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Copper (Cu) is a catalyst broadly used in industry for hydrogenation of carbon dioxide, which has broad implications for environmental sustainability. An accurate understanding of the degeneration behavior of Cu catalysts under operando conditions is critical for uncovering the failure mechanism of catalysts and designing novel ones with optimized performance. Despite the widespread use of these materials, their failure mechanisms are not well understood because conventional characterization techniques lack the necessary time and spatial resolution to capture these complex behaviors. In order to overcome these challenges, we carried out transmission electron microscopy (TEM) with a specialized in situ gas environmental holder, which allows us to unravel the dynamic behavior of the Cu nanowires (NWs) in operando. The failure process of these nanoscale Cu catalysts under CO2 atmosphere were tracked and further rationalized based on our numerical modeling using phase-field methods.

Nonplanar GaN p–n junctions formed by selective area regrowth were analyzed using pulsed laser atom probe tomography. Dilute Al marker layers were used to map the evolution of the p-GaN growth inte...

Dental enamel is a principal component of teeth.[1] It has evolved to bear large masticatory forces, resist mechanical fatigue, and withstand wear over decades of use.[2] Functional impairment or loss, as a consequence of developmental defects or tooth decay (caries), has a dramatic impact on health and quality of life, with significant costs to society.[3] While the last decade has seen great progress in our understanding of enamel formation (amelogenesis) and the functional properties of mature enamel, attempts to repair enamel lesions or synthesize enamel in vitro have had limited success.[4–6] This is partly due to the highly hierarchical structure of enamel and the additional complexities arising from chemical gradients that we are only beginning to understand.[7–9] Herein, we show, using atomic-scale quantitative imaging and correlative spectroscopies, that the nanoscale crystallites of hydroxylapatite (OHAp; Ca5(PO4)3(OH)) that are the fundamental building blocks of enamel are comprised of two nanometric layers enriched in magnesium flanking a core rich in sodium, fluoride, and carbonate ions; this sandwich core is surrounded by a shell with lower concentration of substitutional defects. A mechanical model based on DFT calculations and X-ray diffraction data predicts that significant residual stresses arise as a consequence of the chemical gradients, in agreement with preferential dissolution of the crystallite core. Further, stresses may impact the mechanical resilience of enamel. Finally, the two additional layers of hierarchy suggest a new model for biological control over crystal growth during amelogenesis and have implications for the preservation of biomarkers during tooth development.

Solvated soft matter, both biological and synthetic, can now be imaged in liquids using liquid-cell transmission electron microscopy (LCTEM). However, such systems are usually composed solely of or...

Nanoscale tailoring of catalytic materials and Li-battery alternatives has elevated the importance of

Significance Nacre exhibits outstanding mechanical performance, which results from coordinated deformation mechanisms synergistically working in characteristic microstructures at multiple length scales. A comprehensive understanding of crystal defects within aragonite is critical for discussing the deformation behavior of nacre on microstructure at the nanoscale through atomic scale. By integrating aberration-corrected transmission electron microscopy, crystallographic analysis, and theoretical calculations, we reveal various crystal defects within aragonite at atomic scale and discuss their potential effects on deformation. Our work will serve as cornerstones for modeling analysis and in-depth discussions on nanoscale deformation mechanisms within nacre. Additionally, these atomic-scale insights will benefit theoretical evaluation of the environmental effect on defect formation, enabling defect control in synthetic aragonite and designing of stronger and tougher bioengineering materials.

The weak van der Waals bonding between monolayers in layered materials enables fabrication of heterostructures without the constraints of conventional heteroepitaxy. Although many novel heterostructures have been created by mechanical exfoliation and stacking, the direct growth of 2D chalcogenide heterostructures creates new opportunities for large-scale integration. This paper describes the epitaxial growth of layered, p-type tin sulfide (SnS) on n-type molybdenum disulfide (MoS2) by pulsed metal–organic chemical vapor deposition at 180 °C. The influence of precursor pulse and purge times on film morphology establishes growth conditions that favor layer-by-layer growth of SnS, which is critical for materials with layer-dependent electronic properties. Kelvin probe force microscopy measurements determine a built-in potential as high as 0.95 eV, and under illumination a surface photovoltage is generated, consistent with the expected Type-II band alignment for a multilayer SnS/MoS2 heterostructure. The bott...

