Kelvin probe force microscopy in liquid using electrochemical force microscopy

• Published in: Beilstein journal of nanotechnology 2015-01, Vol.6 (1), p.201-214
• Main Authors: Collins, Liam, Jesse, Stephen, Kilpatrick, Jason I, Tselev, Alexander, Okatan, M Baris, Kalinin, Sergei V, Rodriguez, Brian J
• Format: Article
• Language: English
• Subjects: diffuse charge dynamics; double layer charging; electrochemical force microscopy; electrochemistry; Full Research Paper; Kelvin probe force microscopy; Nanoscience; NANOSCIENCE AND NANOTECHNOLOGY; Nanotechnology
• ISSN: 2190-4286; 2190-4286
• DOI: 10.3762/bjnano.6.19

Conventional closed loop-Kelvin probe force microscopy (KPFM) has emerged as a powerful technique for probing electric and transport phenomena at the solid-gas interface. The extension of KPFM capabilities to probe electrostatic and electrochemical phenomena at the solid-liquid interface is of interest for a broad range of applications from energy storage to biological systems. However, the operation of KPFM implicitly relies on the presence of a linear lossless dielectric in the probe-sample gap, a condition which is violated for ionically-active liquids (e.g., when diffuse charge dynamics are present). Here, electrostatic and electrochemical measurements are demonstrated in ionically-active (polar isopropanol, milli-Q water and aqueous NaCl) and ionically-inactive (non-polar decane) liquids by electrochemical force microscopy (EcFM), a multidimensional (i.e., bias- and time-resolved) spectroscopy method. In the absence of mobile charges (ambient and non-polar liquids), KPFM and EcFM are both feasible, yielding comparable contact potential difference (CPD) values. In ionically-active liquids, KPFM is not possible and EcFM can be used to measure the dynamic CPD and a rich spectrum of information pertaining to charge screening, ion diffusion, and electrochemical processes (e.g., Faradaic reactions). EcFM measurements conducted in isopropanol and milli-Q water over Au and highly ordered pyrolytic graphite electrodes demonstrate both sample- and solvent-dependent features. Finally, the feasibility of using EcFM as a local force-based mapping technique of material-dependent electrostatic and electrochemical response is investigated. The resultant high dimensional dataset is visualized using a purely statistical approach that does not require a priori physical models, allowing for qualitative mapping of electrostatic and electrochemical material properties at the solid-liquid interface.