Isotope Labeled Oxidation Studies of Nitrides with SIMS

The central aim of this project is the investigation of the oxidation process of "pure" and mixed nitrides by the use of isotope labeled gases and subsequent SIMS analysis of the oxide films. The oxidation behavior of metals and alloys was during the last decades and continues to be a vast field of investigation. Contrary to this, the interest of the oxidation of nitrides has only arisen in the last years and is not well understood. Nitride coatings play an important role in many technical tasks. Due to their high hardness and their temperature- and oxidation- stability their main field of application lies in milling and drilling operations. Comparable to metals it is expected that the oxidation behavior and the wear resistance of nitride coatings can be optimized by "alloying" them with additives. In the center of interest are the addition of nitrides to build oxides with lubrication ability. High temperature (up to 1000C) oxidation tests using isotope-enriched gases ( 18O and 15N) are powerful tools to investigate the growth of oxide layers and the diffusion of gases and the bulk material through them. The interaction of gaseous nitrogen with the nitride coatings will bee observable by isotope labeling. The role of humidity in the oxidation process can be monitored because oxygen originated from H 2 16O can be separated form oxygen originated from 18O2 . SIMS depth profiles can clear up the structure of oxide layers. SIMS is not only isotope sensitive, but is also able to detect hydrogen und thus to monitor the incorporation of hydrogen. By using isotope-enriched gases during the oxidation process, advantage can be taken of this feature to examine the growth- relevant diffusion mechanisms of oxide layers on nitride-coated materials.

Initial the aim of the project was to investigate only the oxidation of nitrides by the use of isotope enriched gases and subsequent dynamic SIMS measurements. Due to a non foreseeable, but pleasant event, the project has been emerged also to related areas. The non foreseeable event was that the project leader was able to finance a new TOF SIMS 5 and to replace the 30 year old CAMECA IMS 3f directly after the project start. The new merits (e.g.: static SIMS, charge compensation of isolating samples, Static SIMS, low energy spattering) of the instrument enables the investigation of additional aspects and sample types. Additional to the planed investigations of the oxidation of nitrides by isotope enriched oxygen the new instrument give the potential to research also the thermodynamic and voltage driven diffusion of oxygen in stoichiometric oxides such as these used for solid oxide fuel cells. The possibility to measure the first monolayer in the so called static SIMS mode was used to measure the growing of metal layers on carbon substrate. The improved figure of merits of the new instrument was used for the investigation of the first oxidation steps of the oxidation of silver surfaces, the measurement of rough surfaces and tribologic treaded surfaces and reaction layers. The diffusion of hydrogen and sodium in oxide layer systems of the area of semiconductors developed to an additional work topic. The improved depth resolution was used to develop new measurement methods for thin metallic layers. Furthermore fundamental contributions in the field of TOF-SIMS were delivered. In total 25 publications in reviewed periodicals were published.