共查询到20条相似文献,搜索用时 15 毫秒
1.
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
2.
Optical nonlinearities in aggregates of nanoparticles formed in silver hydrosols (SHs) are studied under pico- and nanosecond
pulsed laser excitation. The dependence of the nonlinear refractive index n
2 on the degree of hydrosol aggregation is studied experimentally at the wavelength λ=1.064 μm. It is found that n
2 changes sign when the degree of hydrosol aggregation is increased. Various physical effects occurring in resonant domains
of the aggregates are analyzed using a simple physical model of two bound silver nanoparticles. The theory takes into account
thermal, elastic, electrostatic, and light-induced effects. Experimental results are discussed in the context of this theory. 相似文献
3.
T. Yoshinari 《Phase Transitions》2013,86(1-4):89-93
Abstract A new absorption band has been found at 5.10 eV in (C n H2n + 1NH3)2CdCl4: n = 1, 2, 3 in addition to the absorption bands of CdCl2 whose electronic structure resembles the former crystals. The energy of the additional peak shifts with temperature by as much as 0.38 eV from 5.10eV at room temperature (RT) to 5.48 eV at liquid nitrogen temperature. This large peak shift is attributed to a structural phase transition between these two temperatures. A new type of electron center has been found in these crystals (M = Cd, Mn; n = 1, 2, 3) irradiated with X-rays at 15 K in addition to the Cl2 ?. This shows optical absorption bands (IR bands) in the infrared region of 10 ~ 20 kcm ?1. The IR bands are assigned to an electron center where an electron is trapped at an ammonium site in the neighborhood of a Cl? vacancy. 相似文献
4.
J. M. Fernández Navarro J. Toudert Y. Rodríguez-Lazcano B. Maté M. Jiménez de Castro 《Applied physics. B, Lasers and optics》2013,113(2):205-213
The formation of silver nanoparticles in 60GeO2–20PbO–20Na2O bulk glass doped with 0.15 wt% of Ag has been studied by optical methods in the near ultraviolet-to-near infrared and mid-infrared ranges. A clear optical absorption band, which grows when increasing the annealing temperature, is observed around 460 nm, as a consequence of the surface plasmon resonance in the Ag nanoparticles. From the simultaneous analysis of optical transmittance and spectroscopic ellipsometry spectra in the near ultraviolet-to-near infrared range, it is demonstrated that the nanoparticles are surprisingly formed only in a thin layer (some tens of nm thick) underneath the sample surfaces. The potential of such a simultaneous optical analysis for determining the localization of the nanoparticles in glasses of any nature is underlined. Based on the results of a complementary mid-infrared spectroscopy characterization, the processes involved in silver migration to the surfaces and further aggregation to form nanoparticles are discussed. 相似文献
5.
It is established that the necessary conditions for spontaneous relaxation of elastic strain energy in a copper-As60Se40 self-organizing dissipative heterostructure is that the elastic deformation energy and the temperature must reach their threshold
values. It is shown that in the temperature range 270–340 K the spontaneous relaxation of elastic deformation energy is accompanied
by structural-chemical ordering and anomalous diffusion of copper into the glassy chalcogenide semiconductor layer. The maximum
concentration of copper dissolved in the films is 40 at. %. Conductivity inversion from p to n type is observed in doped layers obtained by this method.
Zh. Tekh. Fiz. 69, 128–129 (August 1999) 相似文献
6.
7.
S. V. Demishev M. V. Kondrin V. V. Glushkov N. E. Sluchanko N. A. Samarin 《Journal of Experimental and Theoretical Physics》1998,86(1):182-189
Thermopower of (BEDT-TTF)
m
X
n
organic conductors has been studied using a dedicated measurement technique in the temperature range of 4.2 to 300 K. It
turned out that some features of the thermopower in quasi-two-dimensional metals, namely the presence of a peak in the thermopower
of α-(BEDT-TTF)2MHg(SCN)4 and a plateau in κ-(BEDT-TTF)2Cu(NCS)2 in the temperature interval between 10 and 50 K, are probably due to the phonon drag effect. Similar temperature dependences
of the Seebeck coefficient can be satisfactorily interpreted in terms of a simple model taking into account the real experimental
curve of the phonon heat capacity versus temperature, C ∝ T
2, which is not described by the Debye formula. One feature distinguishing organic superconductors from magnetically ordered
metals is a stronger temperature dependence of the characteristic electron-phonon scattering time τ
e-ph(T). Phonon drag effects also determine the behavior of the thermopower in the (BEDT-TTF)3Cl2·2H2O organic conductor, which is characterized by a metal-insulator transition at T∼150 K. An analysis of measurements of the conductivity and thermopower vs. temperature taken together indicates that the
transition in this compound has a complex nature: first (at T∼150 K) a metal-insulator transition occurs, which produces an energy gap in the band spectrum, then at a lower temperature
(T∼20 K) a transition to a charge-density wave state takes place.
