Nanometer-scale features produced by electric-field emission

Nanometer-scale features have been formed in air on metallic surfaces with various tip/sample material combinations (W/Au, Au/Au, Au/Pt, and W/Pt) using a scanning tunneling microscope (STM) instrument. The instrument has sufficient stability, computer control, and in-process measurement capability to record important processing signals while creating nanoscale patterns. The sample surface can be quantitatively characterized using both tunneling spectroscopy and imaging before and after pulsing the tip-sample voltage (Vt). Images show that the form of the created features ranges from craters to mounds when Vt exceeds a threshold value, Vc, which is dependent on the tunneling resistance (R). Results of measurement of Vc vs R combined with results of the measurement of tip displacement versus Vt allow the determination of the threshold electric field (Ec). For the W tip and the Pt sample, Ec has been determined to be 0.23 V/Å. Electric fields of this magnitude are sufficient to remove atoms by high-field emission.