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1.
B. Huber M. Moseler 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(3):485-489
We showed in a recent density functional study that small
palladium cluster on a MgO surface with F-centers can be oxidized
to epitaxial PdxOy nano-oxides below
room temperature [1].
Here, we employ density functional theory in order to explore
different methods for an experimental verification of the PdxOy
formation. The electronic density of states (DOS) of bare, O2-decorated and of oxidized palladium cluster was calculated.
For many cluster sizes a clear difference in the DOS could be observed allowing
for a detection of the oxidation with surface sensitive spectroscopic methods.
In addition, adsorption sites and stretch frequencies of a single CO molecule
on bare and oxidized Pd4 clusters were calculated.
While CO prefers hollow sites on Pd4, top
adsorption sites are found for Pd4O2. Markedly different CO stretch
frequencies indicate a possible discrimination of bare clusters and oxides
by Fourier transform infrared spectroscopy. 相似文献
2.
E. Barborini C. Lenardi P. Piseri P. Milani R. G. Agostino T. Caruso E. Colavita S. La Rosa M. Bertolo C. Ducati 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):273-276
Inclusions of metals in the growth process of carbon
cluster assembled materials (ns-C) induce modifications in the
structural and electronic properties of the material. A novel
pulsed microplasma cluster source (PMCS) is able to deliver
highly intense, collimated and stable beams suitable for
producing bulk quantities of cluster-assembled nanocomposite
films. Loading of metal nanoparticles into carbon cluster based
films is obtained either by mixing a gas phase metallorganic
compound with the carrier gas (He) before entering into the
source (for example molybdenum (V) isopropoxide), or by using a
double component sputtering target (metal (Ti, Ni)/graphite). The study of film
morphology on nanometer scale, carried out by transmission
electron microscopy (TEM), reveals the dispersion in a ns-C
matrix of metallic particles and, in the case of molybdenum
containing films, also of carbide particles. Spatially resolved
ultraviolet photoemission spectroscopy confirms the segregation
of metal particles and exhibits evident anisotropy in the
Mo:ns-C films, mainly ascribable to the formation of carbide
nanoparticles. 相似文献
3.
C. Hébert M. Willinger D.S. Su P. Pongratz P. Schattschneider R. Schlögl 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(4):407-414
Band-structure (BS) calculations of the density of states (DOS) using the full potential augmented plane waves code WIEN97
were performed on the four single-valence vanadium oxides VO, V2O3, VO2 and V2O5. The DOS are discussed with respect to the distortions of the VO6 octahedra, the oxidation states of vanadium and the orbital hybridisations of oxygen atoms. The simulated oxygen K-edge fine
structures (ELNES) calculated with the TELNES program were compared with experimental results obtained by electron energy-loss
spectrometry (EELS), showing good agreement. We show that changes in the fine structures of the investigated vanadium oxides
mainly result from changes in the O-p DOS and not from the shift of the DOS according to a rigid band model.
Received 17 December 2001 / Received in final form 19 June 2002 Published online 13 August 2002 相似文献
4.
Sun Guoya Xing D.Y. Shen R. Lin H.Q. 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(1):33-38
The Nambu spinor Green's function approach is applied to calculating the density of states (DOS) and superconducting order
parameter in normal-metal/insulator/ferromagnet/superconductor (NM/I/FM/SC) junctions. It is found that the s-wave superconductivity and ferromagnetism can coexist near the FM/SC interface, which is induced by proximity effect. On
the SC side, the spin-dependent DOS appears both within and without the energy gap. On the FM side, the superconducting order
parameter displays a damped oscillation and the DOS exhibits some superconducting behavior. The calculated result for the
DOS in FM for “0 state” and “π state” can reproduce recent tunneling spectra in Al/Al2O3/PdNi/Nb tunnel junctions.
Received 1st July 2002 Published online 19 November 2002 相似文献
5.
C. Herwig J.A. Becker 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):51-54
The growth of small tellurium clusters in helium and the influence of a metal impurity (dysprosium atoms) on the cluster size
distribution are investigated in a double laser vaporization source. A model describing the role of the carrier gas as collision
partner is presented, emphasizing the crucial influence of the gas pressure on cluster formation. Changes in cluster reactivity
due to dysprosium addition are discussed in terms of ionic structures Dy
3 +(Te
N)3 - containing a radical electron.
Received 28 November 2000 相似文献
6.
