Kinetic stability of nitrogen cubane inside the fullerene cage: Molecular dynamics study

Abstract

Using tight-binding molecular dynamics simulations, we study kinetic stability of the nitrogen cubane inside the fullerene carbon cage. The main identified mechanism of N₈ decomposition is the N–N bond breaking with the further rapid “splitting” into the N₂ molecules that can form the strong covalent bonds with the inner surface of the fullerene cage. It is found that the fullerene cage significantly increases the stability of the N₈ cube, but its lifetime at room temperature is insufficient to observe the endohedral complex N₈@C₆₀ without the use of extreme temperature conditions. It can be synthesized and investigated only at cryogenic temperatures.     

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.     

A new route to graphene starting from heavily ozonized fullerenes: Part 3 – an electron spin resonance study

It is shown that graphite oxide (GO) and both heavily ozonized C₆₀ and C₇₀ fullerenes, known as “fullerene ozopolymers,” are paramagnetic materials with a very strong electron spin resonance (ESR) signal at room temperature. When thermally annealed, the paramagnetic centers are gradually lost in large part. This occurs at 350°C in the case of GO, while for fullerene ozopolymers, a higher temperature is required, reaching the same results in the end. The half-width of ESR signal is linked to the distribution of paramagnetic centers. Once again, striking analogies were found in the half-width of the ESR signal measured on GO and fullerene ozopolymers, at least in the temperature range of 25–450°C. Similarly, the same g-factor values, which are diagnostic for understanding the chemical nature of paramagnetic centers, were found on both GO and fullerene ozopolymers in all ranges of temperature considered.     

A Review on Endohedral Metallofullerenes: Structures and Properties

The present review deals with some recent results on endohedral metallofullerenes obtained by the Nagoya group. The present structural analyses reveal unique of endohedoral metallofullerenes: (1) the presence of structural isomers with different fullerene cage structures; (2) encaged metal atoms are situated close to the carbon cage and not in the center of the cage; (3) metal atoms in Y@C82 and Sc2@C84 are at a standstill, not moving around, even at room temperature.     

Electronic charge transfer in cobalt doped fullerene thin films and effect of energetic ion impacts by x-ray absorption spectroscopy

We report on the electronic charge transfer in cobalt doped fullerene thin films by means of near-edge x-ray-absorption fine structure (NEXAFS) spectroscopy measurement. Co-doped fullerene films were prepared by co-deposition technique and subjected to energetic ion irradiation (120 MeV Au) for possibly alignment or interconnect of randomly distributed metal particles. Polarization dependent NEXAFS spectra revealed the alignment of Co and C atoms along the irradiated ionic path. The structural changes in Co-doped as-deposited and ion irradiated fullerene films were investigated by means of Raman spectroscopy measurements. Downshift of pentagonal pinch mode A_g(2) in Raman spectroscopy indicated the electronic charge transfer from Co atom to fullerene molecules, which is further confirmed by NEXAFS at C K-edge for Co-doped fullerene films.     

Deposition and STM characterization of luminescent organic molecules on metal substrates

The porphyrin-based molecules including H₂TBPP, ZnTBPP and P_tTBPP as well as the perinone derivatives (PD) molecules were deposited on Au(100), Au(111) and Cu(100) substrates in the form of single molecule, molecular line, submonolayer, monolayer and multilayer. The features of the performed molecular nanostructures were characterized by an ultrahigh vacuum scanning tunneling microscopy (STM) at room temperature. The observed molecular topographies matched very well with the molecule structures in spite of the fact that the molecular adsorption states were influenced by different metal surface. STM-induced photon emission was generated from the surface of H₂TBPP multilayer structures on Au(100) in tunneling junction when the applied bias exceeds the “turn-on” voltages ∼− 1.6 V or + 1.3 V at 0.5 nA.     

Organic fractal nano-dimensional structures based on fullerene C60

The ways for a synthesis of nanoporous and close-packed types of fullerene C₆₀ aggregates in two-component organic solvents (toluene?+?tetrahydrofuran) were established as well as their structural and dimensional features - were studied by high-resolution transmission electron microscopy and atomic-force microscopy methods. The physical features and regularities that characterize the processes of self-organization of fullerene molecules in the initial molecular solution were determined. The method for producing nanoscale fullerene C₆₀ fractal coatings (thickness up to ～1200?nm) on a flat dielectric glass surface was proposed.     

