Trapping of solvent by a C60 fullerene film

Mass spectrometry was used over a wide temperature range to compare processes of solvent (toluene) release and desorption of C₆₀ fullerene molecules from a fullerite film formed from solution on an oxidized metal substrate. It is shown that toluene is strongly retained in the fullerite film and that it is almost impossible to remove the toluene from the film without damaging its structure. Quantitative characteristics of the toluene retention and trapping effect are determined. Pis’ma Zh. Tekh. Fiz. 24, 23–29 (December 12, 1998)     

Analysis of metallofullerenes using a mass reflectron

A high-resolution mass reflectron has been used to analyze an extract of a fullerene mixture containing the metallofullerene Gd@C₈₂. It is shown that various metallofullerenes can be analyzed by means of thermal desorption followed by electron impact ionization. The C₆₀, C₈₂, and Gd@C₈₂ ion currents are obtained as functions of the evaporation temperature. Doubly charged (Gd@C₈₂)²⁺ metallofullerene ions are identified in the mass spectra. Pis’ma Zh. Tekh. Fiz. 24, 1–5 (March 12, 1998)     

Using C60 molecules for deep carbonization of rhenium in ultrahigh vacuum

The adsorption of C₆₀ molecules on the surface of a rhenium ibbon heated to 1800 K is investigated quantitatively. It is found that the C₆₀ molecules are adsorbed without reflection and then dissociate, and the carbon formed in the process is dissolved in the bulk of the rhenium to the limit of solubility. Then a graphite monolayer forms on the rhenium surface, and the dissociation of the C₆₀ molecules stops. It is shown that the C₆₀ molecules can be used as an effective carbonizing object on metals in ultrahigh vacuum. Pis’ma Zh. Tekh. Fiz. 23, 26–30 (December 12, 1997)     

Ab Initio Quantum Chemical Methods for Investigations of Fullerene C60, CS2 and Tetrathiafulvalene Molecules and Their Complexes

Abstract

Geometry and energy of formation of single molecules: fullerene C₆₀, CS₂ and tetrathiofulvalene (TTF) and their complexes: C₆₀ +CS₂ and C₆₀ +TTF were obtained using Hartree-Fock (HF) and Density Functional Theory methods in various basis sets. Weak chemical interactions were estimated enough well using HF/6-31G for a comparison of various geometrical conformations of these complexes. Energy of formation evaluation in charge-transfer complex C₆₀ +TTF is performing additionally calculating complex with far-separated molecules.     

Mass-spectrometric investigation of the thermal stability of polymethyl methacrylate in the presence of C60 fullerene

The thermal degradation of polymethyl methacrylate, synthesized by the method of free-radical polymerization, in a mixture with C₆₀ fullerene has been investigated by mass-spectrometric thermal analysis. C₆₀ suppresses the first two, low-temperature, stages in the thermal degradation of polymethyl methacrylate and thereby increases its thermal stability. Pis’ma Zh. Tekh. Fiz. 23, 81–85 (September 26, 1997)     

Effect of C60 on the thermal stability of polyethylene glycol grafted to it

The thermal degradation of regular polymer networks, cross-linked by C₆₀ molecules along the end groups of polyethylene glycol, has been investigated by mass-spectrometric thermal analysis for the example of polyethylene glycol grafted to fullerene C₆₀. The character of the thermal degradation of the networks is substantially different from that of free polyethylene glycol and other polymer systems investigated earlier. The grafting to C₆₀ increases the thermal stability of polyethylene glycol. Pis’ma Zh. Tekh. Fiz. 23, 19–24 (September 26, 1997)     

Nature of the anomalous dispersion of particles in fullerite-alkali-metal-halide composites

The occurrence of a solid-phase reaction between powders of the fullerite C₆₀ and potassium halides under the conditions of mechanical grinding is established. The electrostatic potential and surface-active properties of C₆₀ molecules are considered as causes of the anomalously high degree of dispersion of the particles within a composite. Pis’ma Zh. Tekh. Fiz. 25, 45–49 (April 26, 1999)     

Characterization of Fullerenes Obtained from Boron Nitrite Containing Graphite Electrodes: Electronic Structure of C60-X-YBXNY and Deformed C60

Abstract

The electronic structure of C₆₀ molecules with carbon substituted by other elements such as boron or nitrogen has been calculated for molecules in the singlet state with even number of electrons. Therefore, in the case of boron and nitrogen substituents, calculations have been performed for ionized molecules. The results obtained from our density functional calculations prove than in the C_60-x-yB_xN_y molecules both HOMO and LUMO levels are split due to the lower symmetry of the molecule Influence of deformation of C₆₀ molecules on electronic states, which is interesting because fullerenes may undergo deformation in solvate crystals, is also shown These C₅₉B and C₅₉N, as well as C₅₈BN molecules are of special interest because samples containing such species can be prepared The Electron Spin Resonance (ESR) in those samples differs from the results obtained in pure C₆₀ samples, it consists of several lines which are very sensitive to the temperature.     

