Raman Spectroscopy Study of the Charge Carrier Concentration and Mechanical Stresses in Graphene Transferred Employing Different Frames

Abstract

Comparative studies of charge carrier concentration (n) and relative strain (e) in graphene synthesized with chemical vapor deposition and transferred to the surface of SiO₂/Si substrate using two different frames, polymethylmethacrylate (PMMA) and paraffin, followed by complex processing, were carried out. The correlation method for determining the positions of Raman active modes was implemented for the analysis. It was established that in the case of paraffin, the concentration of charge carriers in graphene was initially lower than for PMMA. Further liquid phase and heat treatment used to remove the paraffin frame led to an increase in n up to 1.2×10¹³ cm^–2. For graphene samples transferred using a PMMA frame, no clear trend in the change in n was observed, regardless of the types of processing. At the same time, the spread of e values for graphene transferred with paraffin followed by liquid phase and heat treatment in vacuum was greater than for graphene transferred with PMMA and passed through a similar treatment, –0.01875 — –0.1488% and –0.04375 — –0.0875%, respectively. The results obtained during the study made it possible to establish that, in addition to the transfer frame material itself, a combination of processing methods had a decisive impact on the quality of graphene. Optimization of these parameters made it possible to increase the efficiency of the graphene transfer technique with a simultaneous improvement in the performance characteristics of graphene nanoelectronic devices.