Au电极作用下C60、2C60与4C60富勒烯分子的电子传输特性

采用扩展的Hückel方法与格林函数方法,研究了Au电极作用下,C60富勒烯、2C60和4C60聚合体分子的电子结构与导电性,并对它们的电子结构与电子输运特性进行了对比.研究结果表明,C60、2C60或4C60富勒烯分子与Au电极 "接触"后,其HOMO、LUMO间的能隙减小;C60、2C60或4C60分子与Au电极之间的结合既有共价键的成分,又有离子键的成分,其中,C60、4C60分子与Au电极结合的离子键特征更为明显;三种富勒烯分子的电子输运性能依次具有C60>2C60>4C60分子的顺序.     

Intramolecular Negative-Effect in the Alkali-Metal-Doped C60; A2C60 and A4C60

It is investigated theoretically why alkali-metal-doped C₆₀, A_xC₆₀, is a nonmagnetic semiconductor for x=2 and 4. We find that this is the consequence of the intramolecular negative- U effect due to the strong electron-phonon interaction and the weak Hund coupling between conduction electrons.     

Electronic structure and electrical transport characteristics of C60, 2C60 and 4C60 fullerene molecules

The extended H?ckel method and the Green s function method were used to calculate the electronic structure and electrical transport of Au electrode-C₆₀, 2C₆₀ or 4C₆₀ fullerene-Au electrode systems. Furthermore, their electronic structure and electrical transport characteristics were compared and analyzed. The results show that (i) owing to the contact with the Au electrodes, the C₆₀, 2C₆₀ and 4C₆₀ molecules change in their electronic structures significantly, and their energy gaps between LUMO and HOMO are narrow; (ii) the bonding between C₆₀, 2C₆₀ or 4C₆₀ fullerene and Au electrodes is partially covalent and partially electrovalent; and (iii) the conductance of the three fullerenes conforms to the order of C₆₀>2C₆₀>4C₆₀.     

The viscosity of Na2CO3 and K2CO3 aqueous solutions in the range 20–60°C

Results of new relative measurements of the density and viscosity of aqueous solutions of Na₂CO₃ and K₂CO₃ at atmospheric pressure are presented. The temperature ranged from 20 to 60°C, and the composition ranged from pure water to near saturation. All the data have been correlated with the aid of double polynomials. Owing to some evidence of chemical attack of the borosilicate viscometers, the accuracy of the viscosity measurements is estimated to be ±1%, whereas that of density is estimated to be ±0.01%.     

Production of single-crystal K3C60

A simplified technique for synthesizing high-quality millimeter-sized single-crystals of K₃C₆₀ is reported. The preparation method consists of a two-step process where pure C₆₀ crystals are first grown and later doped with potassium vapor. The undoped crystals are grown using an open-tube vapor transport with a flowing helium gas carrier. Doping occurs in a highvacuum environment inside a specialized quartz tube which allows phase purity to be monitored via magnetization measurements of the superconducting state. Utilizing the aforementioned procedure, one can attain samples with magnetically determined superconducting transition widths (10–90% diamagnetic shielding) of less than 1 K.     

K~+和Na~+在C_3S-纳米SiO_2浆体上的存在形式

以拌合液为KOH和NaOH混合溶液的C_3S-纳米SiO_2浆体为对象,研究了液固比对浆体在去离子水中释放K~+和Na~+的影响以及浆体对K~+和Na~+的滞留能力;并采用29Si MAS NMR分析讨论了K~+和Na~+在C_3S-纳米SiO_2浆体上的存在形式。结果表明:随着液固比的增大,浆体释放的K~+和Na~+的百分数逐渐增大;经去离子水充分洗涤后仍有一部分K~+和Na~+存在于浆体中,且浆体对K~+和Na~+的滞留能力随着纳米SiO_2掺量的增加以及拌合液碱浓度的增大而增强。29Si MAS NMR分析证实了K~+和Na~+能够进入C-S-H凝胶层间形成不可逆的化学结合。K~+和Na~+通过取代C-S-H凝胶层间≡SiOCa+中的Ca2+,缩短了C-S-H凝胶中[SiO4]4-四面体链长,从而使凝胶中Q1和Q2峰向左移动。     

