Analysis of S-rich CuIn(S,Se)2 layers for photovoltaic applications: Influence of the sulfurization temperature on the crystalline properties of electrodeposited and sulfurized CuInSe2 precursors

This paper reports the microstructural analysis of S-rich CuIn(S,Se)2 layers produced by electrodeposition of CuInSe2 precursors and annealing under sulfurizing conditions as a function of the temperature of sulfurization. The characterization of the layers by Raman scattering, scanning electron microscopy, Auger electron spectroscopy, and XRD techniques has allowed observation of the strong dependence of the crystalline quality of these layers on the sulfurization temperature: Higher sulfurization temperatures lead to films with improved crystallinity, larger average grain size, and lower density of structural defects. However, it also favors the formation of a thicker MoS2 interphase layer between the CuInS2 absorber layer and the Mo back contact. Decreasing the temperature of sulfurization leads to a significant decrease in the thickness of this intermediate layer and is also accompanied by significant changes in the composition of the interface region between the absorber and the MoS2 layer, which becomes Cu rich. The characterization of devices fabricated with these absorbers corroborates the significant impact of all these features on device parameters as the open circuit voltage and fill factor that determine the efficiency of the solar cells.

Transport properties across the La2/3Ca1/3MnO3/SrTiO3 heterointerface

The transport properties across La2/3Ca1/3MnO3/SrTiO3 (LCMO/STO) heterostructures with different thicknesses of the STO insulating barrier have been studied by using atomic force microscopy measurements in the current sensing (CS) mode. To avoid intrinsic problems of the CS method we have developed a nanostructured contact geometry of Au dots. The conduction process across the LCMO/STO interface exhibits the typical features of a tunneling process.

Properties of nitrogen doped silicon films deposited by low-pressure chemical vapor deposition from silane and ammonia

Nitrogen doped silicon (NIDOS) films have been deposited by low-pressure chemical vapor deposition from silane SiH4 and ammonia NH3 at high temperature (750°C) and the influences of the NH3/SiH4 gas ratio on the films deposition rate, refractive index, stoichiometry, microstructure, electrical conductivity, and thermomechanical stress are studied. The chemical species derived from silylene SiH2 into the gaseous phase are shown to be responsible for the deposition of NIDOS and/or (silicon rich) silicon nitride. The competition between these two deposition phenomena leads finally to very high deposition rates (100 nm/min) for low NH3/SiH4 gas ratio (R¿0.1). Moreover, complex variations of NIDOS film properties are evidenced and related to the dual behavior of the nitrogen atom into silicon, either n-type substitutional impurity or insulative intersticial impurity, according to the Si¿N atomic bound. Finally, the use of NIDOS deposition for the realization of microelectromechanical systems is investigated.

Structural and optical properties of dilute InAsN grown by molecular beam epitaxy

We perform a structural and optical characterization of InAs1¿xNx epilayers grown by molecular beam epitaxy on InAs substrates x 2.2% . High-resolution x-ray diffraction HRXRD is used to obtain information about the crystal quality and the strain state of the samples and to determine the N content of the films. The composition of two of the samples investigated is also obtained with time-of-flight secondary ion mass spectroscopy ToF-SIMS measurements. The combined analysis of the HRXRD and ToF-SIMS data suggests that the lattice parameter of InAsN might significantly deviate from Vegard"s law. Raman scattering and far-infrared reflectivity measurements have been carried out to investigate the incorporation of N into the InAsN alloy. N-related local vibrational modes are detected in the samples with higher N content. The origin of the observed features is discussed. We study the compositional dependence of the room-temperature band gap energy of the InAsN alloy. For this purpose, photoluminescence and optical absorption measurements are presented. The results are analyzed in terms of the band-anticrossing BAC model. We find that the room-temperature coupling parameter for InAsN within the BAC model is CNM=2.0 0.1 eV.

Structural and gas-sensing properties of WO3 nanocrystalline powders obtained by a sol-gel method from tungstic acid

WO3 nanocrystalline powders were obtained from tungstic acid following a sol-gel process. Evolution of structural properties with annealing temperature was studied by X-ray diffraction and Raman spectroscopy. These structural properties were compared with those of WO3 nanopowders obtained by the most common process of pyrolysis of ammonium paratungstate, usually used in gas sensors applications. Sol-gel WO3 showed a high sensor response to NO2 and low response to CO and CH4. The response of these sensor devices was compared with that of WO3 obtained from pyrolysis, showing the latter a worse sensor response to NO2. Influence of operating temperature, humidity, and film thickness on NO2 detection was studied in order to improve the sensing conditions to this gas.

