Structure of nanocrystalline Re–Si thin film composites and their unusual thermoelectric properties

Abstract

The structure of nanocrystalline rhenium-silicon composite ReSi x films with 1.4ϽxϽ2.2 has been studied as a function of the time by means of high temperature x-ray diffraction and transmission electron microscopy. Simultaneously, the thermoelectric transport properties were measured during the heat treatment. The nanocrystallization was achieved by annealing of amorphous films deposited onto oxidized Si wafers by magnetron cosputtering. The crystallization process is characterized by a decreasing average crystallite size in the range between 7 and 19 nm. An unknown mechanism limits the grain growth after reaching a maximum size, which decreases with increasing Si content. In the final state the films contain only two phases: the amorphous phase and the nanocrystalline ReSi 1.75 phase. The electrical conductivity and the thermoelectric power of these thin film composites show nonmonotonic dependence on the volume fraction of the nanocrystalline phase and depend on different parameters, which suggests a way to optimize the thermoelectric efficiency.

Energy filtering enhancement of thermoelectric performance of nanocrystalline Cr1− Si composites

“…Since the crystallization is characterized by an incubation time, t inc (see Fig. 3), which is strongly dependent on annealing temperature [14], the peculiarity in the ρ(T ) and S(T ) dependences are observed at a higher temperature in comparison with XRD.…”

“…The state of the film composite in the course of its transformation from amorphous to NC composite was controlled by means of the in-situ transport measurements -simultaneous measurements of electrical resistivity (ρ = 1/σ) and S. Standard DC 4 points configuration was used in the resistivity measurements, while differential method was utilized for thermopower [13]. Transmission Electron Microscopy and X-Ray Diffraction were utilized for structural characterization of the samples [14].…”

Nanostructure and thermoelectric properties of ReSi 2±x thin films

“…The mean grain size versus annealing time shows an unexpected behaviour. Because of a preferred growth of large grains up to 100 nm at the beginning of the crystallisation and the formation of smaller grains on later annealing stages [8], the grain size decreases with increasing annealing time. The time up to which the larger grains are growing is limited to about 30 min.…”

“…Therefore, results of X-ray investigations after long annealing times [8] have been used for calibrating the ordinate. On the other hand, measurements of the thermopower S have been carried out as function of the annealing time t in He atmosphere.…”

Synthesis and Characterization of Bi2Se3 Thermoelectric Nanopowders

“…Since 1993, when Hicks and Dresselhaus [1] reported that the dimensionless thermoelectric figure of merit ZT (= 2 T/ , here , , and are the electrical conductivity, the Seebeck coefficient, and the thermal conductivity of the material, respectively, and T is absolute temperature) of a material can be markedly increased as its dimensionality is reduced, the preparation and thermoelectric properties of nanostructured materials have attracted more and more attention [2][3][4][5][6][7][8][9]. For example, Lin et al [2,3] studied the transport properties of Bi and Bi 1-x Sb x nanowires and found that the Seebeck coefficient of Bi nanowires and the electrical conductivity of Bi 1-x Sb x nanowires both dramatically increased as the diameter of the corresponding nanowires decreased.…”