共查询到20条相似文献,搜索用时 15 毫秒
1.
G.J. Ashwell D.W. Allen G.H. Cross D.A. Kennedy I.W. Nowell 《Solid State Communications》1982,43(10):731-733
(Dimethyldiphenylphosphonium)+(7,7,8,8-tetracyanoquinodimethanide)?2 is monoclinic, space group Cc, with a = 32.01(2), b = 6.56(1), , β = 107.4(8)°. The TCNQ's stack plane-to-plane in columns parallel to b with (i) a mean interplanar spacing of 3.28 Å along the conducting chains and (ii) an exocyclic bond to quinonoid ring overlap of adjacent molecules. The conductivity along b, the needle axis, varies as where σ300 K = 0.05 S cm?1 and Ea = 0.20 eV (Diethyldiphenylphosphonium)+(7,7,8,8-tetracyanoquinodimethanide)?2 is similarly monoclinic, space group Cc, with a = 31.48(2), b = 6.51(1), , β = 104.2(8)°. The conductivity at 300 K and activation energy, both determined along b, are 1–10 S cm?1 and 0.05 eV respectively. There is evidence of a lattice distortion in the dimethyl analogue only. 相似文献
2.
The decay kinetics and the yield of the π luminescence from the lowest triplet state of the self-trapped exciton have been studied in NaCl containing Li+ ions. It is found that the π luminescence band which is observed at 6K is replaced by a luminescence band peaked at 3.34 eV above 77K. The 3.34 eV luminescence band is ascribed to the recombination of the relaxed exciton trapped by a Li+ ion, (Vke)Li. The decay of the π luminescence induced by an electron pulse and the time change of the luminescence from (Vke)Li are explained in terms of the characteristic equation of the diffusion-limited reaction of the lowest triplet self-trapped excitons with the Li+ ions. From the analysis of the dependence of the decay rate of the π luminescence on temperature and on the Li+ concentration, we found the diffusion constant D of the lowest triplet self-trapped exciton in NaCl to be given by with and E0 = 0.13 eV. The present result can be regarded as the first clear experimental evidence for the hopping diffusion of the self-trapped exciton in alkali halides. The obtained values of Ea and D0 are discussed using the small polaron theory. The effect of the anharmonicity on the hopping of the self-trapped excitons is suggested to be significant. 相似文献
3.
R.M. Macfarlane 《Solid State Communications》1974,15(3):535-538
We have observed inter-term Raman scattering from 5T2g→5Eg Frenkel excitons in antiferromagnetic FeF2. It differs qualitatively from previously observed intra-term scattering in a sharply reduced zero-phonon cross section and the appearance of relatively strong exciton-phonon scattering. Since the Raman process is fully allowed, it is possible to measure excited state Debye-Waller factors, D, and we find and . 相似文献
4.
Elastoresistances of TCNQ high conducting salts have been measured at room temperature by an original strain gauge technique. The effects, on the longitudinal and transverse resistivities ?, of an elementary uniaxial strain ? applied along one of the three axes, a, b or c1 respectively, have been estimated.For TTF-TCNQ, they are: ; ; (5% risk).So, in an hydrostatic pressure experiment, the fraction of piezoresistivity attributable to transverse effects is 43± 10% of the total value χb (Kba and Kbc effects accumulated).Low values have been found for the anisotropy (?a/?b) variations due to strains. So one may write: ; ; .The TTF-, HMTTF-, TSF-, HMTSF-TCNQ elastoresistance values are coherent with the previously measured hydrostatic pressure piezoresistivity values.All these experimental results are in good agreement with a model where the longitudinal but also the transverse elastoresistivities are essentially due to variations with strains of the longitudinal scattering time τν defined by σb = ne2τν/m1. 相似文献
5.
H. Van Cong S. Brunet S. Charar J.L. Birman M. Averous 《Solid State Communications》1983,45(7):611-614
The band-gap narrowing ΔEg, opt and ΔEg, elec (or ΔEg, eff) for optical and electrical energy gaps of the n-type impure silicon at 300 K, are investigated based on simplified models of heavily doped semiconductors. It is suggested that, for is significantly larger than ΔEg, opt, in good agreement with observed results. This difference is caused especially by the effect of the polaron. 相似文献
6.
