Electrochemical scanning tunneling microscopy

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Principle of an electrochemical scanning tunneling microscope. AE is the working electrode (surface to be examined), RE the reference electrode and GE the counter electrode. As a fourth electrode, the tunnel tip is moved over the surface to measure the topography.

The electrochemical scanning tunneling microscopy ( English electrochemical scanning tunneling potentiometry , ECSTM ) is a modification of the scanning tunneling microscope and was developed by K. Itaya and E. Tomita 1988th With the help of the ECSTM it is possible to record the local morphology of a surface Angstrom precisely within an electrochemical environment. It thus combines the integral electrochemical measurement with the local investigation of the topography.

Measuring principle

Based on classic scanning tunneling microscopy , the topography measurement principle remains basically identical. A voltage is applied between the tunnel tip and the surface, which enables a tunnel current if the distance is sufficiently small. With the ECSTM, however, the surface and the tip are immersed in an electrolyte and so the electrochemical behavior can also be examined. For the electrochemical measurement, the potential of the working electrode (the surface to be examined) is set and measured in relation to a reference electrode, with the current flowing through a counter electrode. Because of this three-electrode technique and the necessary setting of the tunnel voltage at the tip in relation to the sample, two potentiostats are used to provide and read out all necessary signals. In this way you can also cyclic voltammetry perform with the ECSTM measurements with simultaneous study of the topography. There is an important problem for the ECSTM. In addition to the desired tunnel effect, electrochemical processes can also take place at the tunnel tip that would prevent the sample surface from being reproduced. Therefore, the electrochemical potential of the tunnel tip is set in such a way that Faraday processes are prevented at the tip. Furthermore, larger changes in potential should be avoided during the topography measurement, since this leads to the reorganization of the electrochemical double layer and thus to disruptive capacitive currents. Since the two interfering contributions to the current signal increase proportionally with the area of ​​the tunnel tip, this is covered over a large area with an insulating wax or plastic. Only the tip apex remains uninsulated and continues to allow the tunneling process between tip and surface.

application

With the help of the ECSTM, the elementary processes for the deposition and dissolution of electrochemical layers on the working electrode can be investigated. This provides a deeper understanding of the electrochemical processes, such as the coverage configuration of the species involved. Particularly in the cyclic voltammetry the ECSTM decisive contributions to improved understanding of the microscopic electrochemistry can afford.

See also

literature

  • Hans Henning Strehblow: Chap. 6: Electrodes, electrode processes and electrochemistry . in Bergmann / Schäfer: Textbook of Experimental Physics. de Gruyter, New York 2006, ISBN 3-11-017484-7 , pp. 561-565 .
  • K. Gentz, K. Wandelt: Electrochemical Scanning Tunneling Microscopy . In: CHIMIA International Journal for Chemistry . tape 66 , no. 1 , February 1, 2012, ISSN  0009-4293 , p. 44-51 (English, ingentaconnect.com ).
  • Ajay Kumar Yagati, Junhong Min, Jeong-Woo Choi: Electrochemical Scanning Tunneling Microscopy (ECSTM) - From Theory to Future Applications . Ed .: IntecOpen online. June 11, 2014, doi : 10.5772 / 57236 (English).

Individual evidence

  1. ↑ K. Itaya, E. Tomita: Scanning tunneling microscope for electrochemistry - a new concept for the in situ scanning tunneling microscope in electrolyte solutions . In: Surf. Sc . tape 201 , no. 3 , 1988, pp. 507-512 , doi : 10.1016 / 0039-6028 (88) 90489-X .
  2. ^ Richard Sonnenfeld, Paul K. Hansma: Atomic-Resolution Microscopy in Water . In: Science . tape 232 , no. 4747 , April 11, 1986, ISSN  0036-8075 , p. 211-213 , doi : 10.1126 / science.232.4747.211 , PMID 17780805 .