Department of Physics

Vellore Institute of Technology (VIT) is a private university located in&nbsp;Tamil Nadu, India. Founded in 1984, as Vellore Engineering College, the institution offers 20 undergraduate, 34 postgraduate, four integrated and four research programs. It has campuses in Vellore, Amravati, Bhopal and Chennai.

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VIT University

Physics

Nanoindentation studies are carried out on epitaxial ZnO and GaN thin films on (0 0 0 1) sapphire and silicon substrates, respectively. A single discontinuity ('pop-in') in the load-indentation depth curve is observed for ZnO and GaN films at a specific depths of 13-16 and 23-26 nm, respectively. The physical mechanism responsible for the 'pop-in' event in these epitaxial films may be due to the interaction behavior of the indenter tip with the pre-existing threading dislocations present in the films during mechanical deformation. It is observed that the 'pop-in' depth is dependent on lattice mismatch of the epitaxial thin film with the substrate, the higher the lattice mismatch the shallower the critical 'pop-in' depth. © 2007 Elsevier B.V. All rights reserved.

School of Advanced Sciences

Chennai Campus

World University root node

Physica B: Condensed Matter

A nanoindentation analysis of the influence of lattice mismatch on some wide band gap semiconductor films

Low-dielectric-constant SiOC(-H) films were deposited on p-type Si (100) substrates by using plasma-enhanced chemical-vapor deposition (PECVD) from triethoxysilane (TES; C6H16O3Si) and oxygen gas as precursors. Factors affecting the carbon and hydrogen incorporation into the SiO2 films during plasma-enhanced chemical vapor deposition were studied for different experimental parameters by using an in-situ residual gas analyzer (RGA), optical emission spectroscopy (OES) and Langmuir probe measurements. Detailed information of the relative radical densities, the electron density (Ne) and the electron temperature (Te) of the bulk plasma was obtained in order to better understand the deposition process of the low-k SiOC(-H) thin films. The silane-to-oxygen (precursor flow rate) ratio in the process gas mixture and the radio-frequency (rf) power determine the chemical nature of the substrate surface and the incorporation rates of Si-O-C and Si-O-Si into the film. We interpret in detail the evolutions of plasma discharge parameters in terms of the variations in the composition of the plasma.

Journal of the Korean Physical Society

Plasma diagnostics during plasma-enhanced chemical-vapor deposition of low-dielectric-constant SiOC(-H) films from TES/O2 precursors

Domestic wastewater contains a considerable amount of pathogenic organisms besides non-biodegradable organics. The conventional technologies followed for the treatment of domestic wastewater are less efficient in removing pathogenic organisms despite substantial removal of dissolved organics. The focal theme of the present investigation was to use a chemo-autotrophic activated carbon oxidation (CAACO) system, an immobilized cell reactor using chemoautotrophs (Bacillus sp.) for the treatment of domestic wastewater. The oxidation of organics and Escherichia coli in wastewater is controlled by the parameters space time, O2/COD, bed height and cod loading. The scheme comprised of anaerobic treatment, sand filtration and CAACO treatment removed BOD. COD, Total organic carbon (TOC), dissolved protein, total Kjeldhal nitrogen (TKN) and bacterial count (most probable number (MPN)) by 81%, 92%, 84%, 94%, 93% and 99.9997%, respectively. The low concentration of E. coli in the CAACO-treated wastewater was completely eliminated through UV irradiation in 3 min at 254 nm. © 2006 Elsevier Ltd. All rights reserved.

Journal of Environmental Management

Oxidative destabilization of dissolved organics and E. coli in domestic wastewater through immobilized cell reactor system

The effect of Sr addition on the CoAl2O4 composites prepared by sol-gel technique was investigated for humidity sensing properties. X-ray diffraction, scanning electron microscopy (SEM), FT-IR spectroscopy and nitrogen adsorption-desorption isotherm at 77 K was employed respectively to identify the structural phases, surface morphology, vibrational stretching frequencies and BET surface area of the composites. The composites were prepared with the addition of strontium of different molar ratios (0, 0.2, 0.4, 0.6, 0.8 and 1.0) to CoAl2O4 and were labeled as CoSA1, CoSA2, CoSA3, CoSA4, CoSA5 and CoSA6, respectively. The samples sintered at 900 °C for 5 h, were subjected to dc resistance measurements as a function of relative humidity (RH) in the range 5-98% and the results revealed that the sensitivity factor increased with an increase in strontium molar ratio. Among the different strontium-added composites, CoSA5 possessed the highest humidity sensitivity of 56,000 while the pure composite CoSA1 possessed a low sensitivity of 14,000. The response and recovery characteristics of the maximum sensitivity sample CoSA5 were 120 and 70 s. © 2006 Elsevier B.V. All rights reserved.

Sensors and Actuators, B: Chemical

Effect of Sr addition on the humidity sensing properties of CoAl2O4 composites

Low dielectric constant SiOC(-H) thin films were deposited by plasma enhanced chemical vapor deposition (PECVD) using methyltriethoxysilane (MTES) and oxygen as precursors. The SiOC(-H) films were prepared with MTES/O2 flow rate ratio of 80%, rf power of 700 W and the working pressure was varied from 110 to 150 mTorr. Then the films were annealed at different temperatures in an Ar ambient for 30 min in order to study their thermal stability. Film thickness and refractive index were measured by SEM and ellipsometry, respectively. Bonding characteristics of the films were investigated by Fourier transform infrared (FTIR) spectroscopy. The dielectric constant of SiOC(-H) film was evaluated by C-V measurements using Al/SiOC(-H)/p-Si structure. The dielectric constants as low as 2.4 have been obtained for the film annealed at 500 °C with the working pressure of 150 mTorr. The annealing treatment was found to reduce dielectric constant significantly due to abundant incorporation of methyl group into the Si-O network. These results demonstrated the promising characteristics of SiOC(-H) thin films deposited by using oxygen and MTES precursor. © 2006 Elsevier B.V. All rights reserved.

