Search

Amphiphilic polypeptoids with defined sequences, versatile in forming various nanostructures, are ideal for mimicking biomacromolecular structures. The predictive design of nanostructures depends on our understanding of the relationship between molecular structure and the locations of atoms in the nanostructure. Factors of importance include chain conformation, crystal motifs, and the arrangement of the molecules within the nanostructure. This review introduces the cryogenic transmission electron microscopy (cryo-TEM) method, sorting and averaging unit cells in nanosheets for resolution enhancement and identifying structural heterogeneity. The resulting atomic-scale images reveal the presence of two types of crystal motifs. The impact of processing conditions, capping group chemistry, and side chain chemistry on structural heterogeneity and crystal motifs can be quantified. The 3D reconstruction of nanosheets, wherein atomic-scale corrugations were revealed, is introduced in this review. New developments in cryo-TEM, such as phase retrieval reconstruction, hold great promise for atomic-scale imaging of soft nanostructures. Graphical abstract: [Figure not available: see fulltext.]

Diamond nucleation and growth from submicron clusters consisting of an amorphous carbon phase with predominantly sp 3 atomic hybridization and randomly oriented diamond nanocrystallites was investigated by various microanalysis techniques. The carbon clusters were created by exposing a highly sp 3 hybridized carbon thin film, deposited on a smooth silicon substrate by a vacuum arc method, to a low-temperature, methane-rich hydrogen plasma in a microwave plasma-enhanced chemical vapor deposition system. Diamond nanocrystallites inside the carbon clusters produced by the pretreatment acted as diamond nucleation sites. Microanalysis results provided insight into the structure and composition of the carbon clusters, the diamond nanocrystallites, and the amorphous ultrathin interlayers at the interfaces of the clusters and the grown diamond film with the silicon substrate. The physical phenomena responsible for the enhancement of diamond nucleation and growth on smooth substrates by the present method are interpreted in the context of the obtained results. Graphical abstract: [Figure not available: see fulltext.]

Abstract: Synthesis remains a challenge for advancing materials science. A key focus of this challenge is how to enable selective synthesis, particularly as it pertains to metastable materials. This perspective addresses the question: how can “spectator” elements, such as those found in double ion exchange (metathesis) reactions, enable selective materials synthesis? By observing reaction pathways as they happen (in situ) and calculating their energetics using modern computational thermodynamics, we observe transient, crystalline intermediates that suggest that many reactions attain a local thermodynamic equilibrium dictated by local chemical potentials far before achieving a global equilibrium set by the average composition. Using this knowledge, one can thermodynamically “shortcut” unfavorable intermediates by including additional elements beyond those of the desired target, providing access to a greater number of intermediates with advantageous energetics and selective phase nucleation. Ultimately, data-driven modeling that unites first-principles approaches with experimental insights will refine the accuracy of emerging predictive retrosynthetic models for complex materials synthesis. Graphical abstract: [Figure not available: see fulltext.]TOC Diagram: Schematic representation of the energy bandgaps, photogenerated charge separation, and photocatalytic activities improvement mechanism over g-C3N4/SmFeO3 nanosheets Z-scheme based nanocomposites.

Abstract: The different magnetic behaviors of LaCoO$$_3$$ 3 films grown on LaAlO$$_3$$ 3 and SrTiO$$_3$$ 3 substrates are related to the Co–O–Co bond angles and the constraints imposed on the Co–O bond lengths by the substrate geometries. The observed magnetic behavior is not consistent with ferromagnetism. Rather, long-range antiferromagnetic order occurs below $$T \approx 90$$ T ≈ 90  K when the Co–O–Co bond angle is greater than 163$$^\circ$$ ∘ , consistent with the behavior of bulk and nanoparticles forms of LaCoO$$_3$$ 3 . A LaAlO$$_3$$ 3 substrate prevents magnetic long-range order at low temperatures near the film–substrate interface and collinear antiferromagnetic sublattices away from the interface. At low temperatures, the antiferromagnetically ordered sublattices are non-collinear in films grown on SrTiO$$_3$$ 3 substrates, leading to a significant net moment. The net moment is controlled by the geometry imposed by the substrate upon which the LaCO$$_3$$ 3 film is grown. Graphical abstract

Amorphous carbon (a-C) films have garnered significant attention over the past few decades, principally due to their remarkable thermophysical properties, strong adherence to various materials, and good chemical inertness. These intrinsic characteristics of a-C films have led to their use as protective overcoats in numerous applications, such as hard-disk drives, microelectromechanical systems, and biomedical implants. The significant thinning of a-C films to a few nanometers, dictated by rapid advances in device miniaturization and compactness, motivated the development of thin-film deposition methods that preserve important film attributes like uniformity, strength, and structural stability. This article provides a comprehensive assessment of the most effective deposition techniques for synthesizing ultrathin films, particularly a-C films due to their wide application range as protective overcoats in contemporary technologies, state-of-the-art microanalysis methods for ultrathin films, and the technology challenges that must be overcome for CVA to capture a bigger share of the thin-film technology marketplace. Graphical abstract: [Figure not available: see fulltext.]

