure with a lattice constant of 5.697Å. Chemical composition was investigated by X-ray photoelectron spectroscopy (XPS). It reveals that absorbed oxygen in the film decreases remarkably on annealing above 423K. The Cu/Se ratio was observed to be the same in as-deposited and annealed films. Both as-deposited and annealed films show very low resistivity in the range of (0.

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“…, can be obtained using the relation Tcorr. = {T(%)/(100 -R (%))} × 100 [19,26]. The α vs hν curve is presented in Fig.…”

Section: Annealing Temperature (K)mentioning

confidence: 99%

Structural, electrical and optical properties of copper selenide thin films deposited by chemical bath deposition technique

Al-Mamun

Islam

Bhuiyan

2005

J Mater Sci: Mater Electron

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“…This finding is in good agreement with the results of other authors using CBD prepared CdS films, and is usually ascribed to quantum size effects. 13,14 According to Nedeljkovic et al 15 the shift of E G corresponds to a mean-crystallite diameter of 7 nm. After the preparation of the CdS layers they were covered with a 200 nm thick tungsten oxide film which was thermally evaporated at a pressure of 10 Ϫ5 mbar from WO 3 pellets.…”

Section: ͓S0003-6951͑96͒01420-9͔mentioning

confidence: 99%

Photochromic coloration of WO3 with visible light

Bechinger

Wirth

Leiderer

1996

Applied Physics Letters

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Thin amorphous films of tungsten oxide (WO 3 ) are well known to change their optical absorption behavior upon light exposure, usually referred to as photochromic effect. Since the formation of color centers is closely related to the optical creation of electron-hole pairs the sensitivity of the photochromic effect in WO 3 is limited to energies above its band-gap energy of 3.25 eV, corresponding to the near-ultraviolet range. We will demonstrate that in case of a thin cadmium sulfide ͑CdS͒ layer underneath the tungsten oxide film the sensitivity of photochromism is shifted into the visible range. This result is interpreted in terms of charge carrier injection from the CdS into the WO 3 . Apart from a more detailed understanding of the photochromic effect this may have also relevance for technical applications. © 1996 American Institute of Physics. ͓S0003-6951͑96͒01420-9͔Due to the high potential of large area optical devices capable to be switched between a transparent and a strong absorptive state there is a large research activity within the last two decades regarding transition metal oxides. 1-3 One of the most promising candidates is tungsten oxide, often discussed in the context of ''smart windows'' in order to control the solar input of buildings or with respect to large area displays. 2,4 For most of these purposes the so-called electrochromic effect is used, where coloration and bleaching of tungsten oxide is caused by an electrochemical reaction. Much less attention has been paid so far to the light-induced coloration of WO 3 , i.e., photochromism, where an identical absorption band is formed upon irradiating bare tungsten oxide thin films with light. 1,5 Taking into account that the photochromic coloration can be made completely reversible by exposing the sample to oxygen gas, 6 the basic requirements for technical applications like erasable optical storage devices are met by the photochromic effect. However, since the formation of color centers in WO 3 requires irradiation in the near-ultraviolet range 1,6 where no compact light sources such as laser diodes are available at the moment, this may impede the development of integrated storage devices based on WO 3 considerably.In this letter we will demonstrate that the spectral sensitivity of photochromism in tungsten oxide can be shifted from the near-UV into the visible range by the use of a thin cadmium sulfide interlayer between the substrate and the WO 3 film. In addition to a more detailed understanding of the coloration mechanism, this result may also have relevance for the above-mentioned applications.It has already been demonstrated that the photochromic effect in tungsten oxide is intimately connected to optically excited electron (e Ϫ ) hole ͑h ϩ ) pairs which can decompose water being incorporated in WO 3 to a considerable amount. 6 The light-induced decomposition of H 2 O can be written as: 7,8 H 2 Oϩ2h ϩ ⇔Oϩ2H ϩ , ͑1͒which describes the creation of protons (H ϩ ) and metastable oxygen radicals ͑O͒. The protons together with the optically e...

