Effect of substrate temperature on ac conduction properties of amorphous and polycrystalline GaSe thin films

X-ray diffraction analysis of GaSe thin films used in the present investigation showed that the as-deposited and the one deposited at higher substrate temperature are in amorphous and polycrystalline state, respectively. The alternating current (ac) conduction properties of thermally evaporated films of GaSe were studied ex situ employing symmetric aluminium ohmic electrodes in the frequency range of 120-10⁵ Hz at various temperature regimes. For the film deposited at elevated substrate temperature (573 K) the ac conductivity was found to increase with improvement of its crystalline structure. The ac conductivity (σ_ac) is found to be proportional to (ω^s) where s < 1. The temperature dependence of ac conductivity and the parameter, s, is reasonably well interpreted by the correlated barrier-hopping (CBH) model. The maximum barrier heights W_m calculated from ac conductivity measurements are compared with optical studies of our previous reported work for a-GaSe and poly-GaSe thin films. The distance between the localized centres (R), activation energy (ΔE_σ) and the number of sites per unit energy per unit volume N(E_F) at the Fermi level were evaluated for both a-GaSe and poly-GaSe thin films. Goswami and Goswami model has been invoked to explain the dependence of capacitance on frequency and temperature.     

Chlorination of ozonated soil fulvic acid: mutagenicity studies in Salmonella

Samples of soil fulvic acid (SFA) were ozonated and subsequently chlorinated under acidic or slightly basic conditions. The residues were tested for His+ reversion in a fluctuation assay, using Salmonella typhimurium TA100 as the tester strain. The ozonated/chlorinated samples were mutagenic, but activity was dependent on the amount of ozone utilized and the pH of the reaction medium. Although increases in cell concentrations were also induced by some mutagenic samples, this alone did not account for the mutagenicity observed. Unchlorinated samples displayed insignificant activity.     

Development and Study of Solid Polymer Electrolyte Based on Polyvinyl Alcohol: Mg(ClO4)2

Magnesium ion-conducting solid polymer electrolytes consisting of polyvinyl alcohol with magnesium perchlorate (Mg(ClO₄)₂) as electrolytic salt have been developed and their experimental investigations are reported. The solid polymer electrolytes have been prepared by well-known solution casting method using double-distilled water as a solvent. The highest room temperature conductivity of the order of 10^?4 S cm^?1 was obtained for the solid polymer electrolyte with the composition 80?mol% polyvinyl alcohol:20?mol% Mg(ClO₄)₂. The pattern of the temperature-dependent conductivity shows Arrhenius behavior. The Fourier transform infrared spectroscopy analysis confirms the complex formation of the polymer with the salt. The X-ray diffraction results reveal that the crystalline phase of polymer host has completely changed on the addition of dopant. Differential scanning calorimetry studies show a decrease in melting temperature of the polyvinyl alcohol with the increasing dopant concentration. The real part of dielectric permittivity shows a strong dispersion at lower frequencies, which implies the space charge effects arising from the electrodes. The loss tangent spectrum reveals that the jumping probability per unit time decreases with the increasing salt concentration. The total ionic transference number measured has been found to be in the range of 0.92–0.94 for all the polymer electrolyte systems. The result reveals that the conducting species are predominantly ions. The solid polymer electrolyte with highest conductivity showed an electrochemical stability of 2?V. The results obtained by cyclic voltammetry on stainless steel/solid polymer electrolyte/stainless steel, Mg/solid polymer electrolyte/Mg symmetrical cells show evidence for reversibility.     

Impact of Ozone on Morphological,Physiological, and Biochemical Changes in Cow Pea (Vigna unguiculata [L.] Walp.)

Morphological and biochemical responses to Acute Ozone Exposure (AOE) by Vigna unguiculata (L.) Walp. cultivar variety CO6 was studied. Plants were grown in controlled conditions and exposed to ozone at 40, 50, 60, 70, and 80 ppbv (T₁-T₅) for 15 min twice a day. Variation among shoot and root length, shoot-root ratio, fresh (FW), dry (DW) weight, leaf area (LA), leaf area ratio (LAR), number of guard cells (G), epidermal cells (E) (abaxial and adaxial), stomatal index (SI), chlorophyll a and b, total chlorophyll (TC), chlorophyll a/b ratio, chlorophyll protein ratio (CPR), ascorbic acid (AA), total phenol (TP), Proline (Pro), nitrate reductase activity (NRA) and Urease activity (UA) were measured in control and ozone-treated plants. The ozone treatment resulted in increase in dry weight, shoot length, leaf area, and number of epidermal cells, stomata and total chlorophyll on exposure up to 60 ppbv. Nitrate Reductase (EC: 1.6.6.3) and Urease (EC: 3.5.15) activities were inhibited by ozone.     

