共查询到20条相似文献,搜索用时 46 毫秒
1.
V. Bonačić-Koutecký C. Bürgel L. Kronik A. E. Kuznetsov R. Mitrić 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(3):471-476
We present structural and optical properties of silver clusters Agn (n=2, 4, 6, 8) at two model support sites of MgO, stoichiometric MgO(100) and FS-center defect, based on density functional theory and embedded cluster model. Our results provide the mechanism responsible
for the absorption and emission patterns due to the specific interaction between the excitations
within the cluster and the support site which is strongly cluster size and structure dependent.
We propose Ag4 at stoichiometric site as well as Ag2, Ag4 and Ag6 at FS-center defects as good candidates for the emissive centers in the visible regime. 相似文献
2.
K.?Koyasu M.?Niemietz W.?Westh?user G.?Gantef?r 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,53(1):59-62
The decay path of an Ag8(O2)- cluster photoexcited by a 3.1 eV photon is elucidated using time-resolved photoelectron spectroscopy. Photoabsorption results
in the formation of an excited state giving rise to a peak in the photoelectron spectra with well-resolved vibrational finestructure.
With a lifetime of about 100 fs this bound state decays into an anti-bonding state which dissociates into O2 and Ag8- on a timescale of 10 ps. In the photoelectron spectra, this corresponds to a broad maximum shifting gradually towards higher
binding energy while the O2 and Ag8- separate. Finally, the spectrum of bare Ag8- appears. This process is unique to small clusters, because on metal surfaces excited state lifetimes are too short to allow
for direct dissociation. 相似文献
3.
T. Rander M. Lundwall A. Lindblad G. Öhrwall M. Tchaplyguine S. Svensson O. Björneholm 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,42(2):253-257
Resonant Auger spectra of O2 clusters excited at the O1s edge are reported. After excitation to the repulsive 1s-13σ* state, the resulting resonant Auger spectrum displays features that remain constant in kinetic energy as the photon energy
is detuned. The shift between known atomic fragment features and these features is consistent with that observed for atoms
and clusters in singly charged states in direct photoemission. These findings are strong evidence for the existence of molecular
ultrafast dissociation processes within the clusters or on their surface. 相似文献
4.
J. Wang J. Zhao L. Ma G. Wang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(2):289-294
The stuffed fullerene structures of medium-sized SiN
(
) clusters have been systemically studied
using the all-electron density functional theory with gradient correction.
For each cluster size, fullerene cages with different topologies and filled
by different number of atoms were constructed and optimized to find the
lowest-energy structure. The core atoms filled in the fullerene cages tend
to form cage-like structures that resemble structural character of bulk
diamond fragments. The size-dependent physical properties such as binding
energies, electronic gaps, and ionization potentials have been discussed.
Si45 exhibits relatively higher stability that can be associated with
the low chemical reactivity observed by experiment. 相似文献
5.
Yu. A. Surnin I. I. Klimovskikh D. M. Sostina K. A. Kokh O. E. Tereshchenko A. M. Shikin 《Journal of Experimental and Theoretical Physics》2018,126(4):535-540
The effect of an ultrathin Pb film deposited on the surface of Bi2Se3 and Sb2Te3 compounds on the electronic state structure of topological insulators is studied experimentally by the angle-resolved photoemission spectroscopy (ARPES) technique. The following features are revealed: formation of two-dimensional quantum-well states in the near-surface region, an increase in the binding energy of the Dirac cone and the core levels, and a simultaneous electronic states intensity redistribution in the system in photoemission spectra. The results obtained show that topological states may coexist at the interface between studied materials and a superconductor, which seems to be promising for application in quantum computers. 相似文献
6.
F.v. Gynz-Rekowski W. Quester R. Dietsche D. C. Lim N. Bertram T. Fischer G. Ganteför M. Schach P. Nielaba Y. D. Kim 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(3):409-413
The possibility of using magic Si7 clusters to form a cluster material was studied experimentally and theoretically. In experiments Si7 clusters were deposited on carbon surfaces, and the electronic structure and chemical properties of the deposited clusters
were measured using X-ray photoelectron spectroscopy (XPS). A non bulk-like electronic structure of Si7 was found in the Si 2p core level spectra. Si7 is suggested to form a more stable structure than the non-magic Si8 cluster and Si atoms upon deposition on carbon surfaces. Theoretically it was possible to study the interaction between the
clusters without the effect of a surface. Density functional theory (DFT) calculations of potential curves of two free Si7 clusters approaching each other in various orientations hint at the formation of cluster materials rather than the fusion
of clusters forming bulk-like structures. 相似文献
7.
