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Combined fast X-ray photoelectron spectroscopy and density functional theory calculations reveal the presence of two types of hydrogen adsorbate structures at the graphene/Ir(111) interface, namely, graphane-like islands and hydrogen dimer structures. While the former give rise to a periodic pattern, dimers tend to destroy the periodicity. Our data reveal distinctive growth rates and stability of both types of structures, thereby allowing one to obtain well-defined patterns of hydrogen clusters. The ability to control and manipulate the formation and size of hydrogen structures on graphene facilitates tailoring of its properties for a wide range of applications by means of covalent functionalization.

Structural and electronic properties of the λ-MnO(2)(001) surface are investigated applying density functional theory approach. The calculations show that all Mn ions at unreconstructed smooth surface preserve the +4 oxidation state observed in the bulk. Upon the λ-MnO(2)(001) reconstruction, one fourth of Mn ions at the surface undergo a change of the oxidation state from +4 to +3, although the reconstruction does not change the Mn coordination number with oxygen. This is accompanied with the filling of initially empty 3d(z(2) ) states localized on cations with one electron denoted by two neighboring O atoms. Although the reconstruction leads to an energy gain of 0.04 eV per surface unit cell, it is not a spontaneous process since it proceeds with an activation energy of 0.12 eV.

Direct D atom desorption, as well as associative desorption of D(2) molecules are observed in thermal desorption from D atoms chemisorbed on a C(0001) surface by combining laser induced T-jumps with resonance enhanced multiphoton ionization detection. Bleaching curves suggest that different classes of chemisorbed D atom clusters are present on the initial surface. The energy resolved atomic desorption flux, obtained via time of flight techniques, compares favorably (via detailed balance) with theoretical calculations of atomic sticking. Density functional theory calculations of chemical processes (atomic desorption, atomic diffusion/cluster annealing, and associative desorption) on an extensive set of four atom H(D) clusters chemisorbed on C(0001) provide a good interpretation of the experiments. State and energy resolved D(2) desorption fluxes are compared with previous state averaged results. In combination with density functional theory calculations these measurements reveal a substantial energy loss (>1 eV) to the surface in the associative desorption.

We present density functional theory calculations and scanning tunneling microscopy experiments investigating the structures and kinetics of extended hydrogen dimer configurations on the graphite (0001) surface. We identify several hydrogen dimer structures where surface mediated interactions between the two hydrogen atoms lead to increased binding energy even at interatom separations as large as 7 A. By modeling the formation of dimers as sequential adsorption of hydrogen atoms, we find that these dimer configurations exhibit decreased barriers to sticking for the second H atom, compared to the sticking barrier of an H atom on the clean surface. According to our calculations, the activation energies for desorption of a single H atom from any of the experimentally observed extended dimers are higher than the barriers for diffusion to the paradimer configuration. Consequently, molecular hydrogen formation out of the extended dimer structures takes place via diffusion over the paradimer configuration.

The enantioselectivity of gold is investigated by x-ray photoelectron spectroscopy (XPS) and density functional theory (DFT). Cysteine molecules on a chiral Au(17 11 9);{S} surface show enantiospecific core level binding energies in the amino and in the thiol group. The sign and order of magnitude of the XPS core level shifts is reproduced by DFT. Identical preparations of D- and L-cysteine layers lead to D-cysteine molecules in the pure NH2 form, while a small portion of L-cysteine molecules maintains a hydrogen rich amino group (NH3). This implies enantiospecific adsorption reaction pathways and is consistent with DFT that indicates an activated hydrogen abstraction reaction from the amino group, which is downhill for D-cysteine.

We present scanning tunneling microscopy experiments and density functional theory calculations which reveal a unique mechanism for the formation of hydrogen adsorbate clusters on graphite surfaces. Our results show that diffusion of hydrogen atoms is largely inactive and that clustering is a consequence of preferential sticking into specific adsorbate structures. These surprising findings are caused by reduced or even vanishing adsorption barriers for hydrogen in the vicinity of already adsorbed H atoms on the surface and point to a possible novel route to interstellar H2 formation.

We present scanning tunneling microscopy results which reveal the existence of two distinct hydrogen dimer states on graphite basal planes. Density functional theory calculations allow us to identify the atomic structure of these states and to determine their recombination and desorption pathways. Direct recombination is only possible from one of the two dimer states. This results in increased stability of one dimer species and explains the puzzling double peak structure observed in temperature programmed desorption spectra for hydrogen on graphite.

Two distinct non-mirror-symmetric conformations of D- and L-cysteine were found after adsorption on Au(17 11 9)S. This demonstrates chiral heterorecognition, i.e., enantioselectivity of S kinks on vicinal Au(111). The structures as determined by angle scanned x-ray photoelectron diffraction agree well with those from density functional theory calculations. The calculations predict adsorption energies of approximately 2 eV where D-cysteine binds 140 meV stronger than L-cysteine. The classical three point contact model for molecular recognition fails to explain these findings.

Using a density functional approach, we study structural and magnetic properties of small Fe(n) clusters (n

Density functional theory calculations are carried out for the adsorption of a chiral molecule, (S)- and (R)-HSCH(2)CHNH(2)CH(2)P(CH(3))(2), on a chiral surface, Au(17 11 9)(S)(). The S-enantiomer is found to bind more strongly than the R-enantiomer by 8.8 kJ/mol, evidencing that the chiral nature of the kink sites at the Au(17 11 9) surface leads to enantiospecific binding. The adsorption of two related chiral molecules, HSCH(2)CHNH(2)COOH ("cysteine") and HSCH(2)CHNH(2)CH(2)NH(2), does not, however, lead to enantiospecific binding. The results of the density functional calculations are broken down into a local binding model in which each of the chiral molecule's three contact points with the surface provides a contribution to the overall adsorption bond strength. The enantiospecific binding is demonstrated to originate from the simultaneous optimization of these three local bonds. In the model, the deformation energy costs of both the molecule and the surface are further included. The model reveals that the molecule may undergo large deformations in the attempt to optimize the three bonds, while the surface deforms to a lesser extent. The most favorable binding configurations of each enantiomer are, however, characterized by small deformation energies only, justifying a local binding picture.

By means of scanning tunneling microscopy measurements and density functional theory calculations, we identify the reaction mechanism for the oxidation of carbon monoxide to carbon dioxide on the Rh(110) surface at 160 K, which appears to be completely different than the one active at room temperature. The reasons for these different behaviors are determined. Our results demonstrate that even for a very simple catalytic reaction, the microscopic mechanism can dramatically change with temperature, following pathways that differ for nucleation sites and surface propagation and involve different surface moieties.

Using scanning tunneling microscopy, thermal energy atom scattering, and density functional theory we have characterized O (2) dissociation on Pt(111) stepped surfaces at the atomic scale. The most reactive site is at the top of the Pt steps. In both the molecular precursor state (MPS) and the transition state (TS), the O (2) has its axis aligned parallel to the step edge. Controlled step decoration with Ag monatomic chains was used to locally tune the reactivity of Pt step sites. The enhanced reactivity at the Pt step sites is not caused by a decrease of the local dissociation barriers from the MPS but is related to a stabilization of both the MPS and TS.