On the temperature behavior of shunt-leakage currents in Cu(In,Ga)Se2 solar cells: The role of grain boundaries and rear Schottky contact

By comparing simulated and measured dark current-voltage (I-V) characteristics of CIGS cells at different temperatures, we investigate the temperature behavior of the shunt leakage current, and find that it can be explained by large donor trap concentrations at grain boundaries (GBs), and by a Schottky barrier at the backside contact where the GBs meets the anode metallization. We studied the I-V characteristics in the temperature range 280 K - 160 K achieving good fits of the measured I-V curves, especially for reverse bias and low forward bias, where the shunt leakage current dominates. The most important parameters determining the shunt leakage current value and its temperature dependence are the peak energy and density of the GB donor distribution, which control the inversion of GBs and the pinning of Fermi level at the anode/GB contact

Variações temporais da linha de costa em praias arenosas dominadas por ondas do sudeste da Ilha de Santa Catarina (Florianópolis, SC, Brasil)

Shoreline variation occurs at several temporal scales and the most useful time span for human context is about 100 years or less. At the Santa Catarina Island, environmental problems related to unplanned human occupation and activities resulted in coastal erosion and lost of environmental quality. This study is about a shoreline variation analysis at inter decadal scale, and inter annual scale involving 64 and 4 years time span evaluation, respectively, to five sandy beaches located at southeast of Santa Catarina Island. The data source was composed by 5 time series of aerial photographs, which was digitized, and managed by geoprocessing techniques, using digital cartography and Geographical Information System tools. The general trend of shoreline variation showed an erosional rate a little bit more than half meter per year, and an average shore retraction less than fifth meters in 64 years. At the interannual scale, rates and beach width was lesser than inter decadal, yet, the ranges at some specific beach location reached rates four times superior. However, not even all beaches showed erosional trend in one or both time spans analyzed. The shoreline variation among both time spans allowed the smoothing coastal processes of short periods making possible to highlight trends in higher temporal horizon. This approach let to explore shoreline variation by the distinct ways of interesting of coastal planning and management.A variação da linha de costa ocorre em diversas escalas temporais, sendo a escala inferior a 100 anos especialmente importante para o contexto humano. Na Ilha de Santa Catarina(SC), problemas decorrentes de ocupação e uso da orla marítima de forma desordenada ocasionaram problemas de erosão costeira e perda de qualidade ambiental. Neste sentido, foi realizada uma avaliação da variação da linha de costa, abrangendo os períodos de 64 e 4 anos, de forma a contemplar a escala interdecadal e interanual, em cinco praias da costa sudeste da Ilha de Santa Catarina. A obtenção dos dados foi realizada através de aerofotos, digitalizadas e tratadas, utilizando técnicas e ferramentas de geoprocessamento. A variação média em escala interdecadal demonstrou uma taxa média superior a meio metro anual de recuo da linha de costa e perda de faixa média de largura de praia inferior a cinqüenta metros em 64 anos. Já em escalainteranual os valores apresentaram-se inferiores, porém, com grande variação, apresentando localmente taxas de variação até quatro vezes superiores à escala interdecadal. No entanto, nem todas as praias apresentaram tendência erosiva. A variação entre os períodos analisados indicou que processos de períodos mais curtos são suavizados com o aumento do horizonte temporal de análise, permitindo ressaltar a tendência de variação num contexto temporal mais abrangente. Tal abordagem permitiu explorar a variação da linha de costa sob diferentes perspectivas temporais, gerando subsídios relevantes ao planejamento e gerenciamento costeiro

Engineering the strain field for the control of quantum confinement: An analytical model for arbitrary shape nanostructures

We describe an analytical method to calculate the strain field and the corresponding band gap modulation induced in a quantum well by a surface stressor of arbitrary shape. In this way, it is possible to engineer the confinement potential of different strained nanostructures based on patterned heterojunctions. Band gap modulations up to 130–140 meV are predicted for suitably designed II–VI/III–V and III–V/III–V heterostructures

Sacrospinous ligament suspension with transobturator mesh versus sacral colpopexy for genital prolapse

