Scanning confocal Raman spectroscopy of silicon phase distribution in individual Si nanowires

Silicon nanowires were grown by gold enhanced CVD self-assembly technique. In the Raman spectra of nanowires, along with phonon band of cubic diamond phase (Si I) at near 521 cm^-1, additional phonon bands at 516 and 496 cm^-1 related to hexagonal wurtzite phase (Si IV) were observed. Spatial distribution of intensities of these Raman bands around single nanowire reveals that both phases coexist along the wire length, even if with variable contributions. In addition, there is a strong alternating shift of Si I phonon band between the two ends of the nanowire (the one end is tipped with Au and the other end is the one that was connected to the substrate). Additionally, reversibility of Si IV phase transformation during laser heating at temperatures about 100 ºC was found. The intensity of Si IV band strongly depends on exciting power in the range of 0.05 to 1 mW/µm². The observed phenomena are discussed in relation with peculiarities of nanowire growth. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)