M. X. Chen X. H. Yan S. Wei 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(3):513-517
Base on the density-functional theory, the structural and magnetic
properties of AunTi2
+ (
) clusters are investigated. The
two titanium atoms form a dimer in the gold clusters. The second-order
energy differences and HOMO-LUMO gap provide a clear explanation of the
abundance peaks and odd-even staggering observed recently in
photofragmentation experiments. The magnetism of AunTi2
+
cluster shows an odd-even effect when n increases from 1 to 4 and drops to
zero at n=5 and 7. The local magnetic moment and charge partition of Ti 4s,
3d orbitals are discussed. The peculiar magnetic properties are related to the
structures and the hybridization between the Au 5d, 6s states and Ti 3d, 4s
states. 相似文献
8.
L. Seetha Lakshmi K. Dörr K. Nenkov A. Handstein V. S. Sastry K.-H. Müller 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(2):115-121
We report the charge state modification effects at the Mn site on the ground
state properties of colossal magnetoresistive manganites. Ta5+
substitution results in an appreciable increase in the lattice parameters
and unit cell volume due to increased Mn3+ concentration. The
ferromagnetic-metallic ground state modifies to a cluster glass insulator
for
. The reduction in the transition temperatures with
increasing x is ∼39 K/at.%. Besides the modification of majority carrier concentration due to increased Mn3+ concentration and enhanced local structural effects, the local
electrostatic potential of the substituent seems to contribute to the
unusually strong reduction of the transition temperatures of the compounds.
Thermo magnetic irreversibility just below Curie temperature (Tc),
non-saturation of magnetization, two distinct magnetic transitions in ac
susceptibility in an appropriate static field: close to Tc and other at
low temperature (the spin freezing temperature (Tg)) and non-stationary
dynamics with a characteristic maximum in the magnetic viscosity close to
Tg confirm a cluster glass state for
. These results
find additional support from a linear low temperature magnetic specific heat
of x = 0.10 with a characteristic broad maximum close to Tg. 相似文献
9.
H. Nagao K. Awazu S. Hayakawa K. Iwamoto M. Toyoda T. Ichihara 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(2):279-287
Various dissociation channels of silver bromide cluster ion
Ag2Br+ and silver cluster ion Ag3
+ were observed in
high-energy collisionally-activated dissociation (CAD) using a Cs target.
The fragment patterns of the high-energy CAD were compared with those of the
metastable dissociation and low-energy CAD. The difference in the fragment
patterns between the high-energy CAD and the other dissociation methods was
explained in terms of the internal energy distributions. The dissociation
mechanisms of neutral silver bromide cluster Ag2Br and silver cluster
Ag3 were also investigated by charge inversion mass spectrometry using
the Cs target. While the fragment ions AgBr- and Ag2
- were
dominantly observed in the charge inversion spectrum of Ag2Br+,
the undissociated ion Ag3
- was observed as a predominant peak in
the case of Ag3
+. The dissociation behavior of Ag2Br*
can be explained on the basis of the calculated thermochemical data.
Contrary to this, the predominant existence of the undissociated
Ag3
- cannot be explained by the reported thermochemical data. The
existence of undissociated Ag3
- suggests that the dissociation
barrier is higher than the internal energy of Ag3
*
(theoretical: 1.03 eV, experimental: 2.31 eV) estimated from the ionization
potentials of Ag3 and Cs. 相似文献
10.
J. Zhao Y. Luo G. Wang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(3):309-316
Tight-binding model is developed to study the structural and electronic properties of silver clusters. The ground state structures
of Ag clusters up to 21 atoms are optimized by molecular dynamics-based genetic algorithm. The results on small Agn clusters (n = 3-9) are comparable to ab initio calculations. The size dependence of electronic properties such as density of states, s-d band separation, HOMO-LUMO gap, and ionization potentials are discussed. Magic number behavior at Ag2, Ag8, Ag14, Ag18, Ag20 is obtained, in agreement with the prediction of electronic ellipsoid shell model. We suggest that both the electronic and
geometrical effect play significant role in the coinage metal clusters.
Received 7 August 2000 相似文献
11.
