PhD Thesis: Dissertation: 2D materials for piezoresistive strain gauges and membrane based nanoelectromechanical systems

  suspendes 2d materials, Raman tomography and electrical characterization Copyright: © Stefan Wagner

Stefan Wagner published his dissertation in which the potential of graphene and platinum diselenide as materials for nanoelectromechanical sensors was investigated. The paper was recently published in the RWTH Aachen Library.

In this work graphene was chosen as an intensively investigated material and the almost unknown platinum diselenide as a 2D material because of its inherent properties. Strain sensors were made of both materials, measured using a bending beam setup and compared to a commercial metallic strain gauge. A strain factor of 1.4 - 1.7 was determined for graphene and -84.8 for platinum diselenide. These results served as a basis for the fabrication of piezoresistive NEMS pressure sensors, where graphene and platinum diselenide are used both as membrane material and as direct readout mechanism. Large device substrates with cavities are fabricated, five transfer methods have been developed to produce unsupported 2D materials and the yield of intact membranes has been compared. Ramantomography has been developed as a new characterization method based on Raman spectrometry to investigate unsupported graphene and platinum diselenide membranes. Based on this, 3D Ramantomography images of these nanoelectronic devices were acquired for the first time. Electrical measurements were performed in-situ on these devices in a self-constructed pressure chamber. The graphene sensors achieve a 20-100 times higher sensitivity compared to other NEMS pressure sensors. For pressure sensors with platinum diselenide as membrane material, the high sensitivity of graphene was even exceeded by several orders of magnitude. These results suggest a very high potential for future miniaturization of sensors and the development of other NEMS applications based on 2D materials.

The research was funded by M-ERANET/German ministry for education and research (BMBF, NanoGraM, 03XP0006) and by the European Commission under the project Graphen Flagship (785219).