Fabrication of optically transparent carbon electrodes by the pyrolysis of photoresist films: Approach to single-molecule spectroelectrochemistry

This paper describes the preparation, physical and chemical characterization, and performance of carbon-based optically transparent electrodes (C-OTEs) fabricated by the pyrolysis of thin films of photoresist. The electrodes are prepared by spin coating dilute solutions of the positive photoresist AZ 4330 onto quartz substrates. Pyrolysis of these samples at 1000 degrees C in a reducing atmosphere yields optically transparent carbon films that have thicknesses ranging between 10 and 80 nm. Sheet resistance measurements, X-ray photoelectron spectroscopy, Raman spectroscopy, and atomic force microscopy were used to determine the physical and chemical properties of the films, and cyclic voltammetry and chronoabsorptometry were employed to delineate the electrochemical and conventional spectroelectrochemical performance of the C-OTEs. These findings showed that the transparency of this material improves as film thickness decreases, but at the expense of an increase in film resistance. At a wavelength of 500 run, for example, 13- and 79-nm-thick films have transparencies of 47 and 10% and sheet resistances of 1100 and 210 Omega/square, respectively. Importantly, adjusting the dilution factor allows the facile and reproducible variation of thickness and transparency. Preliminary results using these C-OTEs for singlemolecule spectroelectrochemistry, which represents a new development in the merger of optical and electrochemical techniques, by probing the potential dependence of the adsorption of individual YOYO-I-labeled lambda-DNA are also presented.