Preliminary Test With Graphite
Before investigating gaphene at high temperature, my co-worker and I tested our idea with a preliminary set up. The graphite sample was heated on a stage by electric current and the Raman signal was detected by a monochromator with a PMT attached to the output slit.
Though the set up was rather easy, we observed the redshift of both G peak and 2D peak of graphite, which was expected as a common phenomenon of heated graphite.
Though the set up was rather easy, we observed the redshift of both G peak and 2D peak of graphite, which was expected as a common phenomenon of heated graphite.
Constructing the High Temperature Raman Spectroscopy
After the preliminary test, my co-worker and I constructed the whole set up of the High Temperature Raman Spectroscopy. The Picture on the left is the optimized version of the Spectroscopy part. The collected Raman signal is detected on a CCD.
As showed in the lower picture, the vacuum chamber is applied for heating. The vacuum system and the spectroscopy system were successfully coupled. Plenty of different experiment can be carried out with this set up. For example, the chamber is also designed as a CVD chamber, which allows us to monitor the CVD growth of samples.
As showed in the lower picture, the vacuum chamber is applied for heating. The vacuum system and the spectroscopy system were successfully coupled. Plenty of different experiment can be carried out with this set up. For example, the chamber is also designed as a CVD chamber, which allows us to monitor the CVD growth of samples.
Thermal Expansion of Graphene
One physical property, the thermal expansion, is our current research focus. Since the thermal expansions of substrate and graphene are different, an extra strain induced by such mismatch will exist during the heating process if the substrate interacts with graphene. This particular extra strain causes an extra shift in Raman mode of graphene, which in previous works, helps to determine the thermal expansion coefficient (TEC) of graphene based on the assumption that the interaction between the substrate and graphene is so strong that the graphene appears to be pinned on the substrate.
In our work, we use High Temperature Raman Spectroscopy to determine the TEC of graphene. And we make one step forward. We eliminated the above assumption by introducing another controllable manual strain to estimate the extent of the interaction between the substrate and graphene. Thus we can determine the TEC of graphene with higher accuracy. (This is a work of collaboration between Zhiguang Zhou and Yudan Su)
In our work, we use High Temperature Raman Spectroscopy to determine the TEC of graphene. And we make one step forward. We eliminated the above assumption by introducing another controllable manual strain to estimate the extent of the interaction between the substrate and graphene. Thus we can determine the TEC of graphene with higher accuracy. (This is a work of collaboration between Zhiguang Zhou and Yudan Su)