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At least 595 records · Page 33

Inline Rolling Shear Alignment: Deposition and Long-Range Order of Block Polymer Templates in a Fast, Single-Step Process

We report the first demonstration of a rapid, single-step technique to align block polymer, thin-film nanostructures that is amenable to continuous speeds ≥10 mm/s. This method, termed Inline Rolling Shear Alignment (IRSA), uses an elastomeric roller coupled with an electric hysteresis brake to shear films before the casting solvent fully evaporates, and it can enable high throughput, large-area manufacturing of patterns such as nanowire templates. IRSA is adaptable to various polymer systems including diblock and triblock polymers, and a post-shear annealing step can yield high-quality nanostructures with orientation parameters >0.99 and defect densities as low as 5 defect-pairs/μm 2 . To demonstrate the effectiveness of IRSA, platinum nanowires were produced from this rapid deposition and alignment approach using poly(styrene-b-2-vinylpyridine), followed by open-air, atmospheric-pressure plasma etching. Furthermore, this integrated concept, with 50x faster operation than existing processes, could be leveraged for cost-effective manufacturing of macroscopically aligned nanostructures in roll-to-roll systems.

36 MATERIALS SCIENCE↗

Ultrathin Plasmonic Tungsten Oxide Quantum Wells with Controllable Free Carrier Densities

Localized surface plasmon resonances (LSPR) of nanostructures can be tuned by controlling their morphology, local dielectric environment, and free carrier concentration. We report the colloidal synthesis of an ~3 tungsten–oxygen (W-O) layer thick (~1 nm), two-dimensional (2D) WO 3-x nanoplatelets (NPLs) (x ≈ 0.55–1.03), which display tunable near-infrared LSPR properties and additionally high free electron density (N e ) that arises predominantly from the large shape factor of 2D NPLs. Importantly, the W to O composition ratios inferred from their LSPR measurements show much higher percentage of oxygen vacancies than those determined by X-ray diffraction analysis, suggesting that the aspect ratio of ultrathin WO 3-x NPLs is the key to producing an unprecedentedly large Ne, although synthesis temperature is also an independent factor. We find that NPL formation is kinetically controlled, whereas thermodynamic parameter manipulation leads to N e values as high as 4.13 × 10 22 cm –3 , which is close to that of plasmonic noble metals, and thus our oxide-based nanostructures can be considered as quasi-metallic. The unique structural properties of 2D nanomaterials along with the high N e of WO 3-x NPLs provide an attractive alternative to plasmonic noble metal nanostructures for various plasmon-driven energy conversions and design of photochromic nanodevices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Orienting Strained Interfaces designed to Direct Energy Flow (Final Technical Report)

This proposal aims to establish a transformative paradigm for oxide heterostructures with an exceptionally large number of interfaces designed to direct energy flow through controlled interface orientation, enabling fast ion transport. A primary focus is on unveiling the key role of interfacial strain in oxygen ion migration at low temperatures. The central challenge is to create, understand, utilize self-assembled vertical heteroepitaxial nanostructures with the goal of obtaining and understanding fast ion transport properties by modulating interfacial strain. The specific objectives are: (1) to synthesize multilayer thin films and vertical heteroepitaxial nanostructures with fluorite Gd-doped CeO 2 (GDC) and bixbyite RE 2 O 3 (RE = Y and Sm), (2) to evaluate the interfacial strain states under various temperatures and ambient conditions, (3) to understand the effect of interfacial strain on ionic conductivity of the proposed nanostructures, (4) to understand the three-dimensional (3D) atomic structure of the proposed material design and interface phenomena at the atomic scale.

