Field ion energy distributions

The narrowness of the field ion energy distribution, though it was initially quite unexpected, has been explained in the theoretical calcu-... 

Fig. 2.6 (a) Field ion energy distributions of H+, Hj and H3 ions obtained by Jason et al.21 Secondary peaks due to resonance field ionization are most pronounced for f/J. are formed right near the surface, and no low energy tail... 

Krishnaswamy. They emphasize the importance of a phase factor in the complex reflection coefficient of electrons from the surface, and propose that field ion energy distributions may be used to measure the phase of electron reflection at the crystal surface. However, neither is the potential barrier known accurately enough nor are the available experimental data good enough, and to this date no such information has been obtained. 

There are basically two kinds of experiments which can be used for studying the mechanisms of the field ionization process near a field ion emitter surface and also the field ion image formation process. They are the measurement of field ion current as functions of tip voltage, tip temperature, and other experimental parameters, and the measurement of the ion energy distribution. 

Fig. 2.3 Magnetic sector mass spectrometer combined with a retarding potential ion energy filter used by Ernst et al 6 for measuring ion energy distributions in field ionization and field evaporation.

Fig. 2.5 An ion kinetic energy distribution of field desorbed He ions taken with a pulsed-laser time-of-flight atom-probe. In pulsed-laser stimulated field desorption of field adsorbed atoms, atoms are thermally desorbed from the surface by pulsed-laser heating. When they pass through the field ionization zone, they are field ionized. Therefore the ion energy distribution is in every respect the same as those in ordinary field ionization. Beside the sharp onset, there are also secondary peaks due to a resonance tunneling effect as discussed in the text. The onset flight time is indicated by to, and resonance peak positions are indicated by arrows. Resonance peaks are pronounced only if ions are collected from a flat area of the...

Fig. 2.14 (a) Ion energy distributions of the doubly charged Ir ions. The distribution width is very narrow without a low energy tail and therefore there is no evidence of post field ionization of field evaporated Ir2+ ions. Evaporation field calculations for low temperatures indicate that Ir will first field evaporate as Ir2+ ions when the field is gradually raised. 

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