電界イオン顕微鏡中のタングステン試料の不活性ガスによる損傷

抄録

The tips of tungsten specimens in a field ion microscope were damaged by heavy imaging gases in the presence of an imaging field. These damages increased in proportion to the gas pressure, the exposure time, and the field strength. This result proved that the damages were due to expelled atoms and vacancies on the surface, which occured by the collisions of gas atoms. The damage caused by a mixture of gases (He+Ar or Kr) was larger than that by pure gas (Ar, Kr). When the field strength is above 90% of the field evaporation strength, the locahhigh field areas of tip surface were not damaged. When the field strength was appropriate to give the best image, the entire surface, in particular {111} and {112} planes, was damaged. When the field strength was below 75% of the field evaporation strength, {Ill} and {114} planes were severely damaged and many clusters were created. These dam-ages are estimated to be due to the penetration probability of imaging gas atoms through the ionization zone, and accounted for by a correction of the thermal accomodation coefficients between various gases and the tungsten surface by field adsorption.