CoSb_3/C_(60)复合材料的固相反应合成和热电性能

用固相反应法和脉冲电流直接通电烧结法制备了CoSb3 C6 0 复合材料 ,其组分通过粉末x射线衍射法确定 ,SEM分析表明C6 0 颗粒是均匀地分布在CoSb3基体中 .在 30 0— 80 0K范围内测量了材料的电导率、赛贝克系数和热导率 ,研究了纳米颗粒的尺寸和分布状态对复合材料热电性能的影响 .外加的C6 0 纳米颗粒在高温时降低了复合材料的晶格热导率 ,而对电传输性能影响较小 ,从而有效地提高了复合材料的热电性能 .与CoSb3相比 ,CoSb3 6 5 4 ? 0复合材料的ZT值提高了 4 0 % .     

Thermodynamic and transport properties of spiro-(1,1')-bipyrrolidinium tetrafluoroborate and acetonitrile mixtures:A molecular dynamics study

Organic salts such as spiro-(1,1')-bipyrrolidinium tetrafluoroborate([SBP][BF4]) dissolved in liquid acetonitrile(ACN) are a new kind of organic salt solution,which is expected to be used as an electrolyte in electrical double layer capacitors(EDLCs).To explore the physicochemical properties of the solution,an all-atom force field is established on the basis of AMBER parameter values and quantum mechanical calculations.Molecular dynamics(MD) simulations are carried out to explore the liquid structure and physicochemical properties of [SBP][BF4] electrolyte at room temperature.The computed thermodynamic and transport properties match the available experimental results very well.The microscopic structures of [SBP][BF4] salt solution are also discussed in detail.The method used in this work provides an efficient way of predicting the properties of organic salt solvent as an electrolyte in EDLCs.     

内陷在C_(60)中的氢原子的性质

在短程球形势阱的模型下 ,运用线性变分法并采用B 样条作为展开基函数计算了内陷于C60 几何中心的氢原子能谱和波函数 ,并计算了势阱深度对能谱的影响 ,详细讨论了内陷氢原子表现出的一系列特殊性质 ,从而对低维半导体材料性能的研究提供了有效的数据 ;同时这一工作也表明 ,用线性变分法结合B 样条函数在处理这类问题时是非常有效的。     

C60和C60／C70的激光脱附飞行时间质谱分析

采用激光脱附并直接测量离子的方法对实验室提取的C_(60)/C_(70)以及进一步分离得到的纯C_(60)进行了飞行时间质谱分析,并讨论了质谱分析过程中实验条件对结果的影响.     

Thermodynamic properties of noble metal clusters:molecular dynamics simulation

The thermodynamics properties of noble metal clusters Au_N, Ag_N, Cu_N, and Pt_N (N = 80, 106, 140, 180, 216, 256, 312, 360, 408, 500, 628, 736, and 864) are simulated by micro-canonical molecular dynamics simulation technique. The potential energy and heat capacities change with temperature are obtained. The results reveal that the phase transition temperature of big noble metal clusters (N ⩾ 312 for Au, 180 for Ag and Cu, and 360 for Pt) increases linearly with the atom number slowly and approaches gently to bulk crystals. This phenomenon indicates that clusters are intermediate between single atoms and molecules and bulk crystals. But for the small noble clusters, the phase transition temperature changes irregularly with the atom number due to surface effect. All noble metal clusters have negative heat capacity around the solid-liquid phase transition temperature, and hysteresis in the melting/freezing circle is derived in noble metal clusters.     

Thermodynamic properties of noble metal clusters: molecular dynamics simulation

The thermodynamics properties of noble metal clusters Au_N, Ag_N, Cu_N, and Pt_N (N = 80, 106, 140, 180, 216, 256, 312, 360, 408, 500, 628, 736, and 864) are simulated by micro-canonical molecular dynamics simulation technique. The potential energy and heat capacities change with temperature are obtained. The results reveal that the phase transition temperature of big noble metal clusters (N ? 312 for Au, 180 for Ag and Cu, and 360 for Pt) increases linearly with the atom number slowly and approaches gently to bulk crystals. This phenomenon indicates that clusters are intermediate between single atoms and molecules and bulk crystals. But for the small noble clusters, the phase transition temperature changes irregularly with the atom number due to surface effect. All noble metal clusters have negative heat capacity around the solid-liquid phase transition temperature, and hysteresis in the melting/freezing circle is derived in noble metal clusters.     

