Investigation of defect formation and electronic transport in microcrystalline silicon deposited by hot-wire CVD

We have investigated doped and undoped layers of microcrystalline silicon prepared by hot-wire chemical vapour deposition optically, electrically and by means of transmission electron microscopy. Besides needle-like crystals grown perpendicular to the substrate's surface, all of the layers contained a noncrystalline phase with a volume fraction between 4% and 25%. A high oxygen content of several per cent in the porous phase was detected by electron energy loss spectrometry. Deep-level transient spectroscopy of the crystals suggests that the concentration of electrically active defects is less than 1% of the undoped background concentration of typically 10^17 cm -3. Frequency-dependent measurements of the conductance and capacitance perpendicular to the substrate surface showed that a hopping process takes place within the noncrystalline phase parallel to the conduction in the crystals. The parasitic contribution to the electrical circuit arising from the porous phase is believed to be an important loss mechanism in the output of a pin-structured photovoltaic solar cell deposited by hot-wire CVD

Modulation of argon pressure as an option to control transmittance and resistivity of ZnO:Al films deposited by DC magnetron sputtering: on the dark yellow films at 10^-7 Torr base pressures

In a previous paper, we reported that thin films of ZnO:Al [aluminum-zinc oxide (AZO)] deposited after achieving a very low base pressure [from 4.0×10-7 Torr (5.6×10-5 Pa) to 5.7×10-7 Torr (7.6×10-5 Pa)] result dark yellow in color and are resistive. These are undesirable characteristics for the application of AZO thin films as front electrodes in solar cells. However, given the increasingly tendency in the acquisition of equipment that allow us to reach excellent vacuum levels, it is necessary to find the deposition conditions that lead to an improving of transmittance without greatly impacting the electrical properties of materials deposited after achieving these levels of vacuum. In this way, the present work is focused on AZO thin films deposited after achieving a very low base pressure value: 4.2×10-7 Torr (5.6×10-5 Pa). For this, we studied the effect of the variation of the oxygen volume percent in the argon/oxygen mixture (by maintaining the deposition pressure constant) and the effect of deposition pressure with only argon gas on the main properties of AZO thin films. The depositions were done at room temperature on glass substrates by direct-current magnetron sputtering with a power of 120 W (corresponding to a power density of 2.63 W/cm2). As results, we found that the variation of deposition pressure with only argon gas is a good option for the control of optical and electrical properties, since the addition of oxygen, although improves transmittance, greatly impacts on the electrical properties. Furthermore, an interesting correlation was found between the optical and electrical properties and the chemical composition of the AZO films, the latter depending on the argon pressure (for this, a careful X-ray photoelectron spectroscopy analysis was performed). Also, the inverse relationship between crystallinity and deposition rate was confirmed, in which deposition rate inversely depends on argon pressure

Neurodevelopmental effects of undernutrition and placental underperfusion in fetal growth restriction rabbit models

Introduction: Chronic reduction of oxygen and nutrient delivery to the fetus has been related to neurodevelopmental problems. Placental underperfusion induces a significant reduction in oxygen and nutrient delivery, whereas maternal undernutrition causes mainly nutrient deficiency. A comparison of the neurodevelopmental effects of both situations in pregnant rabbits was performed. Materials and Methods: The placental underperfusion model was induced after uteroplacental vessel ligation at 25 days of pregnancy. The undernutrition model was induced after a reduction of 70% of the basal maternal intake at 22 days of pregnancy. Neurobehavioral tests were applied in the derived offspring at the neonatal period and over the long term. Structural brain differences were evaluated by brain networks obtained from diffusion magnetic resonance imaging. Results: Birth weight was significantly lower in both cases. However, stillbirth was only increased in the placental underperfusion model. Cases from both models presented poorer neurobehavioral performance and network infrastructure, being more pro-nounced in the placental underperfusion model. Discussion: Prenatal insults during the last third of gestation resulted in functional and structural disturbances. The degree of neurodevelopmental impairment and its association with structural brain reorganization seemed to be related to the type of the prenatal insult, showing stronger effects in the placental underperfusion model. (C) 2017 S. Karger AG, Base

SiPMs coated with TPB : coating protocol and characterization for NEXT

Silicon photomultipliers (SiPM) are the photon detectors chosen for the tracking readout in NEXT, a neutrinoless {\beta}{\beta} decay experiment which uses a high pressure gaseous xenon time projection chamber (TPC). The reconstruction of event track and topology in this gaseous detector is a key handle for background rejection. Among the commercially available sensors that can be used for tracking, SiPMs offer important advantages, mainly high gain, ruggedness, cost-effectiveness and radio-purity. Their main drawback, however, is their non sensitivity in the emission spectrum of the xenon scintillation (peak at 175 nm). This is overcome by coating these sensors with the organic wavelength shifter tetraphenyl butadienne (TPB). In this paper we describe the protocol developed for coating the SiPMs with TPB and the measurements performed for characterizing the coatings as well as the performance of the coated sensors in the UV-VUV range.Comment: Submitted to the Journal of Instrumentation on december 26th 201

In vitro determination of the antibacterial effect of a quebracho colorado Schinopsis lorentzii extract

