A. P. Thakoor

Bio: A. P. Thakoor is an academic researcher from Indian Institutes of Technology. The author has contributed to research in topics: Seebeck coefficient & Annealing (metallurgy). The author has an hindex of 7, co-authored 8 publications receiving 203 citations.

Electron transport properties of thin copper films. I.

Abstract: The thickness dependence at 300 and 80 K of the electrical resistivity and its temperature coefficient, Hall coefficient, mobility, and thermoelectric power of as‐deposited and annealed thin (< 1000 A) evaporated polycrystalline copper films and films deposited at elevated temperatures have been studied. All transport parameters in carefully prepared and well‐characterized films exhibit monotonically increasing size effects with decreasing film thickness. Both annealing and deposition at elevated temperatures cause considerable reduction of the ’’apparent’’ size effects in all the transport parameters of the room‐temperature deposited films. A critical analysis of the observed size effects shows that the data in all cases depart markedly from the predictions of the Fuchs‐Sondheimer theory (and also that of the Mayadas‐Shatzkes theory which takes into account the grain boundary surface scattering). The departure from theory is different for each transport parameter. The annealing studies show that the enhanced size effects are due to the presence of a large concentration of structural defects in the films. The observed behavior may be understood by assuming the large concentration of point and/or line defects to decrease with film thickness and with annealing as well as deposition of films at elevated temperatures. The thermopower data suggest strongly that the large concentration of defects causes distortion of the Fermi surface and thereby a strong energy dependence of the mfp or relaxation time at the Fermi surface.

Role of structural defects in electron transport properties of copper films

Abstract: Kinetics of annealing of the electrical resistivity (ρ), Hall coefficient RH, mobility μ, and thermoelectric power TEP of thin (160–5000 A) copper films deposited at temperatures ranging from 80 to 600 K have been studied. The activation energy for the associated recovery process has been obtained from the observed isothermal and isochronal changes in the resistance of the films. This energy increases from a value of 0.7 eV at 2000 A to 1.4 eV at 180 A for room‐temperature‐deposited Cu films. Changes in ρ, RH, and μ on annealing are found to decrease with film thickness and deposition and annealing temperatures. On the other hand, changes in TEP due to annealing increase with film thickness up to 3000 A; the rate of change depends sensitively on deposition temperature. With decreasing temperature of deposition, the reduction in TEP occurs at successively higher annealing temperature. Annealing does not affect the temperature dependence of RH and TEP. These results, together with the information on the mic...

Electron transport properties of copper films. II. Thermoelectric power

Abstract: Thermoelectric power (TEP) of as‐deposited and annealed polycrystalline and epitaxially grown copper films of thickness 100–5000 A has been measured The TEP increases with the film thickness to reach a saturation value at about 3000 A The thickness dependence decreases markedly with increasing annealing temperature and also with increasing temperature of deposition The saturation value of the TEP of as‐deposited films is about 15 times the bulk value of copper and decreases rapidly with annealing to approach the single‐crystal bulk value In sharp contrast to the behavior of the TEP, the resistivity and its temperature coefficient and the carrier concentration of the same copper films exhibit little size effects and insignificant changes due to annealing for thicknesses larger than 1000 A The observed thickness dependence of the TEP of unannealed and annealed films shows no agreement with the Fuchs‐Sondheimer (F‐S) theory Further, there is no correlation between the thickness dependence of the TEP a

Structural defect thermoelectric power in thin copper films

Abstract: Thermoelectric power and electrical resistivity of thin (<1000 A) copper films annealed at different temperatures have been studied. The data have been utilized to obtain the contribution to thermoelectric power by the structural defects in the films. This contribution is comparable in magnitude to the bulk value. It increases with film thickness giving rise to a strong thickness dependence of thermoelectric power at thicknesses considerably larger than the mean free path of the conduction electrons.

Thermoelectric power of Cu‐based dilute alloy films

Abstract: The thermoelectric power (TEP) of structurally characterized Cu‐based dilute alloy films containing 1, 2, and 5 at.% Al, Ge, or Sn has been studied in the temperature range 80–350 K. The TEP of alloy films increases with thickness to reach a saturation value at ≳2800 A. The addition of impurities reduces the magnitude of the TEP of copper films while its sign remains positive. The temperature dependence of the TEP is affected markedly by the presence of impurities. Structural disorder, impurity, and phonon‐drag contributions to the TEP have been separated by using the Nordheim‐Gorter relation. Contribution of the Fermi‐surface distortions (and thus change in the neck radius of the Fermi surface) to the TEP has been estimated.

Large thermoelectricity via variable range hopping in chemical vapor deposition grown single-layer MoS2.

Abstract: Ultrathin layers of semiconducting molybdenum disulfide (MoS2) offer significant prospects in future electronic and optoelectronic applications. Although an increasing number of experiments bring light into the electronic transport properties of these crystals, their thermoelectric properties are much less known. In particular, thermoelectricity in chemical vapor deposition grown MoS2, which is more practical for wafer-scale applications, still remains unexplored. Here, for the first time, we investigate these properties in grown single layer MoS2. Microfabricated heaters and thermometers are used to measure both electrical conductivity and thermopower. Large values of up to ∼30 mV/K at room temperature are observed, which are much larger than those observed in other two-dimensional crystals and bulk MoS2. The thermopower is strongly dependent on temperature and applied gate voltage with a large enhancement at the vicinity of the conduction band edge. We also show that the Seebeck coefficient follows S ∼ T(1/3), suggesting a two-dimensional variable range hopping mechanism in the system, which is consistent with electrical transport measurements. Our results help to understand the physics behind the electrical and thermal transports in MoS2 and the high thermopower value is of interest to future thermoelectronic research and application.

Electron transport properties of thin copper films. I.

Abstract: The thickness dependence at 300 and 80 K of the electrical resistivity and its temperature coefficient, Hall coefficient, mobility, and thermoelectric power of as‐deposited and annealed thin (< 1000 A) evaporated polycrystalline copper films and films deposited at elevated temperatures have been studied. All transport parameters in carefully prepared and well‐characterized films exhibit monotonically increasing size effects with decreasing film thickness. Both annealing and deposition at elevated temperatures cause considerable reduction of the ’’apparent’’ size effects in all the transport parameters of the room‐temperature deposited films. A critical analysis of the observed size effects shows that the data in all cases depart markedly from the predictions of the Fuchs‐Sondheimer theory (and also that of the Mayadas‐Shatzkes theory which takes into account the grain boundary surface scattering). The departure from theory is different for each transport parameter. The annealing studies show that the enhanced size effects are due to the presence of a large concentration of structural defects in the films. The observed behavior may be understood by assuming the large concentration of point and/or line defects to decrease with film thickness and with annealing as well as deposition of films at elevated temperatures. The thermopower data suggest strongly that the large concentration of defects causes distortion of the Fermi surface and thereby a strong energy dependence of the mfp or relaxation time at the Fermi surface.

Thermoelectric power of thin polycrystalline metal films in an effective mean free path model

Abstract: Starting from an effective Fuchs-Sondheimer conduction model, the theoretical expression for the thermoelectric power of polycrystalline metal films is derived. From the approximate expression for thick films, a procedure is proposed to determine the variation in the electronic mean free path.

The size effect and the temperature coefficient of resistance in thin films

Abstract: An expression for the temperature coefficients of resistance of thin metal films is derived wherein size effects, thermal strain and difference in the thermal expansion coefficients between film and its substrate are taken into account.