Zh. éksp. Teor. Fiz. 113, 323–338 (January 1998) 相似文献
8.
Optical properties and ultrafast electron dynamics in gold–silver alloy and core–shell nanoparticles
Silver and gold are the two most popular metals used for many nanoparticle applications, such as surface enhanced Raman scattering
or surface enhanced fluorescence, in which the local field enhancement associated with the excitation of the localized surface-plasmon–polariton
resonance (SPR) is exploited. Therefore, tunability of the SPR over a wide energy range is required. For this purpose we have
investigated core–shell nanoparticles composed of gold and silver with different shell thicknesses as well as the impact of
alloying on these nanoparticles due to a tempering process. The nanoparticles were prepared by subsequent deposition of Au
and Ag atoms or vice versa on quartz substrates followed by diffusion and nucleation. Their linear extinction spectra were
measured as a function of shell thickness and annealing temperature. It turned out that different gold shell thicknesses on
silver cores allow a tuning of the SPR position from 2.79 to 2.05 eV, but interestingly without a significant change on the
extinction amplitude. Heating of core–shell nanoparticles up to only 540 K leads to the formation of alloy nanoparticles,
accompanied by a back shift of the SPR to 2.60 eV. Calculations performed in quasi-static approximation describe the experimental
results quite well and prove the structural assignments of the samples. In additional experiments, we applied the well-established
persistent spectral hole burning technique to the alloy nanoparticles in order to determine the ultrafast dephasing time T
2. We obtained a dephasing time of T
2=(8.1±1.6) fs, in good agreement with the dephasing time of T
2,∞=8.9 fs, which is already included in the dielectric function of the bulk. 相似文献
9.
Hsing-Ying Lin Meei-Ling Hung Chen-Han Huang Hsiang-Chen Chui Jui-Sheng Lin 《Applied Physics A: Materials Science & Processing》2014,115(2):399-402
We observe that silver atoms deposited by thermal evaporation deposition onto n-layer graphene films condense upon annealing to form nanoparticles with an average diameter and density that is determined by the layer numbers of graphene films. The optical microscopy and Raman spectroscopy were utilized to identify the number of the graphene layers and the SEM (scanning electron microscopy) was used to observe the morphologies of the particles. Systematic analysis revealed that the average sizes of the nanoparticles increased with the number of graphene layers. The density of nanoparticles decreased as the number of graphene layers increased, revealing a large variation in the surface diffusion strength of nanoparticles on the different substrates. The mechanisms of formation of these layer-dependent morphologies of silver nanoparticles are related to the surface free energy and surface diffusion of the n-layer graphenes. 相似文献
10.
Transport properties of a binary mixture of CO2ben N2 from the pair potential energy functions based on a semi-empirical inversion method 下载免费PDF全文
The potential energy surface of a CO2-N2 mixture is determined by using an inversion method, together with a new collision integral correlation [J. Phys. Chem. Ref. Data 19 1179 (1990)]. With the new invert potential, the transport properties of CO2-N2 mixture are presented in a temperature range from 273.15 K to 3273.15 K at low density by employing the Chapman-Enskog scheme and the Wang Chang-Uhlenbeck-de Boer theory, consisting of a viscosity coefficient, a thermal conductivity coefficient, a binary diffusion coefficient, and a thermal diffusion factor. The accuracy of the predicted results is estimated to be 2% for viscosity, 5% for thermal conductivity, and 10% for binary diffusion coefficient. 相似文献
11.
F. Calvo F. Spiegelman M. A. Gaveau M. Briant P. R. Fournier J. M. Mestdagh J. P. Visticot 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):215-218
The finite temperature optical spectroscopy of
CaArn clusters in the range
6
n
146
is investigated using a Diatomics-In-Molecule (DIM) Hamiltonian
and classical parallel tempering Monte Carlo simulations. The
absorption spectrum is calculated in the vertical approximation
at various temperatures between 2 K and 50 K. Several typical
situations are reported. CaAr6 shows a
strong thermal broadening and shift of the spectral lines,
possibly associated with isomerization.
