Robert A. MacGill

High current ion source

An ion source utilizing a cathode and anode for producing an electric arc therebetween. The arc is sufficient to vaporize a portion of the cathode to form a plasma. The plasma leaves the generation region and expands through another regon. The density profile of the plasma may be flattened using a magnetic field formed within a vacuum chamber. Ions are extracted from the plasma to produce a high current broad on beam.

Ion charge state distributions in high current vacuum arc plasmas in a magnetic field

We have investigated the charge state distributions of metal ions produced in a high current vacuum arc plasma located in a strong magnetic field. The arc current was varied over the range 200 A to 4 kA and the magnetic field was from zero up to 10 kG. In general, the effect of both high arc current and high magnetic field is to push the distribution to higher charge states-the mean ion charge state is increased and new high charge states are formed. These effects are explained in terms of increased power input (higher plasma temperature) and delayed freezing of the charge state distribution during the plasma expansion process.

Streaming metal plasma generation by vacuum arc plasma guns

We have developed several different embodiments of repetitively pulsed vacuum arc metal plasma gun, including miniature versions, multicathode versions that can produce up to 18 different metal plasma species between which one can switch, and a compact high-duty cycle well-cooled version, as well as a larger dc gun. Plasma guns of this kind can be incorporated into a vacuum arc ion source for the production of high-energy metal ion beams, or used as a plasma source for thin film formation and for metal plasma immersion ion implantation and deposition. The source can also be viewed as a low-energy metal ion source with ion drift velocity in the range 20–200 eV depending on the metal species used. Here we describe the plasma sources that we have developed, the properties of the plasma generated, and summarize their performance and limitations.

S-shaped magnetic macroparticle filter for cathodic arc deposition

A new magnetic macroparticle filter design consisting of two 90/spl deg/ filters forming an S shape is described, The transport properties of this S filter are investigated using Langmuir and deposition probes. It is shown that the filter efficiency is the product of the efficiencies of two 90/spl deg/ filters, and the deposition rate is still acceptably high to perform thin-film deposition. Films of amorphous hard carbon have been deposited using a 90/spl deg/ filter and the S filter, and the macroparticle contents of the films are compared.

Recent advances in surface processing with metal plasma and ion beams

Abstract Surface processing by metal plasma and ion beams can be effected using the dense metal plasma formed in a vacuum arc discharge embodied either in a “metal plasma immersion” configuration or as a vacuum arc ion source, as well as by many other well-established methods. In the former case the substrate is immersed in the plasma and repetitively pulse-biased to accelerate the ions across the sheath and allow controlled ion energy implantation+deposition, and in the latter case a high energy metal ion beam is formed and ion implantation is done in a more-or-less conventional way. These methods have been used widely; here we limit consideration to work carried out at the Lawrence Berkeley National Laboratory. A number of advances have been made both in the plasma technology and in the surface modification procedures that enhance the effectiveness and versatility of the methods. Recent improvements in plasma technology include dual-source plasma mixing, ion charge state enhancement, and some scale-up of the hardware. We have made and explored some novel kinds of surface films and modified layers, including for example doped diamond-like carbon (DLC), novel multilayers, alumina and more complex ceramic materials such as mullite (3Al 2 O 3 .2SiO 2 ), high temperature superconducting films, and others. Recent research has included investigations of these and other surface materials for many different basic and applied applications, such as for high temperature tolerant protective coatings, biomedical compatibility, surface resistivity tailoring of ceramics, novel catalytic surfaces, corrosion resistance of battery electrodes, and more. Here we briefly review the fundamentals of the techniques, and describe some of the applications to which the methods have been put at the Lawrence Berkeley National Laboratory.

Twist filter for the removal of macroparticles from cathodic arc plasmas

Abstract Cathodic arc plasmas are known to be contaminated with macroparticles. A variety of magnetic plasma filters have been used with various success in removing the macroparticles from the plasma. In this publication, an open-architecture, double-bent filter that is twisted (‘Twist Filter™’) is described. A cathodic arc plasma deposition system was designed around this novel, very compact and efficient filter. Its major application is the deposition of ultrathin amorphous hard carbon (a-C) films for the magnetic storage industry.

Efficient, compact power supply for repetitively pulsed, “triggerless” cathodic arcs

A power supply for “triggerless,” repetitively pulsed cathodic arcs has been developed. It is based on a thyristor-switched, high-voltage, high-current, pulse-forming network (PFN). It can provide high pulsed currents (up to 2 kA), with duration of 600 μs, and pulse repetition rate of up to 10 Hz. Higher repetition rates are possible at lower current. The rectangular pulse shape and amplitude are reproducible to within a few percent. Cathodic arc initiation is extremely reliable because the charging voltage is much higher than the minimum starting voltage for the triggerless arc initiation method. The energy utilization efficiency is very high by intentionally mismatching load and PFN impedances and by using an efficiency-enhancing diode; the stored energy is dissipated primarily in the arc.

High ion charge states in a high‐current, short‐pulse, vacuum arc ion source

Ions of the cathode material are formed at vacuum arc cathode spots and extracted by a grid system. The ion charge states (typically 1–4) depend on the cathode material and only a little on the discharge current as long as the current is low. Here we report on experiments with short pulses (several μs) and high currents (several kA); this regime of operation is thus approaching a more vacuum sparklike regime. Mean ion charge states of up to 6.2 for tungsten and 3.7 for titanium have been measured, with the corresponding maximum charge states of up to 8+ and 6+, respectively. The results are discussed in terms of Saha calculations and freezing of the charge state distribution.

Hybrid gas-metal co-implantation with a modified vacuum arc ion source

Energetic beams of mixed metal and gaseous ion species can be generated with a vacuum arc ion source by adding gas to the arc discharge region. This could be an important tool for ion implantation research by providing a method for forming buried layers of mixed composition such as e.g. metal oxides and nitrides. In work to date, we have formed a number of mixed metal-gas ion beams including Ti+N, Pt+N, Al+O, and Zr+O. The particle current fractions of the metal-gas ion components in the beam ranged from 100% metallic to about 80% gaseous, depending on operational parameters. We have used this new variant of the vacuum arc ion source to carry out some exploratory studies of the effect of Al+O and Zr+O co-implantation on tribology of stainless steel. Here we describe the ion source modifications, species and charge state of the hybrid beams produced, and results of preliminary studies of surface modification of stainless steel by co-implantation of mixed Al/O or Zr/O ion beams. 5 figs, 21 refs.

Cathodic arc deposition of copper oxide thin films

LBL-35678 UC-426 Submitted to Surface and Coatings Technology Cathodic Arc Deposition of Copper Oxide Thin Films R. A. MacGill, S. Anders, A. Anders, R. A. Castro, M. R. Dickinson, K. M. Yu and I. G. Brown Lawrence Berkeley Laboratory, University of California, Berkeley, CA 94720 May 23,1994 This work was supported by the Electric Power Research Institute under Contract RP 8042-03, and the U.S. Department of Energy, Division of Advanced Energy Projects, under Contract No. DE-AC03-76SF00098.