Graphene suspended over grids for transmission electron microscopy (TEM) can have numerous interesting applications in studies of material properties for technological applications. Two recent publications from TU Wien demonstrate the use of graphene on TEM grids for studies of material quality and integration with indium oxide, another technologically relevant material.
The quality of growth of other materials on graphene is of fundamental importance for device applications. The crystallinity and orientation of indium oxide grown on graphene affects the quality of displays and sensors produced from such a heterostructure. In a study published in Advanced Functional Materials, researchers have shown that arrangement of indium oxide crystals on graphene depends on the pressure on which the crystals form. That can have a major impact on the application properties of the combined materials.
Image: Graphene on TEM grid.
Crucial to the success of this study was the availability of free-standing graphene, on which indium oxide is grown. Having graphene which is suspended in vacuum provides a clean picture of the crystal structure, without any background from a substrate. This is achieved by using commercially available graphene suspended over a metallized mesh – a TEM grid. Transmission electron microscopy across such graphene has the best possible resolution, down to the atomic level.
In a second study, the team of scientists showed that graphene on TEM grids can be used to gauge the quality of the graphene itself. Although grown at a high quality on metal substrates with chemical vapour deposition, transfer of graphene to any useful substrate or a TEM grid requires first coating it with a transfer polymer. Numerous polymer removal processes are used at the industrial scale today, nevertheless it has been shown that some residue persists regardless of the cleaning process. The amount of residue directly impacts graphene film performance.
The study, published in the Journal of Chemical Physics, reveals that ion beam spectroscopy can be used as a tool to map with high resolution the local cleanliness of graphene. The results indicate that although some residue always remains, it clusters in small areas, leaving large clean areas that can be used for devices.
These novel studies highlight the usefulness of graphene on TEM grids as a tool in material science and technology research.