Showing papers by "Sitaram Dash published in 2011"

Enhanced Surface Potential Variation on Nanoprotrusions of GaN Microbelt As a Probe for Humidity Sensing

Abstract: Surface potential (SP) using Kelvin probe microscopy is employed, as a measure to sense humidity, exploiting localized nanoprotrusions of freestanding GaN microbelts. These belts with distinct nano...

Continuous multi cycle nanoindentation studies on compositionally graded Ti1−xAlxN multilayer thin films

Abstract: Two types of Compositionally Graded Multilayer (CGM) films of Ti 1− x Al x N consisting of 21 layers were synthesized by reactive magnetron co-sputtering technique. The first one begins with a layer of Ti 0.4 Al 0.6 N from substrate and ends with TiN, whereas exactly a reverse order has been followed in the second one. As deposited CGM films are poly-crystalline with rocksalt structure similar to stoichiometric TiN. Secondary Ion Mass Spectrometry (SIMS) depth profile of the films showed the presence of 21 layers of equal thickness (50 nm) with varying aluminum content in steps. Continuous Multi Cycle (CMC) nanoindentation technique was used to analyze the failure modes of these films. Topographic examination of the indented zone revealed the presence of edge cracks inside and outside the indentation area when the load exceeds beyond 90 mN. The load–displacement profiles of CMC and single indentations exhibited the onset of pop-ins at a depth of ∼200 nm.

Reactive pulsed laser deposition and characterization of niobium nitride thin films

Abstract: We present a systematic study to explore the effect of important process variables on the composition and structure of niobium nitride thin films synthesized by Reactive Pulsed Laser Deposition (RPLD) technique through ablation of high purity niobium target in the presence of low pressure nitrogen gas. Secondary Ion Mass Spectrometry has been used in a unique way to study and fix gas pressure, substrate temperature and laser fluence, in order to obtain optimized conditions for one variable in single experimental run. The x-ray diffraction and electron microscopic characterization have been complemented by proton elastic backscattering spectroscopy and x-ray photoelectron spectroscopy to understand the incorporation of oxygen and associated non-stoichiometry in the metal to nitrogen ratio. The present study demonstrates that RPLD can be used for obtaining thin film architectures using non-equilibrium processing. Finally the optimized NbN thin films were characterized for their hardness using nano-indentation technique and found to be similar to 30 GPa at the deposition pressure of 8 Pa. (C) 2011 Elsevier B.V. All rights reserved.

Air trapped nanocavity induced superhydrophobicity on GaN microbelt

Abstract: In the present study, nanotextured surface protrusion induced superhydrophobicity in GaN microbelt is reported. The results show that along with nanometer-scale topographic features, the special air trapped nanocavities formed beneath the liquid droplet are solely responsible for the transition of superhydrophobicity having hydrophilic origin in GaN. The built-in nanocavities, ( ~ 80 nm in diameter) provide an ideal model for producing stable air trapped region. A calculation of shape of the meniscus at the interface of air and water in an isolated cavity correlates well with the macroscopic surface wetting behavior.

Evolution of Tribological Properties of Reactor-Grade NiCr-B Coating

Abstract: The tribological properties of reactor-grade NiCr-B hardfaced coating were studied at a constant load and sliding velocity. The objective of the present article is to investigate the changes in coefficient of friction that accompanies morphological and phase changes occurring in wear scars. Such changes result from the sliding with a spherical steel ball. The transition from the low to high coefficient of friction at higher sliding distance is attributed to severe cracking as well as fretting wear–induced deformation of surface oxide scales. Increased value of coefficient of friction arises from protracted sliding over longer distances continued to deform and detachment of weakly adhered oxides like Fe2O3 and Cr2O3. Such scales are tribochemically formed on the wear scars and contribute to alteration in the coefficient of friction. The evolution of oxide phases in wear scars is found to be one of the main mechanisms for dissipation of frictional force.

