Low Temperature Electrical Resistivity Studies in Lead Thin Films

Thin lead films of thickness, 100 nm, 150 nm, 200 nm and 250 nm have been deposited using electron beam evaporation technique at room temperature onto glass substrates under high vacuum conditions. Films were investigated for electrical resistivity at low temperatures from 77 K to 300 K. Resistivity variation with temperature indicates transition from metallic to semiconductor behavior. Transition tem-perature increased with increasing film thickness. Temperature coefficient of resistance in the metallic re-gion has been determined for all the four films. Using Arrhenius relation, activation energy for conduction in metallic region has been determined. Mott’s small polaron hopping model has been employed to deter-mine activation energy in the semiconducting region. In a film of 250 nm thick, deviation from Mott’s small polaron hopping model for below 100 K was noted and that has been considered under Mott’s variable range hopping model. The complete understanding of electrical properties of Pb films has been necessitat-ed by the fact that the band gap in CdS decreases when Pb is incorporated into it, which in turn can be used to fabricated large efficient solar cells. It is for the first time that lead films of the present thickness have been investigated for low temperature resistivity. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3197

MAGNETIC AND ELECTRICAL PROPERTIES OF ELECTRON BEAM GUN DEPOSITED [Mn/Al] MULTILAYERED FILMS

By following electron beam gun evaporation technique, the magnetic multilayers in the configuration, [Mn(60nm)/Al(20nm)]n; n =1, 2 and 9 were deposited at 473K,  under high vacuum conditions. From grazing incidence X- ray diffraction (GIXRD) studies, the grain sizes were determined and they were in the order of few nanometers. Atomic force microscope (AFM) were employed to study surface structure and grain sizes. The magnetization as a function of field at 150K and 200K have been measured using the MPMS SQUID - vibrating sample magnetometer (VSM). From the hysteresis loops, coercive field, saturation magnetization, remanent magnetization and antiferromagnetic coupling were determined. All the three films hinted at the existence of at antiferromagnetic interaction between Mn layers through Al layer. Electrical resistivity in the temperature range from 5K to 300K has been measured. Films exhibited semiconducting to metallic transition. The power law variation of resistivity with temperature was established for the metallic region. Conductivity data for semiconducting region of a film has been analysed using polaran hopping models, activation energy and density of states at Fermi level were established. This is for the first time that antiferromagnetic coupling between Mn layers through interfacer layer and semiconducting to metallic transition have been noticed in the present configuration of [Mn/Al] multilayers

Magnetic and Low Temperature Conductivity Studies in Oxidized Nano Ni Films

A set of single layered nanostructured Ni films of thickness, t = 25 nm, 50 nm, 75 nm and 100 nm have been deposited using electron beam gun evaporation technique at 473 K under high vacuum condition. From the grazing incidence X-ray diffraction (GIXRD) studies, NiO phase formation has been noted. Grain sizes of the films were determined. The microstructure was examined by scanning electron microscope (SEM) studies. Average surface roughness was determined by atomic force microscope (AFM). The room temperature magnetization has been measured using the vibrating sample magnetometer (VSM). The coercive field was observed to be increasing with increasing t and became maximum for t = 75 nm and decreases for further increase in t. The behavior of coercive field with t indicated softness of the films. Low temperature electrical conductivity in the range from 5 K to 300 K has been measured. Temperature dependence of electrical conductivity showed semiconducting behavior. At temperatures above θD/2 (θD is the Debye temperature), the conductivity behavior has been understood in the light of Mott’s small polaron hopping model and activation energies were determined. An attempt has been made to understand conductivity variation below θD/2 using variable range hopping models due to Mott and Greaves. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2371

The study of quantum oscillations in the normal and superconducting states of V_3Si

SIGLEAvailable from British Library Document Supply Centre-DSC:DXN023205 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Dielectric Poperties and AC Conductivity Studies of PTh-Co Nanocomposites

Polythiophene (PTh) and cobalt nanoparticles (Co-nps) were prepared by chemical oxidation and modified polyol processes respectively. Composites were made by mixing them in the proportions, PTh1-xCox; x = 0.1, 0.2, 0.3, 0.4, 0.5.  Morphology of the samples has been studied by SEM technique. Dielectric properties with temperature and frequency as variables were investigated. Dielectric constant and loss factor decreased with frequency and increased with temperature. AC conductivity was estimated from the dielectric data. Ac conductivity decreased with increase of Co-nps in the composites which indicates that electrically insulating effect has been induced by Co-nps. Small polaron hopping mechanism is found to be the conduction mechanism operated. Activation energy for ac conduction decreased with increase of frequency and weight percent of Co-nps in the composites.  Electric modulus was determined and its analysis leads to the estimation of dielectric relaxation time. Relaxation time decreased with increase of temperature for all the five composites. For the first time PTh-Co nanocomposites have been reported for dielectric properties and ac conductivity as a function of frequency and temperature

Structural, dielectric and magnetic studies of ferrite-ferroelectric composites

The composites of ferrite-ferroelectric system (x) Mg0.2Cu0.5Zn0.3Fe2O4 thorn (1-x) BaTiO3 (x = 15%, 30% and 45%) were synthesized by sintering the mixtures of ferroelectric BaTiO3 (BTO) and ferrite component Mg0.2Cu0.5Zn0.3Fe2O4 (MCZF). Ferrimagnetic MCZF was prepared using auto-combustion method where as ferroelectric BTO was procured commercially from Sigma-Aldrich. The presences of two phases in magnetoelectric composites were probed by X-ray diffraction (XRD) studies. The peaks observed in the XRD spectrum indicated spinel cubic structure for MCZF ferrite and tetragonal perovskite structure for BTO and, both spinel and pervoskite structures for synthesized composites. Surface morphology of the samples has been investigated using Field Emission Scanning Electron Microscope (FESEM). Frequency dependent dielectric properties of synthesized composites were measured from 100 Hz to 1 MHz at room temperature (RT) using HIOKI LCR HI-TESTER. The dielectric dispersion is observed at lower frequencies for the synthesized ME composites. The magnetic properties of synthesized composites were analyzed using a Vibrating Sample Magnetometer. It is observed that the composites exhibited magnetic hysteresis with narrow loops indicating the magnetic ordering in the composites. All the measurements were carried out at room temperature

Conduction Mechanisms in Polypyrrole-Copper Nanocomposites

By mixing independently synthesized polypyrole and copper nanoparticles in different proportions, nanocomposites were prepared. Bulk and surface structures were probed by X-ray diffraction and Scanning electron microscopes. DC resistivity with temperature as a variable of all the composites has been investigated. Conductivity has been calculated using resistivity and found it to be of the order 10 – 4 (Ω – 1m – 1), which is greater by one order of magnitude than that reported for polypyrole nanoparticles. Temperature behaviour of conductivity in all the samples revealed semiconducting nature. By applying Mott’s theory of small polaron hopping, activation energy for conductivity at high temperature has been determined. Activation energy is found to be increasing with increase in copper content in the composites. Using data deviated from small polaron model, the density of states at Fermi level is calculated by employing the theory of variable range hopping of polarons due to Mott. It is for the first time that PPy-Cu nanocomposites have been probed for structural and temperature dependence of conductivity and conduction mechanisms operated in these composites in different temperature regions have been understood

Electrical Conduction in Borophosphate Glasses Doped With CoO and Li 2 O

Abstract Oxide glasses in the compositions, (B 2 0.5-X , where x = 0.05, 0.1, 0.15, 0.20, 0.25, 0.30, 0.40 and 0.5