共查询到20条相似文献,搜索用时 31 毫秒
1.
X. J. Kuang X. Q. Wang G. B. Liu 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,61(1):71-80
An all-electron scalar relativistic calculation on
Au
n
NO (n = 1–10) clusters has been performed by using density functional
theory with the generalized gradient approximation at the PW91 level. The
small gold cluster would like to bond with nitric and the nitric monoxide
molecule prefers to occupy the on-top and single fold coordination site. The
Au
n
structures in all Au
n
NO clusters are only distorted slightly
and still keep the planar structures. With the bend of Au-N-O bond, the
structures of Au
n
NO clusters evolve from the 2D structure to 3D
structure. The most favorable adsorption between small gold cluster and
nitric monoxide molecule takes place in the case that nitric monoxide
molecule is adsorbed onto an odd-numbered pure Au
n
cluster and becomes
odd-numbered Au
n
NO cluster with even number of valence electrons. The
scalar relativistic effect strengthens the Au–Au, Au–N interaction and
weakens the N–O interaction, appearing as the shorter Au–Au, Au–N
bond-length and the longer N–O bond-length. The differences between our work
and previous work are believed to be the reflection of the scalar
relativistic effect. 相似文献
2.
Novel synthesis of amine-stabilized Au–Ag alloy nanoparticles with controlled composition has been devised using poly(ethylenimine)
(PEI) as a reducing and a stabilizing agent simultaneously. The composition of Au–Ag alloy nanoparticles was readily controlled
by varying the initial relative amount of HAuCl4 and AgNO3. Due to the presence of abundant amine functional groups in PEI, which could act as the dissolving ligand for AgCl, the precipitation
problem of Ag+ in the presence of Cl− from the gold salt was avoided. On this basis, the relatively high concentrations of HAuCl4 and AgNO3 salts were used for the fabrication of Au–Ag alloy nanoparticles. The PEI thus plays triple roles in this study that include
the co-reducing agents for HAuCl4 and AgNO3, the stabilizing agents for Au–Ag alloy nanoparticles, and even the dissolving agents for AgCl. As a novel material for use
in catalysis, the Au–Ag alloy nanoparticles including pure Au and Ag samples were exploited as catalysts for the reduction
of 4-nitrophenol in the presence of NaBH4. As the Au content was increased in the Au–Ag alloy nanoparticles, the rate constant of the reduction was exponentially increased
from pure Ag to pure Au. 相似文献
3.
The adsorption site and energetics of Mo4S6 on the unreconstructed (111) gold surface was determined by density-functional band-structure calculations. Mo4S6 adsorbs preferably via three S atoms at Au–Au bridging sites and three Mo atoms at adjacent threefold hollow sites of the Au(111) surface. The perfectly tetrahedral free cluster becomes trigonally distorted upon adsorption, which indicates the presence of attractive Au–S and Au–Mo interactions. The work of separation amounts to 4.2 eV including gradient corrections. Small peak shifts in the density of electronic states indicate electron transfer from Au to S states and from Mo to Au states, such that a Bader analysis yields a neutral cluster. Electron density difference maps, which visualize the electron redistribution between cluster and substrate in the interface region, show that the electron redistribution is confined to the cluster-surface contact region. PACS 61.46.+w; 73.22.-f; 72.20.-v 相似文献
4.
Comparative studies of the emission of quasi-thermal atomic and cluster ions from V, Nb, Ta, Au, and In targets bombarded
by cluster ions Au
m
−(m = 1–9), as well as from Si and Bi targets bombarded by cluster ions Au
m
−(m = 1–9) and Bi
m
−(m = 1–5), with energy E
0 ranging from 6 to 21 keV are carried out. In the case of bombardment by heavy cluster ions, the fraction of the quasi-thermal
component in the energy spectra of sputtered atomic ions reaches 50 (for V, In, and Au), 70 (Nb), or more than 90% (Ta). In
addition, quasi-thermal ions play a considerable part in the emission of small cluster ions Au2+, In2+, In3+, and Bi
n
+(n = 2–7). The results of the generalizing investigation favor the presence of thermal spike conditions at cluster bombardment
and their appreciable contribution to the emission of atomic and small cluster ions. 相似文献
5.