Investigation of Absolute Photonic Band Gaps in Two-dimensional Dielectric Structures

Abstract

We examine the photonic band structure of two-dimensional (2D) arrays of dielectric holes using the coherent microwave transient spectroscopy (COMITS) technique. Such 2D hole arrays are constructed by embedding low-index rods (air) in a dielectric background of higher-index Stycast material (n = 3·60). The dispersion relation for electromagnetic wave propagation in these photonic crystals is directly determined using the phase sensitivity of COMITS. We find that both the square and triangular lattice structures exhibit photonic band gaps that are common to both polarizations for all wave-vectors along major symmetry axes. In addition, the connectivity of the high-index dielectric and the opening of a large gap for propagation with E field perpendicular to the hole cylinders are found to be important criteria for generating a large absolute photonic band gap.     

Mass Spectrometry Study of C60 and C60-NiF2 Fluorination with Molecular Fluorine

Abstract

Fluorination of [60]fullerene and [60]fullerene-NiF₂(s) has been studied in situ by Knudsen cell mass spectrometry with admission of molecular fluorine. The fluorination processes were controlled in the temperature range 500 ? 800 K at molecular fluorine pressure 10^?4 ? 10^?5 atm. Temperature, time of fluorination and fluorine pressure were varied during the investigation. It was found that variation of these parameters did not lead to the selective fluorination. It was shown that NiF₂(s) significantly influences the composition of the product mixture: a large amount of nickel difluoride in the system suppresses the fluorination reaction while the presence of a small amount promotes the selective fluorination. C₆₀Fi₁₈ (50% in the gas phase) was produced in our experiments under the following conditions: 20 h, 720 K, P(F₂) = 2 10^?4 atm in the prefluorinated (inner surface covered with NiF₂(s) layer) Ni-reactor. An important point of the study was verification of the thermodynamic equilibrium in the system. It was concluded that the equilibrium is not established in the system under study, and the fluorination is governed by kinetic factors.     

Mass Spectrometry Study of C60 and C60-NiF2 Fluorination with Molecular Fluorine

Fluorination of [60]fullerene and [60]fullerene-NiF₂(s) has been studied in situ by Knudsen cell mass spectrometry with admission of molecular fluorine. The fluorination processes were controlled in the temperature range 500 - 800 K at molecular fluorine pressure 10^-4 - 10^-5 atm. Temperature, time of fluorination and fluorine pressure were varied during the investigation. It was found that variation of these parameters did not lead to the selective fluorination. It was shown that NiF₂(s) significantly influences the composition of the product mixture: a large amount of nickel difluoride in the system suppresses the fluorination reaction while the presence of a small amount promotes the selective fluorination. C₆₀Fi₁₈ (50% in the gas phase) was produced in our experiments under the following conditions: 20 h, 720 K, P(F₂) = 2 10^-4 atm in the prefluorinated (inner surface covered with NiF₂(s) layer) Ni-reactor. An important point of the study was verification of the thermodynamic equilibrium in the system. It was concluded that the equilibrium is not established in the system under study, and the fluorination is governed by kinetic factors.     

Band gap and density of states of the hydrated C60 fullerene system at finite temperature

We examine the electronic properties of the hydrated C60 fullerene under ambient conditions using a sequential Monte Carlo/density functional theory scheme. In this procedure, the average electronic properties of the first hydration shell of C60 equilibrate for ca. 40 uncorrelated configurations of the fullerene aqueous solution. We obtain a systematic red-shift of 0.8 eV in the band gap of the hydrated system, which is mainly attributed to the thermal fluctuations of the aqueous environment.     

