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 σ orbitais, the C 2s spectra of C2H 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 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/ alkylatipn process. The C2H5-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 CH3- and C2H 5-functionalized Si(111) surfaces.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films