Exploring Local Electrostatic Effects with Scanning Probe Microscopy: Implications for Piezoresponse Force Microscopy and Triboelectricity

Abstract

The implementation of contact mode Kelvin probe force microscopy (cKPFM) utilizes the electrostatic interactions between tip and sample when the tip and sample are in contact with each other. Surprisingly, the electrostatic forces in contact are large enough to be measured even with tips as stiff as 4.5 N/m. As for traditional noncontact KPFM, the signal depends strongly on electrical properties of the sample, such as the dielectric constant, and the tip properties, such as the stiffness. Since the tip is in contact with the sample, bias-induced changes in the junction potential between tip and sample can be measured with higher lateral and temporal resolution compared to traditional noncontact KPFM. Significant and reproducible variations of tip-surface capacitance are observed and attributed to surface electrochemical phenomena. Observations of significant surface charge states at zero bias and strong hysteretic electromechanical responses at a nonferroelectric surface have significant implications for fields such as triboelectricity and piezoresponse force microscopy.

Ferroelectric or non-ferroelectric: Why so many materials exhibit “ferroelectricity” on the nanoscale

“…99,335,346 A straightforward way to separate these contributions is to consider potentialdependence of forces acting on the junction in contact, i.e. to consider the so-called on-field observables.…”

“…The more complex qualitative method to measure the DC-bias-dependence of the PFM signal was introduced through a technique called contact KPFM (cKPFM 346 ). The disadvantage of just measuring the hysteresis loops in a spectroscopic manner as described above is that the fact that the remnant state which is altered by the DC voltage is only probed at 0Vdc.…”

“…Therefore, cKPFM was introduced to probe the small amplitude DC voltage dependence after large amplitude DC voltage pulses. This can be done with a linear DC voltage sweep or spectroscopically as described in detail in ref 346 . Here, the small amplitude DC voltage needs to be small enough to not change the bias-induced state of the material and is often denoted by the parameter Vread to differentiate it from the large amplitude DC voltage pulses Vwrite.…”

Non-piezoelectric effects in piezoresponse force microscopy

“…Such local and non-local electrostatic effects can arise from the various electrical interactions between the AFM tip/cantilever and sample surface, such as the capacitive interaction, [80,81] the CPD, [79,82] the application of an external voltage to the entire sample, and the corresponding injected charges on the sample surface. [83][84][85] Hong et al reported a significant influence of the electrostatic effect on piezoresponse hysteresis loop measurements. [81] A piezoresponse hysteresis loop is generally measured using a triangular waveform, which can be of two kinds, referred to as continuous and pulsed dc modes, as shown in Figs.…”

Exploring functional material behaviour with voltage modulated atomic force microscopy modes

“…KPFM conducted in contact mode allows to differentiate electromechanical and electrostatic phenomena and provides higher lateral resolution than non-contact mode KPFM (Balke et al, 2014).…”