Shihao Pu

Biocompatibility and bioactivity of plasma-treated biodegradable poly(butylene succinate).

Poly(butylene succinate) (PBSu), a novel biodegradable aliphatic polyester with excellent processability and mechanical properties, is a promising substance for bone and cartilage repair. However, it typically suffers from insufficient biocompatibility and bioactivity after implantation into the human body. In this work, H(2)O or NH(3) plasma immersion ion implantation (PIII) is conducted for the first time to modify the PBSu surface. Both the treated and control specimens are characterized by X-ray photoelectron spectroscopy, contact angle measurements and atomic force microscopy. The plasma treatments improve the hydrophilicity and roughness of PBSu significantly and the different PIII processes result in similar hydrophilicity and topography. C-OH and C-NH(2) functional groups emerge on the PBSu surface after H(2)O and NH(3) PIII, respectively. The biological results demonstrate that both osteoblast compatibility and apatite formability are enhanced after H(2)O and NH(3) PIII. Furthermore, our results suggest that H(2)O PIII is more effective in rendering PBSu suitable for bone-replacement implants compared to NH(3) PIII.

Ag and Ag/N2 plasma modification of polyethylene for the enhancement of antibacterial properties and cell growth/proliferation.

Polyethylene (PE) is one of the most common materials used for medical implants. However, it usually possesses low biocompatibility and insufficient antibacterial properties. In the work described here, plasma immersion ion implantation (PIII) is employed to implant silver into PE to enhance both its antibacterial properties and its biocompatibility. Our results show that Ag PIII can give rise to excellent antibacterial properties and induces the formation of functional groups such as C-O and C=C. These C-O and C=C groups on the modified surface can trigger the growth of the human fetal osteoblastic cell line (hFOB). Furthermore, combining N(2) and Ag PIII prolongs the antibacterial effects, but nitrogen-containing functional groups such as C-N and C=N created by N(2) co-PIII negatively impact proliferation of hFOB on the surface. According to our experimental investigation on cell proliferation, functional groups such as C-N and C=N created by nitrogen PIII are disadvantageous to cell growth whereas the C-O and C=C groups benefit cell growth. Both the antibacterial activity and biocompatibility of PE can be enhanced by means of the proper plasma surface treatment.

Effects of magnetic field gradient on ion beam current in cylindrical Hall ion source

The effects of the magnetic gradient on the ion beam current in an end Hall-type ion source with a magnetic mirror field are investigated. In a cylindrical Hall ion source in which a cylindrical magnetic ring other than a regular magnetic pole is shortened and centrally inserted, a mirror magnetic field profile can be formed around the annular anode. A positive-negative variable magnetic gradient is shown experimentally to enhance ionization; the ionization efficiency is substantially affected by the different magnetic gradient. The high ionization results in 60% efficiency in the conversion of discharge current to ion beam current. The experimental results and interpretation of the effects are presented in this paper.

Linear ion source with magnetron hollow cathode discharge

A linear ion source with magnetron hollow cathode discharge is described in this paper. The linear ion source is based on an anode layer thruster with closed-drift electrons that move in a closed path in the E×B fields. An open slit configuration is designed at the end of the ion source for the extraction of the linear ion beam produced by the magnetron hollow cathode discharge. The special configurations enable uninterrupted and expanded operation with oxygen as well as other reactive gases because of the absence of an electron source in the ion source. The ion current density and uniformity were experimentally evaluated. Using the ion source, surface modification was conducted on polyethylene terephthalate polymer films to improve the adhesion strength with ZnS coatings.

Dependence of ion sheath collapse on secondary electron emission in plasma immersion ion implantation

The collapse of the ion sheath in front of a dielectric substrate during argon plasma immersion ion implantation is investigated using a Langmuir probe. The probe signals during the buildup and collapse of the ion sheath are recorded from a lime glass substrate with a magnesium metal plate placed on top. The collapsing speed of the ion sheath is shown to strongly depend on the secondary electron emission coefficient of the substrate. The authors’ results show that it is possible to derive secondary electron emission coefficients from insulating materials based on the probe signals.