G. Mandaglio G. Fazio G. Giardina F. Hanappe M. Manganaro A. I. Muminov A. K. Nasirov C. Saccá 《Physics of Atomic Nuclei》2009,72(10):1639-1650
The measured yield of evaporation residues in reactions with massive nuclei have been well reproduced by using the partial
fusion and quasifission cross sections obtained in the dinuclear-system model. The influence of the orientation angles of
the projectile- and target-nucleus symmetry axes relative to the beam direction on the production of the evaporation residues
is investigated for the 48Ca + 154Sm reaction as a function of the beam energy. At the low beam energies only the orientation angles close to αP = 30° (projectile) and αP = 0°–15° (target) can contribute to the formation of evaporation residues. At large beam energies (about E
c.m. = 140–180 MeV) the collisions at all values of orientation angles αP and α
T
of reactants can contribute to the evaporation residue cross section which ranges between 10–100 mb, while at E
c.m. > 185 MeV the evaporation residue cross section ranges between 0.1–1 mb because the fission barrier for the compound nucleus
decreases by increasing its excitation energy and angular momentum. 相似文献
6.
D. O. Eremenko A. A. Dermenev V. A. Drozdov S. Yu. Platonov O. V. Fotina O. A. Yuminov 《Physics of Atomic Nuclei》2009,72(10):1651-1658
A combined dynamical and statistical approach to describing induced fission of heavy nuclei is proposed. This approach takes
into account the nuclear-dissipation phenomenon and the double-humped structure of the fission barrier. A method that is intended
for calculating the angular distribution of fission fragments and which is applicable over a broad range of excitation energies
is discussed. The potential of the approach is demonstrated by addressing the problems of self-consistently describing experimental
data on fission probabilities for plutonium and americium isotopes, the yields of shape isomers in the α+238U reaction at alpha-particle energies in the range E
α
= 20–32 MeV and the d+242,240Pu reactions at deuteron energies in the range E
d
= 20–30 MeV, fission times in the α + 238U reaction at alpha-particle energies in the range E
α
= 20–32 MeV, and angular distributions of fission fragments in the α + 238U, 237Np reactions at alpha-particle energies in the range E
α
= 20–100 MeV. 相似文献
7.
Composite Au–SnO2 nanoparticles (NPs) are synthesized by nano-soldering of pure Au and SnO2 NPs. The multi-step process involves synthesis of pure Au and SnO2 NPs separately by nanosecond pulse laser ablation of pure gold and pure tin targets in deionized water and post-ablation
laser heating of mixed solution of Au colloidal and SnO2 colloidal to form nanocomposite. Transmission Electron Microscopy (TEM) and High-Resolution Transmission Electron Microscopy
(HRTEM) were used to study the effect of laser irradiation time on morphology of the composite Au–SnO2 NPs. The spherical particles of 4 nm mean size were obtained for 5 min of post-laser heating. Increased mean size and elongated
particles were observed on further laser heating. UV–vis spectra of Au–SnO2 nanocomposites show red shift in the plasmon resonance absorption peak and line shape broadening with respect to pure Au
NPs. The negative binding energy shift of Au 4f7/2 peak observed in X-ray Photoelectron Spectra (XPS) indicates charge transfer in the nano-soldered Au–SnO2 between gold and tin oxide and formation of soldered nanocomposite. 相似文献
8.
Mass distribution and evaporation residue measurements have been carried out in the reaction 19F + 197Au using the recoil catcher technique followed by off-line γ-ray spectrometry. The random neck rupture model (RNRM) has been
used to compute the variance of the mass distribution ( σ2A) and the average kinetic energy ( ˉ) of the fission fragments for the present system. The results of model calculations have
been found to be in good agreement with the experimental observations. Measured evaporation residue cross-sections have been
compared with the statistical model calculations. 相似文献
9.
Xin Dong 《The European Physical Journal C - Particles and Fields》2009,61(4):659-664
I report the most recent measurements on open heavy flavor production at RHIC on behalf of the STAR collaboration. The total
charm production cross section in midrapidity at RHIC energy is found to approximately scale by number of binary collisions
in d + Au, Cu + Cu and Au + Au collisions. The nuclear modification factor of non-photonic electrons is strongly suppressed in
central Au + Au collisions, suggesting substantial heavy quark energy loss at RHIC. The bottom decay contribution to non-photonic
electrons was studied via the e–h and e–D
0 azimuthal angular correlations. The bottom contribution is found to be important at p
T
>5 GeV/c, and is consistent with the FONLL calculation within uncertainties. Charm production through gluon jet splitting was measured
by studying the D
*± contents in the fully reconstructed jets in p+p collisions. This rate is consistent with pQCD evaluation of gluon splitting into a pair of charm quarks and subsequent hadronization. 相似文献
10.
