2, Binghamton University, State University of New York, Binghamton, New York, United States
A key part of efforts to tune the chemical, electrical, and optical properties of graphene oxide (GO) is the need to accurately characterize GO’s complex structure. Raman spectroscopy and confocal Raman mapping are widely used for insight into the size of GO’s nanoscale graphene-like domains, the degree of lattice order, and sheet stacking structure. It has also been shown, however, that GO can be intentionally modified by laser sources similar to those used for Raman spectroscopy. The extent to which GO is modified under typical Raman measurement conditions has not previously been studied, making it unclear how reliable published Raman data is.
In this presentation, we will discuss the effects of Raman laser exposure on GO structure and recommend protocols for accurate Raman characterization of GO. We exposed GO to laser doses spanning over four orders of magnitude. Subsequent Raman spectroscopy (performed using minimally invasive conditions), X-ray photoelectron spectroscopy, and atomic force microscopy revealed that GO reduction occurs at all laser intensities that are practical for Raman characterization, with the degree of reduction increasing with laser dose. At higher laser doses, GO was ablated, resulting in significant material loss. These sample modifications can lead to erroneous Raman data. For example, Raman metrics, such as the 2D- to G-band intensity ratio, can drop by as much as 50% during acquisition at a high laser dose. To minimize the physical damage that takes place in GO during Raman spectroscopy, and obtain data that is representative of unmodified GO, we encourage the use of a minimal laser dose (8 x 107 J/m2 or below), despite the loss in signal. In other words, reliable measurements can be obtained when sample integrity is prioritized over signal intensity.