Electrochemical Machining of Gold Microstructures in LiCl/Dimethyl Sulfoxide

Abstract

LiCl/dimethyl sulfoxide (DMSO) electrolytes were applied for the electrochemical micromachining of Au. Upon the application of short potential pulses in the nanosecond range to a small carbon-fiber electrode, three-dimensional microstructures with high aspect ratios were fabricated. We achieved machining resolutions down to about 100 nm. In order to find appropriate machining parameters, that is, tool and workpiece rest potentials, the electrochemical behavior of Au in LiCl/DMSO solutions with and without addition of water was studied by cyclic voltammetry. In waterless electrolyte Au dissolves predominantly as Au(I), whereas upon the addition of water the formation of Au(III) becomes increasingly important. Because of the low conductivity of LiCl/DMSO compared with aqueous electrolytes, high machining precision is obtained with moderately short pulses. Furthermore, the redeposition of dissolved Au can be effectively avoided, since Au dissolution in LiCl/DMSO is highly irreversible. Both observations render LiCl/DMSO an appropriate electrolyte for the routine electrochemical micromachining of Au.

Locally enhanced cathodoluminescence of electrochemically fabricated gold nanostructures

“…The electrochemical cell was open to air, which resulted in uptake of water from the environment during machining. However, as investigated in [32], this is of minor influence for the machining of Au. Further details on the experimental setup can be found in [30,31].…”

“…It should be mentioned that apparently only a small part of the applied potential pulse is actually polarizing the workpiece DL. As discussed in detail in [32], due to the small DL capacitance of the carbon tool in comparison with the Au workpiece most of the pulse amplitude will drop in the tool's DL. Furthermore, the conductivity of the carbon fiber is fairly small compared to a metallic conductor.…”

“…In other words, longer pulses could be applied for achieving the same machining resolution. For this reason we already studied the applicability of LiCl solutions in dimethyl sulfoxide (DMSO) [32]. In DMSO based electrolytes the specific electrolyte conductivity is lowered by a factor of 10 in comparison with the corresponding aqueous electrolyte by increasing the viscosity of the solvent.…”

“…[32], for routinely fabricating such structures machining parameters have to be optimized with respect to spatial resolution, machining speed and absence of corrosion of the workpiece. For optimum machining speed, i.e., full control of the spatial resolution by the pulse duration in combination with high machining speed, the dissolution rate of Au should be limited by the charge transfer step of the electrochemical reaction rather than by mass transport of dissolved Au in the small tool-workpiece gap.…”

“…Tool preparation is described in detail in Ref. [32]. Counter and pseudo reference electrodes were prepared from Pt wires.…”