M. Naglis 《The European Physical Journal C - Particles and Fields》2009,61(4):835-840
The PHENIX experiment at RHIC has measured a variety of light neutral mesons (π
0, K
S
0, η, ω, η
′, φ) via multi-particle decay channels over a wide range of transverse momentum. A review of the recent results on the production
rates of light mesons in p + p and their nuclear modification factors in d + Au, Cu + Cu and Au + Au collisions at different
energies is presented. 相似文献
11.
《Pramana》2003,61(5):865-876
Particle production in Au+Au collisions has been measured in the PHOBOS experiment at RHIC for a range of collision energies
for a large span of pseudorapidities, |η| < 5.4. Three empirical observations have emerged from this data set which require
theoretical examination. First, there is clear evidence of limiting fragmentation. Namely, particle production in central
Au + Au collisions, when expressed as dN/dη′ ( η′ ≡ – ybeam), becomes energy independent at high energy for a broad region of η′ around η′ = 0. This energy-independent region grows
with energy, allowing only a limited region (if any) of longitudinal boost-invariance. Second, there is a striking similarity
between particle production in e+e−and Au + Au collisions (scaled by the number of participating nucleon pairs). Both the total number of produced particles
and the longitudinal distribution of produced particles are approximately the same in e+e−and in scaled Au + Au. This observation This presentation is based in large part on the PHOBOS summary talk by M Baker at
the16th Int. Conf. on Ultrarelativistic Nucleus- Nucleus Collisions, Quark Matter 2002, Nantes, France was not predicted and has not been explained. Finally, particle production has been found
to scale approximately with the number of participating nucleon pairs for (N
part
) > 65. This scaling occurs both for the total multiplicity and for highp
T
particles (3 <p
T
< 4.5 GeV/c).
This presentation is based in large part on the PHOBOS summary talk by M Baker at the16th Int. Conf. on Ultrarelativistic Nucleus-Nucleus Collisions, Quark Matter 2002, Nantes, France 相似文献
12.
T. Tabarin R. Antoine M. Broyer P. Dugourd 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,52(1-3):191-194
The formation of isolated [ (Trp-2H)+Ag9] + and [ (Tyr-2H)+Ag9] + amino-acid-Ag9 hybrids is reported. The photofragmentation yields of the aromatic amino acid-silver cluster hybrids, as well as those of the protonated tryptophan and tyrosine molecules ([Trp+H]+ and [Tyr+H]+) have been recorded. The fragmentation yields of the complexes are higher than the yields for [Trp+H]+and [Tyr+H]+ and present an extension of the fragmentation on the red side of the spectrum. The photofragmentation spectrum of [ Trp+Ag9] + was recently reported [Mitric et al., J. Chem. Phys. 127, 134301 (2007)]. While the optical spectra of substituted [ (Trp-2H)+Ag9] + and non-substituted [ Trp+Ag9] + complexes are very similar, a strong modification of the fragmentation channels between the two complexes is observed. The fragmentation channels are sensitive to the type of bonding in aromatic amino acid-silver cluster hybrids and can be used as fingerprints of structures. 相似文献
13.
M. Vogel K. Hansen A. Herlert L. Schweikhard 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):73-76
The decay pathway competition between monomer and dimer evaporation of photoexcited cluster ions Au
+
n, n = 2-27, has been investigated by photodissociation of size-selected gold clusters stored in a Penning trap. For n > 6 the two decay pathways are distinguished by their experimental signature in time-resolved measurements of the dissociation.
For the smaller clusters, simple fragment spectra were used. As in the case of the other copper-group elements, even-numbered
gold cluster ions decay exclusively by monomer evaporation, irrespective of their size. For small odd-size gold clusters,
dimer evaporation is a competitive alternative, and the smaller the odd-sized clusters, the more likely they decay by dimer
evaporation. In this respect, Au
+
9 shows an anomalous behavior, as it is less likely to evaporate dimers than its two odd-numbered neighbors, Au
+
7 and Au
+
11. This nonamer anomaly is typical for copper-group cluster ions M
+
9 (M = Cu, Ag, Au) and a similar behavior is found in the anionic heptamers M
-
7. It is discussed in terms of the well-known electronic shell closing at n
e = 8 atomic valence electrons.
Received 2 November 2000 相似文献
14.
