Assessment of an ionized CO2 gas cluster accelerator

Abstract

A 150 kV gas cluster ion accelerator was constructed. Using a retarding field analyzer and time-of-flight (TOF) mass spectrometry, the gas cluster source was characterized. To form cluster beams, the CO2 gas was expanded through a quartz Laval nozzle at a pressure of 1-5 bar. It is confirmed that clusters formed with a mean size of more than 500 molecules. The effect of source temperature on cluster size was also examined. When CO2 cluster ions were irradiated onto a highly oriented pyrolytic graphite (HOPG) at the acceleration voltage of 40 kV, isolated impact of the cluster ions was found to generate hillocks about 0.8 nm in height and 20 nm in diameter. (C) 2001 Elsevier Science B.V. All rights reserved.