Structure and electrochemical properties of carbon films prepared by a electron cyclotron resonance sputtering method

This paper describes the characterization, electrochemical properties, and applications of carbon films prepared by the electron cyclotron resonance (ECR) sputtering method. The ECR-sputtered carbon film was deposited within several minutes at room temperature. The optimized sputtering conditions significantly change the film structure, which includes many more sp³ bonds (sp³/sp² = 0.702) than previously reported film (sp ³/sp² = 0.274)¹ with an extremely flat surface (0.7 Å). The ECR-sputtered carbon films exhibit excellent electrochemical properties. For example, they have nearly the same potential window in the positive direction as that of high-qualify, boron-doped diamond (moderately doped, 10¹⁹-10²⁰ boron atoms/cm³)² and an even wider potential window in the negative direction with a low background current, high stability, and suppression of fouling by electroactive species without pretreatment. The electron-transfer rates at ECR-sputtered carbon films are similar to those of glassy carbon (GC) for Ru(NH ₃)₆^2+/3+ and Fe(CN)6^3-/4-, whereas they are much slower than those of GC for Fe^2+/3+, dopamine oxidation, and O₂ reduction due to weak interactions between electroactive species and the ECR-sputtered carbon film surface. Such a response can be attributed to the ultraflat surface and low surface O/C ratios of ECR-sputtered carbon films. ECR-sputtered carbon film is advantageous for measuring biochemicals with high oxidation potentials because of its wide potential window and high stability. Highly reproducible and well-defined cyclic voltammograms were obtained for histamine and azide ions with a peak potential at 1.25 and 1.12 V vs Ag/AgCl, respectively. The film is very stable for continuous voltammetry measurements in 10 μM bisphenol A, which usually fouls the electrode surface with oxidation products.