We report on the magnetic behaviour of exchange-coupled closed chains (rings) of increasing length made of two alternating spin sublattices . Taking into account the geometrical and spin space symmetries of such syste the problem is shown to be tractable up to 10 spins for distinct values of the ga/gb ratio between Landé factors; the results are discussed for an antiferromagnetic coupling. The limiting behaviour for the infinite chain is determined by extrapolation of the data obtained for finite rings. At very low temperatures, the analogy with the regular ferromagnetic chain is underlined. 相似文献
7.
The absorption and MCD spectra of the , , and spin-allowed transitions of Cr3+ in K2NaGaF6 are reported. It is shown that transitions to the . states are induced by T1u vibratio the other spin-allowed transition, , there are three competing intensity mechanisms: electric dipole induced by T1u vibrations, electric dipole induced by T2u vibrations and magnetic dipole, and an estimate is made of the relative importance of these. The magnetic dipole zero-phonon line is observed to be accompanied by a vibrational sideband for which the coupling is predominantly with T2u vibrations. Other weak transitions are observed in MCD spectra and their origin briefly discussed. 相似文献
8.
He+, Ne+ and Ar+ ions with energies E1 between 50 and 1000 eV were used to bombard a polycrystalline Cu target at an angle of 45°. The energies, E2, of the Cu1+ ions sputtered at 90° to the primary beam were investigated using a UHV magnetic sector mass spectrometer. The maxima of the energy distributions as measured by the instrument, were at values of E2 of about 4 eV (±1 eV), nearly independent of e1 and primary ion mass. Plots of log N(E2) versus log E2 displayed limited linear portions over which the functional dependence of N(E2) is proportional to E2?0.5. Plots of the average secondary ion energy, ē2, versus the energy transferred by the primary ion to a Cu atom in a direct collision , indicate that ē2 increases linearly with transfer energy up to a transferred energy of about 200 eV, independent of primary ion mass. Above about 200 eV transferred energy, ē2 asymptotically approaches values which depend upon primary ion mass. At transferred energies below about 200 eV, the collision kinematics in the fust few collisions appears to dominate the emission process. 相似文献
9.
We calculate the effective electron-hole interaction Vre in the presence of an exciton gas, which reads in real space: The parameters Ci and Zi are given explicitly for GaAs. For this material, we show the binding energy of the exciton is weakly modified so long as . (R0, exciton Rydberg, a0 exciyon radius, ?ex exciton density, T temperature). 相似文献
10.
Differential cross sections were measured for 46Ti(p, p) and 46Ti(p, p1) at four angles between Ep = 1.5 and 3.1 MeV, with an overall energy resolution of about 300 eV. Spins, parities, total and partial widths were extracted for 144 resonances. Six analogue states were identified. The s-wave states have expected spacing and width distributions, while the states behave anomalously. The , and strength functions were determined. 相似文献
11.
The one-electron momentum distribution function for an electron gas is investigated by a diagrammatic analysis of perturbation theory. It is shown that has the following exact asymptotic form for large k (k ? pF; pF, the Fermi momentum): , where g?(0) is the zero-distance value of the spin-up-spin-down pair correlation function. The physical implications of the above asymptotic form are discussed. 相似文献
12.
R. Oppermann 《Solid State Communications》1982,44(8):1297-1299
An n-orbital model describing both elastic impurity scattering and exchange interaction is examined near its instability for itinerant ferromagnetism. At the critical point and at zero temperature, long range spin fluctuations cause anomalous enhancements of the density of states near the Fermi energy with in three-dimensions (3D) and with ln2|E ? EF| in 2D. An estimation of the conductivity in a continuum analog model reveals Ω -and ln2-corrections in 3D and 2D respectively. 相似文献
13.
The temperature coefficient of the CdxHg1?xTe energy gap dEg/dT as a sum of lattice dilatation and the phonon-electron interaction terms has been calculated as the function of molar composition x, for 0?x?0.3, in the temperature range 4.2–300 K. A non-linear dependence of vs x and a strong effect of temperature on values have been obtained and a comparison with experimental data is discussed. 相似文献
14.
The excitation functions of have been measured in the energy range Ep = 14.2 to 17.4 MeV in 50 keV steps at θlab = 120°, 140° and 160°. The isobaric analog resonances of the parent states in 209Pb up to Ex = 2.5 MeV and the optical-model background were fit simultaneously at all energies and angles. The spreading widths and the values of a parameter β2, which measures the isospin purity of the IAR, were determined for the , and resonances. An average value of the isospin purity of β2 = 66% was found. 相似文献
15.
