Clusters Of Carbon Atoms Research Articles

The physical and chemical properties of gamma ray irradiated polymer electrolyte films

The physical and chemical properties of Gamma ray irradiated polymer electrolyte (PEO-CdCl2) films have been investigated. The FT-IR result evidenced the degradation due to chain scission/cross linking in the irradiated films. The DSC and TGA results show that thermal stability and crystallinity are significantly decreased in irradiated films. The optical micrograph image shows the size of spherulite structure and surface roughness found to be decreased with increasing the irradiation dose. The increase in the optical absorption and shifts toward higher wavelength side was observed in the irradiated film. Also optical band gaps (Eg), Urbach energy is estimated and found to be decreased, meanwhile the number of carbon atoms in cluster increased with the dose. The changes of dielectric permittivity, AC conductivity and optical band gap after irradiation were attributed due to degradation. The high conductivity of 1.156×10−4Scm−1 observed in the 150kGy irradiated film; it was about to order magnitudes higher than that of non-irradiated film. The electric modulus results were depicts the relaxation time (τ) found decreased and broadening of peaks signifies it is the Non-Debye relaxation behavior. These obtained results reveal that there is a possibility of improving physical properties polymer electrolyte and it may open up various opportunities to use these materials in different applications.

Synthesis and 11C-Radiolabelling of 2-Carboranyl Benzothiazoles.

Dicarba-closo-dodecaboranes, commonly known as carboranes, possess unique physico-chemical properties and can be used as hydrophobic moieties during the design of new drugs or radiotracers. In this work, we report the synthesis of two analogues of 2-(4-aminophenyl)benzothiazole (a compound that was found to elicit pronounced inhibitory effects against certain breast cancer cell lines in vitro) in which the phenyl ring has been substituted by a m-carborane cage. Two different synthetic strategies have been used. For the preparation of 1-(9-amino-1,7-dicarba-closo-dodecaboran-1-yl)-benzo-thiazole, the benzothiazole group was first introduced on one of the cluster carbon atoms of m-carborane and the amine group was further attached in three steps. For the synthesis of 1-(9-amino-1,7-dicarba-closo-dodecaboran-1-yl)-6-hydroxybenzothiazole, iodination was performed before introducing the benzothiazole group, and the amino group was subsequently introduced in six steps. Both compounds were radiolabelled with carbon-11 using [11C]CH3OTf as the labelling agent. Radiolabelling yields and radiochemical purities achieved should enable subsequent in vitro and in vivo investigations.

Acyl chloride carbon insertion into dicarbaborane cages – new route to tricarbollide cages

Abstract Reactions between the arachno-6,9-C2B8H14 dicarbaborane and acyl chlorides, RCOCl, in the presence of amine bases in CH2Cl2, followed by acidification with conc. H2SO4 at 0 °C, generate in high yields a series of neutral alkyl and aryl tricarbollides of structure 8-R-nido-7,8,9-C3B8H11 (where R=alkyls and aryls). These skeletal alkylcarbonation (SAC) reactions are consistent with an aldol-type condensation between the RCO group and open-face dicarbaborane hydrogen atoms, which is associated with the insertion of the acyl chloride RC unit into the structure under elimination of three extra hydrogen atoms as H2O and HCl. The reactions thus result in an effective cross-coupling between R and the tricarbollide cage. High-temperature reactions between 8-Ar-nido-7,8,9-C3B8H11 (where Ar=Ph, 1-C10H7, and 2-C10H7) compounds and [CpFe(CO)2]2 produced the first types of monoaryl substituted twelve-vertex ferratricarbollide complexes of general constitution [1-(CpFe)-closo-ArC3B8H10] with three different arrangements of cluster carbon vertexes. The Fe-complexation is accompanied by extensive rearrangement of the cluster carbon atoms over the twelve-vertex cage and the complexes isolated can be regarded as ferrocene analogues.

