Scanning tunnelling microscopy characterization of gold film surfaces processed using an argon radio frequency (RF) plasma

Abstract

STM investigation has revealed that the initially flat topography of gold film surfaces as-deposited on mica substrates at an elevated temperature (∼440°C) is changed substantially by argon RF plasma processing at various power levels for a short period (5min). When the power level is relatively low (≤20W), the processed gold film surfaces show well defined, uniformly distributed, dome-shaped mounds with similar lateral dimensions. When plasma processing is conducted at higher power levels (e.g. 30 and 50W), the modified gold surfaces still exhibit mounded topographical features but now these are less uniformly distributed and of slightly smaller size, showing less well defined boundaries. Moreover, plasma processing can roughen the surfaces of gold, i.e. the value of FWHM (full-width-half-maximum) obtained from the height histogram is in the range ∼10–∼24Å for the plasma processed surfaces with power levels between 10–50W. Whereas, it is only ∼5.6Å for the initially flat and unprocessed surface of the gold film studied. All the phenomena observed can be attributed to a mechanism involving the local redeposition of the gold atoms sputtered by argon ions in the plasma and the reorganization of the plasma-disturbed surfaces via plasma-induced diffusion processes.