Molecular self-assembly of DBBA on Au(111) at room temperature.

We have investigated the self-assembly of the graphene nanoribbon molecular precursor 10,10'-dibromo-9,9'-bianthryl (DBBA) on Au(111) with frequency modulation scanning force microscopy (FM-SFM) at room temperature combined with ab initio calculations. For low molecular coverages, the molecules aggregate along the substrate herringbone reconstruction main directions while remaining mobile. At intermediate coverage, two phases coexist, zigzag stripes of monomer chains and decorated herringbones. For high coverage, the molecules assemble in a dimer-striped phase. The adsorption behaviour of DBBA molecules and their interactions are discussed and compared with the results from ab initio calculations.

Structures of Small Platinum Cluster Anions Ptn-: Experiment and Theory.

The structures of platinum cluster anions Pt6--Pt13- have been investigated by trapped ion electron diffraction. Structures were assigned by comparing experimental and simulated scattering functions using candidate structures obtained by density functional theory computations, including spin-orbit coupling. We find a structural evolution from planar structures (Pt6-, Pt7-) and amorphous-like structures (Pt7--Pt9-) to structures based on distorted tetrahedra (Pt9--Pt11-). Finally, Pt12- and Pt13- are based on hcp fragments. While the structural parameters are well described by density functional theory computations for all clusters studied, the predicted lowest energy structure is found in the experiment only for Pt6-. For larger clusters, higher energy isomers are necessary to obtain a fit to the scattering data.

Structural Evolution of Palladium Clusters Pd55--Pd147-: Transition to the Bulk.

We present a study of the structural evolution of palladium cluster anions in a size range from 55 to 147 atoms using a combination of trapped ion electron diffraction and density functional theory computations. We show that Pdn- clusters (n = 55, 65, 75, 85, 95, 105, and 147) change from an icosahedral motif at Pd55- to the bulk fcc motif at Pd147-. This size-dependent structure transition is probed experimentally at a temperature of 95 K and characterized by a continuously increasing fraction of fcc isomers over the considered size range showing a crossover to the fcc motif at n ≈ 90.

Photodissociation of Free Metalloporphyrin Dimer Multianions.

We have used action photofragmentation spectroscopy in the visible spectral range (410 to 650 nm) to investigate the optical properties of different monomeric and dimeric M(II)-meso-tetra-(4-sulfonatophenyl)-porphyrin (with M = Pd(II), Cu(II), Zn(II)) multianions isolated in the gas phase without solvent. In particular, we report the position of the Q-bands (S0 → S1 transitions) as a function of charge state, counterions, oligomerization, and dimer structure type. The results for the monomers (charge states = 4- and 3-, sodiated and protonated) are in good agreement with TDDFT calculations and condensed-phase spectra. For both homo and heterometallic dimers, photofragmentation spectra were recorded for two charge states, 5- and 3-, corresponding to coplanar and cofacial structure types, respectively. The fragmentation patterns observed for the dimers depend significantly on charge state, with fragmentation into monomers being dominant for the 5- species, while the 3- charge state predominantly fragments by SO2 loss. The monomer → dimer Q-band spectral shifts observed in the gas phase were compared with the optical properties of porphyrin aggregates in solution.

Growth patterns and structural motifs of cadmium clusters with up to 60 atoms: disordered or not?

Using two different approaches, the structures of Cdn clusters are optimized. At first, parameterized density-functional calculations using the DFTB method in combination with evolutionary algorithms provide one set of candidate structures. Second, earlier proposed structures based on the Gupta potential provide a second set. Subsequently, all structures of each set are re-optimized using parameter-free density-functional calculations. It turned out that those based on the DFTB calculations in almost all cases were those of the lowest total energy. By analysing the structural properties as a function of cluster size information on growth patterns can be extracted. Thereby, the results show a certain preference that the atoms of the inner parts have surroundings as found in bulk hcp Cd. Furthermore, for larger size ranges, we could identify a specific growth pattern, implying that most of these clusters cannot be classified as being disordered. The results show also that the 4d electrons have only a weak influence on the properties of the clusters that, however, is so strong that a jellium-like model occasionally becomes inaccurate in describing the properties. In particular, the question at which size the clusters can be considered to be metallic becomes non-trivial to answer. Further arguments based on a comparison of the HOMO-LUMO gaps with the Kubo gap, however, suggested the non-metallic properties in the studied size range.