What is the difference between a Kelvin probe microscopy for scanning and electrostatic force microscopy

In SKPM, a conductive cantilever is scanned across the surface of the sample to be analyzed at a constant height to map its ‘work function’. Work function determination is based on measuring the electrostatic forces between the AFM tip and the sample to be analyzed. This application is derived from the structure of the AFM.

SKPM is similar to Electrostatic Force Microscopy (or EFM), which is often used in labs to measure the special resolution of a surface potential map. EFM images can be created by measuring the cantilever oscillation, phase and frequency shift in response to the electrostatic force gradients, which is similar to the techniques adopted by SKPM.

Both methods offer a similar approach to sample analysis, i.e. they both use a contactless cantilever, but there are crucial differences between the two applications.

An AFM’s cantilever is a reference electrode – that is, it is stable and has a known electrode potential. It forms a capacitor with the surface of the sample, over which it is scanned laterally with constant separation. An alternating current (AC) voltage is generally applied at this frequency because the cantilever is not driven with its mechanical resonance frequency.

The work surface itself covers many surface phenomena and can be observed on an atomic or molecular scale. The microscope used by the researcher analyzes the sample and measures its catalytic activity; reconstruction of the surface; doping and band bending of semiconductors; charge confinement in dielectrics and corrosion.

The information obtained by the scope would then provide the researcher with data on the composition and electronic state of the local structures on the surface as a solid sample. When there is a DC (DC) potential difference between the tip and the surface of the sample, the AC + DC voltage offset will make the cantilever vibrate.

This is usually detected using scanned probe microscope methods, usually with a diode laser and a four-quadrant detector. A zero circuit is then used to drive the DC potential of the tip to a value that minimizes vibration. A map of the DC potential versus the position coordinate and shows the working function of the surface to be analyzed.

SKPM’s principles are similar to those of Enhanced EFM in that they both operate from a DC bias feedback loop and require the use of metal cantilevers to conduct electricity. The DC bias that sets the force to zero provides the researcher with a measure of the surface potential of a sample.

EFM directly measures the force produced by the electric field from the surface at a charged point. This application works in the same way as magnetic force microscopy in that it measures the frequency or amplitude of the cantilever oscillation to detect the sample’s electric field. The main difference is that the MFM technique measures magnetic force gradients instead of electrostatic force gradients.

In EFM, the force is created by attracting repulsion of the separated charges when used at long distances. The cantilever oscillates and does not contact the surface of the sample.

The main difference between EFM and SKPM methods is how the signal is obtained from a lock-in amplifier. This signal is used to measure the surface potential of a sample. EFM is also much more sensitive to topographic artifacts than SKPM.



Source by Stevens P