共查询到20条相似文献,搜索用时 703 毫秒
1.
V. A. Pushkarchuk S. Ya. Kilin A. P. Nizovtsev A. L. Pushkarchuk V. E. Borisenko C. von Borczyskowski A. B. Filonov 《Optics and Spectroscopy》2005,99(2):245-256
The electronic and spin properties of different nanocrystals of carbon are studied. The properties of these cluster systems are modeled in terms of the ab initio (Hartree-Fock) and semiempirical (PM3, AM1) quantum-chemical methods. The calculations are performed for different carbon nanocluster systems: defect-free and with [NV]? centers, hydrogen passivated (C38H42, C71H84, C86H78), and with a free (unpassivated) surface (C38, C71, C86). The spin properties of unhydrated nanoclusters were studied for the first time. The structure of all the clusters under study was optimized using the total energy minimization principle. It is shown that, in the case of hydrated carbon nanocrystals passivated by hydrogen atoms, diamond-like clusters are formed. The atomic structure of an unpassivated nanocrystal depends on the number of atoms in the cluster, as well as on its initial geometrical parameters. In some cases, clusters with a fullerene-like surface are formed. In hydrogenpassivated diamond nanocrystals with [NV]? centers, the spin density is localized at the nuclei of C atoms nearest to the center vacancies. For the unpassivated counterparts, the spin density is localized at the nuclei of C atoms forming the surface of the corresponding nanocrystal. 相似文献
2.
V. A. Pushkarchuk S. Ya. Kilin A. P. Nizovtsev A. L. Pushkarchuk A. B. Filonov V. E. Borisenko 《Journal of Applied Spectroscopy》2007,74(1):95-101
We have used the density functional method to model the atomic and electronic structure of diamond nanocrystals passivated
by hydrogen atoms and either not containing defects or containing a single [NV]− center. We have shown that in all cases, after relaxation the nanocrystals are formed as diamond-like structures.
We have studied the features of the electronic structure of the nanocrystals. We have analyzed in detail the mechanism for
the formation of energy levels in the bandgap due to [NV]− centers. We have established that the optical absorption and fluorescence spectra for the [NV]− centers are mainly associated with transitions of electrons between the highest occupied β orbitals (projection of the electron
spin equal to +1/2) and lower unoccupied α orbitals (projection of the electron spin equal to −1/2). The results on the localization
and energy position of the states in the bandgap match data obtained for the [NV]− center in bulk diamond.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 86–92, January–February, 2007. 相似文献
3.
The binding energy of a hydrogen molecule on metal atoms (Li, Be, Na, and Mg) attached to aromatic hydrocarbon molecules (benzene
and anthracene) was calculated using an ab initio molecular orbital method at the MP2(FC)/cc-pVTZ level with basis set superposition
error (BSSE) correction. The energy tended to become more negative as the metal atom had a more positive charge and a smaller
radius. The energies of Li2C6H6-H2, Li2C14H10-H2, Na2C14H10-H2, and MgC14H10-H2 were −2.7 to −2.2, −4.0 to −3.1, −2.8 to −0.3, and −1.3 kcal/mol, respectively. Most of these energies were more negative
than those on the hydrocarbons without metal atoms (ca. −1 kcal/mol). Analyzing the Lennard–Jones type potential with the
parameters determined by the MP2 calculations, it was found that these energies mainly consisted of the induction force caused
by the positive charge of the metal atom and the dispersion force from the nearest C6-ring. The energy of BeC14H10-H2 was more negative (−8.6 kcal/mol) than of the other complexes. The hydrogen molecule in this complex had a comparatively
longer H–H distance and a more positive H2 charge than the others. These data suggest that the hydrogen adsorption on this complex involves a charge transfer process
in addition to physisorption interactions. The hydrogen binding energies in some Li2C14H10-H2 systems (∼−4.0 kcal/mol) and BeC14H10-H2 are promising to operate hydrogen storage/release at ambient temperature with moderate pressure. 相似文献
4.
The effects of symmetric lattice relaxation around the tetrahedral (T) and the hexagonal (H) interstitial sites are calculated
for normal muonium (Mu) in diamond using the non-semiempirical method of Partial Retention of Diatomic Differential Overlap
(PRDDO). We use clusters containing 3 and 4 host atom shells around the T and the H sites (C20H32 and C30H40). The only significant relaxations are the outward displacement of the 6 nearest neighbors (NN) to the H site and, when the
muon is at the T site, the simultaneous outward displacement of the first and second NN to the T site. In the case of diamond,
the effects of these relaxations on the energy profiles and spin densities are small. 相似文献
5.
