Temperature dependence of Raman spectra for individual silicon nanowires

The temperature dependence of the Stokes first-order optical phonon frequency has been measured for individual silicon nanowires with diameters between 33 to 180 nm in the temperature range of 20 to 300 degrees C. The nanowires were synthesized via both the vapor-liquid-solid method and electrochemical etching of bulk silicon. Significant laser-induced local heating was avoided by using a laser power of 0.5 mW or less, corresponding to fluxes of <= 0.7 mW/mu m(2). For both types of nanowires the slope of Raman frequency vs temperature closely matches the value of bulk Si, (d omega/dT) = - 0.022 +/- .001 cm(-1) degrees C(-1), across the entire diameter range, indicating no change in lattice anharmonicity. These results have important implications for understanding nanowire lattice thermal conductivity and extending the domain for Raman thermometry of silicon nanostructures.