Nanofabrication with a scanning tunneling microscope

Nanometer-scale structures as small as 1 nm were fabricated on graphite surfaces using a scanning tunneling microscope in the presence of low-pressure (10^-4 Torr) trimethylaluminum. The studies were performed under controlled conditions of gas purity and gas pressure, allowing systematic measurements. We studied the voltage threshold and other features of the fabrication process as a function of the tip-surface biasing voltage and the tunneling current. The studies lead us to believe that the structures were formed by bombardment of the graphite surface by ions produced by electron-assisted field ionization localized in the region of the tunneling gap.