The kinetics of the optical orientation of atoms in a helium-cesium gas-discharge plasma are considered, and kinetic equations
describing the optical orientation of atoms in the case of two simultaneously occurring processes, viz., an elastic process
(spin exchange) and an inelastic process (chemi-ionization), are derived. The rate constants of these processes are determined
experimentally: C
se=(2.8±0.8)×10−9 cm3s−1, C
ci=(1.0±0.3)×10−9 cm3s−1.
Zh. Tekh. Fiz. 69, 36–40 (September 1999) 相似文献
6.
A. P. Nizovtsev S. Ya. Kilin F. Jelezko T. Gaebal I. Popa A. Gruber J. Wrachtrup 《Optics and Spectroscopy》2005,99(2):233-244
In an effort to realize a two-bit processor for a quantum computer on the basis of single nitrogen-vacancy defect centers (NV centers) in diamond, the optically detected nutations of the electron spin of a single NV center in the ground state and of the nuclear spin of a 13C atom located at a diamond lattice site nearest to the NV center are studied. The photodynamics of NV and NV + 13C centers under different temperatures and optical excitation conditions is discussed. A seven-level model of a center excited by radiation from an Ar+ laser at room temperature is proposed. On the basis of this model, the experimental spectra of optically detected electron paramagnetic and electron-nuclear double resonances of single NV and NV + 13C centers in diamond nanocrystals, as well as experimental data on the optically detected nutations of the electron and nuclear spins of these centers caused by the actions of pulsed microwave and radiofrequency fields, respectively, are interpreted. 相似文献
7.
A. P. Nizovtsev S. Ya. Kilin P. Neumann F. Jelezko J. Wrachtrup 《Optics and Spectroscopy》2010,108(2):239-246
The spin Hamiltonian method in combination with ab initio calculations of the spin characteristics of quantum registers that
include an electron spin S = 1 of a single NV center in the ground electronic state and nuclear spins I = 1/2 of several atoms 13C located at different lattice sites near the vacancy of the NV center is applied to find eigenvalues and eigenfunctions of
spin systems NV + n
13C for cases where the lattice sites nearest to the vacancy of the NV center contain one, two, or three 13C nuclear spins, as well as for cases where 13C atoms are located at sites more distant from the vacancy. For these single spin NV + n
13C systems, the spectra of optically detected magnetic resonance (ODMR) are calculated, which agree well with available experimental
data. 相似文献
8.
Molecular structure of tris(acetylacetonato)scandium, Sc(C5H7O2)3, is investigated by gas-phase electron diffractometry. The main structural parameters of the molecule are evaluated. The
average intemuclear distances and angles correspond to C3 symmetry. The chief structural motif is trigonal antiprisms of six oxygen, carbon, and hydrogen atoms with a scandium atom
at the center. It is found that rg[Sc-O) = 204.1(8) pm and rg(C−O) = 124.7(4) pm
Translated fromZhurnal Struktumoi Khimii, Vol. 39, No. 4, pp. 633–639, July–August, 1998. 相似文献
9.
Yu. V. Piskunov V. V. Ogloblichev I. Yu. Arapova A. V. Sadykov A. P. Gerashchenko S. V. Verkhovskii 《Journal of Experimental and Theoretical Physics》2011,113(5):826-834
The effect of charge disorder on the formation of an inhomogeneous state of the electron system in the conduction band in
BaPb1 − x
Sb
x
O3 superconducting oxides is investigated experimentally by NMR methods. The NMR spectra of 17O are measured systematically, and the contributions from 17O atoms with different cation nearest surroundings are identified. It is found that microscopic regions with an elevated spin
density of charge carriers are formed within two coordination spheres near antimony ions. Nuclei of the superconducting phase
of the oxide (regions with an elevated antimony concentration) microscopically distributed over the sample are detected in
compounds with x = 0.25 and 0.33. Experiments in which a double resonance signal of the spin echo of 17O-207Pb and 17O-121Sb are measured in the metal phase of BaPb1 − x
Sb
x
O3 oxides are carried out for the first time. The constants of indirect heteronuclear spin-spin 17O-207Pb interaction are determined as functions of the local Knight shift 207
Ks. The estimates of the constants of the indirect interaction between the nuclei of the nearest neighbors (O-Pb and Pb-Pb atoms)
and analysis of evolution of the NMR spectra of 17O upon a change in the antimony concentration are convincing evidence in favor of the development of a microscopically inhomogeneous
state of the electron system in the metal phase of BaPb1 − x
Sb
x
O3 oxides. 相似文献
10.
