Disorder in H(+)-irradiated HOPG: effect of impinging energy and dose on Raman D-band splitting and surface topography

Disorder was induced in pristine highly oriented pyrolytic graphite (HOPG) by irradiation with H(+) ions with energies of 0.4 MeV and 1 MeV, and doses of 10(14) ions/cm(2) and 10(16) ions/cm(2). Raman spectroscopy was used as the main technique to characterize different samples and gain new insights on the splitting of the D band into two components (D(1) and D(2)), trying to correlate this feature of the vibrational spectrum with the impinging energy and dose. An increased I(D2)/I(G) ratio in comparison with I(D1)/I(G) was observed in the irradiated samples. This behavior indicates that the impinging energy mainly affects the D(1) component, while the D(2) component is strongly dominated by the dose. We expect a larger contribution of defects (originating from the rupture of C–C sp(2) symmetry through the formation of C–H sp(3) bonds) to the D(2) component than to the D(1) component. SQUID measurements of the irradiated samples showed an enhancement in the normalized remanence, as well as an increment in coercivity compared to pristine HOPG, consistent with H(+)-induced point-like defects as well as C–H bonds. AFM scanning after Raman and SQUID characterization showed a distribution of surface defects, which were ascribed to the burst of hydrogen blisters formed as a consequence of the irradiation process. The results presented in this work contribute to the current trend in nanotechnology in areas devoted to the control of properties by defect engineering in carbon-based materials.