How Reliable Are Raman Spectroscopy Measurements of Graphene Oxide?

Abstract

Graphene oxide (GO) has garnered attention for its tunable chemical, electrical, and optical properties. An integral part of the efforts to manipulate and improve the performance of GO is the ability to reliably characterize its complex structure. Raman spectroscopy and confocal Raman mapping are widely used for insight into the extent of GO's nanoscale graphene-like domains, the degree of lattice order, and its sheet stacking structure. It has also been reported, however, that laser sources, similar to those used for Raman spectroscopy, can be used to intentionally reduce and ablate GO. In light of this, it is unclear how invasive Raman measurements of GO are and how reliable published Raman data is. In this study, we employ Raman laser doses spanning 4 orders of magnitude to investigate the impact of Raman measurements on GO structure. We find that GO undergoes reduction at all practical laser doses, with the degree of reduction increasing with dose. Lattice damage and ablation dominate at high laser doses. Based on our findings, we encourage the use of a minimal laser dose (8 × 10 7 J/m 2 or below) for Raman measurements of GO. Despite the resulting loss in signal, these conditions limit sample modification and measurement inaccuracies.

Spatially resolved solid-state reduction of graphene oxide thin films

“…Raman measurements were performed on the boundary between dendrites and the unaffected GO film. To decrease as much as possible the structural effects on GO induced by the Raman laser, [38][39][40] the integration time, the scan average, the laser wavelength and the laser doses were optimized. The optical image of the investigated spot is presented in Fig.…”

Algorithm-improved high-speed and non-invasive confocal Raman imaging of 2D materials

“…For GO, reliable Raman characterization has been a major challenge due to laser-induced sample damage [ 35 , 43 ]. To mitigate this problem, the laser dose needs to be reduced as much as possible [ 11 , 35 , 43 ]. Many previous works used mW scale power to characterize GO [ 44–48 ].…”

“…Many previous works used mW scale power to characterize GO [ 44–48 ]. A recent study [ 35 ] suggested that laser-induced reduction of GO cannot be prevented even when the laser intensity is down to a dose of 8 × 10 7 J/m 2 , which corresponds to 48 μW during 1 s in the confocal spot. Such laser intensity is already a few orders of magnitude lower compared to preceding studies [ 47 , 48 ].…”

“…3 d), and the I(D)/I(G) ratio changes with time (Supplementary Fig. 6a), which is a typical consequence of the reduction of GO [ 35 ]. In contrast, the intensity loss is substantially reduced when illuminated with 4 μW of laser irradiation (4.9 × 10 5 J/m 2 intensity) for 500 s with 50 ms per spectrum (Fig.…”

“…A recent study suggested that even a laser dose of 48 μJ, i.e. 48 μW in 1 s, is still too high to prevent sample damage [ 35 ].…”