Melt pool vorticity in deep penetration laser material welding

Abstract: In the present study, the vorticity of melt motion in the keyhole and weld pool has been evaluated in case of high power CO 2 laser beam welding. The circulation of vorticity is obtained as a function of Reynolds number for a given keyhole volume which is linked to Mach number variation. The shear stress and thermal fluxes present in the turbulent pool are linked to diffusivity and Prandtl number variation. It was shown that below a critical value of Rayleigh number, the conduction mode of melt transfer signifying beam absorption becomes dominant. Above this value, convective heat transfer indicates melting and evaporation occurring in the weld pool during laser welding. The evaporative recoil pressure expels the liquid while surface tension and hydrostatic pressure help to retain the melt in the keyhole cavity in this high power laser beam welding. The understanding of several hydrodynamic phenomena occuring in the weld pool is valuable not only for understanding basic mechanistic aspects but also for process optimization involved in laser beam welding.

Fabrication of TiO 2 nanofibers by electrospinning technique

Abstract: TiO 2 nanofibers were synthesized by incorporating sol-gel and electrospinning techniques using polyvinyl pyrrolidone and titanium tetraisopropoxide sol-gel as precursor. The as prepared composite fibres were of ∼300 nm average diameter. Calcination of these composite fibres at 500° C in air resulted in pure anatase titania nanofibres, of 84 nm mean diameter with smooth surfaces, without contamination of the other phases. In contrast, surfaces that are more granular evolved when they were calcined at higher temperatures. The phase of the as prepared as well as annealed samples was revealed by micro Raman investigations. This electronic document is a “live” template. The various components of your paper [title, text, heads, etc.] are already defined on the style sheet, as illustrated by the portions given in this document.

Tribomechanical studies on PLD grown DLC/Ni multilayers

Abstract: Tribomechanical properties of pulsed laser deposited diamond like carbon (DLC) with Ni interlayers are studied. Low coefficient of friction is found for DLC/Ni multilayer when compared to DLC/Ni bilayer. The behavior of low friction coefficient of DLC/Ni multilayer is attributed to the formation of graphitized tribofilm.

Effect of annealing temperature on structural and morphological stability of TiO 2 nanotube arrays

Abstract: Self aligned TiO 2 nanotube arrays were synthesized on Ti foils by electrochemical anodization technique. The qualitative mechanistic aspect of nanotube formation is discussed based on the results of potentiostatic transient measurements. The structural and morphological stability of the nanotube arrays synthesized were investigated by annealing the anodized foils at various temperatures and then carrying out the XRD and FESEM analysis. The phase transformation and crystallization of nanotubes are discussed briefly.

Nanoscale gate insulator for organic field effect transistor applications

Abstract: The High k thin films of ZrO2 were deposited by electron beam evaporation for creating high capacitance devices. Capacitance as high as 0.2 μF/cm2 is obtained for the 80 nm thick ZrO2 films that forms thickness equivalent of SiO2~16 nm (teq). Grazing incidence XRD confirmed crystalline tetragonal phase. Morphology of ZrO2 films investigated using atomic force microscopy showed high roughness and pin holes that related to high leakage current. Whereas low leakage anodized Al nanogate insulator (teq of SiO2 ~ 3.55 nm) were prepared varying the voltage and utilized as high capacitance gate oxide to realize low powered organic field effect transistor with polytriarylamine semiconductor. The observed threshold voltage is 0.35V.

Structural and optical investigations of ZnO nanofibers synthesized by electro spinning technique

Abstract: ZnO nanofibers were synthesized by sol-gel processing and electrospinning technique using a 1∶1 mixture of zinc acetate dissolved in distilled water at a weight ratio of 1∶4 and poly vinyl pyrolidone dissolved in absolute ethanol at 1∶5 weight ratio as the spinning solution The fibers were characterized using thermogravimetry, FESEM, XRD and micro Raman spectroscopy

Carbon supported In-Sn oxide films

Abstract: Sol-gel derived indium-tin oxide (ITO) films, spin coated on to pulsed dc magnetron sputtered carbon layers, were studied using the techniques like atomic force microscopy (AFM), glancing incidence X-ray diffractometry (GIXRD), photoluminescence (PL), and electrical resistivity. The effect of carbon substrate on the physical properties (structural, luminescence and conductivity) of the deposited films was examined. The radiant relaxation energy obtained from PL studies and the electron band gap energy Eg computed from the conductivity versus temperature plot are compared.