Size effect of thermal conductivity of Si nanocrystals

• Published in: Solid state communications 2008-08, Vol.147 (7), p.274-277
• Main Authors: Cheng, Wei, Ren, Shang-Fen
• Format: Article
• Language: English
• Subjects: A. Nanostructures; A. Semiconductors; Condensed matter: structure, mechanical and thermal properties; D. Heat conduction; D. Phonons; Exact sciences and technology; Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves; Physics; Thermal properties of condensed matter; Thermal properties of small particles, nanocrystals, nanotubes; Transport properties of condensed matter (nonelectronic)
• ISSN: 0038-1098; 1879-2766
• DOI: 10.1016/j.ssc.2008.06.001

Thermal conductivities of spherical Si nanocrystals (NCs) are investigated with three different models: a macroscopic approximation, a semi-microscopic model that calculates the heat capacity of NCs with a microscopic Valence–Force–Field Model (VFFM), and a full microscopic description of phonon thermal conduction that calculate both heat capacity and phonon group velocity by the VFFM. The results are compared, and the advantages and limitations of each of these models are discussed. It is shown that for spherical Si NCs, the macroscopic approximation is quite good for NCs with a diameter larger than 1.33 nm. For smaller NCs, the VFFM predicts that the thermal conductivity increases quickly when the size decreases, opposite to the macroscopic approximation, and VFFM also predicts that the minimum of thermal conductivity for spherical Si NCs occurs at a diameter of 1.33 nm, the limit at which the macroscopic approximation applies.