Preparation of graphene on Cu foils by ion implantation with negative carbon clusters

We report on few-layer graphene synthesized on Cu foils by ion implantation using negative carbon cluster ions,followed by annealing at 950？C in vacuum. Raman spectroscopy reveals IG/I2 Dvalues varying from 1.55 to 2.38 depending on energy and dose of the cluster ions, indicating formation of multilayer graphene. The measurements show that the samples with more graphene layers have fewer defects. This is interpreted by graphene growth seeded by the first layers formed via outward diffusion of C from the Cu foil, though nonlinear damage and smoothing effects also play a role. Cluster ion implantation overcomes the solubility limit of carbon in Cu, providing a technique for multilayer graphene synthesis.

Solvent-free Synthesis of Flowable Carbon Clusters with Customizable Size and Tunable Optical Performance

We propose a rapid and solvent-flee route for synthesizing luminous carbon clusters by controlling carbonization of polyethylene glycol （PEG）. This approach does not involve solvents yet uses the precursor itself as suspend- ing medium, thus features mild and green chemistry, and also enables the formation of uniform-sized carbon clus- ters, of which the diameter can be easily tuned from 0.7 to 3.5 nm via control of reaction time. In term of the di- mension, the resultants are denoted as sub-nano carbon clusters （SNCs） and carbon dots （CDs）, respectively. Bene- fiting from surface anchored PEG segments, both of the two show favorable flowability at room temperature and excellent solubility in aqueous and organic solvents. Comparison of their optical performances and structures re- veals that they share the same chromophores. Particularly, the SNCs demonstrate robust photo- and pH-stable pho- toluminescence and can be directly applied to cell-imaging regarding to its prominent biocompatibility. Moreover, its quantum yield （5.5%）, which is approximately 3 times higher than that of CDs （1.5%）, can be dramatically en- hanced to 18.8% by facile chemical reduction. We anticipate that these PEG derivatives marked with easy synthesis, controllable optical performances and excellent physical properties will be highly appealing in future applications.

Pseudopotential Density-Functional Calculations for Structures of Small CarbonClusters CN （N=2-8）

We introduce a first-principles density-functional theory,i.e.the finite-difference pseudopotential density- functional theory in real space and the Langevin molecular dynamics annealing technique,to the descriptions of structures and some properties of small carbon clusters(C_N,N=2～8).It is shown that the odd-numbered clusters have linear structures and most of the even-numbered clusters prefer cyclic structures.

Cluster-assisted generation of multicharged ions in nanosecond laser ionization of carbon bisulfide clusters at 1064nm

The photoionization of seeded carbon bisulfide molecular beam by a 1064nm nanosecond Nd-YAG laser with intensities varying from 0.8 × 10^11 to 5.6 × 10^11 W/cm^2 have been studied by time-of-flight mass spectrometry. Multiply charged ions of S^q＋ （q = 2 6） and C^q＋ （q = 2-4） with kinetic energy of hundreds of electron volts have been observed, and there are strong experimental evidences indicating that those multicharged ions originate from the ionization of CS2 neat clusters in the beam. An electron reeolliding ionization model is proposed to explain the appearance of those multiply charged atomic ions under such low laser intensities.

Molecular dynamics simulation of an argon cluster filled inside carbon nanotubes

The effects of the diameters of single-walled carbon nanotubes （SWCNTs） （7.83A to 27.40A） and temperature （20 K-45 K） on the equilibrium structure of an argon cluster are systematically studied by molecular dynamics simulation with consideration of the SWCNTs to be fixed. Since the diameters of SWCNTs with different chiralities increase when temperature is fixed at 20 K, the equilibrium structures of the argon cluster transform from monoatomic chains to helical and then to multishell coaxial cylinders. Chirality has almost no noticeable influence on these cylindrosymmetric structures. The effects of temperature and a non-equilibrium sudden heating process on the structures of argon clusters in SWCNTs are also studied by molecular dynamics simulation.

Hybridization of Carbon Atomic Orbitals in the Carbon Cluster Cn

In recent years,the stable existence of the C180 has been observed in mass spectroscopy.The existence of C180, C540,…with Ih symmetry can be calculated theoretically, and it has been expected that C540 is a stable construction.

The Analysis of the Equilibrium Cluster Structure in Supercritical Carbon Dioxide

The monomer fraction density based analysis of precise thermophysical data for pure fluids is developed to study the molecular structures in supercritical fluids in general and in CO2 in particular. The series expansion by powers of the monomer fraction density of the potential energy density is used to discover the cluster structure in supercritical fluids and the clusters’ bond energies in CO2. The method of clusters separation between classes of loose and dense clusters in the CO2 supercritical fluid is developed. The method of the energetically averaged number of dense clusters is developed to study the mechanism of the soft structural transition between the gas-like and liquid-like fluids in the supercritical CO2.

