Electrical characterization of graphene-like films at microscopic and macroscopic scale

Graphene has recently been shown to be an outstanding material: among its astonishing properties are the carrier mobility at room temperature (200 000 cm² V^-1 S^-1) and the Young modulus (1.5 TPa). Graphene is a one-atom thick two-dimensional carbon crystal and has been first produced by mechanical exfoliation to obtain high purity defect-free sheets. Chemical vapour deposition (CVD) is a promising method producing larger areas of graphene but the process of transfer and deposition is not mastered. Finally much work has been done on graphene oxide (GO) for applications ranging from electronics to sensors. In this work we describe recent work on a method of production of graphene flakes based on liquid exfoliation and spraying. The challenge is to produce a nanometric uniform and covering film by tuning the spraying process. For many electronics applications a high quality junction between the graphene and the metallic contact is crucial. Hence the aim of our study is fabricating a film from the overlapping of graphene flakes with sufficient conducting properties. The factors that determine the contact resistance are, as yet, unclear. In this work we try to bring some light on the transport mechanisms involved in graphene metal junctions. Experimental measurements are performed both with a conductive probe Atomic Force microscope (AFM) and a Van der Pauw type method. Various types of graphene films are deposited on gold or silicon substrates and investigated. Various contact resistance contributions are discussed and assumptions are made to analyse quantitatively the results.