Buckling of carbon nanotubes wrapped by polyethylene molecules

The discovery of a buckling instability of a single-walled carbon nanotube wrapped by a polyethylene molecule subjected to compression is reported through molecular mechanics simulations. A decrease up to 44% in the buckling strain of the nano-structure owing to the van der Waals interaction between the two molecules is uncovered. A continuum model is developed to calculate both the interaction between the tube and the polymer and the decreased buckling strain of the structure by fitting the molecular mechanics results.     

Axisymmetric vibration of single-walled carbon nanotubes in water

A double shell-Stokes flow model is developed to study the axisymmetric vibration of single-walled carbon nanotubes (SWCNTs) immerged in water. In contrast to macroscopic solid-liquid system, a submerged SWCNT is coupled with surrounding water via the van der Waals interaction. It is shown that this unique feature substantially reduces viscous damping of the axisymmetric radial, longitudinal and torsional vibrations and significantly up-shifts the frequency of the radial vibration of an SWCNT. The study offers a theoretical explanation for the experimental observation and molecular dynamics simulations available in particular cases, and provides an efficient modelling tool and useful guidance for the study of the general dynamic behaviour of SWCNTs in a fluid.     

Rotational Spectra of Argon Acetone: A Two-Top Internally Rotating Complex

The rotational spectra of the argon acetone weakly bound complex was studied by pulsed jet Fabry-Perot Fourier transform microwave spectroscopy. Over 500 transitions of the complex were measured between 5.5 and 26 GHz from J=2-1 to J=12-11. The two methyl groups undergo hindered internal rotation resulting in four or five internal rotation states. The microwave transitions are within these states, resulting in a splitting of each rotational transition into four and sometimes five distinct transitions. The three-fold barrier to internal rotation is determined to be 260 cm⁻¹, 2% less than the 266 cm⁻¹ barrier in acetone itself. The structure of the complex has the argon atom above the heavy atom plane of the acetone, 3.52 Å from the CO bond and approximately in the C_s plane, which is perpendicular to the CCC plane of acetone.     

Rotational Spectrum, Dynamics, and Bond Energy of the Oxirane···Krypton van der Waals Complex

From the free jet millimeter-wave spectra of four isotopomers of the weakly bonded oxirane···Kr complex, information on the equilibrium conformation, dynamics, and dissociation energy has been deduced. A C_s symmetry is found for the complex, with Kr lying in the σ_v plane of symmetry of oxirane. The equilibrium distance of Kr with respect to the center of mass of bare oxirane is 3.67 Å, with Kr tilted 13.6° from the perpendicular to the center of mass of the ring toward the oxygen atom. The dissociation energy is estimated, from the centrifugal distortion constant D_J, to be ca. 3.1 kJ/mol.     

Theoretical calculations of thermophysical properties of single-wall carbon nanotube bundles

Carbon nanotube bundles are promising thermal interfacial materials due to their excellent thermal and mechanical characteristics.In this study,the phonon dispersion relations and density of states of the single-wall carbon nanotube bundles are calculated by using the force constant model.The calculation results show that the inter-tube interaction leads to a significant frequency raise of the low frequency modes.To verify the applied calculation method,the specific heat of a single single-wall carbon nanotube is calculated first based on the obtained phonon dispersion relations and the results coincide well with the experimental data.Moreover,the specific heat of the bundles is calculated and exhibits a slight reduction at low temperatures in comparison with that of the single tube.The thermal conductivity of the bundles at low temperatures is calculated by using the ballistic transport model.The calculation results indicate that the inter-tube interaction,i.e.van der Waals interaction,hinders heat transfer and cannot be neglected at extremely low temperatures.For(5,5) bundles,the relative difference of the thermal conductivity caused by ignoring inter-tube effect reaches the maximum value of 26% around 17 K,which indicates the significant inter-tube interaction effect on the thermal conductivity at low temperatures.     

