Ultra-high vacuum Kelvin probe force microscopy (UHV KPFM)
Kelvin probe force microscopy can be used simultaneously with non-contact AFM (under UHV environment), providing spatially resolved measurements of the surface potential of conducting and semi-conducting samples. In principle, this surface potential provides the work function difference between the surface under investigation and the probe (i.e., a relative value of the surface’s work function).
KPFM allows as well the absolute work function investigation by previous probe calibration against a reference surface. Additionally, UHV environment permits the surface sample preparation (heating, sputtering, sample cleavage) without the influence of ambient conditions, as well as to proceed the measurements under stable environmental conditions.
Furthermore, the surface potential can be measured under sample illumination to extract the surface photovoltage (i.e. the difference between the surface potential measured under sample illumination and measured when sample is in dark conditions). Surface photovoltage is a surface quantity based on the charge reorganization and so the origin of surface photovoltage can be linked with surface band bending or charge recombination. Accordingly, one type of carrier diffuses toward the surface causing a partial band flattening while the other type diffuses toward the bulk, thus the sign of photovoltage indicate the carrier type. At high photon flux, the band may be completely flattened. Additionally, the charge recombination time might be estimated under modulated light (10ms – 100ns range), when rather high values of photovoltage (>100 mV) can be detected under continues light illumination.
Kelvin probe force microscopy, surface potential, work-function, surface photovoltage, band bending.
Sample dimension 1×1cm max. Explored material must be stable under UHV conditions.
- Nano for Quantum Technologies
- Disruptive Devices
- Advanced Integration
Key Enabling Technologies
- Metrology / Characterisation: Physical
User requests a local electrical surface characterisation, e.g. surface potential, work function, band bending. Measurement can be done using imaging mode or in spectroscopy mode.
Such characterization is essential in the case of several devices like light emitting diodes, solar cells, photodetectors and transistors.