Mechanisms of the oxidation of defect-free surfaces of carbon nanostructures: the influence of surface curvature

This work is concerned with reaction paths in the interaction of carbon defect-free nanostructures with different surface curvatures (graphene, tubulenes, and fullerene C₆₀) with atomic and molecular oxygen. The interaction energies of atoms were calculated by the density functional theory method using the basis set of plane waves and the VASP package. The potential surface of reactions with molecular oxygen was studied by the nudged elastic band method. The energy parameters of the reaction (released energy and barrier) strongly depended on the curvature of carbon structure surfaces. The interaction of atomic oxygen in the ground state with the surface of carbon nanostructures is an exothermic reaction. The barrier to the reaction with molecular oxygen (0.5–2.5 eV) decreases as the curvature of nanostructure surfaces increases. The calculation results are in agreement with the experimental data and other ab initio calculations.     

Calcium as the superior coating metal in functionalization of carbon fullerenes for high-capacity hydrogen storage

We explore theoretically the feasibility of functionalizing carbon nanostructures for hydrogen storage, focusing on the coating of C60 fullerenes with light alkaline-earth metals. Our first-principles density functional theory studies show that both Ca and Sr can bind strongly to the C60 surface, and highly prefer monolayer coating, thereby explaining existing experimental observations. The strong binding is attributed to an intriguing charge transfer mechanism involving the empty d levels of the metal elements. The charge redistribution, in turn, gives rise to electric fields surrounding the coated fullerenes, which can now function as ideal molecular hydrogen attractors. With a hydrogen uptake of >8.4 wt % on Ca32C60, Ca is superior to all the recently suggested metal coating elements.     

Self-organization of iron-atom nanostructures in the first layer of the (100) copper surface

Mechanisms of the diffusion of surface vacancies and iron atoms in the first layer of the Cu(100) surface have been studied by molecular dynamics and the kinetic Monte Carlo method. The diffusion of embedded atoms results in the self-organization of bound iron-atom nanostructures. The time dependences of the number of most widespread nanostructures have been obtained. According to the results, the self-organization of embedded nanostructures can be divided into three stages in which the copper surface has significantly different morphologies.     

Molecular dynamics study of Laplace pressure in solid-state nanostructures

The paper provides a comprehensive molecular dynamics study of nanostructures compressed by a system of surface atoms to analyze their surface tension. Surface tension is here understood as phenomena resulting from the presence of surface atoms. All main properties of nanostructures are conditioned by a highly developed surface. The number of surface atoms and their energy are comparable to those of bulk atoms.It is shown that at cryogenic temperatures, spherical solid-state clusters of size up to 10 nm reveal excess pressure. This pressure owes to compression of the clusters by surface atoms.The molecular dynamics study of thermodynamic properties of the nanostructures demonstrates that the increase in pressure in clusters of size from 2 to 9 nm with temperature is due to the gas component and the slope on the temperature dependence of thermal pressure does not depend on the cluster size. It is also shown that the surface tension coefficient decreases with an increase in temperature. A theoretical expression for this dependence is derived suggesting that there exists a certain Laplace temperature at which compressive pressure in a cluster is balanced by thermal gas pressure.     

Molecular Geometry Optimization, Two-Photon Absorption and Electrochemistry of New Diphenylethylene Derivatives Linking with Benzophenone Moiety Through Ether Covalent Bond

This paper presents the molecular geometry optimization, two-photon absorption and electrochemistry of new dyes containing benzophenone part, including 4-(p-benzoyl-benzyloxy)yl-4'-nitro-diphenylethylene (C1), 4-[N-methyl-N-(2-(p-benzoyl-benzyloxy)yl-ethyl]-4'-nitro-diphenylethylene (C2), 4-[N-ethyl-N-(2-(p-benzoyl-benzyloxy)yl-ethyl]-4'-nitro-diphenylethylene (C3), and 4-N, N-bis[(2-(p-benzoyl-benzyloxy)yl-ethyl]-4'-nitro-diphenyl ethylene (C4). The molecular structural parameters show that the coplanarity of diphenylethylene moiety is diminished in the excited state for C1, while it is enhanced for C2, C3 and C4. The electron density distribution of frontier orbital suggests that the derivatives exhibit (π, π) transition with internal charge transfer character, and the extent of charge transfer of C2, C3 and C4 is larger than that of C1. The derivatives display remarkable two-photon absorption (TPA) induced up-converted emission under 800 nm Ti: Sapphire femtosecond laser excitation. The maximal TPA emission wavelength of C2, C3 and C4 is red-shifted with respect to that of C1. TPA cross sections of C2, C3 and C4 are larger than those of C1. The cyclic voltammograms and the fluorescence lifetimes of the derivatives were determined and discussed.     

