Kelvinprobeteknik

Kelvinprobeteknik, or the Kelvin probe technique, is a non-contact method for measuring the contact potential difference between a conducting probe and a sample surface. It is commonly implemented as Kelvin probe force microscopy (KPFM) when integrated with an atomic force microscope (AFM) to map work function variations with high spatial resolution.

The principle relies on a vibrating reference probe forming a capacitor with the sample surface. An alternating voltage is applied to the tip together with a dc bias. The electrostatic force between tip and surface contains a component at the modulation frequency, which can be detected and fed back to adjust the dc bias until the force is nulled. The bias value that cancels the force equals the contact potential difference, which is related to the difference in work functions between tip and sample. With a known tip work function, the sample work function can be determined, or relative work function differences can be mapped directly.

Instrumentation typically involves an AFM in non-contact or tapping mode, using either amplitude-modulated (AM) or frequency-modulated (FM) KPFM. Measurements can be performed in ambient air, vacuum, or controlled environments. The lateral resolution is influenced by the tip radius and geometry and generally ranges from several to tens of nanometers.

Applications span surface science and materials research, including semiconductor devices, metals, organic films, two-dimensional materials, photovoltaics, corrosion studies, and energy storage materials. Limitations include dependence on the tip work function and potential drift or contamination of the tip, requiring careful calibration and controlled conditions. The technique has historical roots in the original Kelvin concept for measuring contact potential difference, with modern implementations dating from the 1990s onward.