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.     

足球烯分子C_(60)及C_(70)的反饱和吸收性质与光限制效应

报道了对足球烯分子纯C_60及纯C_70的光限制效应的研究结果,讨论了样品的浓度及三重态寿命对光限制阈值的影响.首次报道在足球稀分子中发现的三重态吸收饱和现象,并阐述了其产生的原因及对光限制效应的影响.     

Thermal desorption states of C<Subscript>60</Subscript> fullerene molecules in polymer matrices

Polymer-C₆₀ fullerene composite coatings are studied using thermal desorption mass spectrometry. It is found that thermal desorption spectra of C₆₀ fullerene molecules can exhibit several resolved peaks (at a specified heating rate) corresponding to thermal desorption states. The relative intensity of the thermal desorption peaks depends on the procedure used for preparing the composite coatings, in particular, on the time of sedimentation of the polymer-fullerene suspension. The occurrence of different stages in thermally stimulated desorption of C₆₀ fullerene molecules is explained by the fact that the fullerene molecules can exist in several phase states characterized by different densities and degrees of ordering in the polymer matrix.     

Delayed Ionization and Delayed Detachment in Molecules and Clusters

被激发到电离阈值以上的分子体系的演化依赖于激发态的特征和与连续态的耦合等多种参数. 这些特性主要是与分子体系的复杂性,更准确地说与分子的大小,态密度,内自由度中的耦合强度有关.本文通过Na2的里德堡态的自电离,富勒烯C60的延迟电离,阴离子小团簇的延迟解离研究了在小分子中起主导作用的自电离和在大分子以及团簇中出现的延迟电离之间的转变过程. 由于这些体系中相对较慢的内能转移过程,这些研究是在纳秒激光的激发下进行.     

Formation of Zero Density Regions During the Dissolving of C60 and C70

Based on a comprehensive review of the calculated and experimental data obtained in this and previous articles by the authors, a phenomenological model of the supramolecular structure of fullerene solutions is proposed. The model suggests the development in the fullerene solutions of some zero density regions due to poor packing of spheroidal fullerene molecules C₆₀ and C₇₀, on the one hand, and columnar or ribbon supramolecular structures formed by solvent molecules, on the other. It is assumed that the source of the long-range energy of fullerenes is a physical vacuum, concentrated not only in the cavities of the fullerene molecules but also in new regions forming outside the fullerenes during their dissolving in single-ring aromatic solvents.     

Electronic interactions in two-dimensional polymers of the C60 fullerene

The electronic structure of tetragonal and rhombohedral polymers of the C₆₀ fullerene is investigated using x-ray emission spectroscopy. It is found that, compared to the C₆₀ molecular crystals, the formation of intermolecular covalent bonds in two-dimensional layers of the C₆₀ fullerene polymers leads to a broadening of the maxima in the CK _α x-ray emission spectra, a decrease in the density of high-energy states, and an increase in the width of the valence band of the polymer. The experimental data are interpreted by analyzing the results of the calculations performed within the density functional theory for the C₆₀ fullerene cage forming eight and twelve covalent bonds. It is shown that the electronic interactions between C₆₀ molecules in the polymerized layers are provided by two types of molecular orbitals located at energies 0.5–3.0 and ∼5.0 eV below the energy of the Fermi level.     

Spatially mapping the spectral density of a single C60 molecule

We have used scanning tunneling spectroscopy to spatially map the energy-resolved local density of states of individual C60 molecules on the Ag(100) surface. Spectral maps were obtained for molecular states derived from the C60 HOMO, LUMO, and LUMO+1 orbitals, revealing new details of the spatially inhomogeneous C60 local electronic structure. Spatial inhomogeneities are explained using ab initio pseudopotential density functional calculations. These calculations emphasize the need for explicitly including the C60-Ag interaction and STM tip trajectory to understand the observed C60 local electronic structure.     

离子化程度对硼取代富勒烯C19Bn+（n=0-3）体系储氢性能的影响

本文采用密度泛函理论方法,研究了氢气分子在硼取代富勒烯C19Bn+（n=0-3）表面的非解离吸附态、化学吸附态、及吸附态之间转换过渡态的结构和能量,得到了吸附态之间转换反应的势能面. 研究表明通过调整体系的离子化电荷可以调整吸附位点的电荷布居数,随着硼取代富勒烯离子化体系C19Bn+的吸氢活性位点电荷布居数增大,氢分子被极化的程度以及氢分子在材料表面的吸附能均逐渐增大,同时改变电荷布居数也对氢气分子在表面吸附态间转变势垒高度产生了量级为几个Kcal/mol的影响. 希望我们的研究能够对富勒烯储氢的进一步发展提供参考.     

The density functional calculations on the structural and electronic properties of the endohedral fullerene dimer (N2@C60)2

The generalised gradient approximation based on density functional theory is used to study the structural and electronic properties of the endohedral fullerene dimer (N 2 @C 60) 2.Four N atoms sit at the cage centres in the form of two N 2 molecules.The density of states and Mulliken charge analysis explore that the energy levels from-6 to-10 eV are mainly influenced by the N 2 molecules.     

Core level photoemission evidence of frustrated surface molecules: a germ of disorder at the (111) surface of C60 before the order-disorder surface phase transition

Using high resolution core level photoemission, we investigated the disordering transition of the fullerene molecules at the (111) surface of C (60) films. The experimental evidence of a two-step mechanism for the rotational disordering of surface fullerene molecules is provided. The data are consistent with a recent model in which the rotational degrees of freedom of one molecule, out of the four inequivalent C (60) molecules of the low temperature (2x2) surface unit cell, melt about 100 K before the bulk phase transition.     