A detailed Raman study on thin single-wall carbon nanotubes prepared by the HiPCO process 总被引:2,自引:0,他引:2
A. Kukovecz Ch. Kramberger V. Georgakilas M. Prato H. Kuzmany 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(2):223-230
The Raman spectrum of single wall carbon nanotubes (SWNTs) prepared by high pressure CO decomposition (HiPCO process) has
been recorded at nine excitation laser energies ranging from 1.83 eV to 2.71 eV. The characteristic nanotubes features: G
band, D band and radial breathing mode (RBM) have been analyzed and compared to those of an arc discharge SWNT material of
similar diameter. A strong Breit-Wigner-Fano type (metallic) contribution to the G band was found in the spectra measured
with green lasers, while spectra measured with red lasers indicate resonances of semiconducting SWNTs. Analysis of the energy
dependence of the position of the D band revealed sinusoid oscillations superimposed on a linear trend. The validity of full
DOS calculations for HiPCO materials has been confirmed by a match found between the estimated spectral contribution of metallic
SWNTs as calculated from the components of the measured G band and as predicted by the (n, m) indexes of the major scatterers of DOS simulations. The RBM region of the HiPCO spectrum is more complex than usually observed
for SWNTs. The analysis performed with a Gaussian distribution and improved fitting parameters leads to a mean diameter and
variance of 1.05 nm and 0.15 nm, respectively. A bimodal Gaussian distribution had little influence on the error sum but reduced
the standard error slightly. The major spectral features of the RBM could be interpreted using available resonance Raman theory.
Received 5 February 2002 / Received in final form 3 April 2002 Published online 19 July 2002 相似文献
7.
E. Fort H. Vach M. Châtelet A. De Martino F. Pradère 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(1):71-76
In this paper, we investigate the global structure of mixed clusters created by coexpansion. To determine the relative dopant
sites within the mixed clusters, we take advantage of the strong dependence of the cluster/surface collision dynamics on the
incident mixed cluster structure. Using both experiments and molecular dynamic simulations, we show that the coexpansion process
leads to the most stable cluster structure for Ar
<880>
Kr
<120> clusters. This structure corresponds to an annealed structure and can be characterized as a nearly homogeneous mixture throughout
the cluster with a thin argon coating.
Received 4 October 2000 相似文献
8.
R. Kishore S. Lamba 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(2):161-164
An exact analytical expression for the specific heat jump at the critical temperature Tc has been obtained directly from the BCS gap equation for any shape of the energy dependent electronic density of states (DOS).
We consider a model which takes into consideration electron-electron repulsion, formulated in the Hubbard model along with
the electron-electron attraction due to electron-phonon interaction in the BCS formalism. We have analyzed this expression
for constant as well as for the Lorentzian forms of DOS. It is shown that the constant DOS in the simple BCS theory cannot
explain the large values of , found in some superconductors. The specific heat versus temperature curve has been found to have a peak, similar to that of Eliashberg theory of superconductivity. The influence
of repulsive interaction is very small and occurs mainly at higher temperatures.
Received: 26 January 1998 相似文献
9.
The quasirelativistic INDO/1 method has been used to generate molecular orbitals for some {Ge
x
}, doped {Ge
x
Ga
y
} and {Ge
x
As
y
} clusters. These one-electron energy levels predefine the density of states (DOS) and/or hole functions. The effect of the cluster size (x=24, 56, 92) and that of dopants on the DOS profiles are discussed. The calculations are compared with those generated by periodic crystal orbitals of the EHT quality. 相似文献
10.
M. Schulze S. Gourley S. A. Brown A. Dunbar J. Partridge R. J. Blaikie 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):291-294
A range of percolating atomic cluster films, with
nanoscale overall dimensions, have been studied using a
combination of in situ and
ex situ electrical transport
measurements, together with field emission electron microscopy
and atomic force microscopy. Bismuth clusters with mean diameter
20 nm were deposited between electrical contacts defined by
electron beam lithography. The morphology of the films can be
understood within percolation theory, and the electrical
measurements show complex behaviour characteristic of both
percolation effects and modification of the cluster films by
current flow and by oxidation. 相似文献
11.
A. Wurl M. Hyslop S.A. Brown B.D. Hall R. Monot 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):205-208
We present new results of electron diffraction experiments on unsupported nanometer-sized bismuth clusters. The high intensity
cluster beam, necessary for electron diffraction, is provided by an inert-gas aggregation source. The cluster beam contains
particles with average cluster sizes between 4.5 and 10 nm. When using Helium as a carrier gas we are able to observe a transition
from crystalline clusters to a new structure, which we identify with that of amorphous or liquid clusters.
Received 28 November 2000 相似文献
12.
