KP-EFM measurements of surface potential and work function of doped graphene

The electronic properties of graphene sheets have recently attracted much experimental and theoretical interest. A single graphene layer is a semimetal or zero-gap semiconductor, and has excellent electronic properties, such as high mobility (200 000 cm2 V-1 s-1), room-temperature quantum Hall effect, and high mechanical elasticity (elastic modulus of about 1 TPa). In addition, high flexibility, optical transmittance, and chemical stability are other technological advantages of single graphene layers. These superb characteristics open new potential applications of graphene in flexible and transparent electronic devices. Among other properties, the work function is an important factor governing the application of graphene as an electrode, for instance, in solar cells and light emitting diodes. The work function determines the band alignment in the contact to facilitate selective electron and hole transport. The work function of graphene also depends on the interaction graphene-substrate and Kelvin-Probe Electrostatic Force Microscopy (KP-EFM) is a suitable approach to measure the graphene work function on various supports. Kelvin-Probe electrostatic force microscopy (EFM) has been widely used to probe graphene layers with different thickness on different substrates, SiO2/Si, SiC, and KBr. In this contribution, we apply the KP-EFM characterization to determine the work function of graphene samples on: -different substrate (SiC, glass, a-Si and SiO2); -with different doping induced by metals ( Al, Au, In, Ga), and by molecular functionalization with self-assembled monolayers (thiols, thienylene-phenylene polymers).