Browsing by Author "Al-Zubeidi, Alexander"

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    Mechanism for plasmon-generated solvated electrons
    (PNAS, 2023) Al-Zubeidi, Alexander; Ostovar, Behnaz; Carlin, Claire C.; Li, Boxi Cam; Lee, Stephen A.; Chiang, Wei-Yi; Gross, Niklas; Dutta, Sukanya; Misiura, Anastasiia; Searles, Emily K.; Chakraborty, Amrita; Roberts, Sean T.; Dionne, Jennifer A.; Rossky, Peter J.; Landes, Christy F.; Link, Stephan; Center for Adapting Flaws into Features
    Solvated electrons are powerful reducing agents capable of driving some of the most energetically expensive reduction reactions. Their generation under mild and sustainable conditions remains challenging though. Using near-ultraviolet irradiation under low-intensity one-photon conditions coupled with electrochemical and optical detection, we show that the yield of solvated electrons in water is increased more than 10 times for nanoparticle-decorated electrodes compared to smooth silver electrodes. Based on the simulations of electric fields and hot carrier distributions, we determine that hot electrons generated by plasmons are injected into water to form solvated electrons. Both yield enhancement and hot carrier production spectrally follow the plasmonic near-field. The ability to enhance solvated electron yields in a controlled manner by tailoring nanoparticle plasmons opens up a promising strategy for exploiting solvated electrons in chemical reactions.
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    Plasmonic hot carrier-driven electrochemistry
    (2022-09-07) Al-Zubeidi, Alexander; Link, Stephan
    The need for renewable energy has sparked widespread interest in photocatalysts, including systems based on plasmonic metal nanoparticles. To take advantage of these materials, a fundamental understanding of how plasmon-induced hot-carriers drive chemical reactions is needed. This work examines how different hot carrier distributions affect electrochemical reactions of plasmonic nanoparticles, and how applied electrochemical potentials can be used to modify the reactivity of hot carriers. Using hot-hole assisted gold nanorod electro-dissolution as a model system, I demonstrated that oxidation reactions are most efficiently driven by athermal holes in the d-band, rather than less energetic holes in the sp-band. Nanorods exhibited reactive hot-spots for d-band holes at the tips. To expand plasmon driven chemical reactions to other materials that allow more tunability of optical and electronic properties, the stability and degreadation mechanism of gold-silver alloy nanoparticles was explored. Alloying provided a significant improvement in nanoparticle stability. A two stage model for alloy nanoparticle degreadation was developed and confirmed using numerial simulations. Finally, with the vision dirving homogeneous reactions with plasmons, a mechanism for plasmon-induced generation of solvated electrons was demonstrated. Hot electrons were found to eject from nanoparticles into water, where they formed solvated electrons, which are powerful solution phase reducing agents. This fundamental insight reveals the opportunity for new reaction pathways for plasmon-induced reactions by moving the reaction site away from the particle surface.
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    Single-Particle Hyperspectral Imaging Reveals Kinetics of Silver Ion Leaching from Alloy Nanoparticles
    (American Chemical Society, 2021) Al-Zubeidi, Alexander; Stein, Frederic; Flatebo, Charlotte; Rehbock, Christoph; Hosseini Jebeli, Seyyed Ali; Landes, Christy F.; Barcikowski, Stephan; Link, Stephan; Smalley-Curl Institute
    Gold–silver alloy nanoparticles are interesting for multiple applications, including heterogeneous catalysis, optical sensing, and antimicrobial properties. The inert element gold acts as a stabilizer for silver to prevent particle corrosion, or conversely, to control the release kinetics of antimicrobial silver ions for long-term efficiency at minimum cytotoxicity. However, little is known about the kinetics of silver ion leaching from bimetallic nanoparticles and how it is correlated with silver content, especially not on a single-particle level. To characterize the kinetics of silver ion release from gold–silver alloy nanoparticles, we employed a combination of electron microscopy and single-particle hyperspectral imaging with an acquisition speed fast enough to capture the irreversible silver ion leaching. Single-particle leaching profiles revealed a reduction in silver ion leaching rate due to the alloying with gold as well as two leaching stages, with a large heterogeneity in rate constants. We modeled the initial leaching stage as a shrinking-particle with a rate constant that exponentially depends on the silver content. The second, slower leaching stage is controlled by the electrochemical oxidation potential of the alloy being steadily increased by the change in relative gold content and diffusion of silver atoms through the lattice. Interestingly, individual nanoparticles with similar sizes and compositions exhibited completely different silver ion leaching yields. Most nanoparticles released silver completely, but 25% of them appeared to arrest leaching. Additionally, nanoparticles became slightly porous. Alloy nanoparticles, produced by scalable laser ablation in liquid, together with kinetic studies of silver ion leaching, provide an approach to design the durability or bioactivity of alloy nanoparticles.
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    Single-particle scattering spectroscopy: fundamentals and applications
    (De Gruyter, 2021) Al-Zubeidi, Alexander; McCarthy, Lauren A.; Rafiei-Miandashti, Ali; Heiderscheit, Thomas S.; Link, Stephan
    Metallic nanoparticles supporting a localized surface plasmon resonance have emerged as promising platforms for nanoscopic labels, sensors, and (photo-) catalysts. To use nanoparticles in these capacities, and to gain mechanistic insight into the reactivity of inherently heterogeneous nanoparticles, single-particle characterization approaches are needed. Single-particle scattering spectroscopy has become an important, highly sensitive tool for localizing single plasmonic nanoparticles and studying their optical properties, local environment, and reactivity. In this review, we discuss approaches taken for collecting the scattered light from single particles, their advantages and disadvantages, and present some recent applications. We introduce techniques for the excitation and detection of single-particle scattering such as high-angle dark-field excitation, total internal reflection dark-field excitation, scanning near-field microscopy, and interferometric scattering. We also describe methods to achieve polarization-resolved excitation and detection. We then discuss different approaches for scanning, ratiometric, snapshot, and interferometric hyperspectral imaging techniques used to extract spectral information. Finally, we provide a brief overview of specialized setups for in situ measurements of nanoparticles in liquid systems and setups coupled to scanning tip microscopes.