B. K. Mathur

Nanostructured icosahedral phase formation in Al70Cu20Fe10 by mechanical alloying: Comprehensive study

A systematic study on the formation and the stability of Al70Cu20Fe10 quasicrystalline alloy has been carried out through mechanical alloying. The influence of the milling parameters, sequence of additive elements, and heat treatment on the formation of icosahedral phase has been investigated through x-ray diffraction analysis and transmission electron microscopy. A combination of milling and heat treatment of Al70Cu20Fe10 composition resulted in the formation of a single icosahedral phase (i-phase) quasicrystal with face-centered structure. We present evidence that suggests the i phase is of a nanoquasicrystalline nature. From the present investigations, we propose an i-phase formation mechanism in Al–Cu–Fe system.

A reverse electrochemical floating-layer technique of SPM tip preparation

An experimental set-up involving a combination of reverse electrochemical etching and the floating-layer technique of tip preparation is presented. In the model only dc bias is used, avoiding the shortcomings of ac bias. The collection of two tips in a single etching process and mechanical auto-breaking of the circuit are emphasized. This cost and time effective, easy in-laboratory approach yields two sharp tips without paying attention to switching off the circuit. The nature of the tip shape arising from the floating-layer technique has been explained in terms of the electrical field distribution between the electrodes. The addition of some new information together with a few established facts will enrich and enlighten the art of tip preparation.

Scanning tunnelling microscopic and spectroscopic investigation of the microstructural and electronic properties of the grain boundaries of giant magnetoresistive manganites

Scanning tunnelling microscopic (STM) and spectroscopic (STS) investigations have been carried out on the grain boundaries (GBs) of sintered pellets of giant magnetoresistive perovskite manganites (LCMO), (LYMCO) and (LPMCO). Based on spectroscopic data obtained and estimation of band gap, it has been concluded that these materials possess some sort of semiconducting intergranular layer (IGL) whose thicknesses are in the range of a few nm to about 100 nm and the band gap is in the range of 0.3-0.45 eV. IGLs are usually more resistive than the grains. For semiconducting samples like LCMO and LYCMO (room temperature band gap = 0.23 and 0.27 eV respectively), IGLs bend the energy band near GBs. This bending has been estimated to be about 40-50 meV with the depletion depth of few tens of nm extending on both sides of the IGL. The decrease in conductivity near the GB is due to the disorder induced carrier scattering and the bending of the band. LPCMO is almost conducting at room temperature. The GBs in this material sometimes exhibit conducting behaviour which may be due to the accumulation of some conducting material or the trapping centres in the IGL. Scanning electron microscopic and electrical measurements also justify the STM/STS results.

Observation of deviation of electronic behaviour of indium tin oxide film at grain boundary using Scanning Tunneling Microscope

Scanning Tunneling Microscopy and Spectroscopy investigations have been carried out on electron beam deposited indium tin oxide films. The STM images reveal a rather smooth surface, which appears to have been formed due to the coalescence of islands with different shapes. The spectroscopic data, in general, exhibit characteristics typical of metal-insulator-semiconductor structures, with a heavily doped semiconductor. From the I-V curves, a band gap of ≈3.5 eV is obtained, which is very close to the bulk value. The I-V studies at some grain boundary interfaces suggest the presence of regions showing electronic characteristics, that differ significantly from what is observed on the rest of the film surface.

Radial distribution function analysis of coir fibre

Radial distribution analysis of X-ray intensities diffracted by natural coir fibre subjected to various thermal and mercerization treatments has been carried out. Interatomic distances, mean square displacements and interatomic coupling constants have been obtained from the radial distribution curves. As coir fibre finds its various applications in its natural form, its study has been carried out without disturbing the configuration of its cellulose-lignin complex during the treatments. Interatomic distances remain more or less the same during thermal and chemical treatments but the coupling constants and the mean square displacements experience changes, reflecting the changed mechanical behaviour of the fibre.