Z.F. Liu W.L. Yim J.S. Tse J. Hafner 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,10(1):105-114
Ab initio Molecular Dynamics (MD) method, based on density functional theory (DFT) with planewaves and pseudopotentials, was used to
study the stability and internal motion in silver cluster Agn, with n
=4-6. Calculations on the neutral, cationic and anionic silver dimer Ag2 show that the bond distance and vibrational frequency calculated by DFT are of good quality. Simulations of Ag4, Ag5, and Ag6 in canonical ensemble reveal distinct characteristics and isomerization paths for each cluster. At a temperature of 800 K,
an Ag4 has no definite structure due to internal motion, while for Ag5 and Ag6the clusters maintain the planar structure, with atomic rearrangement observed for Ag5 but not for Ag6. At a temperature of 200 K, Ag4 can exist in two planar structures whilst Ag5 is found to be stable only in the planar form. In contrast Ag6 is stable in both planar trigonal and 3D pentagonal structures. Micro-canonical MD simulation was performed for all three
clusters to obtain the vibrational density of states (DOS).
Received 5 May 1999 and Received in final form 20 August 1999 相似文献
13.
X. Wu A.K. Ray 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(3):345-351
The electronic and geometric structures of bulk PuO2 and its (110) surface have been studied using a periodic model within the generalized gradient approximation (GGA) of density
functional theory (DFT). The sixty core electrons of the Pu atom have been represented by a relativistic effective core potential
and scalar relativistic effects have been incorporated on the valence orbitals. For bulk PuO2, we predict an equilibrium lattice constant of 10.10 a.u. and a cohesive energy of 17.28 eV, in good agreement with experimental
data. For the (110) surface, upon relaxation, the distance between the top layer and the next layer is found to decrease by
0.12 ?, i.e. 5.3% of the corresponding interlayer distance in the bulk. The distance between the two oxygen atoms on the top layer is
found to increase by 0.15 ?, i.e. 5.6% of the corresponding bulk value. The small surface relaxation energy of 0.268 eV per unit cell indicates the fair stability
of this surface. The effective charges on Pu and O atoms show that the chemical bonding in this system is not purely ionic.
Together with the metallic feature of the density of states (DOS) on the surface, the effective charge distribution provides
some basis for understanding surface reactivity and corresponding support for catalysis.
Received 16 June 2000 相似文献
14.
L. Bartosch P. Kopietz 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(1):29-36
We consider the effect of Coulomb interactions on the average density of states (DOS) of disordered low-dimensional metals
for temperatures T and frequencies ω smaller than the inverse elastic life-time 1/τ. Using the fact that long-range Coulomb interactions in two dimensions (2d) generate ln2-singularities in the DOS ν(ω) but only ln-singularities in the conductivity σ(ω), we can re-sum the most singular contributions
to the average DOS via a simple gauge-transformation. If σ(ω) > 0, then a metallic Coulomb gapν(ω) ∝ |ω|/e
4 appears in the DOS at T = 0 for frequencies below a certain crossover frequency Ω
2 which depends on the value of the DC conductivity σ(0). Here, - e is the charge of the electron. Naively adopting the same procedure to calculate the DOS in quasi 1d metals, we find ν(ω) ∝ (|ω|/Ω
1)1/2exp(- Ω
1/|ω|) at T = 0, where Ω
1 is some interaction-dependent frequency scale. However, we argue that in quasi 1d the above gauge-transformation method is on less firm grounds than in 2d. We also discuss the behavior of the DOS at finite temperatures and give numerical results for the expected tunneling conductance
that can be compared with experiments.
Received 28 August 2001 / Received in final form 28 January 2002 Published online 9 July 2002 相似文献
15.
A. Kohen F. Giubileo Th. Proslier F. Bobba A. M. Cucolo W. Sacks Y. Noat A. Troianovski D. Roditchev 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,57(1):21-25
Using Scanning Tunneling Microscope at low temperature
we explore the superconducting phase diagram in the π-band of
the two-band superconductor MgB2. In this band the peculiar
shape of the local tunneling spectra and their dynamics in the
magnetic field reveal the complex character of the quasiparticle
density of states (DOS). The gap in the DOS is first rapidly
filled with states in raising the magnetic field up to 0.5 T and
then slowly approaches the normal state value: the gap is
observed up to 2 T. Such a change in the DOS dynamics suggests the
existence of two terms in the DOS of the π-band: a first one,
reflecting an intrinsic superconductivity in the band and a second
one, originating from an inter-band coupling to the σ-band.
Our findings allow a deeper understanding of the unique phase
diagram of MgB2. 相似文献
16.
