Effect of surface reactions of low-energy carbon ions on the secondary electron emission of TiN:O thin films

Abstract

Low-energy secondary electron emission coatings are required for antimultipactor applications in several important technologies and their study and development is also a matter of scientific interest. For this purpose, titanium nitride was deposited on Si(100) substrates by reactive sputtering and the influence of low-energy carbon ion bombardment on the secondary electron emission yield of TiN:O coatings was studied. The composition and chemical bonds formed in the films after carbon ion implantation were analyzed by x-ray photoelectron spectroscopy (XPS). XPS revealed the formation of both carbidic and graphitic bonds. N was displaced while Ti-C bonds were formed up to a limiting value of 0.103 for the carbidic carbon atomic fraction, beyond which a graphitic surface layer was deposited. The secondary electron emission yields for TiN:O were measured before and after low-energy CHn+ ion bombardment and air exposure, and after heating. Initially, the carbon ion implantation reduced the secondary electron emission yield. Then an increase in secondary electron emission was obtained when the excess graphitic carbon was deposited on the sample. On the other hand, subsequent thermal treatment at 700 °C of the carburized samples produced a further reduction of the secondary electron emission yield. The maximum yields are about 53% lower for thermal annealed films than for similarly treated previously measured as-deposited layers. A narrowing of XPS peak line shapes is observed as a consequence of the annealing away of structural and chemical defects in the near-surface region. In addition, secondary electron emission (SEE) yield curves were used in a simulation of multipactor discharge. Both experimental multipactor threshold tests and computer multipactor simulations indicate that SEE yield values for low primary-electron energies are the most influencing parameters on multipactor threshold.