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  • Park AFM
    Electrical Modes
    For engineers and researchers that need accurate data on conductance, sample resistance,
    and other electrical and topographic properties, Park offers a range of electrical scanning modes.

Scanning Kelvin Probe Microscopy (SKPM)

High Resolution and High Sensitivity Imaging of Surface Potential

Principle of SKPM is similar to Enhanced EFM with DC bias feedback. DC bias is controlled by feedback loop to zero the ω term. The DC bias that zeros the force is a measure of the surface potential. The difference is in the way the signal obtained from the Lock-in Amplifier is processed. As presented in previous section, the ω signal from Lock-in Amplifier can be expressed as following equation. scanning-kelvin-probe-microscopy-skpm-f3 The ω signal can be used on its own to measure the surface potential. The amplitude of the ω signal is zero when VDC = Vs, or when the DC offset bias matches the surface potential of the sample. A feedback loop can be added to the system and vary the DC offset bias such that the output of the Lock-in Amplifier that measures the ω signal is zero. This value of the DC offset bias that zeroes the ω signal is then a measure of the surface potential. An image created from this variation in the DC offset bias is given as an image representing the absolute value of the surface potential.

scanning-kelvin-probe-microscopy-skpm-f41

Schematic diagram of the enhanced EFM of the XE-series.

 
skpm-graphene

Surface Potential distribution on graphene

Graphene
Scan size: 15 µm
Using Probe: Contsc Pt
Imaged on a Park XE-Series using SKPM Mode.
 

Electrical Modes