Synthesis of Lanthanofullerenes by Laser Ablation Using Pulsed and CW-Nd:YAG Lasers

Endohedral lanthanum fullerenes, La@C₆₀, La@C₈₂ and La₂C₈₀, were synthesized by ablation of graphite and La₂O₃ in flowing Ar buffer gas with a 1064 nm beam from a pulsed-Nd: YAG laser in which the graphite was heated by the CW-Nd:YAG laser up to 2500 °C. The La-fullerenes were also prepared by laser ablation of a lanthanum-graphite composite rod. The extractant fullerenes from the carbon soot were analyzed by laser-desorption time of flight mass spectrometry (LD-TOF MS). The relative yield of La@C₈₂, increased with increasing temperature of the rod in the range of 700-2300 °C.     

On the Evaporation of C60 in Vacuum and Inert Gases at Temperatures Between 830 K and 1050 K

The binary diffusion coefficient D_AB of subliming C₆₀ in He, N₂ and Ar gas has been determined at a gas pressure between 5 and 10 kPa. It resulted D_AB/(cm^2/s)=D_o(P_o/P_t(T/T_o)ⁿ as a function of the total pressure P_t of the vapor phase and temperature T. At T_o=273 K and P_o=1.0133×10⁵ P_a, the values D_o = (0.059±0.004) cm²/s, (0.011±0.003) cm²/s, (0.012±0.007) cm²/s, n = 1.77±0.06, 2.02±0.18, 1.77±0.37 were obtained for He, N₂, Ar and (830-1000) K, (800-1020) K, (875-1095) K, respectively. Only 40 wt% of the initial C₆₀ material yielded reliable D_AB where the vapor pressure of C₆₀ followed log₁₀(P/Pa) = -(8976±60)/T/K+(11.05±0.07) for T between 640 and 1055 K.     

Investigation of Iron-Fullerene Mixture Plasmas in ECR Discharge

Fullerene+iron (C₆₀+Fe) mixture plasmas were produced and studied in the ECR ion source of ATOMKI. The two main components of the plasma were obtained by different filament ovens. In this series of measurements we concentrated on the maximum ratio of C₅₈ (damaged fullerene) in the plasma. C₅₈ is less stable than C₆₀ and the probability to form new materials is higher. Using this method we produced molecules of mass M=752 both in single- and double-charged states with beam intensities of 8 · 10^-10A and 2 · 10^-10A, respectively. We identified this beam as a mixture of FeC₅₈, O₂C₆₀ and CO₂C₅₉, while the experiment did not give information on the exact location of the iron and oxygen in the carbon ball.     

Carburization performance of Incoloy 800HT in CH4/H2 gas mixtures

Carburization performance of Incoloy 800HT has been studied after cyclic and isothermal exposures to CH₄/H₂ carburizing gas mixtures at high temperatures for 500 h. At 800 °C in 2% CH₄/H₂, Incoloy 800HT suffered external oxidation and carburization, the external continuous layer of reaction products consists primarily of Cr₇C₃, Mn_1.5Cr_1.5O₄, and FeCr₂O₄ with Fe(Cr, Al)₂O₄ as a minor phase. At 1100 °C in 10% CH₄/H₂, external carburization did not occur likely due to high carbon dissolution in the alloy substrate at this temperature. A thermodynamic analysis indicated that 1000 °C was an approximate critical temperature, below which the environment should result in mixed oxidizing/carburizing behavior, while above this temperature reducing carburizing behavior should occur. The experimental results approximately agree with the thermodynamic analysis. Metal dusting was not observed under highly carburizing conditions (a_C>1). The size and morphology of Cr-rich phases (or Cr-carbides) are both temperature- and time-dependent, while the external continuity is more temperature-dependent rather than time-dependent.     

Thermolysis and Photolysis of C60 Diozonides

Ozonation of C₆₀ in o-xylene produced three C₆₀(O₃)₂ diozonides that were separated from one another and from two C₆₀(O₃)₃ triozonides by High Performance Liquid Chromatography (HPLC). Upon thermolysis at 10, 15, and 16.6°C, each of the diozonides dissociated sequentially, first to a C₆₀O(O₃) oxyozonide, then to a C₆₀O₂ diepoxide. The three diepoxides were stable in solution for at least 3 weeks. The mean lifetimes of the three diozonides were 52 ± 5, 62 ± 6, and 17.3 ± 1.8 min, respectively (all at 15°C). The mean lifetimes of the three oxyozonides were 69.7 ± 0.7 and 58 ± 6 min at 16.6°C, respectively and about 240 min at 10°C. Photolysis of the diozonides yielded two dioxidoannulenes with UV-Vis adsorption maxima at 333 and 332 nm, and what appeared to be an epoxide-oxidoannulene with UV-Vis adsorption maximum at 327 nm. These annulenes were observed to form dimers. We have synthesized and characterized six C₆₀O₂ dioxides, at least three and possibly four of which were hitherto unknown. We report the discovery of oxyozonides that form during the dissociation of diozonides.     

