The chemical state, electronic properties, and geometric structure of methyl-terminated Si͑111͒ surfaces prepared using a two-step chlorination/alkylation process were investigated using high-resolution synchrotron photoelectron spectroscopy and low-energy electron diffraction methods. The electron diffraction data indicated that the methylated Si surfaces maintained a ͑1 ϫ 1͒ structure, where the dangling bonds of the silicon surface atoms were terminated by methyl groups. The surfaces were stable to annealing at 720 K. The high degree of ordering was reflected in a well-resolved vibrational fine structure of the carbon 1s photoelectron emission, with the fine structure arising from the excitation of C-H stretching vibrations having h = 0.38± 0.01 eV. The carbon-bonded surface Si atoms exhibited a well-defined x-ray photoelectron signal having a core level shift of 0.30± 0.01 eV relative to bulk Si. Electronically, the Si surface was close to the flat-band condition. The methyl termination produced a surface dipole of −0.4 eV. Surface states related to CH 3 and Si-C bonding orbitals were identified at binding energies of 7.7 and 5.4 eV, respectively. Nearly ideal passivation of Si͑111͒ surfaces can thus be achieved by methyl termination using the two-step chlorination/ alkylation process.

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.

The electronic structure of Cu(111)/pentacene and Ag(111)/pentacene interfaces were investigated with photoelectron spectroscopy and the hole barrier heights were determined to be 0.74 and 0.90 eV, respectively. When combined with previous measurements of the Au(111)/pentacene interface, the slope of the plot of metal work function against barrier height for Schottky barrier formation was determined to be 0.36, in agreement with current-voltage (I−V) measurements in the literature. However, the absolute barrier heights from photoemission measurements are 0.16 eV higher. The offset between the I−V measurement and the x-ray and ultraviolet photoelectron spectroscopy measurements was attributed to differences in how the highest occupied molecular orbital position is determined. Photoemission data indicates that at low coverages the pentacene molecules lie flat on the metal substrates, whereas at higher coverages the molecular orientation changes to orient the long molecular axis normal to the surface. Thicker films then tend to form three-dimensional islands, resulting in structured rather than flat films forming on clean Ag(111) and Cu(111) at room temperature.

Chrysene, a two-dimensional (2D) chiral isomer of tetracene, was deposited onto inert metallic (Au(111), Cu(111), Ag(111), and highly oriented pyrolytic graphite (HOPG)) and semiconducting (SnS 2) substrates with hexagonal symmetry. The interface formation was investigated in situ with photoelectron spectroscopy (X-ray photoelectron spectroscopy and UV photoelectron spectroscopy (UPS)). A detailed analysis of core-level and valence band spectra revealed that the barrier height for holes or electrons is independent of the identity and work function of the metal substrate. Metal/chrysene interfaces are therefore an example of pure Fermi level pinning where changes in the interface dipole potential directly offset changes in the metal work function. The results provide evidence that the pinning may result from a hybridization mechanism between metal s states and organic π states. UPS spectra indicate that the 2D structures of the chrysene wetting layer is different for high work function materials (Au(111), SnS2) compared to low work function materials (Ag(111) and HOPG). Stranski−Krastanov growth was observed on all substrates and is in agreement with optical microscope images of thick chrysene films.