One of the most promising methods for combining these two components is multilayer stacking of biotin/self assembled monolayer (SAM)/Au/Si. In this method, the boundary Au/Si should be studied. We observed and revealed the boundary physics between Au and Si under in-situ transmission electron microscope (TEM) observation.
A MEMS device was fabricated with bulk micromachining and a novel three-dimensional focused ion beam (FIB) for the formation of Au/Si boundary in TEM. The MEMS device has two opposing tips; one is a silicon movable tip and the another is a gold fixed tip. The movable tip is moved towards the fixed tip using MEMS electrostatic actuators inside the TEM and a bias voltage was applied between the tips.
The resulting electrical short formed quite a lot of gold nano clusters of less than 10 nm in diameter on the silicon tip when the gap between the tips was less than 5 nm. Then, the boundary between Au/Si was obtained.
One of the gold nanoclusters attached on the silidon surface was observed using TEM at room temperature conditions. The gold nanocluster was not crystalline in structure due to the interdiffusion between gold and silicon, though it was initially crystalline.
The boundary was moved into silicon and the height of the nanocluster decreased. The gold diffusion constant towards silicon at room temperature was compared among previous bulk data at high temperature. This room temperature data also matched with the other ones, resulting in the similar activation energy.
Gold diffusion into silicon was not different between bulk and nano scale. It is also the same characteristic in temperature from room temperature to one thousand degree in celcius. From this result, diffusion itself is phenomenon at atomic scale and the mechanism is same from low temperature to high temperature. Then, you have to consider about this diffusion phenomenon when you build up the nano systems using the biotin/SAM/Au/Si multilayer stacking method.