Structural Characterization of the New Fullerene-Rare Gas Compound Ar1C60

Abstract

We communicate how C₆₀ Hot Isostatically Pressed (HIPed) at 200° or 400°C with a pressure of 1.7 kbar of Ar produces the new fullerene-rare gas compound Ar₁C₆₀. We have shown, using Xray powder diffraction and subsequent Rietveld analysis, that this solid can be characterised stoichiometrically as Ar₁C_60- The stoichiometry has also been confirmed by thermal gravimetric analysis (TGA) showing 5% by weight to be Ar (expected=5.25%). The presence of Ar is confirmed by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). This material is found to be remarkably stable to loss of Ar over several weeks at room temperature. This represents the first full characterisation of an interstitial rare gas fullerene compound.

     

Magnetic Properties of Some Fullerene Compounds

Magnetic properties of some fullerene intercalation compounds are detailed. A few examples are presented including properties of 1) Acceptors: MoF₆ From magnetic measurements the existence of positively charged C₆₀ (C₆₀⁺) can be inferred 2) Donnors: Yb_xC₆₀ and Eu₃C₆₀ compounds. Magnetic properties of (Yb_xC₆₀) are dominated by crystal field effects. A high field magnetic transition (17 T at 4 K) occurs in Eu₃C₆₀ associated with a large hysteresis of the magnetization and relaxation effects. This complex magnetic behaviour is attribued to Eu²⁺.     

Amorphous Ni---N---W film as a diffusion barrier between aluminum and silicon

The influence of nitrogen on the diffusion barrier properties of amorphous Ni---W films was studied. Nitrogen was introduced into the amorphous Ni---W film by co-sputtering nickel and tungsten in a premixed gas mixture of 90% Ar and 10% N₂, resulting in the formation of amorphous Ni₃₀N₂₁W₄₉ film. X-ray analysis indicates a detectable crystallization of the amorphous film after 30 min annealing in vacuum at 600°C, accompanied by the formation of W₂N, but backscattering spectrometry (BS) reveals a reaction with silicon only at about 725°C. The Schottky barrier height of this amorphous film on n-Si is stable for 30 min annealing up to at least 550°C. With an aluminum overlayer, BS indicates that an amorphous Ni₃₀N₂₁W₄₉ film effectively prevents the metallurgical interaction between aluminum and silicon for 30 min up to 600°C. The Schottky barrier height of that contact configuration is also stable up to at least 550°C, suggesting that amorphous Ni---N---W films have attractive features as diffusion barriers.     

Corrosion resistant coatings (Al2O3) produced by metal organic chemical vapour deposition using aluminium-tri-sec-butoxide

The metal organic chemical vapour deposition (MOCVD) of amorphous alumina films on steel was performed in nitrogen at atmospheric pressure. This MOCVD process is based on the thermal decomposition of aluminium-tri-sec-butoxide (ATSB). The effect of the deposition temperature (within the range 290–420 °C), the precursor vapour pressure (5.33×10^-3−2.67×10^-2 kPa), and the gas flow (6.5−12.5 1 min^-1) of the MOCVD process have been studied in relation to corrosion properties at high temperatures. The corrosion experiments were performed at 450 °C in a gas atmosphere containing 1% H₂S, 1% H₂O, 19% H₂, and balanced Ar.

It was found that the amount of corrosion products on an alumina film (0.20±0.05 mg cm^-2)-AISI 304 combination decreased with increasing deposition temperature of the coating. This was more pronounced for the products formed through the coating owing to a certain porosity. The crack density, where products were also formed, was almost unaffected.     

Kinetics of Carbon Multi-wall Nanotube Synthesis by Catalytic Pyrolysis of Methane

By method of isothermal gravimetry at 600-700°C, CH₄ concentration 32-100% in Ar and 91-100% in H₂ under atmospheric pressure the kinetics of CH₄ pyrolysis under Ni/La₂O₃ catalysts is studied. Estimated apparent activation energy of reaction is 73 kJ/mol for fresh catalyst and 71 kJ/mol for aged one. The reaction order on CH₄ changes from 1.05 at 600°C to 1.3 at 700°C. The influence of H₂ concentration on the reaction rate is more complicated. On the basis of kinetics measurements continuously working laboratory-scale reactor with gas and catalyst counter-flow is constructed and tested.     

