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 sigma orbitals, the C 2s spectra Of C2H5-terminated Si(111) surfaces showed a symmetric splitting of the occupied sigma 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 similar to 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 degrees C, whereas CH3-Si(111) surfaces were stable up to at least 440 degrees C. The data clearly highlight the similarities and identify some significant differences between the behavior of the CH3- and C2H5-functionalized Si(111) surfaces.