Sub-particle Level Research Articles

Revealing operando surface defect–dependent electrocatalytic performance of Pt at the subparticle level

Understanding the operando defect-tuning performance of catalysts is critical to establish an accurate structure-activity relationship of a catalyst. Here, with the tool of single-molecule super-resolution fluorescence microscopy, by imaging intermediate CO formation/oxidation during the methanol oxidation reaction process on individual defective Pt nanotubes, we reveal that the fresh Pt ends with more defects are more active and anti-CO poisoning than fresh center areas with less defects, while such difference could be reversed after catalysis-induced step-by-step creation of more defects on the Pt surface. Further experimental results reveal an operando volcano relationship between the catalytic performance (activity and anti-CO ability) and the fine-tuned defect density. Systematic DFT calculations indicate that such an operando volcano relationship could be attributed to the defect-dependent transition state free energy and the accelerated surface reconstructing of defects or Pt-atom moving driven by the adsorption of the CO intermediate. These insights deepen our understanding to the operando defect-driven catalysis at single-molecule and subparticle level, which is able to help the design of highly efficient defect-based catalysts.

Asynchronous domain dynamics and equilibration in layered oxide battery cathode

To improve lithium-ion battery technology, it is essential to probe and comprehend the microscopic dynamic processes that occur in a real-world composite electrode under operating conditions. The primary and secondary particles are the structural building blocks of battery cathode electrodes. Their dynamic inconsistency has profound but not well-understood impacts. In this research, we combine operando coherent multi-crystal diffraction and optical microscopy to examine the chemical dynamics in local domains of layered oxide cathode. Our results not only pinpoint the asynchronicity of the lithium (de)intercalation at the sub-particle level, but also reveal sophisticated diffusion kinetics and reaction patterns, involving various localized processes, e.g., chemical onset, reaction front propagation, domains equilibration, particle deformation and motion. These observations shed new lights onto the activation and degradation mechanisms of state-of-the-art battery cathode materials.

Multiscale Analysis of Electrocatalytic Particle Activities: Linking Nanoscale Measurements and Ensemble Behavior.

Nanostructured electrocatalysts exhibit variations in electrochemical properties across different length scales, and the intrinsic catalytic characteristics measured at the nanoscale often differ from those at the macro-level due to complexity in electrode structure and/or composition. This aspect of electrocatalysis is addressed herein, where the oxygen evolution reaction (OER) activity of β-Co(OH)2 platelet particles of well-defined structure is investigated in alkaline media using multiscale scanning electrochemical cell microscopy (SECCM). Microscale SECCM probes of ∼50 μm diameter provide voltammograms from small particle ensembles (ca. 40-250 particles) and reveal increasing dispersion in the OER rates for samples of the same size as the particle population within the sample decreases. This suggests the underlying significance of heterogeneous activity at the single-particle level that is confirmed through single-particle measurements with SECCM probes of ∼5 μm diameter. These measurements of multiple individual particles directly reveal significant variability in the OER activity at the single-particle level that do not simply correlate with the particle size, basal plane roughness, or exposed edge plane area. In combination, these measurements demarcate a transition from an "individual particle" to an "ensemble average" response at a population size of ca. 130 particles, above which the OER current density closely reflects that measured in bulk at conventional macroscopic particle-modified electrodes. Nanoscale SECCM probes (ca. 120 and 440 nm in diameter) enable measurements at the subparticle level, revealing that there is selective OER activity at the edges of particles and highlighting the importance of the three-phase boundary where the catalyst, electrolyte, and supporting carbon electrode meet, for efficient electrocatalysis. Furthermore, subparticle measurements unveil heterogeneity in the OER activity among particles that appear superficially similar, attributable to differences in defect density within the individual particles, as well as to variations in electrical and physical contact with the support material. Overall this study provides a roadmap for the multiscale analysis of nanostructured electrocatalysts, directly demonstrating the importance of multilength scale factors, including particle structure, particle-support interaction, presence of defects, etc., in governing the electrochemical activities of β-Co(OH)2 platelet particles and ultimately guiding the rational design and optimization of these materials for alkaline water electrolysis.

