Raman spectral band oscillations in large graphene bubbles

May 10, 2018, Institute for Basic Science
Bubbles form when molecules are trapped between the graphene sheet and the silica (SiO2/Si) substrate. The image shows also the hottest spot in red, which corresponds to the highest part of the bubble. Credit: Institute for Basic Science

A team of researchers at the Center for Multidimensional Carbon Materials, within the Institute for Basic Science (IBS) have measured and controlled the temperature of individual graphene bubbles with a single laser beam for the first time. The study is now available from Physical Review Letters.

The highly elastic and flexible nature of allows for the creation of stable large bubbles, in a more or less controlled fashion. 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, so they might be more prone to be decorated with chemical groups. Bubbles might serve as tiny, closed reactors, and their curved surface could provide a lens effect. Understanding how 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," says Yuan Huang, the first author of the study.

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

Raman spectral band oscillations in large graphene bubbles

As also predicted by the theorists of the team, Xiao Wang and Feng Ding, the temperature oscillates 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 a graphene bubble is illuminated with a laser beam, incident and reflected rays overlap forming an optical standing wave on the surface. Increasing the laser power has the effect of selectively heating specific regions of the bubble, which correspond 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.

"Standing waves near surfaces have been ignored for a long time and have only rarely been observed in a direct manner. The results are surprising. The can efficiently heat the graphene, and we can determine the thermal conductivity in graphene bubbles from its temperature distribution," explains Wolfgang Bacsa, one of the members of the team, and visiting scientist from CEMES-CNRS and University of Toulouse in France.

"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," concludes Rod Ruoff, coauthor and director of the Center for Multidimensional Carbon Materials. "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."

For example, an intriguing application could be the creation of graphene sheets with circular holes, like a 'polka dot' pattern. As overheating of the bubbles causes them to burst, the pores decorated with specific chemical groups could work as molecular selective filters. Graphene's unique properties never cease to amaze.

Explore further: Bubble technique used to measure shear forces between graphene sheets

More information: Yuan Huang et al. Raman Spectral Band Oscillations in Large Graphene Bubbles, Physical Review Letters (2018). DOI: 10.1103/PhysRevLett.120.186104

Related Stories

Turning graphene into light nanosensors

April 25, 2018

Graphene has many properties; it is e.g. an extremely good conductor. But it does not absorb light very well. To remedy this limiting aspect of what is an otherwise amazing material, physicists resort to embedding a sheet ...

3D graphene: Super-capacitors from sugar bubbles

January 24, 2014

Graphene sheets are immensely strong, lightweight and excellent at conducting electricity. Theoretically, macroscopical three-dimensional graphene assemblies should retain the properties of nanoscale graphene flakes. However, ...

A way to create liquid droplets inside of air bubbles

February 8, 2018

A team of researchers at Zhejiang University in China has developed a technique to create liquid droplets inside of air bubbles. In their paper published in the journal Physical Review Letters, the group describes the technique ...

Graphene under pressure

August 25, 2016

Small balloons made from one-atom-thick material graphene can withstand enormous pressures, much higher than those at the bottom of the deepest ocean, scientists at the University of Manchester report.

Recommended for you

Graphene's magic is in the defects

December 18, 2018

A team of researchers at the New York University Tandon School of Engineering and NYU Center for Neural Science has solved a longstanding puzzle of how to build ultra-sensitive, ultra-small electrochemical sensors with homogenous ...

Carbon nanotubes mime biology

December 18, 2018

Cellular membranes serve as an ideal example of a system that is multifunctional, tunable, precise and efficient.

Deep learning democratizes nano-scale imaging

December 18, 2018

Many problems in physical and biological sciences as well as engineering rely on our ability to monitor objects or processes at nano-scale, and fluorescence microscopy has been used for decades as one of our most useful information ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.