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“…Além disso, o transporte de carga inter-partícula também parecia algo complicado, uma vez que o transportador deveria vencer uma barreira coulombiana de até 50 meV, dependendo do contato entre os cristalitos, 41 com resistividades da ordem de 10 9 Ω cm. 44 Afora isso, o efeito favorável de ganho de área pela penetração do eletrólito, que é estimado em 1000 vezes para um filme com algumas unidades de µm de espessura, 41 parecia bastante promissor, principalmente para o desenvolvimento de células solares fotosensibilizadas por corante.…”

Section: Fotoexcitação Separação E Transporte De Carga Em Filmes Nanunclassified

Fotoeletrocatálise Em Semicondutores: Dos Princípios Básicos Até Sua Conformação À Nanoescala

Baccaro¹,

Gutz²

2017

Quim. Nova

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PHOTOELECTROCATALYSIS ON SEMICONDUCTORS: FROM THE FUNDAMENTALS TO ITS CONFORMATION AT THE NANOSCALE LEVEL. The science of semiconductors, essential in electronics, is pivotal also for the most active research fields of environmental science and engineering today -the development of solar energy conversions and advanced oxidation processes, exemplified by the harvesting of sun daylight to produce electric energy, environmentally friendly fuels and to clean up water from harmful pollutants. The advancement of such fields relies on the fundamentals of the photocatalysis at semiconductors, summarized in this review in language familiar to chemists. The theory and experimental onrush emerged mainly during the first half of the 20 th century but the rising interest in the science of nanostructured materials in recent decades, besides many insights about the potential of this scale-down of sizes, also forced a revision of the theoretical models. Essentially, the interfacial model of the space-charge layer cannot explain the behavior of nanoparticulate films, even at doped conditions comparable to monocrystalline materials. The present work encompasses the conformation of classical photocatalytic models to the nanoscale size, critically reviewing their features and role for modern electrochemical applications.Keywords: photoelectrocatalysis; monocrystalline semiconductors; nanoparticulate semiconductors; space-charge layer; band bending. INTRODUÇÃOO tema fotocatálise já foi alvo de diversas revisões na literatura, inclusive em alguns manuscritos de cunho exaustivo com centenas de referências. Nesse sentido, destacam-se entre os trabalhos clássicos o do professor Michael R. Hoffmann e col.1 que acumula mais de 17 mil citações desde 1995 e os do professor Akira Fujishima e col. 4,5 visando a discussão da aplicação do TiO 2 para remediação ambiental e a discussão de mecanismos de fotodegradação de compostos orgânicos catalisados por ele. A fotoeletrocatálise, entretanto, nunca foi focalizada em trabalhos de revisão em vernáculo. Por algumas vezes, ela foi abordada em trabalhos de inovação técnica contemplando novas aplicações, 6-9 mas não uma visão fundamentada e sistematizada do tema balizada em literatura selecionada e acompanhada de discussão crítica do estado da arte e possíveis tendências. A fundamentação teórica da fotoeletrocatálise remonta ao final da Segunda Guerra Mundial, com os estudos da semicondução no silício e germânio orientados por Lark-Horovitz 10 e que desencadearam o enorme avanço tecnológico representado por componentes eletrônicos como diodos e transistores, formados por junções entre semicondutores com dopagem diferente, presentes hoje em praticamente todos os dispositivos eletrônicos. Os componentes semicondutores também se impuseram na detecção e emissão de radiação eletromagnética, servindo de exemplos os fotodiodos e os diodos emissores de luz (LEDs). Assim, segue a fundamentação teórica da matéria. A TEORIA DE BANDAPor definição simples, um semicondutor é um material com condutividade elétrica ...

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Three-dimensional quantum-size effect in chemically deposited cadmium selenide films

Cited by 320 publications

References 14 publications

Structural, electrical and optical properties of copper selenide thin films deposited by chemical bath deposition technique

Structural, electrical and optical properties of copper selenide thin films deposited by chemical bath deposition technique

Photochromic coloration of WO3 with visible light

Fotoeletrocatálise Em Semicondutores: Dos Princípios Básicos Até Sua Conformação À Nanoescala

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