Full data acquisition in Kelvin Probe Force Microscopy: Mapping dynamic electric phenomena in real space

Abstract

Kelvin probe force microscopy (KPFM) has provided deep insights into the local electronic, ionic and electrochemical functionalities in a broad range of materials and devices. In classical KPFM, which utilizes heterodyne detection and closed loop bias feedback, the cantilever response is down-sampled to a single measurement of the contact potential difference (CPD) per pixel. This level of detail, however, is insufficient for materials and devices involving bias and time dependent electrochemical events; or at solid-liquid interfaces, where non-linear or lossy dielectrics are present. Here, we demonstrate direct recovery of the bias dependence of the electrostatic force at high temporal resolution using General acquisition Mode (G-Mode) KPFM. G-Mode KPFM utilizes high speed detection, compression, and storage of the raw cantilever deflection signal in its entirety at high sampling rates. We show how G-Mode KPFM can be used to capture nanoscale CPD and capacitance information with a temporal resolution much faster than the cantilever bandwidth, determined by the modulation frequency of the AC voltage. In this way, G-Mode KPFM offers a new paradigm to study dynamic electric phenomena in electroactive interfaces as well as a promising route to extend KPFM to the solid-liquid interface.

Rapid mapping of polarization switching through complete information acquisition

“…Further mining of the G-VS data is performed through multivariate statistical methods, such as principal component analysis (PCA), k -means clustering and Bayesian linear unmixing (BLU)535455. PCA separates data into orthogonal components that are arranged in descending order by variance56.…”

Recent advances in hybrid measurement methods based on atomic force microscopy and surface sensitive measurement techniques

“…342 Ongoing research is devoted to enhancing the time resolution, because the scan speed of FM mode is slow 343 and AM mode measurements are burdened with artifacts, such as the stray capacitance effect 344 and interfering signals, leading to topographical coupling. 345,346 Several approaches try to couple the lateral resolution and reproducibility of FM mode KPFM with enhanced time resolution similar to AM mode KPFM, such as time-resolved electrostatic force microscopy, pump-probe KPFM, 347 general acquisition mode, 348 open loop (OL) KPFM 349 and Heterodyne (H) KPFM. 350 For example, H-KPFM improved the scan rate while maintaining the spatial resolution and voltage sensitivity comparable to FM-KPFM.…”

Quantitative comparison of closed-loop and dual harmonic Kelvin probe force microscopy techniques

“…Here we adopt an approach where we measured X gain directly at each tip-sample separation and applied bias by recording A ω with excitation at ω and 2ω, consecutively. 7,13,44 Other approaches based on half-harmonic excitation, 13 resonance tracking, 45 band excitation, 7,13,14,46 or G-mode 19,20,47,48 may also be used to determine X gain . Figure 4(a) shows the thermal spectra at a tip-sample separation of ∼3 µm with excitation A ω applied at 12.5 kHz.…”

“…6,7 Traditional KPFM is a closed-loop KPFM (CL-KPFM) technique where a feedback loop is used to apply a DC bias to compensate the electrostatic force between a tip and a sample. 8 Open-loop KPFM (OL-KPFM) techniques are increasingly being adopted as feedback-free methods, 7,9,[18][19][20][10][11][12][13][14][15][16][17] eliminating the need for the application of a DC bias 7 and enabling the mapping of voltage-sensitive materials 9,15,21,22 and surface potentials in liquid environments. [10][11][12]16,17,[23][24][25] These techniques are also of interest for their reduced sensitivity to electronic offsets and electronic cross talk instrumentation a) Authors to whom correspondence should be addressed: jason.kilpatrick@ ucd.ie and brian.rodriguez@ucd.ie issues, 4,7,[32][33][34][35]13,22,[26][27][28][29][30][31] which can affect both OL-and CL-KPFM operation to varying degrees.…”