High-Resolution Synchrotron Photoemission Studies of the Electronic Structure and Thermal Stability of CH3- and C2H5-Functionalized Si(111) Surfaces

Abstract

The relative coverage, thermal stability, and electronic properties of CH_(3-) and C_2H_(5-)functionalized Si(111) surfaces prepared by a two-step chlorination/alkylation procedure have been compared using high-resolution synchrotron photoemission spectroscopy. Whereas the CH_(3-) terminated Si(111) surface showed only one C 2s peak for the occupied σ orbitals, the C 2s spectra of C_2H_(5-)terminated Si(111) surfaces showed a symmetric splitting of the occupied σ orbitals, as expected for an ethyl moiety bonded to the surface. The C_2H_5 termination resulted in an unpinning of the Si surface Fermi level, with a band bending of ∼0.2 eV, and produced a surface dipole potential step of −0.23(15) eV. The observed close-to-flat-band condition is similar to that of CH_3−Si(111) and is consistent with H termination of the non-alkylated Si atop sites in the two-step chlorination/alkylation process. The C_2H_(5-)functionalized Si(111) surfaces decomposed at temperatures >300 °C, whereas CH_3−Si(111) surfaces were stable up to at least 440 °C. The data clearly highlight the similarities and identify some significant differences between the behavior of the CH_3- and C_2H_(5-)functionalized Si(111) surfaces.