Rechargeable ion batteries are efficient energy storage devices widely employed in portable to large-scale applications such as electric vehicles and grids. Electrochemical reactions within batteries are complex phenomena, and they are strongly dependent on the battery materials and systems used. These electrochemical reactions often include detrimental irreversible reactions at various length scales from atomic- to macro-scales, which ultimately determine the overall electrochemical behavior of the system. Understanding such reaction mechanisms is a critical component to improve battery performance. To help this effort, this review article discusses recent advances and remaining challenges in both computational and experimental approaches to better understand dynamic electrochemical reactions in batteries across multiple length scales. Important related findings from this focus issue will also be highlighted. The aim of our focus issue is to contribute to the battery community towards having better understanding of complex reactions occurring in battery devices and of computational and experimental methods to investigate them. Graphical abstract: [Figure not available: see fulltext.]

Abstract: A method for small-scale testing and imaging of freestanding, microtomed polymer films using a push-to-pull device is presented. Central to this method was the development of a sample preparation technique which utilized solvents at cryogenic temperatures to transfer and deposit delicate thin films onto the microfabricated push-to-pull devices. The preparation of focused ion beam (FIB)-milled tensile specimens enabled quantitative in situ TEM tensile testing, but artifacts associated with ion and electron beam irradiation motivated the development of a FIB-free specimen preparation method. The FIB-free method was enabled by the design and fabrication of oversized strain-locking push-to-pull devices. An adaptation for push-to-pull devices to be compatible with an instrumented nanoindenter expanded the testing capabilities to include in situ heating. These innovations provided quantitative mechanical testing, postmortem TEM imaging, and the ability to measure the glass transition temperature, via dynamic mechanical analysis, of freestanding polymer films. Results for each of these mentioned characterization methods are presented and discussed in terms of polymer nanomechanics. Graphic Abstract: [Figure not available: see fulltext.]

Abstract: A method for small-scale testing and imaging of freestanding, microtomed polymer films using a push-to-pull device is presented. Central to this method was the development of a sample preparation technique which utilized solvents at cryogenic temperatures to transfer and deposit delicate thin films onto the microfabricated push-to-pull devices. The preparation of focused ion beam (FIB)-milled tensile specimens enabled quantitative in situ TEM tensile testing, but artifacts associated with ion and electron beam irradiation motivated the development of a FIB-free specimen preparation method. The FIB-free method was enabled by the design and fabrication of oversized strain-locking push-to-pull devices. An adaptation for push-to-pull devices to be compatible with an instrumented nanoindenter expanded the testing capabilities to include in situ heating. These innovations provided quantitative mechanical testing, postmortem TEM imaging, and the ability to measure the glass transition temperature, via dynamic mechanical analysis, of freestanding polymer films. Results for each of these mentioned characterization methods are presented and discussed in terms of polymer nanomechanics. Graphic Abstract: [Figure not available: see fulltext.]

While rhenium has proven to be an ideal material in fast-cycling high-temperature applications such as rocket nozzles, its prohibitive cost limits its continued use and motivates a search for viable cost-effective substitutes. We show that a simple design principle that trades off average valence electron count and cost considerations proves helpful in identifying a promising pool of candidate substitute alloys: The Mo-Ru-Ta-W quaternary system. We demonstrate how this picture can be combined with a computational thermodynamic model of phase stability, based on high-throughput ab initio calculations, to further narrow down the search and deliver alloys that maintain rhenium's desirable hcp crystal structure. This thermodynamic model is validated with comparisons to known binary phase diagram sections and corroborated by experimental synthesis and structural characterization demonstrating multiprinciple-element hcp solid-solution samples selected from a promising composition range.

Silicon is a promising material for lithium-ion batteries. However, it expands by 300% on lithiation, leading to fracture. Nanostructuring of silicon is expected to be a promising method to improve the mechanical strength of the silicon electrodes. In the present work, a unique battery test cell was designed and fabricated to study the in situ stress evolution in the silicon nanowire (SiNW) electrode during electrochemical lithiation using synchrotron X-ray microdiffraction. The stress in the SiNWs at pristine state and during lithiation was evaluated using energy scans. The average stress in the pristine nanowires was found to be ∼40 MPa tensile, which changed to ∼325 MPa compressive on lithiation. Further, the deviatoric stress state in the SiNWs during lithiation was evaluated using Laue diffraction and the lithiated nanowires were found to be in triaxial stress state with high shear stresses. The technique and the findings provide new and more in-depth understanding of the stress evolution in the SiNWs during electrochemical lithiation.

