Use of X-ray photoelectron spectroscopy and spectroscopic ellipsometry to characterize carbonaceous films modified by electrons and hydrogen atoms

X-ray Photoelectron Spectroscopy (XPS) and Spectroscopic Ellipsometry (SE) have been used to interrogate and spatially map changes that occur to ultra-thin (<10 nm) carbonaceous films as a result of exposure to electrons and hydrogen atoms. Due to post-deposition electron irradiation, as-deposited sp3-like carbon was converted into a more graphitized sp2-like carbon species. This process resulted in measurable changes to the C 1s peak profiles (XPS) of the carbon atoms. Changes to dielectric functions (SE), made possible through XPS's identification of pure as-deposited and graphitic carbon regions were also observed. These transformations could be characterized as a function of electron dose and spatially mapped using: (i) a linear combination of the individual as-deposited and graphitized C 1s components obtained in XPS and, (ii) a Bruggeman effective medium approximation of the SE film response for both types of carbon species. SE and XPS were found to produce very similar results in terms of both film composition (sp2 vs sp3 carbon) and film thickness. XPS and SE analysis also revealed that exposure of carbonaceous films to hydrogen atoms resulted in the conversion of graphitized sp2-like carbon back into sp3-like carbon species, a process ascribed to the lower atomic hydrogen (AH) etching rates observed for sp2-like vs sp3-like carbon. In summary, this paper highlights the ability and complementary nature of XPS/SE analysis to study and spatially map the chemical and structural transformations that can occur to ultra-thin carbonaceous films.