Electronic structure and screening dynamics of ethene on single-domain Si(001) from resonant inelastic x-ray scattering

Abstract

We present a resonant inelastic x-ray scattering ͑RIXS͒ study of a strongly bound adsorbate on a semiconductor surface, C 2 H 4 /Si(001). The valence electronic structure as well as the photon energy dependence in RIXS can be studied without the dominating effect of dynamic metallic screening. We demonstrate that for this strongly coupled system the RIXS spectrum resulting from a selective excitation into the unoccupied CSi * resonance can be interpreted with the help of density-functional calculations. In addition, we show how excitation into different resonances leads to a significant photon energy dependence of the RIXS spectral features, not seen in strongly coupled adsorbate systems on metals. DOI: 10.1103/PhysRevB.69.153408 PACS number͑s͒: 73.20.Hb, 78.70.En The investigation of resonant inelastic scattering in the soft x-ray spectral range using third-generation synchrotron radiation sources has recently attracted great interest as a powerful method for detailed electronic structure determination.1 The inelastic-scattering process can be described as a transition from the electronic ground state of a system via an intermediate resonant core-excited state into a final state which is electronically and/or vibrationally excited. This event can be studied by either detecting scattered photons or secondary Auger electrons. The former case involving photons in the incoming as well as the outgoing channel has the advantage of being almost independent of the sample environment, thus enabling even electronic structure studies of complex interfaces and liquids. Resonant inelastic x-ray scattering ͑RIXS͒ is governed by the dipole operator, and therefore has a well-defined polarization dependence and anisotropy, which provides insight into spatial orientation and symmetry properties of the systems studied.2 Furthermore, due to the element specificity of the resonant excitation process, one is able to probe the electronic structure of complex heteronuclear systems for selected states. 1,3 In crystalline solids, momentum conservation in RIXS can be used to access the k-resolved band structure. 4 In adsorption systems, RIXS effectively suppresses contributions from the much larger number of substrate atoms and thus permits to access the atom-specific valence electronic structure of the adsorbate, 2,3,5 allowing significantly improved understanding of the surface chemical bond. 3,5 In free molecules, RIXS depends strongly on the energy of the incoming photon as a result of the interference of degenerate or near-degenerate intermediate states in the scattering process. 6 Furthermore, excitation to different resonances leads to significant differences in the spectral shape of the scattering spectra because of strong symmetry selection rules. 6 For adsorbed molecules, this situation changes because coupling to the substrate, which modifies the dynamic response of the core-hole RIXS intermediate state, has to be taken into account. To date only adsorbates on metallic substrates have been investigated with RIXS. For these...