Highly Reduced Graphene Oxide Obtained by Langmuir-Blodgett Technique_ Controlled Synthesis and Properties at the Nano-Scale

JOSE M. RAMALLO-LOPEZ; FACUNDO C. HERRERA; FELIX G. REQUEJO; PAULA C. DOS SANTOS CLARO; GUSTAVO MORALES; JAVIER LOHR; R. D. SANCHEZ; GABRIELA I. LACCONI; JOSE AVILA; MARIA C. ASENSIO

Moscow

Conferencia; XII International Conference on Nanostructured Materials (NANO 2014); 2014

Moscow University

We present a controlled method for the production of highly reduced graphene oxide (HRGO)  thin films using the Langmuir-Blodgett (LB) technique. In order to have precise and detailed information of the chemical species in the samples and their spatial distribution, a multiple characterization on the different stages of the material (i.e. before and after each reduction treatment) was performed employing both spectroscopic and image-based analysis such as: SEM, AFM, grazing XRD, RAMAN, XPS and their space-solved versions: micro-RAMAN and nano-XPS. Finally, a set of current-voltage curves on macroscopic and microscopic distance between electrodes were obtained. Graphene oxide was obtained by Hummers? method [1] anddeposited on Si(100) by LB technique. Different thermal reduction treatments were performed under UHV conditions. Grazing XRD experiments were performed at the DRX2 beamline at the LNLS (Campinas, Brazil), XPS and nano-XPS analysis were performed at the ANTARES beamline at the SOLEIL Synchrotron (Saint Aubin, France). The microscopic determinations of currentvoltage curves were obtained using the assistance of a nanomanipulator and a probe  station. The thickness of the samples was analyzed by AFM and grazing XRD and they became thinner after the thermal treatments, reaching between 1.3 and 1.8 nm after reduction treatments at 600 °C, which is very close to the expected value for very few layers of HRGO. RAMAN experiments show the decrement of the D band (associated with defective centers) after the thermal treatments. C1s XPS showed that carbon species associated with different oxygen funcionalities were eliminated after each thermal treatment. From micro-RAMAN and nano-XPS we could establish the high spatial homogeneity of the film after the reduction treatments. The transport properties determined for GO and HRGO sheets by employing a nanomanipulator, clearly show a change of conductivity regime in the GO sheets after the deeper reduction. While a semiconductor behavior is observed before the reduction treatment at 600 C, an ohmic  conductivity is reached for the HRGO.References [1] W.S. Hummers Jr., R.E. Offeman, J. Am. Chem. Soc. 80 (1958) 1339.