Thermoelectric and Magnetic Nanowires

Abstract

Approximately 90 per cent of the world’s power is generated by heat engines that use fossil fuel combustion as a heat source and typically operate at 30–40 percent efficiency, such that roughly 15 terawatts of heat is lost to the environment (Hochbaum et al., 2008). Thermoelectric modules could potentially convert part of this low-grade waste heat to electricity (Lecher, 1905). In addition, it can also be used for thermoelectric cooler instead of Freon (succedaneum for Freon) and will not cause any environmental pollution (Thompson, 1932). According to solid state physics, semiconductor, semimetal, and some alloys are ideal thermoelectric material, and the efficiency of the thermoelectric materials depends on the thermoelectric figure of merit ZT (ZT=TS2σ/κ): a function of the absolute temperature (T), of the Seebeck coefficient (S, or thermoelectric power), and of the electrical (σ) and thermal conductivities (κ) (Bucherer, 1900). Unfortunately, over the past ten decades it has been challenging to increase ZT for bulk thermoelectric materials, which are difficult to be used widely due to the low thermoelectric efficiency (Bell, 2008). Since the 1990s, Q1D nanostructures, particularly for NWs, have made great progress, in which many conventional materials have been made into the structural and morphology of NWs and then the unique properties appear (Masuda et al.,1997; Li et al., 1998; Ling et al., 1999; Gudiksen & Lieber, 2000; Wu et al., 2002; Gao et al., 2003; Lee et al., 2006; Zhou et al., 2008; Zhou et al., 2009; Zhou et al., 2010; Zhou et al., 2011). Under the one-dimensional, with improvement of the system of states near the Fermi energy density, the Seebeck coefficient of the system is improved. Simultaneously, with scaling down to a certain size, phonon scattering is enhanced without affecting the transmission of electronic. So thermoelectric NW shows a quite higher thermoelectric figure of merit ZT and the interest in thermoelectric NWs has been stimulated greatly by the discovery of its excellent thermoelectric properties (Ying, J. & Heremans,1998). In order to produce a variety of thermoelectric NWs, some new methods such as solvothermal and electro-deposition have been employed (Jin et al., 2004; Li, 2003; Li, 2006). Here we review the research status of NWs of thermoelectric materials, which include elements, alloys, and the development of thermoelectric super-lattice NWs will be also introduced. NW materials show excellent characteristics, which exhibit different property compared to bulk materials. In addition, as for magnetic NW section, it is found that magnetic NWs have a significant magnetic anisotropy and exhibit a large coercivity and a large remanence ratio when magnetization direction along NWs. Because of these unique low-dimensional properties,