Shedding Light On Bubbly Graphene

Scientists at the Institute of Basic Science in South Korea have used a single laser beam to probe the behavior of graphene bubbles.

AsianScientist (May 21, 2018) – A team of researchers at the Institute for Basic Science (IBS), South Korea, have measured and controlled the temperature of individual graphene bubbles with a single laser beam. Their study was published in Physical Review Letters.

The highly elastic and flexible nature of graphene allows for the creation of large, stable bubbles. The strain and curvature introduced by the bubbles is known to tune the electronic, chemical and mechanical properties of this material.

Generally, graphene bubbles are more reactive than flat graphene, making them possibly easier to decorate with chemical groups. Bubbles might serve as tiny, closed reactors, and their curved surface could provide a lens effect. Understanding how temperature varies within bubbles is an important factor for several applications.

“If you think that chemical reactions could be carried out inside the bubble or on the surface of each graphene bubble, then changing the temperature distribution in a bubble will significantly influence reactions taking place,” said Dr. Huang Yuan of IBS, the first author of the study.

In this study, bubbles were formed at the interface between a graphene sheet and a silica (SiO2/Si) substrate. The silica surface attracts molecules that evaporate when heated, creating bubbles.

As predicted by the researchers, the temperature oscillated with the bubble height. Although each bubble is only several micrometers in width and about one micrometer in height, the scientists could detect a variation in temperature, not only between the center and the edges, but also at different heights of the bubble.

When the researchers illuminated a graphene bubble with a laser beam, incident and reflected rays overlapped, forming an optical standing wave on the surface. Increasing the laser power had the effect of selectively heating specific regions of the bubble, which corresponded to the maximum interference of the standing optical wave. IBS scientists detected local changes in temperature within each bubble using Raman spectroscopy, a standard technique to measure graphene characteristics and morphology.

“These results confirm the high thermal conductivity of graphene previously measured, demonstrate the excellent adhesion around the perimeter of the graphene bubble, and provide new perspectives on how to heat graphene bubbles on specific locations,” said Professor Rodney Ruoff, coauthor and director of the Center for Multidimensional Carbon Materials at IBS.

“The more we know about the physical properties of graphene bubbles, the more we might be able to make use of them in different ways.”

The article can be found at: Huang et al. (2018) Raman Spectral Band Oscillations in Large Graphene Bubbles.


Source: Institute for Basic Science; Photo: Shutterstock.
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