Study on the energy-loss mechanism of fast neutral particles at crystal surfaces

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A time of flight (TOF) system was developed to measure energy of fast neutral particles. Using this TOF system, energy losses of reflected particles, both ions and neutral atoms, were measured at glancing angle incidence of 12 - 30 keV rare gas ions on the (001) surface of SnTe single crystal. The observed neutral fractions were larger than 96% and the observed energy losses of the reflected ions were almost equal to those of the neutral particles. These experimental results indicate that almost all incident ions were neutralized at the surface. The position dependent stopping powers for neutral rare gas atoms were derived from the observed incident-angle dependence of the energy loss. The obtained stopping power was successfully explained in terms of single collisions of neutral atom with valence electrons permeated outside the surface. A new method to determine the electron ditsribution outside a crystal surface was proposed.