Zhang Xiaoji

Broad beam high average current metal ion source

For industrial application in material surface modification it is necessary to obtain higher average beam current for metal ion implantation. Two new versions of MEVVA ion source, MEVVA‐II and MEVVA‐IIA, in which the size of the extraction area is expanded to 60 mm in diameter have been developed, based on MEVVA‐I being constructed early. The sources are operated in pulsed mode with a maximum beam duty cycle of 6%. A time average beam current of up to 10–30 mA has been extracted from a range of different cathode materials, such as C, Mg, Al, Ti, V, Cr, Fe, Ni, Cu, Zn, Y, Zr, Mo, Nb, Sn, Ta, W, and Pb. In the MEVVA‐IIA, particularly, a movable cathode is used for compensating the consumption of the cathode material during the source operation, so that the running time may be extended, for example, it has been operated stably more than 16 h with a 10 mA beam current with a Ti cathode. In this paper, we will describe the source and some preliminary results.

High‐current metal‐ion source for ion implantation

High‐current metal‐ion beams, as needed for material modification of metal surfaces, can be produced using the MEVVA ion source. In this article a brief description of the ion source is given, and its operational characteristics and preliminary results are presented. A range of metal ions such as Cu, Ti, Al, Fe, Mo, and W, etc., have been extracted from the source. The ion‐beam current is 0.5–1 A (total current in all charge states) and is a function of the cathode material, arc current, and extractor voltage. The beam pulse width is 300–550 μs, the repetition rate several pulses per second, the extraction voltage about 30 kV, and the arc current 150–350 A. The extraction system has a set of three multiaperture extractor grids, including three different sizes: 37 holes 2 mm in diameter, and 207 and 495 holes 1 mm in diameter. The operating pressure is in the 2×10−6‐Torr range, obtained with a diffusion pump.

Industrialization of MEVVA source ion implantation

Abstract Ion implantation is being successfully applied for the reduction of corrosion, wear and oxidation of materials. As a result, ion implantation as an engineering tool is a powerful and relatively important technique. In order to develop applications of ion implantation for precision tooling, moulds and large number of engineering components, improvement in the MEtal Vapor Vacuum Arc (MEVVA) source implantor for industrial ion implantation now offers more attractive costs per unit area and a potentially greater throughput. Material modification was produced by MEVVA source implantation at high target temperature (200∼550°C) with high ion flux (25∼100 μA/cm 2 ). Metal ion implantation has yielded good results in the improvement of drills, cutters, dies, bearings and off-gas pumps for returnable artificial satellites using MEVVA source implantors. The results show that reduction of manufacturing costs and the challenges to improve component performance justify consideration of metal ion implantation in industrial processing. The ion implantation workshop was established with two implantors for industrial application. Millions of drills were processed per year. A large number of ion-implanted products have been exported up to now.

Influence of nanostructure on electrical and mechanical properties for Cu implanted PET

Abstract Polyethylene terephthalate (PET) has been modified by 40 KeV Cu ion using a metal vapor vacuum arc (MEVVA) source to fluence ranging from 1×10 16 to 2×10 17 ions/cm 2 . The surface morphology was observed by atomic force microscopy (AFM). The Cu atom precipitation and nano-structure of Cu implanted PET were observed. It is believed that the structure change improves the electrical properties and wear resistance of PET. The electrical properties of PET have been improved extremely after ion implantation. The surface resistance of implanted PET decreased obviously with an increase of ion dose. When metal ion dose was higher than 1×10 17 cm −2 , the surface resistivity of PET could be less than 0.1 Ω m. The results show that the conductive behavior of a Cu ion implanted sample is much better than that of non-metal Si- and C-ion implanted one. After Cu implantation, the surface hardness and Youngs modulus increase and the cross-section area of cutting groove is narrow and shallow comparing with the unimplanted PET. The modification mechanism of PET was discussed.

Polymer modification by MEVVA source deposited and ion implantation

Polyethylene terephthalate (PET) has been modified by Ti, Ni and W deposition using a metal vapor vacuum arc (MEVVA) source and implantation. The surface resistance of deposited PET could decrease to several hundred ohms. The adhesion of metal coating on polymers is very strong. The thickness of the deposited metal coating could be controlled from tens of nanometers to 1 μm. The hardness for thick Ti and W deposited PET is 3.81 and 2.54 GPa, which are several times greater than that of PET. The elastic modulus of deposited PET increases also. Similar results have been observed for other metal implanted PET. The thickness and atomic distribution of deposited metal coating was analyzed using RBS. The surface structure has varied after deposition and implantation. It is believed that the change would cause the improvement of the conductive properties and wear resistance.