Engineering structures that bridge between elements with disparate mechanical properties are a significant challenge. Organisms reap synergy by creating complex shapes that are intricately graded. For instance, the wear-resistant cusp of the chiton radula tooth works in concert with progressively softer microarchitectural units as the mollusk grazes on and erodes rock. Herein, we focus on the stylus that connects the ultrahard and stiff tooth head to the flexible radula membrane. Using techniques that are especially suited to probe the rich chemistry of iron at high spatial resolution, in particular synchrotron Mossbauer and X-ray absorption spectroscopy, we find that the upper stylus of Cryptochiton stelleri is in fact a mineralized tissue. Remarkably, the inorganic phase is nano disperse santabarbaraite, an amorphous ferric hydroxyphosphate that has not been observed as a biomineral. The presence of two persistent polyamorphic phases, amorphous ferric phosphate and santabarbaraite, in close proximity, is a unique aspect that demonstrates the level of control over phase transformations in C. stelleri dentition. The stylus is a highly graded material in that its mineral content and mechanical properties vary by a factor of 3 to 8 over distances of a few hundred micrometers, seamlessly bridging between the soft radula and the hard tooth head. The use of amorphous phases that are low in iron and high in water content may be key to increasing the specific strength of the stylus. Finally, we show that we can distill these insights into design criteria for inks for additive manufacturing of highly tunable chitosan-based composites.

Significance The ability to control light has driven advances from optical microscopy to fast communication. Metal nanoparticles can trap light at the nanoscale in the form of surface plasmons; these localized excitations are important in sensing and designing miniaturized photonic devices. Although very narrow plasmon linewidths are desirable, they tend to be broad because of limitations in fabrication methods. Here, we describe how to achieve ultranarrow plasmon resonances with linewidths that approach the calculated limit by thermally annealing 2D lattices of metal nanoparticles. Our results indicate that exquisite control over structural features of nanoparticles can dramatically improve their plasmonic response and open promising strategies for manipulating light–matter interactions at the nanoscale.

Made available in DSpace on 2020-12-12T01:20:36Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-08-01 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) W. M. Keck Foundation Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Materials Research Science and Engineering Center, Harvard University In this study, β-tantalum oxide (β-Ta2O5) thin film was synthesized via magnetron sputtering to improve the surface properties, cytocompatibility and electrochemical stability of titanium. X-ray diffraction analysis confirmed a crystalline orthorhombic phase of Ta2O5 film on the β-Ta2O5 experimental surface. A granular structure with a complex and hierarchical nature was demonstrated by atomic force microscopy. Ta2O5-treated surfaces exhibited greater roughness and hydrophilicity compared with untreated titanium discs (control). Enhanced electrochemical stability in simulated body fluid (pH 7.4) was noted for Ta2O5-treated surfaces wherein higher values of charge transfer resistance, nobler corrosion potential, and lower capacitance, corrosion current density, and corrosion rate values were observed vs untreated control. Real-time monitoring of albumin and fibrinogen proteins adsorption by an electrochemical quartz crystal microbalance disclosed similar protein interactions for control and Ta2O5-treated discs, with higher fibrinogen adsorption rates for Ta2O5-treated surfaces. Cell culture assays (MC3T3-E1 cells) demonstrated that Ta2O5-treated discs featured greater in vitro mineral nodule formation, normal cell morphology and spreading, and increased mRNA levels of runt-related transcription factor 2 (Runx-2), osteocalcin (Ocn), and collagen-1 (Col-1). Therefore, it can be concluded that β-Ta2O5 thin films may be considered a promising strategy to trigger superior long-term stability and biological properties of titanium implants. University of Campinas (UNICAMP) Piracicaba Dental School Department of Prosthodontics and Periodontics, Av. Limeira, 901 Institute of Biomaterials Tribocorrosion and Nanomedicine (IBTN) São Paulo State University (UNESP) School of Sciences Department of Physics, Av. Eng. Luís Edmundo C. Coube, 14-01 University of Campinas (UNICAMP) Piracicaba Dental School Department of Physiological Science, Av. Limeira, 901 University of Illinois at Chicago College of Dentistry Department of Restorative Dentistry, 801 S. Paulina Department of Materials Science and Engineering Northwestern University NUANCE Center Northwestern University São Paulo State University (UNESP) School of Sciences Department of Physics, Av. Eng. Luís Edmundo C. Coube, 14-01 FAPESP: 2016/07269-3 FAPESP: 2016/11470-6 FAPESP: 2017/18916-2 Materials Research Science and Engineering Center, Harvard University: NSF DMR-1720139

