Neon gas imaging of gold in the field ion microscope

Abstract

An improved field ion microscope (FIM) technique has been developed for the neon gas imaging of gold specimens. The technique produces images which are stable at best image voltage at a tip temperature ( T T) of 30 K or less. The first stage of the technique consisted of the development of an end form at 55 K in the presence of a partial pressure of air (∼ 2 × 10 −8 Torr gauge pressure) and neon gas (∼ 3 × 10 −5 Torr gauge pressure) followed by further field evaporation at 28 K. The second stage involved neon gas imaging of the previously developed end form in a baked FIM in a background pressure of (0.5 to 3) × 10 −9 Torr. The FIM images obtained in conjunction with the field ionization characteristic curves showed that there is a working range (in the sense defined by Southon and Brandon). A detailed study was made of artifact vacancies detected in the {203}, {321}, {315}, {421}, {671} and {731} planes, and it was found that at 28 K their concentration was < 2.5 × 10 −3 at.fr. Approximately 191,000 atomic sites were examined for artifact vacancies. The artifact vacancy concentrations measured in the present study were a factor of 13 to 60 lower than those measured earlier by Schmid and Balluffi who employed a background pressure of ∼ 5 × 10 −8 Torr in their FIM. Hence, the artifact vacancy concentrations detected in gold are dependent upon the background partial pressure employed in the FIM. This latter result plus the result that the images are only stable in ultra-high vacuum (UHV) conditions indicates the need for UHV conditions for the successful imaging of gold surfaces.