The Beijing metal vapor vacuum arc ion source program

Work on metal vapor vacuum arc (MEVVA) ion source development was initiated at the Institute of Low Energy Nuclear Physics, Beijing Normal University, in 1988. MEVVA ion sources I, II, IIA, and III have been designed, fabricated, and tested, and an ion implantation facility with three MEVVA ion sources has been developed and is now undergoing testing. Here the status of the MEVVA ion source research and development program is described.

A modified, filtered, pulsed cathodic vacuum arc implantation and deposition apparatus with the filtering duct working as a second anode

Abstract A modified filtered pulsed cathodic vacuum arc implantation and deposition apparatus with the filtering duct biased positively 30–60 V relative to the cathode has been set up. Pulsed cathodic vacuum arc discharge between the duct and the cathode was observed. As a result of this, the cathode erosion rate and ion intensity at the substrate increased dramatically. The influence of the focusing magnetic field of the MEVVA plasma source as well as the positive bias and the guide magnetic field of the filtering duct on the arc discharge and the duct output were studied. Experimental results show that the output of the duct and the duct current increased with increasing duct potential and increasing arc source focusing magnetic field. It is also shown that the duct current decreased with an increase in the guiding magnetic filed, and 7–8 mT duct magnetic field is the optimum for the duct output.

Nanometer structure and conductor mechanism of polymer modified by metal ion implantation

Polyethylene terephthalate (PET) has been modified by Ag, Ti, Cu and Si ion implantation with a dose ranging from 1×1016 to 2×1017 ions/cm2 using a metal vapor vacuum arc (MEVVA) source. The electrical properties of PET have been improved by metal ion implantation. The resistivity of implanted PET decreased obviously with an increase in ion dose. The results show that the conductive behavior of a metal ion implanted sample is different from Si-implantation samples. In order to understant the mechanism of electrical conduction, the structures of implanted layer were observed in detail by XRD and TEM. The nano carbon particles were dispersed in implanted PET. The nano metallic particles were built up in metallic ion implanted layers with dose range from 1 × 1016 to 1 × 1017 ions/cm2. The nanometer metal net structure was formed in implanted layer when a dose of 2 × 1017ions/cm2 is reached. Anomalous fractal growths were observed. These surface structure changes revealed conducting mechanism evolution. It is believed that the change would result in an improvement of the conductive properties. The conducting mechanism will be changed with increasing metal ion dose.

Ranges, straggling and carrier concentration profiles of 0.5-6.0 MeV phosphorus in silicon

Abstract Using an lonex Company 2×1.7 MeV Tandem experiments were conducted to obtain a more detailed knowledge of ranges, straggling and carrier concentration profile for P + implanted into P-type (111) Si at 0.5–6.0 MeV to doses ranging from 4×10 12 to 1×10 13 cm −2 . The annealing of the samples was carried out by Rapid Thermal Annealing (RTA) at 1000–1050°C for 10 s to achieve a high electrical activation and small spreading. The carrier concentration profiles were measured by Spreading Resistance Probe (SRP). It is found that the profiles are two joined half-Gaussian distribution with different standard deviations σ front and σ back . σ front is greater than σ back . The buried layers of N -type carrier appear when the P + energy is higher than 3.0 MeV. The ranges and straggling of 0.5–6.0 MeV P + implantation in Si have been obtained, but the values of measured ranges are less than that of the theoretical values. Some characteristics of the high energy P + implantation in Si are discussed.

Properties of corrosion resistance in C++W+ dual implanted steel with nanometer phases

Abstract The property of corrosion resistance for C + +W + dual-implanted H13 steel was studied using multi-sweep cyclic voltammetry. The phase formation conditions for corrosion resistance and its effects were researched. The super-saturation solid station solution of W + and C + atoms was formed in tungsten plus carbon dual-implanted steel. Nanometer size precipitates consisting of the phases of Fe 2 W, FeW, WC, Fe 5 C 3 and Fe 7 C 3 were formed in the dual-implanted layer. The passivation layer consisted of the nanometer phases. The corrosion resistance of the dual implanted layer is better than that of single implantation. The corrosion resistance of the dual implantation was enhanced following increase of ion dose. When the W + ion dose was 6×10 17 /cm 2 in the dual implantation, J p of the dual implanted sample is 17–33 times less than that of J p in H13 steel.