Raman analysis of gold catalyst vapor liquid solid germanium nanowires
Résumé
Germanium nanowires (GeNWs) were synthesized in a
low pressure chemical vapor deposition reactor (LPCVD)
using a vapor-liquid-solid process (VLS). In this work,
the focus is put on the characterization of these GeNWs
using scanning electron microscopy (SEM) combined
with Raman spectroscopy. In particular, NWs with conical
shape grown at a moderate temperature (320 °C) were
investigated in terms of the intensity measured for the
Ge-related Raman line. The two main observations, discussed
in this paper, are the anomalous magnitude of this
line, as compared to measurements under the same conditions
on a Ge(100) substrate, and the oscillations observed
when the Raman line intensity is measured while
scanning the laser beam along the axis of the conical
shaped NWs, from the tip to the bottom. These effects
are discussed involving the fact that optical modes appear
in such NWs (both for the incident and Raman scattered
light) when conditions on the diameter, the laser excitation
wavelength, and substrate (on which the NWs are
transferred after growth) are fulfilled. Taking into account
these specific optical modes, the effects observed
can be explained.