Carba-closo-dodecaborate anions with two functional groups: [1-R-12-HC≡C-closo-1-CB₁₁H₁₀]⁻ (R = CN, NC, CO₂H, C(O)NH₂, NHC(O)H).

Disubstituted carba-closo-dodecaborate anions with one functional group bonded to the cluster carbon atom and one ethynyl group bonded to the antipodal boron atom were synthesized from easily accessible {closo-1-CB11} clusters. [Et4N][1-NC-12-HC≡C-closo-1-CB11H10] ([Et4N]4b) was prepared starting from Cs[12-Et3SiC≡C-closo-1-CB11H11] (Cs1c) via salts of the anions [1-HO(O)C-12-HC≡C-closo-1-CB11H10](-) (2b) and [1-H2N(O)C-12-HC≡C-closo-1-CB11H10](-) (3b). In a similar reaction sequence [Et4N][1-CN-12-HC≡C-closo-1-CB11H10] ([Et4N]7b) was obtained from Cs[1-H2N-12-HC≡C-closo-1-CB11H10] (Cs5b) by formamidation to yield [Et4N][1-H(O)CHN-12-HC≡C-closo-1-CB11H10] ([Et4N]6b) and successive dehydration. In addition, the synthesis of the isonitrile [Et4N][1-CN-closo-1-CB11H11] ([Et4N]7a) is presented. The {closo-1-CB11} derivatives were characterized by multinuclear NMR as well as vibrational spectroscopy, mass spectrometry, and elemental analysis. The crystal structures of [Et4N][1-HO(O)C-12-HC≡C-closo-1-CB11H10] ([Et4N]2b), [Et4N][1-H2N(O)C-12-HC≡C-closo-1-CB11H10] ([Et4N]3b), [Et4N][1-NC-12-HC≡C-closo-1-CB11H10] ([Et4N]4b), [Et4N][1-H(O)CHN-12-HC≡C-closo-1-CB11H10] ([Et4N]6b), [Et4N][1-CN-12-HC≡C-closo-1-CB11H10] ([Et4N]7b), and K[1-H(O)CHN-closo-1-CB11H11] ([Et4N]6a) were determined. The transmission of electronic effects through the carba-closo-dodecaboron cage was studied based on (13)C NMR spectroscopic data, by results derived from density functional theory calculations, and by a comparison to the data of related benzene and bicyclo[2.2.2]octane derivatives.

Investigation of the Effect of a He-Ne Laser on the Optical Properties through Etched CN-85 and CR-39 Containing Alpha Tracks

In the present work, the effect of a He-Ne laser on the etching parameter, optical, and photoluminescence properties of CN-85 and CR-39 has been studied. The two types of polymers were bombarded with 5.44 MeV alpha particles using an ^(241) Am source. The bombarded samples were exposed to a laser beam at an energy density up to 217 J/cm^2. A remarkable change in the bulk etch rate was observed for both bombarded polymers with a change in the laser energy density. A considerable increase in the optical absorption was observed for the laser-irradiated samples, when compared to that of the alpha bombarded polymers and a pristine one. The optical absorption studies reveal that the optical band gap energy for both polymers decreases with increasing laser energy density. A correlation between the energy gap and the number of carbon atoms in the clusters is investigated. A noticeable decrease in the photoluminescence spectral intensity was observed with increasing laser energy density.

First-principles study of the stability of graphene and adsorption of halogen atoms (F, Cl and Br) on hydrogen passivated graphene