Aggregation of fullerene (C_(60)) nanoparticle:A molecular-dynamic study

We present the results of molecular dynamics simulations of net positively charged fullerene nanoparticles in salt- free and salt-added solution. The aggregation of fullerene （C60）-like nanoparticle and counterion are studied in detail as a function of temperatures and a finite salt concentration. Our simulations show that the strong conformation changes as temperature changes. The net positively-charged nanoparticles do not repel each other but are condensed under proper temperatures. If salts are added, the aggregated nanoparticles will be disaggregated due to the Debye screening effect.     

A study of the structural and thermodynamic properties of water by the molecular dynamics method

The thermodynamic and structural properties of four rigid water models were studied by the molecular dynamics method over a wide temperature range. Two three-center (SPC/E and TIP3P) and two five-center (ST4 and TIP5P) models were considered. The results discussed include the boiling and condensation temperatures, VT phase transition diagrams, three-dimensional spatial distributions of atoms, the temperature dependences of the total energy, density, heat capacity, the number of H-bonds per molecule, the distribution of H-bonds over the ∠HOO angle, the self-diffusion coefficient, and the radial distribution functions. The boiling points of all the models did not correspond to 100°C and were noticeably different from each other. The condensation points were also different. The data on the structural parameters led us to conclude that the TIP5P model reproduced the local structure of water most correctly. However, if the reproduction of the local structure is not a necessary condition, less resource consuming three-center models can be used.     

Eu@Sc_(20)C_(60):Magnetic Volleyballene

Recently,a stable hollow Sc_(20)C_(60) cage with T_h point group symmetry has been proposed,due to its volleyballlike shape called volleyballene.Here the structural and electronic properties for Sc_(20)C_(60) cage with a europium atom are further studied based on density functional theory.The results give two stable low-lying Eu@Sc_(20)C_(60)isomers,called cage-a and cage-b,respectively,which still retain the cage-like shape of Sc_(20)C_(60) volleyballene.After a Eu atom is encaged into the Sc_(20)C_(60) volleyballene,the HOMO-LUMO gaps decrease from 1.47 eV of the Sc_(20)C_(60) cage to 0.46 eV of cage-a and 0.21 eV of cage-b.Due to the half-filled 4 f-electron orbital states of the Eu atom,the two low-lying Eu@Sc_(20)C_(60) isomers have net magnetic moments of 7μ_B.This study further provides the possible applications for the Sc_(20)C_(60) volleyballene,and enriches the species of magnetic cage-like molecules,which provides more information for magnetic storage and magnetic control.     

聚苯乙烯/纳米铝复合材料的流变特性及纺丝研究

为有效制得Z箍缩氘代聚苯乙烯/纳米铝(DPS/AlNPs)导电丝阵材料,采用PS中掺入AlNPs制备PS/AlNPs复合材料纤维进行模拟研究。研究了温度及剪切速率等因素对PS/AlNPs复合材料流变性能的影响、复合材料熔体的结构变化及流动状态与可纺性能的关系,以及PS/AlNPs纤维的形貌、热稳定性能和力学性能。结果表明：PS/AlNPs熔体属于典型剪切变稀型非牛顿流体,熔体的表观粘度与温度呈现负相关,240~260 ℃时复合材料的非牛顿指数介于0.462~0.546,结构黏度系数介于1.8~2.1,黏流活化能介于77.2~104.6 kJ·mol^-1,具有良好的可纺性。PS/AlNPs纤维表面光滑,对AlNPs粒子包覆良好且对其抗氧化非常有利,其中当AlNPs质量分数为1%时纤维的断裂伸长率突出、掺量为5%时其断裂强度较高。     

Lennard-Jones binary fluids: A comparative study between the molecular dynamics and Monte Carlo descriptions of their structural properties

Molecular dynamics and Monte Carlo techniques are employed for the study of binary Lennard-Jones fluids. Systematic comparisons between the predictions of both techniques are discussed, with particular emphasis on the dependency of the structural properties with respect to temperature and Lennard-Jones potential parameters.     

