Abstract
The electronic states and the optical-transitions of Si(111) clean and Cl-adsorbed surfaces have been calculated using time-dependent density functioal theory (TD-DFT). Two clusters, Si21H27 and Si21H27Cl, are chosen for the models to stand for the clean and Cl-adsorbed Si(111) surfaces, respectively. The imaginary part of the dielectric function is related to the transition probability obtained by calculation of optical-transitions to the excited states. The imaginary part is transformed into the real part through Kramers-Kronig relation, and the reflectance is figured out. Surface differential reflectivity (SDR) spectrum of Cl-adsorption is obtained from the reflectance of clean and Cl-adsorbed surfaces. The calculated spectrum is in good agreement with experimental spectrum. Moreover, applying TD-DFT to the electronic excitation on the Si(111) surface, we can analyze the surface adsorption by means of optical measurements.
