Phototransistor with nanocrystalline Si/amorphous Si bilayer channel

We report a field-effect phototransistor with a channel comprising a thin nanocrystalline silicon transport layer and a thicker hydrogenated amorphous silicon absorption layer. The semiconductor and dielectric layers were deposited by radio-frequency plasma enhanced chemical vapor deposition. The phototransistor with channel length of 24 microns and photosensitive area of 1.4 mm(2) shows an off-current of about 1 pA, and high photoconductive gain in the subthreshold region. Measurements of the quantum efficiency at different incident light intensities and biasing conditions, along with spectral-response characteristics, and threshold voltage stability characterization demonstrate the feasibility of the phototransistor for low light level detection.

A 3-phase model for VIS/NIR mu C-Si : H p-i-n detectors

The spectral response and the photocurrent delivered by entirely microcrystalline p-i-n-Si:H detectors an analysed under different applied bias and light illumination conditions. The spectral response and the internal collection depend not only on the energy range but also on the illumination side. Under [p]- and [n]-side irradiation, the internal collection characteristics have an atypical shape. It is high for applied bias and lower than the open circuit voltage, shows a steep decrease near the open circuit voltage (higher under [n]-side illumination) and levels off for higher voltages. Additionally, the numerical modeling of the VIS/NIR detector, based on the band discontinuities near the grain boundaries and interfaces, complements the study and gives insight into the internal physical process.

Bias dependent photocurrent collection in p-i-n a-Si : EVSiC : H heterojunction

A series of large area single layers and heterojunction cells in the assembly glass/ZnO:Al/p (SixC1-x:H)/i (Si:H)/n (SixC1-x:H)/Al (0 sistances around 10(5)Ohm are also measured Simulated results confirm the experimental findings suggesting that the transport in dark depends almost exclusively on field-aided drift while under illumination it is dependent mainly on minority carriers the diffusion.

Bias-dependent photocurrent collection in p-i-n a-Si : H/SiC : H heterojunction

A series of large area single layers and glass/ZnO:AVp(SixC1-x:H)/i(Si:H)/n(SixC1-x:H)/AI (0 < x < 1) heterojunction cells were produced by plasma-enhanced chemical vapour deposition (PE-CVD) at low temperature. Junction properties, carrier transport and photogeneration are investigated from dark and illuminated current-voltage (J-V) and capacitance-voltage (C-V) characteristics. For the heterojunction cells atypical J-V characteristics under different illumination conditions are observed leading to poor fill factors. High series resistances around 106 Q are also measured. These experimental results were used as a basis for the numerical simulation of the energy band diagram, and the electrical field distribution of the structures. Further comparison with the sensor performance gave satisfactory agreement. Results show that the conduction band offset is the most limiting parameter for the optimal collection of the photogenerated carriers. As the optical gap increases and the conductivity of the doped layers decreases, the transport mechanism changes from a drift to a diffusion-limited process.

Enhanced short wavelength response in laser-scanned-photodiode image sensor using an a-SiC : H/a-Si : H tandem structure

We report in this paper the recent advances we obtained in optimizing a color image sensor based on the laser-scanned-photodiode (LSP) technique. A novel device structure based on a a-SiC:H/a-Si:H pin/pin tandem structure has been tested for a proper color separation process that takes advantage on the different filtering properties due to the different light penetration depth at different wavelengths a-SM and a-SiC:H. While the green and the red images give, in comparison with previous tested structures, a weak response, this structure shows a very good recognition of blue color under reverse bias, leaving a good margin for future device optimization in order to achieve a complete and satisfactory RGB image mapping. Experimental results about the spectral collection efficiency are presented and discussed from the point of view of the color sensor applications. The physics behind the device functioning is explained by recurring to a numerical simulation of the internal electrical configuration of the device.

ITO/SiOx/Si optical sensor with internal gain

A visible/near-infrared optical sensor based on an ITO/SiOx/n-Si structure with internal gain is presented. This surface-barrier structure was fabricated by a low-temperature processing technique. The interface properties and carder transport were investigated from dark current-voltage and capacitance-voltage characteristics. Examination of the multiplication properties was performed under different light excitation and reverse bias conditions. The spectral and pulse response characteristics are analysed. The current amplification mechanism is interpreted by the control of electron current by the space charge of photogenerated holes near the SiOx/Si interface. The optical sensor output characteristics and some possible device applications are presented.