Understanding Photo(electro)catalysts for Energy Conversion via Operando Functional Imaging.

Understanding the fundamental processes of charge carrier generation, separation, transport, and reactivity on the surface of semiconductors is crucial for the rational design of high-performance photo(electro)catalysts for various energy conversion applications. Nevertheless, the ubiquitous and intricate heterogeneity exhibited by individual catalysts poses a significant obstacle to achieving a comprehensive understanding of the structure-function relationships using bulk-level, ensemble-averaged characterizations. This review highlights the emerging operando imaging techniques capable of providing local functional information, such as surface photovoltage, photoluminescence, charge carrier reaction rate, and photocurrent, at the single particle to subparticle level. By establishing correlations between the acquired local functional information and the specific structural characteristics of the catalyst, a quantitative, holistic understanding of the structure-function relationship in photo(electro)catalysts can be achieved. This understanding can serve as a foundation for guiding the design of photocatalysts with enhanced energy conversion performance.

Super-Resolution Electrogenerated Chemiluminescence Microscopy for Single-Nanocatalyst Imaging.

Electrogenerated chemiluminescence microscopy (ECLM) provides a real-time imaging approach to visualize the surface-dependent catalytic activity of nanocatalysts, which helps to rationalize the design of catalysts. In this study, we first propose super-resolution ECLM that could measure the facet- and site-specific activities of a single nanoparticle with nanometer resolution. The stochastic nature of the ECL emission makes the generation of photons obey Poisson statistics, which fits the requirement of super-resolution radial fluctuation (SRRF). By processing an SRRF algorithm, the spatial resolution of ECL images achieved ca. 100 nm, providing more abundant details on electrocatalytic reactivities at the subparticle level. Beyond conventional wide-field ECL imaging, super-resolution ECLM provided the spatial distribution of catalytic activities at a Au nanorod and nanoplate with scales of a few hundred nanometers. It helped uncover the facet- and defect-dependent surface activity, as well as the dynamic fluctuation of reactivity patterns on single nanoparticles. The super-resolution ECLM provides high spatiotemporal resolution, which shows great potential in the field of catalysis, biological imaging, and single-entity analysis.

Compaction and Tableting Behavior of a Novel Co-Processed Excipient in the Formulation of Metoprolol Succinate Tablets

Background: Pregelatinized starches exhibit good swelling and flow properties, imparting fast disintegration time but low mechanical strength in tablets. On the other hand, acacia gum acts as a binder in tablets by imparting high mechanical strength but prolonged disintegration time. Development of a co-processed excipient involving combination of the two excipients at sub-particle level will improve the functionality of the final product.Objective: To develop a direct compressible co-processed excipient with pregelatinized cocoyam starch and acacia gum and to evaluate its compaction behavior and tableting properties in metoprolol succinate tablets.Material and Methods: Batches of the co-processed excipient were prepared by co-fusion using different ratios (97.5:2.5; 95:5; 92.5:7.5; 90:10; 85:15; 80:20) of pregelatinized cocoyam starch and acacia gum. Flow and compaction properties and Fourier transform Infrared (FT-IR) analysis were carried out on native and pregelatinized starches and on the co-processed excipients. Metoprolol succinate tablets were formulated by direct compression using selected batches of co-processed excipients, pregelatinized cocoyam starch and acacia gum and then evaluated for mechanical strength and drug release.Results: Pregelatinization produced starch with larger granules (138.75±59.21μm), improved swelling (2.03±0.00) and flow (flow rate 0.52±0.03g/s). The FTIR analysis of the co-processed excipients confirmed absence of chemical interaction. Flow properties, compressibility (Kawakita value, a = 0.190 – 0.223) and rate of packing (Consolidation rate, K = 0.1221 – 0.2551) of the co-processed excipients were enhanced. Metoprolol succinate tablets containing the co-processed excipients had higher mechanical strength (Crushing strength 106.03±15.80 MNm-2) than those containing starch alone but faster drug release (disintegration time 1.80 ±0.20 -5.75±0.25; dissolution time; t80 30-50 min) than those containing acacia gum. Cocoyam starch: acacia gum ratio 97.5:2.5 gave the optimum formulation with high crushing strength (106.03 ± 15.8MNm-2) and fast release (t80 = 30 min).Conclusion: Co-processed excipients of pregelatinized cocoyam starch and acacia gum could serve as suitable alternatives to other directly-compressible excipients for the formulation of tablets.
 Keywords: Acacia gum, Cocoyam starch, Compaction properties, Co-processing, Metoprolol

