Nanoscale heat transfer - from computation to experiment

Heat transfer can differ distinctly at the nanoscale from that at the macroscale. Recent advancement in computational and 5 experimental techniques has enabled a large number of interesting observations and understanding of heat transfer processes at the nanoscale. In this review, we will first discuss recent advances in computational and experimental methods used in nanoscale thermal transport studies, followed by reviews of novel thermal transport phenomena at the nanoscale observed in both computational and experimental studies, and discussion on current understanding of these novel 10 phenomena. Our perspectives on challenges and opportunities on computational and experimental methods are also presented.University of Notre Dame (Startup fund)United States. Dept. of Energy. Office of Basic Energy Sciences (Solid-State Solar-Thermal Energy Conversion Center

Raman spectroscopy of Bi-Te thin films

The deposition of micro- and nanocrystalline bismuth telluride thin films with tailored structure and composition is of interest in view of improving the well-known material thermoelectric properties. Only a few works exist that discuss Raman scattering of Bi2Te3 crystals and films, while a Raman characterization of other phases, i.e. other lesser known compounds of the Bi-Te system, such as tsumoite (BiTe) and pilsenite (Bi4Te3), is still completely lacking. We here present a Raman investigation of Bi-Te polycrystalline thin films with controlled structure (stoichiometry and growth orientation), morphology and phase composition, produced by nanosecond pulsed laser deposition. Interpretation of Raman spectra from Bi-Te films was supported by scanning electron microscopy, energy dispersive spectroscopy (EDS) and X-Ray diffraction measurements, together with the predictions of the group theory. In this way, the first Raman characterization of Bi-rich phases (namely BiTe and Bi4Te3) has been obtained. For Bi-Te compositions characterized by a high Bi or Te content, Raman spectra reveal that segregation of elemental Bi or Te occurs

Enhanced thermoelectric properties of SnSe thin films grown by pulsed laser glancing-angle deposition

SnSe single crystals have been demonstrated to possess excellent thermoelectric properties. In this work, we demonstrate a grain size control method in growing nanocrystalline SnSe thin films through a glancing angle pulsed-laser deposition approach. Structural characterization reveals that the SnSe film deposited at a normal angle has a preferred orientation along a axis, while by contrast, the SnSe film deposited at an 80° glancing angle develops a nanopillar structure with the growth direction towards the incident atomic flux. The glancing angle deposition greatly reduces the grain size of the thin film due to a shadowing effect to the adatoms, resulting in significantly increased power factor for more than 100%. The maximum Seebeck coefficient and power factor are 498.5μV/K and 18.5μWcm−1K−2, respectively. The enhancement of thermoelectric property can be attributed to the potential barrier scattering at grain boundaries owing to the reduced grain size and increased grain boundaries in the film. Given this enhanced power factor, and considering the fact that the nanopillar structure should have much lower thermal conductivity than a plain film, the zT value of such made SnSe film could be significantly larger than the corresponding single crystal film, making it a good candidate for thin film-based thermoelectric device