4He Adsorption and Superfluid Transition on C60

We present adsorption isotherm data of⁴He on C₆₀ for 1.50 K<T<1.68 K determined by measurements of the frequency of quartz crystal microbalances (QCM’s) coated with C₆₀ films. We find a Kosterlitz-Thouless transition with a jump in the areal superfluid density close to predictions. By comparing the adsorbed⁴He on two QCM’s we derive an upper limit for the amount of⁴He intercalated into C₆₀ at low temperature of 0.05⁴He atoms per C₆₀ molecule. The low coverage portion of the adsorption data shows an apparent excess adsorption of⁴He onto the C₆₀.     

Ferrocene Derivatives in Diels-Alder [4+2] Cycloaddition Reactions to Fullerenes C60 and C70

The synthesis and characterization of adducts of C₆₀ and C₇₀ with diene 5 is described. When 5 was reacted with fullerene C₆₀, a mixture of mono 7 and bisadduct 8 was found, while with C₇₀ a novel monoadduct 9 was formed.     

Normal-incidence reflectance of crystalline K(6)C(60), Rb(6)C(60), and Cs(6)C(60)

The structure factors and normal-incidence reflectances of the alkali-metal-doped fulleride crystals M(6)C(60) (where M = K, Rb, or Cs) were calculated, and the peak reflectances are in the 2-20% range for incident wavelengths of 9-17 ?, which indicates that C(60) may be a promising transmissive (spacer) material for normal-incidence mirrors that have relatively high normal-incidence reflectance in the x-ray region.     

K3C60晶体中钾离子的平衡位置

分析八面体空隙中心碱金属的相互作用势能, 研究碱金属沿[111]、[110]和[100]三个不同方向移动时, 势能的变化情况, 结果表明, 对于K3C60晶体, K+离子在三个不同方向上都存在非中心平衡位置, 而且在三个不同方向上, 非中心平衡位置相对中心的偏移量不同, 在[111]轴上为0.98, 在[110]轴方向上为0.78, 在[100]方向上为0.56, 在[111]轴方向的非中心的势能是最小值, 为-508.59meV.通过对计算结果的分析, 认为非中心平衡位置的出现应归因于短程相互作用, 其中与C60的相互作用是最主要的, 其势能最低点对应的位置不在中心;三个不同方向的非中心平衡位置偏离中心距离不同, 是因为与之对应晶面上的C60面密度不同.     

Hydrothermal Crystallization in the Na2CO3–ZrO2–SiO2–H2O System at 500°C and 0.1 GPa: Na2ZrSi4O11, Na2ZrSi2O7, and Na4Zr2Si3O12 Phase Relations

The phases crystallizing in the Na₂CO₃–ZrO₂(cr)–SiO₂(silica gel)–H₂O system at 500°C, 0.1 GPa, ZrO₂ : SiO₂ = 1 : 2 to 1 : 6, and ZrO₂ : Na₂CO₃ = 1 : 1 to 1 : 3 are ZrSiO₄ (zircon), Na₂ZrSi₄O₁₁ (vlasovite), Na₂ZrSi₂O₇ (parakeldyshite), and Na₄Zr₂Si₃O₁₂ (NASICON). The structures of the three Na–Zr silicates are built up of the same polyhedral structural units—M octahedra and T tetrahedra—connected so as to form a three-dimensional MT framework. The crystallization behavior of these phases can be understood in terms of the matrix assembly of crystal structures from suprapolyhedral structural units in the form of cyclic clusters. The structures of Na₂ZrSi₄O₁₁ and Na₂ZrSi₂O₇ contain invariant six-polyhedron precursors of composition Na₂ M ₂ T ₄, each made up of two ZrO₆ octahedra and four SiO₄ tetrahedra. The formation of Na₄Zr₂Si₃O₁₂ involves four-polyhedron Na-containing clusters of composition Na₂ M ₂ T ₂.