Abstract
Robust devices for chronic neural stimulation demand electrode materials which exhibit high charge injection (Qinj) capacity and long-term stability. Boron-doped diamond (BDD) electrodes have shown promise for neural stimulation applications, but their practical applications remain limited due to the poor charge transfer capability of diamond. In this work, we present an attractive approach to produce BDD electrodes with exceptionally high surface area using porous titanium nitride (TiN) as interlayer template. The TiN deposition parameters were systematically varied to fabricate a range of porous electrodes, which were subsequently coated by a BDD thin-film. The electrodes were investigated by surface analysis methods and electrochemical techniques before and after BDD deposition. Cyclic voltammetry (CV) measurements showed a wide potential window in saline solution (between −1.3 and 1.2 V vs. Ag/AgCl). Electrodes with the highest thickness and porosity exhibited the lowest impedance magnitude and a charge storage capacity (CSC) of 253 mC/cm2, which largely exceeds the values previously reported for porous BDD electrodes. Electrodes with relatively thinner and less porous coatings displayed the highest pulsing capacitances (Cpulse), which would be more favorable for stimulation applications. Although BDD/TiN electrodes displayed a higher impedance magnitude and a lower Cpulse as compared to the bare TiN electrodes, the wider potential window likely allows for higher Qinj without reaching unsafe potentials. The remarkable reduction in the impedance and improvement in the charge transfer capacity, together with the known properties of BDD films, makes this type of coating as an ideal candidate for development of reliable devices for chronic neural interfacing.
Highlights
Nanocrystalline diamond films synthesized by means of chemical vapor deposition (CVD) represent a unique class of materials with outstanding physical and chemical properties, including superior hardness and the ability to resist extreme corrosive environments (Williams, 2011)
The remaining films, deposited at N2 flow rates ranging from 120 sccm and above, consisted of rough surfaces displaying pyramidal-like features whose lateral dimensions decreased at higher N2 flow rates (Samples II–V, Figure 1A)
The typical cross-section profile of porous titanium nitride (TiN) films is shown in the Supplementary Figure 1
Summary
Nanocrystalline diamond films synthesized by means of chemical vapor deposition (CVD) represent a unique class of materials with outstanding physical and chemical properties, including superior hardness and the ability to resist extreme corrosive environments (Williams, 2011). Besides these features, electrically conductive boron-doped diamond (BDD) exhibits a wide potential window and low background currents, which make it a fascinating material for electrochemical applications (Rao and Fujishima, 2000). This is a drawback for neural stimulation applications, as the amount of charge that can be effectively injected through electrodes with relatively small contact sites is quite limited
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