UNDERSTANDING THE BURNING OF HETEROGENEOUS SOLID PROPELLANTS THROUGH MESOSCALE MODELING

Heterogeneous solid propellants are widely used in the rocket industry. They consist of oxidizer particles embedded in a polymeric binder. The combustion and ignition of such propellants remain poorly understood, partly because they are complex and driven by physical mechanisms occurring at the micrometer scale. This paper gives an overview of some recent achievements in understanding the physics of propellant burning using mesoscale direct simulations. In this modeling, the propellant microstructure is explicitly modeled, and basic governing equations (reactive Navier-Stokes equations) are solved in three dimensions at the subparticle level. Most present findings suggest a salient role of propellant microstructure. This is the case for steady combustion where the orientation of particles (assumed as spheroids) has a strong impact on burn rate, while particle shape has a more limited effect. Ignition can also be addressed; it is found that ignition physics is strongly related to particles on the surface, like flame spreading from ignited particles. Mesoscale simulations can be part of a more general multiscale strategy applied to real motors. Two applications are discussed: the first is related to the effects of the grain manufacturing process on burning rate, and the second focuses on how local small-scale burning fluctuations above the propellant surface can trigger flow instabilities in a motor. This strengthens the interest of mesoscale modeling, both for understanding physics and predicting actual systems.

A New Theory for the Essence and Origin of Electron Spin

Spin is an intrinsic form of angular momentum carried by elementary particles, composite particles, and atomic nuclei. It is wildly believed that spin is a purely quantum mechanical concept and has no classical analogue. In fact, elementary particles are conceived as point objects which have no axis to “spin” around. Therefore, there is no explaining how spin arises at the fundamental level, why particles have the values they do, and what underpins the Pauli Exclusion principle and Bose-Einstein behavior. However, spin is like a vector quantity; it has a definite magnitude, and it has a “direction”, in order to spin should be composite. In this paper we propose a physical explanation for spin of the electron at the sub-particle level, relying on the vortex model of the electron. The electron is described as a superfluid frictionless vortex which has a mass, angular momentum and spin to provide a complete explanation of all properties of the electron: it composite, spinning around its own axis, produces a tiny magnetic fields independent of those from its orbital motions. The classical hydrodynamic laws are used to describe the quantum properties of the electron, such as spin, angular momentum, magnetic momentum and a magnetic dipole. The circulation in the vortex is constant, and the angular momentum of the vortex is conserved and has the same value of Planck constant. The direction of the angular momentum of a spinning electron vortex is along the axis of rotation and determined by the direction of spin. The spin quantum number 1/2 has a fixed value which represents the gap between the circulation rate of the core of the vortex and the boundaries of the vortex. The changeable values +1/2 “spin-up” or -1/2 “spin-down” indicate the direction of the magnetic dipole of the vortex. The relation between spin and Planck constant is discussed and the origin h/4pi angular momentum units are revealed.