Analysis of leakage properties and guiding conditions of rib antiresonant reflecting optical waveguides

Power leakage properties and guiding conditions of rib antiresonant reflecting optical waveguides (rib-ARROW) have been theoretically and experimentally studied as a function of wavelength and polarization of the light for different geometrical and optical parameters that characterize the rib-ARROW structure. Obtained results show that rib-ARROWs can only be fabricated with low losses in a wavelength range when determined rib configurations are adopted. Furthermore, these waveguides exhibit a polarization sensitivity that largely depends on the core-substrate refractive index difference. Together with the experimental results, theoretical calculations from different modeling methods are also presented and discussed.

Enhancement of the photoelectrochemical properties of Cl-doped ZnO nanowires by tuning their coaxial doping profile

Arrays of vertically aligned ZnO:Cl/ZnO core-shell nanowires were used to demonstrate that the control of the coaxial doping profile in homojunction nanostructures can improve their surface charge carrier transfer while conserving potentially excellent transport properties. It is experimentally shown that the presence of a ZnO shell enhances the photoelectrochemical properties of ZnO:Cl nanowires up to a factor 5. Likewise, the ZnO shell promotes the visible photoluminescence band in highly conducting ZnO:Cl nanowires. These lines of evidence are associated with the increase of the nanowires" surface depletion layer

Gas-sensing properties of sprayed films of (CdO)x(ZnO)1-x mixed oxide

A novel NO2 sensor based on (CdO)x(ZnO)1-x mixed-oxide thin films deposited by the spray pyrolysis technique is developed. The sensor response to 3-ppm NO2 is studied in the range 50°C-350°C for three different film compositions. The device is also tested for other harmful gases, such as CO (300 ppm) and CH4 (3000 ppm). The sensor response to these reducing gases is different at different temperatures varying from the response typical for the p-type semiconductor to that typical for the n-type semiconductor. Satisfactory response to NO2 and dynamic behavior at 230°C, as well as low resistivity, are observed for the mixed-oxide film with 30% Cd. The response to interfering gas is poor at working temperature (230°C). On the basis of this study, a possible sensing mechanism is proposed.

Gas sensing properties of catalytically modified WO3 with copper and vanadium for NH3 detection

Ammonia gas detection by pure and catalytically modified WO3 based gas sensor was analysed. The sensor response of pure WO3 to NH3 was not only rather low but also presented an abnormal behaviour, probably due to the unselective oxidation of ammonia to NOx. Copper and vanadium were introduced in different concentrations and the resulting material was annealed at different temperatures in order to improve the sensing properties for NH3 detection. The introduction of copper and vanadium as catalytic additives improved the response to NH3 and also eliminated the abnormal behaviour. Possible mechanisms of NH3 reaction over these materials are discussed. Sensor responses to other gases like NO2 or CO and the interference of humidity on ammonia detection were also analysed so as to choose the best sensing element.

Spatial variability of the chemical, physical and biological properties in lowland cultivated with irrigated rice

In the areas where irrigated rice is grown in the south of Brazil, few studies have been carried out to investigate the spatial variability structure of soil properties and to establish new forms of soil management as well as determine soil corrective and fertilizer applications. In this sense, this study had the objective of evaluating the spatial variability of chemical, physical and biological soil properties in a lowland area under irrigated rice cultivation in the conventional till system. For this purpose, a 10 x 10 m grid of 100 points was established, in an experimental field of the Embrapa Clima Temperado, in the County of Capão do Leão, State of Rio Grande do Sul. The spatial variability structure was evaluated by geostatistical tools and the number of subsamples required to represent each soil property in future studies was calculated using classical statistics. Results showed that the spatial variability structure of sand, silt, SMP index, cation exchange capacity (pH 7.0), Al3+ and total N properties could be detected by geostatistical analysis. A pure nugget effect was observed for the nutrients K, S and B, as well as macroporosity, mean weighted diameter of aggregates, and soil water storage. The cross validation procedure, based on linear regression and the determination coefficient, was more efficient to evaluate the quality of the adjusted mathematical model than the degree of spatial dependence. It was also concluded that the combination of classical with geostatistics can in many cases simplify the soil sampling process without losing information quality.

Consequences of modified lipid and glucose metabolism on peripheral nervous system structure and function

