Fabrication of nano-electrodes by means of controlled electrochemical deposition of gold

Abstract

In the emerging fields of nano- and molecular electronics a strong need for nano-electrodes arises from the wish to contact objects such as quantum dots or single molecules. In this contribution we show the use of a controlled electrochemical deposition scheme to fabricate stable electrodes with spacings below 10 nm. In our experiments we start with a pair of gold electrodes separated by a 200 nm gap prepared by electron beam lithography. These electrodes are immersed into a solution of KI and I₂ in ethanol which has been saturated by dissolving gold in it [1]. Both nano-electrodes are connected to the same DC potential, while an AC voltage between them is used to in-situ monitor the conductance with a lock-in amplifier. For the deposition a DC voltage is applied to the counter electrode until the recorded conductance reaches the desired value. It is also possible to reversibly close and open the electrode gap by applying positive and negative voltages, respectively, to the counter electrode. With this technique gaps of around 1 nm can be realized, as conductance measurements after rinsing and drying as well as SEM micrographs show. When the electrodes are grown together slowly, we observe a step-wise increase in the conductance which corresponds to integer multiples of the conductance
quantum 2e²/h.

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