Multi-Length Scale Analysis of Individual NMC811 Particle Degradation Using X-Ray Computed Tomography

Due to issues with toxicity and price, many manufacturers are reducing the cobalt content within lithium-ion (Li-ion) batteries by moving towards nickel-rich cathode chemistries, such as layered nickel-manganese-cobalt-oxide LiNi0.8Nm0.1Co0.1O2 (NMC811). Increasing the Ni content is accompanied by higher theoretical capacities, as high as 275 mAh g-1. However, the complex degradation of this material is not fully understood (1)(2)(3) and consequently practical capacities can be significantly lower (~200 mAh g-1) and capacity retention can be low, e.g. ~70% over 100 cycles to 4.3 V vs. Li/Li+ (4). The cracking of electrode particles (5) is a prominent degradation mechanism, but in order to gain a more comprehensive understanding of its origins and propagation, a multi-scale approach is required (6).X-ray computed tomography (CT) has revolutionised the characterisation of energy materials as it enables the non-destructive imaging of microstructure in 3D (7) . In this work, the effect of cycle number, C-rate and upper cut-off voltage on the morphology of NMC electrodes and particles have all been investigated using lab-based X-ray CT. This was achieved through post-mortem 3D analysis of the samples using micro- and nano-CT to reveal the electrode and particle degradation across multiple length scales.The individual particles within the 3D tomograms (Figure 1) have been quantitatively and qualitatively assessed to build a comprehensive understanding of the electrode state of health for a wide library of electrochemical histories. This has been achieved through carrying out greyscale intensity analysis in 3D on individual particles, and comparing them across cycling conditions, size ranges and categorizing each particle through machine learning.Due to the number of particles assessed, this work presents unprecedented materials statistics with detail of the degradation of NMC811 from the electrode to sub-particle level. Here, we discuss the methodology and findings from the multi-length-scale study, investigating both the electrochemical and mechanical response due to the variations in voltage, C-rate and number of cycles, and the implications of this research on the Li-ion field. Birkl CR, Roberts MR, McTurk E, Bruce PG, Howey DA. Degradation diagnostics for lithium ion cells. J Power Sources 2017;341:373–86.Jung R, Morasch R, Karayaylali P, Phillips K, Maglia F, Stinner C, et al. Effect of Ambient Storage on the Degradation of Ni-Rich Positive Electrode Materials (NMC811) for Li-Ion Batteries. J Electrochem Soc. 2018;165(2):A132–41.Hwang S, Kim SY, Chung KY, Stach EA, Kim SM, Chang W. Determination of the mechanism and extent of surface degradation in Ni-based cathode materials after repeated electrochemical cycling. APL Mater 2016;4(9).Noh HJ, Youn S, Yoon CS, Sun YK. Comparison of the structural and electrochemical properties of layered Li[NixCoyMnz]O2 (x = 1/3, 0.5, 0.6, 0.7, 0.8 and 0.85) cathode material for lithium-ion batteries. J Power Sources. 2013;233:121–30.Tsai PC, Wen B, Wolfman M, Choe MJ, Pan MS, Su L, et al. Single-particle measurements of electrochemical kinetics in NMC and NCA cathodes for Li-ion batteries. Energy Environ Sci. 2018;11(4):860–71.Finegan DP, Tudisco E, Scheel M, Robinson JB, Taiwo OO, Eastwood DS, et al. Quantifying bulk electrode strain and material displacement within lithium batteries via high-speed operando tomography and digital volume correlation. Adv Sci. 2015;3(3):1–11.Shearing PR, Howard LE, Jørgensen PS, Brandon NP, Harris SJ. Characterization of the 3-dimensional microstructure of a graphite negative electrode from a Li-ion battery. Electrochem commun 2010;12(3):374–7. Figure 1

Quantifying redox heterogeneity in single-crystalline LiCoO2 cathode particles.

