Formation of Carbon Nitride Films by Nitrogen Ion Bombardment on C_(60) Films

The synthesis of covalent carbon nitride films becomes an important subject in the materials research field.As a new synthetic method two low-energy(400 and 1000eV)nitrogen ion beams are used to bombard on C_(60) thin films individually.The bombarded films are used for Raman and x-ray photoelectron spectroscopy(XPS)measurements.The results of the analyses show that under the bombardment of 400eV nitrogen ion beam,the film still contains a large amount of undestructed C_(60) molecules.In the case of l000eV bombardment,only a little amount of C_(60) molecules is kept undestructed.The experimental results also show that the destructed carbon species will combine chemically with nitrogen ions to form stable covalent carbon nitride,confirmed by the Raman peaks of,e.g.,2240cm-1.The XPS Nls and Cls lines also indicate the formation of covalent carbon nitride in the bombarded films.

Reliable Lateral Manipulation of Single Adatom on Metal fcc（lll） Surfaces with a Single-Atom Tip

Using molecular statistics simulations based on the embedded atom method potential, we investigate the reliability of the lateral manipulation of single Pt adatom on Pt（111） surface with a single-atom tip for different tip heights （tip-surface distance） and tip orientations. In the higher tip-height range, tip orientation has little influence on the reliability of the manipulation, and there is an optimal manipulation reliability in this range. In the lower tip- height range the reliability is sensitive to the tip orientation, suggesting that we can obtain a better manipulation reliability with a proper tip orientation. These results can also be extended to the lateral manipulation of Pd adatom on P d （111） surface.

Magic Number Behaviour and Structures of Silicon Dioxide-Based Clusters

The lowest energy structures of （SiO2）nO2 duster skeletons with size from n = 2 to 12 is investigated theoretically by genetic algorithm. The calculations based on the Tsuneyuki-Tsukada Aoki Matsui （TTAM） and Flikkema- Bromley （FB） potentials give the same result： n = 4 and n = 8 are the magic numbers in the virtual （SiO2）nO2 cluster sequence. This conclusion is in agreement with the experimental observation on the [（SiO2）nO2H3]- cluster sequence. The comparison of the present results with those from the density-functional-theory calculations on （SiO2）nO2H4 shows that addition of II atoms to the O terminals of （SiO2）nO2 clusters to form the complex （SiO2）nO2H4 clusters has only minor influence on the relative energies and the structures of different isomers. This means that the magic behaviour of the dusters [（SiO2）nO2H3]^- （n=4,8） observed in our previous experiment is originated from the stability of the cluster skeletons （SiO2）nO2 （n = 4, 8） .

Fragmentation Mechanism of Fullerenes in the Positive and Negative Ion Channels

The authors have performed the photofragmentation studies of pristine C_(60) and C_(60)/C_(70) composites on the reflectron time-of-flight mass spectrometer(RTOF MS)in the positive and negative ion channels.The mechanism of the formation of daughter fullerenes in the negative ion channel and the enhancement of fullerene coalescence reactions have been discussed compared to our previous studies on the linear TOF.The 5 cm free expansion path in the RTOF experiments provides sufficient time and favorable environment for the electrons to attach to the neutral daughter species,so it is thought to play a key role for the appearance of strong mass peaks of anionic fragmentation and aggregation fullerene products.The appearance of odd-numbered“fullerene”fragments is briefly discussed.

Optimization of Scatterer Concentration in High-Gain Scattering Media

We report the scatterer concentration-dependent behaviour of laser action in high-gain scattering media.A modified model of random laser is proposed to explain the experimental results in good agreement.We may use this modified model to design and optimize random laser system.A further detailed model is needed to quantitatively analyse the far-field distribution of random laser action.

Dissociation of Oxygen on a Polycrystalline Ag Surface: A Second-Harmonic Generation Study

An optical second-harmonic generation study on the dissociation of oxygen on a polycrystalline Ag surface is reported in this paper.The adsorption of oxygen at room temperature exhibits two kinds of adsorption states:diatomic and atomic states.The existence of atomic state oxygen hinders the further dissociation of diatomic oxygen.

Adatom self-diffusion on Pt (100) surface by an ad-dimer migrating

We study the self-diffusion of adatom on Pt(100) surface by molecular dynamics. The metal is modeled by the surface embedded-atom potential. Besides the conventional concerted exchange mechanism, a new exchange mechanism in which an ad-dimer diffuses by a concerted motion of three atoms is observed. The importance is that it could become a dominant diffusion mechanism in some cases.

A Time-of-flight Mass Spectrometric Study of the Laser Desorption Dissociation of C_(60) and C_(70)

1 Introduction C60 and other cage-like carbon molecules, or the fullerenes, have become one ofthe most interesting materials in physics, chemistry and materials science in recentyears. In 1985, C60+ ion was found to be prominent in the laser-ablation mass spec-trum of graphite and unusual stability was proposed for C60 later. The discovery byKratschmer and his co-workers of a method for producing macroscopic.quantities ofC60 and C70 in 1990 has stimulated great interest to investigate the properties of C60and other fullerenes. Many papers have been concerned with the dissociationand stability of C60 and its ions. Studies of C60+ dissociation by means

Simulation of dimer diffusion on metal fcc (001)surfaces by molecular dynamics

We study systematically the dimer diffusion on metal fcc (001) surfaces through molecular dynamics calculations based on embedded atom method. Besides the conventional hopping and exchange mechanisms, some other interesting diffusion mechanisms are observed, such as the exchange rotation mechanism, the cooperative hopping mechanism, and the cooperative exchange mechanism. On the different kinds of metal surfaces, we find that not only the dominant diffusion mechanism but also the physical model for the exchange mechanism is different.