Electrochemical scanning tunneling microscope
Encyclopedia
The electrochemical scanning tunneling microscope
, or ESTM, was invented in 1988 by Kingo Itaya in Japan. With ESTM, the structures of surfaces and electrochemical reactions in solid
-liquid
interfaces can be observed at atom
ic or molecular
scales.
Electrochemical reactions occur in electrolytic solutions
—for example electroplating
, etching, batteries
, and so on. On the electrode
surface, many atoms, molecules, and ion
s 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.
In electrolytic solutions, a very complicated electrical double layer of H2O 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.
Scanning tunneling microscope
A scanning tunneling microscope is an instrument for imaging surfaces at the atomic level. Its development in 1981 earned its inventors, Gerd Binnig and Heinrich Rohrer , the Nobel Prize in Physics in 1986. For an STM, good resolution is considered to be 0.1 nm lateral resolution and...
, or ESTM, was invented in 1988 by Kingo Itaya in Japan. With ESTM, the structures of surfaces and electrochemical reactions in solid
Solid
Solid is one of the three classical states of matter . It is characterized by structural rigidity and resistance to changes of shape or volume. Unlike a liquid, a solid object does not flow to take on the shape of its container, nor does it expand to fill the entire volume available to it like a...
-liquid
Liquid
Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...
interfaces can be observed at atom
Atom
The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...
ic or molecular
Molecule
A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...
scales.
Electrochemical reactions occur in electrolytic solutions
Electrolyte
In chemistry, an electrolyte is any substance containing free ions that make the substance electrically conductive. The most typical electrolyte is an ionic solution, but molten electrolytes and solid electrolytes are also possible....
—for example electroplating
Electroplating
Electroplating is a plating process in which metal ions in a solution are moved by an electric field to coat an electrode. The process uses electrical current to reduce cations of a desired material from a solution and coat a conductive object with a thin layer of the material, such as a metal...
, etching, batteries
Battery (electricity)
An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...
, and so on. On the electrode
Electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...
surface, many atoms, molecules, and ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
s 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
Ultra high vacuum
Ultra-high vacuum is the vacuum regime characterised by pressures lower than about 10−7 pascal or 100 nanopascals . UHV requires the use of unusual materials in construction and by heating the entire system to 180°C for several hours to remove water and other trace gases which adsorb on the...
(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.
In electrolytic solutions, a very complicated electrical double layer of H2O molecules and anions is formed. In this layer, as the distribution of anions changes with the potential
Potential
*In linguistics, the potential mood*The mathematical study of potentials is known as potential theory; it is the study of harmonic functions on manifolds...
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
Reference electrode
A reference electrode is an electrode which has a stable and well-known electrode potential. The high stability of the electrode potential is usually reached by employing a redox system with constant concentrations of each participants of the redox reaction.There are many ways reference...
. 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.