Dynamical properties of potassium ion K+ trapped in a fullerene C60 cage: An MD simulation

We have simulated a system composed of endohedral fullerene K⁺@C₆₀ molecules. Atomically detailed MD simulations have allowed us to analyze the dynamics of a potassium ion inside a fullerene cage and the motion of K⁺@C₆₀ molecules. The mean square displacement, the translational velocity correlation functions and their Fourier transforms, and the librational frequency of a K⁺ ion inside a C₆₀ cage have been calculated for several temperatures of the studied system. The librational frequency of a potassium ion inside a fullerene cage has been estimated. The solid-fluid phase transition has been observed in the system.     

Morphology of F8T2/PC71BM Blend Film as Investigated by Scanning Transmission X-ray Microscope (STXM)

Clarification of the morphology of bulk heterojunction (BHJ) is indispensable for true comprehension of the organic solar cells. Here, we performed scanning transmission X-ray microscopy (STXM) for a poly-(9,9-dioctylfluorene-co-bithiophene) (F8T2)/[6,6]-phenyl C71-butyric acid methyl ester (PC₇₁BM) blend film annealed at various temperatures (T_an). We found that the fullerene concentration within the polymer-rich domain decreases with T_an while the domain size (～230 nm) is essentially unchanged. We will discuss the interrelation between the film morphology and the photovoltaic performance.     

Small-angle X-ray scattering study of the structure of powder fullerene C<Subscript>60</Subscript> and fullerene soot

Powder samples of fullerene C₆₀ and fullerene soot have been studied by the small-angle X-ray scattering method. The radii of gyration of scattering elements have been determined by constructing small-angle diffraction patterns in Guinier coordinates. The data obtained agree well with the results of wide-angle X-ray scattering study, the available data on the structure of the powder fullerene C₆₀ prepared by the Huffman-Krätschmer technique, and the structure of the C₆₀ molecules. Conglomerates of two C₆₀ molecules, along with crystallites ～20 nm in size that are distributed in an amorphous matrix, are present in fullerene powders. Fullerene soot contains C₆₀ crystallites 20–25 nm in size and graphite crystallites ～2–3 nm in size that are distributed in an amorphous matrix.     

Crystal and molecular structures of trifluoromethyl derivatives of C82 fullerene: C82(CF3)12 and C82(CF3)18

Trifluoromethyl derivatives of C₈₂ have been obtained by the reaction between a higher fullerene mixture and trifluoromethyliodide, with subsequent isolation by high-performance liquid chromatography. The crystal and molecular structures of C₈₂(CF₃)₁₂ and C₈₂(CF₃)₁₈ have been determined by single crystal X-ray diffraction using synchrotron radiation. Both molecules are derivatives of C ₂-C₈₂ fullerene (isomer 3).     

Novel carbon materials obtained by reactions of C60 fullerene with phosphorus at high temperature

C₆₀ fullerene reacted with phosphorus at high temperatures to graphitic materials with strongly differing properties. Several spectroscopic investigations as Raman, ESR, XPS and ³¹P-NMR as well as TEM and ESEM have shown that the structural order of the mostly micro-crystalline materials increased with increasing reaction temperatures and decreasing phosphorus content. At suitable preparation conditions carbon nanotubes are formed, which are disordered in most cases, but partly exhibit high structural order (single-wall nanotubes), too. The prepared materials are very hard, e.g. harder than silica, intensely coloured and electrically conductive. Their hardness decreased with rising phosphorus content, and their conductivity increased with decreasing phosphorus content.     

Small-angle neutron scattering data on C60 clusters in weakly polar solutions of fullerenes

Solutions of fullerence C₆₀ in carbon disulfide CS₂ have been investigated by small-angle neutron scattering. Combination of solubility, contrast, and incoherent scattering make it possible to measure and analyze the relatively small scattering cross section of this system. Along with single fullerene molecules, a small amount of large fullerene clusters (more than 100 Å in size) is found in these solutions. The formation of these clusters depends on the procedure of solution preparation. The size distribution functions of clusters are compared with the results of the phenomenological cluster model of fullerene solubility.     

Synthesis and structure of fullerene halides in the C60-(TiCl4 + Br2) system: Molecular structures of (C60Cl5)2, C60 X 6, C60 X 8, and C60 X 24( X = Cl, Br)

The reactions in the C₆₀-(TiCl₄ + Br₂) system have been performed in ampoules at elevated temperatures. The molecular structure of the fullerene halides (C₆₀Cl₅)₂, C₆₀ X ₆, C₆₀ X ₈, and C₆₀ X ₂₄ (X = Cl, Br) has been determined and refined using single-crystal X-ray diffraction. It has been established that an increase in the bromine concentration results in an increase in the number of halogen atoms attached to the fullerene cage and in an increase in the relative fraction of bromine atoms in mixed halogen derivatives from almost pure chlorides (C₆₀Cl₅)₂ and C₆₀Cl₆ to halides C₆₀ X ₈ and C₆₀ X ₂₄ with a high relative bromine content. Original Russian Text ? S.I. Troyanov, A.V. Burtsev, E. Kemnitz, 2009, published in Kristallografiya, 2009, Vol. 54, No. 2, pp. 268–275.     