Solvated soft matter, both biological and synthetic, can now be imaged in liquids using liquid-cell transmission electron microscopy (LCTEM). However, such systems are usually composed solely of organic molecules (low

The direct observation of amorphous barium carbonate (ABC), which transforms into a previously unknown barium carbonate hydrate (herewith named gortatowskite) within a few hundred milliseconds of formation, is described. In situ X-ray scattering, cryo-, and low-dose electron microscopy were used to capture the transformation of nanoparticulate ABC into gortatowskite crystals, highly anisotropic sheets that are up to 1 μm in width, yet only about 10 nm in thickness. Recrystallization of gortatowskite to witherite starts within 30 seconds. We describe a bulk synthesis and report a first assessment of the composition, vibrational spectra, and structure of gortatowskite. Our findings indicate that transient amorphous and crystalline precursors can play a role in aqueous precipitation pathways that may often be overlooked owing to their extremely short lifetimes and small dimensions. However, such transient precursors may be integral to the formation of more stable phases.

The weak van der Waals bonding between monolayers in layered materials enables fabrication of heterostructures without the constraints of conventional heteroepitaxy. Although many novel heterostructures have been created by mechanical exfoliation and stacking, the direct growth of 2D chalcogenide heterostructures creates new opportunities for large-scale integration. This paper describes the epitaxial growth of layered

The characteristic shapes, structures and properties of biominerals arise from their interplay with a macromolecular matrix1, 2. The developing mineral interacts with acidic macromolecules, which are either dissolved in the crystallization medium or associated with insoluble matrix polymers3, that affect growth habits and phase selection or completely inhibit precipitation in solution4, 5, 6. Yet little is known about the role of matrix-immobilized acidic macromolecules in directing mineralization. Here, by using in situ liquid-phase electron microscopy to visualize the nucleation and growth of ¿CaCO3 in a matrix of polystyrene sulphonate (PSS), we show that the binding of calcium ions to form Ca–PSS globules is a key step in the formation of metastable amorphous ¿calcium carbonate (ACC), an important precursor phase in many biomineralization systems7. Our findings demonstrate that ion binding can play a significant role in directing nucleation, independently of any control over the free-energy barrier to nucleation.

Understanding and controlling nucleation is important for many crystallization applications. Calcium carbonate (CaCO3) is often used as a model system to investigate nucleation mechanisms. Despite its great importance in geology, biology, and many industrial applications, CaCO3 nucleation is still a topic of intense discussion, with new pathways for its growth from ions in solution proposed in recent years. These new pathways include the so-called nonclassical nucleation mechanism via the assembly of thermodynamically stable prenucleation clusters, as well as the formation of a dense liquid precursor phase via liquid–liquid phase separation. Here, we present results from a combined experimental and computational investigation on the precipitation of CaCO3 in dilute aqueous solutions. We propose that a dense liquid phase (containing 4–7 H2O per CaCO3 unit) forms in supersaturated solutions through the association of ions and ion pairs without significant participation of larger ion clusters. This liquid acts as the precursor for the formation of solid CaCO3 in the form of vaterite, which grows via a net transfer of ions from solution according to z Ca2+ + z CO3 2− → z CaCO3. The results show that all steps in this process can be explained according to classical concepts of crystal nucleation and growth, and that long-standing physical concepts of nucleation can describe multistep, multiphase growth mechanisms.

This article describes an experimentally versatile strategy for producing inorganic/organic nanocomposites, with control over the microstructure at the nano- and mesoscales. Taking inspiration from biominerals, CaCO3 is coprecipitated with anionic diblock copolymer worms or vesicles to produce single crystals of calcite occluding a high density of the organic component. This approach can also be extended to generate complex structures in which the crystals are internally patterned with nano-objects of differing morphologies. Extensive characterization of the nanocomposite crystals using high resolution synchrotron powder X-ray diffraction and vibrational spectroscopy demonstrates how the occlusions affect the short and long-range order of the crystal lattice. By comparison with nanocomposite crystals containing latex particles and copolymer micelles, it is shown that the effect of these occlusions on the crystal lattice is dominated by the interface between the inorganic crystal and the organic nano-objects, rather than the occlusion size. This is supported by in situ atomic force microscopy studies of worm occlusion in calcite, which reveal flattening of the copolymer worms on the crystal surface, followed by burial and void formation. Finally, the mechanical properties of the nanocomposite crystals are determined using nanoindentation techniques, which reveal that they have hardnesses approaching those of biogenic calcites.