Dual-heterodyne Kelvin probe force microscopy

Area of Science:

• Surface science
• Nanoscale imaging
• Spectroscopy

Background:

• Kelvin probe force microscopy (KPFM) is crucial for surface potential analysis.
• Existing KPFM methods have limitations in analyzing time-periodic potentials.
• Optical or electrical pumping creates dynamic surface electrostatic potentials.

Purpose of the Study:

• To introduce a novel open-loop KPFM implementation for Fourier spectrum analysis.
• To enable selective probing of harmonic frequencies of time-periodic surface potentials.
• To demonstrate advanced imaging and spectroscopic capabilities for dynamic surface phenomena.

Main Methods:

• Exploiting a double heterodyne frequency mixing effect.
• Utilizing cantilever mechanical oscillation and ac bias modulation.
• Employing two cascaded numerical lock-in amplifiers for phase-coherent demodulation.
• Transferring specific harmonic frequencies to the second cantilever eigenmode.

Main Results:

• Developed Dual-heterodyne KPFM (DHe-KPFM) for mapping amplitude and phase of potential harmonics.
• Achieved selective harmonic probing and signal demodulation at the second eigenmode.
• Demonstrated DHe-KPFM spectroscopy for Fourier spectrum recording.
• Acquired 2D dynamic images in data cube mode.
• Successfully applied DHe-KPFM to diverse surfaces including organic photovoltaics and perovskite nanosheets.

Conclusions:

• DHe-KPFM offers versatile capabilities for time-resolved measurements and surface photovoltage (SPV) imaging.
• The technique is sensitive to weak SPV signals.
• Future improvements and applications in optoelectronics and material science are anticipated.