C.Z. Tan 《Journal of Physics and Chemistry of Solids》2002,63(1):179-183
The infrared reflection spectra of silica glass were monitored at different incident angles of the wave. The density of states (DOS) and frequency ωLO of the longitudinal optic (LO) mode were found to be the functions of the incident angle. The DOS of the LO mode increases with increasing incident angle as a whole. However, two regions can be divided in which one is below ∼30° and the other is above 30°. The frequency ωLO of the LO mode increases linearly with incident angle. The earlier proposed relationship between the shifted frequency produced by the Doppler effect and the source frequency of the main transverse optic (TO) mode was investigated by studying the infrared spectra of the annealed glass capillaries. The shifted frequency was found to be linearly proportional to the source frequency of the TO mode, as depicted by the Doppler effect. 相似文献
17.
G. E. Ntamack F. Chandezon B. Manil H. Lebius S. Tomita C. Guet M. G. Kwato Njock B. A. Huber 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):153-156
Highly charged sodium clusters produced in collisions
between neutral clusters and multiply charged ions are formed
within a large range of temperatures and fissilities, and
identified by means of a high-resolution reflectron-type
time-of-flight mass spectrometer ( m/m
14000). The limit of stability of these charged clusters is
experimentally investigated, and the time-of-flight spectra are
compared with theoretical spectra based on Monte-Carlo
simulations. The results indicate that the maximum fissility
(X) of stable clusters is
approaching the Rayleigh limit (X = 1) for larger clusters sizes. It is
mainly limited by the initial neutral cluster temperature (
T 100 K) and the energy
transfer in the ionizing collision. In addition, the comparison
between the measured and simulated spectra suggests for high
cluster charges a multi-fragmentation process, in which most of
charge is emitted, creating low charged residual cluster ions. 相似文献
18.
C. Binns S.H. Baker M.J. Maher S.C. Thornton S. Louch S.S. Dhesi N.B. Brookes 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):189-192
A portable UHV-compatible gas aggregation cluster source, capable of depositing clean mass-selected nanoclusters in situ, has been used at synchrotron radiation facilities to study the magnetic behaviour of exposed and Co-coated Fe clusters in
the size range 250 to 540 atoms. X-ray magnetic circular dichroism (XMCD) studies of isolated and exposed 250-atom clusters
show a 10% enhancement in the spin magnetic moment and a 75% enhancement in the orbital magnetic moment relative to bulk Fe.
The spin moment monotonically approaches the bulk value with increasing cluster size but the orbital moment does not measurably
decay till the cluster size is above ∼ 400 atoms. The total magnetic moments for the supported particles though higher than
the bulk value are less than those measured in free clusters. Coating the deposited particles with Co in situ increases the spin moment by a further 10% producing a total moment per atom close to the free cluster value. At low coverages
the deposited clusters are super-paramagnetic at temperatures above 10 K but a magnetic remanence at higher temperature emerges
as the cluster density increases and for cluster films with a thickness greater than 50 ?(i.e. 2-3 layers of clusters) the remanence becomes greater than that of an Fe film of the same thickness produced by a conventional
deposition source. Thick cluster-assembled film show a strong in-plane anisotropy.
Received 14 December 2000 相似文献
19.
We have experimentally studied the dissociation/coalescence of internal Plateau borders (PBs) in simple monolayer bubble clusters, as a result of changing the liquid fraction. At large liquid content, the clusters consist of n bubbles of the same size, symmetrically placed around an internal n-sided PB (n-PB). On decreasing the liquid fraction we observed symmetry-breaking transitions in the 4- and 5-bubble clusters (but not in the 3-bubble cluster), followed by dissociation of the PBs. We used the Surface Evolver to determine the various equilibrium configurations of the corresponding two-dimensional wet clusters and their surface energies. The sequence of 4-bubble cluster configurations observed on varying the liquid fraction correlates qualitatively with that predicted on the basis of Surface Evolver calculations. The same is not true of the 5-bubble cluster. 相似文献
20.
W. Vervisch C. Mottet J. Goniakowski 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):311-314
Morphology and atomic structure of supported Pd clusters
on MgO(100) substrate are investigated theoretically using a
mixed approach: a semi-empirical potential for the metal bonding
within the cluster and a potential fitted to
ab initio calculations for
the metal-oxide interaction. We find that the clusters adopt a
truncated pyramidal morphology in agreement with experimental
results. The detailed study of the epitaxial relation as a
function of cluster size shows the existence of a critical size
around 3 nm where elastic strain due to the misfit between the
substrate and the deposit is released by the introduction of
interfacial dislocations. 相似文献