Surface chemistry study of Mn-doped germanium nanowires

Single crystal germanium nanowires have been grown by vapour-liquid-solid deposition onto silicon oxide substrates with Au catalyst nanoparticles. They have been doped by two different techniques: Ge and Mn co-evaporation during growth and post-growth Mn implantation. Scanning electron microscopy images show that Mn-implanted nanowires have a lower surface density and a smaller average diameter (18.8 nm) than the un-doped ones and those Mn doped by co-deposition. The effectiveness of Mn doping has been verified by X-ray photoemission spectroscopy and by energy-dispersive X-ray measurements, indicating in the two cases significant Mn atomic concentration in the nanowire. X-ray diffraction indicates that the nanowires are single crystals and that they do not contain precipitates of Mn extrinsic phases. Both SEM and XPS experimental evidences are in line to indicate that the Mn doping by ion implantation is preferable with respect to that one performed by co-evaporation as it reduces the thickness of the outer oxide sheath of the nanowires and their diameter. (C) 2008 Elsevier B. V. All rights reserved.