Machi I. Z. Connell S. H. Sellschop J. P. F. Bharuth-Ram K. 《Hyperfine Interactions》2001,136(3-8):723-726
A preliminary study of the diamagnetic (μd) and the paramagnetic (Mu
T
) states in a synthetic 13C diamond has been performed using the Transverse Field Muon Spin Rotation method. This system could be used to verify the
quantum diffusion behaviour observed before, however, with a more reliable extraction of the hopping rate. The results were
obtained in an applied magnetic field of 7.5 mT and at sample temperatures of 10 K, 100 K and 200 K. The prompt fraction,
f, of the μd state remains constant at 22(5)% in the range 10–200 K; that of the Mu
T
state increases from 53(10)% at 10 K to 78(10)% at 200 K. The fractions of the two states add to 100% at 200 K, suggesting
non-population of the bond-centred state, MuBC, which is often observed in other diamond samples. The μd state has a spin relaxation rate of 0.20(5) μs−1, in contrast to the zero value obtained in type II diamond samples. This indicates appreciable interaction of the μd state with the 13C atoms. The Mu
T
state has a large spin relaxation rate ranging from 3.0(5) μs−1 at 10 K to 7.0(5) μs−1 at 200 K, consistent with values obtained in diamond samples with defects. This work is part of ongoing studies of muon/muonium-defect
interactions in diamonds.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
11.
M. Babamoradi M. Heidari Saani A. Ranjbar M. A. Vesaghi Y. Kawazoe 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,84(1):1-9
Using a generalized Hubbard Hamiltonian, many-electron wavefunctions of negatively
charged (NV−) and neutral nitrogen-vacancy (NV0) centers in diamond
were calculated. We report the effect of symmetric relaxation of surrounding atoms on the
spin density, calculated from the many electron wavefunctions in the ground and excited
states. We evaluated the error, that, arises in estimation of spin density when lattice
relaxation effect is neglected in Electron Paramagnetic Resonance experiment and showed
that the ground state spin density distribution is accessible in outward relaxations. The
computed oscillator strengths give a higher efficiency for the 1.945 eV photoluminescence
(PL) line of NV− with respect to 2.156 eV PL line of NV0 which
agrees well with experiment. This result is explained based on the largest the ground
state spin among available values for the NV− with respect to NV0.
The transition probability between degenerate ground and excited states slightly depends
on the S
z
value. Finally, we report on the
electronic configurations which contribute to the ground and excited states and discuss
the population variation of electronic configurations with relaxation. 相似文献
12.
Absolute cross sections σ−(E, N) of electron attachment to clusters (H2O)
N
, (N2O)
N
, and (N2)
N
for varying electron energy E and cluster size N are measured by using crossed electron and cluster beams in a vacuum. Continua of σ−(E) are found that correlate well with the functions of electron impact excitation of molecules’ internal degrees of freedom.
The electron is attached through its solvation in a cluster. In the formation of (H2O)
N
−
, (N2O)
N
−
, and (N2)
N
−
, the curves σ−(N) have a well-defined threshold because of a rise in the electron thermalization and solvation probability with N. For (H2O)900, (N2O)350, and (N2)260 clusters at E = 0.2 eV, the energy losses by the slow electron in the cluster are estimated as 3.0 × 107, 2.7 × 107, and 6.0 × 105 eV/m, respectively. It is found that the growth of σ− with N is the fastest for (H2O)
N
and (N2)
N
clusters at E → 0 as a result of polarization capture of the s-electron. Specifically, at E = 0.1 eV and N = 260, σ− = 3.0 × 10−13 cm2 for H2O clusters, 8.0 × 10−14 cm2 for N2O clusters, and 1.4 × 10−15 cm2 for N2 clusters; at E = 11 eV, σ− = 9.0 × 10−16 cm2 for (H2O)200 clusters, 2.4 × 10−14 cm2 for (N2O)350 clusters, and 5.0 × 10−17 cm2 for (N2)260 clusters; finally, at E = 30 eV, σ− = 3.6 × 10−17 cm2 for (N2O)10 clusters and 3.0 × 10−17 cm2 for (N2)125 clusters.
Original Russian Text ? A.A. Vostrikov, D.Yu. Dubov, 2006, published in Zhurnal Tekhnicheskoĭ Fiziki, 2006, Vol. 76, No. 12,
pp. 1–15. 相似文献
13.
