FIELD-INDUCED OXIDATION OF SILICON BY SPM - STUDY OF THE MECHANISM ATNEGATIVE SAMPLE VOLTAGE BY STM, ESTM AND AFM

Nanometer scale oxidation of silicon surfaces by STM and AFM is an imp ortant subject in the SPM community, and its application for nanofabri cation has been demonstrated by several groups. Most published work sh ow that the surface can only be oxidized if a positive sample voltage is applied to the sample with respect to the tip (anodization). In the present work we have studied the oxidation mechanism at negative samp le voltage with STM and AFM in air and with an electrochemical STM in KF solution. It is demonstrated that two oxidation mechanisms exist, a nd that the frontier between both oxidation mechanisms is the voltage at which the surface is in the flat band condition. The influence of t he electrical field is evaluated and a mechanism for the cathodic oxid ation is proposed.