Shasha Liu

Bio: Shasha Liu is an academic researcher from Nanjing University. The author has contributed to research in topics: Etching (microfabrication) & Hysteresis. The author has an hindex of 3, co-authored 5 publications receiving 33 citations.

Tracking Sub-Nanometer Shift in the Scattering Centroid of Single Gold Nanorods during Electrochemical Charging

Abstract: While conventional wisdom suggests the scattering centroid of a plasmonic nanoparticle reflects its geometric center, here we uncover the dependence of a scattering centroid of a single gold nanoro...

Imaging the Thermal Hysteresis of Single Spin-Crossover Nanoparticles.

Abstract: The magnetic hysteresis property during the spin transition of spin-crossover (SCO) materials holds great promise for their applications in spin electronics, information storage, thermochromic, and nanophotonic devices. Existing studies often measured the averaged property of a bulk sample consisting of lots of individuals. When considering the significant heterogeneity among different individuals and the inevitable interparticle interactions, ensemble measurement not only blurred the structure-property relationship but also compromised the intrinsic hysteresis property and cyclability. Herein, we employed a recently developed surface plasmon resonance microscopy (SPRM) method to measure the thermal hysteresis curve of single isolated SCO nanoparticles. The thermal-induced spin transition was found to alter the optical contrast of single SCO nanoparticles, which was optically readout using SPRM in a quantitative, nonintrusive, and high-throughput manner. Single nanoparticle measurements revealed an intrinsic transition temperature that was independent of the temperature scan rate and superior stability after over 11 000 cycles of single SCO nanoparticles. Correlations between the hysteresis and the size and morphology of the same individuals further uncovered the significant nanoparticle-to-nanoparticle heterogeneity with implications for the size-property relationship and rational design of SCO materials with improved performance.

Visualizing the Zero-Potential Line of Bipolar Electrodes with Arbitrary Geometry

Abstract: In a typical bipolar electrochemistry (BPE) configuration, voltage applied between the two driving electrodes induced a potential drop through solution filled in the microchannel, resulting in an interfacial potential difference between solution and BPE varied along the BPE. In the present work, we employed a recently developed plasmonic imaging technique to map the distribution of surface potential of bipolar electrodes with various geometries including round, triangle, hexagon, star, and rhombus shapes under the nonfaradaic charging process, from which the line of zero potential (LZP) was visualized and determined. We further investigated the dependence of LZP on electrode geometry and the distribution of external electric field and explained the experimental results with a charge balance mechanism. The triangular and star-shaped BPEs show quite different LZP features from the other ones with symmetrical geometry. These experimentally obtained potential distributions are all in good agreement with electromagnetic simulations. Finally, the line of zero overpotential (LZO) of the triangular-shaped BPE under faradaic reactions were investigated. The results confirm the shift of LZO when faradaic reactions occurred at the corresponding ends of BPE. The present work demonstrates the first experimental capability to map the potential distribution of BPE with arbitrary geometry under an arbitrary driving field. It is anticipated to help the design and optimization on the geometry of electrodes and microchannels with implications for boosting their applications in chemical sensing and materials synthesis.

Tracking the optical mass centroid of single electroactive nanoparticles reveals the electrochemically inactive zone

Abstract: The inevitable microstructural defects, including cracks, grain boundaries and cavities, make a portion of the material inaccessible to electrons and ions, becoming the incentives for electrochemically inactive zones in single entity. Herein, we introduced dark field microscopy to study the variation of scattering spectrum and optical mass centroid (OMC) of single Prussian blue nanoparticles during electrochemical reaction. The “dark zone” embedded in a single electroactive nanoparticle resulted in the incomplete reaction, and consequently led to the misalignment of OMC for different electrochemical intermediate states. We further revealed the dark zones such as lattice defects in the same entity, which were externally manifested as the fixed pathway for OMC for the migration of potassium ions. This method opens up enormous potentiality to optically access the heterogeneous intraparticle dark zones, with implications for evaluating the crystallinity and electrochemical recyclability of single electroactive nano-objects.

Photoassisted Electrochemical Micropatterning of Gold Film.

Abstract: Electrochemical etching is a powerful and popular method for fabricating micropatterns on metal substrates for use in electronic devices, electrochemical sensors, and plasmonic substrates. In order to achieve micropatterning, either a prepatterned insulating layer (mask) or a scanning microelectrode is often required to selectively trigger electrochemical etching at the desired locations. In the present work, we employed a well-focused light beam to enable the photoassisted electrochemical etching of gold film with a spatial resolution close to the optical diffraction limit (∼300 nm). It was found that the simultaneous application of light irradiation and appropriate potential were critical for the oxidative dissolution (i.e., etching) of gold to occur. Superior controllability of light beam allowed for the direct-write micropatterning without the need of mask or probe. Etching kinetics and mechanism were also studied by monitoring the dynamic evolution of optical transparency with a conventional transmission bright-field microscope, together with characterizations on the as-obtained patterns with atomic force microscopy and electron microscopy. This study is anticipated to contribute a feasible method for the micropatterning of gold film with implications for nanoelectronics and electrochemical sensors.

Recent Advancements in Bipolar Electrochemical Methods of Analysis.

