Temperature-variable electrochemical scanning tunneling microscopy
The working principle of an electrochemical scanning tunneling microscope (EC-STM) [1,2] is that of a scanning tunneling microscope, with the difference that the EC-STM is designed to run in an electrochemical cell.
The figure shows a sketch of the working principle of an EC-STM: Here, the STM-tip dips into an electrolyte-filled electrochemical cell during image recording. The probed sample is the working electrode (WE). The reference electrode (RE) and the counter electrode (CE) ensure the control of all electrochemical processes within the cell and at the working electrode surface. For the tunneling process a bias is applied between WE and the tip. Hence, the tip itself serves as a further electrode within the cell.
Typical electrochemical currents are of the order of µA, too large to detect an underlying tunneling current down to nA or even pA! Therefore, any influence of electrochemical currents at the tip must be avoided. This is provided by a special tip coating which leaves merely the foremost part of the tip in contact with the liquid . The 4-electrode arrangement in the electrochemical cell is controlled by a bipotentiostat.
At PGI-6, we have a Topometrix Discoverer TMX 2010 modified to allow temperature-variable measurements [5,6,7].
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