Keynote 1: Contribution of Excited States of Molecular Nitrogen to Surface Reactions in Nitrogen Plasmas

Nitrogen plasmas are utilized in surface nitriding of metallic and semiconductor materials. In addition, the synthesis of ammonia using nitrogen-hydrogen mixture plasmas becomes an active research topic in plasma science. The most important reactive species in nitrogen plasmas is believed to be atomic nitrogen, but in this talk, we will discuss the importance of molecular nitrogen at excited states.In many years ago, we compared the nitriding rates of Si [1] and SiC [2] in nitrogen plasmas with the densities of atomic nitrogen. The experimental results did not indicate the correlation, suggesting that the existence of more effective species for the surface nitriding. We also measured the density of molecular nitrogen at the electronic metastable state. As a result, we observed the better correlation between the nitriding rate and the density of the metastable state. Now, we are working on the synthesis of ammonia using nitrogen-hydrogen mixture plasmas. The synthesis of ammonia is a catalytic reaction, where the adsorption of nitrogen on the catalysis surface is the rate limiting step. We compared the synthesis rate of ammonia with the fluxes of atomic nitrogen and molecular nitrogen at vibrational excited states. The experimental results indicate the better correlation between the synthesis rate and the flux of vibrationally excited molecular nitrogen. We believe that we should consider the contribution of molecular nitrogen at excited states when we design surface reaction processes using nitrogen plasmas.