OBJECTIVE: To compare the safety and efficacy of abdominal sacral colpopexy and sacrospinous ligament suspension with the use of vaginal mesh for apical prolapse. METHOD: This retrospective study was conducted from 2005 to 2012 and included 89 women with apical prolapse who underwent surgery. Assessments included pre- and postoperative Pelvic Organ Prolapse Quantification (POP-Q) stage. Rates of objective cure and immediate/late complications were compared. RESULTS: In total, 41 of the 89 women underwent sacrospinous ligament suspension, and 48 of the women underwent abdominal sacral colpopexy. A total of 40.4% of the women had vault prolapse (p=0.9361). Most of them had no complications (93.2%) (p=0.9418). Approximately 30% of the women had late complications; local pain was the main symptom and was found only in women who underwent the abdominal procedure (25.6%) (p=0.001). Only the women who were submitted to the vaginal procedure had mesh exposure (18.4%). The objective success rate and the rate of anterior vaginal prolapse (p=0.2970) were similar for both techniques. CONCLUSION: Sacrospinous ligament suspension was as effective and had a similar objective success rate as abdominal sacral colpopexy for the treatment of apical prolapse. Sacrospinous ligament suspension performed with the use of vaginal mesh in the anterior compartment was effective in preventing anterior vaginal prolapse after surgery

Determination of surface lattice strain in ZnTe epilayers on {100}GaAs by ion channeling and reflectance spectroscopy

We report on the direct measurements of surface lattice strain in ZnTe epitaxial layers on {100}GaAs substrates by ion channeling Rutherford backscattering spectrometry and low‐temperature (10 K) reflectance spectroscopy measurements. The measured ZnTe strain is the superposition of the expected thermal (tensile) strain and a thickness‐dependent residual compressive strain. Our data indicate that the removal of this residual strain is slower than the rate predicted by the equilibrium theory, following an apparent h−1/2 power‐law dependence on the epilayer thickness h, above ∼100 nm

Transmission Electron Microscopy, High Resolution X-Ray Diffraction and Rutherford Backscattering Study of Strain Release in InGaAs/GaAs Buffer Layers

Strain release and dislocation distribution in InGaAs/GaAs double heterostructures, step-graded and linear-graded buffer layers have been studied. A higher misfit dislocation density at the inner interface between the InGaAs layer and the substrate was found in all the samples. This corresponded to a strain release of the inner ternary layers much larger than predicted by equilibrium theories. The residual parallel strain of the external layers as a function of their thickness was found to follow a curve approximately of slope -0.5, in agreement with previous investigations on single InGaAs layers. This result has been interpreted as evidence that the elastic energy per unit interface area remains constant during the epilayer growth. The presence of numerous single and multiple dislocation loops inside the substrate was attributed to the strain relaxation occurring through dislocation multiplication via Frank-Read sources activated during the growth. A comparison with InGaAs/GaAs step-graded and linear-graded heterostructures is also shown and briefly discussed. Finally, lattice plane tilts between epilayers and substrates have been found due to the imbalance in the linear density of misfit dislocations with opposite component of the Burgers vector, b⊥eff, perpendicular to the interface

The impact of chemical short-range order on the thermophysical properties of medium- and high-entropy alloys

The unusual behavior observed in the coefficient of thermal expansion and specific heat capacity of CrFeNi, CoCrNi, and CoCrFeNi medium/high-entropy alloys is commonly referred to as the K-state effect. It is shown to be independent of the Curie temperature, as demonstrated by temperature-dependent magnetic moment measurements. CoCrFeNi alloy is chosen for detailed characterization; potential reasons for the K-state effect such as texture, recrystallization, and second-phase precipitation are ruled out. An examination of the electronic structure indicates the formation of a pseudo-gap in the Density of States, which suggests a specific chemical interaction between Ni and Cr atoms upon alloying. Hybrid Monte Carlo/Molecular Dynamic (MC/MD) simulations indicate the presence of non-negligible chemical short-range order (CSRO). Local lattice distortions are shown to be negligible, although deviations around Cr and Ni elements from those expected in a fully disordered structure are experimentally observed by X-ray absorption spectroscopy. The determined bonding distances are in good agreement with MC/MD calculations. A mechanism is proposed to explain the anomalies and calorimetric experiments and their results are used to validate the mechanism