Since the graphene surface is hydrophobic, both mechanical force and back pressure are combined to deposit droplets. Finally, the chip is placed onto a hotplate and heated to 350°C and annealed for 45 minutes to assure an ohmic contact. Conductivity improvement after deposition was reported in previous works with thin film structures [15,16]. Finally, the picoprobes are put in contact with the electrodes for current and voltage monitoring with the Keithley 6517b under the focused laser source (Fig. 3d).