El Jamal Ghada, Gouder Thomas, Eloirdi Rachel, Tereshina-Chitrova Evgenia, Horákd Lukáš, Jonsson Mats
School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Department of Chemistry, Applied Physical Chemistry, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden.
European Commission, Joint Research Centre, Postfach 2340, DE-76215 Karlsruhe, Germany.
Dalton Trans. 2021 Sep 21;50(36):12583-12591. doi: 10.1039/d1dt01020d.
X-ray photoelectron spectroscopy (XPS) has been used to study the effect of mixed HO/H gas plasma on the surfaces of UO, UO and UO thin films at 400 °C. The experiments were performed under ultra-high vacuum conditions. Deconvolution of the U4f peaks into U(IV), U(V) and U(VI) components revealed the surface composition of the films after 10 min plasma exposure as a function of H concentration in the feed gas of the plasma. Some selected films (unexposed and exposed) were also analysed using grazing-incidence X-ray diffraction (GIXRD). The XPS results show that U(V) is formed as a major product upon 10 minutes exposure of UO by a mixed HO/H plasma in a fairly wide H concentration range. When starting with U(V) (UO), rather high H concentrations are needed to reduce U(V) to U(IV) in 10 minutes. In the plasma induced oxidation of UO, U(V) is never observed as a major product after 10 minutes and it would seem that once U(V) is formed in the oxidation of UO it is rapidly oxidized further to U(VI). The grazing incidence X-ray diffraction analysis shows that there is a considerable impact of the plasma and heating conditions on the crystal structure of the films in line with the change of the oxidation state. This structural difference is proposed to be the main kinetic barrier for plasma induced transfer between U(IV) and U(V) in both directions.
X射线光电子能谱（XPS）已被用于研究混合HO/H气体等离子体在400℃下对UO、UO和UO薄膜表面的影响。实验在超高真空条件下进行。将U4f峰解卷积为U(IV)、U(V)和U(VI)成分，揭示了在等离子体进料气体中H浓度的函数关系下，等离子体暴露10分钟后薄膜的表面组成。还使用掠入射X射线衍射（GIXRD）对一些选定的薄膜（未暴露和暴露的）进行了分析。XPS结果表明，在相当宽的H浓度范围内，UO在混合HO/H等离子体中暴露10分钟后，U(V)作为主要产物形成。当以U(V)（UO）开始时，需要相当高的H浓度才能在10分钟内将U(V)还原为U(IV)。在等离子体诱导的UO氧化过程中，10分钟后从未观察到U(V)作为主要产物，并且似乎在UO氧化过程中一旦形成U(V)，它就会迅速进一步氧化为U(VI)。掠入射X射线衍射分析表明，等离子体和加热条件对薄膜的晶体结构有相当大的影响，这与氧化态的变化一致。这种结构差异被认为是等离子体诱导U(IV)和U(V)双向转移的主要动力学障碍。
