Switching Spectroscopy Piezoresponse Force Microscopy (SS-PFM) mode enables highly accurate nanoscale characterization of the properties of ferroelectric materials, expanding upon standard Piezoresponse Force Microscopy (PFM) by greatly improving the sensitivity and accuracy of measurements. This mode:
Used alone or in conjunction with other AFM operational modes, SS-PFM provides new insights into the material microstructure/polarization switching relationship.
The signal levels in PFM are generally small, with typical amplitudes <10 pm/V. This is at the limit of what an AFM can detect. To address this, one of two approaches are generally taken:
For many samples, arbitrarily increasing the AC stimulation voltage is not a practical approach. Sample domains will flip (pole) if coercive bias is exceeded; the measured amplitude will not be accurate. This is especially true for thin films where the coercive bias is often lower.
Standard PFM allows the measurement of ferroelectric behavior with nanoscale resolution, but measured signals can be influenced by electrostatic forces on the cantilever, as well as ferroelectric response. These can cause errors in hysteresis loop quantification, and can even misidentify non-ferrous materials as ferroelectric. The electrostatic artifact can be significantly decreased by positioning the beam-bounce laser at the lever's electrostatic blind spot (ESBS) while using sub-resonance PFM (Killgore, Nanoscale Advances, 4, 8, 2022).
SS-PFM mode provides:
By collecting and analyzing an array of SS-PFM spectra, it is possible to generate maps of the key piezoelectric parameters, demonstrating the variation in the ferroelectric properties across the XY plane with nanoscale resolution.
Standard PFM operates in contact mode, which is not suitable for samples that are susceptible to damage or displacement by the AFM tip dragging across the sample surface during the scan. Softer probes could partially mitigate this issue, but are more prone to electrostatic artifacts in the PFM measurements.
Like Bruker's unique DCUBE-PFM modes, SS-PFM avoids dragging the tip on the surface. This eliminates the harmful lateral forces that plague conventional contact mode based approaches. When combined with PeakForce Tapping and MIROView for pre-scanning and navigation, contact mode can be avoided completely.
SS-PFM mode supports:
Bruker's state-of-the-art, easily accessible software and analysis tools provide the flexibility researchers need.
PFM-type experiments are particularly sensitive to background and crosstalk influences. Integration with the new NanoScope 6 controller reduces these influences, providing highest performance background and crosstalk via optimized lock-in amplifiers and signal routing.
This benefits many AFM operational modes, yet it provides unique advantages for PFM-type modes (like SS-PFM) including: