Nanocrystalline Diamond Nanoelectrode Arrays and Ensembles

Abstract

In this report, the fabrication of all-nanocrystalline diamond (NCD) nanoelectrode arrays (NEAs) by e-beam lithography as well as of all-diamond nanoelectrode ensembles (NEEs) using nanosphere lithography is presented. In this way, nanostructuring techniques are combined with the excellent properties of diamond that are desirable for electrochemical sensor devices. Arrays and ensembles of recessed disk electrodes with radii ranging from 150 to 250 nm and a spacing of 10 μm have been fabricated. Electrochemical impedance spectroscopy as well as cyclic voltammetry was conducted to characterize arrays and ensembles with respect to different diffusion regimes. One outstanding advantage of diamond as an electrode material is the stability of specific surface terminations influencing the electron transfer kinetics. On changing the termination from hydrogen- to oxygen-terminated diamond electrode surface, we observe a dependence of the electron transfer rate constant on the charge of the analyte molecule. Ru(NH(3))(6)(+2/+3) shows faster electron transfer on oxygen than on hydrogen-terminated surfaces, while the anion IrCl(6)(-2/-3) exhibits faster electron transfer on hydrogen-terminated surfaces correlating with the surface dipole layer. This effect cannot be observed on macroscopic planar diamond electrodes and emphasizes the sensitivity of the all-diamond NEAs and NEEs. Thus, the NEAs and NEEs in combination with the efficiency and suitability of the selective electrochemical surface termination offer a new versatile system for electrochemical sensing.

Diamond Ultramicro- and Nano-electrode Arrays

“…Our NEEs were characterized with conductive atomic force microscopy [57]. The density determined by AFM is 8.5 × 10 5 cm −2 , which is in good agreement with the expected values from the sphere concentration in the solution.…”

“…In addition, spatially separated carbon nanofibers and diamond nanograss as well as porous diamond film have been utilized as NEEs for electrochemical applications [82][83][84][85][86][87][88][89][90][91]. For the first time, we fabricated all-diamond NEAs and NEEs with nanocrystalline diamond (NCD) films [57]. As shown in Fig.…”

“…The boron concentrations of doped NCD films were measured by secondary ion mass spectroscopy and in the range of 1 to 4 × 10 21 cm −3 . E-beam lithography was applied to fabricate NEAs [57]. On a 200 nm thin boron-doped NCD film, a 200 nm thick SiO 2 is deposited.…”

“…With the removal of SiO 2 in hydrofluoric acid, arrays of recessed boron-doped NCD electrodes surrounded by insulating diamond are obtained. Nanosphere lithography is an approach we developed to fabricate NEEs [57]. Initially, a photolithography step is used to deposit metal contacts on NCD films.…”

“…They amplify the signal of individual microelectrodes but do not lose the beneficial characteristics of individual small dimensional electrodes [1][2][3][4]. Several works have been conducted on the fabrication, characterization, and applications of diamond micro-, ultramicro-, and nano-electrode arrays/ensembles [42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57]. For example, they have been applied for sensor applications [49][50][51][52][53][54][55].…”