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

We report the preparation of anisotropic chitosan nanofibers prepared using an electrospinning technique. The effect of electrospinning on the formation of nanofibers was examined from results of bulk chitosan. The morphological, structural characterizations and thermal properties of the chitosan bulk and electrospun nanofibers were analyzed by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetry (TGA), Fourier transform infrared (FTIR), and Raman spectroscopy. Matrixassisted laser desorption ionization time-of-flight (MALDI-TOF) was performed to accurately characterize the high aspect ratio nanofiber structure by the direct identification of mass resolved chains. FE-SEM showed that the electrospun chitosan nanofibers had diameters ranging from 10 to 1,200 nm with an anisotropic nature. MALDI-TOF revealed the presence of lower mass group protonated amino groups, which was the main constituent for the formation of the ultrafine nanofibers in chitosan. [Figure not available: see fulltext.] © 2011 The Polymer Society of Korea and Springer Netherlands.

World University root node

School of Advanced Sciences

Chennai Campus

Macromolecular Research

Preparation and characterizations of anisotropic chitosan nanofibers via electrospinning

We report on the preparation and characterization of ultrafine polyamide-6 nanofibers by the electrospinning technique. The effect of electrospinning on the formation of ultrafine polyamide-6 nanofiber structure was examined. The morphological and structural characterizations and thermal properties of the ultrafine polyamide-6 nanofibers were investigated in comparison with bulk polyamide-6 pellets. In order to accurately characterize the ultrafine polyamide-6 nanofiber structure by direct identification of mass resolved components, we performed matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry. Field emission scanning electron microscopy images revealed the presence of ultrafine polyamide-6 nanofibers bound between the main fibers. The diameter of the polyamide-6 nanofibers was observed to be in the range 75-110 nm, whereas the ultrafine structures consisted of regularly distributed very fine nanofibers with diameters of about 9-28 nm. The MALDI-TOF spectra showed the presence of protonated and sodiated ions that were assigned to polyamide-6 chains. © 2011 Society of Chemical Industry.

Polymer International

Preparation and characterization of electrospun ultrafine polyamide-6 nanofibers

Gallium nitride (GaN) nanowire (NW) arrays were grown on a gold-coated Si(111) substrate by metalorganic chemical vapor deposition (MOCVD). Here we adopted two different experimental procedures to grow GaN NWs namely, with and without Ga predeposition on Au-coated Si(111) substrate before annealing. Comparative studies based on the morphology and growth behavior of GaN NWs were performed by using Au catalyst and Au + Ga solid solution nano-droplets. The grown GaN NWs were characterized by field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray (EDX) spectroscopy, photoluminescence (PL), cathodoluminescence (CL), high-resolution transmission electron microscopy (HR-TEM) and Raman spectroscopy. The nucleation of GaN NWs was explained in terms of Ga predeposition. As a result, we showed that the advantages of using the Au + Ga solid solution nano-droplets for growing GaN NWs. © 2010 Elsevier B.V. All rights reserved.

Current Applied Physics

Different growth behaviors of GaN nanowires grown with Au catalyst and Au + Ga solid solution nano-droplets on Si(111) substrates by using MOCVD

We report on the selective area growth of GaN nanowires (NWs) on nano-patterned Si(111) substrates by metalorganic chemical vapor deposition. The nano-patterns were fabricated by the oxidation of Si followed by the etching process of Au nano-droplets. The size of formed nano-pattern on Si(111) substrate was corresponding to the size of Au nano-droplet, and the diameter of GaN NWs grown was similar to the diameter of fabricated nano-pattern. The interesting phenomenon of using the nano-patterned Si(111) substrates is the formation of very clear substrate surface even after the growth of GaN NWs. However, in the case of GaN NWs grown using Au nano-droplets, there was several nanoparticles including GaN bulk grains on the Si(111) substrates. The smooth surface morphology of nano-patterned Si(111) substrates was attributed to the presence of SiO2 layer which prevents the formation of unnecessary GaN particles during the GaN NW growth. Therefore, we believe that nano-patterning method of Si(111) which was obtained by the oxidation of Si(111) substrate and subsequent Au etching process can be utilized to grow high-quality GaN NWs and its related nano-device applications. © 2011 Elsevier B.V.

Thin Solid Films

Selective area growth of GaN nanowires using metalorganic chemical vapor deposition on nano-patterned Si(111) formed by the etching of nano-sized Au droplets

We report a fiber-optic sensor for measuring the refractive index (RI) of a liquid sample. The sensing probe is constructed from an extrinsic cavity formed by a micromirror and a lensed photonic crystal fiber (PCF) tip. We show that PCF lens with an unconventionally large radius of curvature is bifunctional; an effective reflector as well as a collimator and thus suitable for realizing long single-arm interferometers, with a cavity length of the order of few mm. A sensing head suitable for measuring the refractive index (RI) of liquids is constructed by encapsulating the bifunctional lens tip and a micromirror in a glass tube. A hole is made in the glass-tube to allow free-flow of the liquid sample in-and-out of the cavity. The cavity length was about 1 mm. The group index of the liquid samples is obtained from the Fourier peak position of the interference signal measured in wavelength with optical spectrometer. The RIs of distilled water, acetone and ethanol (at 829 nm, 20 °C) were measured to be 1.32822, 1.35416, and 1.35715, respectively. The resolution of the sensor was analytically found to be 2.6 × 10-5 and the response was experimentally shown to be linear. © 2011 IEEE.

