충청지부 초청 세미나

일시: 2015년 3월 19일 (목), 오후 4시 30분
장소: 한남대학교 생명나노과학대학 세미나실
연사: Prof. Christoph Bubeck (독일 Max-Planck 고분자연구소)
연제: Ultrathin Films of Graphene Oxide-Critical Assessment of Photoreduction Strategies
주관: 한남대(이광섭 교수)/한국고분자학회 충청지부

Abstract

Approaches to graphene-based electronic materials and devices frequently use graphene oxide (GO), combined with a suitable reduction process to remove the oxygen-containing groups. Photoreduction of GO films is applied to generate reduced graphene oxide (RGO). Specially designed lateral structures of electrically conducting RGO can be fabricated for device applications by means of irradiation masks or laser direct writing techniques. However, the photoreduction mechanisms are not fully resolved yet as the distinction between photothermal and photochemical reaction pathways still needs fundamental clarification.
We have prepared ultrathin films of GO by spin-coating from aqueous solutions, irradiated them with monochromatic light obtained from a high-pressure mercury arc combined with narrow band filters, or with a femtosecond laser system at 800 nm. We used UV-Vis-NIR absorption spectroscopy to characterize the conversion and reaction rate of the photoreduction quantitatively. The kind of photoreaction is analyzed by the characteristic influence of the light intensity on the reaction yield. Photothermal reactions show a threshold behavior, i.e., a minimum sample heating is required. Photochemical reactions can occur via single- or multiple photon absorption. We verify pure photochemical photoreduction of GO by single-photon-absorption at UV and even at visible light irradiation wavelengths, and two-photon induced photoreduction with high-intensity laser pulses at 800 nm. We observe onsets of reduction of GO at significantly lower temperatures and photon quantum energies as reported earlier. Our work has critical implications on stability issues of RGO devices which will be discussed.


Biography

Dr. Christoph Bubeck is Professor at the Max Planck Institute for Polymer Research, Mainz, Germany. He received his PhD in Physics from the University of Stuttgart in 1979. After a post-doctoral year at the IBM Research Laboratory in San Jose, USA, he studied optical properties of Langmuir-Blodgett multilayers at the University of Freiburg. Since 1984 he is a member of the scientific staff of the Max Planck Institute for Polymer Research in Mainz, Germany. He received the Habilitation degree in Experimental Physics in 1993 for his work on spectroscopy and nonlinear optics of ultrathin layers of organic materials. His current research interests focus on thin polymer films for photonics and optoelectronics, especially their linear and nonlinear optical properties.