Effects of hydrogen on Au migration and the growth kinetics of Si nanowiresElectronic supplementary information (ESI) available: Fig. S1: HAADF images and EDX analysis of SiNW (10 : 50 sccm). Fig. S2: HR-TEM image and FFT image of SiNW (10 : 200 sccm). See DOI: 10.1039/c0ce00239a

Silicon nanowires (SiNWs) were synthesized by means of a Vapor-Liquid-Solid (VLS) procedure using Au as a catalyst in a UHV-CVD system. The growth of the SiNWs was critically dependent on the flow rate of H 2 . In our system, the nanowires showed novel features such as faceting phenomenon and the migration of Au atoms on the lateral surface, which were dependent on the flow rate of H 2 . In particular, Au that diffused from the catalyst tip to the facet edge was transformed into Au clusters, resulting in the formation of numerous Au stripes that entirely surrounded the pillar during the growth process. A one step synthesis of branched SiNWs can be achieved via the presence of Au clusters at the lateral surface under conditions of a high flow rate of H 2 . The growth kinetics of SiNWs as a function of H 2 flow rate lead to the conclusion that the influence of the effect of hydrogen is a major factor in controlling the growth of SiNWs under conditions of a low partial pressure of silane. Aligned Au stripes can be seen in hexagonal pillar-shaped SiNWs at projected facets grown under growth condition with the flow rate ratio of SiH 4 to H 2 .