AFM Modes for in-Situ Hyperspectral Mapping of Nanomechanics, Conductivity, and Local Electrochemical Activity

Abstract

The local differences in structural, mechanical, electrical, and/or electrochemical properties all together account for the reactivity heterogeneity of materials on the nanoscale. This requires approaches capable of simultaneously capturing correlated multidimensional information at this level. Additionally, in situ, in vivo, non-invasive methodologies are also highly desired. Atomic force microscopy (AFM) is a well-adopted method with its capability of measuring surface topography, mechanics, electricity, chemistry, optical properties, and electrochemistry in different environments. Traditional AFM modes operate in either ‘imaging’ or ‘spectroscopic’ modes, in situ or ex situ. The traditional imaging modes performed at discrete operation conditions captured only snap-shot-wise information in an inefficient way. In conventional spectroscopic mode, however, only a single or few sample point locations are selected. Our DataCube modes combine the ‘imaging’ and ‘spectroscopic’ modes into a single approach providing a spectrum of a property or multiple properties in every pixel of the image. This new approach probing in situ, in operando, continuous, complete, and structured information about the system performance when critical properties are varying by control. We have recently also developed batch-fabricated, high-quality and robust nanoelectrode probes. These probes have the exposed Pt-coated tip apex of ~200 nm height and the end tip radius of ~25 nm. Modes enabled by these probes include include PeakForce scanning electrochemical microscopy (SECM) for the simultaneous acquisition of local EC, conductivity and nanomechanical information. This has also been extended to DataCube SECM, which provides highly-dimensional, big-data results allowing us to perform in-depth data mining for improved electrochemical kinetic quantification, 3-D nano-EC and nanomechanical characterization. In addition, many applications require performing nanoelectrical studies in electrolyte solutions, e.g. battery, bioelectricity, and bioelectromechanics. However, these are technically challenging. The general implementation requires avoiding electrical shorting, liquid spilling and chemical corrosion. Minimal parasitic electrochemistry and stray capacitance are also needed. With the use of these nanoelectrode AFM tips, we have developed a suite of solutions to conduct multi-dimensional nanoelectrical measurements in liquid, where the DataCube method has been also integrated with these implementations. This work introduces our recent developments with a variety of applications examples in different research areas. All these cases demonstrate the versatile capabilities of these solutions for today’s highly-multidisciplinary research. Figure 1. Left: SEM images of the probe. Middle: PeakForce SECM images of a mesh pattern with 1 µm wide platinum strands separated by 2 µm x 2 µm square silicon nitride islands. Right: DataCube conductive AFM mode in aqueous solution. Reference: [1] Cui et al., Nanotechnology, 2019, 30, 235701 Nellist et al., Nanotechnology, 2017, 28, 095711. [2] Jiang et al., ChemSusChem 2017, 10, 4657 Figure 1