Active cathode particles are fundamental architectural units for the composite electrode of Li-ion batteries. The microstructure of the particles has a profound impact on their behavior and, consequently, on the cell-level electrochemical performance. LiCoO2 (LCO, a dominant cathode material) is often in the form of well-shaped particles, a few micrometres in size, with good crystallinity. In contrast to secondary particles (an agglomeration of many fine primary grains), which are the other common form of battery particles populated with structural and chemical defects, it is often anticipated that good particle crystallinity leads to superior mechanical robustness and suppressed charge heterogeneity. Yet, sub-particle level charge inhomogeneity in LCO particles has been widely reported inthe literature, posing a frontier challenge in this field. Herein, this topic isrevisited and it is demonstrated that X-ray absorption spectra on single-crystalline particles with highly anisotropic lattice structures are sensitive to thepolarization configuration of the incident X-rays, causing some degree of ambiguity in analyzing the local spectroscopic fingerprint. To tackle this issue, a methodology is developed that extracts the white-line peak energy in the X-ray absorption near-edge structure spectra as a key data attribute for representing the local state of charge in the LCO crystal. This method demonstrates significantly improved accuracy and reveals the mesoscale chemical complexity in LCO particles with better fidelity. In addition to the implications on the importance of particle engineering for LCO cathodes, the method developed herein also has significant impact on spectro-microscopic studies of single-crystalline materials at synchrotron facilities, which is broadly applicable to a wide range of scientific disciplines well beyond battery research.

Direct numerical simulation (DNS) of alkali metals released during char combustion

Alkali metals in pulverized coal easily released in gas phase, cause significant fouling, atmospheric pollution and etc. during combustion and gasification. A TURE DNS method, based on fictitious domain strategy with finite volume (FV) scheme, was developed to describe the behavior of alkali metals release and transport in reacting fluid–solid flow at sub-particle level. Taking water-soluble sodium chloride (NaCl) of high harmfulness as an example, alkali metals release and transport in physical field of char combustion, as the main stage of coal combustion, was simulated. A 50 × 10−6 m single particle, and 150 1 × 10−3 m closely spaced particles combustion at 1273 K air environment were respectively calculated. Computational results revealed that continuous release of alkali metals depends heavily on the local high temperature from the stable combustion stage (approximately 85% of the whole combustion stage) which produces stable heat. And complicated movement of fluid medium has a great effect on the transport behavior of alkali metals in gas phase, especially the entrainment of vortexes, which results in the local enrichment of alkali metals in gas phase.

In Situ Imaging Facet-Induced Spatial Heterogeneity of Electrocatalytic Reaction Activity at the Subparticle Level via Electrochemiluminescence Microscopy.

Investigating catalytic behavior of heterogeneous catalysts, especially at the crystal facets level, is crucial for rational catalyst design in the energy and environmental fields. Here we demonstrate an efficient approach to in situ visualize and analyze the heterogeneity of electrocatalytic activity on different facets at the subparticle level via electrochemiluminescence (ECL) microscopy. ZnO crystals with various exposed facet proportions were synthesized, and the correlation between their electrocatalytic performance toward luminol analogue degradation and the exposed facets is established. It is clearly imaged that the ZnO (002) facet has superior catalytic performance compared to the ZnO (100) facet, which is supported by theoretical computation and electrochemical experiments as the facet-induced heterogeneity of the catalytic effect on oxygen reduction into the key reactant for ECL. Accordingly, the spatial heterogeneity of electrocatalytic activity at different facets on one particle is visualized for the first time. The realization of subparticle ECL imaging and kinetic analysis could provide a special approach to visualize facet-induced spatial heterogeneity of catalytic behavior and valuable information for the catalysis study and analysis.

Site-selective CO disproportionation mediated by localized surface plasmon resonance excited by electron beam.

Recent reports of hot-electron-induced dissociation of small molecules, such as hydrogen, demonstrate the potential application of plasmonic nanostructures for harvesting light to initiate catalytic reactions. Theories have assumed that plasmonic catalysis is mediated by the energy transfer from nanoparticles to adsorbed molecules during the dephasing of localized surface plasmon (LSP) modes optically excited on plasmonic nanoparticles. However, LSP-induced chemical processes have not been resolved at a sub-nanoparticle scale to identify the active sites responsible for the energy transfer. Here, we exploit the LSP resonance excited by electron beam on gold nanoparticles to drive CO disproportionation at room temperature in an environmental scanning transmission electron microscope. Using in situ electron energy-loss spectroscopy with a combination of density functional theory and electromagnetic boundary element method calculations, we show at the subparticle level that the active sites on gold nanoparticles are where preferred gas adsorption sites and the locations of maximum LSP electric field amplitude (resonance antinodes) superimpose. Our findings provide insight into plasmonic catalysis and will be valuable in designing plasmonic antennas for low-temperature catalytic processes.

