Time-of-Flight Atom-Probe Field-Ion Microscope for the Study of Defects in Metals. Report No. 2357.

摘要

An ultra-high vacuum time-of-flight (TOF) atom-probe field ion microscope (FIM) specifically designed for the study of defects in metals is described. The variable magnification FIM image is viewed with the aid of an internal image intensification system based on a channel electron-multiplier array. The specimen is held in a liquid-helium-cooled goniometer stage,and the specimen is exchanged by means of a high-vacuum (less than 10exp -6torr) specimen exchange device. This stage allows the specimen to be maintained at a tip temperature anywhere in the range from 13to 450exp 0 K. Specimens can also be irradiated in-situ with any low-energy (less than 1keV) gas ion employing a specially constructed ion gun. The pulse-field evaporated ions are detected by a Chevron ion-detector located 2.22 m from the FIM specimen. The TOF of the ions are measured by a specially constructed eight-channel digital timer with a resolution of +-10ns. The entire process of applying the evaporation pulse to the specimen,measuring the dc and pulse voltages,and analyzing the TOF data is controlled by a NOVA 1220computer. The computer is also interfaced to a Tektronix graphics terminal which displays the data in the form of a histogram of the number of events versus the mass-to-charge ratio. An extensive set of computer programs to test and operate the atom-probe FIM have been developed. With this automated system we can presently record and analyze 10 TOF s exp -1 . In the performance tests reported here the instrument has resolved the seven stable isotopes of molybdenum,the five stable isotopes of tungsten,and the two stable isotopes of rhenium in a tungsten--25at. percent rhenium alloy. (ERA citation 01:019962)