Intrinsic impurity-band Stoner ferromagnetism in C60Hn

We identify Stoner ferromagnetism in fcc C60H(n) (n=odd) by using a local density approximation in the framework of the density functional theory. Hydrogen chemisorption on fullerenes creates quasilocalized π electrons on the fullerene surface, overlapping of their wave functions giving rise to a narrow half filled impurity band in the fcc C60H(n). The Stoner-type ferromagnetic exchange between the itinerant electrons leads to spin-split impurity bands. The magnetic moment per C60H(n) molecule is 1 μ(B) (for n=odd) or 0 (for n=even, including zero), only one of the hydrogens contributing to the spin-split states. Direct overlapping of the quasilocalized π-electron orbitals is essential for the ferromagnetism.     

Enhanced cohesion of photo-oxygenated fullerene films: A new opportunity for lithography

The irradiation of sublimed fullerene (C₆₀ and C₇₀) thin films with ultraviolet light in an oxygen-rich ambient has been found to lead to a substantially increased cohesive energy in the fullerene solid. The decreased solubility and lower vapor pressure of the phototransformed material enables wet (organic solvents) or dry (thermal or photon-induced sublimation) development of photo-defined negative images. One micrometer wide lines with good edge definition are demonstrated. X-ray, infrared, optical absorption, and high performance liquid chromatography reveal that photo-oxygenated C₆₀ retains its fcc crystal structure but with a substantial fraction of the C₆₀ molecules modified with carbonyl (C=O) bonds.     

C60与聚乙烯咔唑（PVK）键合物和共混物在紫外激光作用下的碳笼增强融合

用飞行时间质谱测量３０８ｎｍ激光熔蚀Ｃ６０化学修饰的聚乙烯咔唑（Ｃ６０－ＰＶＫ）与Ｃ６０／聚乙烯咔唑共混物（Ｃ６０／ＰＶＫ）的产物分布，分析了正负离子质谱，发现明显的碳笼融合现象。比较分析了融合过程的增强机理，认为Ｃ６０与ＰＶＫ间的化学键合以及电荷转移络合分别在Ｃ６０－ＰＶＫ键合物和Ｃ６０／ＰＶＫ共混物的富勒烯融合过程中起了重要作用。     

The study of polystyrene-fullerene solid-phase composites

Polystyrene-based films containing from 0 to 45 mol % of C₆₀ fullerene are investigated. It is found that the introduction of fullerene increases the molecular packing density of polystyrene chains, thus affecting the transport of small molecules through the polymer films. Gas diffusion through the composite films is slower than through the polystyrene films, while the gas-distributing properties of the composites are higher. The dielectric relaxation method shows that the solution-grown films retain the cluster state of fullerene. When the films containing more than 0.15 mol % of fullerene are heated above the glass transition temperature of polystyrene away from air, the relaxation time of the α transition in polystyrene is found to increase. This effect is associated with strong chain interaction via fullerene molecules incorporated into polystyrene-C₆₀ complexes. The NMR spectroscopy method allows us to observe the typical changes in the composites.     

Thermally stimulated desorption of C<Subscript>60</Subscript> and C<Subscript>70</Subscript> fullerenes from rigid-chain polyimide films

Polyimide-fullerene composite thin coatings are investigated using thermal desorption mass spectrometry in the temperature range 20–800°C. It is found that, at temperatures below the temperature of decom-position of the polymer matrix, thermally stimulated desorption of fullerene molecules is limited by the diffusion of fullerene molecules in the matrix. The diffusion coefficients and activation energies of diffusion of C₆₀ and C₇₀ fullerene molecules are determined from the experimental data on thermally stimulated desorption in the framework of several approaches. It is revealed that the diffusion of C₇₀ molecules in the polyimide matrix is more hindered than the diffusion of C₆₀ molecules in the same matrix.     

Raman spectroscopy of the interface between a thin nanostructured ZnO film and fullerene C60

The resonance and nonresonance Raman scattering in the interface between a thin ZnO film with a well-developed nanostructured surface morphology and a layer of fullerene C60 molecules deposited on this film has been investigated. It is shown that the intensity of the interaction between the C60 molecules and ZnO film surface can be estimated based on the spectral scattering characteristics.     

Diagnostics of atoms encapsulated into fullerenes by the polarization bremsstrahlung from accelerated electrons

It is shown that the polarization bremsstrahlung (PB), which arises during scattering of coherent electromagnetic fields of fast charged particles by atomic electrons and resonantly reacts to changes of the density of a substance, allows one to diagnose the states of atoms that are encapsulated in fullerene. As a result of modeling, by comparing the spectra of an empty fullerene and fullerene with an encapsulated atom and using difference fitting, it is possible to detect compressions or expansions of an electron shell of the atom that is encapsulated in a fullerene. The calculations are fulfilled for the model approximation of the P@C₆₀ endohedral compound.     

Ar 原子内嵌对C60 富勒烯碰撞的影响

基于半经验势的分子动力学模型， 研究了相同能量下 C₆₀ +C₆₀ 与 Ar@C₆₀ +Ar@C₆₀ 的对心碰撞后形成的富勒烯结构的不同。 发现在相同的能量下， Ar@C60 +Ar@C60 形成的碰撞产物的结构相比 C₆₀ +C₆₀ 碰撞产物的结构有着明显的不同: 前者形成“花生”状的新富勒烯结构， 后者形成“哑铃”状的双富勒烯结构。     

Z oscillations in ion-induced fullerene fragmentation

Multiply charged ion-induced fragmentation and ionization of C60 is governed by electronic and nuclear stopping of the projectile as well as charge exchange. We have studied the collision dynamics as a function of the projectile atomic number Z ( 2相似文献