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.

VIT is one of the top ranked private universities in India according to NIRF, THE and QS Rankings.&nbsp;Govt. of India has recognized&nbsp;VIT, Vellore as an&nbsp;Institution of Eminence. This has allowed VIT to take independent quality initiatives and move up in world ranking.

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VIT University

Physics

Strontium(II)-added ZnAl 2O 4 nanomaterials with spinel structure were prepared by modified sol-gel method using ethylenediamine followed by sintering at 900°C. The samples were labeled as ZnSA1-900, ZnSA2-900, ZnSA3-900, ZnSA4-900, ZnSA5-900, ZnSA6-900, respectively, where the molar ratios of Zn:Sr was 1.0:0.0, 0.9:0.1, 0.8:0.2, 0.7:0.3, 0.6:0.4 and 0.5:0.5 and aluminum molar ratio was kept constant, 900 refers to the sintering temperature. The effect of Sr addition on the structural, morphological and optical properties of zinc aluminate nanomaterials were investigated by X-ray diffraction (XRD), Fourier transform infrared spectra (FT-IR), high resolution scanning electron microscopy (HR-SEM), nitrogen adsorption/desorption isotherms, diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) spectroscopy. The addition of Sr improves the performance of the zinc aluminate towards the selective oxidation of alcohols and decreases the grain size. The effect of solvent, oxidant and reaction time on the Sr(II)-added zinc aluminate nanomaterials for the oxidation of benzyl alcohol was studied. Higher activity was obtained for the conversion of benzyl alcohol to benzaldehyde for 0.3 molar percentage Sr(II)-added zinc aluminate (ZnSA4-900) which was used for the selective oxidation of other alcohols. Stability and reusability of the nanomaterials was also investigated. © 2012 Elsevier B.V.

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School of Advanced Sciences

Chennai Campus

Powder Technology

Synthesis, characterization and performance of porous Sr(II)-added ZnAl2O4 nanomaterials for optical and catalytic applications

The effect of ethylenediamine addition in the sol-gel method for the preparation of nano CuAl 2O 4 spinel for the enhancement in their structural, electrical, optical and catalytic properties was investigated. The samples were prepared by two different methods: sol-gel and modified sol-gel technique using ethylenediamine. X-ray diffraction (XRD), Fourier transform infrared spectra (FT-IR), scanning electron microscopy (SEM), high resolution-transmission electron microscopy (HR-TEM), energy dispersive X-ray analysis (EDX), nitrogen adsorption/desorption isotherms, temperature dependent conductance measurements, thermoelectric power (TEP) measurements and UV-visible diffuse reflectance (UV-vis-DRS) spectra were used to characterize the samples prepared. CuAl 2O 4 prepared by modified sol-gel technique was found to possess a higher surface area, lower crystallite size, lower activation energy and high porosity than the one prepared by sol-gel method which in turn lead to the improved performance of it towards the selective oxidation of benzyl alcohol to benzaldehyde. Effect of solvent on the catalytic oxidation of benzyl alcohol by the nano CuAl 2O 4 prepared by modified sol-gel technique was also investigated. © 2012 Elsevier B.V. All rights reserved.

Journal of Alloys and Compounds

Comparative study of nano copper aluminate spinel prepared by sol–gel and modified sol–gel techniques: Structural, electrical, optical and catalytic studies

