Loucas K. Loumakos, UT-Austin

"Fingerprinting of Si surface bonds using non-resonant optical second-harmonic generation"

Abstract: Modern electronic device structures require monitoring and control of surface structure at the atomic level during epitaxial growth. We demonstrate an optical fingerprinting technique that isolates, identifies and monitors individual types of bonds (e.g. step-edge rebonds, terrace dimers) and their chemical activity on a single-domain, vicinal Si(001) surface in ultra-high vacuum. The method uses optical second-harmonic generation (SHG) at a single wavelength, but at multiple incidence angles and polarizations (MAP) — hence we call it SHG-MAP. SHG-MAP identifies bonds via the unique dependence of their SHG response on azimuthal sample rotation. Using a simplified bond hyper-polarizability model (SBHM), we developed an automated two-step algorithm for identifying all opportunities for isolating a certain bond type geometrically without multi-parameter fitting: firstly, the full parameter space is used to create a 4-D model of the expected macroscopic SHG radiation and secondly a search is preformed to isolate unique bond group contributions. We demonstrate SHG-MAP by monitoring adsorption of atomic hydrogen and chemical etching of rebonded double steps on clean vicinal Si(001) in ultra high vacuum.