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What makes things twist? Crystallization and chirality have been entangled since Pasteur's observations on chiral tartaric acid crystals, yet there is still limited understanding of how chiral compounds form chiral crystal morphologies. For example, although a chiral seed crystal can promote a particular handedness, it is not clear why such seeds do not do so with 100% efficiency. Ben-Moshe et al. examined chiral nanocrystals of tellurium grown from solution using various electron microscopy and diffraction techniques (see the Perspective by Popov). They found that screw dislocation- mediated growth is responsible for chiral polyhedral shape formation, and chiral crystals can thus form even in the presence of achiral ligands. Science , this issue p. 729 ; see also p. 688

Author(s): Viseshchitra, P; Ercius, P; Monteiro, PJM; Scott, M; Ushizima, D; Li, J; Xu, K; Wenk, HR | Abstract: © 2020 American Ceramic Society (ACERS) Calcium silicate hydrate (C-S-H), is the principal hydration product of Portland cement that mainly contributes to the physical and mechanical properties of concrete. This paper aims to investigate the three-dimensional structure of C-S-H with Ca/Si ratios of 1.0 and 1.6 at the nanoscale using electron tomography. The 3D reconstructions and selected region of interest analysis confirm that the morphology of both C-S-H materials are foil-like structures. The difference between the two materials is the density of elongated structures. C-S-H with Ca/Si ratio 1.6 is clearly composed of denser particles compared to the other C-S-H material due to overlapping of the foil-like structure. Pore analysis shows that C-S-H 1.0 and C-S-H 1.6 have porosities 69.2% and 49.8% respectively. Pore size distribution also reveals that C-S-H 1.0 has pore size range between 0-250nnm and C-S-H 1.6 between 0-100nnm. The pore network's size of C-S-H 1.0 is significantly larger than 1.6. This study illustrates the capability of using electron tomography to determine the 3D nanoscale structure of cementitious products and to distinguish between C-S-H 1.0 and 1.6.

The structure of MX3 transition metal trichalcogenides (TMTs, with M a transition metal and X a chalcogen) is typified by one-dimensional (1D) chains weakly bound together via van der Waals interactions. This structural motif is common across a range of M and X atoms (e.g., NbSe3, HfTe3,TaS3), but not all M and X combinations are stable. We report here that three new members of the MX3 family which are not stable in bulk, specifically NbTe3, VTe3, and TiTe3, can be synthesized in the few- (2-4) to single-chain limit via nanoconfined growth within the stabilizing cavity of multiwalled carbon nanotubes. Transmission electron microscopy (TEM) and atomic-resolution scanning transmission electron microscopy (STEM) reveal the chain-like nature and the detailed atomic structure. The synthesized materials exhibit behavior unique to few-chain quasi-1D structures, such as few-chain spiraling and a trigonal antiprismatic rocking distortion in the single-chain limit. Density functional theory (DFT) calculations provide insight into the crystal structure and stability of the materials, as well as their electronic structure.

Significance The efficiency with which renewable fuels and feedstocks are synthesized from electrical sources is largely limited by the sluggish water oxidation reaction. We show that the optimal water oxidation catalyst could be achieved by systematically modulating the coordination of the Ir active sites using an in situ cryogenic–photochemical reduction synthesis method. We achieved a highly oxidized Ir single site (Ir+5.3) in the best atom utilization by single-atom catalysts on electrochemically stable supports. The origin of water oxidation activity in an Ir single-atom catalyst is revealed experimentally and theoretically. The concept and strategy of this work are expected to pioneer novel approaches to engineer single-atom catalysts., The efficiency of the synthesis of renewable fuels and feedstocks from electrical sources is limited, at present, by the sluggish water oxidation reaction. Single-atom catalysts (SACs) with a controllable coordination environment and exceptional atom utilization efficiency open new paradigms toward designing high-performance water oxidation catalysts. Here, using operando X-ray absorption spectroscopy measurements with calculations of spectra and electrochemical activity, we demonstrate that the origin of water oxidation activity of IrNiFe SACs is the presence of highly oxidized Ir single atom (Ir5.3+) in the NiFe oxyhydroxide under operating conditions. We show that the optimal water oxidation catalyst could be achieved by systematically increasing the oxidation state and modulating the coordination environment of the Ir active sites anchored atop the NiFe oxyhydroxide layers. Based on the proposed mechanism, we have successfully anchored Ir single-atom sites on NiFe oxyhydroxides (Ir0.1/Ni9Fe SAC) via a unique in situ cryogenic–photochemical reduction method that delivers an overpotential of 183 mV at 10 mA ⋅ cm−2 and retains its performance following 100 h of operation in 1 M KOH electrolyte, outperforming the reported catalysts and the commercial IrO2 catalysts. These findings open the avenue toward an atomic-level understanding of the oxygen evolution of catalytic centers under in operando conditions.

