Low Temperature Growth of Germanium Oxide Nanowires by Template Based Self Assembly and their Raman Characterization

We have synthesized ∼100 nm diameter GeO₂ nanowires by electrodepositing Ge within the nanopores of anodized alumina films on aluminium substrates from an electrolyte, and then oxidizing the nanowires in air at ambient temperature for 24 hours, to form GeO₂ nanowires. These nanowires have been imaged with scanning electron microscopy that shows excellent control over the diameter which varies by less than 10%. The nanowire length is more variable, with the maximum length being about 3 μm. They are vertically standing nanowires surrounded by alumina with the top exposed to air and the bottom in contact with the aluminum substrate. Plasmons from the aluminum substrate couple into the nanowires and affect their phonon modes. The plasmon coupling changes the phonon energies and spawns new phonon modes. The Raman spectra of the nanowires show the usual low wavenumber peaks characteristic of phonons in GeO₂ nanowires (with slight wavevector shifts), but we also observe two unusual high wavenumbers peaks that could possibly be due to phonon-plasmon coupling.