Phonon confinement and laser heating effects in Germanium nanowires

We explore the combined effects of phonon confinement and local heating caused by laser beam absorption on the Raman spectra of Germanium nanowires of different diameters (60.3em0exnm, 70.3em0exnm, and 120.3em0exnm). The asymmetric broadening and downshifting of the first order Raman band is studied as a function of the average wire diameter and the local temperature of the nanowires. The basic phenomenological model with a modified confinement function incorporated with thermal effects is in good agreement with our experimental results. We also show the effects of the nanowire diameter, thermal conductivity of the underlying substrate, and the mediating substance (gallium in this case) on the local temperature of the nanowires.