36 MATERIALS SCIENCE↗

Advanced Electron Microscopy of Nanophased Synthetic Polymers and Soft Complexes for Energy and Medicine Applications

After decades of developments, electron microscopy has become a powerful and irreplaceable tool in understanding the ionic, electrical, mechanical, chemical, and other functional performances of next-generation polymers and soft complexes. The recent progress in electron microscopy of nanostructured polymers and soft assemblies is important for applications in many different fields, including, but not limited to, mesoporous and nanoporous materials, absorbents, membranes, solid electrolytes, battery electrodes, ion- and electron-transporting materials, organic semiconductors, soft robotics, optoelectronic devices, biomass, soft magnetic materials, and pharmaceutical drug design. For synthetic polymers and soft complexes, there are four main characteristics that differentiate them from their inorganic or biomacromolecular counterparts in electron microscopy studies: (1) lower contrast, (2) abundance of light elements, (3) polydispersity or nanomorphological variations, and (4) large changes induced by electron beams. Since 2011, the Center for Nanophase Materials Sciences (CNMS) at Oak Ridge National Laboratory has been working with numerous facility users on nanostructured polymer composites, block copolymers, polymer brushes, conjugated molecules, organic–inorganic hybrid nanomaterials, organic–inorganic interfaces, organic crystals, and other soft complexes. This review crystalizes some of the essential challenges, successes, failures, and techniques during the process in the past ten years. It also presents some outlooks and future expectations on the basis of these works at the intersection of electron microscopy, soft matter, and artificial intelligence. Machine learning is expected to automate and facilitate image processing and information extraction of polymer and soft hybrid nanostructures in aspects such as dose-controlled imaging and structure analysis.

36 MATERIALS SCIENCE↗

Polymer Solar Cells with 18.74% Efficiency: From Bulk Heterojunction to Interdigitated Bulk Heterojunction

The most popular approach to fabricating organic solar cells (OSCs) is solution processing a mixture of donor (D) and acceptor (A) materials into an active layer with a bulk heterojunction (BHJ) nanostructure. In this work, it is demonstrated that the interdigitated heterojunction (IHJ) is a more suitable nanostructure of the active layer for high-performance OSCs whereas it is a long standing challenge to realize well-defined IHJ structures. Here, a facile and versatile sequential solution processing method is developed to produce an IHJ nanostructure with power conversion efficiency reaching 18.74% (18.10% for BHJ the counterpart) by fabricating a donor film with nanopores created by a wax additive, sequentially casting the acceptor on top of infiltrating the nanopores. Compared to the BHJ, the IHJ structure with an interpillar distance within the exciton diffusion length can afford a large bulk D/A interface for efficient exciton dissociation with a minimized charge recombination while free electrons and holes can transport to the respective electrodes through more straightforward pathways, thus enhance performance. Furthermore, the D or A phase in the IHJ device contacts with only one electrode, which can prevent shunting between the anode and cathode and facilitate the industrial mass production of OSCs.

36 MATERIALS SCIENCE↗

Kinetics and evolution of solid-state metal dealloying in thin films with multimodal analysis

Thin-film solid-state metal dealloying (thin-film SSMD) is an emerging technique that uses self-organization to design nanostructured thin films. The resulting 3D bicontinuous nanostructures are promising for a wide range of applications, such as catalysis and energy storage. In this work, we prepared thin films by SSMD using Ti-Cu as the parent alloy and Mg as the solvent. Using a multimodal approach, we combined synchrotron X-ray spectroscopy, diffraction, and high-resolution electron-based spectroscopy and imaging to study their morphological, structural, and chemical evolution. The processing-structure relationship was analyzed as a function of parent alloy composition and dealloying temperature and time. Morphological transitions from globular, to lamellar, to bicontinuous structures, in conjunction with a ligament size evolution, were identified as functions of the parent alloy composition. The dealloying rate increased with increasing concentration of interdiffusing elements (dissolving component) in the parent alloy. The parting limit, a dealloying compositional threshold, was systematically analyzed and determined to be 30%–40%. The order of crystalline phase formation is CuMg 2 , Cu 2 Mg, and Ti; the Ti phase first shows self-reorganization during dealloying, separate from the crystallization process. The coarsening in thin-film SSMD was identified and not entirely self-similar; in addition to the increase of ligament size over time, the formation of larger globular ligaments were also observed. This work furthers our fundamental understanding of thin-film SSMD and nanostructured thin-film design, where the thermodynamic and kinetic effects differ from the bulk counterparts. The fact that dealloying and diffusion outpaces the crystallization and new phase formation also offers opportunities to utilize thin-film SSMD in certain alloy systems in which deleterious intermetallic phases need to be suppressed, that may not be possible in the bulk geometry.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