Variations in the structure of aromatic solvents under the influence of microadditives of the C<Subscript>60</Subscript> fullerene

The structural ordering of aromatic solvents is investigated using wide-angle X-ray diffraction. It is shown that the degree of structural ordering of aromatic solvents at room temperature decreases in the following sequence: benzene, toluene, and n-xylene. The introduction of the C₆₀ fullerene (～0.001%) into these solvents leads to an increase in the degree of their ordering. Upon introduction of the fullerene, the degree of structural ordering increases significantly in n-xylene and only slightly in toluene and remains virtually unchanged in benzene. An analysis of the small-angle X-ray diffraction patterns of C₆₀ fullerene solutions in benzene likewise demonstrates that the introduction of the fullerene into benzene leads to an insignificant change in the degree of structural ordering of this solvent. The specific features of the structure and behavior of benzene upon interaction with C₆₀ fullerene additives are discussed.     

Variations in the structure of aromatic solvents under the influence of dissolved fullerene C70

Dilute solutions of the C₇₀ fullerene (at concentrations from 0.0001–0.0005% to a few hundredths of a percent) in benzene, toluene, and p-xylene are investigated using small-angle and wide-angle X-ray diffraction. It is revealed that an increase in the C₇₀ fullerene concentration leads to a nonmonotonic shift of the small-angle X-ray diffraction patterns along the intensity axis: the intensity first decreases, reaches a minimum, and then increases. The wide-angle X-ray diffraction patterns of all the solutions under investigation exhibit two halos: as the fullerene concentration in the solution increases, the intensity of the first halo increases, whereas the intensity of the second halo decreases. The variations observed in the X-ray diffraction patterns of the fullerene solutions are interpreted in terms of structuring of the solvents, i.e., the formation of a specific order on the molecular and supramolecular levels. The X-ray diffraction data are in good agreement with the nonmonotonic concentration dependences of the density of the fullerene solutions in aromatic solvents. A structural interpretation of the initial decrease in the density of the fullerene solutions is proposed.     

Ultraviolet Photoelectron Spectra of Mono Metal Atom Encapsulated Fullerenes

Abstract

Ultraviolet photoelectron spectra of mono metal atom encapsulated fullerenes, M@C₈₂ (M = La, Gd and Sc), are measured with a synchrotron radiation light source. When the excitation energy is tuned, spectral intensity oscillation is observed in these mono metal atom encapsulated fullerenes as was in empty fullerene, C₈₂. Their incident photon energy dependence is essentially the same. Their spectra deeper than 5 eV are almost identical and are similar to those of empty fullerene. The noticeable difference among the spectra is in the energy region between the Fermi level and 4 eV, which reveals the degree of electron transfer from the metal atom to the fullerene cage.     

Can Two-Dimensional Fullerene Polymers Be Intercalated?

Abstract

Two-dimensional C₆₀ polymers can be produced by treatment at high T and high p. Attempts have previously been made to intercalate these layered materials by alkali metals using the gas phase method but the polymers have always decomposed. We investigate here whether intercalated 2D polymers can be formed by other methods, such as by polymerization in the presence of alkali metals. Preliminary x-ray and Raman data can be interpreted to indicate the presence of an alkali metal intercalated tetragonal fullerene polymeric structure.     

Structurization of a solvent interacting with fullerene C<Subscript>60</Subscript>

Solutions of fullerene C₆₀ in toluene and p-xylene were investigated by small-angle X-ray diffraction. In all small-angle scattering curves, the scattering intensity decreases to constant value I_C with an increase in the scattering angle. The value of I_C nonmonotonically depends on the fullerene concentration. The radii of gyration of scattering elements were determined by constructing small-angle X-ray diffraction patterns in Guinier coordinates.     

Synthesis and structure of fullerene halides C<Subscript>70</Subscript><Emphasis Type="Italic">X</Emphasis><Subscript>10</Subscript> (<Emphasis Type="Italic">X</Emphasis> = Br,Cl) and C<Subscript>78</Subscript>Cl<Subscript>18</Subscript>

The crystal and molecular structures of the fullerene halides C₇₀Br₁₀ · 3C₆H₂Cl₄, C₇₀Cl_8.4Br_1.6, and C₇₈Cl₁₈ have been determined and refined using single-crystal X-ray diffraction with synchrotron radiation. In the molecular structure of C₇₀ X ₁₀ (X = Br, Cl), ten X halogen atoms are located in the equatorial region of the molecule and form one 1,2 and nine 1,4 contacts in C₆ X ₂ hexagons. The structure of the higher fullerene chloride C₇₈Cl₁₈ contains two isomers with symmetry C _2v , which results in the hexagonal symmetry of the crystal due to disordering.     

