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1.
All regioisomers of fullerene adducts C20(CH2)n have been found and their stability and polarizability have been studied by the PBE/3ζ method. As in the case of the C60 and C70 adducts, mean polarizability of C20(CH2)n quadratically depends on the number of addends and demonstrates the depression, viz. negative deviation of polarizability from the linear additive scheme. Another, linear formula is proposed for calculating mean polarizability of the C20 and C60 fullerene adducts with mixed functionalization C20(CH2)nOm and C60(CH2)nOm and fixed number of addends. The obtained results will be further used to work out the algorithm for counting all possible C60Xn cycloadducts and searching a general formula for calculation of the C60XnYm polarizability with variable (n + m) number of addends.  相似文献   

2.
C60,C180,C60@C180富勒烯分子的压缩力学特性与电子结构   总被引:4,自引:0,他引:4  
采用分子动力学方法模拟了C60,C180,C60@C180富勒烯分子的压缩过程,用PM3半经验量子力学方法计算了压缩C60,C180,C60@C180分子的电子结构,讨论了C60,C180,C60@C180分子压缩力学特性的差异,以及电子结构在压缩过程中的变化.结果表明,由于分子几何构形上的差异,C60分子的承载与吸收能量能力显著高于C180和C60@C180分子,而CC60@C180分子略高于C180分子;C60分子具有最高的化学稳定性,而C60@C180分子的稳定性最低;C60和C60@C180分子的压缩变形越大,越容易失去电子,稳定性越低;C180分子在加载点处发生压缩“塌陷”时,化学活性明显增加.  相似文献   

3.
Abstract

Owing to the three-fold degeneracy of the LUMO in C60, its hexa-anion is not subjected to Jahn-Teller distortions. In contrast to the accepted presumptions, however, computations at the MNDO, AMI, PM3, SAM1, HF/STO-3G, HF/3-21G, and HF/4-31G levels show that the completely relaxed, non-icosahedral cage of C6? 60is lower in energy. The computed energy gain varies between 60 and 150 kJ/mol and thus, it is consistently significant (the most sophisticated approach, HF/4-31G, yields 93 kJ/mol). The longest C-C bond in the relaxed structures is at most computed 0.05 Å longer compared to the 5/6 bond in the icosahedral C6? 60The symmetry of C6? 60is relaxed to D2 A C2v, isomer is discussed, too.  相似文献   

4.
We investigate the electronic properties of individual C(60) nanowhiskers by exploiting conductive atomic force microscopy at room temperature in ambient atmosphere. The pristine individual C(60) nanowhiskers exhibit conducting behavior. The outer C(60) oxide covering, confirmed by Auger electron spectroscopy, shelters the conductive properties of the C(60) nanowhiskers. It is proposed that the insulating outer C(60) oxide covering might be used as the dielectric layer in potential single C(60) nanowhisker-based field-effect transistors for nanoelectronics.  相似文献   

5.
Hydrogen-free scintillators are indispensable for determining the small, resonance-dominated neutron capture cross-sections of light and neutron magic nuclei, data which are needed for advanced reactor concepts, for transmutation of radioactive wastes as well as for astrophysical scenarios of neutron capture nucleosynthesis. A critical comparison of the existing detector concepts by means of detailed GEANT simulations revealed large differences in neutron sensitivity. Based on these simulations, an optimized detector was developed and successfully tested. Compared to a commercial detector, the neutron sensitivity of this solution is more than an order of magnitude lower, thus allowing even extremely small capture/scattering ratios to be measured reliably.  相似文献   

6.
Soluble C60–N-vinylcarbazole copolymers with different C60 contents were synthesized in lithium naphthalene-initiated anionic polymerization reactions. 13C nuclear magnetic resonance (NMR) results provided strong evidence for the covalent attachment of poly(N-vinylcarbazole; PVK) units to the C60 cores. The chemical shifts located at 142.16, 143.21, 144.70, 145.61, 146.65, 147.09, 149.08 and 170.28 p.p.m. in the 13C NMR spectrum of the copolymer are assigned to the unsaturated carbon signals of the substituted C60 cage. Its ultraviolet–visible absorption spectrum tends to move to the longer wavelength compared with those of the N-vinylcarbazole (NVC) monomer and PVK, and the peak range also extended from about 350 to 640 nm due to charge-transfer interaction between C60 and N-ethylcarbazole units. X-ray diffraction evidence suggests that the structure of the resultant copolymer might be a layered structure. Like the C60 chemically modified PVK, this material also exhibits good photoconductivity and temperature sensitivity. An unusual temperature dependence of the ESR spectrum is observed. In addition, it is also found that both [60] fullerene polyanion salts [(Cn-60) M+n, M=Li, Na, K] and fullerene itself are unable to initiate the polymerization of such monomers as N-vinylcarbazole, styrene and acrylonitrile, etc. © 1998 Kluwer Academic Publishers  相似文献   

