Previously we reported on the etch rates of C on TiO2 by oxidizers including NO, O3 and H2O2 when irradiated by extreme ultraviolet (EUV) radiation at 13.5 nm [Faradzhev et al., J.Phys. Chem. C, 117 (2013) 23072-23081]. We demonstrated that the intensity-averaged etch rates under EUV irradiation are much greater than those in the dark, and we ranked the effectiveness of the oxidizers at removing a carbonaceous layer that was formed by photodecomposition of n tetradecane on a TiO2 film. Here we extend that work by presenting temporally and spatially resolved measurements of the C-etching by these oxidizers as a function of EUV intensity in the range (0.3 to 3) mW/mm2 [(0.2 to 2)×1016 photons s-1 cm-2] We find that the rates for NO scale linearly with intensity and are much smaller than those for O3 which exhibit a very weak, sub- linear intensity dependence in this range. We demonstrate that these behaviors are consistent with adsorption of the oxidizing precursor on the C surface followed by a photon-stimulated reaction resulting in volatile C-containing products. The kinetics of photon-induced etching by hydrogen peroxide, however, appear to be more complex. The spatially resolved measurements reveal that C removal by H2O2 begins at the edges of the C-spot, where the light intensity is the lowest, and proceeds toward the center of the spot as the perimeter shrinks. This localization of the reaction may occur because hydroxyl radicals are produced efficiently on the catalytically active TiO2 surface. Although the net EUV-induced removal rate of C on TiO2 is much larger for H2O2 than for O3 or NO, the H2O2 rate may be much smaller on a substrate that is less catalytically active.
and Hill, S.
EUV-induced oxidation of carbon on TiO2, Surface Science, [online], https://doi.org/10.1016/j.susc.2016.03.025, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=919871
(Accessed June 5, 2023)