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

Abstract

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 1014 ions/cm2 and 1016 ions/cm2. 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 (D1 and D2), 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 D1 component, while the D2 component is strongly dominated by the dose. We expect a larger contribution of defects (originating from the rupture of C–C sp2 symmetry through the formation of C–H sp3 bonds) to the D2 component than to the D1 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.

Influence of modified ammonium polyphosphate on the fire behavior and mechanical properties of polyformaldehyde

“…Laser Raman spectroscopy is a powerful technique for the characterization of the carbonaceous material formed during combustion 35 . The Raman spectra of char residues of flame‐retardant samples after cone test were presented in Figure 7a”’–d”’.…”

“…Laser Raman spectroscopy is a powerful technique for the characterization of the carbonaceous material formed during combustion. 35 The Raman spectra of char residues of flame-retardant samples after cone test were presented in Figure 7a"'-d"'. The peaks centered at 1326/cm (D-band) and 1580/cm (G-band) were the reflection of disordered and sp 2 hybridized carbon atoms, respectively.…”

Effect of Stress on Irradiation Responses of Highly Oriented Pyrolytic Graphite

“…The most significant change caused by the irradiation is the appearance of a sharp D mode at 1335 cm −1 . The D mode is defect-activated and related to disorders such as kinks, vacancies, and impurities [ 8 , 9 , 10 , 11 ]. The irradiation-induced D band is very different from bump-like signals centered around the same region.…”

“…For bulk materials, the traditional methods, such as channeling Rutherford backscattering, is difficult due to large minimum yields caused by polycrystalline structure, even in high-quality HOPG [ 7 ]. Raman, on the other hand, has been widely used to indirectly characterize defects in various carbon materials, including graphene, carbon nanotubes, and graphite [ 8 , 9 , 10 , 11 ]. The intensity ratio change of the D to G Raman modes is linked to a defect population through a modified Tuinstra–Koenig (TK) model [ 8 ].…”

A macro-scale ruck and tuck mechanism for deformation in ion-irradiated polycrystalline graphite

“…The ion mass can be easily varied and hence the change of the recoil spectrum 12 . Ion irradiation is also used for introducing disorder and surface modification to carbon-based materials and is currently a subject of interest for many nanotechnological applications 13 . A brief summary of the current understanding in irradiation damage of polycrystalline graphite is introduced below to put the current work in context.…”