A general rigorous quantum dynamics algorithm to calculate vibrational energy levels of pentaatomic molecules

An exact variational algorithm is presented for calculating vibrational energy levels of pentaatomic molecules without any dynamical approximation. The quantum mechanical Hamiltonian of the system is expressed in a set of orthogonal coordinates defined by four scattering vectors in the body-fixed frame. The eigenvalue problem is solved using a two-layer Lanczos iterative diagonalization method in a mixed grid/basis set. A direct product potential-optimized discrete variable representation (PO-DVR) basis is used for the radial coordinates while a non-direct product finite basis representation (FBR) is employed for the angular variables. The two-layer Lanczos method requires only the actions of the Hamiltonian operator on the Lanczos vectors, where the potential-vector products are accomplished via a pseudo-spectral transform technique. By using Jacobi, Radau and orthogonal satellite vectors, we have proposed 21 types of orthogonal coordinate systems so that the algorithm is capable of describing most five-atom systems with small and/or large amplitude vibrational motions. Finally, an universal program (PetroVib) has been developed. Its applications to the molecules , and the van der Waals cluster He₃Cl₂ are also discussed.     

The influence of surface effect on vibration behaviors of carbon nanotubes under initial stress

An analytical method is presented to solve the influence of surface effect on non-coaxial resonance of multi-walled carbon nanotubes embedded in matrix utilizing laminated structures model. Due to coupled van der Waals forces between adjacent tubes and surface effect exerted carbon nanotubes, the resonance frequencies and amplitude ratios of multi-walled carbon nanotubes under initial stresses show that the resonant characteristics of the multi-walled carbon nanotubes become complex and the numbers of vibrational modes do not keep increase under identical conditions after considering surface effects. The result obtained can be used as a beneficial reference for investigating the electronic and physical behaviors of carbon nanotubes.     

基态原子与理想金属Au表面间的范德瓦尔斯作用

研究了基态碱金属原子与理想金属Au表面间的范德瓦尔斯(vdW)作用.通过分析电四极跃迁对vdW的贡献,构建了计算超精细能级碱金属原子与理想金属表面间vdW作用系数C3的理论模型.以85Rb、133Cs为例,计算了其基态原子超精细能级的C3系数.其中85Rb: 52S1/2 (F=2)及52S1/2 (F=3)对应的C3系数分别为:2.2409 及2.2425 ;133Cs: 62S1/2 (F=3)及62S1/2 (F=4)分别对应 2.4480 及2.4538 .研究还发现随着 的增大,C3增大,z (原子与金属表面之间的距离)不变时,原子与理想金属表面间vdW作用增强. 这一研究在实现原子囚禁及介质表面量子反射等方面具有重要意义     

基态原子与理想金属Au表面间的范德瓦尔斯作用

研究了基态碱金属原子与理想金属Au表面间的范德瓦尔斯(vdW)作用.通过分析电四极跃迁对vdW的贡献,构建了计算超精细能级碱金属原子与理想金属表面间vdW作用系数C3的理论模型.以85Rb、133Cs为例,计算了其基态原子超精细能级的C3系数.其中85Rb: 52S1/2 (F=2)及52S1/2 (F=3)对应的C3系数分别为:2.2409 及2.2425 ;133Cs: 62S1/2 (F=3)及62S1/2 (F=4)分别对应 2.4480 及2.4538 .研究还发现随着 的增大,C3增大,z (原子与金属表面之间的距离)不变时,原子与理想金属表面间vdW作用增强. 这一研究在实现原子囚禁及介质表面量子反射等方面具有重要意义     

超精细能级中85Rb激发态(｜52P1/2F>、｜52P3/2F>)原子与理想金属表面间范德瓦尔斯作用系数C3的估算

利用碱金属原子与理想金属表面间范德瓦尔斯(vdW)作用势和不可约张量方法,首次计算了85Rb激发态52P1/2 (F=2,3)及52P3/2 (F=1,2,3,4) 原子超精细结构的C3系数.数值分别对应为:4.0542 、4.0553 及4.3012 、4.3312 、4.3369 、4.3104 .为了说明其结果的准确性,还与其他作者的理论数据和相关实验数据进行了比较,结果表明本文所得到的85Rb激发态52P1/2 (F=2,3)及52P3/2(F=1,2,3,4)原子的C3数值是可靠的     

