CO-DEPOSITION OF FULLERENES AND SULFUR FROM DILUTED SOLUTION

A new method to synthesize fullerene and sulfur compounds has been developed. Using this method, C₆₀S₁₆ and C₇₀S₁₆ compounds were grown from dilute fullerene and sulfur toluene solution. Their atomic structures were analyzed by x-ray diffraction with the single crystal. The C₆₀S₁₆ crystal is C-centered monoclinic structure of a=2.0874 nm, b=2.1139 nm, c=1.05690 nm and β=111.93°, and the C₇₀S₁₆ has a primitive monoclinic, P2₁/c, with lattice parameters of a=1.5271 nm, b=1.49971 nm, c=2.18024 nm and β=109.791°. In this compound, the structure of fullerenes is maintained and sulfur atoms form S₈ rings placed around the fullerenes.     

Growth of C60 single crystal films on metal substrates

High-quality C₆₀(111) single crystal films have been grown on Ni₃Fe(111), Ni₃Co(111) and Ni₃Fe(110) surfaces using hot-wall diffusion method. X-ray diffraction results show that well-ordered films can be obtained near 150°C on these substrates. The high quality of the films could be attributed to the perfect lattice match between C₆₀ film and substrates, low growth rate of C₆₀, and the suitable substrate temperature.     

Computations of metal-covered C60 and C70

Semiempirical quantum-chemical PM3 calculations are reported for a new class of exohedral metallo-fullerenes – metal-coated or metal-covered fullerenes: C₆₀M_n and C₇₀M_n. The exohedral species have been observed in gas phase, however, their geometrical and electronic structures are not known yet. Relatively-even metal-atom distributions over the fullerene rings are considered – such regular forms are computed for M = Be, Mg, Al. Three selected types of stoichiometries are treated in particular: C₆₀M₁₂/C₇₀M₁₂ (metal atoms above all pentagons), C₆₀M₂₀/C₇₀M₂₅ (metal atoms above all hexagons), and C₆₀M₃₂/C₇₀M₃₇ (metal atoms above all rings). If an odd number of electrons should result (Al), the related cation is computed, or one metal atom added or removed. This interesting arrangement above the rings is possible only for some types of atoms, while other elements are localized above bonds or atoms, or inside the cage, or even react and destroy the cage. Other limitation comes from the parametrization of the computational technique used – the PM3 semiempirical method is parametrized only for some selected metals. Metal-layer atomization heats are suggested as a stability measure. Structural characteristics are also presented and interesting reductions of the cage symmetry are found. Their relationship to Jahn–Teller effect is discussed. The metal covered fullerenes can represent models for metal catalysis in the nanotube synthesis and could eventually lead to new interesting materials.     

A three-step process for epitaxial growth of (111)-oriented C60 films on alkali–halide substrates

Epitaxial (111)-oriented C₆₀ films have been grown on alkali–halide substrates, KCl (100), KBr (100) and NaCl (100) by a three-step process: (1), substrate surface cleaning by high temperature heating; (2), initial deposition with a low deposition rate to grow two or three monolayers (ML); and (3), deposition with a high deposition rate to grow a film with expected thickness. It was found that (111)-oriented epitaxial C₆₀ films could be grown at low temperatures in a wide temperature range, from 40 to 120°C. By this three-step process, we can also grow epitaxial C₆₀ films at deposition rates as high as 35 Å/min.     

HMTTEF.C60-A 2-D close-packed layered compound of C60

The analysis of high resolution synchrotron X-ray powder diffraction data of HMTTEF.C₆₀, (HMTTEF = hexamethylenetetratellurafulvalene) gave a triclinic unit cell with a 9.9297 Å, B = 9.9359 Å, C = 13.1472 Å, = 106.966 °, β = 95.887 ° and γ = 118.252 ° in the space group P . Steric considerations suggest that there is a nearly close-packed layer of C₆₀ molecules in the plane, and HMTTEF molecules are sandwiched between layers of C₆₀. The compound is insulating and weakly paramagnetic and the charge-transfer is small.     

Thermal desorption of fullerene C60 from polymer matrices

The data on thermally stimulated desorption (TSD) study of fullerene C₆₀ molecules from different polymer matrices are compared in view of the temperature positions and relative intensities of resolved thermal desorption stages. An increase of the low temperature C₆₀ desorption stages is observed for polydimethylsiloxane (PDMS) and polystyrene (PS) contrary to polyimide (PI). This is in agreement with the difference in glass transition temperatures (T_g) of these polymers. The TSD data allow us to conclude that above T_g of the polymer the solubility of fullerene C₆₀ in PDMS and PS is up to the order of magnitude higher compared with C₆₀ solubility in low molecular weight solvents.     

