The vibrational features of self-organized submonolayer trans-stilbene on the Ag/Ge(111)−(√3 × √3)R30° surface have been investigated by Raman spectroscopy in ultrahigh vacuum at 100 K. A red shift in the CC stretching mode of the olefinic group at 1625 cm−1 and enhanced Raman activity of the peak at 1568 cm−1 were observed, as compared with those corresponding to a multilayer trans-stilbene. Electronic interaction between trans-stilbene and the underneath surface and Raman spectra were calculated based on density functional theory. The calculated Raman spectra are in good agreement with the experimental results, supporting the calculated molecular geometry of the adsorbed trans-stilbene, which exhibits a predominant bond elongation in the olefinic group and a torsional angle between the phenyl ring and the olefinic plane. Analysis of the partial density of states shows that the lowest unoccupied molecular orbital is broadened and lowered to cross the surface Fermi level by the interaction with the surface, facilitating surface charge transfer and thus destabilizing the CC double bond.

The strategy of using the thermal expansion of a copper single crystal can provide an approach to produce homogeneous strain along the basal plane to study the strain characteristic of graphene with temperature. Using an in situ Raman measurement under an ultrahigh vacuum (UHV) environment, the ability to remove contaminations allowed the direct observation of the strain property in as-grown chemical vapor deposited graphene (CVD-graphene) with temperature on a Cu(100) substrate. In this study, the strain coefficients of the G and G′ bands with temperature were investigated from the in situ temperature-dependent Raman spectra of the asgrown CVD-graphene on the Cu(100) single crystal under UHV. By eliminating the minor contributions of the lattice expansion and anharmonic phonon-scattering effects, we were able to estimate the strain coefficient of the G and G′ bands of graphene over a wide temperature range from 100 to 800 K. On the basis of the strain coefficients and the correlation map of the G-and G′-band frequencies, we made a reasonable presumption that a uniaxial-like strain is exhibited in graphene on Cu(100). For a correction to the magnitude of the uniaxial strain, the mode Gruneisen parameters at room temperature are estimated to be about ∼1.8 for the G bands, in reasonable agreement of the literature values. This strategy made it possible to estimate the temperature-dependent mode Gruneisen parameters of the G and G′ bands for the first time.

Deposition of organic molecules on inorganic substrates is an important step in the fabrication of organic electronic devices with designated optoelectronic properties. Their interaction with the surface underneath and the interaction among themselves influence the molecular orientation of the first adsorbed layer and thus energy and charge transport properties of the grown organic films. We show that these interactions of transstilbene, trans,trans-distyrylbenzene, and trans-azobenzene adsorbed on Ag/Ge(111) -( 3 × 3)R30°surface are reflected on their Raman signatures. Detailed spectral analysis reveals the characteristic vibrational features corresponding to the molecules residing in the first adlayer and in the layers above, separately. The results further show that for all the three different molecular systems, the integrated intensity of the multilayer Raman signature increases linearly with the molecular coverage. This study explores potential utilization of Raman spectroscopy as a sensitive, noninvasive tool to characterize the intricate molecule-surface interaction and to quantify physisorbed molecular systems.