Porous Alumina Template-directed Growth Of Ge Nanowires By Chemical Vapor Deposition

Due to their surprising physical and chemical properties, nanomaterials have significant potential applications in materials' intelligentization, highly integration of components, highly density storage and ultra fast transportation. Therefore, the research on nanomaterials is flourishing, especially the research on semiconductor nanowires, for instance, carbon nanotube, GaN and ZnO nanowires arrays, Si nanowires and Ge nanowires et al.In this paper, we first presented a comprehensive review of current research status of Ge nanowires preparation and characterizations. On the basis of our low pressure chemical vapor deposition system with the background of ultra high vacuum, we conducted a detailed study of the growth of Ge nanowires by porous alumina templates and achieved some encouraging results. We could realize the controllable growth of Ge nanowires with the constraint of porous alumina template, and hold the potential of synthesizing Ge nanowires arrays. This work has not been reported yet, that is to say, it is innovative.The main work include two contents as following:1. We synthesized the uniform and regular alumina templates with the controllability of the diameters and depth of the pores by bi-anodization.2. For the first time, we reported the growth of Ge nanowires by low pressure chemical vapor deposition combined with the porous alumina templates, and discussed the influence of the growth parameters on Ge nanowires, and the growth mechanism of Ge nanowires.The temperature determined the crystal structure of Ge nanowires during deposition. When the temperature was as low as 600C, the Ge nanowires were tetragonal structured. When the temperature was up to 740C, the Ge nanowires had the cubic structure. When the temperature was between the above, the Ge nanowireswere the crystal consisting of tetragonal and cubic structures.During chemical vapor deposition, the flux of germane had the influence on the morphology of the Ge nanowires. Only with the proper flux of germane, the pores of the alumina template were not blocked, and the growth of Ge nanowires always followed the crystal vapor-liquid-solid growth mechanism, and the uniform Ge nanowires were achieved with the constraint of the templates.The gold film deposited on the backside of the alumina template was used as catalyst. And the Ge nanowires growing at 660℃ were polycrystal composed of tetragonal structure and cubic structure with the dominance of tetragonal structure. The Ge nanowires were around 30nm in diameter and 600nm in length. It is expected that the growth of Ge nanowires proceeded basing on the crystal vapor-liquid-solid (VLS) growth mechanism and the constraint of the alumina template.The synthesis of Ge nanowires by LPCVD combined with alumina template is a newly practicable method, capable of controlling diameter and length of single Ge nanowires and Ge nanowires arrays.