First-principles calculations based on Hartree–Fock (HF) and density functional theory (DFT) levels of approximation have been carried out in order to study the stability of graphene clusters as a function of number of carbon atoms (N). The variation of calculated binding energy per carbon atom with corresponding number of carbon atoms (N) in graphene cluster almost saturates after the cluster size consisting of 96 carbon atoms, with binding energy per carbon atom 8.24 eV/atom. Adsorption of halogen atoms, ( F , Cl and Br ), on hydrogen passivated graphene ( H -graphene) was also studied systematically through first-principles DFT calculations by taking five different H -graphene clusters. The calculations showed that the most stable adsorption site for halogen adatoms on H -graphene being T site with binding energy 2.41 eV ( F ), 1.48 eV ( Cl ) and 1.19 eV ( Br ) on the H -graphene cluster consisting 96 carbon atoms. Moreover, on increasing the size of H -graphene cluster, the binding energy of halogen adatoms found to be increasing. The distances of adatom from the nearest carbon atom of H -graphene sheet were 1.47 Å ( F ), 2.71 Å ( Cl ) and 3.01 Å ( Br ), however, the adatom heights from the H -graphene basal plane were 2.22 Å ( F ), 2.90 Å ( Cl ), and 3.19 Å ( Br ). The bonding of halogen adatoms on H -graphene were through the charge transfer; 0.30 | e | ( F ), 0.37 | e | ( Cl ) and 0.19 | e | ( Br ), from H -graphene to adatoms and includes the negligible local distortion in the underlying planner H -graphene. Charge redistribution upon adsorption induces significant dipole moments 2.16 D ( F ), 4.81 D ( Cl ) and 3.08 D ( Br ) on H -graphene. The calculated HOMO–LUMO energy gap of adatom- H -graphene and H -graphene does not differ significantly up to the cluster size N = 30, however, beyond N = 30 adsorption of halogen adatoms significantly opens the HOMO–LUMO energy gap on H -graphene and the opening of HOMO–LUMO energy gap also saturates from N = 96. Correlation of computed HOMO–LUMO energy gap and corresponding binding energy of adatom- H -graphene systems have been also studied.

Influence of Tempering Temperature on Low Cycle Fatigue of High Strength Steel

In this study, the mechanical and low cycle fatigue properties for a heat-treatment steel subjected to quenching and tempering (QT) were evaluated. The steel had a modified chemical composition with respect to a conventional material and was subjected to tempering at various temperatures. It was shown that the material tempered at 250°C exhibited superior fatigue properties in the short life regions. Carbon atom clusters in concentration of 18 at% in martensite were observed using atom probe tomography (APT) for the steel tempered at 250°C. It is believed that these clusters contribute to the improvement of fatigue properties by hindering the motion of dislocations.

The atomistic mechanism of carbon nanotube cutting catalyzed by nickel under an electron beam.

The cutting of single-walled carbon nanotubes by an 80 keV electron beam catalyzed by nickel clusters is imaged in situ using aberration-corrected high-resolution transmission electron microscopy. Extensive molecular dynamics simulations within the CompuTEM approach provide insight into the mechanism of this process and demonstrate that the combination of irradiation and the nickel catalyst is crucial for the cutting process to take place. The atomistic mechanism of cutting is revealed by a detailed analysis of irradiation-induced reactions of bond reorganization and atom ejection in the vicinity of the nickel cluster, showing a highly complex interplay of different chemical transformations catalysed by the metal cluster. One of the most prevalent pathways includes three consecutive stages: formation of polyyne carbon chains from the carbon nanotube, dissociation of the carbon chains into single and pairs of adatoms adsorbed on the nickel cluster, and ejection of these adatoms leading to the cutting of the nanotube. Significant variations in the atom ejection rate are discovered depending on the process stage and nanotube diameter. The revealed mechanism and kinetic characteristics of the cutting process provide fundamental knowledge for the development of new methodologies for control and manipulation of carbon structures at the nanoscale.

Parasitic Light Absorption Processes in Transparent Polycrystalline MgAl2O4 and YAG

Parasitic radiation absorption by impurities located in transparent polycrystalline ceramic hosts may significantly impair their functioning. At least two classes of impurity which can act as parasitic absorbers were encountered: transition or rare‐earth metal cations and neutral species (molecules or atoms) trapped in lattice void spaces. The most ubiquitous parasitic absorbers, able to affect transmission in the visible domain, have been identified for the case of MgAl2O4‐spinel and Y3Al5O12‐garnet hosts; their spectral effect was described and explained. In the case of spinel, S8 type molecules and carbon atom clusters are the most damaging impurities, with Ce3+ and Y2+ also of significance for YAG host. Oxygen vacancy formation assists some of the redox processes which generate uncontrolled absorption. For instance, the Ti4+ reduction to Ti3+ is facilitated by such a process.

