Raman spectra of samarium-fullerene intercalation compounds

Samarium-fullerene intercalation compounds of nominal composition Sm_xC₆₀ (x=1,2,…,6) have been synthesized by a solid-state reaction method. We obtain a Sm_2.75C₆₀ superconducting phase with orthogonal structure and a Sm₆C₆₀ phase with body-centered cubic structure. The broadening and weakening of Raman peaks of the Sm_xC₆₀ compounds are due to the distortion of C₆₀ and electron-phonon interaction. The Raman measurements reveal that the distortion of C₆₀ decrease in Sm_xC₆₀ (x=3,4,5) exposed to air, although the fulleride solids have transformed into an amorphous state. The Raman results also show that the distortion of C₆₀ is still very large in the Sm₆C₆₀ exposed to air, or the C₆₀ molecules have been destroyed and become some amorphous carbide.     

Experimental investigation of C60/NMP/toluene solutions by UV-Vis spectroscopy and small-angle neutron scattering

The transformation of the C₆₀ fullerene cluster state into C₆₀/N-methylpyrrolidone (NMP) solution after the addition of a nonpolar solvent (toluene, electric permittivity ?= 2.4) is studied. The results of ultraviolet-visible spectroscopy and small-angle neutron scattering measurements are used for comparison of the C₆₀/NMP/toluene system with C₆₀/NMP mixtures with a high-polar solvent (water, ? = 80). As to the observed reorganization of the cluster state, the C₆₀/NMP/toluene system is similar to the C₆₀/NMP/water system. This effect is explained by the formation of charge-transfer complexes in the initial C₆₀/NMP solution. These complexes are thought to be soluble in both binary mixtures. The connection between the cluster-reorganization effect and solvatochromism is discussed.     

A comparative study of ion-induced damages in C60 and C70 fullerenes

The stability of fullerenes (C₆₀ and C₇₀) under swift heavy ion irradiation is investigated. C₆₀ and C₇₀ thin films were irradiated with 120 MeV Ag ions at fluences from 1×10¹² to 3×10¹³ ions/cm². The damage cross-section and radius of damaged cylindrical zone were found to be higher for C₆₀ than C₇₀ as evaluated by Raman spectroscopy, which shows that the C₇₀ molecule is more stable under energetic ion impact. The higher damage cross-section of the C₆₀ molecule compared with that of the C₇₀ molecule is explained on the basis of thermal conductivity in the framework of the thermal spike model. The surface morphology of pristine C₆₀ and C₇₀ films is studied by atomic force microscopy. UV-visible absorption studies revealed that band gap for C₆₀ and C₇₀ fullerenes thin films decreases with increasing ion fluence. Resistivity of C₆₀ and C₇₀ thin films decreases with increasing ion fluence but the decrease is faster for C₆₀ than C₇₀, indicating higher damage in C₆₀. Irradiation at a fluence of 3×10¹³ ions/cm² results in complete damage of fullerenes (C₆₀ and C₇₀) into amorphous carbon.     

Sm富勒烯的芯态光电子能谱

用X射线光电子能谱研究了Sm掺杂的固态C₆₀相衍变和芯电子态.在Sm_xC₆₀中Sm的含量x小于0.5时，样品是固溶相；在x=0.5和x=2.75之间的掺杂阶段，样品是这两个相的混合.在x=2.75和x=6之间的高掺杂阶段未观察到相分离的X射线光电子能谱证据.Sm 4f, 4d的实验数据表明Sm的价态是+2.二价Sm 3d_5/2芯态谱线存在两个子峰. 关键词： 60的Sm填隙化合物')" href="#">C₆₀的Sm填隙化合物 相结构 电子态 X射线光电子能谱     

Morphologies of C60 deposited on a substrate

The morphologies of deposited C₆₀ on a copper substrate from a C₆₀-benzene solution were evaluated by using Scanning Electron Microscopy. It was found that the forms of deposited C₆₀ were dependent on the aggregation of C₆₀ in its original solution. During natural vaporization of benzene solution on a copper substrate, independent C₆₀ molecules in the solution assembled into crystal C₆₀ on the substrate, whereas the aggregates of C₆₀ in the solution were remained as amorphous C₆₀ particles on the substrate. However, if spinning was employed during vaporizing solvent, the C₆₀ aggregates were destroyed, leading to the formation of crystal C₆₀. Furthermore, the speed of spinning a substrate can tune the size and shape of deposited C₆₀.     

