Thomas Schuelke

Comparison of filtered high-current pulsed arc deposition (φ-HCA) with conventional vacuum arc methods

Abstract Special features of the filtered high-current pulsed arc deposition (φ-HCA) are presented in comparison with the conventional dc-arc method. The high-current arc technique allows pulse currents of some kiloamperes and averaged arc currents of approximately 1 kA. Due to the high spot velocity the droplet density is already markedly reduced. The remaining particles may be completely eliminated by combination with a magnetic filter. The optimum design of this device together with the high efficiency of the pulsed arc source yields ion currents at the filter exit above 100 A during a pulsed arc and above 10-A averaged current. High quality films with deposition rates of industrial relevance may be produced by advanced arc techniques. Various coatings such as metal refractory nitrides, oxides and hard coatings are investigated and compared with the conventional dc-arc deposition. It is shown that the φ-HCA module is a promising supplementary device that can be attached to industrial standard equipment for various applications demanding smooth mirror-like metallic hard coatings.

Biocompatibility and mechanical properties of diamond-like coatings on cobalt-chromium-molybdenum steel and titanium-aluminum-vanadium biomedical alloys

Diamond-like carbon (DLC) films are favored for wear components because of diamond-like hardness, low friction, low wear, and high corrosion resistance (Schultz et al., Mat-wiss u Werkstofftech 2004;35:924-928; Lappalainen et al., J Biomed Mater Res B Appl Biomater 2003;66B:410-413; Tiainen, Diam Relat Mater 2001;10:153-160). Several studies have demonstrated their inertness, nontoxicity, and the biocompatibility, which has led to interest among manufacturers of surgical implants (Allen et al., J Biomed Mater Res B Appl Biomater 2001;58:319-328; Uzumaki et al., Diam Relat Mater 2006;15:982-988; Hauert, Diam Relat Mater 2003;12:583-589; Grill, Diam Relat Mater 2003;12:166-170). In this study, hydrogen-free amorphous, tetrahedrally bonded DLC films (ta-C) were deposited at low temperatures by physical vapor deposition on medical grade Co28Cr6Mo steel and the titanium alloy Ti6Al4V (Scheibe et al., Surf Coat Tech 1996;85:209-214). The mechanical performance of the ta-C was characterized by measuring its surface roughness, contact angle, adhesion, and wear behavior, whereas the biocompatibility was assessed by osteoblast (OB) attachment and cell viability via Live/Dead assay. There was no statistical difference found in the wettability as measured by contact angle measurements for the ta-C coated and the uncoated samples of either Co28Cr6Mo or Ti6Al4V. Rockwell C indentation and dynamic scratch testing on 2-10 μm thick ta-C films on Co28Cr6Mo substrates showed excellent adhesion with HF1 grade and up to 48 N for the critical load L(C2) during scratch testing. The ta-C coating reduced the wear from 3.5 × 10(-5) mm(3)/Nm for an uncoated control sample (uncoated Co28Cr6Mo against uncoated stainless steel) to 1.1 × 10(-7) mm(3)/Nm (coated Co28Cr6Mo against uncoated stainless steel) in reciprocating pin-on-disk testing. The lowest wear factor of 3.9 × 10(-10) mm(3)/Nm was measured using a ta-C coated steel ball running against a ta-C coated and polished Co28Cr6Mo disk. Students t-test found that the ta-C coating had no statistically significant (p < 0.05) effect on OB attachment, when compared with the uncoated control samples. There was no significant difference (p < 0.05) in the Live/Dead assay results in cell death between the ta-C coated Co28Cr6Mo and Ti6Al4V samples and the uncoated controls. Therefore, these ta-C coatings show improved wear and corrosion (Dorner-Reisel et al., Diam Relat Mater 2003;11:823-827; Affato et al., J Biomed Mater Res B Appl Biomater 2000;53:221-226; Dorner-Reisel et al., Surf Coat Tech 2004;177-178:830-837; Kim et al., Diam Relat Mater 2004;14:35-41) performance and excellent in vitro cyto-compatibility, when compared with currently used uncoated Co28Cr6Mo and Ti6Al4V implant materials.

Fabrication and properties of ultranano, nano, and microcrystalline diamond membranes and sheets

Thin diamond membranes and free-standing sheets are of interest for a variety of potential applications. This article describes the film nucleation, microwave plasma-assisted chemical-vapor-deposition synthesis, and subsequent processing steps required to make free-standing strong and flexible diamond foils of several cm2. Films are initially deposited on silicon wafers as ultrananocyrstalline, nanocrystalline, or microcrystalline diamond by varying selected deposition parameters including gas composition, nucleation, power, substrate temperature, and pressure. Subsequently the diamond is separated from the original substrate and applied either to new substrates or to frames. Diamond membranes and sheets with thickness between 1 and 3μm have been fabricated from each of these film types. The sheets are drapable and can be applied to curved surfaces and wrapped around cylinders. Properties of the films including optical transmission, Young’s modulus and fracture strength are described. Several examples of ...

Deposition of hard amorphous carbon coatings by laser and arc methods

Abstract The principal deposition conditions for the preparation of hard amorphous carbon films with hardness values above 50 GPa are now well known: the high energy of the impinging carbon particles and low deposition temperature. Such conditions are in good accordance with the widely accepted subplantation concept. Notwithstanding this basic understanding, the influence of specific plasma conditions such as electron temperature and ion energy distribution are rather uncertain. A number of suitable carbon ion sources: ArF and Nd-YAG lasers, laser-controlled Arc (Laser Arc) and filtered high-current pulsed Arc (ϕ-HCA) have been applied. The use of the same investigation methods for all plasma sources enables a direct comparison of plasma parameters and film properties. The plasma investigation includes electron temperature, ionization state and distribution of kinetic energy, and the film characterization evaluates the mechanical and optical properties. A very productive plasma source is the filtered high current pulsed Arc (ϕ-HCA), which will be applied in industrial coating machines. A general insight into the necessary plasma conditions allows us to improve the ϕ-HCA and develop new plasma sources.