The formation of complex hierarchical nanostructures has attracted a lot of attention from both the fundamental science and potential applications point of view. Spherulite structures with radial fibrillar branches have been found in various solids; however, their growth mechanisms remain poorly understood. Here, we report real time imaging of the formation of two-dimensional (2D) iron oxide spherulite nanostructures in a liquid cell using transmission electron microscopy (TEM). By tracking the growth trajectories, we show the characteristics of the reaction front and growth kinetics. Our observations reveal that the tip of a growing branch splits as the width exceeds certain sizes (5.5–8.5 nm). The radius of a spherulite nanostructure increases linearly with time at the early stage, transitioning to nonlinear growth at the later stage. Furthermore, a thin layer of solid is accumulated at the tip and nanoparticles from secondary nucleation also appear at the growing front which later develop into fibrillar branches. The spherulite nanostructure is polycrystalline with the co-existence of ferrihydrite and Fe3O4 through-out the growth. A growth model is further established, which provides rational explanations on the linear growth at the early stage and the nonlinearity at the later stage of growth.

Suppression of electronic defects induced by GeO x at the high- k gate oxide/SiGe interface is critical for implementation of high-mobility SiGe channels in complementary metal-oxide-semiconductor (CMOS) technology. Theoretical and experimental studies have shown that a low defect density interface can be formed with an SiO x-rich interlayer on SiGe. Experimental studies in the literature indicate a better interface formation with Al2O3 in contrast to HfO2 on SiGe; however, the mechanism behind this is not well understood. In this study, the mechanism of forming a low defect density interface between Al2O3/SiGe is investigated using atomic layer deposited (ALD) Al2O3 insertion into or on top of ALD HfO2 gate oxides. To elucidate the mechanism, correlations are made between the defect density determined by impedance measurements and the chemical and physical structures of the interface determined by high-resolution scanning transmission electron microscopy and electron energy loss spectroscopy. The compositional analysis reveals an SiO x rich interlayer for both Al2O3/SiGe and HfO2/SiGe interfaces with the insertion of Al2O3 into or on top of the HfO2 oxide. The data is consistent with the Al2O3 insertion inducing decomposition of the GeO x from the interface to form an electrically passive, SiO x rich interface on SiGe. This mechanism shows that nanolaminate gate oxide chemistry cannot be interpreted as resulting from a simple layer-by-layer ideal ALD process, because the precursor or its reaction products can diffuse through the oxide during growth and react at the semiconductor interface. This result shows that in scaled CMOS, remote oxide ALD (oxide ALD on top of the gate oxide) can be used to suppress electronic defects at gate oxide semiconductor interfaces by oxygen scavenging.

We present the first report of ligand-sensitized, actinide luminescence in a lanthanide nanoparticle host. Amplified luminescence of 248Cm3+ doped in a NaGdF4 lattice is achieved through optical pumping of a surface-localized metal chelator, 3,4,3-LI(1,2-HOPO), capable of sensitizing Cm3+ excited states. The data suggest the possibility of using such materials in theranostic applications, with a ligand-sensitized actinide or radio-lanthanide serving the dual roles of a nuclear decay source for radiotherapeutics, and as a luminescent center or energy transfer conduit to another emissive metal ion, for biological imaging.

Orthogonal to guided growth of nanoparticle (NP) crystals using DNA or supramolecules, a trace amount of polymeric impurities (, Growing nanoparticle crystals typically requires strict control over interparticle interactions and assembly. Here, the authors show that a trace amount of polymeric impurities induces reproducible, rapid growth of high quality 3D nanoparticle crystals in solution and on patterned substrates.

Due to their rarity and radioactive nature, comparatively little is known about the actinides, particularly those with atomic numbers higher than that of plutonium, and their compounds. In this work, we describe how transmission electron microscopy can provide comprehensive, safe, and cost-effective characterization using only single nanogram amounts of highly-radioactive, solid compounds. Chlorides of the rare elements berkelium and californium are dropcast and then converted in situ to oxides using the electron beam. The f-band occupancies are probed using electron energy loss spectroscopy and an unexpectedly weak spin-orbit-coupling is identified for berkelium. In contrast, californium follows a jj coupling scheme. These results have important implications for the chemistries of these elements and solidify the status of californium as a transitional element in the actinide series., The obtention and study of actinide elements is challenging due to various factors including their radioactivity and scarcity. Herein, the authors characterize the atomic and electronic structure of Am, Cm, Bk, and Cf compounds using a transmission electron microscopy-based workflow that only requires nanogram amounts of the actinide element.

