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.

A New Method for Thin Film Deposition-Faced Microwave Electron Cyclotron Resonance Plasma Sources Enhanced Direct-Current Magnetron Sputtering

A new reactive magnetron sputtering system enhanced by the faced microwave electron cyclotron resonance plasma source was designed and amorphous CN_(x) films has been prepared by using this system.The character ization of the films by interference microscopy,atomic force microscopy,and x-ray photoelectron spectroscopy shows that the deposition rate is strongly affected by the direct-current bias,and the films are composed by a single carbon nitride phase and the N/C ratio is 4:3.2,which is close to that of C_(3)N_(4)(4:3).

Effect of temperature on vacuum hot bulge forming of BT20 titanium alloy cylindrical workpiece

Temperature is one of the key parameters for BT20 titanium alloy cylindrical workpiece manufactured by vacuum hot bulge forming. A two-dimensional nonlinear thermo-mechanical coupled FE model was established. Numerical simulation of vacuum hot bulge forming process of titanium alloy cylindrical workpiece was carried out using FE analysis software MSC Marc. The effects of temperature on vacuum hot bulge forming of BT20 titanium alloy cylindrical workpiece were analyzed by numerical simulation. The simulated results show that the Y-direction displacement and the equivalent plastic strain of the workpiece increase with increasing bulge temperature. The residual stress decreases with increasing bulge temperature. The optimal temperature range of BT20 titanium alloy during vacuum hot bulge forming is 750-850 ℃. The corresponding experiments were carried out. The simulated results agreed well with the experimental results.

Improvement of wear resistance of AZ31 and AZ91HP by high current pulsed electron beam treatment

The surface modification of magnesium alloys (AZ31 and AZ91HP) was studied by a high current pulsed electron beam(HCPEB). The results show that the cross-sectional microhardness of treated samples increases not only in the heat affected zone(HAZ), but also beyond HAZ, reaching over 250μm. This is due to the action of quasi-static thermal stress and the shock thermal stress wave with materials, which result in its fast deformation on the surface layer and so increases microhardness. For the AZ91HP alloy, a nearly complete dissolution of the intermetallic phase Mg_ 17Al_ 12 is observed, and a super-saturated solid solution forms on the re-melted surface, which is due to the solute trapping effect during the fast solidification process. Measurements on sliding wear show that wear resistance is improved by approximately 5.6 and 2.4 times for the AZ31 and AZ91HP respectively, as compared with as-received samples.

Non-Uniformity of Ion Implantation in Direct-Current Plasma Immersion Ion Implantation

particle-in-cell 模拟被开发学习 dc 血浆沉浸离子培植。特别注意对在目标表面上在离子路径，和离子流动分发上用于目标的电压的影响被给予。在血浆区域以内的孔附近的潜力不是血浆潜力，这被发现，并且被用于植入的目标的电压影响。一个弄弯的等位的轮廓通过孔膨胀进血浆区域，扩大的程度取决于电压。电场在鞘加速的离子在目标表面上形成横梁形状和流动分布，它强烈依赖于应用电压。模拟的结果表明格子阴影效果的形成机制，它与试验性地观察的结果一致。[从作者抽象]

Self-Consistent Model for Pulsed Direct-Current N_2 Glow Discharge

A self-consistent analysis of a pulsed direct-current (DC) N2 glow discharge is presented. The model is based on a numerical solution of the continuity equations for electron and ions coupled with Poisson's equation. The spatial-temporal variations of ionic and electronic densities and electric field are obtained. The electric field structure exhibits all the characteristic regions of a typical glow discharge (the cathode fall, the negative glow, and the positive column). Current-voltage characteristics of the discharge can be obtained from the model. The calculated current-voltage results using a constant secondary electron emission coefficient for the gas pressure 133.32 Pa are in reasonable agreement with experiment.

Transition from Spark Discharge to Constricted Glow Discharge in Atmospheric Air by Capacitor Coupled Discharge

The transition from a spark discharge to a constricted glow discharge in atmospheric air was studied with a capacitor coupled pin-to-water plasma reactor. The reason of the transition is considered to be of various factors, namely the change of the air gap due to the polarization of water molecules by the electric field, the feedback effect of the capacitors, and the ion trapping mechanism. The effects of the frequency of the power supply, inter-electrode gap, and coupled capacitance on the discharge transition were also investigated.

Anomalous Photofragmentation of Fullerene Doped in Silica Aerogel-Enhanced Formation of Odd-Numbered "Fullerene" Fragments

Photofragmentation of fullerene-doped silica aerogels has been investigated by the excimer laser ablation reflectron time-of-flight mass spectrometric technique. Great enhancement in the formation of odd-numbered ‘fullerene’ fragments has been observed in the negative-ion channel for the chemically doped aerogel sample. Generally, oddnumbered species C57, C55, C53 and C51 appeared in the mass spectra. Under optimM experimental conditions C55 can be even more intense than the neighbouring even-numbered carbon clusters. In contrast, for the physicallydoped sample, just like pristine C6o, only weak odd-numbered fragments were observed. In the positive-ion channel, the behaviour of all these samples is similar, no odd-numbered species was ever detected. A mechanism related to the interaction between the fullerene dopant and the silica aerogel host is suggested for the anomalous enhancement of the odd-numbered duster formation. A preliminary discussion on the structures of the oddnumbered‘fullerene’ fragments is given.

Deposition of ZnO Films on Freestanding CVD Thick Diamond Films

For ZnO/diamond structured surface acoustic wave （SAW） filters, performance is sensitively dependent on the quality of the ZnO films. In this paper, we prepare highly-oriented and fine grained polycrystalline ZnO thin films with excellent surface smoothness on the smooth nucleation surfaces of freestanding CVD diamond films by metal organic chemical vapour deposition （MOCVD）. The properties of the ZnO films are characterized by x-ray diffraction （XRD）, scanning electron microscopy （SEM）, and photoluminescence （PL） spectrum. The influences of the deposition conditions on the quality of ZnO films are discussed briefly. ZnO/freestanding thick-diamond-film layered SAW devices with high response frequencies are expected to be developed.

