A low energy electron beam under 1 keV is often used to investigate the structural and chemical properties of surfaces. It has been shown that electron irradiation produces defects on silicon surfaces [1]. Nevertheless, electronic properties induced by electron irradiation have not been well understood. We have studied this effect by means of two optical reflectance spectroscopy methods; surface differential reflectance (SDR) and reflectance difference spectroscopy (RDS). The former can be used to monitor the coverage of adsorbates as precisely as Auger electron spectroscopy [2]. The latter is more sensitive to the anisotropy at the interface. It turned out that the reflectance difference signal, obtained by both techniques after electron irradiation, reached the amount almost equal to the signal for monolayer oxidation. This may indicate that Si-Si bonds are largely distorted not only at surfaces but also at subsurface region. The spectral features and lineshapes of the time-courses would provide unique information on kinetics of defect formation with low-energy electron beams on Si surfaces. Electron-stimulated chemical reaction on silicon surfaces might also draw considerable interests in terms of nanostructure fabrication [3]. We have successfully observed enhancement of oxidation on a clean and hydrogen-adsorbed Si(001) surface. Electron-stimulated oxidation mechanism is compared with the conventional thermal oxidation process based on our optical measurements.
[1] K. Nakayama and J.H. Weaver, Phys. Rev. Lett. 82, 980 (1999).
[2] J. Takizawa et al., J. Phys.: Condens. Matter 18, L209 (2006).
[3] S. Ohno and J.T. Yates, Jr., J. Vac. Sci. Technol. A 23, 475 (2005). |