Ion Energy/Momentum Effects During Ion Assisted Growth of Nb X N Y Films
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ION ENERGY/MOMENTUM EFFECTS DURING ION ASSISTED GROWTH OF NbXNY FILMS M.L. KLINGENBERG Concurrent Technologies Corporation, Johnstown, PA, USA
J.D. DEMAREE AND J.K. HIRVONEN US Army Research Laboratory, Aberdeen Proving Ground, MD, USA
R. MESSIER Pennsylvania State University, University Park, PA, USA
ABSTRACT In a previous paper, it was shown that the tribological properties of NbxNy thin films produced by ion beam assisted deposition (IBAD) depend strongly on the beam energy and the ion-to-atom (R) ratio. 1 This study was designed to separate ion energy vs. ion momentum effects on film stress, crystalline phase, grain size, morphology, and composition, all of which influence the tribological properties of the films. Inert ion beams (Kr, Ar, and Ne) were used in conjunction with a nitrogen gas backfill to independently control ion energy and ion momentum transfer to NbxNy films. The ion species, energies, and R ratios were chosen to create a matrix of coatings that exhibited the same total energy deposition with different momentum transfer or the same momentum transfer but different total energy deposition. The resultant films were characterized using Rutherford Backscattering Spectroscopy (RBS), x-ray diffraction (XRD), atomic force microscopy (AFM), and residual stress analysis. Crystalline phases and texture, as well as residual stress, were more closely correlated with ion momentum transfer to the coating atoms than with overall ion energy input. INTRODUCTION Niobium nitride has been studied extensively for its superconducting properties, but more recently as a hard, tribological coating.2-4 Chemical vapor deposition, electron beam evaporation, unbalanced magnetron sputtering, cathodic arc deposition, and ion beam assisted deposition (IBAD) have all been used to produce hexagonal, tetragonal, and cubic varieties of the compound with up to seven phases reported.2,5-8 IBAD was chosen for these experiments because it offers increased control of composition, internal stress, morphology, and texture, leading to improved adhesion, coating density, and mechanical properties.9,10 Amorphous, nanocrystalline, textured crystalline, epitaxial, or metastable crystalline coatings have all been made by altering deposition species, ion mass, ion energy, and substrate temperature.11,12 Previous work on IBAD NbxNy identified the deposition parameters required for good tribological behavior , albeit with complex wear behavior.1 This study was conducted in an attempt to determine whether IBAD coating properties such as morphology and stress could be described in terms of energy per arriving atom (E/a) or momentum per arriving atom (p/a), as has been suggested in other studies of IBAD nitride films.13 EXPERIMENTAL Depositions were conducted in an IBAD system with electron beam evaporation (MDC Vacuum Model CVS-6) in conjunction with ion irradiation (3-cm, Ion Tech RF ion source, model RFB-1200). Silicon, grafoil (carbon), and glass samples were heat sunk to a glass slide using a silver powder/vacuum grease slurry, and fa
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