The equilibrium and photoinduced absorption spectra of copper-and silver-doped Bi12SiO20 crystals are studied. It is demonstrated that the impurity absorption is due to Ag2+, Ag+, Cu3+, Cu2+, and Cu+ ions occupying almost octahedral Bi3 positions. A mechanism of photochromism is suggested, involving changes in the charge states of copper and silver impurity ions according to schemes Cu2+-e → Cu3+ and Ag+-e → Ag2+. 相似文献
12.
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
13.
D. P. Kozlenko S. V. Trukhanov E. V. Lukin I. O. Troyanchuk B. N. Savenko 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(4):361-365
The crystal and magnetic structures of the oxygen deficient manganites
La0.7Sr0.3MnO3-d (d = 0.15, 0.20) have been studied by means
of powder neutron diffraction over the 0–5.2 GPa pressure and 10–290 K
temperature ranges. La0.7Sr0.3MnO2.85 exhibits a coexistence
of rhombohedral
and tetragonal (I4/mcm) crystal structures and below
Tg ~ 50 K a spin glass state is formed.
La0.7Sr0.3MnO2.80 exhibits a tetragonal (I4/mcm) crystal structure.
Below Tg ~ 50 K a phase separated magnetic state is formed,
involving coexistence of C-type AFM domains with spin glass domains. In both
compounds the crystal structure and magnetic states remain stable upon
compression. The factors leading to the formation of different magnetic
states in La0.7Sr0.3MnO3-d (d = 0.15, 0.20) and their specific
high pressure behavior, contrasting with that of the stoichiometric
A0.5Ba0.5MnO3 (A = Nd, Sm) compounds showing pressure-induced
suppression of the spin glass state and the appearance of the FM state, are analysed. 相似文献
14.
I. Popov T. Kunze S. Gemming G. Seifert 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(3):439-446
The preferred adsorption sites and the propensity for a self-organised growth of the molybdenum sulfide cluster Mo6S8 on the Au(111) surface are investigated by density-functional band-structure calculations with pseudopotentials and a plane
wave basis set. The quasi-cubic cluster preferentially adsorbs via a face and remains structurally intact.
It experiences a strong, mostly non-ionic attraction to the surface
at several quasi-isoenergetic adsorption positions. A scan of the potential energy surface exhibits only small barriers between
adjacent strong adsorption sites. Hence, the cluster may move in a potential well with degenerate local energy minima at room
temperature. The analysis of the electronic structure reveals a negligible
electron transfer and S-Au hybridised states, which indicate that the cluster-surface
interaction is dominated by S-Au bonds, with minor contributions from
the Mo atom in the surface vicinity. All results indicate that Mo6S8 clusters
on the Au(111) surface can undergo a template-mediated self-assembly to an ordered inorganic monolayer, which is still redox
active and may be employed as surface-active agent in the integration of noble metal and ionic or biological components within
nano-devices.
Therefore, a classical potential model was developed on the basis of the DFT data,
which allows to study larger cluster assemblies on the Au(111). 相似文献
15.
Chih-Yuan Lu Patrick J. Shamberger Esmeralda N. Yitamben Kenneth M. Beck Alan G. Joly Marjorie A. Olmstead Fumio S. Ohuchi 《Applied Physics A: Materials Science & Processing》2008,93(1):93-98
Phase transformation of thin film (∼30 nm)In2Se3/Si(111) (amorphous→crystalline) was performed by resistive annealing and the reverse transformation (crystalline→amorphous)
was performed by nanosecond laser annealing. As an intrinsic-vacancy, binary chalcogenide semiconductor, In2Se3 is of interest for non-volatile phase-change memory. Amorphous In
x
Se
y
was deposited at room temperature on Si(111) after pre-deposition of a crystalline In2Se3 buffer layer (0.64 nm). Upon resistive annealing to 380°C, the film was transformed into a γ-In2Se3 single crystal with its {0001} planes parallel to the Si(111) substrate and
parallel to Si
, as evidenced by scanning tunneling microscopy, low energy electron diffraction, and X-ray diffraction. Laser annealing with
20-ns pulses (0.1 millijoules/pulse, fluence≤50 mJ/cm2) re-amorphized the region exposed to the laser beam, as observed with photoemission electron microscopy (PEEM). The amorphous
phase in PEEM appears dark, likely due to abundant defect levels inhibiting electron emission from the amorphous In
x
Se
y
film. 相似文献
16.