Ceramics are strong but brittle. According to the classical theories, ceramics are brittle mainly because dislocations are suppressed by cracks. Here, the authors report the combined elastic and plastic deformation measurements of nanoceramics, in which dislocation-mediated stiff and ductile behaviors were detected at room temperature. In the synchrotron-based deformation experiments, a marked slope change is observed in the stress-strain relationship of MgAl2O4 nanoceramics at high pressures, indicating that a deformation mechanism shift occurs in the compression and that the nanoceramics sample is elastically stiffer than its bulk counterpart. The bulk-sized MgAl2O4 shows no texturing at pressures up to 37 GPa, which is compatible with the brittle behaviors of ceramics. Surprisingly, substantial texturing is seen in nanoceramic MgAl2O4 at pressures above 4 GPa. The observed stiffening and texturing indicate that dislocation-mediated mechanisms, usually suppressed in bulk-sized ceramics at low temperature, become operative in nanoceramics. This makes nanoceramics stiff and ductile.

When a metal oxide surface is immersed in aqueous solution, it has the ability to bind, orient, and order interfacial water, affecting both chemical and physical interactions with the surface. Structured interfacial water thus possesses time-averaged, spatially varying polarization charge and potential that are comparable to those arising due to ion accumulation. It is well established that interfacial water structure propagates from the surface into bulk solution. Here, we show that interfacial water structure also propagates laterally, with important consequences. The constant pH molecular dynamics was used to impose a pH difference between opposite faces of a model goethite (α-FeOOH) nanoparticle and quantify water polarization charge on intervening faces. We find that the structure of water on one face is strongly affected by the structure on nearby surfaces, revealing the importance of long-range lateral hydrogen bonding networks with implications for particle aggregation, oriented attachment, and processes such as dissolution and growth.

Calcium-based renal calculi demonstrated significant heterogeneity in the structure, density, mineral composition, and material hardness not elucidated by routine clinical testing. Mineral density distributions within calcium oxalate stones revealed differential areas of low (590±80 mg/cc), medium (840±140 mg/cc), and high (1100±200 mg/cc) densities. Apatite stones also contained regions of low (700±200 mg/cc), medium (1100±200 mg/cc), and high (1400±140 mg/cc) densities within layers extending from single or multiple nucleation sites. Despite having lower average mineral density, calcium oxalate (CaOx) stones demonstrated higher material hardness compared to apatite stones, suggesting other chemical components might be involved in determining stone hardness properties. Carbon concentrated sites were identified between morphologic layers in CaOx stones and in stratified layers of apatite stones. Elemental analyses revealed numerous additional trace elements in both stone types. Despite the widespread assumption that stone mineral density is an indicator of susceptibility to lithotripsy, calcium stone mineral density estimates do not directly correlate with actual ex vivo stone hardness. Underlying stone heterogeneity in both structure and mineral density could explain why historical approaches have failed in accurately predicting response of stones to lithotripsy.

Data mining has revolutionized sectors as diverse as pharmaceutical drug discovery, finance, medicine, and marketing, and has the potential to similarly advance materials science. In this paper, we describe advances in simulation-based materials databases, open-source software tools, and machine learning algorithms that are converging to create new opportunities for materials informatics. We discuss the data mining techniques of exploratory data analysis, clustering, linear models, kernel ridge regression, tree-based regression, and recommendation engines. We present these techniques in the context of several materials application areas, including compound prediction, Li-ion battery design, piezoelectric materials, photocatalysts, and thermoelectric materials. Finally, we demonstrate how new data and tools are making it easier and more accessible than ever to perform data mining through a new analysis that learns trends in the valence and conduction band character of compounds in the Materials Project database using data on over 2500 compounds.

Dentinogenesis imperfecta type II (DGI-II) lacks intrafibrillar mineral with severe compromise of dentin mechanical properties. A Dspp knockout (Dspp-/-) mouse, with a phenotype similar to that of human DGI-II, was used to determine if poly-L-aspartic acid [poly(ASP)] in the "polymer-induced liquid-precursor" (PILP) system can restore its mechanical properties. Dentin from six-week old Dspp-/- and wild-type mice was treated with CaP solution containing poly(ASP) for up to 14 days. Elastic modulus and hardness before and after treatment were correlated with mineralization from Micro x-ray computed tomography (Micro-XCT). Transmission electron microscopy (TEM)/Selected area electron diffraction (SAED) were used to compare matrix mineralization and crystallography. Mechanical properties of the Dspp-/- dentin were significantly less than wild-type dentin and recovered significantly (P < 0.05) after PILP-treatment, reaching values comparable to wild-type dentin. Micro-XCT showed mineral recovery similar to wild-type dentin after PILP-treatment. TEM/SAED showed repair of patchy mineralization and complete mineralization of defective dentin. This approach may lead to new strategies for hard tissue repair.