S. N. Grigorov

Bio: S. N. Grigorov is an academic researcher from National Technical University. The author has contributed to research in topics: Thermoelectric effect & Seebeck coefficient. The author has an hindex of 6, co-authored 11 publications receiving 226 citations.

Quantum size effects in PbSe quantum wells

Abstract: In PbSe epitaxial thin films grown by thermal evaporation on KCl(001) substrates and covered with an EuS protective layer, oscillatory dependences of the galvanomagnetic and thermoelectric properties (electrical conductivity σ, the Hall coefficient RH, charge carrier mobility μ, and the Seebeck coefficient S) on the PbSe layer thickness d (3

Quantum-size effects in n-type bismuth thin films

Abstract: Oscillatory thickness dependences of the electrical conductivity, Hall coefficient, charge carrier mobility, and Seebeck coefficient were obtained at room temperature for n-type thin Bi films (d=3–300 nm) fabricated by the thermal evaporation of a bismuth crystal in a vacuum and deposition on mica substrates at 380 K. We attribute this oscillatory behavior to quantum-size effects, which are observable when the electron mean-free path and Fermi wave length exceed the film thickness d.

Oscillatory behaviour of the transport properties in PbTe quantum wells

Abstract: Oscillatory behaviour was detected in the dependences of the transport properties (electrical conductivity, Hall coefficient, charge carrier mobility, Seebeck coefficient and thermoelectric power factor) on the PbTe layer thickness d (d = 2–200 nm) in (001) KCl/PbTe/EuS quantum well (QW) structures at room temperature. The non-monotonic character of these dependences is attributed to quantum size effects, which manifest themselves in PbTe QWs at sufficiently small values of d. The positions of the extrema in the thickness dependences of the transport properties shift with changing electron concentration in PbTe QWs.

Effect of oxidation on the thermoelectric properties of PbSe thin films

Abstract: The effect of oxidation at room temperature on the thermoelectric properties of PbSe/KCl (001) thin films prepared by thermal evaporation was investigated. The dependences of the electrical conductivity, the Hall coefficient, charge carrier mobility, and thermopower on the PbSe layer thickness (d=4–200 nm) were obtained. An inversion of the sign of the dominant carriers from n to p at d∼80 nm was observed under decreasing d. The d dependences of the thermoelectric properties were interpreted, taking into consideration the oxidation processes at the film/air interface within the framework of models considering both n-type and p-type carriers.

Quantum spin Hall effect and enhanced magnetic response by spin-orbit coupling.

Abstract: We show that the spin-Hall conductivity in insulators is related to a magnetic susceptibility representing the strength of the spin-orbit coupling. We use this relationship as a guiding principle to search real materials showing quantum spin-Hall effect. As a result, we theoretically predict that two-dimensional bismuth will show the quantum spin-Hall effect, both by calculating the helical edge states, and by showing the nontriviality of the ${Z}_{2}$ topological number, and propose possible experiments.

Enhancement of the thermoelectric properties in nanoscale and nanostructured materials

Abstract: Thermoelectric materials can be used for solid state power generation and heating/cooling applications. The figure of merit of thermoelectric materials, ZT, which determines their efficiency in a thermoelectric device, remains low for most conventional bulk materials. Nanoscale and nanostructured thermoelectric materials are promising for increasing ZT relative to the bulk. This review introduces the theory behind thermoelectric materials and details the predicted and demonstrated enhancements of ZT in nanoscale and nanostructured thermoelectric materials. We discuss thin films and superlattices, nanowires and nanotubes, and nanocomposites, providing a ZT comparison among various families of nanocomposite materials. We provide some perspectives regarding the origin of enhanced ZT in nanoscale and nanostructured materials and suggest some promising and fruitful research directions for achieving high ZT materials for practical applications.

Enhanced thermopower in PbSe nanocrystal quantum dot superlattices.

Abstract: We examine the effect of strong three-dimensional quantum confinement on the thermopower and electrical conductivity of PbSe nanocrystal superlattices. We show that for comparable carrier concentrations PbSe nanocrystal superlattices exhibit a substantial thermopower enhancement of several hundred microvolts per Kelvin relative to bulk PbSe. We also find that thermopower increases monotonically as the nanocrystal size decreases due to changes in carrier concentration. Lastly, we demonstrate that thermopower of PbSe nanocrystal solids can be tailored by charge-transfer doping.

p-Type PbSe and PbS Quantum Dot Solids Prepared with Short-Chain Acids and Diacids

Abstract: We show that ligand exchange with short-chain carboxylic acids (formic, acetic, and oxalic acid) can quantitatively remove oleic acid from the surface of PbSe and PbS quantum dot (QD) films to yield p-type, carboxylate-capped QD solids with field-effect hole mobilities in the range of 10−4−10−1 cm2 V−1 s−1. For a given chemical treatment, PbSe devices have 10-fold higher mobilities than PbS devices because of stronger electronic coupling among the PbSe QDs and possibly a lower density of surface traps. Long-term optical and electrical measurements (i) show that carboxylate-capped PbSe QD films oxidize much more gradually in air than do thiol-capped PbSe films and (ii) quantify the slower and less extensive oxidation of PbS relative to PbSe QDs. We find that whereas the hole mobility of thiol-capped samples decreases continuously with time in air, the mobility of carboxylate-capped films first increases by an order of magnitude over several days before slowly decreasing over weeks. This behavior is a conse...