High-k dielectric amorphous LaAlO3 thin films have been grown on n-type Si(100) substrates by laser molecular beam epitaxy. The interfacial characteristics of the LaAlO3 films on Si were measured by high-resolution transmission electron micrography and X-ray photoemission spectroscopy. A sharp interface without a silica inter-layer between the LaAlO3 film and Si substrate was observed. Atomic force microscopy measurements indicated that the root-mean-square surface roughness within a 2m×2m area of the LAO films was 0.12 nm. The flatband voltage and fixed charge density of the 8 nm thickness LaAlO3 films were about 0.355 V and 1.8×1012/cm2, respectively. The leakage currents of the LaAlO3/Si(100) samples with different film thicknesses of 5, 8 and 12 nm were 0.45, 0.23 and 0.05 mA/cm2, respectively, at a +1 V dc bias voltage. LaAlO3 appears to be one of the most promising high dielectric constant materials for use in future ultra large scale integrated devices. PACS 77.55+f; 77.84.Bw; 73.40.Qv 相似文献
17.
A. S. Shulakov A. P. Braiko S. V. Bukin V. E. Drozd 《Physics of the Solid State》2004,46(10):1935-1939
The phase chemical composition of an Al2O3/Si interface formed upon molecular deposition of a 100-nm-thick Al2O3 layer on the Si(100) (c-Si) surface is investigated by depth-resolved ultrasoft x-ray emission spectroscopy. Analysis is performed using Al and Si L2, 3 emission bands. It is found that the thickness of the interface separating the c-Si substrate and the Al2O3 layer is approximately equal to 60 nm and the interface has a complex structure. The upper layer of the interface contains Al2O3 molecules and Al atoms, whose coordination is characteristic of metallic aluminum (most likely, these atoms form sufficiently large-sized Al clusters). The shape of the Si bands indicates that the interface layer (no more than 10-nm thick) adjacent to the substrate involves Si atoms in an unusual chemical state. This state is not typical of amorphous Si, c-Si, SiO2, or SiOx (it is assumed that these Si atoms form small-sized Si clusters). It is revealed that SiO2 is contained in the vicinity of the substrate. The properties of thicker coatings are similar to those of the 100-nm-thick Al2O3 layer and differ significantly from the properties of the interfaces of Al2O3 thin layers. 相似文献
18.
Resonant magnetic X-ray scattering was employed to investigate the magnetic state of epitaxial a* oriented thin films of the heavy fermion superconductor UNi2Al3. The observed incommensurate propagation vector as well as the Ne
l temperature correspond to
those of bulk samples. The 1200
film shows magnetic order with a correlation length >800 ? parallel to the growth axis. Out of the three possible magnetic
domains the one with the moment direction perpendicular to the film surface is not realized. 相似文献
19.
Equilibrium geometries, charge distributions, stabilities and electronic properties of the Ag-adsorbed (MgO)
n
(n = 1–8) clusters have been investigated by density functional theory (DFT) with generalized gradient approximation (GGA) for
exchange-correlation functional. The results show that hollow site is energetically preferred for n⩾4, and the incoming Ag atoms tend to cluster on the existing Ag cluster. The Mulliken populations indicate that the interaction
between the Ag atom and Magnesia clusters is mainly induced by a weak atomic polarization. The adsorbed Ag atom only causes
charge redistributions of the atoms near itself. The effect of the adsorbed Ag atom on the bonding natures and structural
features of Magnesia clusters is minor. Furthermore, the investigations on the first energy difference, fragmentation energies
and electron affinities show that the Ag(MgO)4 and Ag(MgO)6 are the most stable among studied clusters.
Supported by the Startup Fund of High-level Personal for Shihezi University (Grant No. RCZX200747) 相似文献
20.
We studied the growth mode and electronic properties of ultra-thin silver films deposited on Ni(1 1 1) surface by means of scanning tunnelling microscopy (STM) and angle resolved photoemission spectroscopy (ARPES). The formation of the 4d-quantum well states (QWS) was analysed within the phase accumulation model (PAM). The electronic structure of the 1 ML film is consistent with the silver layer which very weakly interacts with the supporting surface. The line-shape analysis of Ag-4dxz,yz QWS spectrum support the notion of strong localization of these states within the silver layer. The asymmetry of the photoemission peaks implies that the decay of the photo-hole appears to be influenced by the dynamics of the electrons in the supporting surface. 相似文献