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Ferritins are highly conserved supramolecular protein nanostructures that play a key role in iron homeostasis. Thousands of iron atoms can be stored inside their hollow cavity as a hydrated ferric oxyhydroxide mineral. Although phosphate associates with the ferritin iron nanoparticles, the effect of physiological concentrations on the kinetics, structure, and reactivity of ferritin iron cores has not yet been explored. Here, the iron loading and mobilization kinetics were studied in the presence of 1-10 mM phosphate using homopolymer and heteropolymer ferritins having different H to L subunit ratios. In the absence of ferritin, phosphate enhances the rate of ferrous ion oxidation and forms large and soluble polymeric Fe(III)-phosphate species. In the presence of phosphate, Fe(II) oxidation and core formation in ferritin is significantly accelerated with oxidation rates several-fold higher than with phosphate alone. High-angle annular dark-field scanning transmission electron microscopy measurements revealed a strong phosphate effect on both the size and morphology of the iron mineral in H-rich (but not L-rich) ferritins. While iron nanoparticles in L-rich ferritins have spherical shape in the absence and presence of phosphate, iron nanoparticles in H-rich ferritins change from irregular shapes in the absence of phosphate to spherical particles in the presence of phosphate with larger size distribution and smaller particle size. In the presence of phosphate, the kinetics of iron-reductive mobilization from ferritin releases twice as much iron than in its absence. Altogether, our results demonstrate an important role for phosphate, and the ferritin H and L subunit composition toward the kinetics of iron oxidation and removal from ferritin, as well as the structure and reactivity of the iron mineral, and may have an important implication on ferritin iron management

We report the growth of epitaxial wurtzite AlScN thin films on Si (111) substrates with a wide range of Sc concentrations using ultra-high vacuum reactive sputtering.

The deluge of sensors and data generating devices has driven a paradigm shift in modern computing from arithmetic-logic centric to data centric processing. At a hardware level, this presents an urgent need to integrate dense, high-performance and low-power memory units with Si logic-processor units. However, data-heavy problems such as search and pattern matching also require paradigm changing innovations at the circuit and architecture level to enable compute in memory (CIM) operations. CIM architectures that combine data storage yet concurrently offer low-delay and small footprint are highly sought after but have not been realized. Here, we present Aluminum Scandium Nitride (AlScN) ferroelectric diode (FeD) memristor devices that allow for storage, search and neural network-based pattern recognition in a transistor-free architecture. Our devices can be directly integrated on top of Si processors in a scalable, back-end-of-line process. We leverage the field-programmability, non-volatility and non-linearity of FeDs to demonstrated circuit blocks that can support search operations in-situ memory with search delay times < 0.1 ns and a cell footprint < 0.12 µm2. In addition, we demonstrate matrix multiplication operations with 4-bit operation of the FeDs. Our results highlight FeDs as promising candidates for fast, efficient, and multifunctional CIM platforms.

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We report the characterization and applications of core-shell Cu-Ir nanocatalysts for fuel cells. Core-shell Cu-Ir particles with tunable thickness of Ir can be oxidized to remove the Cu core and obtain Ir shells. The thickness of the Ir shells determines the stability and optimization of the precious metals. We showed with in situ scanning transmission electron microscopy the remarkable stability of the Ir shells at elevated temperatures under oxidative and reductive environments. In situ microscopy and in situ X-ray absorption spectroscopy showed that traces of remaining copper could be detected in the Ir shells. Electrochemical measurements for oxygen reduction reaction and oxygen evolution reactions show promising activity and stability compared to a commercial catalyst. Thin Ir shells, with high surface area per gram of Ir, were more active but less stable than thicker shells. In contrast, thicker Ir shells were more stable and had excellent electrochemical properties in both aqueous and alkaline environments. Hence, Ir nanoshells appear as promising candidates to reduce the cost of catalysis while improving chemical performance in fuel cells.