Infrared Spectra and Photoinduced Absorption of C60 Doped Polyhexylthiophene

Abstract

We report the IR spectra and the photoinduced absorption of polyhexylthiophene(PHT) doped with C₆₀. The presence of C₆₀ ^?n anions is observed in the IR spectra by a mode at 1383 cm^?1 and a broad electronic transition at 1.2 eV, while most of the C₆₀ molecules stay neutral. This is indicative that for a small fraction of C₆₀ molecules, charge transfer occurs in the ground state.

The photoinduced absorption spectra display a sharp transition at 1.15 eV peculiar to C₆₀ monoanion, the spectral features change with fullerene concentration. The intensity of the polymer photoinduced bands increases 5-10 times due to photoinduced charge transfer to C₆₀.     

Order Parameters and Distribution Function of 4'-(N-(p-Pentyloxy Carbonyloxy-Benzylidene)Amino) Valerophenone in Smectic Phase from X-ray Diffraction Measurements

Abstract

X-ray diffraction studies of 4'-(N (p-pentyloxycarbonyloxy-benzylidene)amino)valerophenone (PCBAV in short) oriented by a magnetic field is reported here. The compound has a smectic A phase which is identified by X-ray studies and texture studies. Orienta-tional order parameters (p ₂) and (P ₄) have been determined from the calculation of f(β), the orientational distribution function. An approximate expression for the angular part of the potential of the mean field is obtained from the temperature variation of the orientational distribution function. The value of d, the layer thickness, and D, the intermolecular distance, have been calculated. An approximate value for the translational order parameter τ₁ and average value of the root mean square displacement ?z²?½ are given. We could not get an accurate estimate of the translational order parameter due to the inaccuracy in the measurement of the intensity of the inner ring.     

NMR and X-ray Investigations of a Plastic Crystalline Phase in MBBA

Abstract

Wideline and high resolution NMR studies have been carried out on MBBA in its isotropic, nematic and solid phases. Isotropic and nematic phase spectra correspond to what has been reported earlier. In the solid phase, contrary to expectations, very intense narrow signals similar to signals of the isotropic phase have been observed for the first time at temperatures close to the solid ? nematic phase transition temperature. This indicates rapid reorientational or translational motion in the system. The X-ray results however confirm the existence of translational order. The results are interpreted as indicative of the existence of a plastic crystalline phase in MBBA.     

On the Structural and Electronic Characteristics of Titanium Sulphide (Tis1.7) Crystals

TiS_1.7 crystals have been grown by vapour transport technique employing a two-zone furnace with the temperatures of reaction and growth zone maintained at 1073 K and 973 K, respectively. We have measured the variation of electrical conductivity (s̀) with temperature (T) of TiS_1.7 single crystals. It has been found that the conductivity increases at temperatures T > 433 K, which provides convincing evidence that the TiS_1.7 crystal is a semiconductor. Another electronic characteristic of TiS_1.7 crystals observed in the present investigation is the occurrence of voltage controlled negative resistance (VCNR) at a field of 32.1 V cm^-1 to 35.7 V cm^-1. All the polytypes of TiS_1.7 were found to exhibit VCNR nearly at the same field which indicates that the VCNR is polytype independent property. The occurrence of VCNR has been explained on the intervally transfer of electrons in the conduction band.     

Glasses and glass-ceramics based on GeSe2–Sb2Se3 and halides for far infrared transmission

New glass compositions have been studied by introducing metallic halides into the well known GeSe₂–Sb₂Se₃ system. Glass forming region and thermo-mechanical properties have been investigated for each added constituent. Nanocrystals with controllable size were reproducibly and homogeneously generated in different glassy matrix with different annealing times and temperatures. We have demonstrated that a controlled crystal growth and a molding process can be combined together. The shaped glass-ceramics are still transparent and show improved mechanical properties.     

High-quality GaMnAs films grown with arsenic dimers

We demonstrate that GaMnAs films grown with As₂ have excellent structural, electrical and magnetic properties comparable or better than similar films grown with As₄. Using As₂, a Curie temperature of 112 K has been achieved, which is slightly higher than the best reported to date. However, more significantly films showing metallic conduction have been obtained over a much wider range of Mn concentrations from 1.5% to 8% than has previously been reported for films grown with As₄. The improved properties of the films grown with As₂ are related to the lower concentration of antisite defects at the low growth temperatures employed.     

The influence of Pb‐ion irradiation on melt‐textured YBa2Cu3Ox crystals

Melt‐textured YBa₂Cu₃O_x crystals have been irradiated along the c‐axis with ²⁰⁸Pb⁵⁶⁺ ions corresponding to dose matching fields, B_Φ = 0.5 T and B_Φ = 2.0 T. Magnetization measurements were conducted along the ab plane of the samples. The strength of pinning sites was investigated by measuring magnetization hysterisis and the saturation remanent magnetization M_R at several temperatures. We have found that the pinning strength was considerably enhanced after irradiation at both doses. Interestingly, the pinning strength at a Pb‐ion irradiation which corresponds to the dose matching field B_Φ = 0.5 T, was found to be significantly larger than that at the dose matching field B_Φ = 2.0 T at all temperatures. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)