IEEE Sensors Journal

Fiber-optic probe based on a bifunctional lensed photonic crystal fiber for refractive index measurements of liquids

We report on the preparation and characterizations of multifunctional baicalein blended poly(vinyl alcohol) (PVA) composite nanofibers via electrospinning process. In order to improve the biocompatibility properties, baicalein was blended in to PVA to prepare composite nanofibers. The morphology, structure and thermal properties of the PVA/baicalein composite nanofibers were analyzed by using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform-infrared (FT-IR) spectroscopy, Raman spectroscopy and thermogravimetry (TGA) analysis. SEM images revealed that the composite nanofibers were well-oriented and had good incorporation of baicalein. FT-IR results indicated that the various bonding groups of PVA/baicalein composite nanofibers with stable structure. TGA analysis revealed that the onset degradation temperature was decreased with increasing baicalein content in the composite nanofibers. Ultraviolet (UV) light blocking efficiency was enhanced with increasing baicalein concentration in the composite nanofibers as observed by UV-vis diffuse reflectance spectroscopy. Further, the bactericidal activity of PVA/baicalein composite nanofibers was also investigated. These results indicated that the PVA blended baicalein composite nanofibers can be utilized as promising candidate materials for many technological applications. © 2011 Elsevier B.V.

Colloids and Surfaces A: Physicochemical and Engineering Aspects

Multifunctional baicalein blended poly(vinyl alcohol) composite nanofibers via electrospinning

We report on the growth of self-assembled GaN nanowires (NWs) on Si(1 1 1) substrates via pulsed metal-organic chemical vapor deposition (MOCVD) technique. Au colloid nanoparticles dispersed on Si(1 1 1) substrate were used as catalyst to conduct the GaN NWs growth. The size of the GaN NWs can be tailored by an easy and simple method of optimizing the Au colloids catalyst using Ga pre-deposition. The pulsed MOCVD growth mode was used to grow GaN NWs in which the group III and group V precursors were introduced alternately in the sequence. The surface morphology and optical characterization of the grown GaN NWs were studied by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), photoluminescence (PL), and cathodoluminescence (CL). The XRD pattern confirmed the hexagonal structure of GaN NWs. The experimental results indicated that the GaN NW diameter depended on the size of AuGa droplets. The pulsed method combined with growth temperature considerably affected the shape and density of the GaN NWs. © 2011 Elsevier B.V.

Journal of Crystal Growth

The growth behavior of GaN NWs on Si(1 1 1) by the dispersion of Au colloid catalyst using pulsed MOCVD

Low-dielectric constant SiOC(H) films were deposited on p-type Si(100) substrates by plasma-enhanced chemical-vapor deposition (PECVD) using dimethyldimethoxy silane (DMDMS, C4H12O2Si) and oxygen gas as precursors. To improve the physicochemical properties of the SiOC(H) films, the deposited SiOC(H) films were exposed to ultraviolet (UV) irradiation in a vacuum. The bonding structure of the SiOC(H) films was investigated by Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The electrical characterization of SiOC(H) films were carried out through I-V measurements using the comb-like patterns of the TiN/Al/Ti/SiOC(H)/TiN/Al/Ti metal-insulator-metal (MIM) structure. Excessive UV treatment adversely affected the SiOC(H) film, which resulted in an increased dielectric constant. Our results provide insight into the UV irradiation of low-k SiOC(H) films. © 2011 Elsevier B.V.

Ultraviolet irradiation effect on the properties of leakage current and dielectric breakdown of low-dielectric-constant SiOC(H) films using comb capacitor structure

We fabricated an enhancement-mode thin film transistor (TFT) using ZnO as an active channel layer deposited by radio frequency (rf) magnetron sputtering. The NH3 plasma passivation was performed in order to improve the electrical properties of the ZnO TFTs. We observed that the NH3 plasma treated ZnO TFTs revealed improved device performances, which include the field effect mobility of 34 cm2/Vs, threshold voltage of 14 V, subthreshold swing of 0.44 V/dec, off-current of 10-11 A and on to off ratio higher than 105. These results demonstrate that NH 3 plasma treatment could effectively enhance the performance of the ZnO based TFT device. © 2011 Elsevier Ltd. All rights reserved.

Vacuum

Effect of NH3 plasma treatment on the device performance of ZnO based thin film transistors

This work was focused on preparation and characterizations of chitosan blended polyamide-6 nanofibers by a new single solvent system via electrospinning process for human osteoblastic (HOB) cell culture applications. The morphological, structural and thermal properties of the polyamide-6/chitosan nanofibers were analyzed by using field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Fourier transform-infrared (FT-IR) spectroscopy, Raman spectroscopy, differential scanning calorimetry (DSC) and thermogravimetry (TGA). SEM images revealed that the nanofibers were well-oriented and had good incorporation of chitosan. FT-IR results indicated that the amino groups of chitosan existed in the blended nanofibers. TGA analysis revealed that the onset degradation temperature was decreased with increasing chitosan content in the blended nanofibers. The morphological features of the cells attached on nanofibers were confirmed by SEM. The adhesion, viability and proliferation properties of osteoblast cells on the polyamide-6/chitosan blended nanofibers were analyzed by in vitro cell compatibility test. © 2010 Elsevier B.V.