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 CH 3 - and C 2 H 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 2 H 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 2 H 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 2 H 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 2 H 5 -functionalized Si(111) surfaces.