Atomic force and scanning tunneling microscopy imaging of graphene nanosheets derived from graphite oxide.

By J. I. Paredes, S. Villar-Rodil, P. Solís-Fernández, A. Martínez-Alonso, J. Tascón. Langmuir, 2009

653 citations recorded by the source corpus.

Graphene nanosheets produced in the form of stable aqueous dispersions by chemical reduction of graphene oxide and deposited onto graphite substrates have been investigated by atomic force and scanning tunneling microscopy (AFM/STM). The chemically reduced graphene oxide nanosheets were hardly distinguishable from their unreduced counterparts in the topographic AFM images. However, they could be readily discriminated through phase imaging in the attractive regime of tapping-mode AFM, probably because of differences in hydrophilicity arising from their distinct oxygen contents. The chemically reduced nanosheets displayed a smoothly undulated, globular morphology on the nanometer scale, with typical vertical variations in the subnanometer range and lateral feature sizes of approximately 5-10 nm. Such morphology was attributed to be the result of significant structural disorder in the carbon skeleton, which originates during the strong oxidation that leads to graphene oxide and remains after chemical reduction. Direct evidence of structural disorder was provided by atomic-scale STM imaging, which revealed an absence of long-range periodicity in the graphene nanosheets. Only structured domains a few nanometers large were observed instead. Likewise, the nanosheet edges appeared atomically rough and ill-defined, though smooth on the nanometer scale. The unreduced graphene oxide nanosheets could only be imaged by STM at very low tunneling currents (approximately 1 pA), being visualized in some cases with inverted contrast relative to the graphite substrate, a result that was attributed to their extremely low conductivity. Complementary characterization of the unreduced and chemically reduced nanosheets was carried out by thermogravimetric analysis as well as UV-visible absorption and X-ray photoelectron and Raman spectroscopies. In particular, the somewhat puzzling Raman results were interpreted to be the result of an amorphous character of the graphene oxide material.

Subfields: Electrical and Electronic Engineering, Materials Chemistry

View Paper: https://www.semanticscholar.org/paper/62ed504815579cf67760be637eb6237fe83bef5b

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Citations in the corpus

Graphene based materials: Past, present and future (2011, background): “[145] demonstrated the influence of attractive mode of AFM to determine the thickness of the sheet.”
UV light exposure of aqueous graphene oxide suspensions to promote their direct reduction, formation of graphene–metal nanoparticle hybrids and dye degradation (2012, methodology): “[29] Paredes JI, Villar-Rodil S, Solı́s-Fernández P, Martı́nez-Alonso A, Tascón JMD.”
A manufacturing perspective on graphene dispersions (2015, background): “formed by the in situ reduction of aqueous GO solutions [68,69].”
The reduction of graphene oxide (2012, neutral): “[46] Paredes JI, Villar-Rodil S, Solís-Fernández P, Martínez-Alonso A, Tascón JMD.”
Evaluation and mechanism of antifungal effects of carbon nanomaterials in controlling plant fungal pathogen (2014, background): “reduction, the maximum red-shifted to approximately 267 nm and the absorption in the whole spectral region (>231 nm) increased, indicating the electronic conjugation had been restored within the graphene nanosheets [23,24].”
Towards full repair of defects in reduced graphene oxide films by two-step graphitization (2013, methodology): “In agreement with previous STM studies of individual, chemically reduced graphene oxide sheets [45], the as-prepared HG film did not exhibit long-range order on the atomic scale (Fig.”