| The thermally-activated coexistence of two diffusion mechanisms, adatom jump and exchange, is a phenomenon that has important potential application in fabrication of quantum dot based devices. If one can initiate the occurrence of a particular diffusion mechanism by changing the temperature, then it is possible to control the moment when an adatom is incorporated into the surface layer. The buried adatom could then serve as a nucleation center for growth of a nanostructure.;This dissertation shows the first experimental evidence for the temperature-activated coexistence of two surface diffusion mechanisms, the adatom jump and adatom exchange, observed in a W on W(100) system. The adatom exchange was identified as the primary diffusion mechanism, and it is activated on a time scale of seconds at temperatures around 650 K. The occurrence of the secondary diffusion mechanism, adatom jump, was observed on a time scale of seconds at temperatures around 700 K. The experiments were conducted using a Field Ion Microscope (FIM) under Ultra-High Vacuum (UHV) conditions (∼ 10-11 Torr). The activation energy for the exchange in a W on W(100) system was found to be 1.6 +/- 0.24 eV. For the jump, the activation energy was estimated as ∼2.1 eV. These values are in very good agreement with results from Density Functional Theory (DFT) calculations. |