CaAr13 only shows some broadening.
CaAr37 exhibits features corresponding to
coexisting isomers at low temperature. Finally, the abrupt
changes in the absorption spectrum in
CaAr146 at about 20 K are indicative of
surface diffusion. 相似文献
12.
A universal probe method for measuring the temperature of large clusters (nanoparticles) in a cluster beam has been proposed
and experimentally implemented. The temperature of large van der Waals clusters (nanoparticles) (CO2)
N
(where N ⩾ 102 is the number of monomers in a cluster) in the cluster beam is measured using this method with SF6 molecules as miniature probe thermometers. The SF6 molecules are captured by the (CO2)
N
clusters in intersecting cluster and molecular beams and sublimate from the surface of the clusters, carrying information
on the velocity and temperature (internal energy) of the clusters. The velocity (kinetic energy) of SF6 molecules sublimating from the surface of the clusters has been measured by the time-of-flight method and the temperature
of the clusters has been determined as T
cl = (105 ± 15) K. 相似文献
13.
Abstract A characteristic of ion mixing in the low temperature portion of the thermally assisted ion mixing regime is that the activation energy obtained from most experiments is in the range of 0.1 to 0.3 eV. These values are typically a factor of 4 to 10 lower than the vacancy migration energy of most elements. This discrepancy is maintained even when the ion mixing data is contrasted to the more comparable data from concentrated homogeneous alloys. It appears that an explanation of the ion mixing activation energy is not possible by radiation enhanced diffusion (RED) where, at the low temperature end of RED, defect annihilation is by direct vacancy-interstitial recombination and the predicted activation energy is Q = 0.5 EM v In an attempt to understand the origin of the low activation energies obtained during ion mixing we have performed calculations of the mutual diffusion coefficients in binary liquid mixtures. A hard sphere fluid model based on the kinetic gas theory of Enskog was used. The model was corrected to agree with molecular dynamic calculations of liquid state diffusion and included thermodynamic driving forces. The calculations resulted in temperature dependent mixing curves which are in good agreement with ion mixing experiments and suggested that the temperature rise in the thermal spike approximately ranged between 1000 and 4000 K. 相似文献
14.
R.P. Taylor P.C. Main L. Eaves S.P. Beaumont S. Thoms C.D.W. Wilkinson 《Superlattices and Microstructures》1989,5(4)
We have studied electron heating in a submicron-size GaAs wire from 4.2 K to 50 K. We find that the energy relaxation rate for the electrons is of the form τE−1 = α + βTen where α, β are constants and Te is the electron temperature. We associate the temperature-independent term with a quasi-elastic surface scattering process in which an electron losses 1% of its energy at each collision. The temperature dependent term may be due to electron-phonon scattering. It is possible to fit the data to 2 < n < 3. 相似文献
15.
It was found that bulk samples of molybdenum 〈Mo〉 are oxidized by supercritical water forming nanoparticles of monocline MoO2. The average size of nanoparticles obtained at uniform heating of 〈Mo〉 with supercritical water was about 27 nm, and the size of agglomerates of nanoparticles was ≤ 1 μm. From time dependence of the amount of formed H2 n H2(t), we have determined kinetic parameters of 〈Mo〉 transition to MoO2 particles. The dependence dn H2/dt is characterized by the presence of two pronounced maxima. This is explained by the change of mutual diffusion of H2 and H2O molecules along with the growth of thickness of the layer of MoO2 nanoparticles. 相似文献
16.
The recrystallization of silver sulfide Ag2S nanoparticles has been studied and the range of the thermal stability of the nanoparticle sizes has been determined. Nanopowders Ag2S with particle sizes of 45–50 nm were obtained by chemical deposition from aqueous solutions. To study the thermal stability of the Ag2S nanoparticle sizes, the nanocrystalline powders have been annealed in a vacuum of 0.01 Pa on heating from room temperature to 493 K and in argon at 623 K. Annealing up to a temperature of 453 K leads to insignificant nanoparticle growth and annealing of microstrains, which allows one to consider this temperature range as the region of thermal stability of the silver sulfide nanostate. The temperature range from 450 to 900 K, in which the particle size increases by a factor of 3–6, corresponds to the temperature of collective recrystallization of the silver sulfide nanopowder. 相似文献
17.