Evolution mechanism of nanocrystalline tungsten-carbon and effects on tungsten implanted amorphous hydrogenated carbon

Tungsten doped amorphous carbon films are prepared on silicon (100) by postimplantation of tungsten ions into pure amorphous hydrogenated carbon using the plasma immersion ion implantation technique. The peak concentration of tungsten reaches 27at.% and W–C nanocrystallites with largest diameters of ∼5nm are formed in the near surface region. Both the quantity and size of these nanocrystallites are observed to undergo unique transformation with increasing depths, enabling gradual release of the compressive stress and subsequently leading to better adhesion between the film and substrate. The film structures are evaluated by x-ray photoelectron spectroscopy and glancing angle x-ray diffraction, and high-resolution transmission microscopy is employed to investigate the structural transformation. The mechanical properties of the films including adhesion strength and hardness are determined by nanoindentation and nanoscratch tests. The formation of the nanocrystalline structures can be explained by ion implan...

Experimental and theoretical investigation of the effects of sample size on copper plasma immersion ion implantation into polyethylene

Polymers are frequently surface modified to achieve special surface characteristics such as antibacterial properties, wear resistance, antioxidation, and good appearance. The application of metal plasma immersion ion implantation (PIII) to polymers is of practical interest as PIII offers advantages such as low costs, small instrument footprint, large area, and conformal processing capability. However, the insulating nature of most polymers usually leads to nonuniform plasma implantation and the surface properties can be adversely impacted. Copper is an antibacterial element and our previous experiments have shown that proper introduction of Cu by plasma implantation can significantly enhance the long-term antibacterial properties of polymers. However, lateral variations in the implant fluence and implantation depth across the insulating substrate can lead to inconsistent and irreproducible antibacterial effects. In this work, the influence of the sample size on the chemical and physical properties of copp...

Response to “Comment on `Effects of magnetic field gradient on ion beam current in cylindrical Hall ion source' '' [J. Appl. Phys. 104, 066102 (2008)]

The comments by Raitses et al. are basically about the comparison between their ion source and the one described in our paper stated in Sec. I. First of all, they do not question our data or the performance of our ion source. After reading their comments carefully, we have the following comments. Raitses et al. may have misread our description. “A cylindrical Hall thruster with a cusp magnetic field for enhanced ionization, especially a low-power Hall thruster, has been investigated by Smirnov et al. The major difference from a conventional end-Hall ion source/thruster is the cylindrical configuration with an enhanced radial component of a cusp-type magnetic field.” In Sec. I of our paper, the above description is also concluded from the following: “A cylindrical Hall thruster CHT , suggested in Ref. 6, is illustrated in Fig. 1 a . The thruster consists of a boron nitride ceramic channel, an annular anode, which serves also as a gas distributor, two electromagnetic coils, and magnetic core. What distinguishes this thruster from conventional annular and end-Hall thrusters is the cylindrical configuration with an enhanced radial component of the cusp-type magnetic field Fig. 1 b .”In our paper, we intended to only briefly introduce other researchers’ works on different Hall ion sources or thrusters, especially about magnetic field distribution. We had no intention to compare the performance of different ion sources, including the CHT and other hall ion sources/thrusters. Therefore, such a detailed comparison is beyond the scope of our paper. In addition, if they want to compare their CHT with the end Hall sources EHS and our cylindrical hall ion source, they should submit a regular paper rather than comment on our paper. It is our belief that comments about a published paper should focus on the data presented, not about one sentence in the introduction that has very little impact on the rest of the paper.

Effects of high temperature ion implantation on titanium nitride coated carbide cutting tools

Summary form only given. The effects of high temperature nitrogen and aluminum ion implantation and plasma implantation on titanium nitride coated carbide cutting tools are investigated. Aluminum implantation is used to enhance the high temperature oxidation wear resistance, and plasma nitriding and high-temperature ion implantation are used to further improve the surface microhardness and corrosion resistance. TiN films are deposited on carbide cutting tools by vacuum arc ion plating, in which a shutter plate is used to avoid line of sight transit of macro-particles from the cathode to the substrate. Nitrogen and aluminum ion implantation at elevated temperature (300-600/spl deg/C) is then achieved in a multi-function ion implantation system. The effects of different substrate temperature, implantation dose and implantation energy on the surface properties are assessed. The corrosion measurements are carried out in a NaCl solution using electrochemical impedance spectroscopy. The oxidation resistance studies are carried out in air at 800/spl deg/C using continues and discontinuous method. The surface microhardness, crystal structure and microstructure are measured by microhardness measurement, XRD, SEM and AES. The process is applied to industrial cutting tools in the production line, and the results are reported in this paper.