David M. A. Mackenzie: Quality Assessment of Graphene: continuity, uniformity and accuracy of mobility measurements

David M. A. Mackenzie, Jonas D. Buron, Patrick R. Whelan, José M. Caridad  Martin Bjergfelt, Birong Luo, Abhay Shivayogimath, Anne L. Smitshuysen, Joachim D. Thomsen, Tim J. Booth,  Lene Gammelgaard, Johanna Zultak, Bjarke S. Jessen, Peter Bøggild, and Dirch H. Petersen Department of Micro & Nanotechnology, Technical University of Denmark, Building 345E, 2800 Kgs. Lyngby, Denmark As the availability of large area graphene increases, accurately assessing uniformity and quality has become critically important. Assessment of the spatial variability in carrier density and carrier mobility (µ) can be time consuming and difficult, but variations must be controlled and minimized. We present a simple framework for assessing the homogeneity of graphene devices. The field effect in large-scale CVD devices [1] (Fig. 1a) and devices of exfoliated graphene encapsulated in hexagonal boron nitride [2] (Fig. 1c) were measured in dual configurations (Fig. 1b inset). We can then derive a gate-dependent homogeneity factor, ß (Fig. 1b/d). Finite element simulations were carried out suggesting that inhomogeneity in spatial doping (as low as 1010 cm-2) rather than inhomogeneity in µ is the significant cause of variations in ß. Such doping variations are shown to lead to systematic errors when calculating µ- errors which are hidden if ß is ignored. In addition, we find that for certain devices Raman mapping (Fig. 1e) can be used as input for finite element simulations and reasonable agreement is found between simulated and experimental gate-dependent electrical data (Fig. 1f). A recent comprehensive study can be found here [3].  1. David M A Mackenzie et al 2015 2D Mater. 2 045003 2. F Pizzocchero et al 2016 Nature Comms. 7 11894 3. David M A Mackenzie et al 2017 Nano. Res. DOI 10.1007/s12274-017-1570-y David Mackenzie is a researcher in the Nanocarbon group based at the Department of Micro & Nanotechnology, Technical University of Denmark. Research interests include fabricating graphene devices, accuracy of electrical measurements, gas sensing measurements, finite element simulations, and Raman spectroscopy.