Physical properties of transition metal doped gold and silicon clusters studied with mass spectrometry and action spectroscopy

In the past decades physics has experienced a major transition, and alongside studying fundamental laws, the investigation of new structures, objects, and phenomena has become a focus. Currently, there is great interest in finding nanoscale structures with specific, application friendly, physical and chemical properties. Clusters, which are entities consisting of several up to thousands of atoms, are considered a valuable research topic. Although they are intermediate in size between atoms and bulk, their properties differ from the analogous bulk material and can in certain cases be superior, even though both are subject to the same fundamental laws. In these small systems, every atom counts, and a clear understanding of the size and composition dependency of their characteristics is necessary. Doping a cluster with a single, transition metal atom allows for flexible tuning of the cluster properties and adds a new dimension in search of tailor-made properties. Combining two different elements in a cluster enables us to change the number of electrons independently of the total number of atoms.For this reason, doped clusters are the ideal research subject to study the physical properties of clusters in a controlled manner. An essential step is to obtain a good knowledge of the geometrical structure, as it will also provide better insight in magnetic, optical, electronic, and chemical properties. The effect of doping is studied for transition-metal doped gold (Au_nCu_m+ and Au_nY{+,0}) and silicon (Si_nX{+,0} with X = V, Cr, Mn, Re, and Cu) clusters.Indirect structural information is obtained via argon adsorption experiments where the likeness of argon attachment is observed in mass spectrometric studies. This size-dependent attachment of argon on the clusters renders information about the position of the dopant atom as well as on the onset towards 3D structures. More detailed information can be found via a direct structural assignment of the clusters. This is done by a combined experimental and theoretical infrared absorption action spectroscopy study and is presented in detail in this thesis. Infrared multiple photon dissociation of cluster-rare gas complexes indicates the vibrational activity of these clusters which is directly related to the geometry of the clusters under investigation. We observed that the addition of different dopant atoms can result in different structural growth patterns. The dopant atom favors a high-coordinated position in one growth mechanism, while in others, it simple adds to a bare cluster. Certain sizes are also of particular interest due to their highly stable and symmetric structures, such as Si_7Mn+ or Si_{16}V+. Because both cationic and neutral clusters are investigated, we were also able to study the relation between the geometric and electronic structures of both charge states. We observed that a cluster (Au_6Y{+,0}) can change its geometry upon electron attachment in order to pursue an electronic shell closure.Additionally, also the electronic structure of small Au_nCu_m+ clusters was investigated by means of near-UV and visible light spectroscopy. From this, the electronic excitation spectra show a blue shift upon increased dopant atom content.In the presented thesis work, the geometric, electronic, and optical properties of transition metal doped gold and silicon clusters were studied by means of mass spectrometry and action spectroscopy. It is observed that both the composition of the cluster and the number of electrons in it, is of importance for the physical properties of these doped clusters.1 Introduction Outline of the thesis 2 Experimental methods 2.1 Pulsed free cluster setup 2.2 Laser systems 2.2.1 OPO systems 2.2.2 Free Electron Laser for Infrared eXperiments (FELIX) 2.3 Rare gas tagging as structural probe 2.4 UV and visible light spectroscopy 2.5 Vibrational spectroscopy 2.5.1 Vibrational modes 2.5.2 Direct absorption vs action spectroscopy 2.5.3 Infrared multiple photon dissociation 2.5.4 Messenger atom technique 2.5.5 Two color ionization technique 2.5.6 Data evaluation 2.5.7 Choice of theoretical methods 3 UV and visible light spectroscopy on copper doped gold clusters 3.1 Temperature-dependent formation of cluster-van der Waals complexes 3.2 UV and visible light spectroscopy: copper doped gold clusters 4 Structures of doped gold clusters 4.1 Neutral and cationic yttrium doped gold clusters 4.1.1 Structures of Au_nY0 (n = 4-9) clusters 4.1.2 Structural assignment of Au_6Y+ 4.2 Comparison between different charge states of Au_6Y 4.2.1 Difference in IR-MPD spectra of Au_6Y0 and Au_6Y+ 4.2.2 Electronic structure of Au_6Y{+,0,-} 5 Structures of doped silicon clusters 5.1 Bare silicon clusters 5.1.1 Cationic bare silicon clusters: Si_n+ 5.1.2 Neutral bare silicon clusters: Si_n0 5.2 Small exohedrally doped silicon clusters 5.2.1 Si_nX+ (n = 4-11, 6-11; X = V, Cu) 5.2.2 Si_nMn+ (n = 6-10) 5.2.3 Si_nX+ (n = 6-10, 3-9; X = Cr, Re) 5.2.4 Si_nX0 (n = 6-9; X = V, Mn) 5.3 Large endohedrally doped silicon clusters 5.3.1 Si_nV+ (n = 12-16) 5.3.2 Si_nMn+ (n = 11-16) 6 Discussion on doped silicon clusters 6.1 Geometrical comparison of cationic and neutral bare silicon clusters 6.2 What is the in uence of a dopant atom on the cluster geometry? 6.2.1 Structures of cationic doped silicon clusters 6.2.2 Structural changes of neutral doped silicon clusters 6.3 Infl uence of the charge state on the electronic structure of Si_nV{+,0} and Si_nMn{+,0} 7 Conclusions Nederlandse samenvatting Bibliography Publications Curriculum vitaenrpages: 227status: publishe