New p-i-n Si : H imager configuration for spatial resolution improvement

Amorphous glass/ZnO-Al/p(a-Si:H)/i(a-Si:H)/n(a-Si1-xCx:H)/Al imagers with different n-layer resistivities were produced by plasma enhanced chemical vapour deposition technique (PE-CVD). An image is projected onto the sensing element and leads to spatially confined depletion regions that can be readout by scanning the photodiode with a low-power modulated laser beam. The essence of the scheme is the analog readout, and the absence of semiconductor arrays or electrode potential manipulations to transfer the information coming from the transducer. The influence of the intensity of the optical image projected onto the sensor surface is correlated with the sensor output characteristics (sensitivity, linearity blooming, resolution and signal-to-noise ratio) are analysed for different material compositions (0.5 < x < 1). The results show that the responsivity and the spatial resolution are limited by the conductivity of the doped layers. An enhancement of one order of magnitude in the image intensity signal and on the spatial resolution are achieved at 0.2 mW cm(-2) light flux by decreasing the n-layer conductivity by the same amount. A physical model supported by electrical simulation gives insight into the image-sensing technique used.

Aplicação da versão em português do instrumento de avaliação de qualidade de vida da Organização Mundial da Saúde (WHOQOL-100)

INTRODUÇÃO: O Grupo de Qualidade de Vida da OMS desenvolveu um instrumento de avaliação de Qualidade de Vida, o WHOQOL-100 que está traduzido para 20 idiomas (WHOQOL GROUP, 1998). A aplicação do instrumento na versão em português é o objetivo do trabalho. MÉTODOS: Foram aplicados em 250 pacientes provenientes de quatro grandes áreas médicas (psiquiatria, clínica, cirurgia e ginecologia) de um hospital de clínicas de Porto Alegre, RS, e em 50 voluntários-controles o Instrumento de Avaliação de Qualidade de Vida da OMS (WHOQOL-100), o Inventário de Beck para a depressão (BDI) e a Escala de Desesperança de Beck (BHS). RESULTADOS E CONCLUSÕES:O Instrumento mostrou bom desempenho psicométrico com características satisfatórias de consistência interna, validade discriminante, validade de critério, validade concorrente e fidedignidade teste-reteste. Concluiu-se que o instrumento está em condições de ser usado no Brasil, sendo importante avaliar seu desempenho em outras regiões e em diferentes amostras de indivíduos.

CVD of CrO2 thin films: Influence of the deposition parameters on their structural and magnetic properties

This work reports on the synthesis of CrO2 thin films by atmospheric pressure CVD using chromium trioxide (CrO3) and oxygen. Highly oriented (100) CrO2 films containing highly oriented (0001) Cr2O3 were grown onto Al2O3(0001) substrates. Films display a sharp magnetic transition at 375 K and a saturation magnetization of 1.92 mu(B)/f.u., close to the bulk value of 2 mu(B)/f.u. for the CrO2.

Fabrication of Three-Dimensional Dendritic Ni-Co Films By Electrodeposition on Stainless Steel Substrates

Co-deposition of nickel and cobalt was carried out on austenitic stainless steel (AISI 304) substrates by imposing a square waveform current in the cathodic region. The innovative procedure applied in this work allows creating a stable, fully developed, and open porous three-dimensional (3D) dendritic structure, which can be used as electrode for redox supercapacitors. This study investigates in detail the influence of the applied current density on the morphology, mass, and chemical composition of the deposited Ni-Co films and the resulting 3D porous network dendritic structure. The morphology and the physicochemical composition were studied by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (W). The electrochemical behavior of the materials was evaluated by cyclic voltammetry (CV). The results highlight the mechanism involved in the coelectrodeposition process and how the lower limit current density tailors the film composition and morphology, as well as its electrochemical activity.

Boron-doped nanocrystalline silicon thin films for solar cells

This article reports on the structural, electronic, and optical properties of boron-doped hydrogenated nanocrystalline silicon (nc-Si: H) thin films. The films were deposited by plasma-enhanced chemical vapour deposition (PECVD) at a substrate temperature of 150 degrees C. Crystalline volume fraction and dark conductivity of the films were determined as a function of trimethylboron-to-silane flow ratio. Optical constants of doped and undoped nc-Si: H were obtained from transmission and reflection spectra. By employing p(+) nc-Si: H as a window layer combined with a p' a-SiC buffer layer, a-Si: H-based p-p'-i-n solar cells on ZnO:Al-coated glass substrates were fabricated. Device characteristics were obtained from current-voltage and spectral-response measurements. (C) 2011 Elsevier B. V. All rights reserved.

