Polarity dependence in pulsed scanning tunneling microscopy fabrication and modification of metal nanodots on silicon

Abstract

We have investigated the fabrication and modification of gold and aluminum nanodots on Si (100) with scanning tunneling microscopy (STM). Dots of similar to10 nm diameter were deposited on a Si (100) substrate by the application of a voltage pulse between a coated STM tip and the sample. The pulse duration required for dot formation is several orders or magnitude longer than on metal substrates, and depends both on dopant type and concentration. Modification of existing nanodots was carried out by the application of additional, larger voltage pulses. For Au, negative tip pulses increase the size of a Au dot, while positive pulses allow "erasure" of Au dots. In contrast, negative tip pulses result in erasing Al dots while positive pulses lead to enlarging Al dots. The sense of the polarity dependence for the fabrication and modification of dots is consistent with the calculated difference in threshold for field evaporation between Au and Al negative and positive ions. (C) 2002 American Institute of Physics.