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.     

Recrystallization in a directionally solidified cobalt-base superalloy

The recrystallization behavior in a range of annealing temperature from 1020 to 1280 °C in a directionally solidified cobalt-base superalloy was studied. Local recrystallization first appeared at 1040 °C. The recrystallized volume increased rapidly as increasing the annealing temperature. Pinning effect of all carbides (M₂₃C₆, M₇C₃ and MC) was observed and large amount of twin formed at low annealing temperature. The size of the recrystallized grains increased significantly at high annealing temperatures accompanied with the sharp decrease of twin. The effect of annealing temperature and the role of carbide and twin on the development of the recrystallization were discussed.     

Stresses in sputtered RUOx thin films

RuO_x thin films have been deposited by reactive sputtering in an O₂/Ar atmosphere. The films were characterized for their stress and resistivity as a function of deposition temperature (room temperature, 300°C) and the O₂ content (25–100%) in the sputtering gas. Additionally, the stresses in these films were determined as a function of annealing temperature (up to 600°C) using an in-situ curvature measurement technique. The as-deposited films were found to be under a state of compressive stress for all deposition conditions. The compressive stresses sharply increased with increasing deposition temperature from a value of around 200 MPa at 200°C to 1400 MPa at 300°C. This dramatic increase has been attributed to differences in microstructure at these deposition temperatures. The microstructural differences also led to the widely differing stress-temperature behavior during annealing of these films. For films deposited at temperatures lower than 200°C, the annealing process resulted in a decrease in the compressive stress and resistivity of the films. However, films deposited at a temperature of 300°C did not show any changes in the compressive stress or resistivity after annealing. The results of this study can be used to deposit RuO_x thin films with low resistivity and minimal stresses.     

Characterization of indium zinc oxide thin films prepared by pulsed laser deposition using a Zn3In2O6 target

Using a Zn₃In₂O₆ target, indium-zinc oxide films were prepared by pulsed laser deposition. The influence of the substrate deposition temperature and the oxygen pressure on the structure, optical and electrical properties were studied. Crystalline films are obtained for substrate temperatures above 200°C. At the optimum substrate deposition temperature of 500°C and the optimum oxygen pressure of 10⁻³ mbar, both conditions that indeed lead to the highest conductivity, Zn₃In₂O₆ films exhibit a transparency of 85% in the visible region and a conductivity of 1000 S/cm. Depositions carried out in oxygen and reducing gas, 93% Ar/7% H₂, result in large discrepancies between the target stoichiometry and the film composition. The Zn/In (at.%) ratio of 1.5 is only preserved for oxygen pressures of 10⁻²–10⁻³ mbar and a 93% Ar/7% H₂ pressure of 10⁻² mbar. The optical properties are basically not affected by the type of atmosphere used during the film deposition, unlike the conductivity which significantly increases from 80 to 1400 S/cm for a film deposited in 10⁻² mbar of O₂ and in 93% Ar/7% H₂, respectively.     

Preparation of Pt-PtOx thin films as electrode for memory capacitors

Pt-PtO_x thin films were prepared on Si(100) substrates at temperatures from 30 to 700°C by reactive r.f. magnetron sputtering with platinum target. Deposition atmosphere was varied with O₂/Ar flow ratio. The deposited films were characterized by X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy. Resistively of the deposited films was measured by d.c. four probe method. The films mainly consisted of amorphous PtO and Pt₃O₄ (or Pt₂O₃) below 400°C, and amorphous Pt was increased in the film as a deposition temperature increased to 600°C. When deposition temperature was thoroughly increased, (111) oriented pure Pt films were formed at 700°C. Compounds included in the films strongly depended on substrate temperature rather than O₂/Ar flow ratio. Electrical resistivity of Pt-PtO_x films was measured to be from the order of 10⁻¹ Ω cm to 10⁻⁵ Ω cm, which was related to the amount of Pt phase included in the deposited films.     

Morphological changes induced by thermal anneals in NiFe/Ag multilayers; their relation to the resistive and magnetoresistive properties

(Ti, Al)N films have drawn much attention as alternatives for TiN coatings, which are oxidized easily in air above 500 °C. We have investigated the effect of Al content on the oxidation resistance of (Ti_{1 − x}Al_x)N films prepared by r.f. reactive sputtering.