Novel effects of grain size and ion implantation on grain boundary segregation in ion irradiated austenitic steel

Nuclear reactor environments are extreme in nature due to the combination of exposure to corrosive coolant, mechanical stresses, and neutron irradiation damage. This combination of environments can lead to irradiation induced/assisted precipitation, segregation, and embrittlement coupled with enhanced creep and stress corrosion cracking. While nanostructured materials are of interest in a variety of applications due to their unique properties including high mechanical strength, for nuclear applications nanostructured materials have the added benefit of irradiation resistance due to the high volume density of sinks for irradiation-induced defects. In this study, we show unique radiation-induced segregation (RIS) behavior in nanocrystalline 304 stainless steel (SS304). Typical RIS in austenitic steels includes Ni enrichment and Cr depletion within the grain boundaries. In nanostructured SS304 this RIS is reduced. Furthermore, interestingly, some grain boundaries in the nanocrystalline SS304 in this study were found to be enriched in Cr after Fe 2+ ion irradiation at 500 °C up to 50 displacements per atom (dpa). To understand this unique observation, lattice-based atomic kinetic Monte Carlo simulations were performed to investigate the effects of grain size, thermal segregation, as well as injected interstitials (introduced as Fe self-ions). The results indicate that the Cr enrichment at grain boundaries may be caused by combined effects of grain size, self-ion injection and preferential Cr diffusion via the interstitial mechanism. In conclusion, the findings also suggest a possible difference in RIS between ion and neutron irradiations.

36 MATERIALS SCIENCE↗

Atomistic modeling of tensile deformation and fracture of carbon fibers: Nanoscale stress redistribution, effect of local structural characteristics and nanovoids

The mechanisms of tensile deformation and fracture of carbon fibers are investigated in large-scale molecular dynamics simulations. The simulations performed for computational samples with different structural characteristics enable analysis of the structural sensitivity of the mechanical properties. It is found that the carbon fiber nanostructure can be represented by a fine (nanoscale) mixture of stiff and soft regions. Despite the nanoscale structural heterogeneity of the computational fibers, their fracture strain and tensile strength exceed the experimental values by almost an order of magnitude. Here, this observation is explained by the ability of the carbon fiber nanostructure, largely consisting of curved and folded layers of turbostratic carbon, to exhibit continuous nanoscale load redistribution during the deformation. The transient, fluid nature of a percolating cluster of stress-holding structural elements prevents stress localization at the early stage of the deformation and enables the fiber nanostructure to adapt to the increasing load. Overall, the results of the simulations suggest that the design of advanced carbon fiber manufacturing and post-processing methods focused on the elimination of critical mesoscopic structural defects (internal voids, foreign inclusions, and surface flaws) can yield a substantial increase in the strength and fracture strain of carbon fibers.

36 MATERIALS SCIENCE↗

Thermoelectric power generation in the core of a nuclear reactor

Thermoelectric energy converters offer a promising solution to generate electrical power using heat in the nuclear reactor core. Despite significant improvements in thermoelectric efficiency of nanostructured materials, the performance of these advanced materials has yet to be demonstrated in the harsh radiation environment of a reactor core. Herein, we demonstrate a thermoelectric generator (TEG) made from nanostructured bulk half-Heusler (HH) materials generating stable electrical power density > 1140 W/m 2 after 30 days in the MIT Nuclear Research Reactor under an unprecedented fast-neutron (>1 MeV) fluence of 1.5 × 10 20 n/cm 2 . Despite an initial degradation due to irradiation damage when operating under relatively low temperatures, our TEG showed a 20-fold increase in power output when operating under high temperature due to in-situ annealing and resulting thermoelectric property recovery. First-principles modeling indicates that a chemically disordered metallic phase was formed under irradiation at lower temperatures, resulting in a drastic degradation in thermoelectric properties, while at sufficiently high temperatures the system returned to the initial chemically ordered HH phase and the thermoelectric properties recovered. Transmission electron microscopy and electron diffraction demonstrated that the chemically disordered phase was formed upon ion irradiation, confirming the prediction from first-principles simulations. Furthermore, the results suggest that with proper control over the TEG operating temperatures, the nanostructured bulk TEGs could produce stable electrical power and operate indefinitely in the core of a nuclear reactor.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

