Abstract
Dynamic surface modification of suspended graphene at high temperatures was directly observed with in situ scanning transmission electron microscopy (STEM) measurements. The suspended graphene devices were prepared on a SiN membrane substrate with a hole so that STEM observations could be conducted during Joule heating. Current–voltage characteristics of suspended graphene devices inside the STEM chamber were measured while monitoring and controlling the temperature of graphene by estimating the electrical power of the devices. During the in situ STEM observation at high temperatures, residual hydrocarbon adsorbents that had remained on graphene effectively evaporated creating large, atomically clean graphene areas. At other places, dynamic changes in the shape, position, and orientation of adsorbents could be directly observed. The temperature of the suspended graphene sample was estimated to reach up to 2000 K during the experiment, making graphene an efficient high-temperature micrometer-sized electron-transparent hot plate for future experiments in microscopes.
Highlights
Graphene is a quasi-two-dimensional 1-atom-thick layer of sp2bonded carbon atoms in a honeycomb structure that, due to its unique and intriguing physical properties,[1−7] has been regarded as a promising material for future electronic devices and sensors
We report in situ scanning transmission electron microscopy (STEM) observation of dynamic changes of graphene and the residual hydrocarbon-based adsorbents at high temperatures induced by Joule heating
Current−voltage (I−V) produced by electrons scattered by atomic nuclei, i.e., characteristics of graphene were measured during STEM Rutherford scattering
Summary
Graphene is a quasi-two-dimensional 1-atom-thick layer of sp2bonded carbon atoms in a honeycomb structure that, due to its unique and intriguing physical properties,[1−7] has been regarded as a promising material for future electronic devices and sensors. Graphitization of polymer residues due to Joule heating on graphene was observed by Westenfelder et al.[19] and Shyam Kumar et al.[20] in separate experiments In these studies, the polymer residue, showed no large-scale dynamics, presumably because the originally molecular residue had transformed into an amorphous network under high-energy electron irradiation (80 and 300 kV were used, respectively). After the remaining PMMA layer was dissolved in our experiments, at 60 kV, the residue shows a clearly acetone and rinsed with isopropanol, the fabrication was completed dynamical behavior while being heated We expect this to be by drying the suspended graphene device using a critical point drying due to a lower extent of molecule-to-network conversion under our gentler electron irradiation conditions. See the Supporting Information movies for the entire dynamic process (Movies S1−S7)
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