Optical and magneto-optical properties of the endohedral La@C82 crystal

The magneto-optical properties of solids are theoretically described by the circular dichroism (CD) and birefringence coefficient (θ). Using the Su-Schrieffer-Heeger (SSH) model in conjunction with the local field method, the optical dielectric tensor, CD and θ of the simple cubic phase of the La@C₈₂ and C₈₂ crystals are calculated. The results obtained from the La@C₈₂ and C₈₂ crystals are compared with those of the C₇₀ and C₆₀ crystals. It is shown that La@C₈₂ has a richer optical spectrum than C₈₂, C₇₀ and C₆₀. In the La@C₈₂ crystal, absorption bands are shown by spectrum in the 0.58 to 7.0?eV region with sharp structures in each band which indicate the localized molecular structure coupled with long-range crystalline order. Results show that the circular dichroism and birefringence coefficient of the La@C₈₂ crystal due to a single spin localized on the C₈₂ cage are very larger than those of the C₆₀, C₇₀ and C₈₂ crystals. Also, results show that the circular dichroism and birefringence coefficient of the C₈₂ crystal are similar to those of the C₆₀ and C₇₀ crystals.     

Rotational viscosity coefficients of nematic and smecticC liquid crystals: Statistical theory

Summary The rotational diffusion of a rodlike molecule in a nematic and smecticC liquid crystal is considered in the molecular-field approximation. The microscopic friction constant, which determines the molecular rotation drag, possesses an exponential temperature dependence with the activation energy determined by the isotropic part of the intermolecular interaction energy. The rotational viscous coefficients,γ ₁ andγ _⊥ are obtained by averaging of the corresponding microscopic stress tensor with the nonequilibrium distribution function. The additional activation energy, proportional to the corresponding order parameter, appears in the expressions for the rotational viscosity coefficients both in nematics andC smectics. Work presented at the second USSR-Italy Bilateral Meeting on Liquid Crystals held in Moscow, September 15–21, 1988.     

Optical limiting behavior of C60 doped ethylenepropylenediene polymethylene polymer

Optical limiting measurements on C₆₀ in toluene-ethylenepropylenediene polymethylene (EPDM) polymer blends and in EPDM polymer films at three different concentrations have been carried out. The measurements were undertaken using 532 nm wavelength, 10 ns pulses from a frequency-doubled Nd-YAG Laser. The results show that the optical limiting efficiency is concentration dependent and that the limiting efficiency for C₆₀ in toluene-EPDM polymer blends is better than in EPDM polymer film samples.     

Thermally induced effects on the diffraction pattern of a dye doped nematic film

We investigate the effects produced on the diffraction pattern of a dyed nematic thin film under the action of an optical field and a low frequency AC electric field. For a homeotropically aligned mixture of the nematic E7 doped with a dichroic dye, a sequence of dynamical regimes of the far field diffraction pattern is observed. For specific values of the beam's power, frequency and amplitude of the AC field, a uniform steady rotational motion (SR) of the pattern sets in with a measured angular velocity ν_exp =2.58 Hz. To account for this and other observed features of the diffraction pattern an analytical model is proposed. This allows us to describe quantitatively the reorientation of the film, to calculate some specific structural features of the diffraction pattern, as well as its angular velocity. We find that the predicted angular velocity ν_theor=5.7 Hz, is in quite good agreement with the measured value.     

Dielectric and optical properties of C60 material studied by ellipsometry and quantitative IR and UV/VIS spectroscopy

Optical properties in the spectral range from 0.06 to 5.5 eV of fullerite films on different substrates, C₆₀ powder, and dissolved fullerene material are investigated by spectroscopic ellipsometry and optical transmission and reflection measurements. Depolarization effects are taken into account during determination of the dielectric function of fullerite films by ellipsometry. The optical gap for C₆₀ films is found to be 1.63 eV. Three optical absorption bands are observed at 2.69, 3.53, and 4.49 eV.The dielectric function in the infrared shows the four characteristic infrared vibrational modes. The interference pattern seen in UV/VIS reflection measurements are used for high-precision thickness determination of the films. The Clausius-Mossotti formula is successfully applied to reproduce the experimental optical data measured in C₆₀/dichlormethane solutions. Deviations between theory and experiments provide interesting information about the intermolecular interaction of the C₆₀ molecules. A tentative interpretation of the measured absorption bands is presented.     

The stability, frontier orbitals, bond character, and static linear polarizability of the fluorinated fullerene H20@C80F60

This paper uses the density functional theory under generalised gradient approximation to analyse the stability,frontier orbitals,bond character,and static linear polarizability of H20@C80F60,which has not been isolated,as well as those of the synthesised H 20 @C 80 H 60.The H20@C80F60 should be considerably stable by analysing its energy and aromaticity.The inside H and outside X will play different role in the chemical reaction involving H 20 @C 80 X 60(X=H and F).The covalence of C-H bond is in the order that the inside C-H bond of H20@C80F60 > the inside C-H bond of H 20 @C 80 H 60 > the outside C-H bond of H 20 @C 80 H 60,whereas the C-F bond of H20@C80F60 have both the covalent and ionic characters.The static linear polarizabilities of C 80 and H 20 @C 80 X 60(X=H and F) are all isotropic.     