Highly Sensitive Detection of Urinary Cadmium to Assess Personal Exposure

A series of Boron-Doped Diamond (BDD) ultramicroelectrode arrays were fabricated and investigated for their performance as electrochemical sensors to detect trace level metals such as cadmium. The steady-state diffusion behavior of these sensors was validated using cyclic voltammetry followed by electrochemical detection of cadmium in water and in human urine to demonstrate high sensitivity (>200 μA ppb(-1) cm(-2)) and low background current (<4 nA). When an array of ultramicroelectrodes was positioned with optimal spacing, these BDD sensors showed a sigmoidal diffusion behavior. They also demonstrated high accuracy with linear dose dependence for quantification of cadmium in a certified reference river water sample from the U.S. National Institute of Standards and Technology (NIST) as well as in a human urine sample spiked with 0.25-1 ppb cadmium.

Nondestructive testing of damage layers in semiconductor materials by surface acoustic waves

Slicing semi-conductor wafers form ingots produces a damage layer that ha to be completely removed by complex polishing and etching processes. Nondestructively controlling the machining process is desirable. Laser induced surface acoustic waves are demonstrated to be a promising method to characterize the state of the surface.

Ion implantation by vacuum arc plasmas

Plasma immersion ion implantation (PIII) is a promising new method to modify surfaces of materials by ion implantation. PIII works without expensive accelerators and therefore this method should have the potential for more applications than conventional ion accelerators. By this method, the samples are immersed into a plasma and high voltage pulses are applied to it for extracting ions from the plasma. Neither an extraction system nor other ion optics are needed. In addition to this great advantage, by using PIII, higher ion current densities and shorter implantation times are possible. The most commonly used plasma immersion arrangements extract the ion current from excited gases, especially from nitrogen. The vacuum arc is an option to produce hydrogen-free carbon plasmas or metal vapor plasmas. These plasmas extend the possibilities of the immersion ion implantation considerably. For an efficient use of PIII in thin film technology, ion sources with currents higher than 1.0 A are necessary. Moreover, t...

Isatin Detection Using a Boron-Doped Diamond 3-in-1 Sensing Platform

Boron-doped diamond (BDD) is a promising electrochemical tool that exhibits excellent chemical sensitivity and stability. These intrinsic advantages coupled with the materials vast microfabrication flexibility make BDD an attractive sensing device. In this study, two different 3-in-1 BDD electrode sensors were fabricated, characterized, and investigated for their capability to detect isatin, an anxiogenic indole that possesses anticonvulsant activity. Each device was comprised of a working, reference, and auxiliary electrode, all made of BDD. Two different working electrode geometries were studied, a 2 mm diameter macroelectrode (MAC) and a microelectrode array (MEA). The BDD quasi-reference electrode was studied by measuring its potential against a traditional Ag/AgCl reference electrode. While the potential shifted as a function of solution pH, a miniscule potential drift was observed when holding the solution pH constant. Specifically, the BDD quasi-reference electrode had a potential of -0.2 V (vs Ag/AgCl) in a pH 7 solution, and this remained stable for a 30-h time period. For the detection of isatin, solutions were analyzed using both sensors in pH 7.4 phosphate buffered saline (PBS). Using the MEA sensor, the limit of detection (LOD, (3σ)/m) for isatin was found to be 0.04 μM; an increase to 0.22 μM was observed with the MAC sensor. These results were compared to those obtained from UV-vis spectrophotometry, where a 0.57 μM LOD was observed. The feasibility for use in a complex sample matrix was also examined by completing measurements in urine simulant. The results presented herein indicate that both 3-in-1 BDD sensors are applicable at low limits of detection with potential application as an electrochemical detector for chromatographic methods.

RF characterization of coplanar waveguide (CPW) transmission lines on single-crystalline diamond platform for integrated high power RF electronic systems

This paper presents the fabrication process of single-crystalline diamond platform used for high power RF components. We report-for the first time to the best of our knowledge-results of a Coplanar Waveguide (CPW) transmission line printed on the single-crystalline diamond substrate using the Aerosol Jet Printing technique. The transmission line is 2.44 mm long and is printed on the 3.5 mm × 3.5 mm × 0.3 mm diamond substrate utilizing a silver ink as the conducting material. The characteristic impedance of the CPW line is designed to be 50 Ω. The measured average loss per millimeter of the line is 0.28 dB/mm and 0.46 dB/mm at 20 GHz and 40 GHz, respectively. This results show the single-crystalline diamond substrate is a good candidate for the development of highly integrated RF circuits.

Microwave plasma assisted reactor design for high deposition rate diamond synthesis

In view of the important, recent, opportunity to commercially synthesize high quality single crystal diamond (SCD) there is a need to continue to improve existing microwave plasma assisted reactor designs that enable high quality and high deposition rate SCD synthesis. It is now widely recognized that both the quality and growth rates of microwave plasma assisted CVD (MPACVD) synthesized diamond are improved by using high power density microwave discharges operating at pressures above 160 Torr [1]. Thus we are developing microwave plasma reactor designs and associated process methods that are both robust and are optimized for high pressure and high power density operation [2], and thereby take advantage of the improved deposition chemistry and physics that exist at high pressures. These reactors operate in the 160–320 Torr pressure regime. Here we describe our the design methodologies, and then we present the specific design details of a 2.45 GHz MPACVD reactor design that enables optimized reactor performance and high growth rate diamond synthesis in the high pressure regime.