F. Laue I. Böttcher M. Debowski A. Förster E. Grosse P. Koczoń B. Kohlmeyer M. Mang M. Menzel L. Naumann H. Oeschler F. Pühlhofer E. Schwab P. Senger Y. Shin J. Speer H. Ströbele C. Sturm G. Surówka F. Uhlig A. Wagner W. Waluś 《The European Physical Journal A - Hadrons and Nuclei》2000,9(3):397-410
Production cross-sections of charged pions, kaons and antikaons have been measured in C+C and C+Au collisions at beam energies
of 1.0 and 1.8 AGeV for different polar emission angles. The kaon and antikaon energy spectra can be described by Boltzmann
distributions whereas the pion spectra exhibit an additional enhancement at low energies. The pion multiplicity per participating
nucleon M(π+)/<A
part> is a factor of about 3 smaller in C+Au than in C+C collisions at 1.0 AGeV whereas it differs only little for the C and the
Au target at a beam energy of 1.8 AGeV. The K+ multiplicities per participating nucleon M(K+)/ <A
part> are independent of the target size at 1 AGeV and at 1.8 AGeV. The K- multiplicity per participating nucleon M(K-)/ <A
part> is reduced by a factor of about 2 in C+Au as compared to C+C collisions at 1.8 AGeV. This effect might be caused by the
absorption of antikaons in the heavy target nucleus. Transport model calculations underestimate the K-/K+ ratio for C+C collisions at 1.8 AGeV by a factor of about 4 if in-medium modifications of K-mesons are neglected.
Received: 10 December 1999 / Accepted: 14 November 2000 相似文献
15.
Bo Chen Dongfang Yang Chii-Wann Lin 《Applied Physics A: Materials Science & Processing》2009,97(2):489-496
Surface plasmon resonance of metal–dielectric composite thin films formed by noble metal nanoparticles embedded in a dielectric
matrix offers a high degree of flexibility and enables many applications such as surface enhanced spectroscopes, and biological
and chemical sensing. In this article, Au–WO3−x
composite films of various Au contents and thicknesses were prepared by the pulsed laser deposition technique, and their
SPR responses were measured in the Kreschmann geometry, using a polarized light beam at 640 nm wavelength. Theoretical calculation
of SPR responses based on the Bruggeman or Maxwell–Garnett model with the MacLeod general characteristic matrix method is
in obvious discrepancy with experimental measurements but it is able to predict the trend in term of the dependence of SPR
responses on Au content and thickness of the Au–WO3−x
films. The SPR responses of the Au–WO3−x
films when exposed to NO gas molecules were measured and the preliminary results indicated that gas sensing using the SPR
responses of metal–dielectric composite films is feasible. 相似文献
16.
Anthony R. Timmins 《The European Physical Journal C - Particles and Fields》2009,62(1):249-254
We report STAR measurements of mid-rapidity yields for the Λ ,
, K
S
0 , Ξ
−,
, Ω
−,
particles in Cu + Cu and Au + Au
GeV collisions. We show that at a given number of participating nucleons, bulk strangeness production is higher in Cu + Cu
collisions compared to Au + Au collisions at the same center of mass energy, counter to predictions from the Canonical formalism.
We compare both the Cu + Cu and Au + Au yields to AMPT and EPOS predictions, and find they reproduce key qualitative aspects
of the data. Finally, we investigate other scaling parameters and find bulk strangeness production for both the measured data
and theoretical predictions, scales better with the number participants that undergo more than one collision. 相似文献
17.
F. Song L. Han C. Zou J. Su K. Zhang L. Yan J. Tian 《Applied physics. B, Lasers and optics》2007,86(4):653-660
Upconversion blue emissions of Tm3+-ion-heavy-doped NaY(WO4)2 crystals are investigated with three different near-infrared pump mechanisms. The dependence of upconversion efficiency on
the pump mechanism is analyzed from the scope of the concentration quenching effect. Three cross-relaxation processes, , , and , which influence the upconversion dominantly in the Tm3+-heavy-doped system, are demonstrated theoretically and experimentally. The results indicate that Yb3+ ions can weaken the concentration quenching effect of Tm3+ ions significantly so that the blue emission efficiency can be enhanced by one order of magnitude. At the same time, the
wavelength of the pump source also has considerable influence on both the population of some crucial energy levels and the
upconversion mechanism. Experiments show that the upconversion blue emission in Tm3+/Yb3+ co-doped NaY(WO4)2 crystal under 980-nm laser diode excitation is the most intensive of these three different near-infrared pump mechanisms.
The conclusions are confirmed by spectra measurements and calculations of Judd–Ofelt theory and Miyakawa–Dexter theory.