D.K. Yu R.Q. Zhang S.T. Lee 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(1):57-63
The structures and energetics of carbon bridged C60 clusters (C
60
)
n
Cm have been studied by simulated annealing technique within the tight-binding molecular-dynamics. The “sp2 addition” ball-and-chain dimers exhibit odd-even alternations over the number of chain atoms, with the dimers containing
even chain atoms more stable against dissociation than their immediate neighbors containing odd chain atoms. In addition to
the usual “sp2 addition” dimers, a pentagon-linked C121 isomer and a hexagon-linked C122 isomer are also found to be stable. Based on our tight-binding calculations, trimers and larger clusters can be simply regarded
as being made up of independent or weakly interacting dimers, if the C-C60 joints on a single cage are not too close to each other. Large C60 clusters connected by chains each containing only one or two carbon atoms have similar stability to that of constituent dimers,
indicating the possibility to form stable C60-carbon polymers.
Received 17 January 2001 and Received in final form 26 February 2001 相似文献
14.
Taketoshi Matsumoto Patricia Nickut Kazuya Watanabe Tatsuya Tsukuda Katharina Al-Shamery 《Surface science》2007,601(22):5226-5231
Reduction of oxidized gold nanoclusters by exposures to foreign gases and irradiation of UV photons has been investigated using X-ray photoelectron spectroscopy. Gold nanoclusters with narrow size distributions protected by alkanethiolate ligands were deposited on a TiO2(1 1 0) surface with dip coating. Oxygen plasma etching was used for removal of alkanethiolate ligands and oxidization of gold clusters. The oxidized gold clusters were exposed to CO, C2H2, C2H4, H2, and hydrogen atoms. Although, C2H4 and H2 did not show any indications of reduction of oxidized gold clusters, CO, C2H2, and hydrogen atoms reduced the oxides on gold cluster surfaces. Among them, hydrogen atoms were most effective for reduction. Irradiation of UV photons around 400 nm could also reduce the oxidized gold clusters. The photochemical reduction mechanism was proposed as follows. The photo-reduction was initiated by electronic excitation of gold clusters and oxygen atoms activated reacted with carbon atoms at the surfaces of gold clusters. Carbon species were likely absorbed in gold clusters or remained at the boundaries between gold clusters when gold clusters agglomerated during oxygen plasma exposures. As the photochemical reduction progressed, carbon atoms segregated to the surfaces of gold clusters. 相似文献
15.
L. R. Fontes R. H. Schonmann V. Sidoravicius 《Communications in Mathematical Physics》2002,228(3):495-518
We study a class of continuous time Markov processes, which describes ± 1 spin flip dynamics on the hypercubic latticeℤ
d
, d≥ 2, with initial spin configurations chosen according to the Bernoulli product measure with density p of spins + 1. During the evolution the spin at each site flips at rate c= 0, or 0 < α≤ 1, or 1, depending on whether, respectively, a majority of spins of nearest neighbors to this site exists and
agrees with the value of the spin at the given site, or does not exist (there is a tie), or exists and disagrees with the
value of the spin at the given site. These dynamics correspond to various stochastic Ising models at 0 temperature, for the
Hamiltonian with uniform ferromagnetic interaction between nearest neighbors. In case α= 1, the dynamics is also a threshold
voter model. We show that if p is sufficiently close to 1, then the system fixates in the sense that for almost every realization of the initial configuration
and dynamical evolution, each site flips only finitely many times, reaching eventually the state + 1. Moreover, we show that
in this case the probability q(t) that a given spin is in state − 1 at time t satisfies the bound: for arbitrary ɛ > 0, q(t) ≤ exp(−t
(1/
d
) −ɛ), for large t. In d= 2 we obtain the complementary bound: for arbitrary ɛ > 0, q(t) ≥ exp(−t
(1/2) +ɛ), for large t.
Received: 12 July 2001 / Accepted: 1 February 2002 相似文献
16.
The present work reports on the synthesis, characterization and performance of a new metal-containing ionic liquid [(C3H7)2-bim]2[CdCl4] (bim = benzimidazole) as an electrocatalyst for trichloroacetic acid (TCA) and bromate reduction. The structure of Cd(II)-containing
ionic liquid (Cd-IL) was characterized by X-ray crystallography, IR spectroscopy, and elemental analysis. The molecular structure
contains two independent cations of 1,3-dipropyl-benzimidazolium and one anion of CdCl42−. The cadmium atom has a tetrahedral geometry by coordinating to four chlorine atoms. The melting point of Cd-IL is 73 °C.
Electrochemical properties of the Cd-IL have been investigated by preparing bulk-modified carbon paste electrode, and Cd-IL
is used as a binder and an electrocatalyst. This modified electrode has good electrocatalytic activity toward reduction of
TCA and bromate. The detection limit and the sensitivity are 0.01 μM and 102.72 μA μM−1 for trichloroacetic acid detection and 0.003 μM and 496.15 μA μM−1 for bromate detection. This work demonstrates that the Cd-IL may become a new kind of functional material in constructing
chemicals and biosensors. 相似文献
17.
