Rapid thermal annealing and reduction process monitoring of graphene oxide thin film on chip

Graphene oxide (GO) is considered as a cost-effective source among the graphene-based materials for various device platforms after its reduction to reduced graphene oxide (rGO). For GO reduction, thermal annealing is a relatively convenient method compatible with top-down batch fabrication processes under precise parameter control. In this work, the influence of temperature changes up to 750°C over reduction of large area GO thin films is addressed in a systematic manner. For this, the dielectric properties such as electrical and optical permittivity of rGO are characterized using high-precision electrical impedance spectroscopy and spectroscopic ellipsometry, while following the reduction process using Raman spectroscopy. To realize the study platform, GO thin films were prepared, micro-patterned and electrically connected using a standard top-down lithography processes. The optical and electrical permittivity are found to be inversely related to the reduction temperature. Graphene and GO are widely studied in the literature due to their unique properties [1]. GO is an electrical insulator with a hydrophilic surface, while graphene is conductive and hydrophobic [2, 3]. By reduction of GO, reduced GO (rGO) with intermediate properties can be achieved [4]. Among various reduction methods (e.g. radiation-based, chemical and thermal techniques), rapid thermal annealing (RTA) is relatively faster, more sustainable and more convenient [5]. In RTA, GO is placed in a vacuum and subjected to high temperatures. After being kept at a certain temperature for a specific time (resting time), GO is cooled to room temperature. The resting time can be limited to a few seconds, and thus the whole process can be performed within minutes. Hence, it is much faster than the common chemical reduction methods that typically take hours to days [6].