Gold-enhanced oxidation of silicon nanowires

Silicon nanowires are frequently grown involving a liquid gold droplet at their tips. Here we show that under certain circumstances the thermal oxidation of a silicon nanowire is drastically enhanced by the presence of this gold droplet. Such a gold-enhanced oxidation was observed in a temperature range from 1000 degrees C down to 250 degrees C. As a consequence, instead of the slow radial oxidation expected and desired for thinning the nanowires, a fast axial oxidation may occur catalyzed by the gold tip. This leads to a shrinking of the length of the Si nanowire and its replacement by a longer nanowire consisting of silicon dioxide. During this gold-enhanced oxidation process the gold droplet migrates from the tip to the base of the nanowire. Our experiments demonstrate that gold droplets lead to an enhanced dissolution of silicon during oxidation in the case that these remain in intimate contact with the Si nanowires.