A search for colour van der Waals interaction

It is suggested that the strength of nuclear colour van der Waals interaction, if present, can be determined by measuring deviations from Rutherford scattering of charged hadrons from nuclei, at energies well below the Coulomb barrier. Experimental limit on the strength of such a potential is obtained asλ<50, when the colour van der Waals potential is given byV(r)=λ(hc/r ₀)(r ₀/r)⁷, withr ₀, the scaling length, taken as 1 fm. This limit is obtained from an analysis of existing experiments and by performing scattering experiments of 3–4.6 MeV protons from a²⁰⁸Pb target.     

超精细能级中133CS激发态(｜62D3/2F>)原子与理想金属表面间范德瓦尔斯作用系数C3的估算

利用碱金属原子与理想金属表面间范德瓦尔斯(vdW)作用势和不可约张量方法,首次计算了133CS激发态62D3/2 (F=2,3,4,5)原子超精细结构的C3系数.数值分别对应为:17.9956 、18.0796 、18.0857 及18.1756 .为了说明其结果的准确性,还与其他作者的理论数据和相关实验数据进行了比较,结果表明本文所得到的133CS激发态62D3/2 (F=2,3,4,5)原子的C3数值是可靠的.     

超精细能级中85Rb激发态(｜52P1/2F>、｜52P3/2F>)原子与理想金属表面间范德瓦尔斯作用系数C3的估算

利用碱金属原子与理想金属表面间范德瓦尔斯(vdW)作用势和不可约张量方法,首次计算了85Rb激发态52P1/2 (F=2,3)及52P3/2 (F=1,2,3,4) 原子超精细结构的C3系数.数值分别对应为:4.0542 、4.0553 及4.3012 、4.3312 、4.3369 、4.3104 .为了说明其结果的准确性,还与其他作者的理论数据和相关实验数据进行了比较,结果表明本文所得到的85Rb激发态52P1/2 (F=2,3)及52P3/2(F=1,2,3,4)原子的C3数值是可靠的     

超精细能级中~(133)Cs激发态|6~2P_(3/2)F〉(F=2,3,4,5)原子与理想金属表面间范德瓦尔斯作用系数C_3的估算

利用碱金属原子与理想金属表面间范德瓦尔斯(vd W)作用势和不可约张量方法,计算~(133)Cs激发态|6~2P_(3/2)F〉(F=2,3,4,5)原子超精细结构的C_3系数.数值分别为:4.338 5 k Hz·μm~3、4.361 9 k Hz·μm~3、4.368 0及4.346 7 k Hz·μm~3.与其它理论数据和实验数据比较,结果表明本文所得到的~(133)Cs激发态|6~2P_(3/2)F〉(F=2,3,4,5)原子的C_3数值是可靠的.     

超精细能级中~(133)C_S激发态(|6~2D_(3/2)F>)原子与理想金属表面间范德瓦尔斯作用系数C_3的估算

利用碱金属原子与理想金属表面间范德瓦尔斯(vd W)作用势和不可约张量方法,导出超精细能级中碱金属原子特定量子态C3的解析表达式,完成133CS原子62D3/2(F=2,3,4,5)的C3数值计算,计算结果表明随着的增大,C3增大,z(原子与金属表面之间的距离)不变时,铯原子与理想金属表面间vd W作用增强.同时对于由电四极矩作用产生的C31效果因贡献不显著,C3数值结果并未见到有异常波动现象.     

