The control for positioning ultramicroelectrode (UME) provides the formation and recording of chemical redox reaction localized at the UME, in addition to the lateral resolution. The mediator species (i.e. Ferrocene and Ru(NH3)63+) as the redox function of are considered as the electron transfer carrier between tip and surface in the aqueous solution. It follows the current (i)-distance (d) curve of I=n F S D C / d.
d is the spacing distance between substrate and tip. C is the sum of concentrations of oxides, including Co(Cr) for its oxidant (reductant) concentration. D=Dr=Do is the diffusion coefficient for reductant and oxidant species.
The feedback mode is based on the diffusion-limited and recycled reactions varied by the insulating and conductive surface via the use of mediator species. The flow of active reductant species (R) is blocked by the limited space decreasingly due to the insulating substrate and the insulating sheath of UME tip, then the closer the tip moves to the substrate and the smaller shows. Oppositely, with a conductive substrate, it provides the electron to oxidant (O) species on the cathode electrode (negative). While d decreases to 0, It becomes the infinite for the direct and fast diffusion movement on the conductive surface.
According to the d-It tendency, we can estimate the end position at the surface with the insulating or conducting property, and identify its inter-distance between tip and surface by the linear Z-encoder of positioning system. Although the current variation is either dependent on the change of topography or conductivity (reactivity), it can be discriminated by the positive/negative response of d-It feedback for its electroactive (conducting) or nonelectroative (insulating) property. The resolution of SECM is dependent of inner (tip size and shape) and outer (current density distribution), the solution resistance, and mechanism of mass and charge transfer; therefore, laser-based micropipette puller and microelectrode beveler are helpful to shape UME into the nanoscale in our Lab. In short, two points are understood to examine the water-related image: (1) electrochemical activity and (2) the redox ability of electrolyte molecule in the aqueous environment. The present projects are divided into three issues: (1) in-situ electrochemical reduciton/electocatalyst of the micro-patterned materials, (2) in-situ nucleation, growth, and study of bio-materials in the interface of metal materials, and (3) in-situ modifiaction and monitor of Li-ion mobility on the TM oxide materials.