Crystallinity effect in the textural properties of titania-TPA catalysts

Catalysts based in titania mixed with tungstophosphoric acid (TPA), H₃PW₁₂O₄₀, in various proportions (1, 15, 25 and 50 wt%) were obtained by the sol-gel method. The gels were prepared by hydrolysis and gellation of titanium n-butoxide with a TPA solution, using HNO₃ as a catalyst to obtain a pH 3. Fresh samples were thermally treated from 100 to 800 °C, in a stepwise increment of 100 °C during 20 h per step. Specific surface areas were calculated by the BET method from the nitrogen adsorption isotherms; it was found that the surface area increased with TPA content. The crystallization behavior was followed by powder X-ray diffraction. Crystallite size measurements showed that anatase remains nanocrystalline in the studied temperature range. From the X-ray data, it was clear that below 700 °C TPA is highly dispersed in an amorphous state.     

Engineering negative differential conductance with the Cu(111) surface state

Low-temperature scanning tunneling microscopy and spectroscopy are employed to investigate electron tunneling from a C60-terminated tip into a Cu(111) surface. Tunneling between a C60 orbital and the Shockley surface states of copper is shown to produce negative differential conductance (NDC) contrary to conventional expectations. NDC can be tuned through barrier thickness or C60 orientation up to complete extinction. The orientation dependence of NDC is a result of a symmetry matching between the molecular tip and the surface states.     

金属杂质辅助低能氩离子束诱导蓝宝石自组织纳米结构

使用实验室自主研发的等离子抛光与刻蚀系统,研究了不同入射能量下不锈钢杂质辅助Ar+离子束刻蚀蓝宝石表面自组织纳米结构的形成机制.采用Taylor Surf CCI2000非接触式表面测量仪和原子力显微镜分别对刻蚀后蓝宝石样品的粗糙度、纳米结构的纵向高度和表面形貌进行了分析.研究表明:引入不锈钢杂质后,当离子束入射角度为...     

Surface diffusion versus atomic addition: using temperature to maneuver the morphology of Pd nanostructures by seeded-growth

We report herein the synthesis of Pd nanostructures ~64–95-nm range in size displaying controlled surface morphologies by a seeded-growth method employing Pd nanoparticles as seeds. Interestingly, we found that the surface texture and thus the surface area of the produced Pd nanomaterials could be tuned by varying the seeded-growth temperature. Pd nanostructures displaying increasingly higher surface textures were obtained as the seeded-growth temperature was decreased from 95 to 30 °C. These results could be explained based on the variations in the relative rates of atom deposition (V _deposition) and surface diffusion (V _diffusion) during the Pd growth. The catalytic activities of the Pd nanostructures toward the reduction of 4-nitrophenol augmented with the increase in the surface texture of the produced nanostructures. The results presented herein can have important implications for designing facile approaches to the synthesis of Pd nanostructures with desired features and optimized catalytic performances that can be highly accessible and attractive for large scale production.     

Controllable synthesis of fullerene nano/microcrystals and their structural transformation induced by high pressure

Fullerene molecules are interesting materials because of their unique structures and properties in mechanical, electrical, magnetic, and optical aspects. Current research is focusing on the construction of well-defined fullerene nano/microcrystals that possess desirable structures and morphologies. Further tuning the intermolecular interaction of the fullerene nano/microcrystals by use of pressure is an efficient way to modify their structures and properties, such as creation of nanoscale polymer structures and new hybrid materials, which expands the potential of such nanoscale materials for di- rect device components. In this paper, we review our recent progress in the construction of fullerene nanostructures and their structural transformation induced by high pressure. Fullerene nano/microcrystals with controllable size, morphology and structure have been synthesized through the self-assembly of fullerene molecules by a solvent-assisted method. By virtue of high pressure, the structures, components, and intermolecular interactions of the assemblied fullerene nano/microcrystals can be finely tuned, thereby modifying the optical and electronic properties of the nanostructures. Several examples on high pressure induced novel structural phase transition in typical fullerene nanocrystals with C60 or C70 cage serving as build- ing blocks are presented, including high pressure induced amorphization of the nanocrystals and their bulk moduli, high pressure and high temperature （HPHT） induced polymerization in C60 nanocrystals, pressure tuned reversible polymeriza- tion in ferrocene-doped C60/C70 single crystal, as well as unique long-range ordered crystal with amorphous nanoclusters serving as building blocks in solvated C60 crystals, which brings new physical insight into the understanding of order and disorder concept and new approaches to the design of superhard carbon materials. The nanosize and morphology effects on the transformations of fullerene nanocrystals have also been discussed. These results provide the foundation for the fabrication of pre-designed and controllable geometries, which is critical in fullerenes and relevant materials for designing nanometer-scale electronic, optical, and other devices.     