Evolution of Local Structural Ordering and Chemical Distribution upon Delithiation of a Rock Salt–Structured Li1.3Ta0.3Mn0.4O2 Cathode

AbstractLithium‐rich disordered rock‐salt oxides have attracted great interest owing to their promising performance as Li‐ion battery cathodes. While experimental and theoretical efforts are critical in advancing this class of materials, a fundamental understanding of key property changes upon Li extraction is largely missing. In the present study, single‐crystal synthesis of a new disordered rock‐salt cathode material, Li1.3Ta0.3Mn0.4O2 (LTMO), and its use as a model compound to investigate Li concentration–driven evolution of local cationic ordering, charge compensation, and chemical distribution are reported. Through the combined use of 2D and 3D X‐ray nanotomography, it is shown that Li removal accompanied by oxygen oxidation is correlated with the development of morphological defects such as particle cracking. Chemical heterogeneity, quantified by subparticle level distribution of Mn valence state, is minimal during Mn redox, which drastically increases upon the formation of cracks during oxygen redox. Density functional theory and bond valence sum mismatch calculations reveal the presence of local short‐range ordering in the pristine oxide, which gradually disappears along with the extraction of Li. The study suggests that with cycling the transformation into true cation–disordered state can be expected, which likely impacts the voltage profile and obtainable energy density of the oxide cathodes.

Evaluation of the sub-surface morphology and composition of gunshot residue using focussed ion beam analysis

Recent work in the forensic analysis of Gunshot residues (GSR) has suggested that the sub-surface or internal composition and morphology of these residues be explored. A particular area of interest is in heavy metal free, or non-toxic ammunition, which are becoming more frequently encountered in the marketplace. As the formulation of the primer compound changes the conditions of the firearm discharge, there is the possibility that different primer formulations may result in the formation of different GSR particles with distinct internal morphologies and compositions. To that end, the internal morphology and composition of GSR particles may provide additional information that could be useful in the investigation of firearms crime.This research investigated the internal morphology of GSR originating from a variety of different ammunition products. Both traditional three-component primed ammunition, and a selection of heavy metal free and non-toxic alternatives were considered. Particles were identified using SEM–EDS, before being cross-sectioned using a focussed ion beam (FIB) instrument. The FIB-sectioned particles were then re-acquired and mapped using SEM–EDS, to assess both internal morphology and composition.Particles observed in this study presented distinct morphological and compositional features at the sub-particle level that may provide an indication of the primer formulation from which they originated. That said, further investigation of a variety of samples should be undertaken to verify the consistency of these features, or any deviations that may be observed based on primer type. However, these results indicate that there may be promise in obtaining additional detail from sub-particle morphology and composition.

Synthesis of 42-faceted bismuth vanadate microcrystals for enhanced photocatalytic activity

Bismuth vanadate (BiVO4) microcrystals enclosed with up to 42 low and high index facets were synthesized through truncation of BiVO4 octahedral crystals via a simple and highly reproducible hydrothermal method. The size and shape of the truncated BiVO4 crystals could be tuned by varying the acid concentration, reaction temperature and reaction period. Compared to the BiVO4 octahedral crystals without truncation, the 42-faceted ones showed an enhanced photocatalytic activity in the degradation of rhodamine B molecules due to the enhanced charge separation on the exposed low and high index facets. This was confirmed at sub-particle level by the photo-deposition of gold and manganese oxide nanoparticles selectively on hot electron and hole accumulated facets, respectively. Our results will provide a guideline for the synthesis of more efficient BiVO4 and many other multinary metal oxide-based photocatalysts. Moreover, the synthesized microcrystals are perfect materials for the study of photocatalytic property of BiVO4 at single and sub-particle level.

