Ilka Schmueser

Comparison of the performance of an array of nanoband electrodes with a macro electrode with similar overall area.

The performance of two electrode architectures with broadly similar overall active electrode areas are examined. The first is an electrode comprising a single contiguous area (a disc) and the second is an electrode in which the cumulative electrode area is dispersed over a wide area as a 50 nm thickness platinum nanoband. A direct comparison of the electrochemical performance of these two electrodes has been made. The relatively simple nanoband electrode architecture is shown to have benefits, including two orders of magnitude greater mass transport limited currents, the ability to measure faster electrode kinetics (by a similar factor), a three orders of magnitude lowering of the Limit of Detection and a significantly reduced susceptibility to hydrodynamic perturbations. The consequences and implications of these performance characteristics on the uses of such a nanoband electrode have been considered.

A systematic study of the influence of nanoelectrode dimensions on electrode performance and the implications for electroanalysis and sensing

Micron resolution photolithography has been employed to make microsquare nanoband edge electrode (MNEE) arrays with reproducible and systematic control of the crucial dimensional parameters, including array element size and spacing and nanoelectrode thickness. The response of these arrays, which can be reproducibly fabricated on a commercial scale, is first established. The resulting characteristics (including high signal and signal-to-noise, low limit of detection, insensitivity to external convection and fast, steady-state, reproducible and quantitative response) make such nanoband electrode arrays of real interest as enhanced electroanalytical devices. In particular, the nanoelectrode response is presented and analysed as a function of nanometre scale electrode dimension, to assess the impact and relative contributions of previously postulated nanodimensional effects on the resulting response. This work suggests a significant contribution of migration at the band edges to mass transfer, which affects the resulting electroanalytical response even at ionic strengths as large as 0.7 mol dm(-3) and for electrodes as wide as 50 nm. For 5 nm nanobands, additional nanoeffects, which are thought to arise from the fact that the size of the redox species is comparable to the band width, are also observed to attenuate the observed current. The fundamental insight this gives into electrode performance is discussed along with the consequent impact on using such electrodes of nanometre dimension.

Marking 100 years since Rudolf Höber’s discovery of the insulating envelope surrounding cells and of the beta-dispersion exhibited by tissue

Abstract Between 1910 and 1913 Rudolf Höber presented proof that the interiors of red blood cells and muscle cells contain conducting electrolytes, and that each conducting core is contained within an insulating membrane. He did this by demonstrating, in a series of remarkable electrical experiments, that the conductivity of compacted cell samples at low frequencies (~150 Hz) was about ten-times less than the value obtained at ~5 MHz. On perforation of the membrane, the low-frequency conductivity increased to a value approaching that exhibited at MHz frequencies. Apart from representing a major milestone in the development of cell biology and electrophysiology, Höber’s work was the first description of what we now call the dielectric β-dispersion exhibited by cell suspensions and fresh tissue.

Characterisation and integration of Parylene as an insulating structural layer for high aspect ratio electroplated copper coils

This paper reports the development of processing methods and test structures for the characterisation and evaluation of Parylene-C as an insulating structural layer material for integration with planar micro-inductors. The process involves the filling of high aspect ratio gaps between copper structures with Parylene and subsequent chemical mechanical planarisation. A test chip has been designed to characterise this process and the results presented. Subsequently complete micro-inductors, with magnetic cores, have been fabricated to demonstrate the capability of the process.

Test structures to support the development and process verification of microelectrodes for high temperature operation in molten salts

This paper reports the design and application of test structures used for the development and characterisation of microelectrodes for operation in the harsh, caustic environment of molten salts operating at 450°C. These structures have been employed to evaluate the effect of electrode area and the dielectric integrity of insulating layers in the molten salt. This has been useful in identifying failures mechanisms, which has facilitated the optimisation of both the design and fabrication of the microelectrodes while at the same time also providing valuable information for process verification.

Improving the Yield and Lifetime of Microfabricated Sensors for Harsh Environments

This paper details improvements in the design and fabrication of electrodes intended to function in the high temperature, corrosive environment of a molten salt. Previously reported devices have displayed low yield and lifetimes and this paper presents two strategies to improve these aspects of their performance. The first one involves reducing the critical area, which increased both the electrode yield and lifetimes. The second element utilized test structures, targeted at identifying failure mechanisms, which helped facilitate the materials/design modifications required to make the devices more robust.