Properties of Graphene Flakes Obtained by Treating Graphite with Ultrasound
Keywords:graphene, Raman spectroscopy, ultrasound treatment, vacancy and edge defects, scanning electron microscopy
A possibility to obtain graphene and graphene layers with the help of the ultrasound (US) treatment of pyrolytic graphite in an N-methyl pyrrolidone (NMP) solution has been demonstrated. Raman spectroscopy is confirmed to be an effective method for monitoring the graphite transformation into graphene. By varying the time of the ultrasonic treatment of pyrolytic graphite in the NMP solution, optimum regimes for the fabrication of graphene flakes with various numbers of layers are determined. In particular, the US treatment for 5 h is shown to be sufficient for producing a colloidal solution of graphene flakes, most of which are single-layered. It is shown that the longer US treatment results in larger intensities of Raman bands D and D′, which testifies to a larger number of defects in the graphene layers. The average distances between defects are estimated for various times of US treatment. The influence of vacancy and edge defects on the intensity band ratio lD/lD′ is analyzed. Vacancies are found to be the prevailing type of defects in the graphene flakes.
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