Abstract: The goal of this review is to provide an overview of the advancements made in the field of bipolar electrochemistry over the past 2 years, with an emphasis on analysis. Bipolar electrodes (BPEs) are versatile, and in electroanalysis, they have been used extensively to screen electrocatalysts(1−4) and to sense biomarkers.(5−10) Their ability to modulate local electric fields lends them to the manipulation of cells and to the enrichment and separation of analytes.(11−17) Finally, by virtue of the polar and often graded profile of the interfacial potential across BPEs, they provide a platform for synthesis of Janus particles, useful as sensors and as microswimmers(18−22) and other materials with compositional gradients.(23,24) BPEs are particularly well-suited to analytical challenges that demand multiplexing or amenability to point-of-need (PON) application because even large arrays of BPEs can be controlled with simple equipment yet yield quantitative information about a system. In this review, we discuss recent progress in reactions that transduce current to a visible signal, sensing mechanisms, bipolar electrochemical cell design, integration of bipolar electrochemistry with spectroscopic techniques, BPEs at the nanoscale, and the application of BPEs to electrokinetics and materials preparation. Throughout the discussion, we identify promising trends, innovative directions, and remaining challenges in the field. Disciplines Analytical Chemistry Comments This document is the unedited Author’s version of a Submitted Work that was subsequently accepted for publication in Analytical Chemistry, copyright © American Chemical Society after peer review. To access the final edited and published work see DOI: 10.1021/acs.analchem.0c04524. Posted with permission. This article is available at Iowa State University Digital Repository: https://lib.dr.iastate.edu/chem_pubs/1283 [Prepared for publication as a Review in Analytical Chemistry for the Annual Review Issue] 1 2 Ms. No. 3 4 Recent Advancements in Bipolar Electrochemical Methods of Analysis 5 6 Kira L. Rahn, Robbyn K. Anand 7 8 Department of Chemistry, Iowa State University, 1605 Gilman Hall, 2415 Osborn Drive, Ames, 9 IA 50011-1021 10 11 12 13 14 15 16 17 18 19

Nanoscale optical imaging in chemistry.

Abstract: Single-molecule-level measurements are bringing about a revolution in our understanding of chemical and biochemical processes. Conventional measurements are performed on large ensembles of molecules. Such ensemble-averaged measurements mask molecular-level dynamics and static and dynamic fluctuations in reactivity, which are vital to a holistic understanding of chemical reactions. Watching reactions on the single-molecule level provides access to this otherwise hidden information. Sub-diffraction-limited spatial resolution fluorescence imaging methods, which have been successful in the field of biophysics, have been applied to study chemical processes on single-nanoparticle and single-molecule levels, bringing us new mechanistic insights into physiochemical processes. However, the scope of chemical processes that can be studied using fluorescence imaging is considerably limited; the chemical reaction has to be designed such that it involves fluorophores or fluorogenic probes. In this article, we review optical imaging modalities alternative to fluorescence imaging, which expand greatly the range of chemical processes that can be probed with nanoscale or even single-molecule resolution. First, we show that the luminosity, wavelength, and intermittency of solid-state photoluminescence (PL) can be used to probe chemical transformations on the single-nanoparticle-level. Next, we highlight case studies where localized surface plasmon resonance (LSPR) scattering is used for tracking solid-state, interfacial, and near-field-driven chemical reactions occurring in individual nanoscale locations. Third, we explore the utility of surface- and tip-enhanced Raman scattering to monitor individual bond-dissociation and bond-formation events occurring locally in chemical reactions on surfaces. Each example has yielded some new understanding about molecular mechanisms or location-to-location heterogeneity in chemical activity. The review finishes with new and complementary tools that are expected to further enhance the scope of knowledge attainable through nanometer-scale resolution chemical imaging.

In Situ Optical Monitoring of the Electrochemical Conversion of Dielectric Nanoparticles: From Multistep Charge Injection to Nanoparticle Motion.

Abstract: By shortening solid-state diffusion times, the nanoscale size reduction of dielectric materials-such as ionic crystals-has fueled synthetic efforts toward their use as nanoparticles, NPs, in electrochemical storage and conversion cells. Meanwhile, there is a lack of strategies able to image the dynamics of such conversion, operando and at the single NP level. It is achieved here by optical microscopy for a model dielectric ionic nanocrystal, a silver halide NP. Rather than the classical core-shrinking mechanism often used to rationalize the complete electrochemical conversion and charge storage in NPs, an alternative mechanism is proposed here. Owing to its poor conductivity, the NP conversion proceeds to completion through the formation of multiple inclusions. The superlocalization of NP during such heterogeneous multiple-step conversion suggests the local release of ions, which propels the NP toward reacting sites enabling its full conversion.

Single-entity electrochemistry at confined sensing interfaces

Abstract: Measurements at the single-entity level provide more precise diagnosis and understanding of basic biological and chemical processes. Recent advances in the chemical measurement provide a means for ultra-sensitive analysis. Confining the single analyte and electrons near the sensing interface can greatly enhance the sensitivity and selectivity. In this review, we summarize the recent progress in single-entity electrochemistry of single molecules, single particles, single cells and even brain analysis. The benefits of confining these entities to a compatible size sensing interface are exemplified. Finally, the opportunities and challenges of single entity electrochemistry are addressed.