284 million people worldwide suffered from type 2 diabetes mellitus (T2DM) in 2010, which will, in approximately half of them, lead to the development of diabetic peripheral neuropathy (DPN). Although DPN is the most common complication of diabetes mellitus and the leading cause of non-traumatic amputations its pathophysiology is still poorly understood. To get more insight into the molecular mechanism underlying DPN in T2DM, I used a rodent model of T2DM, the db/db mice.¦ln vivo electrophysiological recordings of diabetic animals indicated that in addition to reduced nerve conduction velocity db/db mice also present increased nerve excitability. Further ex vivo evaluation of the electrophysiological properties of db/db nerves clearly established a presence of the peripheral nerve hyperexcitability (PNH) phenotype in diabetic animals. Using pharmacological inhibitors we demonstrated that PNH is mostly mediated by the decreased activity of Kv1 channels. ln agreement with these data 1 observed that the diabetic condition led to a reduced presence of the Kv1.2 subunits in juxtaparanodal regions of db/db peripheral nerves whereas its mANA and protein expression levels were not affected. Lmportantly, I confirmed a loss of juxtaparanodal Kv1.2 subunits in nerve biopsies from type 2 diabetic patients. Together these observations indicate that the type 2 diabetic condition leads to potassium-channel mediated changes of nerve excitability thus identifying them as potential drug targets to treat sorne of the DPN related symptoms.¦Schwann cells ensheath and isolate peripheral axons by the production of myelin, which consists of lipids and proteins in a ratio of 2:1. Peripheral myelin protein 2 (= P2, Pmp2 or FABP8) was originally described as one of the most abundant myelin proteins in the peripheral nervous system. P2, which is a member of the fatty acid binding protein (FABP) family, is a 14.8 kDa cytosolic protein expressed on the cytoplasmic side of compact myelin membranes. As indicated by their name, the principal role of FABPs is thought to be the binding and transport of fatty acids.¦To study its role in myelinating glial cells I have recently generated a complete P2 knockout mouse model (P2-/-). I confirmed the loss of P2 in the sciatic nerve of P2-/- mice at the mRNA and protein level. Electrophysiological analysis of the adult (P56) mutant mice revealed a mild but significant reduction in the motor nerve conduction velocity. lnterestingly, this functional change was not accompanied by any detectable alterations in general myelin structure. However, I have observed significant alterations in the mRNA expression level of other FABPs, predominantly FABP9, in the PNS of P2-/- mice as compared to age-matched P2+/+ mice indicating a role of P2 in the glial myelin lipid metabolism.¦Le diabète de type 2 touche 284 million de personnes dans le monde en 2010 et son évolution conduit dans la moitié des cas à une neuropathie périphérique diabétique. Bien que la neuropathie périphérique soit la complication la plus courante du diabète pouvant conduire jusqu'à l'amputation, sa physiopathologie est aujourd'hui encore mal comprise. Dans le but d'améliorer les connaissances moléculaires expliquant les mécanismes de la neuropathie liée au diabète de type 2, j'ai utilisé un modèle murin du diabète de type 2, les souris db/db.¦ln vivo, les enregistrements éléctrophysiologiques des animaux diabétiques montrent qu'en plus d'une diminution de la vitesse de conduction nerveuse, les souris db/db présentent également une augmentation de l'excitabilité nerveuse. Des mesures menées Ex­ vivo ont montré l'existence d'un phénotype d'hyperexcitabilité sur les nerfs périphériques isolés d'animaux diabétiques. Grâce à l'utilisation d'inhibiteurs pharmacologiques, nous avons pu démontrer que l'hyperexcitabilité démontrée était due à une réduction d'activité des canaux Kv1. En accord avec ces données, j'ai observé qu'une situation de diabète conduisait à une diminution des canaux Kv1.2 aux régions juxta-paranodales des nerfs périphériques db/db, alors que l'expression du transcrit et de la protéine restait stable. J'ai également confirmé l'absence de canaux Kv1.2 aux juxta-paranoeuds de biopsies de nerfs de patients diabétiques. L'ensemble de ces observations montrent que les nerfs périphériques chez les patients atteints de diabète de type 2 est due à une diminution des canaux potassiques rapides juxtaparanodaux les identifiant ainsi comme des cibles thérapeutiques potentielles.¦Les cellules de Schwann enveloppent et isolent les axones périphériques d'une membrane spécialisée, la myéline, composée de deux fois plus de lipides que de protéines. La protéine P2 (Pmp2 "peripheral myelin protein 2" ou FABP8 "fatty acid binding protein") est l'une des protéines les plus abondantes au système nerveux périphérique. P2 appartient à la famille de protéines FABP liant et transportant les acides gras et est une protéine cytosolique de 14,8 kDa exprimée du côté cytoplasmique de la myéline compacte.¦Afin d'étudier le rôle de P2 dans les cellules de Schwann myélinisantes, j'ai généré une souris knockout (P2-/-). Après avoir validé l'absence de transcrit et de protéine P2 dans les nerfs sciatiques P2-/-, des mesures électrophysiologiques ont montré une réduction modérée mais significative de la vitesse de conduction du nerf moteur périphérique. Il est important de noter que ces changements fonctionnels n'ont pas pu être associés à quelconque changement dans la structure de la myéline. Cependant, j'ai observé dans les nerfs périphériques P2-/-, une altération significative du niveau d'expression d'ARNm d'autres FABPs et en particulier FABP9. Ce dernier résultat démontre l'importance du rôle de la protéine P2 dans le métabolisme lipidique de la myéline.