Development of disk ultramicroelectrodes based on low melting or softening point metal fibers by low temperature plasma enhanced chemical vapor deposition

A procedure of insulating the low melting or softening point metal fibers for preparing disk ultramicroelectrodes (UMEs) is presented that employs low temperature plasma enhanced chemical vapor deposition (PECVD) technique. Specially, the development of Au disk UME is described. The 25 μm diameter Au fibers are concentrically coated by PECVD with an insulating layer of silicon nitride thin film that is performed with lower PECVD electrode temperature of 340 ± 10 °C. The silicon nitride thin films are found to be free of microcracks and characterized with excellent adhesion at the silicon nitride thin film-Au interfaces by scanning electron microscopy measurements. The corrosion resistance is investigated on exposure to the normal saline that indicates the fabricated disk UMEs can be used as the disposable basal electrodes. Prior to the electrochemical experiments the surgical scissors are used to produce tip surfaces. The electrochemical responses are sigmoidal in shape at different scan rates and indicate that the fabricated disk electrodes exhibit electrochemical response of UMEs. The data of cyclic voltammetry show that the diffusion-limited steady-state current of the electrode tip produced by the surgical scissors is too large for a 25 μm diameter disk electrode, so a polishing machine should be specifically developed to produce the electrode active surface for the quantitative analyses of disk UMEs with small overall size based on PECVD technique.