Mechanisms of inelastic scattering of low-energy protons by C6H6, C60, C6F12, and C60F48 molecules

The mechanisms of inelastic scattering of low-energy protons with a kinetic energy of 2–7 eV by C₆H₆, C₆F₁₂, C₆₀, and C₆₀F₄₈ molecules are studied using the methods of quantum chemistry and nonempirical molecular dynamics. It is shown that, for the C₆H₆ + proton and C₆₀ + proton systems, starting from a distance of 6 Å from the carbon skeleton, the electronic charge transfer from the aromatic molecule to H⁺ occurs with a probability close to unity and transforms the H⁺ ion into a hydrogen atom and the neutral C₆H₆ and C₆₀ molecules into cation radicals. The mechanism of interaction of low-energy protons with C₆F₁₂ and C₆₀F₄₈ molecules has a substantially different character and can be considered qualitatively as the interaction between a neutral molecule and a point charge. The Coulomb perturbation of the system arising from the interaction of the noncompensated proton charge with the Mulliken charges of fluorine atoms results in an inversion of the energies of the electronic states localized, on the one hand, on the positively charged hydrogen ion and, on the other hand, on the C₆F₁₂ and C₆₀F₄₈ molecules. As a result, the neutral molecule + proton state becomes the ground state. In turn, this inversion makes the electronic charge transfer energetically unfavorable. Quantum-chemical and molecular-dynamics calculations on different levels of theory showed that, for fluorine derivatives of some aromatic structures (C₆F₁₂, C₆₀F₄₈), the barriers to proton penetration through carbon hexagons are two to four times lower than for the corresponding parent systems (C₆H₆, C₆₀). This effect is explained by the absence of active π-electrons in the case of fluorinated molecules.     

Self-assembled growth of C60 nanowhiskers on anodic porous alumina membranes

Unique structured claw-like C₆₀ nanowhiskers were fabricated on an anodic porous alumina membrane. Tips of the C₆₀ nanowhiskers are shaped like cusps, which directly extend into the nanopores of the alumina membrane. It is revealed that the surface stress of the alumina membrane with a highly ordered nanopore arrangement due to thermal treatment is responsible for self-assembled growth of the observed C₆₀ nanowhiskers. The ordering of the nanopore arrangement in the anodic porous alumina membrane helps to form the C₆₀ nanowhiskers along the nanopore channels. The shape and structure of the C₆₀ nanowhiskers are promising characteristics for applications in nanodevices such as field-emission tips and nanoprobes. PACS 61.46.+w; 61.48.+c; 33.20.Fb     

Stoichiometrically controlled direct solid-state synthesis of C60H2

The direct solid-state synthesis of C₆₀H₂ has been demonstrated by controlling the amount of hydrogen introduced into the reaction with C₆₀. Palladium hydride has been used as the source of hydrogen. The main product 1,2-C₆₀ is the isomer predicted to have the lowest energy of the possible 23 isomers; in addition, small amounts of the thermodynamically most stable isomer of C₆₀H₄, 1,2,3,4-C₆₀H₄, have also been obtained.     

Characterization of fullerenes using positrons

Positron distributions and lifetimes in the K_xC₆₀ crystals for x=0, 3, 4, 6 have been calculated using the superposed-atom model and the numerical relaxation technique. It is revealed that positrons are distributed predominantly at the octahedral interstices in the fcc lattice of pure C₆₀. The distributions and lifetimes of positrons are significantly changed by potassium doping. In the fcc K₃C₆₀, the positron density shows its maxima in the interstitial region between the octahedral and tetrahedral interstices and has some amplitude in the inner space of the C₆₀ molecules. In contrast to this, positrons are distributed one-dimensionally along the [001] direction in the bct K₄C₆₀ while positrons are nearly localized into the C₆₀ molecules in the bcc K₆C₆₀.     

