Metallic monoclinic phase in VO2_2 induced by electrochemical gating: in-situ Raman study

We report in-situ Raman scattering studies of electrochemically top gated VO$_2$ thin film to address metal-insulator transition (MIT) under gating. The room temperature monoclinic insulating phase goes to metallic state at a gate voltage of 2.6 V. However, the number of Raman modes do not change with electrolyte gating showing that the metallic phase is still monoclinic. The high frequency Raman mode A$_g$(7) near 616 cm$^{-1}$ ascribed to V-O vibration of bond length 2.06 \AA~ in VO$_6$ octahedra hardens with increasing gate voltage and the B$_g$(3) mode near 654 cm$^{-1}$ softens. This shows that the distortion of the VO$_6$ octahedra in the monoclinic phase decreases with gating. The time dependent Raman data at fixed gate voltages of 1 V (for 50 minute, showing enhancement of conductivity by a factor of 50) and 2 V (for 130 minute, showing further increase in conductivity by a factor of 5) show similar changes in high frequency Raman modes A$_g$(7) and B$_g$(3) as observed in gating. This slow change in conductance together with Raman frequency changes show that the governing mechanism for metalization is more likely to the diffusion controlled oxygen vacancy formation due to the applied electric field.Comment: 5 pages, 6 figure

Pull-in analysis of non-uniform microcantilever beams under large deflection

Cantilever beams under the influence of electrostatic force form an important subclass of microelectromechanical system(MEMS) and nanoelectromechanical system. Most of the studies concerning these micro-nano resonators are centered around uniform cantilever beams. In this paper, we have investigated another class of micro-resonators consisting of non-uniform cantilever beams. The study is focused around investigating pull-in voltage and resonance frequency of non-uniform cantilever beams when they operate in the linear regime about different static equilibriums. In this paper, we term this frequency as “linear frequency.” Calculation of the linear frequency is done at different static equilibriums corresponding to different DC voltages. We have studied two classes of beams, one with increasing cross sectional area from the clamped edge (diverging beam) and other with decreasing cross sectional area from the clamped edge (converging beam). Within each class, we have investigated beams with linear as well as quartic variation in width. We start by obtaining Euler beam equation for non-uniform cantilever beams considering large deflection and their corresponding exact mode shapes from the linear equation. Subsequently, using the Galerkin method based on single mode approximation, we obtain static and dynamic modal equations for finding pull-in voltage and resonance frequency as a function of DC voltage, respectively. We found that the linear frequency of converging beams increases with increase in non-uniform parameter (α) while those of diverging beams decreases with α. A similar trend is observed for pull-in voltage. Within the converging class, beams with quartic variation in width show significant increase in both frequency and pull-in voltage as compared to corresponding linearly tapered beams. In quantitative terms, converging beams with quartic variation in width and α=−0.6 showed an increase in linear frequency by a factor of 2.5 times and pull-in voltage by 2 times as compared to commonly used uniform beams. Our investigation can prove to be a step forward in designing highly sensitive MEMS sensors and actuators

New insights on structure and tectonics over the Laxmi Ridge using EIGEN6C4 modelled gravity data

1999-2005A comparative analysis has been attempted for the study of structural and tectonic trends over and around (140–190 N latitudes and 640–700 E longitudes) the Laxmi ridge. Initially, three different edge enhancement techniques comprising total horizontal derivative (THD), analytical signal (AS) and Theta map have been tested over synthetic prismatic models with varying depths. It is observed that Theta map technique is relatively suitable for delineation of the edges for the sources at different depths. The free-air gravity (FAG) of the Laxmi ridge and surroundings have been generated using EIGEN6C4 high resolution combined earth gravity modelled data. Upward continued gravity anomaly at 20 Km, 40 km, 60 km, 90 km and 150 km heights have been estimated and these are further enhanced using Theta map technique. The enhanced upward continued maps at different height reveal that the sources of the Laxmi ridge low anomaly is constituted by crust, low density upper mantle materials and recent sediments. Present study reveals that the EIGEN6C4 modelled data could be used effectively to identify various structural features of different wavelength. The study reveals that the major lineaments trends are found along N-S, NE-SW and NW-SE directions followed by E-W, ENE-WSW and NNW-SSE directions including different regional and shallow lineaments trends. The delineated lineaments and their orientations are the results of multiple phases of rifting and breakup of India, Madagascar and Seychelles, since its initial stage

Study of Eutectic Etching Process for Defects Analysis in n type 4H SiC

Silicon Carbide (SiC) is a wide bandgap material with unique properties attractive for high power, high temperature applications. The presence of defects in the crystal is a major issue prior device fabrication. These defects affect the performance of the device. To delineate and identify the defects an easy and quick method is desirable. In this study defects delineation in n-type 4H-SiC has been carried out by KOH, KOH+NaOH and KOH+Na2O2 melts. Variation in etch pits size was found at various concentrations of the NaOH in KOH and for different total etching times in the KOH+Na2O2 melt. The eutectic solution etching technique is found to be more efficient to delineate defects and provides control on etching and surface roughness. The etching rates have been estimated under different experimental conditions. Detailed morphological investigations have been performed by wide field high resolution optical microscopy and scanning electron microscopy

A semi-analytical approach to perturbations in mutated hilltop inflation

We study cosmological perturbations and observational aspects for mutated hilltop model of inflation. Employing mostly analytical treatment, we evaluate observable parameters during inflation as well as post-inflationary perturbations. This further leads to exploring observational aspects related to Cosmic Microwave Background (CMB) radiation. This semi-analytical treatment reduces complications related to numerical computation to some extent for studying the different phenomena related to CMB angular power spectrum for mutated hilltop inflation.Comment: 7 pages, 2 figures. Improved version to appear in IJMP

Maximizing Sustainability: Leveraging Indigenous Fungal Cellulases for Sugarcane Bagasse Bioethanol Production and Agricultural Waste Management in Kano

This study aimed to investigate the potential of locally isolated cellulolytic fungi in the production of bioethanol from sugarcane bagasse. The research encompassed the identification of effective fungal isolates, the stimulation of cellulase production, the characterization and purification of these cellulases, and the assessment of their efficiency in the hydrolysis of pre-treated sugarcane bagasse to facilitate ethanol production via the Simultaneous Saccharification and Fermentation (SSF) process. In the pursuit of the most effective isolate, cellulolytic fungi were isolated from soil samples and subjected to a rigorous screening process. Subsequently, the chosen fungus was cultivated in an environment rich in cellulose to promote cellulase production.The purified cellulases exhibited a noteworthy enzymatic activity, measuring 0.108 FPU/ml. These meticulously purified cellulases were subsequently harnessed for the enzymatic depolymerization of pre-treated sugarcane bagasse. This process culminated in the generation of a hydrolysate instrumental in ethanol production via SSF, in conjunction with Saccharomyces cerevisiae.This study underscores the feasibility of utilizing locally isolated fungal cellulases to transform pre-treated sugarcane bagasse into a viable bioethanol feedstock. This study highlights the conversion of abundant agricultural waste, specifically sugarcane bagasse, into valuable bioethanol by leveraging cellulases from locally isolated fungi. This eco-friendly approach not only addresses waste management challenges but also provides a renewable and sustainable energy source. Particularly beneficial in regions with substantial sugarcane bagasse disposal, this research promotes cost-effective waste utilization and sustainable energy productio