Two-dimensional chalcogenide semiconductors have recently emerged as a host material for quantum emitters of single photons. While several reports on defect and strain-induced single photon emission from 2D chalcogenides exist, a bottom-up, lithography-free approach to producing a high density of emitters remains elusive. Further, the physical properties of quantum emission in the case of strained 2D semiconductors are far from being understood. Here, we demonstrate a bottom-up, scalable, and lithography-free approach to creating large areas of localized emitters with high density (~150 emitters/um2) in a WSe2 monolayer. We induce strain inside the WSe2 monolayer with high spatial density by conformally placing the WSe2 monolayer over a uniform array of Pt nanoparticles with a size of 10 nm. Cryogenic, time-resolved, and gate-tunable luminescence measurements combined with near-field luminescence spectroscopy suggest the formation of localized states in strained regions that emit single photons with a high spatial density. Our approach of using a metal nanoparticle array to generate a high density of strained quantum emitters opens a new path towards scalable, tunable, and versatile quantum light sources., Comment: 45 pages, 20 figures (5 main figures, 15 supporting figures)

The development of new catalyst materials for energy-efficient chemical synthesis is critical as over 80% of industrial processes rely on catalysts, with many of the most energy-intensive processes specifically using heterogeneous catalysis. Catalytic performance is a complex interplay of phenomena involving temperature, pressure, gas composition, surface composition, and structure over multiple length and time scales. In response to this complexity, the integrated approach to heterogeneous dilute alloy catalysis reviewed here brings together materials synthesis, mechanistic surface chemistry, reaction kinetics, in situ and operando characterization, and theoretical calculations in a coordinated effort to develop design principles to predict and improve catalytic selectivity. Dilute alloy catalysts─in which isolated atoms or small ensembles of the minority metal on the host metal lead to enhanced reactivity while retaining selectivity─are particularly promising as selective catalysts. Several dilute alloy materials using Au, Ag, and Cu as the majority host element, including more recently introduced support-free nanoporous metals and oxide-supported nanoparticle "raspberry colloid templated (RCT)" materials, are reviewed for selective oxidation and hydrogenation reactions. Progress in understanding how such dilute alloy catalysts can be used to enhance selectivity of key synthetic reactions is reviewed, including quantitative scaling from model studies to catalytic conditions. The dynamic evolution of catalyst structure and composition studied in surface science and catalytic conditions and their relationship to catalytic function are also discussed, followed by advanced characterization and theoretical modeling that have been developed to determine the distribution of minority metal atoms at or near the surface. The integrated approach demonstrates the success of bridging the divide between fundamental knowledge and design of catalytic processes in complex catalytic systems, which can accelerate the development of new and efficient catalytic processes.

The bottom-up approach has been widely used for large-scale synthesis of carbon nanodots (CNDs). However, the structure and origin of photoluminescence in CNDs synthesized by the bottom-up approach is still a subject of debate. Here, using a series of separation techniques like solvent extraction, column chromatography, gel electrophoresis and dialysis, we present three distinct fluorescent components in CNDs synthesized from pyrene, a well-known precursor molecule. The separated components have qualitative and quantitatively different absorption and emission spectral features including quantum yield (QY). Optical and vibrational spectroscopy techniques combined with electron microscopy indicate that a subtle balance between the extent of graphitization and the presence of molecular fluorophores determines the nature of fluorescence emission. A substantial difference in photons/cycle, single-particle fluorescence blinking, ON-OFF photoswitching strongly supports the distinct nature of the components.

