  Real time electron microscopy observation on morphological changes in gold
nano structures deposited on Si (100) surfaces as a function of annealing
temperatures has been reported. Two types of interfaces with the substrate
silicon were used prior to gold thin film deposition: (i) without native oxide
and on ultra-clean reconstructed Si surfaces and (ii) with native oxide covered
Si surfaces. For a \approx 2.0 nm thick Au films deposited on reconstructed
Si(100) surfaces using molecular beam epitaxy method under ultra high vacuum
conditions, aligned four-fold symmetric nanogold silicide structures formed at
relatively lower temperatures (compared with the one with native oxide at the
interface). For this system, 82% of the nanostructures were found to be nano
rectangles like structures with an average length \approx 27 nm and aspect
ratio of 1.13 at \approx 700{\deg}C. For \approx 5.0 nm thick Au films
deposited on Si (100) surface with native oxide at the interface, formation of
rectangular structures were observed at higher temperatures (\approx 850{\deg}
C). At these high temperatures, desorption of the gold silicide followed the
symmetry of the substrate. Native oxide at the interface was found to act like
a barrier for the inter-diffusion phenomena. Structural characterization was
carried out using advanced electron microscopy methods.
