Kelvin Probes and Work Function Difference

Kelvin probe techniques are used to measure the work functions of materials. These techniques are applied successfully in surface science under UHV conditions. For example, if you want to study the adsorption of molecular or reconstruction processes of single-crystal surfaces, that will cause a change in surface or dipole potential. Recently, Kelvin probes have been applied to corrosion science and found to be highly successful. This probe is named after Lord Kelvin.

What is Kelvin Probe?

The Kelvin Probes are a non-contact and non-destructive calculative device used to investigate the properties of the materials. Here, the probe is based on the vibrating capacitor and calculates the work function difference. In the case of non-metals, it is surface potential and in between a conducting specimen & vibrating tip. The work function is a sensitive indicator of surface condition and is affected by the following:

·         Absorbed layers

·         Surface Reconstruction

·         Surface Charging

·         Oxide Layer Imperfections

·         Surface & bulk contamination

What is Kelvin probe force microscopy (KPFM)?

KPFM or Kelvin probe force microscopy is known as surface potential microscopy and it is also a non-contact type of atomic force microscopy (AFM). These techniques are mainly used for measuring corrosion and coatings. The work function of the surfaces is measured either in atomic or molecular scales. The work function is related to the following surface phenomena:

·         Catalytic Activity

·         Reconstruction of surfaces

·         Doping and band-bending of semi-conductors

·         Charge tapping & Corrosion

The work function map generated by KPFM provides information about the composition and electronic local structures on the surface of a solid. Equip Test provides Kelvin Test Probes with following features:

1.       4 wire measurement

2.       Industrial solution

3.       Easy integration

As the Kelvin probes (KP) techniques find the Contact Potential Difference (CPD) between two surfaces that are in close proximity. In the 1st case, there will be two metals, but there is no electrical connection between them. In the second case, as the two metal pieces are connected by an electrical wire, here the electrons with a smaller work function will travel to the metal with a larger work function. As a result that, the metal with a smaller work function is to be charged with positive whereas others would be charged negatively. This will create electric potential between the two metals as their electronic state is changed relative to each other.