Cesium-induced transient effects on the Si+ and Si− secondary ion emissions from Si and SiO2

Measurements of the concentration and speciation of Cs implanted into Si and SiO2 thin film surfaces as a result of 1 keV Cs+ ion impact have been carried out using X-ray photoelectron spectroscopy. In most cases, the presence of Cs resulted in enhanced Si− and quenched Si+ secondary ion intensities. These intensities could be correlated to the Cs concentration via exponential functions over and following the transient regions noted in secondary ion mass spectrometry. These trends are predicted by the electron tunneling model in which a resonance charge transfer mechanism is assumed to dominate. An exception arises in the case of the Si+ secondary ions from SiO2; these initially rose in intensity with increasing Cs concentration. This exception is believed to result from the introduction of an Auger de-excitation process that is active in the excited sputtered neutral Si population some distance from the surface. The Cs retained in the Si substrate was found to exist as a mixture of Cs2O with some form of CsSi complex in Si. Cs in SiO2 existed primarily as CsO2.