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61.
E. Barborini I. N. Kholmanov A. M. Conti P. Piseri S. Vinati P. Milani C. Ducati 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):277-282
Nanostructured titanium dioxide films have been deposited
by supersonic cluster beam deposition (CBD). Nanoparticles are
produced by a pulsed microplasma cluster source (PMCS) and
selected by aerodynamic separation effects. The as-deposited
film is a complex mixture where amorphous material coexists, at
the nanoscale, with anatase and rutile crystal phases. The
nanocrystalline fraction of the film is characterized by crystal
size ranging from 100 nm to less than 5 nm. We have
characterized the film structure by transmission electron
microscopy, Raman spectromicroscopy, X-ray diffraction, and
UV-visible spectroscopy showing that correlations exist between
cluster size and film properties. In particular if very small
clusters are deposited, the film shows a predominant rutile
phase whereas larger clusters form films with mainly anatase
structure. Our observations suggest that phonon confinement
effects are responsible for a significant shift and broadening
observed for the Raman peaks. In addition, optical gap tuning is
provided by mass selection: large clusters assembling generates
a film with 3.22 eV optical gap, while smallest clusters 3.52
eV. 相似文献
62.
Magnetotransport measurements with the quasi two-dimensional misfit-layer compound (LaSe)1.14(NbSe2) with critical temperature T
c = 1.23 K are presented. The temperature dependence of the upper critical magnetic field H
c2 has been determined from an analysis of magnetoresistance data through the scaling procedure obtained theroretically by Ullah and Dorsey for the fluctuation conductivity. We show that in contrast to a direct determination of H
c2(T) with a positive curvature the temperature dependence of H
c2 obtained via the scaling procedure reveals a negative curvature in agreement with the Werthammer-Helfand-Hohenberg theory for conventional type-II superconductors. 相似文献
63.
The two-dimensional temporal mixing layer shows spiraling and merging vortices and is an example of a flow problem in which, despite the complexity, the vortices as individual coherent structures can be clearly visualized. In this paper we present a method for the analysis of the data that describes the spiraling and merging of vortices. To that end we define a parameterized set of structures, the ‘phenomenological model manifold’, which approximates the apparent spatial structures. Then we let the parameters of the manifold vary in such a way that the succession of states resembles the evolving flow as well as possible. Two different model manifolds were designed, one model for which the vortices are described with Gaussian profiles, and another in which a more optimal spatial structure is used. Projection of the numerical data on these manifolds results in information about the strength, ellipticity and trajectories of the vortices. The method is also used to study the successive merging of vortices; differing from scaling arguments for an inviscid flow, the results show that the first pairwise merging evolves approximately 2.11 times faster than the second merging. Efficient procedures are described for the required extensive optimisation problems. 相似文献
64.
J.J. Liu S.F. Zhang Y.X. Li X.J. Kong 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(1):17-20
Using a two-parameter wave function, we calculate variationally the binding energy of an exciton bound to an ionized donor
impurity (D+,X) in GaAs-AlxGa1-xAs quantum wells for the values of the well width from 10 to 300 ?, when the dopant is located in the center of the well and
at the edge of the well. The theoretical results confirm that the previous experimental speculation proposed by Reynolds et al. [Phys. Rev. B 40, 6210 (1989)] is the binding energy of D+,X for the dopant at the edge of the well. In addition, we also calculate the center-of-mass wave function of the exciton and
the average interparticle distances. The results are discussed in detail.
Received 17 July 2000 and Received in final form 13 November 2000 相似文献
65.
Pengwei Li Xiaolong Liu Yiqiang Zhang Chao Liang Gangshu Chen Fengyu Li Meng Su Guichuan Xing Xutang Tao Yanlin Song 《Angewandte Chemie (International ed. in English)》2020,59(17):6909-6914
1,4‐butanediamine (BEA) is incorporated into FASnI3 (FA=formamidinium) to develop a series of lead‐free low‐dimensional Dion–Jacobson‐phase perovskites, (BEA)FAn?1SnnI3n+1. The broadness of the (BEA)FA2Sn3I10 band gap appears to be influenced by the structural distortion owing to high symmetry. The introduction of BEA ligand stabilizes the low‐dimensional perovskite structure (formation energy ca. 106 j mol?1), which inhibits the oxidation of Sn2+. The compact (BEA)FA2Sn3I10 dominated film enables a weakened carrier localization mechanism with a charge transfer time of only 0.36 ps among the quantum wells, resulting in a carrier diffusion length over 450 nm for electrons and 340 nm for holes, respectively. Solar cell fabrication with (BEA)FA2Sn3I10 delivers a power conversion efficiency (PCE) of 6.43 % with negligible hysteresis. The devices can retain over 90 % of their initial PCE after 1000 h without encapsulation under N2 environment. 相似文献
66.