Structure and Properties of Small Aurocarbons: A Selective Study

Gold clusters are versatile catalysts, and adding nonmetal dopants can allow tuning of their electronic properties via both shape and composition alteration. In the present work, mixed clusters of carbon and gold atoms are studied in terms of structure, stability, and the correlation between the shape and electronic properties by using a density functional theory approach. Four series of isomers (hydrocarbon analogues, carbon chains and cycles on gold surface, and carbon cores encapsulated by gold atoms) are investigated, exhibiting variation of the relative stability with the system size. Calculated vertical ionization energies, vertical electron affinities, and HOMO-LUMO energy gaps of the mixed clusters show a considerable change relative to the values for the pure gold clusters, the properties generally altering more strongly for the gold-encapsulated-carbon isomers. Also discussed are the structure, stability, and properties of larger clusters with a few such encapsulated-carbon units, with pronounced effects due to aggregation.

Carba‐closo‐dodecaborate Anions with Cluster Carbon–Phosphorous Bonds

AbstractSalts of monocarba‐closo‐dodecaborate anions with different phosphanyl groups that are bonded to the cluster carbon atom were studied. The series includes the anions [1‐R2P‐closo‐1‐CB11H11]– (R = Cl (1a), H (1b), iPr (1c)) as well as the related anions [1‐iPr2(O)P‐closo‐1‐CB11H11]– (1d) and [1‐H(HO)(O)P‐closo‐1‐CB11H11]– (1e) that were isolated either as cesium or [Et3NH]+ salts. All salts were characterized by NMR spectroscopy and the crystal structures of the Cs+ salts of the anions 1c and 1d were determined. In addition, the reactive anions [1‐Cl2P‐closo‐1‐CB11Hal11]– (Hal = F (2), Cl (3), Br (4), I (5)) were prepared and characterized by multinuclear NMR spectroscopy in solution.

The optical band gap and surface free energy of polyethylene modified by electron beam irradiations

In this study, investigations have been carried out on electron beam irradiated ultra high molecular weight polyethylene (UHMWPE). Polyethylene samples were irradiated with 1.5MeV electron beam at doses ranging from 50 to 500kGy. Modifications in optical properties and photoluminescence behavior of the polymer were evaluated by UV–vis and photoluminescence techniques. Changes of surface layer composition of UHMWPE produced by electron irradiations were studied by Rutherford back scattering spectrometry (RBS). The change in wettability and surface free energy induced by irradiations was also investigated. The optical absorption studies reveal that both optical band gap and Urbach’s energy decreases with increasing electron dose. A correlation between energy gap and the number of carbon atoms in clusters is discussed. Photoluminescence spectra were reveal remarkable decrease in the integrated luminescence intensity with increasing irradiation dose. Contact angle measurements showed that wettability and surface free energy increases with increasing the irradiation dose.

Purification of Carbon Nanotubes Synthesized by Pyrolysis Flame

Pyramid shaped pyrolysis flame is a new method for carbon nanotubes (CNTs) synthesis, using this method has successfully produced high properties carbon nanotubes. But, because at the first 1min of sampling time, there are not tubes produced, so catalyst particles and carbon atom clusters assemble on the sampling substrate in the first 1min. Also, lots of amorphous carbon, deformity tubes, and graphite segment were produced in the experimental. In order to eliminate these impurities, ultrasonic treatment, aether cleaning, acid pickling, and co-processing were used. Ultrasonic treatment can separate particles from tubes, aether can clear amorphous carbon and graphite segment while acid pickling can dissolve catalyst particles. Using ultrasonic oscillation separation and aether as diluent can gain pure sample. Ultrasonic oscillation and nitric acid as diluent can purify products also, but not as good as aether as diluent. Concentrated nitric acid and long time immersion will destroy the structure of carbon nanotubes.

