Variable Temperature STM/STS Investigations of Ag Nanoparticles Growth on Semiconductor Surfaces

Abstract

We have investigated the growth of Ag nanoparticles deposited on Si(111), H/Si(111)-(1×1) and Bi 2 Te 3 substrates using a variable temperature scanning tunneling microscopy. These substrates are different as regards the model system for cluster and islands growth at the nanometer scale. Ag was evaporated onto the sample mounted at the scanning tunneling microscopy stage in vacuum of 10 - 1 0 Torr range during evaporation. The substrates were kept at different temperatures: -150°C, room temperature, and 300°C during the deposition process. In general, we have observed 3D growth mode up to several ML coverage. The density of clusters and their size were functions of the substrate's temperature during the deposition process - a higher density and a smaller size at -150°C were in opposition to the 300°C results - a lower density and a larger size. Low temperature depositions led to continuous layers above 10 ML coverage but the surface was covered by small Ag clusters of 1-2 nm in heights and 2-3 nm in diameters. The log-log graphs of height and projected diameter of Ag clusters revealed different slopes indicating different growth mechanisms at low and high temperatures. We obtained the value of n = 0.25 ′ 0.02, typical of the so-called droplet model of cluster growth, only at 300°C. Scanning tunneling spectroscopy measurements revealed clearly different I-V (and dI/dV vs. bias voltage) curves measured above clusters and directly above the substrate. In discussion, we compared our results to theoretically calculated density of states from other papers, finding conformity for partial density of states.