A Physical Explanation for Particle Spin

CONTEXT The spin of a particle is physically manifest in multiple phenomena. For quantum mechanics (QM), spin is an intrinsic property of a point particle, but an ontological explanation is lacking. In this paper we propose a physical explanation for spin at the sub-particle level, using a non-local hidden-variable (NLHV) theory. APPROACH Mechanisms for spin were inferred from the Cordus NLHV theory, specifically from theorised structures at the sub-particle level. RESULTS Physical geometry of the particle can explain spin phenomena: polarisation, Pauli exclusion principle (Einstein-Podolsky-Rosen paradox), excited states, and selective spin of neutrino species. A quantitative derivation is provided for electron spin g-factor g = 2, and a qualitative explanation for the anomalous component. IMPLICATIONS NLHV theory offers a candidate route to new physics at the sub-particle level. This also implies philosophically that physical realism may apply to physics at the deeper level below QM. ORIGINALITY The electron g-factor has been derived using sub-particle structures in NLHV theory, without using quantum theory. This is significant as the g-factor is otherwise considered uniquely predicted by QM. Explanations are provided for spin phenomena in terms of physical sub-structures to the particle.

Optical resonances of hollow nanocubes controlled with sub-particle structural morphologies

The structural details of nanoparticles at the sub-particle level are critical for our understanding of their functionalities and the basic mechanisms involved in their formation. In particular, the geometries of such features determine the particle's overall optical response. Hollow metallic nanoparticles (hollow-MNPs) that have cubic geometries, with varying morphologies on their walls and voids in their body, offer a platform to study the effects of such structural features on the properties of single nanoparticles and their ensemble. Here, we report the control over sub-particle pinholes and voids by modifying the dynamics of the galvanic reaction, and we connect these structures to the optical response of the hollow nanocubes. We observe that symmetry breakage in individual particles, caused by pinholes and voids, has a drastic effect on the plasmon-resonance peak positions in their UV-Vis-NIR spectra. Via electron microscopy imaging, statistical analyses, and electromagnetic simulations, we observe that enlargement in a pinhole's diameter and an increase in their number produce a redshift in the resonance absorption peak of the ensemble. Our results outline nanoparticle design avenues via sub-particle morphologies for several applications, including those operating in the biological window and those carrying chemical payloads in organisms.

Visualizing Facet-Dependent Hydrogenation Dynamics in Individual Palladium Nanoparticles.

Surface faceting in nanoparticles can profoundly impact the rate and selectivity of chemical transformations. However, the precise role of surface termination can be challenging to elucidate because many measurements are performed on ensembles of particles and do not have sufficient spatial resolution to observe reactions at the single and subparticle level. Here, we investigate solute intercalation in individual palladium hydride nanoparticles with distinct surface terminations. Using a combination of diffraction, electron energy loss spectroscopy, and dark-field contrast in an environmental transmission electron microscope (TEM), we compare the thermodynamics and directly visualize the kinetics of 40-70 nm {100}-terminated cubes and {111}-terminated octahedra with approximately 2 nm spatial resolution. Despite their distinct surface terminations, both particle morphologies nucleate the new phase at the tips of the particle. However, whereas the hydrogenated phase-front must rotate from [111] to [100] to propagate in cubes, the phase-front can propagate along the [100], [11̅0], and [111] directions in octahedra. Once the phase-front is established, the interface propagates linearly with time and is rate-limited by surface-to-subsurface diffusion and/or the atomic rearrangements needed to accommodate lattice strain. Following nucleation, both particle morphologies take approximately the same time to reach equilibrium, hydrogenating at similar pressures and without equilibrium phase coexistence. Our results highlight the importance of low-coordination number sites and strain, more so than surface faceting, in governing solute-driven reactions.

In situ Visualization of Plasmon-Mediated Chemical Transformations at the Single and Sub-particle Level

In situ Visualization of Plasmon-Mediated Chemical Transformations at the Single and Sub-particle Level