Interaction of CO,NO, and H<Subscript>2</Subscript> molecules on the surface of a Ni/MgO(111) metal oxide system

The adsorption and interaction of carbon monoxide (CO), nitrogen oxide (NO), and hydrogen (H₂) molecules on the surface of a system produced when nanosize nickel clusters are formed on the surface of a magnesium oxide film [MgO (111)] has been studied in an ultrahigh vacuum by IR, thermal desorption, and photoelectron spectroscopy. It is shown that, at a substrate temperature of 85 K, CO and NO molecules at low surface concentrations, are mostly adsorbed on the surface of Ni particles, whereas at higher surface coverage CO molecules are forced to the Ni/MgO(111) interface. The adsorption of hydrogen results in NO molecules also being displaced to the interface. The particular state of the molecules at the interface between the metal and the polar surface of the oxide is responsible for the observed processes in which CO is converted to CO₂ due to the reduction of NO to N₂.     

Phase maps for sputter deposited refractory metal oxide ceramic coatings: review of niobium oxide,yttrium oxide,and zirconium oxide growth

Abstract

Reactive sputter deposition is a widely used glow discharge process for growing high melting point coatings near room temperature, and metastable and multiphase structures not attainable in bulk material grown under conditions of thermodynamic equilibrium. It is therefore ideally suited for growing refractory metal oxide coatings. In this study, ‘phase maps’ are constructed for the sputter deposition of the refractory metal oxides of Nb, Y, and Zr. These diagrams interrelate process parameters, the growth environment, and metallurgical phase in the growth regime of near room substrate temperature, low surface diffusion, and sticking coefficient of unity. Phase boundaries are discussed in terms of: (i) the fractional flux of metal atoms and metal oxide molecules to the substrate; (ii) a complete oxide layer at the metal target surface; (iii) oxygen species in the plasma available for reaction at the substrate.

MST/1693     

A new route to graphene starting from heavily ozonized fullerenes: Part 1—thermal reduction under inert atmosphere

It is shown that heavily ozonized C₆₀ or C₇₀ fullerenes (known also as “fullerene ozopolymers”) are suitable substrates for the preparation of graphene or nanographene in place of graphite oxide (GO) by thermal reduction in inert atmosphere. TGA-FTIR study shows that the release profile of CO₂ and CO from fullerene ozopolymers in the temperature range between 25°C and 900°C is comparable to that shown by GO. Furthermore, the FT-IR spectral evolution of fullerene ozopolymers from room temperature to 630°C under inert atmosphere is once again strikingly comparable to that observed on GO under the same conditions.     

Ionic‐Activated Chemiresistive Gas Sensors for Room‐Temperature Operation

The development of high performance gas sensors that operate at room temperature has attracted considerable attention. Unfortunately, the conventional mechanism of chemiresistive sensors is restricted at room temperature by insufficient reaction energy with target molecules. Herein, novel strategy for room temperature gas sensors is reported using an ionic‐activated sensing mechanism. The investigation reveals that a hydroxide layer is developed by the applied voltages on the SnO₂ surface in the presence of humidity, leading to increased electrical conductivity. Surprisingly, the experimental results indicate ideal sensing behavior at room temperature for NO₂ detection with sub‐parts‐per‐trillion (132.3 ppt) detection and fast recovery (25.7 s) to 5 ppm NO₂ under humid conditions. The ionic‐activated sensing mechanism is proposed as a cascade process involving the formation of ionic conduction, reaction with a target gas, and demonstrates the novelty of the approach. It is believed that the results presented will open new pathways as a promising method for room temperature gas sensors.     

Temperature-dependent Thermodynamic Behaviors of Carbon Fullerene Molecules at Atmospheric Pressure

The study aims at investigating the linear and volumetric thermal expansion coefficients (CTEs) at temperature below the Debye temperature and phase transformation behaviors at atmospheric pressure of carbon fullerenes, i.e., C₆₀, C₇₀ and C₈₀, through a modified Nosé-Hoover (NH) thermostat method incorporated with molecular dynamics (MD) simulation. The calculated results are compared with those obtained from the standard NH and "massive" NHC (MNHC) thermostats and also with the literature experimental and theoretical data. Results show that at temperature below the Debye temperature, the CTEs of the fullerene molecules would significantly decrease with a decreasing temperature and tend to become negative at temperature below 5K. The present results are much more consistent with the literature experimental and theoretical data, in contrast to the other two thermostat algorithms. Besides, it is found that C₆₀ fullerene directly undergoes a solid-vapor phase transformation, instead of a solid-liquid phase transition, implying that the molecule will sublimate when heated rather than melt under atmospheric pressure. This phenomenon is coincident with that of graphite at pressures below 10MPa. The sublimation point of C₆₀ fullerene is about 4350±20K, comparable to that of graphite in the range of about 4000-4500K at pressures below 10 MPa.     