7.
We have studied the I-V characteristics, the dc resistance at the origin R(T), and the critical current I c (T) of arrays consisting of n × n (n = 10, 20, 30, and 40) In squares separated by Au/In regions. The superconducting squares have side d s (In) from 7.5 to 15 m and d N (Au/In) from 2.5 to 11 m. These devices show two transition temperatures in their R(T) curve; one at T cG near T c (In) and another one at T c * above T c (Au/In). The I-V curves for each temperature region resemble recent published results on NbN granular films. These arrays follow a formalism proposed by Wolf, Gubser, and Imry to describe the transition to a resistanceless state at T c *. The measured values of I c (T) are larger than expected from n noninteracting Bardeen-Johnson junctions in parallel, although the exponential behavior in temperature is followed. They are compatible with the idea of bands in the quasiparticle spectrum in the Au/In regions. Deviations in I c (T) from an exponential behavior in T near T c * have been analyzed by applying to SNS arrays ideas developed for phase transitions in SIS arrays. Evidence that at T c * we may be observing a phase transition at T cJ due to the Josephson coupling between In squares exists but it needs the development of theoretical work to be put on more solid grounds.Supported by the Swiss National Science Foundation.  相似文献   

8.
Abstract

A new molecular complex of [60]fullerene with composition 2(C60)·2(TMTSF)·(C6H6) was synthesized. The structure and composition of the complex were found by an x-ray study. Crystal data: 2(C60)2(C10H12Se4)(C6H6), M = 2415.4, monoclinic, a = 19.388(4), b = 13.410(2), c = 32.467(6) A, β = 92.71(2)°, V = 8432(3) [Adot]3, space group P21/n, Z = 4, dcalc = 1.903 g/cm3, R = 0.0606. The crystal structure was shown to be layered with the alternating layers of three types. Two of them have the same composition (C60, TMTSF) but different interorientation of molecules in a layer and different number of shortened contacts C…C and C…Se. The third layer consists of benzene molecules. The energy of intermolecular interactions C60…. TMTSF was estimated by ab initio calculations. The TMTSF molecule has a “boat” conformation.  相似文献   

9.
新奇的C60     
C_(60)是除石墨和金刚石外碳的第三种稳定的同素异构体。掺杂C_(60)超导电性的发现,立即在国内外引起研究C_(60)的热潮。简要介绍固体C_(60)及其衍生物的性质及应用的可能性。  相似文献   

10.
采用分子动力学方法对C60,C180,C60@ C180富勒烯分子的压缩过程进行了模拟,根据模拟结果,讨论了C60,C180,C60@ C180分子压缩力学特性的差异。研究表明,C6。分子具有相对优越的承载与能量吸收能力,而C60@ C180分子略高于C180分子。  相似文献   

11.
12.
Abstract

The water‐soluble composites with fullerene content up to 5 wt% based on poly‐(N‐vinylpyrrolydone) (PVP) were obtained. The higher fullerene content is achieved by means of introducing tetraphenylporphyrine (TPP) and KBr into composites. The synthesis includes the formation of C60–TPP complex and its further interaction with polymer. The formation of C60–TPP complex was confirmed by 13C NMR, SANS, and translational diffusion. The hydrodynamic and electrooptical studies of C60–TPP–PVP complexes indicate the higher symmetry of the polymer coil in the complex as compared to PVP. The C60–PVP–KBr composites were also obtained by the solid state interaction under vacuum, KBr promoting the destruction of fullerene aggregates.  相似文献   

