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

Department of Physics

The optical reflectance, dielectric functions and phonon vibrational modes of Ti 1-x Nb x N (0≤x≤0.77) thin films are reported. Films of 500-nm thickness were deposited on 316LN nuclear grade stainless steel substrates by radio-frequency magnetron sputtering. The reflectance spectra of the films, in the energy range 1.5 to 5.5 eV, are fitted using the Drude-Lorentz model as the response of one Drude parameter and four Lorentz oscillators. It is demonstrated that the properties studied are dependent on Nb concentration, x, and exhibit a behavior transition threshold at x=0.5. The optical properties studied are closer to TiN for x&lt;0.5 and resemble NbN for x&gt;0.5. For example, the films showed a minimum in reflectance at ∼2.33 eV for values of x up to 0.5, corresponding to the Ti-N charge transfer band. Increase in Nb concentration beyond 0.5 caused a large shift in this energy to 3.2 eV, corresponding to the Nb-N charge transfer excitation. Similarly, the real part of the dielectric function is characterized by a screened plasma energy of 2.25 eV for values of x&lt;0.5 (∼TiN) and 3.25±0.2 eV for x&gt;0.5 (∼NbN). The energy at which the loss function reaches a peak value increases linearly for values of x from 0 to 0.41 and decreases very drastically for x&gt;0.5. Phonon-vibrational modes of Ti 1-x Nb x N thin films studied by Raman spectroscopy show that Nb substitution in TiN results in first-order Raman scattering. The single-phonon acoustical peak at 270 cm -1 of TiN shifted to 265 cm -1 for x=0.77, while the two-phonon acoustical peak of TiN at 620 cm -1 shifted to 630 cm -1 for the same value of x. The reasons for the existence of a behavior transition threshold in Nb concentration are discussed. © 2012 Springer-Verlag.

School of Advanced Sciences

Vellore Campus

World University root node

Applied Physics A: Materials Science and Processing

Optical reflectance, dielectric functions and phonon-vibrational modes of reactively sputtered Nb-substituted TiN thin films

In this Letter, we show that a superconducting two-dimensional electron gas is formed at the LaTiO 3/SrTiO 3 interface whose transition temperature can be modulated by a back-gate voltage. The gas consists of two types of carriers: a majority of low-mobility carriers always present, and a few high-mobility ones that can be injected by electrostatic doping. The calculation of the electron spatial distribution in the confinement potential shows that the high-mobility electrons responsible for superconductivity set at the edge of the gas whose extension can be tuned by the field effect. © 2012 American Physical Society.

Physical Review Letters

Two-dimensional superconducting phase in LaTiO 3/SrTiO 3 heterostructures induced by high-mobility carrier doping

This study highlights the use of adaptive planning to accommodate testicular shielding in helical tomotherapy for malignancies of the proximal thigh. Two cases of young men with large soft tissue sarcomas of the proximal thigh are presented. After multidisciplinary evaluation, preoperative radiation therapy was recommended. Both patients were referred for sperm banking and lead shields were used to minimize testicular dose during radiation therapy. To minimize imaging artifacts, kilovoltage CT (kVCT) treatment planning was conducted without shielding. Generous hypothetical contours were generated on each "planning scan" to estimate the location of the lead shield and generate a directionally blocked helical tomotherapy plan. To ensure the accuracy of each plan, megavoltage fan-beam CT (MVCT) scans were obtained at the first treatment and adaptive planning was performed to account for lead shield placement. Two important regions of interest in these cases were femurs and femoral heads. During adaptive planning for the first patient, it was observed that the virtual lead shield contour on kVCT planning images was significantly larger than the actual lead shield used for treatment. However, for the second patient, it was noted that the size of the virtual lead shield contoured on the kVCT image was significantly smaller than the actual shield size. Thus, new adaptive plans based on MVCT images were generated and used for treatment. The planning target volume was underdosed up to 2% and had higher maximum doses without adaptive planning. In conclusion, the treatment of the upper thigh, particularly in young men, presents several clinical challenges, including preservation of gonadal function. In such circumstances, adaptive planning using MVCT can ensure accurate dose delivery even in the presence of high-density testicular shields. © 2012.

VIT Unitversity

Fulltext

Medical Dosimetry

Adaptive planning using megavoltage fan-beam CT for radiation therapy with testicular shielding

Lithium doped cobalt ferrites (Li 0.2CoFe 1.8O 4) were prepared by a sol-gel combustion method by using Lithium nitrate, cobalt nitrate, and ferric nitrate as source materials. Here, Citric acid and polyvinyl alcohol used as a burning agent and agglomeration reducing agent respectively. The pH value of precursor was maintained between 7 and 8 while preparation of the sample. The average particle size of the ferrite obtained at 300°C about ∼15-20 nm. Further, single phase spinel structure has been confirmed by X-ray diffraction (XRD) and Cubic morphology was confirmed by High resolution scanning electron microscopy (HR-SEM). The composition of elements has been confirmed by Infrared spectroscopy (FT-IR). Moreover, the electrical studies of the prepared sample have been analyzed by four point probe method. The observed results inferred that conductivity of the ferrite sample has been reduced by addition of lithium. © 2012 Elsevier Ltd.

