Interaction of fast grazing-incidence ions with a silicon(100) surface


R. Minniti (a), S. B. Elston (b), C. O. Reinhold (b) and J. Burgdorfer (b)


Absolute measurements of electron emission spectra were obtained by performing coincidence measurements between electrons emitted in the interaction of carbon ions scattered from a silicon(100) surface. The carbon ions, with total kinetic energies between 300 keV/amu and 500 keV/amu, were produced by the EN Tandem Van de Graff accelerator at Oak Ridge National Laboratory, and were directed towards a silicon(100) surface at grazing angles of incidence (between 0.1 and 0.5 degrees). The present setup permitted, in addition, the measurement of angular as well as charge state distributions of ions scattered from the surface.

Convoy electrons produced in ion-surface collisions result from electron capture and loss to continuum states of the projectile and constitute a prominent feature in the electron emission spectrum. A value for the yield of convoy electrons has been determined to be ~ 0.4 electrons per ion, in the present velocity regime. The study of the projectile velocity dependence of the convoy electron yields allowed addressing the origin of convoy electron emission in ion-surface collisions. It has been found that convoy electrons result from capture of valence and core electrons in the silicon target.

The study of the measured angular distributions of ions scattered from the silicon(100) surface suggests an experimental method which permits determining a critical angle of incidence for which projectile ions penetrate the surface in fast grazing-incidence ion-surface collisions.

This work was performed at the EN Tandem Van de Graaf facility at Oak Ridge National Laboratory.

a) Now at National Institute of Standards and Technology
b) The University of Tennessee and Oak Ridge National laboratory