Abstract
Hydrogen clusters accelerated at 600 keV have been used to desorb secondary ions from inorganic (CsI) and organic (phenylalanine) dielectric materials. Time-of-flight spectrometry has been applied to the measurement of the yield of both positive and negative species over a cluster mass range from 7 to 61. As a function of the electronic additive stopping power ( n times the electronic stopping of the proton at the same velocity), all the yields exhibit a ( dE dx ) e.a. x dependence. For CsI, the Cs + yield has two different components, one with a fourth power dependence in the mass range 7–23 and the other with a quadratic dependence in the mass range 33–61. With a velocity range including the Bohr's velocity, the concept of a cluster stopping involving close and distant collisions is still controversial. Among the possible interpretations we propose a hypothesis allowing the two-step regime to be characterized by a single quadratic dependence. This is consistent with the models developed for heavy ions. The almost linear dependence of the I − yield with S clust. is not fully understood. An identical variation for the yields of the molecular ions of phenylalanine suggests comparable desorption mechanisms. If there are some arguments favoring the ultratrack model, more data are needed for a satisfactory interpretation.
Published Version
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