Langmuir探针在等离子体诊断中的抗干扰方法

本文介绍了三种Langmuir探针在等离子体诊断中抗干扰的方法:积分平均技术--采用积分电路,有效抑制波动干扰,提高探针信噪比;滤波器--利用同轴电缆构成级连滤波器网络,消除射频源基频及谐频干扰;差分放大器--两根同轴电缆与差分放大器配合使用,消除由于同轴电缆电阻电容(RC)特性引起的诱导噪音.上述方法分别从抗干扰原理、抗干扰装置和实验结果三方面予以了说明,指出了目前使用Langmuir探针进行等离子体诊断时存在的问题,并提出了解决方案.     

Prediction of pork belly fatness from the intact primal cut

Research was successfully undertaken to identify one or more non-invasive measuring sites on the primal belly which would predict belly fatness as well as or better than backfat depth at the grading site. Crossbred market weight gilts (n = 297) were slaughtered, dressed, graded, chilled and fabricated into primals according to commercial Canadian practice. A series of measurements were made on the primal both directly on the belly/loin cut, and from images of the cut. The ribbed, skinned and trimmed belly was ground for NIR compositional analysis. Both grade fat depth and one direct fat measurement (SFt) on the belly were equally strongly correlated with % fat in the belly (r = 0.86, P < 0.0001). Stepwise regression showed that calculated fat depths (Nolean 1 and 2) supplemented by a lean measurement (SLn) returned an R² of 0.854 (RMSE 3.20), outperforming the grade site data (R² = 0.762, RMSE 4.09). Prediction of belly fatness from measurements taken at the intersection of the belly/loin and belly/shoulder cuts was found to be poor.     

Development of a novel tool for semiconductor process control

A collaborative project between the Surrey Ion Beam Centre and the positron beam group at the University of Bath is developing a bench-top positron tool suitable for use in the semiconductor industry. The technique's non-destructive nature, coupled with its high sensitivity to defects, makes it a potentially ideal method for detecting process problems at an early stage. Measurements on the existing laboratory-based system have shown, for example, a high sensitivity to variations in parameters such as temperature in the growth of epitaxial layers. An instrument suitable for use in the fabrication environment is described, together with diagnostic studies of PECVD-deposited SiN layers, of thicknesses in the range 21–133 nm, performed in conjunction with ellipsometric and RBS measurements. The technique is sensitive to the atomic composition of the SiN epilayers and, in conjunction with ellipsometry, is able to measure the density of the layers and to quantify the densification on annealing at 900°C.     

Effect of mono and composite coating on dynamic fracture toughness of metals at different temperatures

It is well known that during the operating condition of any metallic structural system the dynamic crack growth speed is in the order of 1–2 km/s. Industrial finishes like coating which form the integral part of manufacturing is adopted to improve fracture toughness of metals. These coated samples coated with thin films are mechanically tested by Charpy V-notch impact tester for estimating dynamic fracture toughness. Coatings improve the wear and corrosion resistance of materials; they tend to reduce the strength of materials, because of the increased residual stresses due to the coating process. Defects cannot be precluded from these coated and treated components; strength of those components in the presence of these defects can be analyzed by fracture mechanics approach. An attempt has been made to analyze the effectiveness of coating methods like electroplating, PVD (Physical Vapour Deposition), coating thickness and the service temperature on the fracture behaviour of metals. Experiments have been carried out on EN8 steel and aluminium for different temperatures and the later samples were corroded for 2400 h and tested for corrosion resistance. The specimen preparation and experimentations were carried out according to the ASTM standard E-23. Finite element analysis was done by FRANC 2D (Fracture Analysis Code) for estimating the stress intensity factor at different crack lengths along with influence of temperature and corrosion. PVD coated samples of Al–N (aluminium nitride) and nano-crystalline layer of Ti–Al–N (titanium aluminium nitride) showed improved dynamic fracture toughness properties. The same set of samples showed decrease in stress intensity factors and excellent corrosion resistance compared to conventional Ni (nickel) and Cr (chromium) coated samples. Mechanical behaviour of selected metals under heat affected zone is of also discussed in this paper, the study aims at both coated and uncoated cases. Performances of metals in cryogenic condition are also paid attention in this paper.     

