The Effect of Atmospheric Oxide Thermodesorption on Negative-Ion Atomic and Cluster Sputtering of Silicon Single Crystal by Cesium Ions

The temperature dependences of the sputtering of negative ions of silicon-oxygen clusters are studied for the first time by the method of ultrahigh-vacuum secondary ion mass spectrometry. In the temperature range of 100-200 degrees C, an increase in the yield of negative ion clusters of silicon suboxide and dioxide is observed, while after a maximum at 200 degrees C and up to 800 degrees C the yield decreases exponentially. At 800 degrees C, the yield of silicon oxide clusters stops while the desorption of suboxide is still observed. The yields of negative oxygen ions correlate with the temperature dependences of the yield of silicon-oxygen clusters and indicate the presence of oxygen adsorbed on the surface and dissolved in the bulk of the silicon crystal. In this work, for the first time, to assess the contribution of these processes a signal from negatively charged silicon dimers, which are an adsorbed silicon atom on a silicon atom located at a substrate lattice site, is used. The temperature dependence of the thermal desorption of negatively charged silicon trimers is measured. In our opinion, this signal is due to a decay negative cluster ion of a surface defect center, the so-called Pb-center, of an adsorbed silicon tetramer-three silicon atoms on the surface closed at the top by an additional silicon atom.