Donald J. Rej

Recent advances in plasma source ion implantation at Los Alamos National Laboratory

Abstract Plasma source ion implantation (PSII) is an environmentally benign, potentially cost-effective alternative to conventional lineof-sight, accelerator-based implantation and wet-chemical plating processes. PSII offers the potential of producing a high dose of ions in a relatively simple, fast and cost-effective manner, allowing the simultaneous implantation of large surface areas (many square meters), complex shapes and multiple components. The dynamics of the transient plasma sheath present during PSII have been modeled in both 1 1/2-D and 2 1/2-D (one or two spatial dimensions, plus time), and recent results from these efforts are compared with measurements of the uniformity of the implanted ion dose in complex configurations. Ammonia gas (NH 3 ) has been used as a nitrogen source for PSII processing of electroplated hard chromium. A retained dose of 2.2 × 10 17 N atoms cm −2 has been demonstrated to increase the surface hardness of the electroplated Cr by 24%, and decrease the wear rate by a factor of four, without any evidence of increased hydrogen concentration in the bulk material. By adjusting the repetition rate of the applied voltage pulses, and therefore the power input to the target, controlled, elevated temperature implantations have been performed, resulting in enhanced diffusion of the implanted species with a thicker modified surface layer. Experimental work has been performed utilizing cathodic arcs as sources of metallic ions for implantation, and preliminary results of this work are given. The area of ion-beam-assisted deposition (IBAD) has been explored utilizing PSII, with large surface area diamond-like carbon (DLC) layers being generated which can exhibit hardnesses in excess of 20 GPa.

Preparation of diamondlike carbon films by high‐intensity pulsed‐ion‐beam deposition

Diamondlike carbon (DLC) films were prepared by high‐intensity pulsed‐ion‐beam ablation of graphite targets. A 350 keV, 35 kA, 400 ns beam, consisting primarily of hydrogen, carbon, and oxygen ions was focused onto a graphite target at a fluence of 15–45 J/cm2. Amorphous carbon films were deposited at up to 30 nm per pulse, corresponding to an instantaneous deposition rate greater than 1 mm/s. Electrical resistivities were between 1 and 1000 Ω cm. Raman spectra indicate that diamondlike carbon is present in most of the films. Electron‐energy‐loss spectroscopy indicates significant amounts of sp3‐bonded carbon, consistent with the presence of DLC. Scanning electron microscopy showed most films contain 100 nm features, but micron size particles were deposited as well. Initial tests revealed favorable electron field‐emission behavior.

Cost estimates for commercial plasma source ion implantation

A semiempirical model for the cost of a commercial plasma source ion implantation (PSII) facility is presented. Amortized capital and operating expenses are estimated as functions of the surface area throughput T. The impact of secondary electron emission and batch processing time is considered. Treatment costs are found to decrease monotonically with T until they saturate at large T when capital equipment payback and space rental dominate the expense. A reasonably sized PSII treatment facility should be able to treat a surface area of 104 m2 per year at a cost of

Key issues in plasma-source ion implantation

0.01 per cm2.

Characterization and performance of diamond-like carbon films synthesized by plasma- and ion-beam-based techniques

Plasma-source ion implantation (PSII) is a scaleable, non-line-of-sight method for the surface modification of materials. In this paper, we consider three important issues which should be addressed before wide-scale commercialization of PSII: (1) implant conformality, (2) ion sources, and (3) secondary electron emission. To ensure a uniform implanted dose over complex shapes, the ion sheath thickness must be kept sufficiently small. This criterion places demands on ion sources and pulsed-power supplies. Another limitation to date is the availability of additional ion species beyond B, C, N, and O. Possible solutions are the use of metal arc vaporization sources and plasma discharges in high vapor-pressure organometallic precursors. Finally, secondary electron emission presents a potential efficiency and X-ray hazard issue, since for many metallurgic applications the emission coefficient can be as large as 20. Techniques to suppress secondary electron emission are discussed.

