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

SUÁREZ, SERGIO; VENOSTA, LISANDRO; BERCOFF, PAULA G; BAJALES, NOELIA

Beilstein Journal of Nanotechnology

Beilstein

Año: 2018 vol. 9 p. 2708 - 2717

Disorder was induced in pristinehighly oriented pyrolytic graphite (HOPG) by irradiation with H+ ions withenergies of 0.4 MeV and 1 MeV, and doses of 1014 ions/cm2and 1016 ions/cm2 . Raman spectroscopy was used as themain technique to characterize different samples and gain new insights on thesplitting of the D band into two components (D1 and D2), trying to correlatethis feature of the vibrational spectrum with the impinging energy and dose. Anincreased ID2/IG ratio in comparison with ID1/IGwas observed in the irradiated samples. This behavior indicates that theimpinging energy mainly affects the D1 component, while the D2 component isstrongly dominated by the dose. We expect a larger contribution of defects (originatingfrom the rupture of C-C sp2 symmetry through the formation of C-H sp3bonds) to the D2 component than to the D1 component. SQUID measurements of the irradiatedsamples showed an enhancement in the normalized remanence, as well as anincrement in coercivity compared to pristine HOPG, consistent with H+-induced point-likedefects as well as C-H bonds. AFM scanning after Raman and SQUID characterizationshowed a distribution of surface defects, which were ascribed to the burst ofhydrogen blisters formed as a consequence of the irradiation process. Theresults presented in this work contribute to the current trend innanotechnology in areas devoted to the control of properties by defectengineering in carbon-based materials.