Highly sensitive and stretchable strain sensor based on wrinkles of a twisted multilayer graphene

Abstract

CVD-grown graphene hosts networks of wrinkles along with minor ripples as structural features which form to release stresses arising from the mismatch in thermal expansion properties of metal catalyst substrate and the graphene. A modified CVD method based on joule-heating of the Ni catalyst produces twisted multilayer graphene (tMLG) with a well-pronounced network of wrinkles, which are the channels of electrical conduction. The present study exploits the response of network of wrinkles in tMLG to mechanical stress and demonstrates a highly cyclable strain sensor. The wrinkles show significant reversible changes in the morphology particularly in the region of interconnections and junctions when subjected to strain, as revealed by the microscopy studies. In-situ Raman measurements reveal that relative rotations among the adjacent layers nucleate at the junctions and to some extent, on the wrinkles, while they are weak in the flat regions. These changes in the structural features result in enormous changes in the sample resistance, which are used in the sensing operation of the device. The sensor showed excellent repeatability and stability after multiple straining and relaxing cycles, withstanding prolonged strains. This sensor based on tMLG grown with simple vacuum deposition, exhibits an ultra-high gauge factor in the order of 10^6 in a wide strain range of 0-45%. With its highly stable and consistent dynamic response characteristics, it is a promising candidate for advanced strain sensing applications.