It is shown that with a single laser beam, it is possible to measure the temperature distribution of a tiny graphene bubble and to control its temperature. At the same time we learned about the thermal conductivity of graphene and learned how well graphene is attached to the substrate. Temperature variations were identified from the observed spectral shifts.
The highly elastic and flexible nature of graphene allows the creation of stable large bubbles on its surface (several micrometers wide and one micrometer high) in a more or less controlled fashion. Such bubbles might serve as micro-lenses or be used to control the morphology of graphene on surfaces or to chemically functionalize graphene on selected regions.
When graphene is illuminated with a laser beam, incident and reflected beams overlap forming an optical standing wave on the surface. While the large graphene bubble is not disturbed much by the standing wave, increasing the laser power has the effect of selectively heating the graphene bubble at the interference maxima of the standing optical wave. Such local changes in temperature can be detected by following the spectral shifts in the vibrational spectrum of graphene, where oscillations in shift and intensity of a spectral peak are recorded when scanning the laser spot across the graphene bubble.
By comparing the experimentally observed spectral shifts with those calculated using a theoretical diffusion model, taking into account curvature and the heat flow in graphene, we discover that the recorded temperature distribution over the bubble depends both on the thermal conductivity of graphene and the adhesion at the edge of the graphene bubble. The highest heating effect is seen in the center region of the bubble, furthest from the bubble boundary. Obtained 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.
Raman spectral band oscillations in large graphene bubbles
Yuan Huang, Xiao Wang, Xu Zhang, Xianjue Chen, Baowen Li, Bin Wang, Ming Huang, Chongyang Zhu, Xuewei Zhang, Wolfgang S. Bacsa, Feng Ding, and Rodney S. Ruoff, 27 April 2018.