K. V. Oreshkina V. D. Dubrovin A. I. Ignat’ev N. V. Nikonorov 《Optics and Spectroscopy》2017,123(4):590-596
The effect of silver on the optical, spectral-luminescent, and crystallization properties of bromide photo-thermo-refractive glasses is studied. Multicomponent photosensitive glasses of the Na2O–ZnO–Al2O3–SiO2 system with photosensitizing agents (cerium, antimony, silver) and halogenides (fluorine and bromine) are synthesized. Ultraviolet irradiation and thermal treatment below the glass-transition temperature of the glasses cause the formation of silver molecular clusters, which exhibit luminescence in the visible and infrared regions. UV irradiation and thermal treatment of glasses above the glass-transition temperature lead to the growth of silver nanoparticles with plasmon resonance peak in the region of 420 nm. Further thermal treatment of glasses above the glass-transition temperature shifts the plasmon-resonance maximum by 70 nm to longer wavelengths, which is related to the growth of a crystalline shell consisting of mixed silver and sodium bromides on nanoparticles. This formation of a crystalline phase on colloidal centers results in a local increase in the refractive index of the irradiated region by +Δn ~ 900 ppm compared to the nonirradiated region. Photo-thermo-refractive glasses with increased silver concentration are promising photosensitive materials for creating holographic optical elements and devices for line narrowing and stabilizing filters, spectral beam combiners, and filters for increasing the spectral brightness of laser diodes. A positive change in the refractive index of Photo-thermo-refractive glasses provides the possibility of recording in them 3D waveguide and integrated-optical structures. 相似文献
18.
The interaction of O2, CO2, CO, C2H4 AND C2H4O with Ag(110) has been studied by low energy electron diffraction (LEED), temperature programmed desorption (TPD) and electron energy loss spectroscopy (EELS). For adsorbed oxygen the EELS and TPD signals are measured as a function of coverage (θ). Up to θ = 0.25 the EELS signal is proportional to coverage; above 0.25 evidence is found for dipole-dipole interaction as the EELS signal is no longer proportional to coverage. The TPD signal is not directly proportional to the oxygen coverage, which is explained by diffusion of part of the adsorbed oxygen into the bulk. Oxygen has been adsorbed both at pressures of less than 10-4 Pa in an ultrahigh vacuum chamber and at pressures up to 103 Pa in a preparation chamber. After desorption at 103 Pa a new type of weakly bound subsurface oxygen is identified, which can be transferred to the surface by heating the crystal to 470 K. CO2 is not adsorbed as such on clean silver at 300 K. However, it is adsorbed in the form of a carbonate ion if the surface is first exposed to oxygen. If the crystal is heated this complex decomposes into Oad and CO2 with an activation energy of 27 kcal/mol(1 kcal = 4.187 kJ). Up to an oxygen coverage of 0.25 one CO2 molecule is adsorbed per two oxygen atoms on the surface. At higher oxygen coverages the amount of CO2 adsorbed becomes smaller. CO readily reacts with Oad at room temperature to form CO2. This reaction has been used to measure the number of O atoms present on the surface at 300 K relative to the amount of CO2 that is adsorbed at 300 K by the formation of a carbonate ion. Weakly bound subsurface oxygen does not react with CO at 300 K. Adsorption of C2H4O at 110 K is promoted by the presence of atomic oxygen. The activation energy for desorption of C2H4O from clean silver is ~ 9 kcal/mol, whereas on the oxygen-precovered surface two states are found with activation energies of 8.5 and 12.5 kcal/mol. The results are discussed in terms of the mechanism of ethylene epoxidation over unpromoted and unmoderated silver. 相似文献
19.
Abstract We have measured resistivity and magnetic susceptibility of Y2Ba4Cu6+nO14+n (n=0,1,2) on bulk material and single crystals as well. We have found a pressure dependence of dTc/dp within the range of 0.05 to 0.55 K/kbar depending on the symmetry. 相似文献
20.
A. Yu. Orlova R. R. Gainov A. V. Dooglav I. N. Pen’kov E. A. Korolev 《JETP Letters》2012,96(6):370-374
Silver sulfo-antimonide Ag5SbS4 (stephanite) has been studied by nuclear quadrupole resonance (NQR) spectroscopy on antimony nuclei. The temperature dependences of the spectroscopic and relaxation parameters have been examined in the range of 4.2?C395 K. A phase transition at 140 K and internal motions with an activation energy of 0.29 eV have been experimentally detected. The nature of the phase transition and diffusion of silver ions has been discussed in view of the reported data. 相似文献