Mid-infrared assisted transport at the nano-junction between graphene and a doped-diamond scanning probe

We report mid-infrared photoconductive atomic-force microscopy (AFM) of a graphene sheet with doped-diamond AFM probes illuminated with a quantum cascade laser. The diamond probe ensures high mechanical and electrical stability. We observe a prominent photoconduction at finite biases that we interpret as the overcoming of a potential barrier formed at the graphene-diamond junction by free carriers excited by mid-infrared photons (220 meV photon energy). Moreover, we observe a small photo-thermoelectric effect of graphene under zero applied bias. We demonstrate that the use of diamond AFM probes for mid-infrared photoconductive AFM has great potential to investigate the nanometric inhomogeneities of the Fermi level and of the work function across integrated semiconductor devices.