Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008

There is much interest in fabricating metallic contacts on semiconductor surfaces by a straightforward class of electrochemical reactions called galvanic displacement [1,2]. The chemistry is carried out via contact of the desired semiconductor with the metal ion solution (generally aqueous); the semiconductor acts as the source of electrons, reducing the metal ions in situ to metal. In the case of gold deposition on silicon, we have evidence that the growth of Au nanoparticles on silicon is epitaxial [3]. In order to better understand the nature of these interfaces, we carried out a series of plan-view and cross-section transmission electron microscopy (TEM) studies. TEM samples were prepared by mechanical grinding followed with ion milling at cryogenic temperatures (below -100°C). TEM images and diffraction patterns were recorded using a 200kV JEOL 2200FS TEM/STEM instrument. In order to complement the work described above on flat silicon, we have also investigated Au nanoparticles deposited on Si nanowires. Au particles have a strong tendency to grow on certain facets, such as (110) for particles on a <112> nanowire; this is demonstrated in Fig. 4. By using a nano beam probe, TEM images and electron diffraction patterns were acquired from the interface area, allowing us to measure relative orientation of Si and Au lattices. While straightforward to carry out, the underlying mechanism of galvanic deposition is complicated and thus the reason for the selectivity is not yet known at this time [2]; nevertheless, the preferential growth may be dictated by the interfacial interaction of the Au/Si epilayers. More control experiments and theoretical calculations are under way to further investigate this issue [6].