Electronic and optical properties of fullerene nanostructures

Two new types of molecular/electronic fullerene nanostructures are considered: 1) highly stable hydrated clusters (I _h symmetry group) and microcrystals (T _h symmetry group) of fullerene C₆₀ in water solution and 2) the single-walled carbon nanotube from C₆₀ fullerenes. The vibrational spectra of these fullerene nanostructures are calculated using molecular dynamics. The electronic properties of a single-walled fullerene nanotube are investigated using the tight-binding method. The theoretical results obtained were compared with available experimental data. Fiz. Tverd. Tela (St. Petersburg) 41, 885–887 (May 1999) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

苝四甲酸二酐有机单晶纳米结构的制备及形成机理的研究

在分子束外延(MBE)系统中, 利用物理气相沉积(PVD)的方法在阳极氧化铝(AAO)模板上制备了有机 染料分子苝四甲酸二酐(PTCDA)的不同纳米结构; 并使用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、 高分辨透射电子显微镜(HRTEM)以及选区电子衍射(SAED)技术进行了系统的研究. 结果发现, 当衬底温度(T_s)为330 ℃时得到的是纳米丝、针、带以及棒; T_s为280 ℃, 230 ℃, 180 ℃时得到的主要是纳米棒, 并且纳米棒的长度随T_s的降低而变短; T_s为50 ℃时只能得到连续的PTCDA薄膜. HRTEM以及SAED结果证实了纳米针与棒为单晶. 依据SEM结果, 提出纳米结构的生成主要受T_s以及衬底表面曲率的影响.     

Shedding light on the nanoworld: diffusion-limited nanostructures from laser-focused atom deposition

We study the role of surface diffusion in the fabrication of nanostructures by laser-focused (“cold”) atom lithography, using kinetic Monte Carlo simulations of a growth model that accounts for spontaneous organisation of 3D islands. Contrary to intuition, we find that the lateral size of the nanostructures is barely affected by surface diffusion of deposited adatoms, even when the adatom diffusion length exceeds the standing-wave field wavelength. To cite this article: F. Nita, A. Pimpinelli, C. R. Physique 5 (2004).     

银电极表面上C60薄膜的表面增强拉曼光谱研究

在银电极表面形成一层C60薄膜,分别在乙腈溶液和水溶液中进行表面增强拉曼光谱(SERS)研究并将两者进行比较,从而消除了溶液中的C60干扰表面吸附C60的SERS谱图的可能性.研究结果表明,C60分子对称性的降低导致SERS谱峰发生了分裂;表面电磁场的作用使得光谱选律在SERS效应中被拓宽,产生了新的拉曼谱峰.该结果与团簇吸附在粗糙银电极表面的C60分子的研究结果相似.与之不同的是在乙腈溶液和水溶液中的SERS谱图的低波数区内分别在348和311 cm-1左右出现一个新峰,经过分析可认为该峰与C60-金属基底的相互作用有关.     

High stability of the goldalloy fullerenes:A density functional theory investigation of M₁₂@Au₂₀（M=Na,Al,Ag,Sc,Y,La,Lu,and Au） clusters

Discovering highly stable metal fullerenes such as the celebrated C 60 is interesting in cluster science as they have potential applications as building blocks in new nanostructures.We here investigated the structural and electronic properties of the fullerenes M 12 @Au 20(M=Na,Al,Ag,Sc,Y,La,Lu,and Au),using a first-principles investigation with the density functional theory.It is found that these compound clusters possess a similar cage structure to the icosahedral Au 32 fullerene.La 12 @Au 20 is found to be particularly stable among these clusters.The binding energy of La 12 @Au 20 is 3.43 eV per atom,1.05 eV larger than that in Au 32.The highest occupied molecular orbital-lowest unoccupied molecular orbital(HOMO-LUMO) gap of La 12 @Au 20 is only 0.31 eV,suggesting that it should be relatively chemically reactive.     