This study deals with the surface functionalization of mesoporous activated carbon, using ethylenediamine and glutaraldehyde to facilitate the strong immobilization of acidic lipase (AL) onto MAC. The AL was produced from Pseudomonas gessardii by using slaughterhouse lipid waste as the substrate. The AL immobilized on functionalized mesoporous activated carbon (ALFMAC) was applied for the hydrolysis of waste cooked oil (WCO). The optimum conditions for the immobilization of AL onto functionalized mesoporous activated carbon (FMAC) were 90 min; pH 3.5; and 35 °C; which resulted at the maximum immobilization of 5440 U/g of FMAC (3.693 mg of AL/g of FMAC or the yield 2.7% or the expressed activity 103.7% or the activity per unit area of FMAC 1.08 mg of AL/m 2). The ALFMAC showed better thermal and storage stabilities than the free AL. The ALFMAC retained a 98% and a 92% initial activity at 40 °C and 50 °C, respectively, while the AL showed the thermal stability (residual activities) 65% and 38%, respectively. The storage stability of ALFMAC at 4 °C showed 100% initial activity up to 15 days from the initial day of the storage, whereas AL showed only 88% initial activity up to 15 days. The FMAC and ALFMAC were characterized by using scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, and X-ray diffraction (XRD) analysis. The K m values of the ALFMAC and AL were 0.112 mM and 0.411 mM, respectively. The v max values of the ALFMAC and AL were 1.26 mM/min and 0.53 mM/min, respectively. Immobilization of AL onto FMAC obeyed the Freundlich and Redlich-Peterson isotherm models. The non-linear models of pseudo first, and second order, intra-particle diffusion, Bangham, and Boyd plot were also performed to understand the dynamic mechanism of immobilization. ALFMAC showed a 100% hydrolysis of WCO up to 21 cycles of reuse, and 60% up to 45 cycles. The hydrolysis of WCO was confirmed by using FT-IR spectra. © 2011 Elsevier Ltd. All rights reserved.

Process Biochemistry

Surface functionalized mesoporous activated carbon for the immobilization of acidic lipase and their application to hydrolysis of waste cooked oil: Isotherm and kinetic studies

Nano copper aluminate spinel catalyst prepared by sol-gel technique using citric acid as gelling agent and sintered at 900 °C was characterized by XRD, FT-IR, SEM to identify the structural phases, stretching frequencies, surface morphology and particle size, respectively. The prepared catalyst was used for the selective oxidation of benzyl alcohol to benzaldehyde in presence of hydrogen peroxide as the oxidant. The effect of solvent, reaction time and amount of catalyst on the catalytic oxidation of benzyl alcohol was studied. Formation, percentage yield and turnover number of benzaldehyde were confirmed by gas chromatography and ammonia chemisorption data. Without using the catalyst or the solvent, very low yield of benzaldehyde was observed. Highest conversion and turnover number of benzaldehyde was observed using acetonitrile as the solvent.

Asian Journal of Chemistry

Selective catalytic oxidation of benzyl alcohol by sol-gel synthesized nano copper aluminate

We have investigated the effect of post growth rapid thermal annealing on self-assembled InAs/GaAs multilayer QDs (MQD) overgrown with a combination barrier of InAlGaAs and GaAs for their possible use in photovoltaic device application. The samples were characterized by transmission electron microscopy and photoluminescence measurements. We noticed a thermally induced material interdiffusion between the QDs and the wetting layer in the MQD sample up to a certain annealing temperature. The QD heterostructure exhibited a thermal stability in the emission peak wavelength on annealing up to 700 .C temperature. A phenomenological model has been proposed for this stability of the emission peak. The model considers the effect of the strain field, propagating from the underlying QD layer to the upper layers of the multilayer QD and the effect of indium atom gradient in the combination barrier layer due to the presence of a quaternary InAlGaAs layer. © 2012 Springer-Verlag.

Applied Physics A: Materials Science and Processing

Inhibition of emission wavelength blueshift in annealed InAs/GaAs quantum dot stacks: An important observation for their potential application in photovoltaic devices

The effect of post-growth rapid thermal annealing on 35-layer In 0.50Ga 0.50As/GaAs quantum dot infrared photodetector (QDIP) with quaternary In 0.21Al 0.21Ga 0.58As capping has been investigated. Transmission electron microscopy showed some as-grown defects were removed by post growth annealing treatment. An increase in the compressive strain in the heterostructure due to annealing was identified from X-ray diffraction curve. A two-color photoresponse in the long-wave region (8.5 and 10.2 μm) was observed in both as-grown device and those annealed at 650 °C temperature. A three-fold enhancement in peak responsivity was observed in the QDIPs annealed at 650 °C (1.19 A/W) compared to that in the as-grown (0.34 A/W). Detectivity also increased by two fold from as-grown to 650 °C annealed device. The changes are attributed to the removal of as-grown defects and dislocations during epitaxial growth. These removals changed the confinement potential profile, which resulted in an improvement in the detectivity and responsivity of the annealed sample. © 2012 Elsevier Ltd. All rights reserved.