Thermal fluctuations and nanoscale effects in the nucleation of carbonaceous dust grains

We investigate the role of thermal fluctuations and of the finite number of monomers in small clusters of carbon atoms on the nucleation rate of carbonaceous grains. Thermal fluctuations are due to the quantized nature of the energy exchanges between the clusters, the gas, and the radiation field. Nanoscale effects modify the spontaneous detachment of monomers due to the finite amount of internal energy contained in small clusters. We find that both corrections have a big impact on the stability of the clusters and on the rate of nucleation. We implement our model within a Monte Carlo code to derive the new stability conditions for clusters as well as nucleation rates. Due to computing limitations, we can explore the consequences of this approach only at high temperatures, at which particle interactions are not much less frequent than photon interactions. We found that the combined effect of the detachment correction and the temperature fluctuations produces faster nucleation. We also found that the nucleation rate depends on the composition of the gas and not only on the partial pressure of the compound that condensates into grains. This is a unique result of this model that can be used to prove or disprove it.

Oxidation of Graphene on Metals

We use low-energy electron microscopy to investigate how graphene is removed from Ru(0001) and Ir(111) by reaction with oxygen. We find two mechanisms on Ru(0001). At short times, oxygen reacts with carbon monomers on the surrounding Ru surface, decreasing their concentration below the equilibrium value. This undersaturation causes a flux of carbon from graphene to the monomer gas. In this initial mechanism, graphene is etched at a rate that is given precisely by the same non-linear dependence on carbon monomer concentration that governs growth. Thus, during both growth and etching, carbon attaches and detaches to graphene as clusters of several carbon atoms. At later times, etching accelerates. We present evidence that this process involves intercalated oxygen, which destabilizes graphene. On Ir, this mechanism creates observable holes. It also occurs mostly quickly near wrinkles in the graphene islands, depends on the orientation of the graphene with respect to the Ir substrate, and, in contrast to the first mechanism, can increase the density of carbon monomers. We also observe that both layers of bilayer graphene islands on Ir etch together, not sequentially.

Iodinated ortho‐Carboranes as Versatile Building Blocks to Design Intermolecular Interactions in Crystal Lattices

The crystal structures of numerous iodinated ortho-carboranes have been studied, which has revealed the diversity of intermolecular interactions that these substances can adopt in the solid state. The nature-mostly as it relates to hydrogen and/or halogen bonds-and relative strength of such interactions can be adjusted by selectively introducing substituents onto the cluster, thus enabling the rational design of crystal lattices. In this work we present the newly determined crystal structures of the following iodinated ortho-carboranes: 9-I-1,2-closo-C(2)B(10)H(11), 4,5,7,8,9,10,11,12-I(8)-1,2-closo-C(2)B(10)H(4), 3,4,5,6,7,8,9,10,11,12-I(10)-1,2-closo-C(2)B(10)H(2), 1-Me-8,9,10,12-I(4)-1,2-closo-C(2)B(10)H(7), 1,2-Me(2)-8,9,10,12-I(4)-1,2-closo-C(2)B(10)H(6), and 1,2-Ph(2)-8,9,10,12-I(4)-1,2-closo-C(2)B(10)H(6). Their 3D supramolecular organization has been thoroughly investigated and compared to similar previously published crystal structures. Such a systematic survey has allowed us to draw some general trends. C(c)-HI--B hydrogen bonds (C(c)= cluster carbon atoms) appear to be significant in the growth of the crystal lattices of these compounds, given the acidity of hydrogen atoms bonded to C(c), and the polarization of B-I bonds. These hydrogen bonds can be disrupted by selectively blocking the positions next to C(c), that is, B(3) and B(6), with bulky substituents that prevent iodine atoms from approaching as hydrogen acceptors. Halogen bonds of the type B-II-B are frequently observed in most cases, thus suggesting that these interactions could be attractive in boron clusters. In addition, different substituents can be grafted onto the ortho-carborane surface, thereby providing further possibilities for homomeric or heteromeric molecular assembly.

