Reactive Sputtering of Cubic-Phase BN:C and Nanostructured B-N-C Films : Growth, Microstructure, and Mechanical Properties

Sammanfattning: Synthesis, structure, and mechanical property related issues in the carbon-containing boron nitride (BN:C) system have been studied. Magnetron sputtering, comprising a B4C target in mixed Ar-N2 discharges and deposition parameters of low ion energy, high ion-to-neutral flux ratio, and substrate temperatures <350 °C were employed for growth. Transmission electron microscopy and electron energy loss spectroscopy (EELS) served as the mainstructure evaluation tools, while nanoindentation experiments were used for mechanical property evaluation.Studies of the growth process as a function of partial pressure of nitrogenin the gas mixture revealed first a saturation of the nitrogen on the target whereas at slightly higher PN2 values the overall system is nitrided. This effect was ascribed to the relatively low enthalpy of compound formation of BN. Furthermore, by the use of an internal solenoid coil, the plasma density and hence the ion flux impinging on the growing film could be increased by more than one order of magnitude, resulting in a maximum ion-to-condensing atom flux ratio of ~24. At these conditions, i.e., with a saturation of the nitrogenin corporation frequency on the growth surface and a high flux ratio, growth of cubic-phase c-BN:C was demonstrated at ion-energies as low as 110 eV. This opens a new process window for c-BN phase formation at conditions not accounted for in the prevailing mechanistic models of momentum transfer.The system exhibits a phase evolution sequence of textured (hexagonal)h-BN:C prior to the nucleation and growth of crystallographically oriented cBN:C. The h-BN:C material obtained at intermediate flux-ratios and floating potential exhibits interesting mechanical properties of extreme elasticity and a structure consisting of curved and buckled basal planes similar to what previously have been reported in fullerene-like CNx films. Growth of CNx/BN:C multilayers was demonstrated by sequential sputtering from B4C and graphite targets, respectively, in mixed Ar-N2 atmospheres. They exhibit similar structure as the single-layer films, but do offer additional means for mechanical property design including strengthening over the single-layer compounds.Results are presented to demonstrate the possibility of using sputter deposition technique to synthesize CNx and template-synthesized B-N-C tubular nanostructures, which promises important advances to tailor the structure (dimension and shape) and number density of various types of nanostructures.Finally, an immiscibility between BN and C(N) in magnetron sputtered graphitic layered B-N-C materials was established by EELS. Nitrogen-rich films exhibited predominantly B-N and C-N type of bonds whereas films prepared with a much lower nitrogen concentration also revealed B-C bonds. Thus, magnetron discharge conditions at low temperature is a promising approach to produce B-N, C-N and B-C type of bonds for controlling the chemical composition of nanostructures in the B-N-C ternary system.