Resonant multi-frequency method for Kelvin probe force microscopy in air

Abstract

The multi-frequency method, recently introduced in atomic force microscopy (AFM), has shown remarkable enhancement of sensitivity and resolution of microscopy with a variety of heterogeneous materials. Under ambient conditions, Kelvin probe force microscopy (KPFM) is commonly carried out using only the first flexural eigenmode of the micro-cantilever probe. Here we report a resonant multi-frequency method for KPFM in air. To implement this method, the first eigenmode of the cantilever probe is used for topography imaging, whereas the second one is used to measure the local contact potential difference in the two-pass mode with the tip lifted. By introducing an additional feedback controller, a multi-frequency KPFM (MF-KPFM) is developed upon a commercial AFM. The performance of MF-KPFM, including the feedback controller, sensitivity and noise, lift height of the cantilever and lateral resolution, is evaluated and optimized. The capabilities of MF-KPFM are demonstrated by characterizing a charge pattern on a polymer electret. The results show that the lateral resolution of KPFM in air can be improved by the resonant multi-frequency method.

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

“…One other major limitation of KPFM is poor spatial resolution (compared to other AFM-based techniques) and the inability to study fast charge dissipation and detrapping processes in nonmetallic materials. Dual-frequency techniques have been implemented to address the long scan times, 4,5 but an improvement of existing techniques is needed to address the remaining problems of lateral and time resolution. Electrostatic forces acting between the tip and the sample also exist when the tip is in physical contact with the sample surface.…”

Applying Second and Third Resonance Frequencies to Surface Potential Measurements with Kelvin Probe Force Microscopy

“…The above results suggest that a higher measurement frequency leads to a decreased cantilever-sample effect, resulting in better lateral resolution for potential measurements in KPFM. In previous studies, cantileversample interactions in lift-mode AM-KPFM were decreased by using the second resonance frequency in the potential measurements, leading to better lateral resolution [15,16]. The probe-sample interactions were estimated from a simple cantilever-sample and tip-sample capacitance model.…”

“…With the aim of preventing this crosstalk, frequency separation between the topography and surface potential scans has been studied. In particular, the crosstalk has been successfully decreased by applying the second resonance frequency of the cantilever to potential imaging and the first resonance frequency to topography imaging [10][11][12][13][14][15]. Furthermore, the crosstalk is effectively decreased by employing lift mode.…”

Nanoscale Characterization of Mock Explosive Materials Using Advanced Atomic Force Microscopy Methods

“…In KPFM often the AC bias voltage is applied at the first resonance frequency x 0 [27] or at the second eigenmode resonance frequency to improve the sensitivity of surface potential measurements [28,29]. However, in this study we are more interested in the local dielectric properties of the sample, which are closely related to the amplitude response of the second harmonic A 2x .…”