Novel approaches for tri-crystalline silicon surface texturing

Tri-crystalline silicon (Tri-Si) is a promising candidate to reduce the cost of solar cells fabrication because it can be made by a low-cost, fast process with a better mechanical strength, and needs a thinner wafer. One of the key parameters in improving the efficiency of the Tri-Si solar cells is the reflectance, which can be lowered by etching methods. However, Tri-Si is a crystal compound consisting of three mutually tilted monocrystalline silicon grains. In all grains boundaries the surface is (1 1 0)-oriented. A standard surface texture of etched random pyramids using an anisotropic etchant, such as NaOH, is not achievable here. In this paper, for the first time, a novel texturing method has been attempted, which consisted of two steps—HF:HNO₃:DI (2.5:2.5:5) etching was followed by exposure to the vapors to generate fine holes and an etching depth of 2.5 μm had been reached. A best result of 12.3% has been achieved for surface reflectance, which is about 10% lower than that using normal acidic texturing. Nanoporous structures were formed and the size of the porous structure varied from 5 to 10 nm. An antireflection coating of SiN_x SLAR was used to optimize the reflectance. A fill factor of 0.78 has been reached with an efficiency of 16.2% in 12.5 cm×12.5 cm. This high efficiency is mainly due to an increased short-circuit current density of 34 mA/cm².     

Smad2/3 Activation Regulates Smad1/5/8 Signaling via a Negative Feedback Loop to Inhibit 3T3-L1 Adipogenesis

Adipose tissues (AT) expand in response to energy surplus through adipocyte hypertrophy and hyperplasia. The latter, also known as adipogenesis, is a process by which multipotent precursors differentiate to form mature adipocytes. This process is directed by developmental cues that include members of the TGF-β family. Our goal here was to elucidate, using the 3T3-L1 adipogenesis model, how TGF-β family growth factors and inhibitors regulate adipocyte development. We show that ligands of the Activin and TGF-β families, several ligand traps, and the SMAD1/5/8 signaling inhibitor LDN-193189 profoundly suppressed 3T3-L1 adipogenesis. Strikingly, anti-adipogenic traps and ligands engaged the same mechanism of action involving the simultaneous activation of SMAD2/3 and inhibition of SMAD1/5/8 signaling. This effect was rescued by the SMAD2/3 signaling inhibitor SB-431542. By contrast, although LDN-193189 also suppressed SMAD1/5/8 signaling and adipogenesis, its effect could not be rescued by SB-431542. Collectively, these findings reveal the fundamental role of SMAD1/5/8 for 3T3-L1 adipogenesis, and potentially identify a negative feedback loop that links SMAD2/3 activation with SMAD1/5/8 inhibition in adipogenic precursors.     

Space charge limited current, variable range hopping and mobility gap in thermally evaporated amorphous InSe thin films

We have analyzed the properties of as-deposited InSe thin films, deposited onto well cleaned glass substrates under a vacuum of 10^–5 Torr, using X-ray diffraction, Rutherford back scattering, energy dispersive analysis of X-rays, optical transmittance and current–voltage (120–390 K) measurements. Allowed and indirect transition was identified and the mobility gap was determined as 1.44 eV. Under low field (<1×10⁵ V cm^–1) and in the temperature range of 130–200 K, the conductivity in the films was behaving like that of Mott's variable-range hopping (VRH) type. Mott's parameters such as characteristics temperature (T ₀), hopping range (R _hop), hopping energy (W _hop), values of localized states density N (E _F), and activation energy (E _a) were estimated. In the temperature range 210–290 K, thermionic conduction mechanism plays a dominant role and its activation energy was calculated. At high field (>2×10⁵ V cm^–1) and in the temperature range of 300–390 K, space charge limited conduction currents (SCLC) mechanism was observed and the related parameters, such as electron density (n ₀), trap density (n _t), the ratio between free electron density to the total electron density (), mobility () and the effective mobility (_eff) of the InSe film of typical thickness 265 nm were calculated and the results are discussed.