Filling and wetting transitions of nematic liquid crystals on sinusoidal substrates

Close to sinusoidal substrates, simple fluids may undergo a filling transition, in which the fluid passes from a dry to a filled state, where the interface remains unbent but bound to the substrate. Increasing the surface field, the interface unbinds and a wetting transition occurs. We show that this double-transition sequence may be strongly modified in the case of ordered fluids, such as nematic liquid crystals. Depending on the preferred orientation of the nematic molecules at the structured substrate and at the isotropic-nematic interface, the filling transition may not exist, and the fluid passes directly from a dry to a complete-wet state, with the interface far from the substrate. More interestingly, in other situations, the complete wetting transition may be prevented, and the fluid passes from a dry to a filled state, and remains in this configuration, with the interface always attached to the substrate, even for very large surface fields. Both transitions are observed only for a same substrate in a narrow range of amplitudes.

Optical Transducers Based on Amorphous Si/SiC Photodiodes

Amorphous Si/SiC photodiodes working as photo-sensing or wavelength sensitive devices have been widely studied. In this paper single and stacked a-SiC:H p-i-n devices, in different geometries and configurations, are reviewed. Several readout techniques, depending on the desired applications (image sensor, color sensor, wavelength division multiplexer/demultiplexer device) are proposed. Physical models are presented and supported by electrical and numerical simulations of the output characteristics of the sensors.

Photodiode with nanocrystalline Si/amorphous Si absorber bilayer

This letter reports a near-ultraviolet/visible/near-infrared n(+)-n-i-delta(i)-p photodiode with an absorber comprising a nanocrystalline silicon n layer and a hydrogenated amorphous silicon i layer. Device modeling reveals that the dominant source of reverse dark current is deep defect states in the n layer, and its magnitude is controlled by the i layer thickness. The photodiode with the 900/400 nm thick n-i layers exhibits a reverse dark current density of 3nA/cm(2) at -1V. Donor concentration and diffusion length of holes in the n layer are estimated from the capacitance-voltage characteristics and from the bias dependence of long-wavelength response, respectively. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3660725]

Especificidades da atividade física no cancro da mama

De acordo com o estudo de Gatta e col, em Janeiro de 2003, 11,6 milhões de europeus apresentaram história clínica de cancro. Destes, uma em cada 73 mulheres tinham história de cancro da mama enquanto que um em cada 160 homens apresentaram história de cancro da próstata. A prevalência em 2003 conduziu a valores estimados de - 13 milhões de europeus afetados por cancro em 2010. O cancro da mama é o tipo de cancro que mais frequentemente é diagnosticado e a segunda causa de morte por cancro nas mulheres a nível mundial e também em Portugal (Plano Nacional de Prevenção e Controlo das Doenças Oncológicas 2007-2010. De acordo com o INE, 12,4/100.000 habitantes das mortes com menos de 65 anos deveram-se a cancro da mama feminino. As opções de tratamento para o cancro podem incluir cirurgia, radioterapia, hormonoterapia, quimioterapia ou imunoterapia, as quais poderão apresentar efeitos colaterais suscetíveis de influenciar a participação no exercício e a resposta ao mesmo. Independentemente da intervenção terapêutica no cancro, a fadiga é um efeito colateral comum. Um cancro é considerado como curado quando as remissões são permanentes ou quando não existe recorrência há mais de 5 anos. Uma das razões frequentemente subestimada como causa de fadiga é a perda de condição física como resultado do acamamento e do incentivo por parte de familiares e/ou prestadores de cuidados de saúde a um maior descanso quando o doente refere fadiga. Esta situação pode limitar ainda mais as atividades da vida diária, conduzindo a um maior descondicionamento e intolerância ao exercício, cujas consequências são mais dramáticas a nível do sistema cardiorrespiratório e serem por si só responsáveis pela perda de cerca de 30 por cento da capacidade funcional do doente. De acordo com estudos efetuados em portadores de cancro da mama, a uma capacidade aeróbia abaixo dos 8 MET’s associa-se um aumento de mortalidade 3 vezes mais elevado quando comparado com mulheres com cancro da mama com capacidade aeróbia superior a 8 MET’s.