Search

The coupling of excitons with atomic vibrations plays a pivotal role on the nonequilibrium optical properties of layered semiconductors. However, how exciton-phonon coupling manifests in the time and energy domains is still an open debate between experiment and theory. By means of time-resolved broadband optical reflectivity combined with ab initio calculations of a bismuth tri-iodide single crystal, we set the spectral fingerprints for the optical detection of exciton-phonon coupling in layered semiconductors. Our joint experimental and theoretical effort allows us to unravel the impact of exciton-phonon coupling by microscopically relating the photoinduced coherent energy modulation of the excitonic resonance to coherent optical phonons. This enables us to track the extent of the photoinduced atomic displacement in real space. Our findings represent a step forward on the road to coherent manipulation of the excitonic properties on ultrafast timescales.

The self-assembly of leucoquinizarin molecules on Au(111) surfaces is shown to be characterized by the molecules mostly being in their keto–enolic tautomeric form, with evidence of their temporary switching to other tautomeric forms. This reveals a metastable chemistry of the assembled molecules, to be considered for their possible employment in the formation of more complex hetero-organic interfaces.

We investigate the nature of the adatom-surface interaction in the adsorption of alkali atoms on Cu(111). Our calculation, exploiting the embedding approach in a density functional theory framework, describes an isolated atom on a metallic surface, which is modeled via a one-dimensional modulated potential. The absence of empirical term in the Hamiltonian guaranties a completely ab initio determination of the electronic properties of the system. The role of the projected energy gap in determining lifetime and binding energy of the adatom resonances is evidenced. On the basis of the electronic properties of the adsorbed alkali atoms the covalent/ionic nature of the bonding with the surface is analyzed. 2012 American Physical Society.

We have investigated the formation of scanning tunneling microscopy (STM) atomically resolved images of the Fe(001)-p1x1-O surface. The latter is characterized by a high in-plane symmetry for both oxygen and iron atoms, thus representing a very appealing template for understanding how to distinguish between oxygen and metal atoms in STM images of an oxidized metal surface. We report on the occurrence of a corrugation reversal as a function of the tip-sample distance, and we use the conclusions of such an investigation for interpreting the experimental images of an oxygen vacancy created on the surface. Our experimental work, supported by ab initio density-functional theory calculations, allows us to assess the fundamental role of the local potential barrier in determining the STM image formation

The surface states generated by the adsorption of a full monolayer of K on Cu(111) are obtained by the embedding method within density functional theory. Their energy dependence is accounted for as function of the surface parallel wave vector and is connected to the spatial distribution of the electronic charge computed at special points in the two-dimensional Brillouin zone. Thanks to the description of a truly semi-infinite substrate within the adopted framework, the elastic linewidth of the surface states is determined with great accuracy and is shown to reflect the different degrees of hybridization of such states with the surface projected bulk bands. © 2010 The American Physical Society.

The adsorption of Cs and Ba on Cu(111) is investigated by means of one- and two-photon photoemission experiments and theoretically by first-principles calculations. The spectral properties of these systems, induced by both surface and adatom states, are studied at submonolayer coverage through angle-resolved measurements. A coverage-dependent analysis is also exploited in the assignment of the observed electronic states. The comparison with ab initio calculations allows identification of all the spectral features induced by Cs and Ba chemisorption. The theoretical analysis concerns the limiting single adatom case, treated in an embedding approach with a one-dimensional potential for the surface. The agreement between the calculated density of states and the experimental spectra confirms that the model substrate retains all the relevant physics entering in the adsorption process. The differences between the electronic structures of Cs and Ba on the Cu(111) surface can be attributed to the group-dependent screening of the core potentials as manifested by the ionic radii and ionization potentials (alkali vs alkaline earth).