Thermodesorption states of fullerene C60 in the polyimide-fullerene system

The data of thermodesorption mass spectrometry indicate that fullerene C₆₀ molecules are desorbed from a polyimide (PI) surface at temperatures below the PI decomposition onset temperature, while the desorption of C₆₀ from the bulk begins in the temperature region of the polymer decomposition. It is suggested that strong chemical bonds between C₆₀ and PI macromolecules are formed in the bulk in the stage of the polyamic acid preparation and are broken upon destruction of the polymer macromolecules. The character of C₆₀ thermodesorption from the PI surface depends on thickness of the surface film of fullerene C₆₀.     

Enhancement of the quantum efficiency of radiative recombination of the fullerene C70 in a toluene solution

An investigation of the spectra and quantum efficiency of photoluminescence provided direct evidence of the presence of C₇₀ aggregates in a toluene solution. Toluene solutions of C₆₀ and C₇₀ in the proportion 1 g/l and artificial mixtures of these were studied. The hypothesis is put forward that mixed aggregates of C₆₀ and C₇₀ exist. Pis’ma Zh. Tekh. Fiz. 24, 70–75 (November 26, 1998)     

Study of Undersaturated C60 Solutions in Cs2 by Small Angle Neutron Scattering

Abstract

We measured precisely, using the Small Angle Neutron Scattering (SANS) technique, the radius of the carbon nuclei shell of the C₆₀ molecule, in spite of its small value. For this purpose, controlled undersaturated solutions of C₆₀ in CS₂, where theC₆₀ molecules are individually distributed, were studied in the room temperature range. Absolute measurements also allowed us to extract from the contrast in scattering length the partial molecular volume of the molecule C₆₀ in solution in CS2.     

Electric-field-controlled memory effect in heterostructures for gas sensors

A capacitive gas sensor has been created on the basis of an n-SnO₂/SiO₂/p-Si heterostructure with two successive oxide layers. The presence of polar C₂H₅OH, NH₃, and H₂O gas molecules in air leads to a significant increase in the capacitance of the structure at room temperature. An important feature of the adsorption process is a memory effect, which is confined to the possibility of maintaining the capacitance value after removal of the active component from the gas mixture. The possibility of quenching the accumulated useful signal by electric-field pulses has been realized for the first time as applied to gas sensors. Pis’ma Zh. Tekh. Fiz. 25, 22–29 (June 26, 1999)     

Computations of Low-Energy Non-Icosahedral Structures of C6− 60

Abstract

Owing to the three-fold degeneracy of the LUMO in C₆₀, its hexa-anion is not subjected to Jahn-Teller distortions. In contrast to the accepted presumptions, however, computations at the MNDO, AMI, PM3, SAM1, HF/STO-3G, HF/3-21G, and HF/4-31G levels show that the completely relaxed, non-icosahedral cage of C^6? ₆₀is lower in energy. The computed energy gain varies between 60 and 150 kJ/mol and thus, it is consistently significant (the most sophisticated approach, HF/4-31G, yields 93 kJ/mol). The longest C-C bond in the relaxed structures is at most computed 0.05 Å longer compared to the 5/6 bond in the icosahedral C^6? ₆₀The symmetry of C^6? ₆₀is relaxed to D₂ A C_2v, isomer is discussed, too.     

Low-frequency dielectric permittivity of C60

Complex dielectric response measurements have been made on a C₆₀/C₇₀ mixture pellet. The frequency and temperature ranges cover from 20 Hz to 1 MHz and from 30 to 300 K. Results show that the real part of the dielectric constant is 5 with a weak thermally activated polarization contribution. This thermal polarization is believed to be related to reorientation of C₆₀ molecules recently observed by many techniques such as NMR, sound velocity, thermal conductivity, and others. Our data yield relaxation frequencies for reorientation, indicating that the presence of an additional electric dipole moment of the orientationally ordered C₆₀ molecules at low temperature contributes 0.2–0.3 to the static dielectric constant.We wish to thank William Jenks and Chris Rey for their assistance and advice in performing the measurements. We appreciate helpful discussions with E. Manousakis and J. Cioslowski. One of us (G.C.) acknowledges the support by the National Science Council of R.O.C. under grant No. NSC82-0208-M-194-030.     