THE COUPLED FEM ANALYSIS OF THE TRANSIENT TEMPERATURE FIELD DURING INERTIA FRICTION WELDING OF GH4169 ALLOY

The inertia friction welding process is a non-linear process because of the interaction between the temperature field and the material properties as well as the friction force. A thermo-mechanical coupled finite element model is established to simulate the temperature field of this process. The transient temperature distribution during the inertia friction welding process of two similar workpieces of GH4169 alloy is calculated. The region of the circular cross-section of the workpiece is divided into a number of four-nodded isoparametric elements. In this model, the temperature dependent thermal properties, time dependent heat inputs, contact condition of welding interface, and deformation of the flash were considered. At the same time, the convection and radiation heat losses at the surface of the workpieces were also considered. A temperature data acquisition system was developed. The temperature at some position near the welding interface was measured using this system. The calculated temperature agrees well with the experimental data. The deformation of the flash and the factor affecting the temperature distribution at the welding interface are also discussed.

The Interactions of Two Cold Atmospheric Plasma Jets

This paper presents the interactions between two cold atmospheric plasma jets. By changing the experimental conditions including the gas flow rate, the applied voltage, the power supply frequency and the inter-electrode distance d, three different interaction modes, attraction, repulsion and combination, were observed. It is shown that the interaction modes of the two jets are principally affected by the electrodes, the gas flow rate, the plasma jets and the power supply frequency.

Effects of Airflows on Dielectric Barrier Discharge in Air at Atmospheric Pressure

Effect of airflow on the dielectric barrier discharge in ambient air at atmospheric pressure is presented. The influence of airflow on the spatial distribution and intensity of a discharge were investigated experimentally. A critical frequency of 1 kHz was found. With the frequency above 1 kHz, when a fast airflow was introduced into the discharge gap, the discharge patterns varied from filaments to curved stripes and the curvature degree rose with an increase in the airflow speed. At the same time, the discharge intensity decreased. However with the discharge frequency below 1 kHz, the discharge intensity would get greater with an increase in the airflow speed.

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.

Simplification of the Plasma Load of Negative-Pulse-Bias Source Used in Arc Ion Plating

Based on the voltage and current fluctuating phenomenon in the arc plasma load under the negative-pulse-bias, usingthe plasma physics theory and analysis of computer simulation expatiates that the nature of plasma load in vacuumarc plasma is a capacitance load caused by plasma sheath and can be simplified as a parallel unit composed of acapacitor and a resistor, which have exact and quantitative description in the plasma physics theory. It concludes thevalues of capacitance and resistance are thousand PF and hundred ohm from the result of simulation and experiment.As a result, this has solved the key theoretical issues for the design of negative-pulse-bias source specifically used forvacuum arc ion plating.

Two-dimensional particle-in-cell plasma source ion implantation of a prolate spheroid target

A two-dimensional particle-in-cell simulation is used to study the time-dependent evolution of the sheath surrounding a prolate spheroid target during a high voltage pulse in plasma source ion implantation. Our study shows that the potential contour lines pack more closely in the plasma sheath near the vertex of the major axis, i.e. where a thinner sheath is formed, and a non-uniform total ion dose distribution is incident along the surface of the prolate spheroid target due to the focusing of ions by the potential structure. Ion focusing takes place not only at the vertex of the major axis, where dense potential contour lines exist, but also at the vertex of the minor axis, where sparse contour lines exist. This results in two peaks of the received ion dose, locating at the vertices of the major and minor axes of the prolate spheroid target, and an ion dose valley, staying always between the vertices, rather than at the vertex of the minor axis.

Novel Plasma Reactor with Rotary Helix Electrode Used in Coupling of CH_4 at Atmospheric Pressure

At the ambient temperature and pressure a glow discharge plasma was used as a new approach for the coupling of methane with the newly-developed rotary multidentate helix electrode. In the presence of hydrogen, the effects of the input peak voltages and gas flow rates on methane conversion, C2 single pass yield and selectivity were investigated, and then the results were compared with those from the three-disc multidentate electrode. This demonstrated, on an experimental scale, that the rotary multidentate helix electrode was better than the multidentate three-disc electrode as there was little accumulation of coke, and the C2 yield per pass was 69.85% and C2 selectivity over 99.14% with 70.46% methane conversion at an input peak voltage of 2300 V and 60 ml/min gas flow rate.

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） .

RC-Coupled Atmospheric Glow Discharge in Air

Resistance and capacity-coupled glow discharge （RCCGD） is a new method to produce atmospheric pressure glow discharge in air. In RCCGD, each electrode is connected with both a resistor R and a capacitor C. The R and C can provide a negative feedback to prevent the transition from glow to spark discharge. The influence of coupled resistance, coupled capacity, inter-electrode gap and power source frequency on the discharge is studied and discussed.

Modeling of Pulsed Direct-Current Glow Discharge

A self-consistent model was adopted to study the time evolution of low-voltage pulsed DC glow discharge. The distributions of electric field, ion density and electron density in nitrogen were investigated in our simulation, and the temporal shape of the discharge current was also obtained. Our results show that the dynamic behaviors of the discharge depends strongly on the applied pulse voltage, and the use of higher pulse voltages results in a significantly increase of discharge current and a decrease of discharge delay time. The current-voltage characteristic cMculated by adjusting secondary electron emission coefficient for different applied pulse voltage under the gas pressure of 1 Torr is found in a reasonable agreement with the experimental results.

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.