Investigating mechanical properties of polymethylmethacrylate/silver nanoparticle composites by molecular dynamics simulation

The molecular dynamics simulation (MD) was carried out to investigate the mechanical properties of pristine polymethylmethacrylate (PMMA) and the composites of PMMA mixed with the silver nanoparticles (PMMA/AgNPs) at two AgNP weight fractions at 0.60 and 1.77 wt%. From the stress–strain profiles by the tensile process, it can be seen that the improvement on Young’s modulus is insignificant at these lower AgNP fractions. The tensile strength of pristine PMMA can be slightly improved by the embedded AgNPs at 1.77 wt%, because the local density and strength of PMMA in the vicinity of AgNP surface within about 8.2 Å are improved. For the temperature effect on the mechanical properties of pristine PMMA and PMMA/AgNP composite, the Young’s moduli and strength of pristine PMMA and PMMA/AgNP composite significantly decrease at temperatures of 450 and 550 K, which are close to the predicted melting temperature of pristine PMMA about 460 K. At these temperatures, the PMMA materials become more ductile and the AgNPs within the PMMA matrix display higher mobility than those at 300 K. When the tensile strain increases, the AgNPs tend to get closer and the fracture appears at the PMMA part, leading to the close values of Young’s modulus and ultimate strength for pristine PMMA and PMMA/AgNP composite at 450 and 550 K.

Open image in new window

Graphical abstract Stress–strain curves of pristine PMMA, polymethylmethacrylate (PMMA)/silver nanoparticles (AgNP) (0.60%), and PMMA/AgNP (1.77%). Inset images: local shear strain of pristine PMMA (red) and PMMA/AgNP (1.77%) (green).

     

C60分子石墨化的研究

测量了不同激光功率照射下，在具有不同导热率的三种衬底上蒸镀膜所吸附的Ｃ６０分子的振动光谱。发现在激光功率达到８００ｍＷ时，Ｃ６０分子发生“石墨子”。对石墨化的起因做了定性分析。     

Mechanical and tribological properties of Ni/Al multilayers—A molecular dynamics study

Mechanical and tribological properties of multilayers with nanometer thickness are strongly affected by interfaces formed due to mismatch of lattice parameters. In this study, molecular dynamics (MD) simulations of nanoindentation and following nanoscratching processes are performed to investigate the mechanical and tribological properties of Ni/Al multilayers with semi-coherent interface. The results show that the indentation hardness of Ni/Al multilayers is larger than pure Ni thin film, and the significant strength of Ni/Al multilayers is caused by the semi-coherent interface which acts as a barrier to glide of dislocations during nanoindentation process. The confinement of plastic deformation by the interface during nanoscratching on Ni/Al multilayers leads to smaller friction coefficient than pure Ni thin film. Dislocation evolution, interaction between gliding dislocations and interface, variations of indentation hardness and friction coefficient are studied.     

Revisiting Laser-Intensity-Dependent Ionization and Fragmentation of C_(60)

We revisit the laser-intensity-dependent ionization and fragmentation yields of C₆₀ molecules irradiated by 25-fs,798-nm laser pulses based on the approach in which photoions are measured via a velocity map imaging spectrometer working in a time-sliced mode.This approach dramatically improves the signal-to-background ratio compared to those using a simple(traditional) time-of-flight mode(spectrometer),and thus allows us to measure the laser-intensity dependences down to a previously u...     

