Electron emission from insulators induced by the impact of fast light ions

Fast atoms, ions or electrons, which impinge on a surface of a solid sample, will transfer energy to electrons of the sample. Some of the excited electrons, which got enough energy, will then escape from the sample. The object of this project was to study this electron emission process for insulating samples, because only very few reliable experimental results were published until now to this topic. A major part of the investigations was to measure the dependence of the mean number of emitted electrons, the emission yield, on the type of insulating sample, on the sample temperature and on the properties of the projectiles, as energy and charge. An new application of electron emission induced by particle impact was also found. Using electron emission the time dependence of the oxidation of aluminum was determined, which was not measured before. The yield measurements did not give surprising results. The emission yield was found to be mainly determined by the energy loss of the projectiles in a surface layer, but also the influence of a positive charge along the track of the projectiles on the yield was observed. The measured yields of the insulators were always larger than the corresponding one of metals, because of a larger escape depth of electrons in insulators compared to metals. These larger escape depths of insulators were experimentally verified. Until now it was assumed, that the sample temperature has only a minor negligible influence on the electron emission process, but no reliable measurements were published yet. Therefore we measured the temperature dependence of the yield for some metal and insulator samples. For metals a small significant decrease of the yield was found for increasing sample temperature, the seize of decrease did also depend on the kind of impinging projectile, but for some insulators a surprisingly large influence of the sample temperature was measured. These insulators showed also a strong dependence of the yield on the sample structure. In addition to the yield also probabilities were measured for emission of certain numbers of electrons. These emission statistics were found for metal oxides to be close to those of metals, whereas some other insulators showed a different behavior, which is yet not understood. Another not expected result gave the investigation of the electron emission yield from thin oxide layers. The time dependence of the yield of an aluminum surface was measured, which was exposed to oxygen and began to oxidize. As the electron emission yield, which could be measured very fast, is sensitive to changes of the surface composition it was possible to measure for the first time the oxidation rates, which determine the velocity of the oxidation process. Therefore investigations of particle induced electron emission does not only contribute to a better understanding of fundamental ion solid interaction processes, but can also be applied to study phenomena on solid surfaces.