Nonisothermal Crystallization Behavior of Polypropylene-C60 Nanocomposites

The nonisothermal crystallization behavior of polypropylene (PP) and PP-fullerene (C₆₀) nanocomposites was studied by differential scanning calorimetry (DSC). The kinetic models based on the Jeziorny, Ozawa, and Mo methods were used to analyze the nonisothermal crystallization process. The onset crystallization temperature (T_c), half-time for the crystallization (t_1/2), kinetic parameter (F(T)) by the Mo method and activation energy (ΔE) estimated by the Kissinger method showed that C₆₀ accelerates the crystallization of PP, implying a nucleating role of C₆₀. Furthermore, due to the reduced viscosity of PP by adding 5% C₆₀, the parameters of crystallization kinetics for the PP-5%C₆₀ nanocomposites changed remarkably relative to that of neat PP and when lower contents of C₆₀ were added to PP.     

Experimental observation of negative group velocity in C60 PMMA

The authors experimentally observed the superluminal propagation at negative group velocity in C₆₀ polymethyl methacrylate (PMMA) firstly. The largest time advancement of 7.61 ms was obtained at 1 mg/cm³ of sample concentration, the corresponding group velocity was −0.657 m/s. Fast light in C₆₀ PMMA offers several advantages over liquids or vapors for a variety of possible applications: (i) easy for experimental measurement and practical applications (ii) easy for manufacture, (iii) sample concentration is another convenient parameter to vary the signal delay.     

Spectroscopic Study of C2 in Carbon Arc Discharge

The influence of self-absorption on intensity distribution in the rotational structure of the emission d ³II_gII → a ³II_u (0–0) band of C₂ radical was studied. The self-absorption effect was used for the determination of C₂ concentration in a DC carbon arc. The proposed method is general and may be used to other molecular bands of a similar rotational structure.     

Ab initio calculations of supramolecular complexes of fullerene C60 with CdTe and CdS

This paper presents the results of ab initio quantum-chemical calculations of supramolecular complexes C₆₀CdHal, [C₆₀]₄CdHal, and [C₆₀]₆CdHal (Hal = S, Te), which simulate the defects forming in fullerite during the absorption or adsorption of cadmium telluride (sulfide). Calculations of the electronic structure of complexes with inclusion of their relaxation to the equilibrium state have been performed in terms of the density functional theory with the B3LYP hybrid functional. The obtained enthalpies of formation of complexes show that their formation leads to the energy gain of the order of 0.5–1.5 eV depending on the complex type. It has been shown that the formation of tetrahedral complexes [C₆₀]₄CdTe with the intercalated CdTe molecule is possible only with a considerable distortion of the tetrahedral void. The energy spectrum of low-lying excited electron states for the linear and octahedral complexes has been calculated. It has been found that a decrease in symmetry with the formation of complexes leads to the appearance of excited states of allowed singlet transitions in the electron spectrum, which are forbidden in optical spectra of initial components.     

Comparative study of optical parameters of fullerene C60 film at different temperatures

Fullerene C₆₀ thin films on glass substrate (around 2000 ? thickness) were prepared by thermal evaporation technique. The structural, surface morphology and optical properties of the films were studied. The optical properties of fullerene C₆₀ were investigated in the spectral range 200 nm to 900 nm using a UV-Vis spectrophotometer at room temperature as well as at liquid nitrogen temperature (77 K). The optical band gap at room temperature is found to be 2.30 eV, which gradually decreases with lowering the temperature and reaches to 2.27 at 77 K. The thickness and refractive index of fullerene C₆₀ film were calculated by ellipsometry. From the X-ray analysis, we have calculated the grain size, dislocation density, number of crystallite per unit area, and strain of the film at room temperature. The surface morphology of film was analyzed by scanning electron microscope (SEM). The present result show that the fullerene C₆₀ film becomes more conducting at low temperature.     

A photonic crystal fiber sensor based on differential optical absorption spectroscopy for mixed gases detection

A photonic crystal fiber sensor based on differential optical absorption spectroscopy for mixed gas detection is presented. In such sensor, hollow core photonic crystal fiber is utilized as gas cell and the feasibility for gas detection is verified by experiment. The components concentration of mixed gas NH₃ and C₂H₂ are measured and the detection sensitivity is 143 ppmv.     

