Abstract
Retrieving electrical impedance maps at the nanoscale rapidly via nondestructive inspection with a high signal-to-noise ratio is an unmet need, likely to impact various applications from biomedicine to energy conversion. In this study, we develop a multimodal functional imaging instrument that is characterized by the dual capability of impedance mapping and phase quantitation, high spatial resolution, and low temporal noise. To achieve this, we advance a quantitative phase imaging system, referred to as epi-magnified image spatial spectrum microscopy combined with electrical actuation, to provide complementary maps of the optical path and electrical impedance. We demonstrate our system with high-resolution maps of optical path differences and electrical impedance variations that can distinguish nanosized, semi-transparent, structured coatings involving two materials with relatively similar electrical properties. We map heterogeneous interfaces corresponding to an indium tin oxide layer exposed by holes with diameters as small as ~550 nm in a titanium (dioxide) over-layer deposited on a glass support. We show that electrical modulation during the phase imaging of a macro-electrode is decisive for retrieving electrical impedance distributions with submicron spatial resolution and beyond the limitations of electrode-based technologies (surface or scanning technologies). The findings, which are substantiated by a theoretical model that fits the experimental data very well enable achieving electro-optical maps with high spatial and temporal resolutions. The virtues and limitations of the novel optoelectrochemical method that provides grounds for a wider range of electrically modulated optical methods for measuring the electric field locally are critically discussed.
Highlights
Transparent electrodes decorated with nanometer- to micrometer-scale light-absorbing structures have been increasingly used in the conversion of solar energy into electricity[1] and in the light-enhanced electrochemical synthesis of important chemicals (e.g., H2 from water[2] and CO from CO23)
This study presents electrically coupled epi-magnified image spatial spectrum (MISS), which combines MISS in reflection geometry, not reported before, with electrical actuation and plain conductive probes coupled with a non-faradaic assay to yield high spatial resolution maps of the optical phase (QPI) and electrical impedance
The system combines a novel MISS set-up[34] in reflection mode (Fig. 1a), an optoelectrochemical cell comprising counter, reference, and working electrodes (CE, RE, and WE), and an electrical AC signal generator (Fig. 1b). This new system yields with high spatial resolution the following quantities: (1) the quantitative phase map via the DC component of the electrically actuated timelapse MISS images and (2) the electrical impedance map of the sample via the distribution of the phaseamplitude oscillation at the frequency of the AC electric field
Summary
Transparent electrodes decorated with nanometer- to micrometer-scale light-absorbing structures have been increasingly used in the conversion of solar energy into electricity[1] and in the light-enhanced electrochemical synthesis of important chemicals (e.g., H2 from water[2] and CO from CO23) These electrodes play an important role in biosensor development[4] and the functional characterization of biological materials from individual living cells to tissue structures[5]. Electrical impedance spectroscopy (EIS) is an established technique used for functional characterization that, when performed across the entire sample, provides an overall quantitative description of the electrical properties of the sample at a certain moment Studying heterogeneous structures, such as cells, biological tissue, or polydisperse particle mixtures, requires adding spatial
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