Phase relations in the Pb-Mo-S ternary system at 1000°C and the superconductivity of PbxMo6S8−y

Lead molybdenum sulfides Pb_xMo₆S_8−y with rhombohedral structure were prepared by vacuum seal technique at 1000°C. The nonstoichiometric range of lead (x) varies between 0.95 and 1.05, and that of sulfur (8−y) varies between 7.55 and 7.80. On the basis of these results and preparing some mixed compounds, the phase diagram of Pb-Mo-S system at 1000°C was established. The compositional dependence of the rhombohedral lattice parameters a_R and _R and that of the superconducting critical temperature Tc of the single phase of Pb_xMo₆S_8−y have been examined. It was difficult to find out the compositional dependence of a_R and _R and that of Tc, because of the narrow ranges of the nonstoichiometry. Among the nonstoichiometric compounds, Pb_0.95Mo₆S_7.55 shows the highest Tc (Tc−ON=15.5K, Tc−END=13.9K). From the measurement of normal state resistivity, all the compounds of the Pb_xMo₆S_8−y showed the properties of metallic condoctors.     

Solubility of Fullerene C60 and C70 in Toluene, o-Xylene and Carbon Disulfide at Various Temperatures

The solubilities of fullerene C₆₀ and C₇₀ in toluene, o-xylene and carbon disulfide between the melting point and boiling point of the solvents, respectively, have been measured. The temperature dependent solubility of C₆₀ displays anomalous behaviors. A solubility maximum of C₆₀ around 0 °C for toluene and carbon sulfide and around 30 °C for o-xylene was observed. The temperature-dependent solubility of C₇₀ behaves normally for all the three solvents studied.     

Photoconductivity, photovoltaic effect and photoluminescence in chemically deposited films of (Cd0.95–Pb0.05)S:CdCl2,Gd

Results of XRD, optical absorption spectra, photoconductivity, photovoltaic effect and photoluminescence are reported for (Cd_0.95–Pb_0.05)S:CdCl₂,Gd films prepared by chemical deposition technique at 60 °C and room temperature (RT). The XRD studies show prominent diffraction lines of CdS and PbS. Optical absorption spectra show direct bandgap nature with decreasing value due to addition of PbS. The saturated photocurrent (I_pc) to dark current (I_dc) ratios 10⁷ are found in films prepared at 60 °C and 10⁴ in films prepared at RT. Photoluminescence is found to be brighter in films prepared at RT. Photovoltaic efficiency 5% has been observed in such films.     

A STUDY ON THE THERMAL STABILITY TO 1000°C OF VARIOUS CARBON ALLOTROPES AND CARBONACEOUS MATTER BOTH UNDER NITROGEN AND IN AIR

The thermal behavior of graphite, C₆₀ fullerene, fullerene black (carbon soot containing fullerenes), extracted fullerene black and diamond has been analyzed to 1000°C by TGA-DTA (thermogravimetric analysis and differential thermal analysis) under a nitrogen flow at a heating rate of 20°C/min. Very small weight losses have been recorded in the case of graphite and diamond. Furthermore no diamond graphitization has been observed. The sublimation of pure C₆₀ and the fullerene fraction of fullerene black (both pristine and extracted) has been observed and discussed.

The combustion reaction in air flow of graphite, C₆₀ and C₇₀ fullerenes, fullerene black (both unextracted and extracted), carbon nanotubes and diamond has been studied by TGA-DTA at a heating rate of 20°C/min. C₇₀ fullerene and fullerene black have been found to be the most reactive carbon materials with O₂. The role played by C₇₀ in the degradation of fullerites has been discussed. Among the carbon materials examined, the best resistance to O₂ attack has been shown by diamond and carbon nanotubes. The behavior of graphite is intermediate between diamond and fullerene blacks. The behavior of C₆₀ fullerene appears closer to that of graphite although it appears to be more reactive with O₂. Samples of graphite and carbon blacks N375 and N234 have been studied by TGA-DTA in air flow before and after a radiation treatment with neutrons or γ radiation. The effect of the radiation damage in the combustion reaction of these carbon materials has been discussed.     

