Electroanalytical Performance of Nitrogen-Containing Tetrahedral Amorphous Carbon Thin-Film Electrodes Xingyi Yang, † Lars Haubold, ‡ Gabriel DeVivo, † and Greg M. Swain* ,† † Department of Chemistry and ‡ The Fraunhofer Center for Coatings and Laser Applications Michigan State University East Lansing, Michigan 48824-1322, United States * S Supporting Information ABSTRACT: Tetrahedral amorphous carbon (ta-C) consists of a mixture of sp 3 - and sp 2 -bonded carbon ranging from 60 to 40% (sp 3 /sp 3 +sp 2 ) depending on the deposition conditions. The physical, chemical, and electrochemical properties depend on the sp 2 /sp 3 bonding ratio as well as the presence of incorporated impurities, such as hydrogen or nitrogen. The ability to grow ta-C at lower temperatures (25-100 °C) on a wider variety of substrates as compared to CVD diamond is an advantage of this material. Herein, we report on the structural and electrochemical properties of nitrogen-incorporated ta-C thin films (ta-C:N). The incorporation of nitrogen into the films decreases the electrical resistivity from 613 ± 60 (0 sccm N 2 ) to 1.10 ± 0.07 Ω-cm (50 sccm N 2 ), presumably by increasing the sp 2 -bonded carbon content and the connectedness of these domains. Similar to boron-doped diamond, these materials are characterized by a low background voltammetric current, a wide working potential window (∼ 3 V), and relatively rapid electron-transfer kinetics for aqueous redox systems, including Fe(CN) 6 -3/-4 and Ru(NH 3 ) 6 +3/+2 , without conventional pretreatment. Additionally, there is weak molecular adsorption of polar molecules (methylene blue) on the ta-C surface. Overall, the properties of the ta-C and ta-C:N electrodes are such that they could be excellent new choices for electroanalytical measurements. T he sp 2 carbon electrodes have been used extensively over the years in electroanalytical measurements. Much is known about the structure-function relationships of these electrodes. 1-3 Boron-doped diamond (BDD) is an sp 3 -bonded carbon material with some superb properties for electro- analytical measurements. 4-9 Even though BDD has been successfully used for electroanalytical measurements, there are some drawbacks that limit more widespread application. One of these is the high temperature required (600-800 °C) for deposition, which limits the substrates that can be used. One class of carbons that has been comparatively unstudied in terms of their electrochemical properties and electro- analytical performance is diamond-like carbon. 10-14 These are composite materials consisting of a mixture of sp 2 - and sp 3 - bonded carbon. Impurities can be incorporated during growth (e.g., N) further adding to their complex structure. Tetrahedral amorphous carbon (ta-C) is one material that has received study over the years. 11 These films typically possess 40-60% sp 3 -bonded carbon. It has been widely used as a protective coating because of its hardness, high wear resistance, and low coefficient of friction. The growth temperature for ta-C is usually from 25 to about 100 °C. This means that nontraditional materials, such as plastics, can be used as substrates for deposition. The ta-C films generally need to be grown thin (100s of nanometers) in order to minimize internal stress. Stressed films tend to delaminate from a substrate. There have been a few reports describing the basic electrochemical properties of ta-C and ta-C:N films as well as their application in electroanalytical measurements. 15-28 The pioneering work was reported by the Miller lab at Case Western Reserve University. They demonstrated that ta-C:N films exhibit a wide working potential window in aqueous media (>3 V), good activity for Ru(NH 3 ) 6 +3/+2 , and micro- structural stability during chlorine electrolysis. 19 In other work, for example, the detection of dopamine and ascorbate with ta- C:N films has been described. The ta-C:N films provide improved sensitivity and linear dynamic range compared to other electrodes. 23 More recently, Tanaka et al. reported that nitrogen-doped hydrogenated amorphous carbon thin films (a- C:N:H) function as an ideally polarizable electrode material with a wide working potential window, low double-layer capacitance, and high stability in strong acid. Fe(CN) 6 3-/4- and Ru(NH 3 ) 6 2+/3+ electrode kinetics were reported on. 28 Even with these published works, there is still an incomplete understanding of structure-function relationships at these interesting electrode materials. Our work is focused on addressing this knowledge gap. The overall goal of this work is to determine the microstructure of the ta-C and ta-C:N films, as deposited by pulsed laser-arc deposition, and to correlate the film micro- structure with the basic electrochemical properties. We tested Received: May 9, 2012 Accepted: June 18, 2012 Published: June 18, 2012 Article pubs.acs.org/ac © 2012 American Chemical Society 6240 dx.doi.org/10.1021/ac301124r | Anal. Chem. 2012, 84, 6240-6248 Downloaded by MICHIGAN STATE UNIV on September 7, 2015 | http://pubs.acs.org Publication Date (Web): July 3, 2012 | doi: 10.1021/ac301124r