Germanium-catalyzed hierarchical Al(2)O(3) and SiO(2) nanowire bunch arrays.

Germanium (Ge), a Group IV semiconductor, was recently used as an effective catalyst to grow individual, single-crystalline ZnO nanowires through a vapor-liquid-solid (VLS) process [Pan et al., Angew. Chem., Int. Ed., 2005, 44, 274-278]. Here, we show that Ge can also act as an efficient catalyst for the large-scale growth of highly aligned, closely-packed polycrystalline Al(2)O(3) and amorphous SiO(2) nanowire bunch arrays. The Ge-catalyzed Al(2)O(3) and SiO(2) nanowire growth exhibits many interesting growth behaviors including (i) multiple nanowire growth catalyzed by one micrometer-size Ge particle, (ii) branching growth and (iii) batch-by-batch growth. These growth phenomena are distinct from the conventional Au-catalyzed nanowire growth but are analogous to the recently reported Ga-catalyzed SiO(2) nanowire growth. It is anticipated that many other oxide nanowires and nanowire assemblies can be synthesized through the Ge-catalyzed VLS process. The Ge-catalyzed Al(2)O(3) and SiO(2) nanowires emit strong visible light under ultraviolet light excitation.