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 be able to contact single nano-objects such as quantum dots (QDs) or molecules. There are different methods
known from literature how to fabricate such electrodes, for example electromigration, mechanically controllable break
junctions, or scanning probe techniques, all of which have their specific advantages and drawbacks. In this talk we will
use a scheme of controlled electrochemical deposition which features the following benefits: the electrodes are stable,
no islands are unintentionally created during the fabrication process, and it is relatively straight forward to implement a
third electrode acting as gate.
In our experiments we start with a pair of gold electrodes separated by a 200 nm gap (Fig. 2 (a)) prepared by
electron beam lithography (EBL). These electrodes are immersed into a solution of KI and I₂ in ethanol which has been
saturated by dissolving gold in it [1]. Gold covered glass sheets are used as counter and reference electrodes. For the
deposition both nano-electrodes are connected to the same DC potential, while a voltage is either applied directly to the
counter electrode or a potentiostat setup is used. Additionally an AC voltage is applied between the two nano-electrodes
which allows us to in-situ monitor the conductance with a lock-in amplifier (see Fig. 1).
When the sample is immersed into the solution, the conductance rises due to ionic currents. For the deposition
a voltage of typically 60 mV is applied to the counter electrode with respect to the working electrodes. The conductance
is recorded until it reaches a threshold value at which the deposition is stopped. After deposition the gap between the
two electrodes is clearly below 10 nm, as conductance measurements after rinsing and drying as well as the SEM
micrograph in Fig. 2 (b) show.
It is planed to place semiconductor QDs or single molecules between the electrodes to measure their transport
characteristics. Furthermore samples with additional back gate electrode are in preparation which will provide an even
wider access to the electrical properties of nano-objects.

Mehr zum Titel