PACS 42.70.Hj; 78.55.-m 相似文献
18.
Results of experimental investigations into current-voltage characteristics of n+-π-p+ structures based on high-purity silicon doped with boron are presented. It is shown that the I–V characteristic at high injection
levels is described by Stafeev's theory, when the thickness d of the π-region is smaller than or close to three ambipolar
diffusion lengths La. For a current density J above (3–50) A/cm2 at varying temperatures, the I–V characteristic obeys a relation usually occurring in the case where charge-carrier recombination
in the n+ and p+-regions dominates that found in the π-region. The effect of mutual electron-hole scattering on the behavior of the I–V characteristic
is evident at J>630 A/cm3. For d/La=9, the I–V characteristic at high injection levels is treated by the theory of double carrier injection into a semiconductor
with consideration for diffusion corrections. In the temperature range below 200–276 K, the I–V curve for all samples studied
exhibits a linear dependence on J followed by a portion corresponding to a maximum occupancy of recombination levels by injected
electrons. Here the Fe or Au donor levels presumably act as recombination levels. The electron and hole capture areas (cross
sections) by recombination centers are roughly estimated.
Siberian Physicotechnical Institute at Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika,
No. 7, pp. 35–45, July 2000. 相似文献
19.
J. J. Camacho M. Santos L. Díaz L. J. Juan J. M. L. Poyato 《Applied Physics A: Materials Science & Processing》2010,99(1):159-175
A spectroscopic study of ambient air plasma, initially at room temperature and pressures ranging from 32 to 101 kPa, produced
by high-power transverse excitation atmospheric (TEA) CO2 laser (λ=9.621 and 10.591 μm; τ
FWHM≈64 ns; power densities ranging from 0.29 to 6.31 GW cm−2) has been carried out in an attempt to clarify the processes involved in laser-induced breakdown (LIB) air plasma. The strong
emission observed in the plasma region is mainly due to electronic relaxation of excited N, O and ionic fragments N+. The medium-weak emission is due to excited species O+, N2+, O2+, C, C+, C2+, H, Ar and molecular band systems of N
2+(_{2}^{+}(
B
2\varSigma u+^{2}\varSigma _{\mathrm{u}}^{+}
–X
2\varSigma g+)^{2}\varSigma _{\mathrm{g}}^{+})
, N2(C3
Π
u–B3
Π
g), N
2+(_{2}^{+}(
D2
Π
g–A2
Π
u) and OH(A2
Σ
+–X2
Π). Excitation temperatures of 23400±700 K and 26600±1400 K were estimated by means of N+ and O+ ionic lines, respectively. Electron number densities of the order of (0.5–2.4)×1017 cm−3 and (0.6–7.5)×1017 cm−3 were deduced from the Stark broadening of several ionic N+ and O+ lines, respectively. Estimates of vibrational and rotational temperatures of N
2+_{2}^{+}
electronically excited species are reported. The characteristics of the spectral emission intensities from different species
have been investigated as functions of the air pressure and laser irradiance. Optical breakdown threshold intensities in air
at 10.591 μm have been measured. 相似文献
20.
Ion cluster desorption yields from LiF were measured at PUC-Rio with ≈0.1 MeV/u N
q+ (q = 2,4,5,6) ion beams by means of a time-of-fight (TOF) mass spectrometer. A 252Cf source mounted in the irradiation chamber allows immediate comparison of cluster emissions induced by ≈65 MeV fission fragments
(FF). Emission of (LiF)
n
Li+ clusters are observed for both the N beams and the 252Cf fission fragments. The observed cluster size n varies from 1 to 6 for N
q+ projectiles and from 1 to ≈40 for the 252Cf-FF. The size dependence of the Y(n) distributions suggests two cluster formation regimes: (i) recombination process in the outgoing gas phase after impact and
(ii) emission of pre-formed clusters from the periphery of the impact site. The corresponding distribution of ejected negative
cluster ions (LiF)
n
F− closely resembles that of the positive secondary (LiF)
n
Li+ ions. The desorption yields of positive ions scale as Y(n) ∼ q
5. A calculation with the CASP code shows that this corresponds to a cubic scaling ∼S
e
3 with the electronic stopping power S
e
, as predicted by collective shock wave models for sputtering and models involving multiple excitons (Frenkel pair sputtering).
We discuss possible interpretations of the functional dependence of the evolution of the cluster emission yield Y(n) with cluster size n, fitted by a number of statistical distributions. 相似文献