J.C.D. Brand U.D. Deshpande A.R. Hoy S.M. Jaywant 《Journal of Molecular Spectroscopy》1983,100(1):143-150
The E-B (0g+-0u+) band system of Br2 has been investigated at Doppler-limited resolution using polarization labeling spectroscopy. Merged E state data for the three naturally occurring isotopes in the range vE = 0–16, expressed in terms of the constants for 79Br2, are (in cm?1) Y0,0 = 49 777.962(54), Y1,0 = 150.834(22), Y2,0 = ?0.4182(28), Y3,0 = 6.6(11) × 10?4, Y0,1 = 4.1876(28) × 10?2, Y1,1 = ?1.607(16) × 10?4, and Y0,2 = 1.39(39) × 10?8. The bond distance is , and the diabatic dissociation energy to . 相似文献
16.
The γ-decay of 26 resonances in the reaction 60Ni(p, γ)61Cu in the range Ep = 3690–3790 keV has been investigated. The isobaric analogue state (IAS) corresponding to the parent state at in 61Mi has been resolved into several fine structure components. The absolute strength for the transition to the antianalogue state is found to be Γγ = 0.24 ± 0.07 W.u. The measured M1 strength distribution for the decay of the . IAS is compared to theoretical predictions. 相似文献
17.
R.F. Curl 《Journal of Molecular Spectroscopy》1973,48(1):165-173
The and transitions of the J = 7 levels of the ground state of CH4 have been observed by infrared-radio frequency double resonance using the 3.39 μ HeNe laser line. The transition frequencies are 423.02 ± 0.02 MHz and 1246.55 ± 0.02 MHz, respectively. Using these frequencies and the splitting of the E and F2 levels of the J = 2 state calculated from the molecular beam magnetic resonance spectra of Ozier, the centrifugal distortion constants are derived to be Dt = 132933 ± 10 Hz, H4t = ? 16.65 ± 0.2 Hz, and H6t = 10 ± 1 Hz. The J = 15 E(1) → E(2) microwave transition is predicted as 14150 ± 9 MHz. 相似文献
18.
William H. Hamill 《Journal of Physics and Chemistry of Solids》1982,43(6):559-562
The time- and temperature-dependent drift mobility μd for dispersive transients in disordered solids is in terms of distance L, field E and transit time tT. Since current I ∝ tsu?(1?α) for t <Tand 0<α<1 by Scher-Montroll theory for hopping among localized states, it follows that where τ≈ 10?13s is estimated. Further and the activation energy Δ0 is time independent. On this basis Δ for the carbazole polymers is ca. zero, that for a-Se is ca. 0.05 eV, and that for a-As2Se3 is 0.35 eV rather than 0.5, 0.3 and 0.6 eV respectively on a phenomenological basis for μd(T,t). Trap-controlled hopping transport may be excluded. Time-resolved optical studies of excess carrier recombination supplement mobility measurements in a-Si:H and a-As2Se3 as well as other systems. Combined results suggest a dielectric response mechanism in which the time-dependent hopping frequency of localized carriers ν ∝ tα?1 arises from distortion of the medium at localization sites. This is satisfied by Δ(T,t) = Δ0+(1?α)KTT ln(t/τ) where τ is the mean initial localization time of the carrier, 10?13?10?12s, Δio is the height of the barrier at T, and 0<α<l. Consequently ν = ν0(t/τ)α?1 exp(frsol|?Δ0/KT) which applies also to bimolecular recombination. 相似文献
19.
By analyzing thick-target excitation functions of the resonance we have determined Γc.m ≦ 530+40?70 eV for the width of the lowest T = 2 state of 24Mg. The beam energy resolution function was measured using a narrow 27Al(p, γ) resonance at Ep = 3671 keV, for which we obtain Γc.m. = 180 ±50 eV. 相似文献
20.
The specific heat (Cp) of the amorphous alloys Ni100-xZrx for x = 75, 65, 55 and 35 was measured from 0.8K to 40K and the composition trends of the transition temperature Tc, the enhanced density of states at the Fermi level Nγ(F) and the Debye temperatures θD(0), θD(T) established. For the three superconducting compositions (x=75, 65, 55) Nγ(EF increases rapidly with increasing [Zr] in agreement with the trend in amorphous Cu-Zr alloys. However, for the Zr-Ni alloys the bare density of states increases strongly with [Zr] in contrast to the Zr-Cu alloys where it is reported to be almost constant. We conclude that for the Ni-Zr alloys the electron-ion matrix element <I2> decreases with increasing [Zr]. Other results are related to recent photoemission studies of these alloys. 相似文献