Mixed H2O/H2plasma-induced redox reactions of thin uranium oxide films under UHV conditions

• X-ray photoelectron spectroscopy (XPS) has been used to study the effect of mixed H2O/H2gas plasma on the surfaces of UO2, U2O5and UO3thin films at 400 °C. The experiments were performedin situunder ultra-high vacuum conditions. Deconvolution of the U4f7/2peaks 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 H2concentration 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 UO3by a mixed H2O/H2plasma in a fairly wide H2concentration range. When starting with U(v) (U2O5), rather high H2concentrations are needed to reduce U(v) to U(iv) in 10 minutes. In the plasma induced oxidation of UO2, 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 UO2it 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. 

Ämnesord

NATURVETENSKAP  -- Kemi -- Oorganisk kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Inorganic Chemistry (hsv//eng)

NATURVETENSKAP  -- Kemi -- Fysikalisk kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Physical Chemistry (hsv//eng)

NATURVETENSKAP  -- Fysik -- Den kondenserade materiens fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Condensed Matter Physics (hsv//eng)

Nyckelord

Crystal structure

Oxidation

Oxide films

Redox reactions

X ray photoelectron spectroscopy

X ray powder diffraction

10 minutes

Condition

Deconvolutions

Gas plasma

Grazing incidence X-ray diffraction

Grazing-incidence X-ray diffraction

Mixed H

Plasma exposure

Plasma-induced

Thin-films

Uranium dioxide

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