Synthesis and characterization of indium intercalation compound of MoS2, InxMoS2 (0≤x≤1)

Preparation des composes In x MoS 2 (0≤x≤1) et donnees des parametres cristallins, conductivite electrique et susceptibilite magnetique pour x=0, 1/3, 2/3 et 1

X-ray diffraction and electron microscopic studies on selenium substituted indium intercalation compounds of tungsten disulphide

Abstract Selenium substituted indium intercalation compounds of tungsten disulphide, In 1/3 WS 2− x Se x (0≤ x ≤2) have been studied for microstructural characterization using X-ray line profile analysis to find out information about crystallite size, r.m.s. strain, dislocation density, variability of interlayer spacing, fraction of planes affected by such defects, stacking fault probability, crystallite size anisotropy etc. Scanning electron microscopic (SEM) and scanning tunneling microscopic (STM) studies are also reported herewith. These results have also been compared with respect to the pure WS 2− x Se x (0≤ x ≤2).

Deposition of Ag0.5Cu0.5InTe2 thin films using a stepwise evaporation method

Abstract Thin films of Ag 0.5 Cu 0.5 InTe 2 are deposited on substrates held at different temperatures using a stepwise evaporation process. The film growth was done by feeding pre-reacted Ag 0.5 Cu 0.5 InTe 2 powder in small steps (a few mg per step) to an unheated tungsten boat and then evaporating the material rapidly to completion. This process has been repeated to get films of sufficient thickness. Structural characterization using transmission electron microscopy has revealed that films deposited at temperatures as low as 100 °C are polycrystalline and single phase. Analysis of film composition using energy dispersive analysis of X-rays has shown that the films are nearly Stoichiometric.

Scanning tunneling spectroscopy of indium tin oxide film in air

Scanning tunneling spectroscopy investigations have been carried out on electron beam deposited indium tin oxide films in air. The spectroscopic data exhibit chatacteristics typical of metal-insulator-semiconductor structure, with a heavily doped semiconductor. The measurements have yielded a band gap of about 3.5 eV, which is very close to the bulk value.

Radial distribution function analyses of polythiohydroquinone

In recent years, the RDF analysis [1-4] of X-ray diffraction patterns has become a powerful tool for studying the structures of non-crystalline disordered materials. This technique may be applied to systems for which the average radial distribution function is spherically symmetrical, such as pure liquids, solutions, glasses and finely divided powders. It yields information not only about structural parameters but also many physical parameters such as Debye temperature, coupling coefficients, coordination numbers and interatomic potentials. The polymer, polythiohydroquinone, reported here does not crystallize and therefore single crystal techniques cannot be used to obtain structural information. Hydroquinone and excess sulphur were mixed thoroughly and poured into a glass tube. The tube was flushed several times with nitrogen and placed in a furnace in a nearly horizontal position. The issuing hydrogen sulphide gas was trapped in a lead acetate solution. After several hours the tube was removed and allowed to cool. The material was washed with concentrated sulphuric acid, followed by concentrated alkali solution to remove low molecular weight products and finally with hot carbon disulphide solutions to remove excess sulphur. The yield was about 70%. X-ray diffraction patterns for the present sample were recorded with the help of a Phillips diffractometer on a strip chart, the scanning rate being 2 ° min -1 , using MoK~ radiation in the range s = 0.77 to s = 8.96 (where s = 4re sin 0/4). The background radiation was suppressed with the aid of a discriminator by running the diffractometer once without sample. Then the sample was mounted and the intensities recorded. Other corrections for polarization and absorption were carried out using procedures described by Kaelble [2]. Tubulated values of atomic scattering factors [5] and incoherent scattering factors [6] were used for obtaining independent scattering curves. The corrected intensities were scaled to electron units by the method described by Kroughmoe [7]. The contribution of the flat-faced diffractometer sample in the small-angle region and that due to multiple scattering were subtracted following the method described by Warren [8]. Following the procedure described by Kaelble, the radial distribution function for polyatomic samples, 47t?2~0(r) is given by