(Ti_{1 − x}Al_xN films (O ≤ x ≤ 0.55) were deposited onto fused quartz substrates by r.f. reactive sputtering. Composite targets with five kinds of Al-to-Ti area ratio were used. The sputtering gas was Ar (purity, 5 N) and N₂ (5 N). The flow rate of Ar and N₂ gas was kept constant at 0.8 and 1.2 sccm, respectively, resulting in a sputtering pressure of 0.4 Pa. The r.f. power was 300 W for all experiments. Substrates were not intentionally heated during deposition. The deposited films (thickness, 300 nm) were annealed in air at 600 900 °C and then subjected to X-ray diffractometer and Auger depth profiling.

The as-deposited (Ti_{1 − x}Al_x)N films had the same crystal structure as TiN (NaCl type). Al atoms seemed to substitute for Ti in lattice sites. The preferential orientation of the films changed with the Al content of the film, x. Oxide layers of the films grew during annealing and became thicker as the annealing temperature increased. The thickness of the oxide layer grown on the film surface decreased with increasing Al content in the film. For high Al content films an Al-rich oxide layer was grown on the surface, which seemed to prevent further oxidation. All of the films, however, were oxidized by 900 °C annealing, even if the Al content was increased up to 0.55.     

Elaboration, microstructure and reactivity of Cr3C2 powders of different morphology

Cr₃C₂ powders have been prepared by heat-treatment of metastable chromium oxides of controlled morphology in H₂---CH₄ atmosphere. Starting with these highly reactive oxides allows formation of Cr₃C₂ at 700 °C. The reaction is pseudomorphic and different grain shapes (needles, rods, spheres and polyhedra) have been obtained. The size distribution is narrow and the grain size is generally of the order of a few tens of micrometers, but the “spheres” are in fact made up of aggregates of small platelets about 1.5 μm wide and 0.7 μm thick. The oxidation in air of the carbides was studied by thermal analyses (TGA, DTG and DSC) and was found to proceed in four steps in the 250–700 °C range. The differences observed between the carbides are related to their morphology and texture.     

Novel soft solution synthesis and characterization of submicromic LiCoVO4

A novel soft solution process has been used to prepare LiCoVO₄ by reacting Co(CH₃CH₂COO)₂, Li₂CO₃, NH₄VO₃ and citric acid. LiCoVO₄ powders were successfully prepared at as low as 450 °C in 4 h. Compared to the solid-state reaction processes, the soft solution process greatly reduced the temperature and the time for preparing LiCoVO₄. The inverse spinel structure and high crystallinity of the synthesized product has been confirmed by X-ray diffraction. Thermal analysis proves that the phase formation of the compound occurs at about 450 °C. The results of the IR investigations show that the band located at 820 cm⁻¹ corresponds to the stretching vibration mode of VO₄ tetrahedron with the A symmetry. SEM examination reveals a spherical grain distribution, the average particle size being typically lower than 1 μm. The quantitative result from ICP-AES analysis is Li_0.967Co_0.994VO₄.     

Preparation and characterization of C60S16 and C70S48 thin films

In this study, we have investigated different methods for preparation of thin films of C₆₀ and C₇₀-sulfur compounds. Films of good quality were obtained by reaction of amorphous C₆₀ and C₇₀ films with a saturated sulfur solution in toluene at 40°C or with saturated sulfur vapour at a temperature of 140°C for several hours. The quality of the fullerene-sulfur films were strongly dependent on the microstructure of the initially deposited fullerene film and the synthesis temperature. X-ray diffraction analyses showed that both methods lead to the formation of films consisting of C₆₀S₁₆ and C₇₀S₄₈ (space groups C 2/c and Amm2, respectively). C₆₀S₁₆ films synthesised on Al₂O₃(012) and Si(100) substrates were texture-free while C₇₀S₄₈ films typically exhibited a preferential (100) orientation. The films were also characterised by Raman and IR- spectroscopy, which confirmed that the interactions between the fullerene molecules and the S₈ rings are weak. The fullerene-sulfur compounds were found to be unstable at high vacuum conditions. Both materials C₆₀S₁₆ and C₇₀S₄₈ are non-conductive at room temperature with conductivities less then 10⁻⁵ (Ω/cm).     

On the Nature of Interaction Between Fullerene and Aniline

Interaction between fullerene C₆₀ and N,N-dialkyl-substituted anilines was studied by gas-liquid chromatography (GLC) and titration calorimetry. The GLC study was performed at 140-200°C in the poly(tetramethylbenzene) solvent with ultra-high solubility of C₆₀. No interaction of the C₆₀-aniline type was registered under such conditions. Calorimetric titration performed at 25°C in a non-aromatic solvent confirmed the lack of complex formation. Minute exoeffect registered is explained by suppressing of the rotation motion of the C₆₀ molecules accompanied by energy dissipation for the aniline environment.