Electron Stimulated Decomposition of Acetylene as a Precursor for Graphene

We report here on the deposition of carbon via C$_2$H$_2$ dissociation by electron beam irradiation and thermal decomposition. The substrates investigated include sapphire, silicon, ALD deposited Al$_2$O$_3$/SiO$_2$, and GaN/sapphire. Raman analyses show that on C-plane sapphire both thermal decomposition and electron beam stimulated dissociation of C$_2$H$_2$ deposit carbon successfully. On other substrates these methods were inactive, showing the decomposition of C$_2$H$_2$ on sapphire is catalytic. We tested different annealing times and C$_2$H$_2$ pressures, gauging absorption saturation with RHEED. Samples exposed to 15 min. C$_2$H$_2$ adsorption during 400 eV electron irradiation and then annealed for 2 hr. to above 600$^{\circ}$C in high vacuum showed the greatest proportion of sp2 to sp3 bonding by Raman analysis. The Raman spectra also suggest hydrogen adsorption, which may hinder further sp2 bonding. Annealing samples in a hydrogen atmosphere does not change their Raman spectra, suggesting hydrogen saturation. \noindent Partial support from the University of Minnesota Institute for Renewable Energy and the Environment