13.
通过控制蒸发源电源、源和样品间距及扩散时间,室温下在C60单晶(111)解理面上制备出Rb3C60。用低温同步辐射角分辨光电子谱测量了样品的能带结构。观察到的能带色散表明样品为单晶薄膜。用X光电子谱首次研究了Rb3C60与C60相界面的稳定性。结果表明温度低于约420K时界面是稳定的。  相似文献   

14.
通过控制蒸发源电流、源和样品间距及扩散时间,室温下在C60单晶(111)解理面上制备出Rb3C60.用低温同步辐射角分辨光电子谱测量了样品的能带结构.观察到的能带色散表明样品为单晶薄膜.用X光电子谱首次研究了Rb3C60与C60相界面的稳定性.结果表明温度低于约420 K时界面是稳定的.  相似文献   

15.
采用Tersoff-Brenner势与L—J势的分子动力学方法,研究了双石墨层作用下C32、C60、C180以及C60@C180富勒烯分子的压缩力学特性。根据计算结果,讨论了几种富勒烯压缩过程中的变形、能量、压缩栽荷等的变化及其差异。研究表明,由于分子几何构形上的差异,压缩时,C180出现了明显的“塌陷”现象,“塌陷”过程中,能量及外载荷一度下降;几种富勒烯压缩时的能量吸收能力排序为:C32〉C60〉C60@C180〉C180,承载能力的排序为:C60@C180〉C180〉C60〉C32。  相似文献   

16.
《Zeolites》1992,12(2):202-209
The effects of (n, γ) and (n, α) reactions of framework atoms on the fate of (n, γ) recoil species 131Ba2+ and 134Cs+ from Ba2+ and Cs+ loaded in high-silica aluminosilicate and borosilicate zeolites (boron-zeotypes) have been studied. Studies were made of the recoil from “open to locked-in” and “locked-in to open” sites. In open to locked-in recoil, target ions were eluted with efficiencies of 90% where only (n, γ) processes were in operation, but in the presence of (n, γ) and (n, α) reactions, the efficiency fell to 80%. For locked-in to open site recoil, the corresponding efficiencies were in the ranges 50–60% and 40–50%. The effect of calcination temperature on the exchange of cations present was also ascertained. The high-silica zeolites used were synthesized according to published methods and were characterized by XRD, i.r., SEM, and t.g.-d.t.g./d.s.c. techniques, and all were found to be crystalline. In boron-zeotype materials, the magnitude of (n, α) damage was increased by the use of 10B isotope.  相似文献   

17.
Au电极作用下C60、2C60与4C60富勒烯分子的电子传输特性   总被引:2,自引:0,他引:2  
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.  相似文献   

18.
Abstract

The role of structural effects on the anomalous superconducting properties of (NH3) x NaK2C60 fullerides was investigated using 23Na and 2H NMR. In the metallic (NH3) x NaK2C60 (0.5 < x < 1) compounds, the 23Na quadrupolar splitting is observed to be independent from ammonia concentration x which, on the other hand, substantially affects the superconducting transition temperature. The marginal influence of sodium cation displacement in the superconducting properties is confirmed also by the absence of any electric field gradients in the recently synthesized nonmagnetic insulator (NH3)2NaK2C60. 2H NMR measurements on deuterated samples enabled us to study the ND3 reorientational dynamics, indicating a hampered ammonia rotation in the insulating (x = 2) case, where the Na+ ions become centered.  相似文献   

19.
20.
Investigations into the thermal characteristics of glass-water heat pipes from 0 °C to 60 °C were carried out at the National Institute of Metrology (NIM), China. In this paper, studies on a glass-water heat pipe with four thermometer wells are described. The experimental results indicated that the temperature stability and uniformity of the thermometer well of the glass-water heat pipes are within several tenths of a millikelvin when the heat pipes are immersed in a constant-temperature liquid bath, since they have a highly effective thermal conductivity. They are able to maintain a constant temperature by the absorption or liberation of the latent heat of evaporation to attenuate temperature fluctuations of the surroundings. Also, above 0 °C to 30 °C, the temperature stability of the thermometer well of the glass-water heat pipe is better than 0.1 mK for approximately 16 h. The maximum temperature differences among the thermometer wells are less than 5.5 mK when the water heat pipes operate in the range from 0 °C to 60 °C. Therefore, water heat pipes are very promising to improve the performance of liquid baths and to accurately calibrate thermometers by comparison.  相似文献   

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