Desorption of organic overlayers by Ga and C60 bombardment

This paper reviews our recent work on computer simulations of Ga and C₆₀ bombardment of thin organic overlayers deposited on metal substrate. A multilayer of benzene, a monolayer of PS4 on Ag{1 1 1} and a self-assembled monolayer of octanethiol molecules on Au{1 1 1} were irradiated with 15 keV monoatomic (Ga) and polyatomic (C₆₀) projectiles that are recognized as valuable sources for desorption of high mass particles in secondary ion and neutral mass spectrometry (SIMS/SNMS) experiments. The results indicate that the sputtering yield decreases with the increase of the binding energy and the average kinetic energy of parent molecules is shifted toward higher kinetic energy. Although the total sputtering yield of organic material is larger for 15 keV C₆₀, the impact of this projectile leads to a significant fragmentation of ejected species. As a result, the yield of the intact molecules is comparable for C₆₀ and Ga projectiles. Our results indicate that the chemical analysis of thin organic films performed by detection of sputtered neutrals will not benefit from the use of C₆₀ projectiles.     

Distinctive features of the thermal degradation of poly-N-vinylpyrrolidone cross-linked by C60 fullerene molecules

The thermal degradation of polymer networks obtained by cross-linking by C₆₀ molecules through the functional groups of pyrrolidone rings has been investigated by mass-spectrometric analysis for the example of poly-N-vinylpyrrolidone. The thermal degradation of the networks differs substantially in character from the case of free poly-N-vinylpyrrolidone. Institute of Problems of Machine Engineering Pis’ma Zh. Tekh. Fiz. 23, 87–92 (September 26, 1997)     

Diffraction pattern of electrons scattered quasi-elastically by adsorbed fullerenes

The diffraction patterns are calculated for 2 keV electrons scattered quasi-elastically by C₆₀ molecules adsorbed on a solid surface. It is shown that when the molecules are bound to the substrate strongly enough the symmetry of these patterns reveals uniquely the orientation of the adsorbed fullerenes. A new and effective method that takes into account phenomenologically the focusing of the scattered electrons is proposed for modeling the diffraction patterns Pis’ma Zh. Tekh. Fiz. 23, 17–22 (February 26, 1997)     

C60 DECOMPOSITION ON SOME TRANSITION METAL AND SEMICONDUCTOR SURFACES

A deep understanding of fullerene-surface interaction regularities is a key to widespread fullerene use. We have studied C₆₀ molecular adsorption, thermal transformation and initial film growth stages on four transition metals: W, Mo, Re and Ir in the wide temperature range 300–2000K. Experiments were performed in ultra-high vacuum (UHV) at P < 10^?9 Torr by high resolution Auger electron spectroscopy, atomic force microscopy and thermal desorption mass-spectrometry using an absolutely calibrated flux of the depositing C₆₀ molecules.     

Kinetics of Fullerene Formation in a Contact Arc Generator

Abstract

A kinetic model of the fullerene growth process in a contact arc generator is developed. On the basis of the kinetic model, the yield of the magic fullerenes C₆₀ and C₇₀ is calculated. The fullerene yield is determined by the temperature gradient in the fullerene formation zone, the carbon vapor concentration and the helium jet velocity in the interelectrode space. We found that the upper boundary value of the magic fullerene yield was about 20%.     

Quantum Chemical ab initio Investigations of Non-Covalent Bonding Derivatives of Fullerene C60 and Li Atom or Cs2, C6H6 Molecules

Abstract

Quantum chemical ab initio investigations of the stability of the non-covalent fullerene complexes: C₆₀ molecule + Li atom, two C₆₀, two C₆₀ + CS₂, C₆₀ + CS₂, C₆₀ + C₆H₆ were performed using Hartree-Fock (HF) and Density Functional Theory (DFT) methods in various basis sets. The inclusion of electron correlation effect calculated by using DFT B3PW91 model during the optimization of Li atom position above hexagonal of C₆₀ gives the smaller distance from the centre of C₆₀ equal to 7.75 Å and large positive energy of formation equal to 4.452 kcal/mol in comparison with HF calculated distance 8.39 Å and energy of formation 1.810 kcal/mol. The positive energy of formation equal to 0.483 kcal/mol for optimized complex two C₆₀ + one CS₂ was found by HF. The presence of CS₂ molecule stabilises this complex with the energy equal to 0.281 kcal/mol. Complexes: C₆₀ + CS₂, C₆₀ + C₆H₆ do not possess the positive energy of formation.