Dual harmonic Kelvin probe force microscopy at the graphene–liquid interface

Abstract

Kelvin probe force microscopy (KPFM) is a powerful technique for the determination of the contact potential difference (CPD) between an atomic force microscope tip and a sample under ambient and vacuum conditions. However, for many energy storage and conversion systems, including graphene-based electrochemical capacitors, understanding electrochemical phenomena at the solid–liquid interface is paramount. Despite the vast potential to provide fundamental insight for energy storage materials at the nanoscale, KPFM has found limited applicability in liquid environments to date. Here, using dual harmonic (DH)-KPFM, we demonstrate CPD imaging of graphene in liquid. We find good agreement with measurements performed in air, highlighting the potential of DH-KPFM to probe electrochemistry at the graphene–liquid interface.

Probing charge screening dynamics and electrochemical processes at the solid–liquid interface with electrochemical force microscopy

“…The red box indicates the frequency space currently accessible using commercial AFM systems (DC -B10 MHz). Notably, it may be possible to determine the electronic properties (for example, CPD 32 and dielectric constant 27,28 ) of the sample when operating in region III, where the electric double-layer charging and ion diffusion processes occur at a timescale much slower than the measurement time (that is, mobile ions are in quasi-static equilibrium) 32 . While measurements of CPD in higher (4100 mM) ion concentrations are attractive for many energy and biological systems, they become impractical in the presence of ion dynamics (region II) and Faradaic processes at longer timescales (region I).…”

Surface Potential Measurement of Bacteria Using Kelvin Probe Force Microscopy

“…Imaging in polar liquid is not currently possible with standard KPFM, and thus the imaging of live cells using KPFM is not as of yet possible. Developments of new open-loop and dual frequency KPFM modes have shown promise in their ability to image surfaces in low-ionic solutions [18][19][20] . It is our hope that in the future this technology is further developed so that imaging can be done on live cell cultures.…”

“…Surface potential resolution using AM and FM modes are in the range of 1 nm laterally [14][15][16] . It should be noted that KPFM imaging can be done in non-polar liquids, and more recently, has been shown to be done in low-ionic (<10 mM) polar liquids (in open-loop KPFM modes which do not require a bias feedback, obviating the application of a DC bias) such as MilliQ water; however, KPFM imaging has yet to be done on live cells in polar solutions [17][18][19][20] . Additional challenges associated with SP imaging in liquid is that solutions commonly used for maintaining cells (i.e., phosphate buffered saline) have high concentrations of mobile ions, which would lead to Faradaic reactions, bias-induced charge dynamics, and ion diffusion/redistribution 20 .…”

Band excitation Kelvin probe force microscopy utilizing photothermal excitation

“…KPFM has been particularly useful for characterizing materials and devices ranging from metals, 1 semiconductors, 8,9 and ferroelectrics, 10,11 to self-assembled monolayers, 12 polymers, 13 and biomolecules. 14,15 The continued success of KPFM necessitates both the advancement of the technique in terms of accuracy and resolution 16,17 across all imaging environments, 18,19 as well as improved capabilities to distinguish and correlate different electronic parameters (i.e., dielectric properties, [20][21][22][23] dissipation 24,25 ) beyond that currently attainable with conventional KPFM.…”