SYSTEMATIC INVESTIGATIONS OF NANOSTRUCTURING BY SCANNING-TUNNELING-MICROSCOPY

Scanning tunneling microscopes allow the formation of structures, by t he application of voltage pulses between tip and sample whose dimensio ns are in the range of some nanometers. Systematic investigations have been carried out on the Si(111)-7x7 using W and Au tips in order to b etter understand the physics of the underlying deposition process. The refore the voltage pulse, current, and z-piezo voltage were measured a s a function of time. Above a threshold voltage, which depends on the pulse duration and the tunneling current, too, hills were created in t he range between 5 and 25 nm. The surface structure was preserved up t o the hills. Further, there is a linear dependence of the diameter on the pulse amplitude and pulse duration. A fit of the data gives a slop e of (0.1+/-0.02) nm/s for tungsten tips and (0.45+/-0.14 nm/s) for go ld tips, respectively. In addition, there is also a logarithmically de pendence of the diameter upon the tunneling current for both tip mater ials. The results obtained are discussed with reference to the formati on mechanisms published to date. None provide a satisfying explanation of our results. (C) 1996 American Vacuum Society.