The electrochemical scanning tunneling microscope (EC-STM) is a
scanning tunneling microscope that measures the structures of surfaces and
electrochemical reactions in
solid-
liquid
A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, it is one of the four fundamental states of matter (the others being solid, gas, a ...
interfaces at
atomic or
molecular
A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioche ...
scales.
Development
Electrochemical reactions occur in
electrolytic solutions—for example
electroplating
Electroplating, also known as electrochemical deposition or electrodeposition, is a process for producing a metal coating on a solid substrate through the reduction of cations of that metal by means of a direct electric current. The part to be ...
, etching,
batteries
Battery most often refers to:
* Electric battery, a device that provides electrical power
* Battery (crime), a crime involving unlawful physical contact
Battery may also refer to:
Energy source
*Automotive battery, a device to provide power t ...
, and so on. On the
electrode surface, many atoms, molecules, and
ions adsorb and affect the reactions. In the past, in order to obtain information about the structure of electrode surfaces and reactions, the sample electrode was taken out of the electrolytic solution and measured under
ultra high vacuum (UHV) conditions. In this case, the structure of the surface changed and could not be observed precisely. By using this microscope, however, these problems are resolved.
Operation
In electrolytic solutions, a complicated
electrical double layer
A double layer (DL, also called an electrical double layer, EDL) is a structure that appears on the surface of an object when it is exposed to a fluid. The object might be a solid particle, a gas bubble, a liquid droplet, or a porous body. The D ...
of H
2O molecules and anions is formed. In this layer, as the distribution of
anions changes with the
potential of the electrode, it is necessary to control the reaction on the electrode. The potentials of the working electrodes (the sample and the tip) are controlled independently against a
reference electrode. In this case, the tunneling bias voltage is the difference between the two potentials. A counter electrode is used to complete the current-carrying circuits with the working electrodes. By using these four electrodes, the electrochemical reaction is controlled precisely by the external voltage, and the surface in liquid can be observed.
References
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Scanning probe microscopy