Axially graded heteroepitaxy and Raman spectroscopic characterizations of $Si1−xGex$ nanowires

We report the axially graded heteroepitaxy of $Si1−xGex$ nanowires, by the kinetic controls of the Au-catalytic decomposition of precursors during chemical vapor syntheses. Transmission electron microscope studies demonstrate that the relative composition of Si and Ge is continuously graded along the uniformly thick nanowires, sharing the same crystal structures with the continuously varying lattices. We also employed a confocal Raman scattering imaging technique, and showed that the local variations in Raman phonon bands, specific to Si and Ge alloying (⁠$νSi–Si$⁠, $νSi–Ge$⁠, and $νGe–Ge$⁠), can be spatially and spectrally resolved along the individual nanowires, within the spatial resolution of $∼500nm$⁠.