Indium oxide on a layer of graphene. Image: TU Wien.
Indium oxide on a layer of graphene. Image: TU Wien.

Graphene consists of a single layer of carbon atoms and boasts exceptional electronic, thermal, mechanical and optical properties, which have made it one of the most studied materials. For many applications in electronics and energy technology, however, graphene must be combined with other materials. Since graphene is so thin, its properties drastically change when other materials are brought into direct contact with it.

But combining graphene with other materials at the molecular level is difficult. The way graphene interacts with other materials depends not only on which other material you choose, but also on how those materials are brought into contact with the graphene. Rather than sticking a finished material layer to the graphene, the appropriate atoms are usually brought into contact with the graphene in such a way that they ‘grow’ on the graphene in the desired crystal structure.

The mechanisms of the ‘growth’ of these other materials on graphene have often remained unclear. Now, researchers from the Vienna University of Technology (TU Wien) and the University of Vienna, both in Austria, have observed in detail how indium oxide grows on graphene. They chose indium oxide because combining it with graphene is important for applications such as displays and sensors. The researchers report their findings in a paper in Advanced Functional Materials.

"As with a pizza, graphene technology is not only dependent on the graphene pizza base but also on its toppings," explains Bernhard Bayer from the Institute of Materials Chemistry at TU Wien, who led the study. "How these toppings are applied to the graphene is, however, crucial."

In most cases, atoms in the gaseous state are condensed onto the graphene. In the case of indium oxide, these atoms are indium and oxygen.

"But there are many parameters such as background pressure, temperature or the speed at which these atoms are directed at the graphene that influence the result drastically," explains Bayer. "It is therefore important to develop a fundamental understanding of the chemical and physical processes that actually take place. But to do this, you have to watch the growth process as it proceeds. "

This is exactly what the researchers have now succeeded in doing. For the first time, they were able to observe the individual steps of growing indium oxide on graphene with an electron microscope at atomic-scale resolution.

"What was particularly interesting for us was the observation that, depending on the background pressure, the indium oxide crystallites either arrange themselves randomly on the graphene's crystal lattice or snap perfectly on one another like Lego bricks. This difference in arrangement can have a major impact on the application properties of the combined materials," says Kenan Elibol from the University of Vienna, who is first author of the paper. These new findings will be useful for making the integration between graphene and other materials more predictable and controllable with respect to future applications.

This story is adapted from material from TU Wien, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.