I. G. Brown

Vacuum Arc Ion Sources

The vacuum arc is a rich source of highly ionized metal plasma that can be used to make a high current metal ion source. Vacuum arc ion sources have been developed for a range of applications including ion implantation for materials surface modification, particle accelerator injection for fundamental nuclear physics research, and other fundamental and applied purposes. The beam parameters can be attractive, and the source has provided a valuable addition to the spectrum of ion sources available to the experimenter. Beams have been produced from over 50 of the solid metals of the periodic table, with mean ion energy up to several hundred keV and with beam current up to several amperes. Typically the source is repetitively pulsed with pulse length of order a millisecond and duty cycle of order 1%, and operation of a dc embodiment has been demonstrated. Here the source fundamentals and operation are reviewed, the source and beam characteristics summarized, and some applications examined.

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.

Nanoindentation and Nanoscratching of Hard Carbon Coatings for Magnetic Disks

Nanoindentation and nanoscratching experiments have been performed to assess the mechanical properties of several carbon thin films with potential application as wear resistant coatings for magnetic disks. These include three hydrogenated-carbon films prepared by sputter deposition in a H{sub 2}/Ar gas mixture (hydrogen contents of 20, 34, and 40 atomic %) and a pure carbon film prepared by cathodic-arc plasma techniques. Each film was deposited on a silicon substrate to thickness of about 300 run. The hardness and elastic modulus were measured using nanoindentation methods, and ultra-low load scratch tests were used to assess the scratch resistance of the films and measure friction coefficients. Results show that the hardness, elastic modulus, and scratch resistance of the 20 and 34% hydrogenated films are significantly greater than the 40% film, thereby showing that there is a limit to the amount of hydrogen producing beneficial effects. The cathodic-arc film, with a hardness of greater than 59 GPa, is considerably harder than any of the hydrogenated films and has a superior scratch resistance.

Hardness, elastic modulus, and structure of very hard carbon films produced by cathodic‐arc deposition with substrate pulse biasing

The hardness, elastic modulus, and structure of several amorphous carbon films on silicon prepared by cathodic‐arc deposition with substrate pulse biasing have been examined using nanoindentation, energy loss spectroscopy (EELS), and cross‐sectional transmission electron microscopy. EELS analysis shows that the highest sp3 contents (85%) and densities (3.00 g/cm3) are achieved at incident ion energies of around 120 eV. The hardness and elastic modulus of the films with the highest sp3 contents are at least 59 and 400 GPa, respectively. These values are conservative lower estimates due to substrate influences on the nanoindentation measurements. The films are predominantly amorphous with a ∼20 nm surface layer which is structurally different and softer than the bulk.

Vacuum arc ion charge-state distributions

Vacuum arc ion charge-state spectra have been measured for a wide range of metallic cathode materials. The charge-state distributions were measured using a time-of-flight diagnostic to monitor the energetic ion beam produced by a metal vapor vacuum arc ion source. Data were obtained for 48 metallic cathode elements: Li, C, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn Fe, Co, Ni, Cu, Zn, Ge, Sr, Y, Zr, Nb, Mo, Pd, Ag, Cd, In, Sn, Ba, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er Yb, Hf, Ta, W, Ir, Pt, Au Pb, Bi, Th, and U. The arc was operated in a pulsed mode with pulse length 0.25 ms: arc current was 100 A throughout. The measured distributions are cataloged and compared with earlier results. Some observations about the performance of the various elements as suitable vacuum arc cathode materials are also presented. >

Multiply stripped ion generation in the metal vapor vacuum arc

We consider the charge state distribution of ions produced in the metal vapor vacuum arc plasma discharge. A new kind of high current metal ion source in which the ion beam is extracted from a metal vapor vacuum arc plasma has been used to obtain the spectra of multiply charged ions produced within the cathode spots. The cathode materials used and the species reported on here are: C, Mg, Al, Si, Ti, Cr, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Rh, Pd, Ag, In, Sn, Gd, Ho, Ta, W, Pt, Au, Pb, Th, and U; the arc current was 200 A for all measurements. Charge state spectra were measured using a time‐of‐flight method. In this paper we report on the measured charge state distributions and arc voltages and compare the distributions with the predictions of a theory in which ionization occurs in the cathode spots via stepwise ionization by electron impact.

Ion velocities in vacuum arc plasmas

Ion velocities in vacuum arc plasmas have been measured for most conducting elements of the Periodic Table. The method is based on drift time measurements via the delay time between arc current modulation and ion flux modulation. A correlation has been found between the element-specific ion velocity and average ion charge state; however, differently charged ions of the same element have approximately the same velocity. These findings contradict the potential hump model but are in agreement with a gasdynamic model that describes ion acceleration as driven by pressure gradients and electron-ion friction. The differences between elements can be explained by the element-specific power density of the cathode spot plasma which in turn determines the temperature, average charge state, and ion velocity of the expanding vacuum arc plasma.

Visible cathodoluminescence of GaN doped with Dy, Er, and Tm

We reported the observation of visible cathodoluminescence of rare-earth Dy, Er, and Tm implanted in GaN. The implanted samples were given isochronal thermal annealing treatments at a temperature of 1100 °C in N2 or NH3, at atmospheric pressure to recover implantation damages and activated the rare-earth ions. The sharp characteristic emission lines corresponding to Dy3+, Er3+, and Tm3+ intra-4fn-shell transitions are resolved in the spectral range from 380 to 1000 nm, and observed over the temperature range of 8.5–411 K. The cathodoluminescence emission is only weakly temperature dependent. The results indicate that rare-earth-doped GaN epilayers are suitable as a material for visible optoelectronic devices.

Transport of vacuum arc plasmas through magnetic macroparticle filters

Vacuum arc plasma deposition combined with magnetic filtering of the plasma to remove macroparticles is a promising technique for the production of metallic, compound and hard amorphous carbon thin films. High efficiency of the magnetic filter is a crucial parameter for the application of this technique. We report investigations of the influence of different filter designs, magnetic field configurations and electric potentials on the filter efficiency. We analyse the transport mechanisms on which the flow of plasma through the filter is based, and describe and discuss the occurrence of instabilities in magnetic filters. With an optimum filter arrangement we were able to obtain a filter output of 25% of the total number of ions produced by the vacuum arc discharge.

Metal plasma immersion ion implantation and deposition using vacuum arc plasma sources

Plasma source ion implantation (PSII) with metal plasma results in a qualitatively different kind of surface modification than with gaseous plasma due to the condensable nature of the metal plasma, and a new, PSII‐related technique can be defined: metal plasma immersion ion implantation and deposition (MPI). Tailored, high‐quality films of any solid metal, metal alloy, or carbon (amorphous diamond) can be formed by MPI using filtered vacuum arc plasma sources, and compounds such as oxides or nitrides can be formed by adding a gas flow to the deposition. Here we describe the plasma formation at cathode spots, macroparticle filtering of the vacuum arc plasma by magnetic ducts, the underlying physics of MPI, and present some examples of MPI applications.