Effects of Ge and Ni catalytic underlayers to nanographene synthesis from pentacene-based film via soft X-ray irradiation

Herein, carbon films, including pentacene oligomers and pentacene-based precursors, were prepared from pentacene and H-2 by hot mesh deposition. Ge and Ni films were used as catalytic underlayers to facilitate the polymerization of the pentacene-based precursors. Thereafter, the hot mesh-deposited C films on the Ge and Ni underlayers were irradiated with soft X-rays of high photon flux density in the NewSUBARU synchrotron facility. The Raman spectra of the Ni underlayer exhibited sharp peaks of the G and D bands, which possibly originated from the nanographene formed after soft X-ray irradiation. Conversely, for the amorphous and the polycrystalline Ge underlayers, broad peaks corresponding to amorphous C or small-sized graphite were observed despite the high-temperature treatment at approximately 1000 degrees C during soft X-ray irradiation. Results suggest that the differences between the properties of the Ge and Ni underlayers lead to the observed difference in their catalytic activities.