A. D. Bass J. H. Bredehöft E. Böhler L. Sanche P. Swiderek 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2012,66(2):53
Thermal desorption spectrometry (TDS) and electron stimulated desorption (ESD) are
employed to investigate mechanisms responsible for the formation of
C2H6 in electron irradiated multilayer films of acetonitrile
(CH3CN) at 30 K. Using a high sensitivity time-of-flight mass spectrometer,
we observe the ESD of anionic fragments H−,
CH2
−,
CH3
−
and CN−. Desorption occurs following dissociative electron attachment (DEA) via
several negative ion resonances in the 6 to 14 eV energy range and correlates well with a
“resonant” structure seen in the TDS yield of C2H6 (i.e., at mass
30 amu). It is proposed that C2H6 is formed by the reactions of
CH3 radicals generated following DEA to CH3CN which also yields
CN−. Between 2 and 5 eV, a second resonant feature is seen in the
C2H6 signal. While DEA is observed in the gas phase at these
energies, no anion desorption occurs since anionic fragments likely have insufficient
kinetic energy to desorb. Since the CH2
−
ion has not been observed in gas-phase measurements, we propose that it is formed, along
with HCN (that is detected in TDS) when dissociation into
CH3
−
and CN is hindered by adjacent molecules. 相似文献
18.
Optical emission spectroscopy (OES) was used to study the plasma generated by the activation of the gas phase CH4 + H2 both by hot filaments and by a plasma discharge (DC HF CVD) during the nucleation of CVD diamond. The effects of nucleation parameters, such as methane concentration and extraction potential, on the plasma chemistry near the surface were investigated. The density of the diamond nucleation and the quality of the diamond films were studied by scanning electron microscopy (SEM) and Raman scattering, respectively. The OES results showed that the methane concentration influenced strongly the intensity ratio of Hβ-Hα implying an increase of electron mean energy, as well as CH, CH+, C2. A correlation between the relative increase of CH+ and the diamond nucleation density was found, conversely the increase of C2 contributed to the introduction of defects in the diamond nuclei. 相似文献
19.
R. H. Scheicher A. N. U. Roy T. P. Das K. Ishida T. Matsuzaki S. N. Nakamura N. Kawamura K. Nagamine 《Hyperfine Interactions》2001,138(1-4):387-395
The study of trapping of He+ ion in solid hydrogen is important both as a problem in solid state physics and also as an applied physics problem in the
field of muon catalyzed fusion (μCF). In μCF, He+ ion acts as a trap for μ−, interrupting the chain reaction aspect of the catalytic role of μ− in producing fusion of deuteron and triton and of triton and triton in solid hydrogen composed of 2H–3H and 3H–3H molecules, respectively. Using the Hartree–Fock procedure, combined with procedures for including many-body effects, as
well as relaxation effects associated with the He+–H2 distances and the adjustment of the H–H separation, we have investigated the trapping of He+ in gaseous and solid state environments. For the former, the environment of He+ is simulated by a single hydrogen molecule and for the solid by clusters appropriately chosen to represent the hexagonal
close-packed structure. Our results for the gaseous state indicate that the trapping is rather strong with a binding energy
of 8.5 eV, with almost equal binding energy in the linear and triangular configurations with respect to the H–H direction.
For the solid, both the likely sites for He+ trapping, namely the tetrahedral and octahedral interstitial sites, are also found to provide deep traps (8.6 eV) of almost
equal strength, independent of the orientations of the neighboring molecules, showing that the trapping is not influenced
by the orientational disorder in the surrounding hydrogen molecules. Further, the influence of next nearest neighbor hydrogen
molecules is found to enhance the trapping energy for He+ substantially, by 0.6 eV, with the incorporation of the third nearest neighbors having a much smaller added effect, demonstrating
the convergence of our results with respect to the size of the cluster chosen to simulate the solid. The substantial influence
on the He+ trapping energy found for the neighbors beyond the nearest ones provides an explanation of the greater accumulation of helium
in the solid state of hydrogen in μCF experiments as compared to the liquid. Suggestions are made regarding the possible reasons
for the almost negligible accumulation of helium in the liquid state.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
20.
本文发展文献[1]的方法到两种不同自旋的原子(Sa=1,Sb=1/2)构成的晶格中,计算了简单立方晶格在具有再次近邻反铁磁相互作用下在外磁场中的基态自旋结构、能量和相界。从文中给出的相图可知:这种晶格有两种反铁磁自旋结构,有四种亚铁磁自旋结构。
关键词: 相似文献