Understanding the morphology and chemical activity of model ZrO x /Au (111) catalysts for CO 2 hydrogenation

In this study, the growth of ZrO x on Au (111) was investigated using scanning tunneling microscopy (STM) and synchrotron-based ambient pressure X-ray photoelectron spectroscopy (AP-XPS). Nanostructures of ZrO x (x= 1,2) at the sub-monolayer (≤ 0.3 ML) level were prepared by vapor depositing Zr metal onto Au (111) followed by oxidation with O 2 or CO 2 . At low coverages of the admetal (< 0.05 ML), the formed ZrO x nanostructures were dispersed randomly on the terraces and steps of the Au(111) substrate. Strong oxide-metal interactions prevented the formation of islands of zirconia. The ZrO x nanostructures displayed a reactivity towards CO 2 and H 2 not seen for bulk zirconia. C 1 s AP-XPS results indicated that CO 2 molecules adsorbed on Zr/ZrO x /Au(111) surfaces could undergo partial decomposition on Zr (CO 2 , gas → CO gas + O ads ), or react with oxygen sites from ZrO x to yield carbonates (Zr-CO 3, ads ). Further, after exposing ZrO 2 /Au (111) surfaces to 1:3 mixtures of CO 2 :H 2 , the formation of HCOO, CO 3 , and CH 3 O was detected in AP-XP spectra. These chemical species decomposed at temperatures in the range of 400-600 K, making them possible reaction intermediates for methanol synthesis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Access to Advanced Functional Materials through Postmodification of Biomimetic Assemblies via Click Chemistry

The design, synthesis, and fabrication of functional nanomaterials with specific properties remain a long-standing goal for many scientific fields. The self-assembly of sequence-defined biomimetic synthetic polymers presents a fundamental strategy to explore the chemical space beyond biological systems to create advanced nanomaterials. Moreover, subsequent chemical modification of existing nanostructures is a unique approach for accessing increasingly complex nanostructures and introducing functionalities. Of these modifications, covalent conjugation chemistries, such as the click reactions, have been the cornerstone for chemists and materials scientists. Herein, we highlight some recent advances that have successfully employed click chemistries for the postmodification of assembled one-dimensional (1D) and two-dimensional (2D) nanostructures to achieve applications in molecular recognition, mineralization, and optoelectronics. Specifically, biomimetic nanomaterials assembled from sequence-defined macromolecules such as peptides and peptoids are described.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Dislocation-Assisted Quasi-Two-Dimensional Semiconducting Nanochannels Embedded in Perovskite Thin Films

Defect engineering in perovskite thin films has attracted extensive attention recently due to the films’ atomic-scale modification, allowing for remarkable flexibility to design novel nanostructures for next generation nanodevices. However, the defect-assisted three-dimensional nanostructures in thin film matrices usually has large misfit strain and thus causes unstable thin film structures. In contrast, defect-assisted one- or two-dimensional nanostructures embedded in thin films can sustain large misfit strains without relaxation, which make them suitable for defect engineering in perovskite thin films. Here, we reported the fabrication and characterization of edge-type misfit dislocation-assisted two-dimensional BiMnO x nanochannels embedded in SrTiO 3 /La 0.7 Sr 0.3 MnO 3 /TbScO 3 perovskite thin films. The nanochannels are epitaxially grown from the surrounding films without noticeable misfit strain. Diode-like current rectification was spatially observed at nanochannels due to the formation of Schottky junctions between BiMnO x nanochannels and conducting La 0.7 Sr 0.3 MnO 3 thin films. Such atomically scaled heterostructures constitute more flexible ultimate functional units for nanoscale electronic devices.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

