GLOW-DISCHARGE PLASMA TREATMENT FOR SURFACE CLEANING AND MODIFICATIONOF METALLIC BIOMATERIALS

Glow discharge plasma treatment is a frequently used method for cleani ng, preparation, and modification of biomaterial and implant surfaces. The merits of such treatments are, however, strongly dependent on the process parameters. In the present work the possibilities, limitation s, and risks of plasma treatment for surface preparation of metallic m aterials are investigated experimentally using titanium as a model sys tem, and also discussed in more general terms. Samples were treated by different low-pressure direct current plasmas and analyzed using Auge r electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS), atomic force microscopy, scanning electron microscopy, and light micr oscopy. The plasma system is a home-built, ultra-high vacuum-compatibl e system that allows sample introduction via a load-lock, and precise control of pressure, gas composition and flow rate, etc. This system a llows uniform treatment of cylindrical and screw-shaped samples. With appropriate plasma parameters, argon plasma remove all chemical traces from former treatments (adsorbed contaminants and other impurities, a nd native oxide layers), in effect producing cleaner and more well-con trolled surfaces than with conventional preparation methods. Removal ( sputtering) rates up to 30 nm/min are possible. However, when inapprop riate plasma parameters are used, the result may be increased contamin ation and formation of unintentional or undesired surface layers (e.g. , carbides and nitrides). Plasma-cleaned surfaces provide a clean and reproducible starting condition for further plasma treatments to form well-controlled surface layers. Oxidation in pure O-2 (thermally or in oxygen plasmas) results in uniform and stoichiometric TiO2 surface ox ide layers of reproducible composition and thicknesses in the range 0. 5-150 nm, as revealed by AES and XPS analyses. Titanium nitride layers were prepared by using N-2 plasmas. While mild plasma treatments leav e the surface microstructure unaffected, heavy plasma treatment can gi ve rise to dramatic morphologic changes. Comparison of these results w ith corresponding analyses of commercial implants and electropolished and/or anodically oxidized samples shows that the plasma treatment off ers superior control of the surface status. However, it is also shown that improper control of the plasma process can produce unwanted and i rreproducible results. (C) 1997 John Wiley & Sons, Inc.