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Ritu Suri

Bio: Ritu Suri 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 6, co-authored 7 publications receiving 195 citations.

Papers
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Journal ArticleDOI
TL;DR: In this paper, a critical analysis of the observed size effects 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).
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.

89 citations

Journal ArticleDOI
TL;DR: In this article, the activation energy for the associated recovery process has been obtained from the observed isothermal and isochronal changes in the resistance of the films, which increases from a value of 0.7 eV at 2000 A to 1.4 EV at 180 A for room-temperature-deposited Cu 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...

38 citations

Journal ArticleDOI
TL;DR: In this article, the thickness dependence of the TEP of polycrystalline and epitaxially grown copper films of thickness 100-5000 A has been measured and shown to be independent of the resistivity and its temperature coefficient.
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

31 citations

Journal ArticleDOI
TL;DR: In this article, the structural defects in thin copper films were used to obtain the contribution to thermoelectric power by the structural defect in the films, which is comparable in magnitude to the bulk value.
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.

15 citations

Journal ArticleDOI
TL;DR: In this article, the effect of vacancies and dislocations on Hall coefficient and thermoelectric power of copper films has been deduced from annealing behaviour of various transport properties.
Abstract: Effect of vacancies and dislocations on Hall coefficient (RH) and thermoelectric power (TEP) of copper films has been deduced from annealing behaviour of various transport properties. The large contributions of these defects may be attributed to variations in the density of hole-like states and/or the energy dependence of conductivity (at the Fermi surface), caused by changes in the extent and/or degree of curvature of the necks at Fermi surface.

10 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, Namba's model that uses the measured surface roughness provides the best description of the resistivity-thickness behavior in sub-40-nm thick Cu films.
Abstract: Ultrathin Cu films with thicknesses d between ∼10 and 40 nm were thermally evaporated onto ∼500-nm thick SiO2 on Si(100) substrates in an ultra high vacuum (UHV) chamber with a base pressure of 5×10−10 torr. The sheet resistance R (Ω/□), was measured in situ at different film thicknesses by a collinear four-point probe. The infinite R at d<10 nm suggested that the film consisted of discontinuous islands at these thicknesses. The R-value dropped rapidly by more than an order of magnitude when the thickness was increased from 10 to 15 nm, indicating the coalescence of islands. Further increases in d resulted in the R value gradually leveling off at 0.65±0.01 Ω/□, corresponding to a resistivity ρ of 2.67 μΩ cm at d∼41 nm. The ρ–d data were fitted by models that assume surface, interface and grain boundary scattering to be dominant mechanisms for the thickness dependence on resistivity. Models that do not include surface roughness do not fit our data in the sub-15-nm thick Cu films regime. The surface roughness was measured by atomic force microscopy (AFM). Our analysis shows that Namba's model that uses the measured surface roughness provides the best description of the resistivity-thickness behavior in sub-40-nm thick Cu films.

213 citations

Journal ArticleDOI
TL;DR: The 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.
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.

209 citations

Journal ArticleDOI
TL;DR: In this paper, a critical analysis of the observed size effects 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).
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.

89 citations

Journal ArticleDOI
TL;DR: In this paper, the theoretical expression for the thermoelectric power of polycrystalline metal films is derived from an effective Fuchs-Sondheimer conduction model, and a procedure is proposed to determine the variation in the electronic mean free path.
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.

64 citations

Journal ArticleDOI
F Warkusz1
TL;DR: In this article, 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.
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.

59 citations