Materials Research Bulletin

A detailed investigation on the impact of post-growth annealing on the materials and device characteristics of 35-layer In 0.50Ga 0.50As/GaAs quantum dot infrared photodetector with quaternary In 0.21Al 0.21Ga 0.58As capping

An InAs/GaAs quantum dot infrared photodetector with strong, multicolor, broadband (5-20 μm) photoresponse is reported. Using a combined quaternary In0.21Al0.21Ga0.58As and GaAs capping that relieves strain and maintains strong carrier confinement, we demonstrate a four color infrared response with peaks in the midwave- (5.7 μm), longwave- (9.0 and 14.5 μm), and far- (17 μm) infrared regions. Narrow spectral widths (7% to 9%) are noted at each of these wavelengths including responsivity value ∼95.3 mA/W at 14.5 μm. Using strain field and multi-band k ṡ p theory, we map specific bound-to-bound and bound-to-quasibound transitions to the longwave and midwave responses, respectively. © 2012 American Institute of Physics.

Fulltext

Applied Physics Letters

A multicolor, broadband (5-20 μm), quaternary-capped InAs/GaAs quantum dot infrared photodetector

We report on the preparation and the characterization of TiO 2 nanoparticles incorporated with nylon-6 composite nanofibers by using electrospinning technique. Two different composite nanofiber mats with TiO 2 nanoparticles sizes of 20 and 300 nm were prepared. The resultant nanofibers exhibited good incorporation of TiO 2 nanoparticles. The doping of TiO 2 nanoparticles into the nylon-6 nanofibers was confirmed by using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD) and energy dispersive X-ray (EDX) spectroscopy. The measurement of the electrical conductivity of the TiO 2 nanoparticles incorporated with nylon-6 nanofibers were carried out. Current-voltage (I-V) characteristics revealed that the current was enhanced for the sample with 300 nm TiO 2 nanoparticles compared to that with 20-nm TiO 2 nanoparticles. © 2012 The Korean Physical Society.

Journal of the Korean Physical Society

A study on electrospun nylon-6/TiO 2 composite nanofibers

We have investigated optical properties and device performance of sub-monolayer quantum dots infrared photodetector with confinement enhancing (CE) barrier and compared with conventional Stranski-Krastanov quantum dots with a similar design. This quantum dots-in-a-well structure with CE barrier enables higher quantum confinement and increased absorption efficiency due to stronger overlap of wavefunctions between the ground state and the excited state. Normal incidence photoresponse peak is obtained at 7.5 μm with a detectivity of 1.2 × 10 11 cm Hz 1/2 W -1 and responsivity of 0.5 A/W (77 K, 0.4 V, f/2 optics). Using photoluminescence and spectral response measurements, the bandstructure of the samples were deduced semi-empirically. © 2012 American Institute of Physics.

Sub-monolayer quantum dots in confinement enhanced dots-in-a-well heterostructure

We report on a systematic study of the effect of barriers on quantum dots-in-a-well infrared photodetectors. Four devices are fabricated and characterized with varying composition for barriers adjacent to quantum dots and away from quantum dots. Effects of these "proximity" and "remote" barriers are studied by comparing photoluminescence, responsivity, dark current, background-limited operating temperature, activation energy, and detectivity. The growth mechanism for a conformal coverage of quantum dots with proximity barriers is described and supported with reflection high-energy electron diffraction and transmission electron microscopy images. It is shown that proximity barriers and remote barriers influence the characteristics of the detector very differently, with increases in proximity barrier energy leading to higher responsivity and lower dark current, while remote barriers reduce the responsivity and dark currents simultaneously. It is demonstrated that confinement enhancing barriers as proximity barriers optimize the SNR at low bias range, suitable for focal plane array applications. © 2012 IEEE.