A technique to study doped ablation in polymethyl methacrylate using molecular dynamics simulation

A doped polymer substrate is studied using molecular dynamics simulations. Photons are preferentially absorbed as thermal energy by a spherical portion of a polymethyl methacrylate sample. Once sufficient energy is absorbed to fragment the polymer-labeled cluster and cleave the residual polymer bonds, ejection of material occurs indicating ablation. The mechanism of ejection is analogous to our previous work where a dopant cluster was represented using a cluster of carbon atoms [P.F. Conforti, M. Prasad, B.J. Garrison, Physical Chemistry Chemical Physics, 10 (2008) 6002]. This labeling procedure can serve as an approximate method to qualitatively explore the effects of different parameters without becoming consumed in the details of the simulation setup procedure.

The Carbon Source Analysis for Diamond Crystal Growth from Fe-C System at High Pressure-High Temperature

Despite many studies have been carried, there is no clear understanding of the growth mechanism involved in the high-pressure and high-temperature (HPHT) diamond synthesis with metal catalyst, especially the problem about carbon source. In this paper, the lattice constants of diamond, graphite and Fe3C at HPHT were calculated with the linear expansion coefficient and elastic constant. Then based on the empirical electron theory of solids and molecules (EET), the valence electron structures of them and their common crystal planes were calculated, and the boundary condition of electron movement in the Thomas-Fermi-Dirac theory modified by Cheng (TFDC) was applied to analyzing the electron density continuity of the interface. It was found that the relative electron density differences across graphite/diamond interfaces are great and discontinuous at the first order of approximation, while the relative electron density differences across Fe3C/diamond interfaces were continuous. The results show that the carbon atom cluster is easier to decompose from Fe3C than from graphite and to transform into diamond structure, so the carbon source for diamond crystal growth may come from the decomposition of Fe3C instead of graphite. Accordingly, the diamond growth mechanism was analyzed from the viewpoint of valence electron structure.

Giant fullerenes formed on C 60 films irradiated with electrons field-emitted from scanning tunneling microscope tips

It has been found that spherical large clusters of carbon atoms are formed by irradiation of crystalline C 60 films grown on Si(1 1 1)-(7 × 7) surfaces with electrons field-emitted from a scanning tunneling microscope probe tip. The size distribution of the clusters deduced from surface profile measurements suggests that the dominant clusters were not necessarily C 60 n ( n = 2–4) expected from the simple fusion of C 60 molecules. It was proposed that electronic excitations of C 60 molecules caused the fragment and coalescence of the molecules to form the giant fullerenes as in the photo-induced similar effects.

Formation of diamondlike nanocrystallites in amorphous carbon films synthesized by radio-frequency sputtering

Transmission electron microscopy (TEM) and fast Fourier transformation (FFT) analysis were used to examine the microstructures of amorphous carbon (a-C) films deposited on Si(100) by radio-frequency (rf) sputtering without magnetron. TEM analysis revealed that a-C films synthesized under certain deposition conditions contained randomly dispersed nanocrystallites ∼35 Å in size. FFT results indicated that the nanocrystallites possessed diamondlike cubic structures with their close-packed {111} planes parallel to the film surface. The formation of diamondlike nanocrystallites is attributed to metastable carbon atom clusters of trigonal carbon hybridization that were sputtered off from the graphite target under certain process conditions. Cluster distortion upon deposition onto the growing film surface by the bombarding Ar+ ions promoted tetrahedral carbon atom hybridization and, possibly, epitaxial growth of diamondlike nanocrystallites for a short duration.