Second-harmonic generation from chemically modified Ge(111)interfaces

摘要

Second-harmonic generation (SHG)was used to investigate chemically modified surfaces of Ge(111).Chemical modification was achieved by wet-chemical covalent binding of decyl and sulfur directly to the Ge interface after oxide stripping.Chemical modification of the interface substntially changes the second harmonic response.The decyl and sulfur terminations are stable in ambient during several weeks,as judged by SHG and XPS measurements.The SHG rotational anisotropy patterns were anslyzed to estimate the relative values of the nonliear susceptibilities describing the surface and bulk response.THe choice of fundamental/SHG polarization combinations for accessing various nonliear coefficients is presented.The factors affecting the relative values of the surface-to-bulk contributions to SHG and their changes upon chemical modification of the surface are discussed.In particular,it was found that the higher the electronegativity of chemically attached species,the higher the contribution of the surface-originating nonliear terms to the overall response.Also,it was found that the relative contribution of surface versus bulk to SHG is different ofr different polarization combinations:the surface contribution to the p-in/p-out response is the greatest.