Search results for "gold"

Collision induced dissociation of stored gold cluster ions

1994

The stability of gold cluster ions Au + (2≦n≦23) has been investigated via collision induced dissociation in a Penning trap. Threshold energies and dissociation channels have been determined. The cluster stability exhibits a pronounced odd — even alternation: Clusters with an odd number of atoms,n, are more stable than the even-numbered ones. Enhanced stabilities are found for Au 3 + , Au 9 + , and Au 19 + in accordance with the Clemenger-Nilsson and the deformed jellium model of delocalized valence electrons. Excited odd cluster ions withn≦15 predominantly decay by evaporation of dimers; all others decay by monomer evaporation. From the dissociation channels estimates of the binding energi…

Photodissociation of small group-11 metal cluster ions: Fragmentation pathways and photoabsorption cross sections

2003

Noble metal cluster ions Cu(n)(+), Ag(n)(+) and Au(n)(+) (n = 3-21) have been stored in a Penning trap and photodissociated by low intensity laser pulses of 10 ns at photon energies of 3.49 eV and 4.66 eV. The fragmentation pathways, neutral monomer and dimer evaporation, have been monitored as a function of cluster size, excitation energy and element. It is found that the behavior of the branching ratio between monomer and dimer evaporation as a function of excitation energy depends on the metal under investigation. In particular, the slope of the energy dependence is positive for silver but negative for gold and copper cluster ions. Furthermore, photoabsorption cross sections are determin…

Fragmentation pattern of gold clusters collided with xenon atoms

1994

Abstract The dissociation channels of gold cluster ions Au n + (2 ≤ n ≤ 23) have been investigated via collision induced dissociation in a Penning trap. Excited odd cluster ions with n ≤ 15 decay by evaporation of dimers, all others decay by monomer evaporation. Information on the binding energies is deduced from these dissociation channels.

Influence of metal–support interaction on the surface structure of gold nanoclusters deposited on native SiOx/Si substrates

2014

The structure of small gold nanoclusters (R ~ 2.5 nm) deposited on different silica on silicon substrates is investigated using several characterization techniques (AFM, XRD, EXAFS and GISAXS). The grain morphology and the surface roughness of the deposited gold clusters are determined by AFM. The in-plane GISAXS intensity is modelled in order to obtain information about the cluster size and the characteristic length scale of the surface roughness. AFM and GISAXS results are in excellent agreement and show that the surface morphology of the deposited clusters depends on whether defect-rich (native) or defect-free (thermal) silica is used as a substrate. Gold clusters show a strong tendency …

Photo fragmentation of metal clusters stored in a penning trap

1996

Photo fragmentation studies of stored mass selected metal cluster ions of a large size range are reported. The experimental method and the data evaluation are described in detail. Gold cluster ions were produced by laser vaporization and stored in a Penning trap. After size selection they were electronically excited by irradiation with a pulsed laser beam. Relaxation by evaporation of neutral atoms and dimers was observed as a function of photon energy. From these data upper and lower limits for dissociation energies are determined for Aun + (n=3 to 23).

A topological isomer of the Au25(SR)18−nanocluster

2020

Energetically low-lying structural isomers of the much-studied thiolate-protected gold cluster Au25(SR)18− are discovered from extensive (80 ns) molecular dynamics (MD) simulations using the reactive molecular force field ReaxFF and confirmed by density functional theory (DFT). A particularly interesting isomer is found, which is topologically connected to the known crystal structure by a low-barrier collective rotation of the icosahedral Au13 core. The isomerization takes place without breaking of any Au–S bonds. The predicted isomer is essentially iso-energetic with the known Au25(SR)18− structure, but has a distinctly different optical spectrum. It has a significantly larger collision cr…

Design and Synthesis of Molecular Reactors for the Preparation of Topologically Trapped Gold Cluster

1999

Ab Initio Simulation of Clusters: Relativistic Effects in Structure and Bonding of Noble Metal Nanoparticles

2005

Resolving the atomic and electronic structures of nanoclusters represents an important preliminary for their controlled use in future nanotechnologies. Here we show through the comparison of density-functional calculations with high-resolution photoelectron spectroscopy that 1.4 nm nanoparticles of silver (negatively charged clusters of 53 to 58 atoms) are icosahedral-based structures displaying a perfect icosahedral-induced electronic shell structure for Ag 55 − and slightly perturbed shell structures for the neighboring cluster sizes. At variance, 55-atom gold clusters exhibit several isomeric structures of low symmetry, with a largely diminished electronic shell structure. This surprisin…

Electron impact ionization/dissociation of size selected gold cluster cations

2000

Abstract Singly charged gold clusters, Au n + in the size range n =12 to 72 have been captured and stored in a Penning trap, size selected and subjected to an electron beam. This interaction leads to further ionization as well as dissociation. The resulting abundance spectra of doubly and triply charged clusters show (a) a lower size limit for the production of multiply charged clusters from an ensemble of hot precursors, which can be understood in terms of the respective decay pathways, (b) an odd/even alternation of singly and doubly charged clusters in the size range below n =30, which inverses sign with change of charge state, and (c) magic numbers, i.e. prominent signals for particular…

Au n+-induced decomposition of N2O

1994

Reactions between small gold cluster ions, Au, and N2O were studied in a Penning trap mass spectrometer. Gold clusters were produced by laser vaporization and injected into a Penning trap. After reaction times of 50–7000ms the products were detected by time-of-flight mass spectrometry. For the major reaction channel, Au + N2OAu1,2N + NO+, rates of (0.9±0.1)×10−12 cm3 s−1 and (2.4±0.4)×10−12 cm3 s−1 were determined which are about a factor 500 below the collision rate. The corresponding activation energies for N2O decomposition were estimated to lie below 0.6 eV and 0.3 eV. Additional products with small branching ratios were detected, viz. the ions Au1O+, Au1N2O+, Au2N+, Au2NO+, Au2N2O+, Au…