Compressibility Studies of Copper Selenides Obtained by Cation Exchange Reaction Revealing the New CsCl Phase

In this study, we conducted a high-pressure investigation of Cu 2-x Se nanostructures with pyramid- and plate-like morphologies, created through cation exchange from zinc-blende CdSe nanocrystals and wurtzite CdSe nanoplatelets respectively. Using a diamond anvil cell setup at the APS synchrotron, we observed the phase transitions in the Cu 2-x Se nanostructures up to 40 GPa, identifying a novel CsCl-type lattice with Pm-3m symmetry above 4 GPa. This CsCl-type structure, previously unreported in copper selenides, was partially retained after decompression. Our results indicate that the initial crystalline structure of CdSe does not affect the stability of Cu 2-x Se nanostructures formed via cation exchange. Both morphologies of Cu 2-x Se sintered under compression, potentially contributing to the stabilization of the high-pressure phase through interfacial defects. These findings are significant for discovering new phases with potential applications in future technologies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Revealing Progressive Degradation of Cobalt Oxide Nanoparticles During Thermochemical Redox Cycling via Operando STEM-EELS

Metal oxides are promising materials for long-duration thermochemical energy storage. Efforts to characterize their reaction kinetics, conversion rate, and morphological evolution during thermochemical cycling have largely focused on bulk and microscale measurements. However, the design of nanostructured metal oxides could improve the reaction reversibility and kinetics, warranting the development of platforms to investigate how these materials behave at the nanoscale. Here, we demonstrate the use of correlative, time-resolved electron energy loss spectroscopy and imaging in an environmental transmission electron microscope for studying the thermochemical cyclability of cobalt oxide nanoparticles with high spatial and temporal resolution. The spectroscopic data reveal a striking decrease in reaction kinetics after the first cycle, resulting from sintering-driven nanostructural densification. Comparison between cycling in humid and dry air shows that atmospheric conditions can modulate reaction transition temperatures but have limited effects on sintering over multiple cycles, suggesting long-term durability will instead rely on synthetic and/or nanostructural modifications.

25 ENERGY STORAGE↗

Nano-Ceramic Cathodes via Co-sputtering of Gd–Ce Alloy and Lanthanum Strontium Cobaltite for Low-Temperature Thin-Film Solid Oxide Fuel Cells

We report the electrochemical performance and structural characteristics of porous nanostructured ceramic cathodes for thin-film solid oxide fuel cells (TF-SOFCs) based on yttria-stabilized zirconia (YSZ) electrolytes. The nanostructured cathode is obtained through magnetron co-sputtering of gadolinium–cerium (Gd–Ce) alloy and lanthanum strontium cobaltite perovskite targets. The resultant nanostructure and composition of the ceramic cathode are controlled by adjusting the co-sputtering conditions. The peak power densities in our fabricated TF-SOFCs are the highest reported values for YSZ-based electrolyte SOFCs, showing 0.14, 0.48, 1.21, 2.56, and 3.01 W/cm2 at 450, 500, 550, 600, and 650 °C, respectively, operating under air and pure hydrogen fuel. The results show that the porosity and composition of the cathode greatly affect the resulting peak power densities. This work illustrates the capability of sputtering to produce stable, scalable, nano-ceramic cathodes with superb peak power densities when integrated in TF-SOFCs.

25 ENERGY STORAGE↗

Sub-100 mA/cm 2 CO 2 -to-CO Reduction Current Densities in Hierarchical Porous Gold Electrocatalysts Made by Direct Ink Writing and Dealloying