We report a synthesis method for highly monodisperse Cu-Pt alloy nanospheres. Small and large Cu-Pt particles with a Cu:Pt ratio of 1:1 can be obtained through colloidal synthesis at 300 °C. The fresh particles have a Pt-rich surface and a Cu-rich core and can be converted into an intermetallic phase after annealing at 800 °C under H2. First, we demonstrated the stability of fresh particles under redox conditions at 400 °C, as the Pt-rich surface prevents substantial oxidation of Cu. Then, a combination of in situ scanning transmission electron microscopy, in situ X-ray absorption spectroscopy, and CO oxidation measurements of the intermetallic CuPt phase before and after redox treatments at 800 °C showed promising activity and stability for CO oxidation. Full oxidation of Cu was prevented after exposure to O2 at 800 °C. The activity and structure of the particles was only slightly changed after exposure to O2 at 800 °C and were recovered after re-reduction at 800 °C. Additionally, the intermetallic CuPt phase showed enhanced catalytic properties compared to the fresh particles with a Pt-rich surface or pure Pt particles of the same size. Thus, the incorporation of Pt with Cu does not lead to a rapid deactivation and degradation of the material, as seen with other bimetallic systems. This work provides a synthesis route to control the design of Cu-Pt nanostructures and underlines the promising properties of these alloys (intermetallic and non-intermetallic) for heterogeneous catalysis.

Supported Au-Pd nanoparticles are an excellent catalyst for the hydrogenation of alkynes, a crucial step for olefin polymerization. They have better selectivity at a high conversion rate for the hydrogenation of 1-hexyne compared to pure Pd. The size, shape, and composition of the supported catalyst ultimately determine their properties. In this work, a combined scanning transmission electron microscopy (STEM) and density functional theory (DFT) study is used to determine how Pd concentration affects the activity and selectivity of Au-Pd particles for the hydrogenation of acetylene. Atomic resolution microscopy shows the increased probability of Pd-rich islands within particles with increasing Pd concentration. DFT models of the surface concentrations of Pd as monomers, dimers, and trimers allowed insight into the origin of the high activity for ethylene production. Specifically, monomers of Pd were found to be more active than dimers and trimers. This provides insight into why Au1-xPdx particles with low Pd concentration have higher production rates, as Pd monomers are more statistically likely. These combined STEM and DFT results explain the existence of an optimum for Au:Pd ratio, where conversion per gram of Pd is maximized at a concentration of 4 % Pd.

Two-dimensional (2D) crystals have renewed opportunities in design and assembly of artificial lattices without the constraints of epitaxy. However, the lack of thickness control in exfoliated van der Waals (vdW) layers prevents realization of repeat units with high fidelity. Recent availability of uniform, wafer-scale samples permits engineering of both electronic and optical dispersions in stacks of disparate 2D layers with multiple repeating units. Here we present optical dispersion engineering in a superlattice structure comprising alternating layers of 2D excitonic chalcogenides and dielectric insulators. By carefully designing the unit cell parameters, we demonstrate greater than 90% narrow band absorption in less than 4 nm of active layer excitonic absorber medium at room temperature, concurrently with enhanced photoluminescence in square-centimetre samples. These superlattices show evidence of strong light–matter coupling and exciton–polariton formation with geometry-tuneable coupling constants. Our results demonstrate proof of concept structures with engineered optical properties and pave the way for a broad class of scalable, designer optical metamaterials from atomically thin layers. Square-centimetre scale, multilayer superlattice structures based on atomically thin two-dimensional chalcogenide monolayers enable the realization of excitonic metamaterials.

Dilute alloy catalysts have the potential to enhance selectivity and activity for large-scale reactions. Highly dilute Pd-in-Au nanoparticle alloys partially embedded in porous silica (“raspberry colloid templated” (RCT)-SiO2) prove to be robust and selective catalysts for oxidative coupling of methanol. Palladium concentrations in the bimetallic nanoparticles as low as ~3.4 at.% catalyze the production of methyl formate with a selectivity of ~95% at conversions of ~55%, whereas conversions are low (