New Method of Generation of Carbon Molecules and Clusters

Firstly the method of joint synthesis of carbon molecules and their hydrides is developed. The stage of high-temperature sublimation of carbon in a new method of generation of carbon molecules is completely excluded. By mass spectrometric method the condensation products of new method of pyrolysis (NMP) benzene are studied. Firstly clusters (C3-C17), typical for carbon vapour, in substances obtained under pyrolysis of hydrocarbons were detected. Fullerene C60 and its hydrides, quasi-fullerenes C48 and C33 inproducts of benzene pyrolysis are detected also. Firstly it is shown what clusters C3-C5 can be generated at so low (100?C-200?C) temperatures of decomposition of substance. Obtained experimental results firstly demonstrate that the small carbon molecules can be generated in reactionary conditions excluding evaporation of carbon. Dehydrogenation and destruction of hydrocarbon molecules is the first stage on a route of the transformation of benzene to carbon molecules.

A QUANTUM CHEMISTRY STUDY ON THE SIZE-DEPENDENCE OF THE CHEMISORPTION OF AMMONIA AND CARBON MONOXIDE ON ALUMINUM CLUSTERS

The chemisorption intensities of NH_3 and CO on aluminum clusters A1_n(n=l-13) have been theoretically predicted by using CNDO/2 method and properly selecting the clusters' geometries.The results show that the chemisorptions of NH_3 and GO on Al_2,Al_6 and Al_12 are magically stable and thus are in good agreement with the experimental results.In addition,an electronic structure analysis is made to expound the nature of such a size effect.

STRUCTURE EFFECTS OF SILICON AND CARBON BY CLUSTER MASS SPECTRA

Microclusters from different structures of silicon and carbon are studied by SIMS under UHV conditions in the mass range below M=200. The sputtered mass spectra of ions Sin+, Cn+ and Cn were obtained from the 10 keV O2+ primary beam bombardment. Comparisons of each spectrum in each group have shown the strong structure effects on the cluster patterns. A brief discussion on the results has been given.

Cluster-Cluster Potentials for the Carbon Nucleus

Two types of potentials are given in the present paper. The two potentials have Gaussian radial dependences. Such shapes of radial functions are suitable for using in the unitary scheme model. The first potential is given in the form of an attractive force and the second is given in the form of a superposition of repulsive and attractive forces. The two potentials are used to calculate the binding energy of the carbon nucleus 12C. For this purpose, we expand the ground-state wave function of carbon in a series of the bases of the unitary scheme model and apply the variational method. To calculate the necessary matrix elements required to obtain the binding energy of carbon, we factorized the unitary scheme model bases in the form of products of two wave functions: the first function represents the set of the A-4 nucleons and the second function represents the set of the last four nucleons by using the well-known four-body fractional parentage coefficients. Good results are obtained for the binding energy of 12C by using the two potentials.

Quantum-Chemical Estimating Interaction of <i>sp²</i>-Carbon Nanoclusters with PE and PP Oligomers

The purpose of this work was to examine the interaction of graphene-like nanoclusters with fragments of polymers of the same nature, but somewhat different structure, for example, polyethylene (PE) and polypropylene (PP) by means of quantum chemistry. By method of density functional theory with the exchange-correlation functional B3LYP, the basis set 6 - 31 G (d, p) and the Grimme’s dispersion correction, the energy values have been calculated of interaction between nanocarbon fragments and oligomers of PE and PP, the most probable structures of their intermolecular complexes being optimized. A graphene-like plane of 40 carbon atoms and 16 atoms of hydrogen was chosen as a model for the surface of the graphene and carbon nanotubes (CNT). In order to take into account the dimensional effect of the surface of the nanotube fragment model on the interaction energy, in addition to the above described, two larger models were used, with the general formula C54H18 and C96N24. It has been found that the interaction energy of nanocarbon fragment with an oligomer of PP is greater, compared with PE, which is consistent with the experimental data on melting temperatures of pure polymers and nanotube-polymer composites. The polymer with a surface of nanocarbon fragment forms an intermolecular complex not bound covalently and retained by intermolecular dispersion forces. Oligomers of polymeric matters and carbon surfaces in formed nanocomplex are placed closer to each other than separate polymeric links between them.

Growth of C30 and C31 Clusters： Structures, Energetics and Dynamics

We obtain the isomer spectra of C30 and C31 dusters by time-going-backward quasi-dynamics method and perform molecular dynamics simulations of the duster growth from isolated atoms in He buffer gas at 2500 K. The geometrical structures of the isomers of C30 and C31 can be classified into closed cages, open cages, bowls, sheets and other irregular shapes, where closed cages are found to have the lowest potential energies. However, dynamics simulations show that the sheet structures of C30 and C31 are the dominant outcome at the simulation temperature. Compared with relevant experimental results, we propose a different view in interpreting the experimental data and a research procedure to predict isomers that would be formed most probably under specific experimental conditions.