P. D. SesionJr E. L. Albuquerque C. Chesman V. N. Freire 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(4):379-387
We study the acoustic-phonon transmission spectra in periodic and quasiperiodic (Fibonacci type) superlattices made up from
the III-V nitride materials AlN and GaN. The phonon dynamics is described by a coupled elastic and electromagnetic equations
within the static field approximation model, stressing the importance of the piezoelectric polarization field in a strained
condition. We use a transfer-matrix treatment to simplify the algebra, which would be otherwise quite complicated, allowing
a neat analytical expressions for the phonon transmission coefficients. Numerical results, for the normal incidence case,
show a strike self-similar pattern for both hexagonal (class 6 mm) and cubic symmetries crystalizations of the nitrides. 相似文献
67.
采用纳米孔模板润湿技术制备了直径为200 nm的低密度聚乙烯(LDPE)纳米线阵列, 并利用纳秒激光闪光法测量了20—80℃时LDPE纳米线阵列的热导率. 测量得到室温时LDPE纳米线阵列的热导率为2.2 W/mK, 大约比其体材料的热导率高1个数量级, 并且纳米线阵列的热导率随温度的升高略有增加. 忽略纳米线之间的声子散射, 估算得到室温下单根LDPE纳米线的热导率高于5 W/mK. 本文制备LDPE纳米线热导率的提高源自其分子链定向度增加导致的低维导热效应的增强, 纳米线的分子链定向度受工艺过程中流体剪切、振动、分子链迁移运动、 纳米孔约束等几种因素的综合影响. 相似文献
68.
Phonon relaxation and heat conduction in one-dimensional Fermiben Pastaben Ulam β lattices by molecular dynamics simulations
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The phonon relaxation and heat conduction in one-dimensional Fermi-Pasta-Ulam (FPU) β lattices are studied by using molecular dynamics simulations. The phonon relaxation rate, which dominates the length dependence of the FPU β lattice, is first calculated from the energy autocorrelation function for different modes at various temperatures through equilibrium molecular dynamics simulations. We find that the relaxation rate as a function of wave number k is proportional to k1.688, which leads to a N0.41 divergence of the thermal conductivity in the framework of Green-Kubo relation. This is also in good agreement with the data obtained by non-equilibrium molecular dynamics simulations which estimate the length dependence exponent of the thermal conductivity as 0.415. Our results confirm the N2/5 divergence in one-dimensional FPU β lattices. The effects of the heat flux on the thermal conductivity are also studied by imposing different temperature differences on the two ends of the lattices. We find that the thermal conductivity is insensitive to the heat flux under our simulation conditions. It implies that the linear response theory is applicable towards the heat conduction in one-dimensional FPU β lattices. 相似文献
69.
采用非平衡分子动力学方法研究了300 K和1000 K时(5,5)碳纳米管热导率随长度的变化.在室温下,碳纳米管长度小于40 nm时热导率与长度呈线性关系,此时导热处于弹道输运阶段,单位面积弹道热导为5.88×109 Wm-2K-1.随着碳纳米管长度的增加,其热导率逐渐增加,但增加速度随长度逐渐减小,此时导热处于弹道—扩散输运阶段,并随长度的增加从以弹道输运为主向以扩散输运为主转变.长度大于10 μm时由于弹道输运可以忽略,导热近似达到完全
关键词:
碳纳米管
热导率
弹道输运
低维导热 相似文献
70.
Photoluminescence(PL) and Raman spectra under uniaxial strain were measured in mono- and bi-layer MoSe_2 to comparatively investigate the evolution of excitonic gaps and Raman phonons with strain. We observed that the strain dependence of excitonic gaps shows a nearly linear behavior in both flakes. One percent of strain increase gives a reduction of ~42 meV(~35 me V) in A-exciton gap in monolayer(bilayer) MoSe_2. The PL width remains little changed in monolayer MoSe_2 while it increases rapidly with strain in the bilayer case. We have made detailed discussions on the observed strain-modulated results and compared the difference between monolayer and bilayer cases. The hybridization between 4d orbits of Mo and 4p orbits of Se, which is controlled by the Se–Mo–Se bond angle under strain, can be employed to consistently explain the observations. The study may shed light into exciton physics in few-layer MoSe_2 and provides a basis for their applications. 相似文献