Combined Ultra High Vacuum Raman and Electronic Transport Characterization of Large‐Area Graphene on SiO 2

Abstract

An original experimental setup which allows for simultaneous sample characterization by Raman spectroscopy and electronic tranport in ultra-high vacuum at low temperatures is presented. We show the applicability of this setup for the case of graphene that is transferred from an Ir(111) single crystal onto SiO2. The transfer of graphene is carried out using a water-promoted electrochemical bubbling technique which is applied to graphene/Ir for the first time. The characterization prior to the transfer includes electron diffraction, photoemission spectroscopy and Raman spectroscopy using ultraviolet excitation. Following the transfer procedure, the graphene layer is electrically contacted and mounted onto a special sample carrier. This carrier allows for combined Raman and transport measurements inside an ultra high vacuum (UHV) system. UHV Raman mapping reveals a large area homogeneous graphene quality over several mm2 characterized by a D/G intensity ratio less than 0.1. UHV electrical characterization of transferred graphene in a field effect transistor geometry yields a carrier mobility of 675 cm2 V−1 s−1. Upon alkali metal doping in UHV conditions using a Cs getter, a decrease of the 4-point resistance from above 2500 Ω to below 10 Ω is observed. The presented approach paves the way for future combined UHV Raman and transport characterization of two-dimensional materials that are doped into superconducting or charge-density-wave ground states.