Kelvin probe

The Kelvin probe ( English Kelvin probe , KP) takes place at the non-destructive measurement of the work function , and in the study of De lamination processes of polymer - oxide - and metal - interfaces use. The combination of a Kelvin probe with an atomic force microscope is referred to as a scanning Kelvin microscope or Kelvin probe microscope (SKPM, or Kelvin probe force microscope , KPFM).

The name of the Kelvin probe goes back to Lord Kelvin .

principle

Measurement setup

If two metals are brought into contact, electrons with a higher energy flow from the metal with a higher Fermi level to the one with a lower Fermi level, until they are at the same level (see contact potential ). This electron flow creates an electric field and a contact voltage . The contact voltage results from the work function difference: ${\ displaystyle \ Delta \ varphi}$ ${\ displaystyle \ Delta \ varphi}$

{\ displaystyle \ Delta W = e \ cdot \ Delta \ varphi}

The two metals have a capacity against each other . The following applies to the flow of charge : ${\ displaystyle C}$

{\ displaystyle Q = C \ cdot \ Delta \ varphi}

.

Measurement

When measuring with a Kelvin probe, the conductive probe, which is vibrated by piezo actuators above the sample , and the sample behave like two capacitor plates . By the oscillation, a current is influenziert which linearly on the work function difference is dependent and non-linear the spacing between probe and sample. The current can be regulated to zero by an external voltage . This determines the work function difference because it applies . ${\ displaystyle i (t)}$ ${\ displaystyle \ Delta \ varphi}$ ${\ displaystyle U}$ ${\ displaystyle i (t)}$ ${\ displaystyle U = \ Delta \ varphi}$

The structure of a KPFM is similar to an atomic force microscope and can provide better spatial resolution than the Kelvin probe. In this case, a very fine, conductive tip serves as the probe. Due to the small geometry of the tip, the capacitance between tip and sample and thus the induced current is very small. With an atomic force microscope, however, the measurement of the smallest forces is possible. For this reason, the electrostatic force between the tip and the sample is measured instead of the current . In the ideal case, the force can also be eliminated here by applying a voltage between the tip and the sample, so that applies. ${\ displaystyle i (t)}$ ${\ displaystyle i (t)}$ ${\ displaystyle U = \ Delta \ varphi}$

Web links

Kelvin Probe information site
Tutorial (PDF; 101 kB; English)

Individual evidence

↑ Equipment. ( Memento of the original from April 30, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. University of Paderborn @1@ 2

↑ K. Lord: Contact electricity of metals . In: Phil. Mag . tape 46 , 1898, pp. 82-120 .

^ Herbert Kliem: Materials in Microelectronics 1. Lecture notes, WS2010 / 11.

↑ K. Besocke, S. Berger: Piezoelectric driven Kelvin probe for contact potential difference studies . In: Review of Scientific Instruments . tape 47 , no. 7 , 1976, p. 840-842 , doi : 10.1063 / 1.1134750 .

[1] Equipment. ( Memento of the original from April 30, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. University of Paderborn @1@ 2

[2] K. Lord: Contact electricity of metals . In: Phil. Mag . tape 46 , 1898, pp. 82-120 .

[3] Herbert Kliem: Materials in Microelectronics 1. Lecture notes, WS2010 / 11.

[4] K. Besocke, S. Berger: Piezoelectric driven Kelvin probe for contact potential difference studies . In: Review of Scientific Instruments . tape 47 , no. 7 , 1976, p. 840-842 , doi : 10.1063 / 1.1134750 .