Deposition and characteristics of GaN films on Ni metal substrate by ECR-PEMOCVD

Gallium nitride (GaN) films were deposited on Ni metal substrate using electron cyclotron resonance plasma-enhanced metal organic chemical vapor deposition system. With this approach, highly c-oriented GaN films with smooth surface were obtained at an extremely low temperature of ~480 °C. The trimethyl gallium (TMGa) flux dependent structural, morphological, and optical characteristics of GaN films were investigated by X-ray diffraction analysis, reflection high energy electron diffraction, atomic force microscopy and photoluminescence analysis. The results indicate that it is feasible to deposit GaN films on Ni metal substrate under the proper deposition procedures. The high quality GaN films with high c-axis orientation and strong ultraviolet emission peak are successfully achieved under the optimized TMGa flux of 1.2 sccm. The GaN/Ni structure has great potential for the development of high power devices with excellent heat dissipation.     

Arrays of Cone‐Shaped ZnO Nanorods Decorated with Ag Nanoparticles as 3D Surface‐Enhanced Raman Scattering Substrates for Rapid Detection of Trace Polychlorinated Biphenyls

A new, highly sensitive and uniform three‐dimensional (3D) hybrid surface‐enhanced Raman scattering (SERS) substrate has been achieved via simultaneously assembling small Ag nanoparticles (Ag‐NPs) and large Ag spheres onto the side surface and the top ends of large‐scale vertically aligned cone‐shaped ZnO nanorods (ZnO‐NRs), respectively. This 3D hybrid substrate manifests high SERS sensitivity to rhodamine and a detection limit as low as 10^?11 M to polychlorinated biphenyl (PCB) 77—a kind of persistent organic pollutants as global environmental hazard. Three kinds of inter‐Ag‐NP gaps in 3D geometry create a huge number of SERS “hot spots” that mainly contribute to the high SERS sensitivity. Moreover, the supporting chemical enhancement effect of ZnO‐NRs and the better enrichment effect ascribed to the large surface area of the substrate also help to achieve a lower detection limit. The arrays of cone‐shaped ZnO‐NRs decorated with Ag‐NPs on their side surface and large Ag spheres on the top ends have potentials in SERS‐based rapid detection of trace PCBs.     

Reduction and removal of aqueous Cr(VI) by glow discharge plasma at the gas-solution interface

Aqueous chromium(VI) reduction and removal induced by glow discharge taking place at the gas-solution interface in an argon atmosphere was studied. The effect of initial pH and hydroxyl radical scavenger (ethanol) on the reduction efficiency was examined. High reduction efficiency was obtained when initial pH ≤ 2.0 or ≥ 8.0. In particular, addition of ethanol into the solution substantially increased the reduction efficiency and facilitated chromium removal from the solution in the form of sediment after discharge. The optimum pH values for Cr(VI) removal were within 6.0-7.0. Fourier transform-infrared (FTIR) spectroscopy and X-ray diffraction (XRD) analysis confirmed that the main constituent of the sediment is chromium hydroxide.     

Numerical calculation and experimental research on crack arrest by detour effect and joule heating of high pulsed current in remanufacturing

The remanufacturing blanks with cracks were considered as irreparable. With utilization of detour effect and Joule heating of pulsed current, a technique to arrest the crack in martensitic stainless steel FV520B is developed. According to finite element theory, the finite element（FE） model of the cracked rectangular specimen is established firstly. Then, based on electro-thermo-structure coupled theory, the distributions of current density, temperature field, and stress field are calculated for the instant of energizing. Furthermore, the simulation results are verified by some corresponding experiments performed on high pulsed current discharge device of type HCPD-I. Morphology and microstructure around the crack tip before and after electro pulsing treatment are observed by optical microscope（OM） and scanning electron microscope（SEM）, and then the diameters of fusion zone and heat affected zone（HAZ） are measured in order to contrast with numerical calculation results. Element distribution, nano-indentation hardness and residual stress in the vicinity of the crack tip are surveyed by energy dispersive spectrometer（EDS）, scanning probe microscopy（SPM） and X-ray stress gauge, respectively. The results show that the obvious partition and refined grain around the crack tip can be observed due to the violent temperature change. The contents of carbon and oxygen in fusion zone and HAZ are higher than those in matrix, and however the hardness around the crack tip decreases. Large residual compressive stress is induced in the vicinity of the crack tip and it has the same order of magnitude for measured results and numerical calculation results that is 100 MPa. The relational curves between discharge energies and diameters of the fusion zone and HAZ are obtained by experiments. The difference of diameter of fusion zone between measured and calculated results is less than 18.3%. Numerical calculation is very useful to define the experimental parameters. An effective method to prevent further extensi