Rheological Behavior of Poly(vinylpyrrolidone)/Fullerene C60 Complexes in Aqueous Medium

Aqueous solutions of complexes formed between poly(vinylpyrrolidone) (PVP), as a matrix polymer, and fullerene C₆₀ were investigated. The effect of the external hydrodynamic field on the supermolecular assemblies formed by the complexes was analyzed. Despite the low content in the complexes (1.5 mass%), fullerene significantly modified the viscosity of aqueous PVP. Thus, the dynamic viscosity of the PVP/C₆₀ complexes grew faster than that of the pure PVP upon increasing the PVP/C₆₀ concentration. The difference in viscosities is especially pronounced for semidilute solutions. As a possible explanation, it is assumed that fullerenes act as crosslinks, in addition to the physical entanglements of the PVP macromolecules, which appear in the vicinity of the crossover concentration. Shear flow corresponding to the high shear rates destroyed fullerene‐induced intermolecular crosslinks in PVP/C₆₀ solutions.     

Structural modification of C60 films induced by 300-keV Xe-ion irradiation

The structural modification of C 60 films induced by 300-keV Xe-ion irradiation was investigated.The irradiated C 60 films were analysed using Fourier transform infrared spectroscopy,the Raman scattering technique,ultraviolet/visible spectrophotometry and atomic force microscopy.The analysis results indicate that the Xe-ion irradiation induces polymerization and damage of the C 60 molecule and significantly modifies the surface morphology and the optical property of the C 60 films.The damage cross-section for the C 60 molecule was also evaluated.     

液晶的转动粘质系数的测试原理与方法

液晶的转动粘质度是液晶用于显示和通讯的重要物理参量.本文设计开发了基于微机的液晶参数测试光学系统，在该系统上研究了液晶的转动粘质系数的测试原理与方法：通过测试液晶盒在偏置电压下相位驰预时间，推导出转动粘质系数的值.测试Merck公司的 E7液晶的转动粘质系数随温度变化的曲线，进行了理论拟合，测试结果与理论符合得很好.通过分析另一系统对液晶介质常数随温度变化的曲线的测试结果，验证了该测试原理与方法的正确性.该测试方法具有简单、自动化的特点.     

Yb2.75C60价带光电子能谱

用角积分紫外光电子能谱技术测量了Yb_2.75C₆₀薄膜的价带电子态密度分布.相纯Yb_2.75C₆₀样品通过C1s芯态x射线电子谱峰的位移表征.结果表明Yb_2.75C₆₀是半导体，在费米能级处几乎没有电子态分布.Yb 6s电子态和C₆₀LUMO能带的杂化效应不可忽略，有部分Yb 6s电子分布在Yb-C₆₀杂化能带上. 关键词： 2.75C₆₀')" href="#">Yb_2.75C₆₀ 电子能谱 电子态密度     

Free energy and orientational phase transition in solid C60

On the basis of a microscopic model, the free energy of the orientationally disordered fcc crystalline phase of C₆₀-fullerite is derived up to fourth order in the rotational density fluctuations. The order parameter variables are symmetry adapted rotator functions which belong to thel=6 andl=10 manifolds. They are basis functions ofT _2g representations of the cubic group. The phase transition to thePa3 structure is discussed, and is found to be of first order. The orientationally ordered phase is described in terms of condensed rotator functions.     

C60中非线性激发的动力学研究

用电子－晶格耦合的紧束缚模型和求解实时牛顿动力学方程的方法研究了Ｃ₆₀受光激发后的动力学过程，得到了受光激发后Ｃ₆₀分子的能量，键结构和电子状态的动态演化，结果表明光激发Ｃ₆₀分子演化成环状双极化子激子。该计算结果与中性富勒烯材料的荧光实验所得出的结论一致。 关键词：     

Electrical and electroluminescence properties of ITO/PEDOT:PSS/TPD:Alq3:C60/Al organic light emitting diodes

Organic light emitting diodes (OLEDs) of ITO/PEDOT:PSS/TPD:Alq₃:C₆₀/Al with different C₆₀ concentrations (0-6.0 wt.%) have been fabricated. The physical parameters including electrical and optical properties of the samples have been measured by Luminance-current-voltage (L-I-V) characteristics and optical absorbance. The current-voltage characteristics indicate that field-emission tunneling injection dominates in the diodes at high applied voltages. It is found that with increasing the concentration of C₆₀, the injection barrier for holes slightly reduces and the hole’s mobility increases over two orders of magnitude. Also, electroluminescence enhances with the presence of C₆₀ in the blend; optimum current efficiency occurs at 3 wt% C₆₀. The method provides a simple way of increasing the efficiency of OLEDs.     

Rotational viscosity in ferrofluids

We have measured the rotational viscosity _r of a concentrated ferrofluid by observing the increase of critical angular velocity in a Taylor cell with two different magnetic field configurations. The results are compared to theoretical calculations for diluted ferrofluids at different relative orientations of the field and the vorticity of the fluid. The observed deviations are attributed to breakdown of the theory for concentrated ferrofluids.