Nitridation of optimised TiO2 nanorods through PECVD towards neural electrode application

Abstract

A neural electrode interface material is a key component for effective stimulation and recording of neural activity. The fundamental requirement of a neural electrode is for it to be able to deliver adequate charge to targeted neuronal population. Coating electrode surfaces with nanostructured material not only provides an increase in surface area, providing relatively more active sites for charge delivery than planar systems, but also allows for the reduction of electrode dimension to reduce invasiveness and increase selectivity. In this work, titanium nitride nanowires (TiN-NWs) synthesised by novel nitridation process in Plasma Enhanced Chemical Vapour Deposition (PECVD) is suggested as an enhanced coating material for neural electrodes. The synthesis involved the solution growth of crystalline titanium oxide nanorods (TiO2-NRs) from a sputtered TiN nucleation layer followed by nitridation. TiO2-NRs exhibited high aspect ratio of 23.1 and were converted into TiN after one hour of nitridation at 600°C. Evidence of conversion was studied by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Transmission electron microscopy (TEM). The nitridation temperature and time reported here are the lowest and shortest as compared to the literature. The near-stoichiometric TiN-NWs (x=0.49) achieved in this work were used subsequently for electrochemical characterisation through Cyclic Voltammetry (CV). The capacitance of relatively high aspect TiN-NWs was 3.78 mF/cm2, which was a 5-fold enhancement compared to thin film of TiN layer (0.7 mF/cm2). A stability test of the nanowires were performed in which the capacitance remained relatively unchanged.