Small-angle neutron scattering in aqueous solutions of fullerene-containing oligopropylene oxides

Propylene-oxide oligomers in heavy water (their molecular mass is ～500, and the concentration C varies from ～0.6 to 5.0 g/dL) and similar systems with C₆₀ and C₇₀ fullerenes and C₆₀(OH) _x fullerenols (x ～ 20), i.e., functionalized oligopropylene oxides, are studied via small-angle neutron scattering. The initial oligomers are found to create spherical micelles (～40 molecules) in the solution. It is ascertained that, in oligopropylene-oxide solutions, the C₆₀, C₇₀, and C₆₀(OH) _x derivatives (～1 wt % of fullerene relative to the oligomer) modify its molecular organization, acting as physical bonds whereby micelles are joined into large-scale linear, twisted, and branched chain superstructures.     

Preparation of supramolecular assembled films of fullerene C60 on the aqueous solution of water-soluble azocalixarene

A convenient procedure was developed to prepare an ultra-thin film of supermolecules of a spherical fullerene C₆₀ and water-soluble azocalix[6]arene. The C₆₀ molecule is so hydrophobic that it easily forms a three-dimensional aggregate on the water surface. When C₆₀ molecules were spread on an aqueous solution of water-soluble azocalixarene that acts as a host for C₆₀, the hydrophobic C₆₀ was captured in the cavity of the host molecule at the boundary of two phases and formed amphiphilic supermolecules. The supermolecules assembled spontaneously into ultra-thin films over 1-cm wide. The monolayer-like film could be transferred onto a solid support by the Langmuir–Blodgett technique or the inverse Langmuir–Schaefer technique. The morphology and the transferability of the supramolecular assembled films were examined by changing the host molecules, the initial density of C₆₀ on the water surface, the subphase temperature and the metal ions in the subphase.     

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：     

Crystalline structure of a C60/C70 membrane

The crystalline structure of a C₆₀/C₇₀ membrane prepared by an original technique has been studied by x-ray diffraction and Raman spectroscopy. The effects of purification of the starting C₆₀/C₇₀ mixture to C₇₀ composition and of spatial separation of the C₆₀ and C₇₀ phases in the membrane have been revealed. The samples studied were established to have a composition gradient from C₆₀ to C₇₀. The main structure of the membrane is shown to be an fcc lattice with a=14.308 Å.     

Temporal pulsewidth and the wavelength dependences of the product ions obtained by laser ablation of solid C<Subscript>60</Subscript>

By ablating solid C₆₀ with a laser pulse, we observe various processes such as the prompt- and the delayed-ionization of C₆₀, the fragmentation into molecular ions and the formation of cluster ions. We found these processes show distinct dependences on the temporal pulse width, the power and the wavelength of the ablation laser. From the observations, we could confirm efficient coupling of laser energy to C₆₀ through the molecular absorption even with a laser pulse width less than the electron-phonon coupling time of the C₆₀ molecule.     

BOND STRUCTURE AND ELECTRON STATES OF CHARGED C60

In the alkali-metal doped C₆₀, the charge transfer induces the distortion of the bond structure and forms the self-trapping electronic bound states. Our theory manifests: 1, the charge transfer reduces the symmetry of C₆₀ from I_h to D_5d. 2, Both the bond distortion and the self-trapping states possess layer structures and are localized in the equatorial area. 3, The carbon atoms in charged C₆₀ are divided into eight layers with an inversion center, then there exist four nonequivalent groups of carbon atoms. It makes the NMR line split into a fine structure with strength ratio 1:1:2:2. 4, The charged C₆₀ has two self-trapping bound states, one is 0.06eV above HOMO with odd parity and the other is 0.05 eV below LUMO with even parity.     

Electron energy-loss studies of NaxC60 compounds

The crystal and electronic structure of Na_xC₆₀ (4< x < 10) has been investigated using electron energy-loss spectroscopy in transmission. Electron scattering experiments confirm that the crystal symmetry remains face centered cubic over the entire intercalation range. The electronic structure shows a close similarity for the Na₆C₆₀ and Na₄C₆₀ compounds compared to the corresponding K and Rb systems. Upon intercalation to higher stochiometries up to Na₁₀C₆₀ the charge transfer from sodium to C₆₀ turns out to be incomplete, something that has never been observed before in alkali intercalated systems. Current theoretical calculations indicate that this can be understood by taking into account additional states related to the Na atoms in the octahedral site. In Na₁₀C₆₀ the partial filling of the t_1G level of C₆₀ leads to additional electronic transitions near the Fermi energy.     