Platinum is the primary catalyst for many chemical reactions in the field of heterogeneous catalysis. However, platinum is both expensive and rare. Therefore, it is advantageous to combine Pt with another metal to reduce cost while also enhancing stability. To that end, Pt is often combined with Co to form Co-Pt nanocrystals. However, dynamical restructuring effects that occur during reaction in Co-Pt ensembles can impact catalytic properties. In this study, model Co2Pt3 nanoparticles supported on carbon were characterized during a redox cycle with two in situ approaches, namely, X-ray absorption spectroscopy (XAS) and scanning transmission electron microscopy (STEM) using a multimodal microreactor. The sample was exposed to temperatures up to 500 °C under H2, and then to O2 at 300 °C. Irreversible segregation of Co in the Co2Pt3 particles was seen during redox cycling, and substantial changes of the oxidation state of Co were observed. After H2 treatment, a fraction of Co could not be fully reduced and incorporated into a mixed Co-Pt phase. Reoxidation of the sample increased Co segregation, and the segregated material had a different valence state than in the fresh, oxidized sample. This in situ study describes dynamical restructuring effects in CoPt nanocatalysts at the atomic scale that are crucial to understand in order to improve the design of catalysts used in major chemical processes.

Summary Solutions to many of the world's problems depend upon materials research and development. However, advanced materials can take decades to discover and decades more to fully deploy. Humans and robots have begun to partner to advance science and technology orders of magnitude faster than humans do today through the development and exploitation of closed-loop, autonomous experimentation systems. This review discusses the specific challenges and opportunities related to materials discovery and development that will emerge from this new paradigm. Our perspective incorporates input from stakeholders in academia, industry, government laboratories, and funding agencies. We outline the current status, barriers, and needed investments, culminating with a vision for the path forward. We intend the article to spark interest in this emerging research area and to motivate potential practitioners by illustrating early successes. We also aspire to encourage a creative reimagining of the next generation of materials science infrastructure. To this end, we frame future investments in materials science and technology, hardware and software infrastructure, artificial intelligence and autonomy methods, and critical workforce development for autonomous research.

Plastics waste has become a major environmental threat, with polyethylene being one of the most produced and hardest to recycle plastics. Hydrogenolysis is potentially the most viable catalytic technology for recycling. Ruthenium (Ru) is one of the most active hydrogenolysis catalysts but yields too much methane. Here we introduce ruthenium supported on tungstated zirconia (Ru-WZr) for hydrogenolysis of low-density polyethylene (LDPE). We show that the Ru-WZr catalysts suppress methane formation and produce a product distribution in the diesel and wax/lubricant base-oil range unattainable by Ru-Zr and other Ru-supported catalysts. Importantly, the enhanced performance is showcased for real-world, single-use LDPE consumables. Reactivity studies combined with characterization and density functional theory calculations reveal that highly dispersed (WO x )n clusters store H as surface hydroxyls by spillover. We correlate this hydrogen storage mechanism with hydrogenation and desorption of long alkyl intermediates that would otherwise undergo further C-C scission to produce methane.

The physical properties of in vitro iron-reconstituted and genetically engineered human heteropolymer ferritins were investigated.

Liquid-cell scanning/transmission electron microscopy (S/TEM) has impacted our understanding of multiple areas of science, most notably nanostructure nucleation and growth and electrochemistry and corrosion. In the case of electrochemistry, the incorporation of electrodes requires the use of silicon nitride membranes to confine the liquid. The combined thickness of the liquid layer and the confining membranes prevents routine atomic-resolution characterization. Here, we show that by performing electrochemical water splitting in situ to generate a gas bubble, we can reduce the thickness of the liquid to a film approximately 30 nm thick that remains covering the sample. The reduced thickness of the liquid allows the acquisition of atomic-scale S/TEM images with chemical and valence analysis through electron energy loss spectroscopy (EELS) and structural analysis through selected area electron diffraction (SAED). This contrasts with a specimen cell entirely filled with liquid, where the broad plasmon peak from the liquid obscures the EELS signal from the sample and induces beam incoherence that impedes SAED analysis. The gas bubble generation is fully reversible, which allows alternating between a full cell and thin-film condition to obtain optimal experimental and analytical conditions, respectively. The methodology developed here can be applied to other scientific techniques, such as X-ray scattering, Raman spectroscopy, and X-ray photoelectron spectroscopy, allowing for a multi-modal, nanoscale understanding of solid-state samples in liquid media.