Characterization of Carbon Plasma Evolution Using Laser Ablation TOF Mass Spectrometry

In this work, a time-of-flight （TOF） mass spectrometer has been used to investigate the distribution of intermediate species and formation process of carbon clusters. The graphite sample was ablated by Nd：YAG laser （532 nm and 1064 nm）. The results indicate that the maximum size distribution shifted towards small cluster ions as the laser fluence increased, which happened because of the fragmentation of larger clusters in the hot plume. The temporal evolution of ions was measured by varying the delay time of the ion extraction pulse with respect to the laser irradiation, which was used to provide distribution information of the species in the ablated plasma plume. When the laser fluence decreased, the yield of all of the clusters obviously dropped.

Parity Alternation of Silicon-doped Ternary Cationic Clusters HC_nSi_2^+(n=1～9)

Systematic study on the electronic/geometrical structures and the parity alternation effect of silicon-doped ternary cationic clusters HCnSi2＋（n = 1 ~9） have been carried out at the coupled cluster level. The ground-state （G-S） isomers of the clusters have been defined. The C, chains of the G-S isomers display polyacetylene-like structures. The even-n cations are more stable than the odd-n ones. Such a trend of even/odd alternation has been elaborated based on concepts of the bond character, atomic charge, incremental binding energy, ionization potential, proton affinity and fragmentation energies of the systems. The findings accord with the relative intensities of HC,,Si2＋ species recorded in the related mass spectrometric experiments.

ADF Studies of Neutral Small C_n(n=3～6)High-symmetry Clusters

The geometries, electronic structures of pure carbon clusters were investigated in the range of C 3 to C 6 size. To obtain accurate results, the STO double zeta basis sets with a polarization function are selected. The main focuses are on the new geometry, electronic structures of carbon clusters, such as the three dimensional structure for C 4, C 5 and so on. The clusters are found to have more isomers corresponding to different geometries and spin multiplicities close to their ground states. We find that the spin multiplicity of the ground state or close to ground state of odd numbered linear chain is 1. But in even numbered linear chains, the spin multiplicity is 3. In odd numbered cyclic structure without branch chain, the spin multiplicity of the ground state or close ground state is 3, and that of even numbered is 1. But the three dimensional structure disagree those principles.

<i>γ</i>-Ray Modifications of Optical/Chemical Properties of Polycarbonate Polymer

This work was aimed to investigate the changes brought about in the polymer polycarbonate irradiated to different doses of γ-radiation. Yellowing of the samples with the increase of γ-absorbed dose was observed. The changes in the optical properties were studied by recording UV-Visible absorbance spectra of the pristine and irradiated polycarbonate films. A simultaneous coexistence of direct and indirect band gaps was observed. The indirect band gap values were found lower in comparison to the corresponding values of direct band gap in the pristine and γ-irradiated poly-carbonate. Both types of the optical band gap energies had decreasing tendency with the increasing γ-radiation dose. Urbach energy was also determined from the tail of absorption edge which was found to have increasing tendency with progressive γ-radiation dose. Increase in carbon cluster size with the increasing γ absorbed dose was also shown. This increase in the number of carbon atoms (N) in a cluster can be correlated to the optical energy band gap (Eg). Moreover, the FTIR spectra of pristine and irradiated PC samples suggest chain scissoring with apparently the elimination of carbon di/monoxide.

Operation Mechanism of Farmers' Professional Cooperatives from the Point of Low-Carbon Agricultural Products

We firstly take a look at internal logic of cluster development of low-carbon agricultural products.In combination with operation features of farmers' professional cooperatives and actual requirements for cluster development of low-carbon agricultural products;we elaborate establishing benefit allocation mechanism,bearing education and training functions,forming low-carbon value,building low-carbon identification system,as well as realizing low-carbon value.According to these situations,we systematically analyze operation mechanism of farmers' professional cooperatives suitable for cluster development of low-carbon agricultural products.To promote cluster development of low-carbon agricultural products,we put forward following suggestions,including government guidance and encouragement,social acceptance and active cooperation,and integration into global low-carbon development system to share benefit of low-carbon development.

Acceleration of C_2^+-C_8^+ Clusters to MeV Energies

Beams of C2+-C8+ clusters have been accelerated to 3 MeV in 1.7 MV tandemaccelerator.The beam intensity of small C-cluster is large enough for some physical ex-periments.The gas density in the stripper cell is an important parameter for obtainingmaximum Cm+ cluster beam.

Nickel Decorated Single-Wall Carbon Nanotube as CO Sensor

Based on spin-polarized density functional theory (DFT) calculations, the interaction between nickel cluster decorated single-wall carbon nanotube (CNT) and CO molecule has been investigated. DFT calculations are performed with generalized gradient approximation (GGA) using Perdew-Burke-Ernzerhof (PBE) functional. Interaction of CNT and cluster induces spin polarization in the CNT. Nickel decorated CNT has a large magnetic moment of 4.00 μB which decreases to 0.10 μB when CO molecule is absorbed to it. Such a drastic reduction in magnetization may be detected by SQUID magnetometer. Hence by measuring magnetization change, CNT-cluster system may be used as gas detectors. The charge transfer between the systems has been discussed through Mulliken charge analysis for different orientations of the adsorbed CO molecule. We observed that CNT-cluster system acts as electron donor and CO molecule acts as electron acceptor in this study.