化学气相沉积法制备二维Cr_(2)S_(3)纳米片及其磁性研究EI北大核心

以三氯化铬和硫粉为原料,采用常压化学气相沉积法(CVD)成功制备出了二维Cr_(2)S_(3)纳米片,并对Cr_(2)S_(3)纳米片表面形貌、晶体结构、宏观磁性等进行系统研究。结果表明:二维Cr_(2)S_(3)纳米片光学形貌以三角形为主,尺寸最大可达到156.8μm,厚度最小为2.59 nm(约2个单元晶胞厚);晶体结构为菱方相结构,类似于单斜NiAs型晶体结构;磁性测试表明:菱方相的二维Cr_(2)S_(3)低温下呈亚铁磁性,面内为磁易轴方向,其奈尔温度约等于120 K,75 K时饱和磁化强度最大;在空气中放置1个月后二维Cr_(2)S_(3)纳米片依然保持较好的磁性性能,是一种环境稳定的二维磁性材料。     

Systematic search for energetically favored isomers of large fullerenes C122–C130 and C162–C180

Based on the methodology by Cioslowski et al. [J. Cioslowski, N. Rao, D. Moncrieff, J. Am. Chem. Soc. 122 (2000) 8265–8270], two empirical fit equations to predict the standard enthalpy of formation are obtained over large number of calculation results at B3LYP/6-31G* theory level for fullerene isomers, which can be used as a preliminary and second-level screening tool, respectively, for large fullerenes. By applying these equations in screening the whole isolated pentagon rule (IPR) isomers, the energetically favored isomers of large fullerenes C₁₂₂–C₁₃₀ and C₁₆₂–C₁₈₀ were predicted at the B3LYP/6-31G* density functional theory level for the first time. Our results show that the lowest energy isomers of C₁₇₄ (2473259: C_3v) and C₁₈₀ (4071832: I_h) possess much lower relative energy and larger HOMO–LUMO gaps. Moreover, the ionization energy and electron affinity of the lowest energy isomers were also investigated.     

Optical and electrical properties of p-type AgInSnxS2−x (x = 0–0.04) thin films prepared by spray pyrolysis

AgInSn_xS_2−x (x = 0–0.2) polycrystalline thin films were prepared by the spray pyrolysis technique. The samples were deposited on glass substrates at temperatures of 375 and 400 °C from alcoholic solutions comprising silver acetate, indium chloride, thiourea and tin chloride. All deposited films crystallized in the chalcopyrite structure of AgInS₂. A p-type conductivity was detected in the Sn-doped samples deposited at 375 °C, otherwise they are n-type. The optical properties of AgInSn_xS_2−x (x < 0.2) resemble those of chalcopyrite AgInS₂. Low-temperature PL measurements revealed that Sn occupying an S-site could be the responsible defect for the p-type conductivity observed in AgInSn_xS_2−x (x < 2) thin films.     

He Ion Bombardment of C70 Fullerene: An FT-IR and Raman Study

C₇₀ fullerene films deposited on a silicon substrate have been bombarded with He⁺ ions at 30 keV at room temperature in vacuum. The structural changes undergone by C₇₀ have been followed by both FT-IR and Raman spectroscopy. The results have been compared to the behavior of C₆₀ fullerene and discussed in an astrochemical context. The main conclusion is that C₇₀, contrary to C₆₀, does not form oligomers at low radiation dose but it is directly and gradually degraded to amorphous carbon (carbon black).     

MoS2/Sb2S3复合光催化剂的制备及其可见光催化性能

通过一步水热法制备出MoS₂/Sb₂S₃可见光复合催化剂,采用XRD、SEM、紫外可见漫反射（UV-Vis DRS）和XPS表征手段对MoS₂/Sb₂S₃复合光催化剂进行了表征,以罗丹明B（RhB）作为目标污染物进行降解实验。与纯Sb₂S₃和MoS₂相比,MoS₂/Sb₂S₃复合光催化剂对RhB的光催化降解具有更高的效率,表现出优异的吸附性能和光催化性能。同时在相同的实验条件下,与TiO₂、Bi₂S₃、C₃N₄、Sb₂S₃等催化剂相比,MoS₂/Sb₂S₃复合光催化剂表现出更为优异的光催化性能。此外,探究了MoS₂/Sb₂S₃复合光催化剂光催化降解机制,阐述了光催化反应机制,提供了一种适用于降解较高浓度有机废水的光催化剂制备方法,具有一定的应用价值。      

Pyrolytic Trifluoromethylation of [76]-, [78]-, [84]-, and Aza[60]Fullerenes with Silver Trifluoroacetate; Evidence for Coordination of Fullerenes to Silver

