August 1, 2012.
The definitive version is available at http://dx.doi.org/.
Graphene’s intrinsic properties of being a good conductor as well as having efficient optical transmission make it a potentially useful material in photovoltaic cells as a transparent conducting electrode. One problem preventing graphene from being fully utilized stems from contaminates created and deposited during the transfer process of multiple graphene layers. After synthesis, TRT (Thermal Release Tape) is applied to the graphene supported on the copper growth substrate. TRT utilizes a unique formulation of adhesive that is temperature sensitive so that it will release when heated. Upon removing the growth substrate in a chemical bath, the TRT is used to transfer the graphene to substrates of interest. Unfortunately, the TRT also transfers small quantities of adhesive along with the graphene, thus creating a contaminant-laden area. To improve the properties of the transferred graphene films, the contaminants must be removed. In this study we investigate the ability for high temperature anneals to remove the residual adhesive. It is found that higher temperature anneals, while increasing the defect intensity within the graphene, also appear to increase the consistency of multiple layer application. This analysis is achieved by comparing Raman Spectroscopic maps of the FWHM of the G’ peak (2680 cm-1) associated with the graphene layer. This consistency correlates with lower resistance values that were achieved using a four-point probe measurement. Although high temperature anneals increase the D/G peak ratio in the Raman Spectra, the resistance values still decrease. Overall, this study gives the first indication that higher temperature anneals may be capable of removing contaminants without sacrificing graphene conductivity
National Renewable Energy Laboratory (NREL)
This material is based upon work supported by the S.D. Bechtel, Jr. Foundation and by the National Science Foundation under Grant No. 0952013 and Grant No. 0833353. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the S.D. Bechtel, Jr. Foundation or the National Science Foundation. This project has also been made possible with support of the National Marine Sanctuary Foundation. The STAR program is administered by the Cal Poly Center for Excellence in Science and Mathematics Education (CESaME) on behalf of the California State University (CSU).