Hydrogen-assisted pulsed KrF-laser irradiation for the in situ photoreduction of graphene oxide films

We report on the use of pulsed KrF-laser irradiation for the in situ reduction of graphene oxide (GO) films under both vacuum and partial hydrogen pressure. By exposing GO films to 500 pulses of a KrF-laser, at a fluence of 10 mJ/cm(2), their sheet resistance (R-s) is dramatically reduced from highly insulating (similar to 10(10) Omega/sq) to conductive values of similar to 3 k Omega/sq. By increasing the laser fluence, from 10 to 75 mJ/cm(2), we were able to identify an optimal fluence around 35 mJ/cm(2) that leads to highly conductive films with R-s values as low as 250 Omega/sq and 190 Omega/sq, under vacuum (10(-5) Torr) and 50 mTorr of H-2, respectively. Raman spectroscopy analyses confirmed the effective reduction of the KrF-laser irradiated GO films through the progressive recovery of the characteristic 2D band of graphene. Furthermore, systematic Fourier-transform infrared spectroscopy analysis has revealed that KrF-laser induced reduction of GO preferentially occurs through photodissociation and removal of carboxyl (COOH) and alcohol (OH) groups. A direct correlation is established between the electrical resistance of photoreduced GO films and their COOH and OH bond densities. The KrF-laser induced reduction of GO films is found to be more efficient under H-2 background than under vacuum. It is concluded that our KrF-laser reduced GO films mainly consist of turbostratic graphite built from randomly organized few-layers-graphene building blocks, which contains some residual oxygen atoms and defects. Finally, by monitoring the KrF-laser fluence, it is shown that reduced GO films combining optical transmission as high as similar to 80% along with sheet resistance as low as similar to 500 Omega/sq can be achieved with this room-temperature and on-substrate process. This makes the laser-based reduction process developed here particularly attractive for photovoltaic hybrid devices using silicon substrates. (C) 2014 Elsevier Ltd. All rights reserved.