Journal of Physics and Chemistry of Solids

Electrical and structural studies of lithium doped cobalt ferrite

We consider the evolution of nonlinear optical pulses in inhomogeneous optical media wherein the pulse propagation is governed by the nonlinear Schrödinger equation with varying dispersion. We adopt the Painlevé analysis in order to obtain the condition for the soliton pulse propagation. We find that there exist two dispersion profiles satisfying this criterion, namely, the constant dispersion and exponentially dispersion decreasing profiles. In the exponentially varying dispersion media, we explain the existence and the formation of chirped optical soliton through the equation for the chirp parameter that results from variational analysis. For further elucidation, we provide the phase-plane diagram in terms of the normalized chirp and intensity (peak power), which explains the physical mechanism of linearly chirped soliton pulse compression in the exponentially dispersion decreasing media. In addition, we discuss the generation of exact chirped higher order solitons using the Bäcklund transformation method. As a special case, we find an oscillatory two-soliton breather pulse, which, at decreasing intervals, evolves into a familiar hyperbolic secant shape whose amplitude is twice that of a fundamental soliton. We highlight on the point that the crux of this work in realizing a compact pulse compressor could possibly result in a myriad of applications in modern optical fiber communications systems. © 2011 Elsevier B.V. All rights reserved.

Optics Communications

Pedestal free pulse compression of chirped optical solitons

Dy 2O 3 nanoparticles were synthesized at room temperature through soft chemical route using dysprosium acetate hexahydrate and hexamethylenetetramine as starting materials. As-synthesized Dy 2O 3 nanoparticles were calcined up to 600°C and the samples were subjected to various characterizations. The decomposition course of as-prepared particles and the formation process of Dy 2O 3 were studied by TG/DTA. The cubic bixbyite phase formation of Dy 2O 3 nanoparticles was confirmed by XRD results. The particle size and morphology were investigated by TEM. The composition and surface passivation were confirmed by EDS and FTIR studies, respectively. The possible formation mechanism has been discussed based on the experimental results. Bandgap of the material was estimated from the UV-vis absorption spectra. A blue-shift was observed in the absorbance as a result of quantum confinement effect, which was supported by PL spectra. © 2012 Elsevier B.V. All rights reserved.

Physica E: Low-Dimensional Systems and Nanostructures

Synthesis and photoluminescence properties of HMT passivated Dy 2O 3 nanoparticles

Growth of bulk zinc thiourea chloride (ZTC) single crystals from aqueous solution by low temperature solution growth technique has been reported. Single crystal X-ray diffraction (XRD) analysis confirms the crystal structure. The crystalline quality was assessed by high resolution XRD technique. The thermal stability of the crystal was investigated using thermogravimetric analysis (TGA). The microhardness measurement has been carried out at room temperature for different forces using Vickers microhardness tester. From the Vickers microhardness, Meyer's index number (n) and minimum level of indentation load (w) of the crystal has been deliberated. The elastic stiffness coefficient C 11 was also calculated using Wooster's empirical relation from the hardness data. The grown crystal possesses good optical transmission in the entire visible region, which is an essential requirement for nonlinear optical crystals. The good optical transmittance in the visible region and second harmonic generation (SHG) conversion efficiency makes the crystal a potential material for nonlinear optical (NLO) applications. Copyright © 2012 Taylor and Francis Group, LLC.

Department of Chemistry

Materials and Manufacturing Processes

Structural and Mechanical Studies of Semi-Organic NLO Material: Zinc Thiourea Chloride

Advanced Materials Research

Preface

In this paper, we generate bright as well as dark soliton type ultrashort laser pulses in a photonic nanowire. The pulse evolution in the photonic nanowire is described by higher order nonlinear Schrödinger equation with an additional effect relating to the nonlinear change of group velocity, which, in turn, is proportional to the field intensity. The pulse evolution equation is solved by coupled amplitude-phase method. Further, we calculate the minimum power required for realizing the ultrashort laser pulses. The main crux of this work stems from the generation of ultrashort pulses by an entirely new nonlinear effect involving change of group velocity.

Department of Instrumentation

School of Electrical Engineering

2012 International Conference on Optical Engineering (ICOE)

Generation of bright and dark solitons in photonic nanowire

The study of scanning tunneling microscopy (STM) induced localized degradation and polarity dependent breakdown (BD) of HfO 2/SiO x dielectric stacks is presented in this work, together with a correlated investigation of the BD locations by transmission electron microscopy (TEM). The localized dielectric BD events are also analysed using conductive-atomic force microscopy. The analysis of the degradation and breakdown phenomenon has been performed from a macroscopic (device) level to a localized nanometer scale BD location. A new technique is adopted to induce the degradation and BD of the HfO 2/SiO x dielectric stacks locally using a combined STM/scanning electron microscopy nano-probing system. The BD locations were identified on blanket wafers and gate electrode area of the dielectric, and the sample containing these regions was prepared using focused ion beam for the physical analysis using TEM. This method of analysis is very useful in studying the nature of the BD events in dielectrics with and without the gate electrode, elucidating the role of the gate electrode in dielectric BD events. © 2012 IEEE.