Cu_2O/C_(60)梯度薄膜的制备

功能梯度材料应用前景广阔 ,特别在 ICF研究中 ,梯度靶是一种重要的基础 -基准靶。以Cu2 O和 C60 为原料 ,用真空蒸镀法在石英基底上制备了 Cu2 O/C60 梯度薄膜 ,并用 XPS,AFM,紫外光谱仪对其成份分布、表面形貌、紫外吸收谱进行了测试。测量结果表明 ,薄膜的组成沿厚度方向呈连续梯度变化 ,符合梯度功能材料的变化规律     

A comprehensive molecular dynamics study of a single polystyrene chain in a good solvent

In this study, molecular characteristics of polystyrene (PS) was calculated measuring its dilute-solution properties in toluene at 288.15 K via molecular dynamics (MD) simulations. The solution models consisted of PS chains with different number of repeating units all of which were in a dilute regime. In order to investigate the compatibility between the polymer and the solvent molecules, interaction energy and Flory-Huggins (FH) interaction parameter were estimated. The simulation results indicate that increasing the chain repeating units enhanced the interaction between the solute and the solvent. Additionally, the chain dimensions were evaluated calculating the radius of gyration (R_g) and end-to-end distance, r0. To determine the dynamic behavior of the chains in the solutions, mean square displacement (MSD) and diffusivity coefficient were calculated. The simulation results indicated that the chain rigidity at low molecular weight and chain flexibility with increasing the molecular weight influenced chains dynamic behavior and diffusivity. Moreover, radial distribution function (RDF) illustrated the effect of steric hindrance of the chains in dilute solution on capturing the solvent molecules. In addition, solution viscosity was calculated by performing non-equilibrium molecular dynamics simulation (NEMD). The obtained results of chain characteristics and viscosity showed a good agreement with experimental results published previously. This agreement confirms the accuracy of the applied simulation method to characterize the dilute solutions and the chains characteristics.     

Energetic and structural evolution of gold nanowire under heating process: A molecular dynamics study

The energetic and structural evolution of a squared gold nanowire under heating process is investigated via molecular dynamics with many-body potential. The simulations reveal that the nanowire undergoes distinct energetic and structural developments during the following four heating processes: low temperature, melting, breaking and high temperature. The cross-section of nanowire is found to change from a square to a circle shape with rising temperature at first. A neck is then found to be initiated above the overall melting point, followed by the formation of a two- to five-atom-thick chain structure before the breaking of neck. The nanowire transforms to a spherical cluster after the final breaking.     

Elastic properties of anatase titanium dioxide nanotubes:A molecular dynamics study

The elastic properties of anatase nanotubes are investigated by molecular dynamics(MD) simulations. Young's modulus, Poisson ratio, and shear modulus are calculated by transversely isotropic structure model. The calculated elastic constants of bulk rutile, anatase, and Young's modulus of nanotube are in good agreement with experimental values, respectively, demonstrating that the Matsui and Akaogi(MA) potential function used in the simulation can accurately present the elastic properties of anatase titanium dioxide nanotubes. For single wall anatase titanium dioxide nanotube, the elastic moduli are shown to be sensitive to structural details such as the chirality and radius. For different chirality nanotubes with the same radius, the elastic constants are not proportional to the chiral angle. The elastic properties of the nanotubes with the chiral angle of 0° are worse than those of other chiral nanotubes. For nanotubes with the same chirality but different radii, the elastic constant, Young's modulus, and shear modulus decrease as the radius increases. But there exist maximal values in a radius range of 10 nm–15 nm. Such information can not only provide a deep understanding of the influence of geometrical structure on nanotubes mechanical properties, but also present important guidance to optimize the composite behavior by using nanotubes as the addition.     

金红石型氧化物晶体结构与性能的分子动力学研究

采用分子动力学的方法,利用新的势能模型,对金红石型氧化物TiO2,GeO2和SnO2完整晶体的热性能和随压力变化特性进行计算模拟;在完整晶体中,引入肖特基型点缺陷,以研究和比较两种状态下的差别,井对GeO2-SnO2固溶体的高温固溶状态进行计算模拟。