Photoelectron spectroscopy of the structure and dynamics of free size selected sodium clusters (original) (raw)
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Free nanoscale sodium clusters studied by core-level photoelectron spectroscopy
Physical Review B, 2007
Free sodium metal clusters have been studied by probing the Na 2p core level using x-ray photoelectron spectroscopy ͑XPS͒ and Auger electron spectroscopy ͑AES͒. The development of electronic structure with size has been studied and discussed in comparison with the atom, dimer, and solid. Information on cluster metallic properties, size, and temperature has been deduced from the XPS measurements. For the large ͗N͘ Ͼ 10 3 Na clusters, the surface and bulk sites have been separated in the photoelectron signal. Auger spectra allowed extracting the information on the valence band. The present study introduces core-level spectroscopies XPS and AES into the field of free neutral metal cluster research.
Structural and electronic properties of sodium clusters under confinement
Physical Review B, 2015
Using real-space density functional theory, electronic structure and equilibrium geometries of sodium clusters in the size range of 2-20 atoms have been calculated as a function of confinement. We have examined the evolution of the five lowest isomers as a function of volume for six different compressions. The minimum volume considered is about 1/15 to 1/10 of the free-space box volume. We observe a strong tendency for isomeric transitions in many cases, with the higher isomers evolving into the ground state under confinement. In general the clusters tend to become more spherical. The changes in the total energies and the geometries are not significant until the volume gets reduced beyond the 1/3 of the original volume. In this sense, the clusters are not easy to compress. Once the critical volume is reached, the changes in the total energies and geometries are rapid. It turns out that the increase in the total energy is mainly due to the ion-ion and Hartree energies of electrons. We also address how anisotropic confinement affects the geometry of clusters. We further show that geometries obtained with anisotropic confinement are strongly supported by the simulation of clusters inside a carbon nanotube using a hybrid quantum-mechanical and molecular-mechanics approach.
Journal of Physics B: Atomic, Molecular and Optical Physics, 1998
We study the linear and nonlinear electron dynamics of a Na + 9 cluster using timedependent density functional theory. Exchange-correlation (xc) effects are treated in the adiabatic local density approximation with and without self-interaction correction (SIC). The latter is implemented within the time-dependent optimized effective potential method, leading to a selfinteraction-free xc potential which is orbital independent. The method is applied to compare the electronic response of the cluster, calculated with and without SIC, in different dynamical regimes. We focus on the dipole response in the weakly excited regime, and on multiphoton ionization induced by strong femtosecond laser pulses. It is found that including SIC produces minor differences in the dipole power spectra and leaves the ionization mechanism essentially unchanged.
Computational Materials Science, 1998
The optical response of sodium clusters is studied using fully three-dimensional electronic dynamics, in real time, with an explicit ionic background. The obtained spectra are shown to come close to experimental results for free clusters. We use the approach also to compute the response of sodium clusters deposited on a NaCI(I 00) surface. The flattening of the clusters induced by the surface results in a shift and a large fragmentation of the plasmon resonance.
Spectroscopy of size-selected sodium clusters
European Physical Journal D, 1991
The method of angular resolved elastic scattering has been used to achieve a size selection of neutral sodium clusters. After the scattering process the clusters are ionized by single photon ionization with various laser energies and detected by a time-of-flight mass spectrometer. The elastic scattering of Na2 by Ne serves as a test for the experimental setup. Angular dependence of scattered sodium clusters ionized with 308 nm shows a significant amount of fragmentation of the neutral Na6 to Na9 clusters which are observed in the Na 5 + and Na 6 + ion channels.
Structure Determination of Medium-Sized Sodium Clusters
Physical Review Letters, 2007
Sodium cluster anions Na ÿ n with n 39-350 have been studied by low temperature photoelectron spectroscopy and density functional theory (DFT). The highly structured experimental spectra are in excellent agreement with the electronic density of states (DOS) of the DFT lowest energy structures. Even for the largest sizes, a pronounced sensitivity of the DOS on fine geometric details could be observed, allowing for a reliable identification of a specific icosahedral growth motif. The intermediate sizes between the closed-shell Mackay clusters with 55, 147, and 309 atoms form by growth of overlayers, which often exhibit a twist deformation with respect to regular (Mackay-type) ones.
Journal of Electron Spectroscopy and Related Phenomena, 1999
The investigation of the electronic structure and dynamics of clusters is a topic of current interest. Spectroscopy with vacuum ultraviolet (VUV) photons has two aspects: (i) systems with a large band gap can be studied and (ii) excitation of inner shell electrons allows us to obtain element-specific information. This paper gives an overview of recent developments in the field of cluster research with VUV radiation. Two topics will be discussed in detail: (i) Electronic excitation and relaxation dynamics in helium clusters studied with fluorescence spectroscopy. It turned out that desorption of electronically excited atoms and molecules is an important relaxation process. (ii) Inner shell photoionisation of NaCl clusters produced with a new pick-up cluster source. The near edge absorption structure (XANES) at the Cl 2p edge contains information on the geometric structure of the clusters.
Effects of Confinement on Structural Stability and Electronic Structure of Sodium Clusters
2016
We have investigated structural stability and electronic properties of sodium clusters in the size range of 2-20 atoms as a function of confinement using real space density functional theory (DFT). We have selected lowest energy structures by examining lowest five isomers as a function of volume for six different compressions. The minimum volume considered is about 10% of the free box volume. We analyze energetics, eigenvalue spectra, molecular orbitals and charge density to examine the stability and electronic properties of the sodium clusters. Our calculations show the insignificant changes in the total energies until the volume gets reduced beyond the one third of the original volume. Once the critical volume is reached, the changes in the total energies are significant. This is accompained by the breaking of degeneracy of electronic levels, the increase in spacing between the energy states. The molecular orbital analysis shows the hybridization of sp-d orbitals, rotations, split...
Temperature-dependent ionization potential of sodium clusters
The European Physical Journal D, 2000
The ionization potential of sodium clusters (8 ≤ N ≤ 55) at a finite temperature is studied using density functional theory and ab initio molecular dynamics. The threshold regions of the photoionization efficiency curves are deduced from the integrated IP distributions, which are obtained from the energy eigenvalues of the highest occupied Kohn-Sham states during molecular dynamics by applying a theoretically well-defined shift. The calculated ionization potentials are directly compared to the experimental values. The energetically best geometry of Na55 is found to be a slightly distorted icosahedron. PACS. 36.40.Cg Electronic and magnetic properties of clusters-36.40.Mr Spectroscopy and geometrical structure of clusters-71.24.+q Electronic structure of clusters and nanoparticles