MASS AND ENERGY-SPECTRA OF MO IONS IN-FIELD EVAPORATION

The field-evaporation behavior of Mo is studied with a high-resolution pulsed-laser time-of-flight atom probe. The ion energy distribution o f Mo2+ shows a double peak structure and the ion energy distribution o f Mo3+ has a broad single energy peak. To explain the formation of the low energy peak of the Mo2+ ions and the abnormally small critical en ergy deficit of the Mo3+ ions, we propose a two-step field-evaporation mechanism for molybdenum in which two Mo atoms line up with the field before they are field-ionized. Also at low field strengths (3.7 to 4. 2 V/angstrom) and high temperature (about 600 K), triply charged Mo di mers can be detected.