Field ion microscope with photostimulable phosphor screen — new approach for quantitative analysis of FIM images-

Abstract

Adaptability of a photostimulable phosphor screen, called an imaging plate (IP), for field emission and field ion microscopies was examined. The photostimulated luminescence (PSL) of the IP for He + is strong enough for field ion microscopy, but that for Ne + is less than one tenth of He +, like an ordinary fluorescent material. The digitized computer-processed images of W, W-Re and Pt-Ir are unexpectedly clear. The image brightness seems to increase with the number of incoming ions and the PSL intensity ratio of a dark atom to a bright atom is found to be as large as 1 to 160, suggesting the possibility of a quantitative analysis of electron tunneling and a field ionization probability over individual surface atoms. However, this ratio is significantly smaller than the expected dynamic range of the IP, 10 4, possibly due to the charge up of the IP's surface, low ion energies and an IP's high outgassing rate, which deteriorates vacuum and induces high background counting. Accordingly, darkly imaged “invisible atoms” of the alloys are hardly recognizable at present.