Pyrolytic trifluoromethylation of [76], [78], [84], and aza[60]fullerenes with silver trifluoroacetate at 300°C results in extensive polyaddition of up to 18, 18, 20 and 20 CF₃ groups, respectively. In contrast to trifluoromethylation of [60]- and [70]fullerenes that give a full range of derivatives ranging upwards from C_n(CF₃)₂, [76]-, [78]-, and [84]-fullerenes only give C_n(CF₃)_6-18 derivatives, largely in the 10-12 CF₃ range; reaction with [76]fullerene is accompanied by formation of C₆₀(CF₃)₆ attributed to cage fragmentation. For aza[60]fullerene the hexa-addition level dominates, in contrast to its other reactions which give predominantly penta-addition products. All the compounds showed peaks at 1256±2 and 1180-1190 cm^-1, due to the CF₃ group, and peaks in this region are shown also by the soluble extract obtained on trifluoromethylation of nanotubes. As in trifluoromethylation of [60]- and [70]-fullerenes, the products obtained initially are involatile, attributed to formation os silver complexes; these are decomposed on subsequent solution in toluene. Mixed isomeric trifluoromethylated C₆₀F₈ derivatives viz. C₆₀F₇CF₃, C₆₀F₆(FG₃)₂, C₆₀F₅(CF₃)₃ and C₆₀F₄(CF₃)₄, and C₆₀F₄CF₃CF₂CF₃ (a C₆₀F₆ derivative) have been isolated from fluorination of [60]fullerene with MnF₃/K₂NilF₆ at 510°C.     

Preparation of porous CdIn2S4 photocatalyst films by hydrothermal crystal growth at solid/liquid/gas interfaces

A chemical method has been used to prepare highly crystalline porous CdIn₂S₄ photocatalyst films at low temperature on a glass substrate. The conversion of cadmium and indium salts with thiourea on CdIn₂S₄ powder particles into CdIn₂S₄ has been achieved via hydrothermal reaction, which acts as a “glue” to connect the original CdIn₂S₄ particles chemically thus forming a mechanically stable photocatalyst film.     

Study of microstructure of epitaxial fullerenes films

A comprehensive study was made on the structure of epitaxial thin films of C₆₀ and C₇₀ by means of transmission electron microscopy. Both the films show similar face-centered cubic structure and are epitaxial on (001) mica with close-packed plane parallel to the substrate surface. Two main kinds of defects-stacking faults and twins-were observed and are discussed. The effect of the remaining C₇₀ impurity on the crystal orientation of C₆₀ films was studied by comparing different samples made from high-purity fullerene and C₆₀/C₇₀ mixtures. The results show that there is a higher density of planar defects in the films containing larger amounts of impurities: moreover, some faint anomalous reflections located at so-called 2a₀ fcc reciprocal lattice points were also detected, probably as a result of C₇₀ contamination. Finally, it is found that stacking disorders can be easily increased by keeping the high-quality pure C₆₀ film in air at room temperature for a few weeks, implying the instability of the crystal orientation of the epitaxial fullerene films.     

Fullerane, the Hydrogenated C60 Fullerene: Properties and Astrochemical Considerations

Hydrogenated C₆₀ fullerene, C₆₀H₃₆ was prepared in different solvents using Zn/HCl as reducing agents. The structure of C₆₀H₃₆ was confirmed both by electronic and FT-IR spectroscopy and the purity of the reaction product was checked by HPLC analysis. It has been confirmed that C₆₀H₃₆ is not stable in air, especially in presence of light which enhances the oxidation. The oxidation of C₆₀H₃₆ was studied by FT-IR spectroscopy and by differential scanning calorimetry (DSC) in air; the formation of hydroxyl groups on the fullerene cage and ketonic groups (involving cage breakdown) have been detected. Furthermore, the action of O₃ on C₆₀H₃₆ was investigated and it has been found that O₃ exerts practically the same effect of air but causing an enhanced cage breakdown. The thermal stability of C₆₀H₃₆ was checked by a thermogravimetric analysis (TGA) coupled with a differential thermal analysis (DTA) under N₂ flow. The vaporization of C₆₀H₃₆ occurs at very high temperature: the DTA trace has shown an endothermic peak at 540°C (at a heating rate of 20°C/min). C₆₀H₃₆ shows an electronic absorption spectrum with a maximum at about 217 nm and it is able to match both in position and in half width the peak at 217.5 nm observed in the spectrum of the interstellar extinction of light which was attributed to hydrogenated, radiation processed and thermally annealed carbon dust. Similarly, the absorption spectrum of C₆₀H₃₆ is able to match several infrared emission bands (called UIBs) detected from certain astrophysical objects like the protoplanetary nebulae (PPNe). It is proposed that hydrogenated fullerenes can be used as model compounds in the laboratory simulation studies of interstellar carbon dust.     

THE ELUSIVE C60S: THREE ATTEMPTED SYNTHESES

Results of semiempirical energy calculations suggested that a [6,6]-closed C₆₀S fullerene sulfide might be stable. Attempts were therefore undertaken to synthesize the compound by UV photolysis of C₆₀ in CS₂ and by the heating of mixtures of C₆₀ and S₈ to 325 and 400°C. Any sulfide, if formed, was present in undetectably small quantities. However, [¹²C₆₀³⁴S]^- ions were observed when a mixture of solid C₆₀ and elemental sulfur was analyzed by Laser Desorption Ionization Time-of-Flight mass spectrometry.