有機物試料の測定時変質(1)

硝酸セルロース・アセチルセルロースのX線光電子分光測定と窒素の1s光電子ピークに対する反応速度論的解析

抄録

Unintended degradation of specimens during X-ray irradiation is a very important phenomenon in quantifying the surfaces using X-ray photoelectron spectroscopy. However, there has been no practical method for quantitative evaluation of the degradation during the measurement. There are some prospective samples to be used for this purpose. We have tried to test a nitrocellulose-celluloseacetate specimen as a reference to evaluate the relative X-ray dose to the specimen using the surface chemical change of it. This sample is stable against the exposed vacuum, and also against the neutralizing flood electrons during the period of measurements. The nitrogen 1s photoelectron peaks of nitrocellulose-celluloseacetate specimen show that two stages of first order reactions occur. At first, N 1s shows the highest binding energy (408 eV) equal to that of -ONO₂ state. Next state shows 405 eV-binding energy of -ONO state (represented using -NO₂), and finally goes to 400 eV, binding energy of -NO, -CN etc. This experiment clarified the two stages of first order photo-reactions of nitrogen atoms in the nitrocellulose-celluloseacetate specimen. N 1s peak of -ONO₂ state decreases its intensity exponentially according to the first order reaction with photons, and this means that this samples can be used to evaluate the amount of X-ray irradiation, and this quantitative relationship between speci-men degradation and X-ray dose can standardize the XPS measurement. The rate constant of dissociation is 7.5×10^-5 min^-1 W^-1 (0.022₅ min^-1 at 300 W) when using the focused X-ray source on the XPS system at 75 degrees of X-ray in-cident angle. And yields are approximately 29% for the first photo-reaction (-ONO₂ → -ONO), and 85% for the fol-lowing (-ONO → -NO, -CN etc.). According to the nature of these reactions, the nitrocellulose-celluloseacetate sample can be used as a good reference material to evaluate the amount of X-ray irradiation.