Lately, the search for natural growth promoters to replace antibiotics, restricted by internationals regulations, has increased. The in vitro inhibitory activity of a red quebracho extract (Schinopsisi lorentzii) composed of polyphenols over some pathogenic bacteria was determined, comparing it to Bacitracin Methylene Disalicylate at 11 %. Of the fi rst one, doses of 500 ppm up to 0,05 ppm in increasing dilutions were tested. The Bacitracin was used of 330 ppm up to 0,03 ppm. The method of diffusion in agar, modifi ed by Vignolo et al, was applied on Salmonella gallinarum, Escherichi coli, Clostridium perfrigens and Staphylococcus aureus. The extract, as well as the Bacitracin, acted against Gram negative and Gram positive bacteria in various concentrations. These data lead us to suppose that polyphenols may become a tool to substitute antibiotic growth promoters, providing a natural product, safe for human health.Fil: Prosdócimo, F. Universidad Nacional de Luján. Departamentos de Tecnología y de Ciencias Básicas. Buenos Aires, ArgentinaFil: Batallé, M. Universidad Nacional de Luján. Departamentos de Tecnología y de Ciencias Básicas. Buenos Aires, ArgentinaFil: Sosa, N. Universidad Nacional de Luján. Departamentos de Tecnología y de Ciencias Básicas. Buenos Aires, ArgentinaFil: De Franceschi, M. Universidad Nacional de Luján. Departamentos de Tecnología y de Ciencias Básicas. Buenos Aires, ArgentinaFil: Barrios, H. Universidad Nacional de Luján. Departamentos de Tecnología y de Ciencias Básicas. Buenos Aires, ArgentinaÚltimamente se incrementó la búsqueda de promotores de crecimiento naturales en reemplazo de antibióticos, restringidos por normativas internacionales. Se determinó la actividad inhibitoria in vitro de un extracto de quebracho colorado (Schinopsis lorentzii) compuesto por polifenoles con catequinas sobre algunas bacterias patógenas comparándolo con Bacitracina Metileno Disalicilato al 11 %. Del primero se utilizaron dosis de 500 ppm hasta 0,05 ppm en diluciones crecientes. La Bacitracina fue utilizada de 330 ppm hasta 0,03 ppm. Se aplicó el método de difusión en agar modifi cado por Vignolo et al sobre Salmonella Gallinarum biotipo gallinarum, Escherichia coli, Clostridium perfrigens y Staphylococcus aureus. Tanto el Extracto como la Bacitracina actuaron contra bacterias Gram positivas como Gram negativas en diversas concentraciones. Estos datos permiten suponer que los polifenoles con catequinas pueden transformarse en una herramienta para sustituir los antibióticos promotores de crecimiento, proveyendo un producto de origen natural inocuo para la salud humana

Photodiodes based on fullerene semiconductor

Fullerene thin films have been deposited by thermal evaporation on glass substrates at room temperature. A comprehensive optical characterization was performed, including low-level optical absorption measured by photothermal deflection spectroscopy. The optical absorption spectrum reveals a direct bandgap of 2.3 eV and absorption bands at 2.8 and 3.6 eV, which are related to the creation of charge-transfer excitons. Various photodiodes on indium–tin-oxide coated glass substrates were also fabricated, using different metallic contacts in order to compare their respective electrical characteristics. The influence of a poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) buffer layer between the indium–tin-oxide electrode and the fullerene semiconductor is also demonstrated. These results are discussed in terms of the workfunction for each electrode. Finally, the behaviour of the external quantum efficiency is analyzed for the whole wavelength spectrum.Peer ReviewedPostprint (published version

Aluminium induced texturing of glass substrates with improved light management for thin film solar cells

Aluminium induced texturing (AIT) method has been used to texture glass substrates to enhance photon absorption in microcrystalline thin film Si solar cells. In this process, a thin Al film is deposited on a glass substrate and a non-uniform redox reaction between the glass and the Al film occurs when they are annealed at high temperature. After etching the reaction products, the resultant glass surface presents a uniform and rough morphology. In this work, three different textures (­σrms ~85, ~95, ~125 nm) have been achieved by tuning the dc sputtering power and over them and over smooth glass, pin microcrystalline silicon solar cells have been fabricated. The cells deposited over the textured substrates showed an efficiency improvement in comparison to the cells deposited over the smooth glass. The best result was given for the glass texture σrms~125 nm that led to an average efficiency 2.1% higher than that given by the cell deposited on smooth glas

Photodiodes based on fullerene semiconductor

Fullerene thin films have been deposited by thermal evaporation on glass substrates at room temperature. A comprehensive optical characterization was performed, including low-level optical absorption measured by photothermal deflection spectroscopy. The optical absorption spectrum reveals a direct bandgap of 2.3 eV and absorption bands at 2.8 and 3.6 eV, which are related to the creation of charge-transfer excitons. Various photodiodes on indium–tin-oxide coated glass substrates were also fabricated, using different metallic contacts in order to compare their respective electrical characteristics. The influence of a poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) buffer layer between the indium–tin-oxide electrode and the fullerene semiconductor is also demonstrated. These results are discussed in terms of the workfunction for each electrode. Finally, the behaviour of the external quantum efficiency is analyzed for the whole wavelength spectrum.Peer Reviewe

Copper phthalocyanine thin filma transistors with polymeric gate dielectric

Copper phthalocyanine (CuPc) thin-film transistors have been fabricated using polymethyl methacrylate (PMMA) as gate dielectric. A bottom gate, staggered structure was selected to study the device performance. CuPc thin-films were deposited by thermal evaporation in a high vacuum system. The maximum process temperature achieved was 100 °C, corresponding to the baking of the PMMA. The devices showed satisfactory p-type electrical characteristics with field-effect mobility and threshold voltage values around 0.2 × 10-4 cm2 V-1 s-1 and 6 V, respectively. The device electrical characteristics were correlated with the structural and morphological properties of the CuPc thin-films.Peer ReviewedPostprint (published version