Nanomagnetic domains of chromium deposited on vertically-aligned carbon nanotubes

The drive to create ever smaller magnetic memory devices has led to the development of new nanomagnetic domains on surfaces. This paper reports the development of nano-chromium magnetic domains obtained using electrodeposition on vertically aligned carbon nanofibers arrays. Attempts to achieve this using conventional aqueous solutions were unsuccessful even after thin nickel underlayers were applied. The use of a novel electrolyte, a deep eutectic solvent, made from choline chloride: chromium (III) chloride enabled highly conformal overcoatings of chromium on individual bare carbon nanotubes to be obtained. Very high aspect ratio metal microstructures could be obtained by this novel technology. Magnetic imaging of the coated nanoarrays showed there to be clear magnetic character to the coating when the thin coatings were applied but this disappeared when the deposits were thicker and more contiguous.     

新型机械解理方法在二维材料研究中的应用

自从石墨烯被发现以来,机械解理技术已经成为制备高质量二维材料的重要方法之一,在二维材料本征物性的研究方面展现出了独特的优势.然而传统机械解理方法存在明显的不足,如制备效率低、样品尺寸小等,阻碍了二维材料领域的研究进展.近些年我们在机械解理技术方面取得了一系列的突破,独立发展了一套具有普适性的新型机械解理方法.这种新型机械解理方法的核心在于通过改变解理过程中的多个参数,增强层状材料与基底之间的范德瓦耳斯相互作用,从而提高单层样品的产率和面积.本文着重以石墨烯为例,介绍了该技术的过程和机理.相比于传统机械解理方法,石墨烯的尺寸从微米量级提高到毫米量级,面积提高了十万倍以上,产率大于95%,同时石墨烯依然保持着非常高的质量.这种新型机械解理方法具有良好的普适性,目前已经在包括MoS₂,WSe₂,MoTe₂,Bi2212等几十种材料体系中得到了毫米量级以上的高质量单层样品.更重要的是,在解理过程中,通过调控不同的参数,可以在层状材料中实现一些特殊结构的制备,如气泡、褶皱结构等,为研究这些特殊材料体系提供了重要的物质保障.未来机械解理技术还有很多值得深入研究的科学问题,该技术的突破将会极大地推动二维材料领域的研究进展.     

Bamboo-shaped carbon nanotubes generated by methane thermal decomposition using Ni nanoparticles synthesized in water-oil emulsions

Ni nanoparticles were synthesized using two water-in-oil emulsions formulated with different surfactants and using n-heptane as the organic phase and aqueous nickel acetate as the catalytic metallic precursor. Characterization by transmission electron microscopy showed that the Ni nanoparticles have diameters ranging from 3 to 12 nm, and that the surface is lightly oxidized. The decomposition of diluted methane catalyzed by the as-prepared Ni nanoparticles was studied in a thermogravimetric analyzer (TGA), operated in the 25–930 °C range. The weight gains measured during the analysis showed that the Ni nanoparticles decomposed methane above 480 °C, producing similar g.C/g.cat ratios (6–7) at the end of the tests. High resolution transmission electron microscopy (HRTEM) confirmed that the carbons collected at 930 °C were bamboo-shaped carbon nanotubes (BSCNTs) with well defined conical compartments. The average outside diameter of the tubes was between 30 and 60 nm.     

单壁碳纳米管受限空间内水的分布

碳纳米管管腔作为分子物质的纳米通道,其储存或输送水的能力具有重要研究价值.为了研究碳纳米管管腔受限空间对水分子团簇结构和分布的影响,本文采用分子动力学方法探究了管径、手性和温度对单壁碳纳米管管腔内水的结构和分布的影响.结果表明:在常温下,管径尺寸范围为1.018—1.253 nm的单壁碳纳米管管内易形成有序的多元环水结构,此范围以外碳纳米管管内难以形成水的有序结构;且随着管径尺寸增大,多元环水呈现由三元环至六元环的结构变化;范德瓦耳斯势分布分析表明,在上述管径范围内,水分子趋向于贴近碳纳米管管壁分布而形成水的有序结构.对比管径尺寸差别较小的碳纳米管,其手性对多元环水结构影响不大.多元环水结构的稳定性表现出温度依赖性,管径较大的碳纳米管内的多元环水的有序结构更易随温度升高而消失.