A phenomenological comparison of some heavy metal fluoride glasses in water environments

The details of corrosive attack by water on several heavy metal fluoride glasses are given. The glasses studied contain either ZrF₄ or HfF₄ as primary constituents, or, are composed of the fluorides of zinc, thorium, barium and either yttrium or ytterbium. Polished specimens were subjected either to room temperature (RT) liquid water or to 100% relative humidity at room temperature. The degree of surface corrosion is correlated to preparatory and compositional effects. Thermogravimetric analysis (TGA) was utilized to determine the extent of corrosion as a function of temperature and as a function of time at constant temperature in an atmosphere of RT helium saturated with water.     

Fullerene-modified Dacron track membranes and adsorption of nitroxyl radicals on these membranes

Fullerene-containing track membranes have been created using a Dacron film with C₆₀ fullerene molecules physically grafted on their surface. The membranes were studied by IR spectroscopy, scanning electron microscopy, atomic force microscopy, and electron paramagnetic resonance. The fullerene molecules form aggregates on the membrane surface. The experiments with adsorption of Tempo nitroxyl radical showed that the sorption capacity of fullerene-containing Dacron track membranes is significantly greater than that of the initial membranes.     

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)     

Room temperature CO and H2 sensing with carbon nanoparticles

We report on a shell-shaped carbon nanoparticle (SCNP)-based gas sensor that reversibly detects reducing gas molecules such as CO and H(2) at room temperature both in air and inert atmosphere. Crystalline SCNPs were synthesized by laser-assisted reactions in pure acetylene gas flow, chemically treated to obtain well-dispersed SCNPs and then patterned on a substrate by the ion-induced focusing method. Our chemically functionalized SCNP-based gas sensor works for low concentrations of CO and H(2) at room temperature even without Pd or Pt catalysts commonly used for splitting H(2) molecules into reactive H atoms, while metal oxide gas sensors and bare carbon-nanotube-based gas sensors for sensing CO and H(2) molecules can operate only at elevated temperatures. A pristine SCNP-based gas sensor was also examined to prove the role of functional groups formed on the surface of functionalized SCNPs. A pristine SCNP gas sensor showed no response to reducing gases at room temperature but a significant response at elevated temperature, indicating a different sensing mechanism from a chemically functionalized SCNP sensor.     

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

Abstract

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).     

Cover Picture: A Two‐Dimensional Porphyrin‐Based Porous Network Featuring Communicating Cavities for the Templated Complexation of Fullerenes (Adv. Mater. 3/2006)

A 2D porous network has been realized by self‐assembly of porphyrin modules on a silver surface, as reported by Diederich and co‐workers on p. 275. The so‐formed pores are able to host single fullerene molecules and mediate long‐range interactions between such carbon guests, resulting in the formation of large supramolecular chains and islands. The cover shows a scanning tunnelling microscopy image of several single C₆₀ molecules (large green protrusions) hosted in the 2D porous network. As indicated by the molecular model, each pore is formed by the symmetric arrangement of three porphyrin molecules and the fullerene guest is located exactly in the center of the cavity.     

On the mechanism of encapsulated particle formation during pulsed laser deposition of WSe x thin-film coatings

We have studied factors influencing the formation of particles with the structure of a spherical metal W core inside a WSe₂ shell during pulsed laser deposition (PLD) of thin films of tungsten diselenide under variable conditions (buffer gas (Ar) pressure, substrate temperature). It is established that the metal core is formed at the stage of laser ablation of a synthesized WSe₂ target, while the shell grows as a result of condensation, migration, and redistribution of atoms during deposition of a laser-initiated atomic flow on the surface of a growing film. Retardation of the atomic flow by a buffer gas at pressures within 2–10 Pa does not ensure activation of the shell condensation process on the metal core in the gas phase. Increasing the substrate temperature from room temperature up to 250°C leads to transformation of the shell structure from amorphous into laminar.     

Thermal transformation of C60 molecules adsorbed on a silicon film on {\text{(10}}\mathop {\text{1}}\limits^-- 0) rhenium surface

The thermal transformation of a layer of fullerene C₆₀ molecules adsorbed on a silicon film deposited onto a ${\text{(10}}\mathop {\text{1}}\limits^-- 0)$ Re surface was studied in a temperature range from 300 to 1400 K. It is shown that this temperature interval can be divided into four regions, each being characterized by its own dominating process in the adlayer.