While most research efforts on CO 2 -to-CO reduction electrocatalysts focus on boosting their selectivity, the reduction rate, directly proportional to the reduction current density, is another critical parameter to be considered in practical applications. This is because mass transport associated with the diffusion of reactant/product species becomes a major concern at a high reduction rate. Nanostructured Au is a promising CO 2 -to-CO reduction electrocatalyst for its very high selectivity. However, the CO 2 -to-CO reduction current density commonly achieved in conventional nanostructured Au electrocatalysts is relatively low (in the range of 1–10 mA/cm 2 ) for practical applications. In this work, we combine direct ink writing-based additive manufacturing and dealloying to design a robust hierarchical porous Au electrocatalyst to improve the mass transport and achieve high CO 2 -to-CO reduction current densities on the order of 64.9 mA/cm 2 with CO partial current density of 33.8 mA/cm 2 at 0.55 V overpotential using an H-cell configuration. Although the current density achieved in our robust hierarchical porous Au electrocatalyst is one order of magnitude higher than the one achieved in conventional nanostructured electrocatalysts, we found that the selectivity of our system is relatively low, namely 52%, which suggests that mass transport remains a critical issue despite the hierarchical porous architecture. We further show that the bulk dimension of our electrocatalyst is a critical parameter governing the interplay between selectivity and reduction rate. In conclusion, the insights gained in this work shed new light on the design of electrocatalysts toward scale-up CO 2 reduction and beyond.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Facile Interfacial Reduction Suppresses Redox Chemical Expansion and Promotes the Polaronic to Ionic Transition in Mixed Conducting (Pr,Ce)O 2−δ Nanoparticles

Mixed ionic/electronic conductors (MIECs) are essential components of solid-state electrochemical devices, such as solid oxide fuel/electrolysis cells. For efficient performance, MIECs are typically nanostructured, to enhance the reaction kinetics. However, the effect of nanostructuring on MIEC chemo-mechanical coupling and transport properties, which also impact cell durability and efficiency, has not yet been well understood. Here, in this work, Pr 0.2 Ce 0.8 O 2−δ (PCO20) nanopowders were prepared by coprecipitation, then sintered in a modified dilatometer at three different temperatures (600, 725, and 850 °C) for microstructure evolution, resulting in three samples with different average particle sizes (23, 30, and 53 nm). The chemical strain and electronic/ionic conductivity were then measured simultaneously on stable nanostructures in four isotherms from 550 to 400 °C with steps in pO 2 (1 to 10 –4 atm O 2 ). A microcrystalline bar was prepared and measured for comparison. Particle size reduction led to a monotonically decreasing isothermal redox chemical strain, confirmed by in situ high-temperature, controlled-atmosphere XRD measurements. The corresponding conductivity measurements provided defect chemical insight into the particle size-dependent chemical expansion behavior. The significant weakening of the pO 2 dependence and decreased activation energy for electrical conduction with decreasing particle size indicated a decrease in the reduction enthalpy of PCO, shifting the transition from (Pr) polaronic to ionic behavior to higher pO 2 . STEM-EELS measurements confirmed the majority of Pr was reduced to 3+ in the nanoparticles, while Ce remained 4+. These results demonstrate suppression of deleterious chemical expansion and tailoring of the dominant charge carrier simply through controlling the particle size, providing insights for MIEC microstructural design.

ceria↗

Assembly of Disordered Cocontinuous Morphologies by Multiblock Copolymers with Random Block Sequence and Length Dispersity

Among the wide variety of nanostructures accessible by self-assembly of block copolymers, cocontinuous morphologies are of great interest for separations, catalysis, sensing, and energy storage due to their ability to integrate distinct properties of the constituent polymers. Furthermore, we investigate the tendency to form disordered cocontinuous phases of multiblock copolymers (MBCs) with random block sequence and length dispersity prepared by step-growth polymerization of pre-made telechelic polymers, specifically using thiol-Michael addition between diacrylate functionalized polystyrene (PS) and poly (D,L - lactide) (PLA) chains and a small molecule dithiol. In the phase diagram so established, disordered cocontinuous nanostructures occupy a wide window (≈ 25 % vol) at a modest segregation strength of χN = 15, close to the critical value for microphase separation. At a higher segregation strength of χN = 30, only a moderately wide (≈ 10 vol %) cocontinuous window is found, with MBCs instead tending to form ordered nanostructures. Although the breadth of the cocontinuous widow is less than that found in prior work on analogous randomly end-linked copolymer networks (RECNs), the MBC architecture offers offsetting advantages in terms of solution and melt processability.

36 MATERIALS SCIENCE↗