C60 sputtering of organics: A study using TOF-SIMS, XPS and nanoindentation

Sputtering of organic materials using a C₆₀ primary ion beam has been demonstrated to produce significantly less accumulated damage compared to sputtering with monatomic and atomic-cluster ion beams. However, much about the dynamics of C₆₀ sputtering remains to be understood. We introduce data regarding the dynamics of C₆₀ sputtering by evaluating TOF-SIMS depth profiles of bulk poly(methyl methacrylate) (PMMA). Bulk PMMA provides an ideal test matrix with which to probe C₆₀ sputter dynamics because there is a region of steady-state secondary ion yield followed by irreversible signal degradation. C₆₀ sputtering of PMMA is evaluated as a function of incident ion kinetic energy using 10 keV C₆₀⁺, 20 keV C₆₀⁺ and 40 keV C₆₀⁺⁺ primary ions. Changes in PMMA chemistry, carbon accumulation and graphitization, and topography as a function of total C₆₀ ion dose at each accelerating potential is addressed.     

Simulations of C60 bombardment of Si, SiC, diamond and graphite

Molecular dynamics simulations of the 20-keV C₆₀ bombardment at normal incidence of Si, SiC, diamond and graphite targets were performed. The unique feature of these targets is that strong covalent bonds can be formed between carbon atoms from the C₆₀ projectile and atoms in the solid material. The mesoscale energy deposition footprint (MEDF) model is used to gain physical insight into how the sputtering yields depend on the substrate characteristics. A large proportion of the carbon atoms from the C₆₀ projectile are implanted into the lattice structure of the target. The sputtering yield from SiC is ∼twice that from either diamond or Si and this can be explained by both the region of the energized cylindrical tract created by the impact and the number density. On graphite, the yield of sputtered atoms is negligible because the open lattice allows the cluster to deposit its energy deep within the solid. The simulations suggest that build up of carbon with a graphite-like structure would reduce any sputtering from a solid with C₆₀⁺ bombardment.     

Electron-energy-loss spectroscopy of KxC60 and K-halides: comparison in the K3p excitation region

We have investigated the electronic structure of K_xC₆₀ (x=0–6) using low-energy electron energy loss spectroscopy (LEELS), especially focusing on the K_3p core-electron excitation spectra. It is found that the structure of the K_3p-excitation spectrum of K_xC₆₀ quite differs from that of KCl. Furthermore, the K_3p-excitation LEELS of K₃C₆₀ has been revealed to be different from that of K₆C₆₀. K_3p electrons are excited into K_4s- and K_3d-derived empty states in both K_xC₆₀ and KCl, but in the case of K_xC₆₀ the K_3d-derived empty states have a rather complicated structure where several levels are not well separated. Consequently, K_3p-excitation LEEL spectra of K_xC₆₀ show wide-spread plateau-like structures. The difference in the K_3p-excitation spectra of K₃C₆₀ and K₆C₆₀ is considered to originate from the different crystal field around K⁺ cations in the C₆₀ molecular crystal.     

High-pressure synthesis, structural and Raman studies of a two-dimensional polymer crystal of

Two-dimensional polymerisation of a C₆₀ single crystal has been obtained under high-pressure high temperature conditions (700 K - 2 GPa). Crystalline order is preserved but the crystal splits into variants (orientational domains). The analysis of X-ray diffraction and Raman spectroscopy data reveals that the polymer crystal is primarily tetragonal with some admixture of rhombohedral phase. Furthermore, Raman spectroscopy gives evidence for additional C₆₀-C₆₀ dimers, which are probably disordered. For the tetragonal phase, it is shown that successive polymer layers are rotated by about the stacking axis, according to the P4₂/mmc space group symmetry. The structure of the rhombohedral phase is also clarified. The role of the interlayer interactions in stabilising the two-dimensional polymer phases of C₆₀ is discussed. Received 8 October 1999