Characterization and modeling of the ablation plumes formed by intense-pulsed ion beam impact on solid targets

Diamond-like carbon (DLC) films have been deposited on dissimilar substrates using three different deposition processes. Two well-studied deposition methods, employing cathodic arcs and r.f. plasma self-bias, have been used. These two processes differ in that cathodic arc processes use gas pressures less than 1 mTorr (0.13 Pa) and deposit atomic ions with energies less than 100 eV, while r.f. plasma self-bias processes use gas pressures greater than 1 mTorr (0.13 Pa) and deposit molecular ions with energies greater than 100 eV. In addition, DLC films have been deposited using a new plasma-based, pulsed-bias process. The pulsed-bias process uses gas pressures greater than 1 mTorr (0.13 Pa) and deposits molecular ions with energies greater than 1000 eV. Both the self-bias and the pulsed-bias processes utilized hydrocarbon gases as the carbon source. Cathodic arc processes generally rely on the arc between two graphite electrodes as the carbon source. Deposited films from all three processes have been characterized using ion backscattering techniques, elastic recoil spectrometry, transmission electron microscopy (TEM) and selected-area diffraction. Films deposited using the cathodic arc process are virtually hydrogen free while the self-bias and pulsed-bias films contain up to 40% H. TEM results indicated that the films are homogeneous and amorphous. The hardness, elastic modulus, coefficient of friction and wear rate of the films are also reported.

Neutron capture induced radiation treatment of polymer materials

An investigation of the properties of the ablation products from intense-pulsed ion beam impact on solid targets is described. Measurements and calculations of the properties of the ablation plume are presented and correlated with incident beam parameters. Experimental techniques include Thomson parabola particle spectroscopy to measure the incident ion beam atomic composition and the energy spectrum of each beam component, thermal imaging to measure the incident-beam energy density, time-resolved photography to measure the plume expansion time history and geometry, and time-resolved energy-density measurements of the plume. The results of a thermal transport model of the beam-target interaction are presented, and a detailed comparison with measurements is made.

Corrosion of diamond-like-carbon-coated nickel in 0.25 m sodium chloride

A precursor composition adapted for neutron capture induced radiation treatment of said precursor composition including a polymer matrix containing dispersed dopant material, the dispersed dopant material characterized as capable of neutron capture whereupon subsequent in situ energetic ion irradiation of the polymer matrix can occur, and further characterized as dispersed so as to provide dopant domain sizes significantly less than the energetic ion range of the dopant material is provided. Also provided is a process of in situ irradiation of bulk polymeric articles by first providing a precursor composition adapted for neutron capture induced radiation treatment of the precursor composition including a polymer matrix containing dispersed dopant material, the dispersed dopant material characterized as dispersed so as to provide dopant domain sizes significantly less than the energetic ion range of the dopant material, and then exposing the precursor composition to a source of neutrons.

Engineering cost & schedule lessons learned on NCSX

Abstract Diamond-like carbon (DLC) was deposited on to high-purity nickel using an acetylene plasma. The corrosion resistance of coated and uncoated nickel was electrochemically measured in 0.25 M NaCl at 22°C. This work presents the first report of the deposition of DLC on to nickel and the first potentiodynamic electrochemical testing of DLC. The DLC-coated nickel had a corrosion rate more than two orders of magnitude less and a corrosion potential 0.22 V greater than those of the uncoated nickel.

Preliminary scoping studies for nozzle‐based coaxial plasma thrusters

The National Compact Stellarator Experiment (NCSX) is designed to test physics principles of an innovative stellarator design developed by the Princeton Plasma Physics Laboratory (PPPL) and Oak Ridge National Laboratory (ORNL). The project was technically very challenging, primarily due to the complex component geometries and tight tolerances that were required. As the project matured these challenges manifested themselves through all phases of the project (i.e. design, R&D, fabrication and assembly). Although the project was not completed, several major work packages, comprising about 65% of the total estimated cost (excluding management and contingency), were completed, providing a data base of actual costs that can be analyzed to understand cost drivers. Technical factors that drove costs included the complex geometry, tight tolerances, material requirements, and performance requirements. Management factors included imposed annual funding constraints that throttled project cash flow, staff availability, and inadequate R&D. Understanding how requirements and design decisions drove cost through this top-down forensic cost analysis could provide valuable insight into the configuration and design of future Stellarators and other devices.