High-resolution synchrotron photoemission studies of the electronic structure and thermal stability of CH3- and C2H5-functionalized Si(111) surfaces

The relative coverage, thermal stability, and electronic properties of CH3- and C2H5-functionalized Si(111) surfaces prepared by a two-step chlorination/alkylation procedure have been compared using high-resolution synchrotron photoemission spectroscopy. Whereas the CH3-terminated Si(111) surface showed only one C 2s peak for the occupied ó orbitals, the C 2s spectra of C2H5-terminated Si(111) surfaces showed a symmetric splitting of the occupied ó orbitals, as expected for an ethyl moiety bonded to the surface. The C2H5 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 CH3-Si(111) and is consistent with H termination of the non-alkylated Si atop sites in the two-step chlorination/ alkylation process. The C2H5-functionalized Si(111) surfaces decomposed at temperatures>300 °C, whereas CH3-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 CH3- and C2H5-functionalized Si(111) surfaces. I