Sven Neukermans

Stability effects of AunXm+ (X = Cu, Al, Y, In) clusters

Bimetallic AunXm clusters (X=Cu, Al, Y, In) have been produced by a dual-target dual-laser vaporization source. Following multiphoton absorption the stability patterns resulting from fragmentation are investigated by time-of-flight mass abundance spectrometry. AunCum+ clusters exhibit the same electronic shell effects as Aun+. Different abundance patterns are observed for AunAl1+ compared to AunY1+ or AunIn1+. The patterns are related to the magic numbers of the electronic shell model for clusters. The differences between the bimetallic clusters are interpreted in terms of different cluster geometries dependent on the nature of the dopant atoms.

Density functional study on structure and stability of bimetallic AuNZn (N⩽6) clusters and their cations

A systematic study on the structure and stability of zinc doped gold clusters has been performed by density functional theory calculations. All the lowest-energy isomers found have a planar structure and resemble pure gold clusters in shape. Stable isomers tend to equally delocalize valence s electrons of the constituent atoms over the entire structure and maximize the number of Au–Zn bonds in the structure. This is because the Au–Zn bond is stronger than the Au–Au bond and gives an extra σ-bonding interaction by the overlap between vacant Zn 4p and valence Au 6s(5d) orbitals. No three-dimensional isomers were found for Au5Zn+ and Au4Zn clusters containing six delocalized valence electrons. This result reflects that these clusters have a magic number of delocalized electrons for two-dimensional systems. Calculated vertical ionization energies and dissociation energies as a function of the cluster size show odd–even behavior, in agreement with recent mass spectrometric observations [Tanaka et al., J. Am. C...

Ionization potentials and structures of small indium monoxide clusters

We report a combined experimental and theoretical study of the structures and ionization potentials of small InNO clusters (N=1–8). The clusters are produced using a laser vaporization cluster source, laser ionized, and mass selectively recorded by a time-of-flight mass spectrometer. Threshold photoionization spectroscopy was performed using photon energies of 4.59–5.96 eV and 6.43 eV. Adiabatic and vertical ionization potentials were compiled from the photoionization efficiency curves. Remarkably low values were obtained for In3O and In7O. Geometric and electronic structures of the InNO and InNO+ clusters were computed with density functional theory using the hybrid B3LYP functional. The bonding in these clusters is analyzed by means of Bader’s atoms in molecules method. Calculated adiabatic and vertical ionization potentials are in good agreement with the experimental values.

On the internal energy of sputtered clusters

We have used laser ionization and time-of-flight mass spectrometry to investigate the internal excitation of neutral clusters that were generated by sputtering from a solid indium surface under bombardment with 15 keV Xe+ ions. More specifically, single photon ionization of the clusters is accomplished by a tunable, frequency doubled laser and the photoionization efficiency (PIE) curves are collected with the photon energy varied around the ionization energy in a range between 4.2–6 eV. The results are compared with the PIE curves of supposedly cold indium clusters which were produced by a supersonic nozzle expansion using a laser vaporization source and investigated under otherwise similar conditions. As a result, the sputtered clusters show a distinctive broadening and shift of the PIE curve in the threshold region, thus illustrating the influence of the sputtering process in increasing the internal energy of the ejected clusters. The experimental PIE curves are interpreted in terms of a simple model using the internal temperature and ionization energy of the cluster as fit parameters. Depending on the cluster size, temperatures between 3850 and about 1000 K are found for sputtered Inn clusters.

Visible and near-infrared photoabsorption spectrum of Li3O: Resonance enhanced two-photon ionization spectroscopy and ab initio calculations

We report the measurement of the photoabsorption spectrum of Li3O using resonance-enhanced two-photon ionization spectroscopy in the energy range between 0.7 and 2.75 eV. Ab initio geometry optimization calculations at the CCSD(T)/6-311+G(d) level of theory are carried out, resulting in a stable D3h ground state symmetry for Li3O. Vertical excitation energies are computed from the CCSD(T) potential, and the flatness of the potential energy surface is analyzed. A comparison of the recorded absorption spectrum with the theoretical predictions allows an assignment of all the observed bands and excited states in terms of a D3h ground state structure. It is argued that the width of the bands is governed by the flat-bottomed shape of the potential energy surface.

Internal excitation of sputtered neutral indium clusters

Abstract The internal energy distribution of neutral indium clusters Inn sputtered from a polycrystalline In surface by 15 keV Xe+ ions is investigated by means of laser post-ionization and time-of-flight mass spectrometry. In particular, the neutral species are ionized by a tunable frequency doubled dye-laser and the photoionization efficiency (PIE) curves were collected with the photon energy varied around the ionization potential. This way, internal energy distributions of sputtered clusters in the size range n=2–35 could be determined using photon energies of 4.2–6 eV. The results are compared with the PIE curves of cold indium clusters which were produced by a supersonic nozzle expansion using a laser vaporization source and investigated under otherwise similar conditions. As a result, the sputtered clusters show a distinctive broadening of the PIE curve in the threshold region, thus illustrating the influence of the sputtering process in increasing the internal energy of the ejected clusters.

Chapter 6 Magic numbers for shells of electrons and shells of atoms in binary clusters

Publisher Summary This chapter discusses the magic numbers for shells of electrons and shells of atoms in binary clusters. It reviews recent studies of small binary clusters, with less than 100 atoms per clusters. Because of these small sizes, many of the species can be considered as molecules, implying the use of molecular language when describing their structure. In that review, the chapter combines this with terminology borrowed from condensed matter physics. There is a concise description of how binary clusters are produced and a summary of relevant cluster models, respectively. In addition, three types of binary cluster systems are reviewed: electronegatively doped main group metals, transition-metal-doped noble metals, and metal-doped semi-metal clusters. In all three cases, special attention is given to binary systems in which the interplay between electronic shell closing and specific geometries gives rise to pronounced or exceptional physico-chemical (stability, reactivity, and magnetic.) properties.