纳米结构影响沸腾换热特性的分子动力学模拟

采用分子动力学方法模拟液体在纳米结构表面的快速沸腾过程.主要研究了纳米结构表面粗糙度以及栏栅形和棋盘形两种排列方式对液体快速沸腾过程以及换热特性的影响.研究结果表明,随着纳米结构表面粗糙度的增加,栏栅形和棋盘形纳米结构表面液体沸腾起始时间均提前.当栏栅形和棋盘形纳米结构表面粗糙度相同时,棋盘形纳米结构表面会进一步缩短液体沸腾起始时间.形成这种现象的原因是纳米结构表面粗糙度的增加,增加了固液接触面积,提高了初始时刻热通量,减小了固液界面热阻,导致表面附近液体动能增大,增大了液体高度方向的温度梯度,有利于液体发生沸腾.当纳米结构表面粗糙度相同时,棋盘形纳米结构表面具有较小的界面热阻,从而缩短了沸腾所需要的时间.     

Nanostructuring of single-crystal silicon carbide by femtosecond laser irradiation in a liquid

The formation of nanostructures on the surface of single-crystal silicon carbide under ablation by femtosecond laser pulses in liquid ethanol has been experimentally investigated. A 800-nm Ti:sapphire laser with a pulse duration of 210 fs was used as a radiation source. Single-scan irradiation of SiC surface leads to the formation of periodic grooves with a period of about 200 nm. Double exposure with a sample rotation by 90° between the scans gives rise to a regular array of nanostructures with average lateral size of 10 to 15 nm. It is determined that the wettability of nanostructured SiC surface is improved in comparison with the initial surface. It is shown that nanostructuring of SiC surface leads to an increase in the red light transmission by a factor of more than 60.     

Controllable growth of low-dimensional nanostructures on well-defined surfaces

The controllable growth of nanostructures with desired geometric order and well-defined shapes has stimulated great interest due to its applicability in the development of microelectronic devices. Self-assembly is an efficient and versatile way to guide the atoms or molecules into low-dimensional nanostructures as a consequence of balancing complex interplay between adsorbate-adsorbate and adsorbate-substrate interfacial interactions. The tailoring of low-dimensional nanostruc- tures by control of inter-adsorbate and adsorbate-substrate interfacial interactions is reviewed. Such inherent interactions greatly influence not only the size and shape of the growing nanostructures, but also their chemical identity. The degree of interaction between adsorbates can be controlled via preparation procedures, opening up the study of the influence of this phenomenon with respect to reactivity and catalytic behavior. The formation of well-defined molecular layers can be controlled not only by repulsive molecule-molecule interaction but also by symmetry matching or charge transfer be- tween adsorbed molecules and the substrate. It has become obvious that inter-adsorbate and adsorbate-substrate interfacial interactions can be tuned to fabricate diverse surface nanostructures from semiconductor, metallic, and molecular materials.     

Surface and bulk normal state transport properties in K(3)C(60)

The temperature dependence of the surface resistivity for a metallic K(3)C(60) ordered film in the nonsuperconducting state has been obtained by reflection electron energy loss spectroscopy. We demonstrate that the normal state electronic and transport properties of the top molecular layer of K(3)C(60) are similar to the corresponding properties measured with bulk sensitive techniques. These observations strengthen and give a general character to the experimental results obtained with surface sensitive techniques on fullerene compounds. In addition, the transport properties may deviate from the Fermi-liquid behavior above 500 K.     

Observation of coexistence of 1D and 2D nanostructures in cobalt dipyrromethene trimer complexes adsorbed on a graphite surface

We report the direct observation of 1D and 2D nanostructures of cobalt dipyrromethene trimer complexes adsorbed on a highly oriented pyrolytic graphite surface using scanning tunneling microscopy (STM). STM images showed two types of ordered structures coexisting on the surface: long 1D molecular chains isolated on the terraces, and 2D hexagonal patterns confined by a 1D chain and/or a graphite step edge. These 1D and 2D structures are attributed to ‘edge-on’ and ‘face-on’ complex alignments on the surface, respectively. In both configurations, substrate-mediated molecule-molecule interactions may play a significant role in stabilizing the nanostructures.