EUV-Driven Carbonaceous Film Deposition and Its Photo-oxidation on a TiO2 Film Surface

Published

September 23, 2013

Author(s)

Nadir S. Faradzhev, Monica McEntee, John Yate, Shannon B. Hill, Thomas B. Lucatorto

Abstract

We report the photo-deposition of a carbonaceous layer grown on a TiO2 thin film by EUV radiation-induced chemistry of adsorbed n-tetradecane and the subsequent photo-oxidation of this film. It is found by chemical analysis of the C layer that irradiation by 92 eV photons converts a fraction of the 14-C-atom alkane into two polycyclic aromatic hydrocarbon (PAH) molecules: anthracene and phenanthrene, both also containing 14 C atoms. Under continuing irradiation, EUV-induced dehydrogenation and cross-linking of PAHs and precursor alkane fragments form a complex network of carbon bonds with the inferred structure of an sp2-C rich film. Exposure of the carbonaceous film to several O-containing molecules has little or no effect in the dark at 300K. In the presence of EUV photons, the ability of all five oxygen-containing molecules studied to etch the C film increases significantly. The relative photo-oxidation activity of the molecules studied follows the trend: H2O2 O3 > NO O2 > H2O. For all oxidizers, the rate of the photo-oxidation reaction increases with the partial pressure of the oxidizer. Raising the substrate temperature has little effect on the photo-oxidation reaction rate, which is in contrast to the rate of EUV-induced carbonaceous film growth that exhibits a strong temperature dependence. In an earlier study, we found that during formation of the C film, the hydrocarbon molecule arrives at the surface in its ground state and forms a weak bond to the bare or film-covered TiO2 surface. The non-volatile C film is produced by a photon-induced decomposition reaction. For photo-oxidation, the first step requires the formation of a strong bond of the oxidizer molecule to the surface. Subsequent direct electronic activation and secondary electron emission from the substrate and capture by the oxidizer molecule, leads to fragmentation of the oxidizer molecule and the reactive fragments aggressively remove carbon as oxidized products.

Citation

Journal of Physical Chemistry C

Pub Type

Journals

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Keywords

EUV, PAH, tetradecane, ozone, hydrogen peroxide, titanium dioxide, surface, photo-induced reactions, oxidation

Citation

Faradzhev, N. , McEntee, M. , Yate, J. , Hill, S. and Lucatorto, T. (2013), EUV-Driven Carbonaceous Film Deposition and Its Photo-oxidation on a TiO2 Film Surface, Journal of Physical Chemistry C, [online], https://doi.org/10.1021/jp4091427 (Accessed April 20, 2024)