Production of liquid cluster ions and their application to surface etching

A new type of cluster ion beam system using organic liquid materials such as ethanol has been developed, and it has several advantages for surface etching and chemical modification based on the different properties of liquid cluster ions. Ethanol vapors were ejected through a nozzle into a high-vacuum region, and ethanol clusters were produced by an adiabatic expansion phenomenon at the vapor pressures larger than 1 atm. In another case of producing ethanol clusters at a lower vapor pressure, He gas was used to mix up with ethanol vapors, and the mixed gases were ejected into a high vacuum region. Even if a vapor pressure of ethanol was 0.1 atm, ethanol clusters were produced at the He gas pressure larger than 1 atm.The ethanol clusters produced were ionized by an electron bombardment method, and the cluster ions were accelerated toward a substrate by applying an acceleration voltage. For the case of ethanol cluster ion irradiation at an acceleration voltage of 9 kV, the sputtering yields for Al, Cu, Ag and Au films, which were used as a substrate, were about ten times larger than that by Ar monomer ion irradiation. In addition, the surface flatness of the metal films was improved by irradiation of ethanol cluster ions.