Buffer layer-assisted growth of Ge nanoclusters on Si

In the buffer layer-assisted growth method, a condensed inert gas layer of xenon, with low-surface free energy, is used as a buffer to prevent direct interactions of deposited atoms with substrates. Because of␣an unusually wide applicability, the buffer layer-assisted growth method has provided a unique avenue for creation of nanostructures that are otherwise impossible to grow, and thus offered unprecedented opportunities for fundamental and applied research in nanoscale science and technology. In this article, we review recent progress in the application of the buffer layer-assisted growth method to the fabrication of Ge nanoclusters on Si substrates. In particular, we emphasize the novel configurations of the obtained Ge nanoclusters, which are characterized by the absence of a wetting layer, quasi-zero dimensionality with tunable sizes, and high cluster density in comparison with Ge nanoclusters that are formed with standard Stranski-Krastanov growth methods. The optical emission behaviors are discussed in correlation with the morphological properties

Electrical transport in ultrathin Cs layers on Si(001)

Electrical transport in ultrathin Cs layers on Si(001) has been studied combining macroscopic conductivity measurements with low-energy electron diffraction, energy loss spectroscopy, and measurements of the work function. At temperatures around 150K, growth of the first three atomic layers proceeds layer-by-layer. The completion of each layer correlates with stepwise increases of the surface sheet conductance with coverage. Calibrating the Cs coverage by combined conductivity and work function measurements, the areal density of a single atomic layer is determined as 0.5 monolayers (3.39×1014cm-2). Electron spectroscopy reveals a semiconductor-metal transition of the surface upon completion of the first atomic layer, which correlates with the onset of a macroscopically measured sheet conductance in the 10-5Ω-1 range. While the conductance can be ascribed to electrical transport within surface states, its dependence on temperature indicates an activation barrier, which, most likely, is due to domain boundaries. At coverages of one monolayer and beyond, the Cs Si(001) surface exhibits a high metal-like conductance in the 10-3Ω-1 range. © 2005 The American Physical Society