Atomic dynamics of In nanoclusters on Si ( 100 )

Using scanning-tunneling microscopy and first-principles total-energy calculations, we have considered the structural properties of the so-called doped clusters formed by depositing additional $0.05$ monolayer of In onto the $4\ifmmode\times\else\texttimes\fi{}3$-periodicity magic-cluster array in the $\mathrm{In}∕\mathrm{Si}(100)$ system. Low-temperature STM observations have revealed that most of the doped clusters have an asymmetric shape. According to the total-energy calculations, these clusters have plausibly ${\mathrm{Si}}_{6}{\mathrm{In}}_{8}$ composition. In such a cluster, one of the In atoms is mobile and can hop between four equivalent sites within a cluster. The hopping between sites, located in the different $2a\ifmmode\times\else\texttimes\fi{}3a$ halves of the cluster, is characterized by the barrier of about $0.7\phantom{\rule{0.3em}{0ex}}\mathrm{eV},$ and this hopping becomes frozen at $55\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. In contrast, the hopping between the neighboring sites within the same cluster half persists up to very low temperatures, as the barrier height here is an order of magnitude lower. Due to the above structural properties, the doped asymmetric ${\mathrm{Si}}_{6}{\mathrm{In}}_{8}$ cluster can be treated as a promising switch, logic gate, or memory cell of the atomic-scale size.