By means of scanning tunneling microscopy and spectroscopy we studied the surface evolution of Si(111)-(7×7) induced with nickel followed by annealing at specified temperatures (400, 600, and 800˚C). Nickel evaporation resulted with 0.05 ML and 0.2 ML coverage was carried out at room temperature with the use of solid phase epitaxy. The characteristic phase formations occurred after gradual annealing the sample depending on the amount of deposited material. At very low coverages scanning tunneling microscopy observation showed two types of ring clusters (1×1 -RC and clusters of the √(19)×√(19) reconstruction) accompanied by the Si(111)-(7×7) surface reconstruction. All above-mentioned phases appeared in that order as the annealing temperature increased. Deposition of about 0.2 ML of Ni followed by annealing at 600˚C formed extended regions of 1×1 nickel silicide reconstruction. Very clear, extended regions of √(19)×√(19) reconstruction appeared when annealed to 800˚C. The electronic properties of observed structures have been studied by the scanning tunneling spectroscopy. Spectroscopy curves measured above certain surface formations revealed the presence of the Si rest atom, NiSi, and NiSi_2 local density of electronic states.
STM images of ZnS:Mn,Cu thin films and spatially resolved current-voltage characteristics are shown. The results make possible to estimate the morphology and conductivity distribution with nanometer resolution.
We carried out scanning tunneling microscopy/spectroscopy studies of Bi_2Te_3 surface, which, to the best of our knowledge, had not been attempted so far. We got images of surface of the material in many scales from micrometers to nanometers, which showed a layered structure of Bi_2Te_3, with many monoatomic terraces. We found agreement between measured heights and corresponding bulk crystal structure derived from X-ray data. In nanoscale we obtained an atomic resolution. Using scanning tunneling spectroscopy we carried out examination of the electronic structure. We observed different I-V characteristics and contrast on current imaging tunneling spectroscopy maps on non equivalent terraces. The dI/dV (~ density of states) curves referred to those terraces were compared with theoretically calculated by Larson et al. density of states derived from Bi p and Te-1 p orbitals. The analysis of our results allowed us to distinguish bismuth from tellurium planes.
We have investigated the growth of Ag nanoparticles deposited on Si(111), H/Si(111)-(1×1) and Bi_2Te_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^{-10} 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.
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