Thin Solid Films

Plasma enhanced chemical vapor deposition of low dielectric constant SiOC(-H) films using MTES/O2 precursor

SiOC(-H) films were deposited on p-Si (100) substrates by using plasma enhanced chemical vapor deposition with methyltrimethoxysilane (MTMS; C 4H12O3Si) and oxygen gas as precursors at different rf powers. In the SiOC(-H) film, the CH3 group as an end group was introduced into the -O-Si-O- network, thereby reducing the density to decrease the dielectric constant. The flat-band voltage at the Al/SiOC(-H)/p-Si(100) structure observed in the negative side is attributed to excess positive charge carriers in the form of -CH3/Si-CH3 and Si-H radicals in the film. The SiOC(-H) films deposited at different rf powers revealed the dominant mechanisms of space-charge-limited current followed by Poole-Frenkel emission. These results suggest that the electrical properties of the SiOC(-H) strongly depend on the excessive (Si-CH3) + and (Si-O)- bonds present in the film.

Comparative study on the structural and electrical properties of low-k SiOC(-H) films deposited by using plasma enhanced chemical vapor deposition

SiOC(-H) films were deposited on p-type Si(100) substrates from dimethyldimethoxysilane (DMDMS; C4H12O2Si) and oxygen precursors with different flow rate ratios by using plasma enhanced chemical vapor deposition. The refractive index and the dielectric constant of the SiOC(-H) film decreased with increasing flow rate ratio. The concentration of the carbon content increased from 5 to 11 % when the precursor flow rate ratio was increased from 50 to 90 %. However, a slight decrease in the carbon concentration was observed when the films were annealed at temperatures up to 400°C The SiOC (-H) film prepared with a lower flow rate ratio showed a higher dielectric constant. However, the annealed films shows lower dielectric constant than the as-deposited SiOC(H) films. The lowest dielectric constant of about 2.15 was obtained for the SiOC(-H) film annealed at 400°C at a DMDMS/O2 flow rate ratio of 70 %.

Low-dielectric-constant SiOC(-H) films prepared from DMDMS and O 2 precursors by using plasma enhanced chemical vapor deposition

Investigations were carried out in batch modes for studying the immobilization behavior of polyphenol oxidase (PPO) on two different mesoporous activated carbon matrices, MAC400 and MAC200. The PPO was immobilized onto MAC400 and MAC200 at various enzyme activities 5 × 104, 10 × 104, 20 × 104, 30 × 104 U l-1, at pH 5-8, and at temperature ranging from 10 to 40 °C. The intensity of immobilization of PPO increased with increase in temperature and initial activities, while it decreased with increase in pH. Immobilization onto MAC400 followed the Langmuir model while Langmuir and Freundlich models could fit MAC200 data. Non-linear pseudo first order, pseudo second order and intraparticle diffusion models were evaluated to understand the mechanism of immobilization. The free and immobilized enzyme kinetic parameters (Km and Vmax) were determined by Michaelis-Menten enzyme kinetics. The Km values for free enzyme, PPO immobilized in MAC400 and in MAC200 were 0.49, 0.41 and 0.65 mM, respectively. The immobilization of PPO in carbon matrices was confirmed using FT-IR spectroscopy and scanning electron microscopy. © 2007 Elsevier Ltd. All rights reserved.

Chemosphere

Immobilization of polyphenol oxidase onto mesoporous activated carbons - isotherm and kinetic studies

Solid-state dye-doped polymers are attractive alternative to the conventional liquid dye solutions. In this paper, nonlinear properties of the dye Pararosanilin has been studied. The third-order nonlinear optical properties of Pararosanilin dye in 1-butanol and dye-doped polymer film were measured by the Z-scan technique using 532 nm diode pumped Nd:Yag laser. This material exhibits negative optical nonlinearity. The dye at 0.4 mM concentration exhibited nonlinear refractive coefficient (n2 = -6.8 × 10-8 and -7.11 × 10-8 (cm2/W) in liquid and solid media, respectively), nonlinear absorption coefficient (β = -7.7 × 10-4 and -7.93 × 10-4 cm/W in liquid and solid media, respectively) and susceptibility (χ(3) = 3.38 × 10-6 and 3.53 × 10-5 esu in liquid and solid media, respectively). These results show that Pararosanilin dye has potential applications in nonlinear optics. © 2006 Elsevier B.V. All rights reserved.

Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy

Nonlinear studies of Pararosanilin dye in liquid and solid media

Nanocrystalline SOFC cathode materials of perovskite family, Lai. xSrxM1-yCoyO3, where 0&lt;x≤0.5, 0&lt;y≤0.8 (M is transitional metal= Mn or Fe) have been synthesized at a relatively low temperature by combustion technique using alanine as novel fuel. The thermal analyses of the precursor gels show sharp single step combustion with low decomposition temperature (170-200°C). Detailed X-ray powder diffraction analyses show 47-96% phase purity in the assynthesized powder and upon calcination at temperature ∼ 825°C, single phase material is obtained wherein the nanocrystallinity (crystallite size -19-24 nm) is retained. Densification studies of the materials are carried out within 900-1100°C The coefficient of thermal expansion (CTE) of the sintered cathodes is also measured. Detailed electrical characterizations of the sintered cathodes are evaluated and correlated with the microstrucmres. The electrochemical performances of SOFC single cells (Ni-YSZ anode-support /YSZ - 20 μm/LaFeO3-based cathodes) with ceria interlayer show high current density of ∼1.2 A/cm2 at 0.7 V at 800°C. © The Electrochemical Society.