The efficiency of the synthesis of renewable fuels and feedstocks from electrical sources is limited at present by the sluggish water oxidation reaction. Single atom catalysts (SACs) with a controllable coordination environment and exceptional atom utilization efficiency open new paradigms towards designing high performance water oxidation catalysts. Here, using operando X-ray absorption spectroscopy measurements with calculations of spectra and electrochemical activity, we demonstrate that the origin of water oxidation activity of IrNiFe SACs is the presence of highly oxidized Ir single atom (Ir5.3+) in the NiFe oxyhydroxide under operating conditions. We show that the optimal water oxidation catalyst could be achieved by systematically increasing the oxidation state and modulating the coordination environments of the Ir active sites anchored atop the NiFe oxyhydroxide layers. Based on the proposed mechanism, we have successfully anchored Ir single-atom sites on NiFe oxyhydroxides (Ir0.1/Ni9Fe SAC) via a unique in situ cryogenic photochemical reduction (in situ Cryo-PCR) method which delivers an overpotential of 183 millivolts at 10 milliamperes per square centimeter and retains its performance following 20 hours of operation in 1 M KOH electrolyte, outperforming the reported catalysts and the commercial IrO2 catalysts. These findings open the avenue towards atomic-level understanding of oxygen evolution of catalytic centers under in operando condition.

Growing nanoparticle (NP) crystals has been pursued extensively using ligand chemistries such as DNA and supramolecules, controlled evaporation and patterned surfaces. Here, we show that a trace amount of polymeric impurities (

This work reports a comprehensive study of a novel polyol method that can successfully synthesize layered LiNi0.4Mn0.4Co0.2O2, spinel LiNi0.5Mn1.5O4, and olivine LiCoPO4 cathode materials. When properly designed, polyol method offers many advantages such as low cost, ease of use, and proven scalability for industrial applications. Most importantly, the unique properties of polyol solvent allow for greater morphology control as shown by all the resulting materials exhibiting monodispersed nanoparticles morphology. This morphology contributes to improved lithium ion transport due to short diffusion lengths. Polyol-synthesized LiNi0.4Mn0.4Co0.2O2 delivers a reversible capacity of 101 and 82 mAh·g−1 using high current rate of 5C and 10C, respectively. It also displays surprisingly high surface structure stability after charge-discharge processes. Each step of the reaction was investigated to understand the underlying polyol synthesis mechanism. A combination of in situ and ex situ studies reveal the structural and chemical transformation of Ni-Co alloy nanocrystals overwrapped by a Mn- and Li-embedded organic matrix to a series of intermediate phases, and then eventually to the desired layered oxide phase with a homogeneous distribution of Ni, Co, and Mn. We envisage that this type of analysis will promote the development of optimized synthesis protocols by establishing links between experimental factors and important structural and chemical properties of the desired product. The insights can open a new direction of research to synthesize high-performance intercalation compounds by allowing unprecedented control of intermediate phases using experimental parameters. [Figure not available: see fulltext.]

Seeing subtle nanoparticle differences A challenge in the fabrication of nanoparticles is that even for particles of uniform size, there will still be a distribution in the atomic arrangements and surface capping ligands from one particle to the next. Using liquid-cell transmission electron microscopy, Kim et al. reconstructed the structure of individual nanocrystals synthesized in one batch while they were still in solution. A comparison of multiple particles showed structural heterogeneity and differences between the interior and the outer shell of the individual nanoparticles, as well as nanoparticles containing extended defects and thus differences in internal strain, all of which can affect the physical and chemical properties of each particle. Science , this issue p. 60

Nonclassical features of crystallization in solution have been recently identified both experimentally and theoretically. In particular, an amorphous-phase-mediated pathway is found in various crystallization systems as an important route, different from the classical nucleation and growth model. Here, we utilize high-resolution in situ transmission electron microscopy with graphene liquid cells to study amorphous-phase-mediated formation of Ni nanocrystals. An amorphous phase is precipitated in the initial stage of the reaction. Within the amorphous particles, crystalline domains nucleate and eventually form nanocrystals. In addition, unique crystallization behaviors, such as formation of multiple domains and dislocation relaxation, are observed in amorphous-phase-mediated crystallization. Theoretical calculations confirm that surface interactions can induce amorphous precipitation of metal precursors, which is analogous to the surface-induced amorphous-to-crystalline transformation occurring in biomineralization. Our results imply that an unexplored nonclassical growth mechanism is important for the formation of nanocrystals.

Watching it all fall apart The control of the shape and size of metal nanoparticles can be very sensitive to the growth conditions of the particles. Ye et al. studied the reverse process: They tracked the dissolution of gold nanoparticles in a redox environment inside a liquid cell within an electron microscope, controlling the particle dissolution with the electron beam. Tracking short-lived particle shapes revealed structures of greater or lesser stability. The findings suggest kinetic routes to particle sizes and shapes that would otherwise be difficult to generate. Science , this issue p. 874

© 2018 Elsevier B.V. Chemical sensing in living systems demands optical sensors that are bright, stable, and sensitive to the rapid dynamics of chemical signaling. Lanthanide-doped upconverting nanoparticles (UCNPs) efficiently convert near infrared (NIR) light to higher energy emission and allow biological systems to be imaged with no measurable background or photobleaching, and with reduced scatter for subsurface experiments. Despite their advantages as imaging probes, UCNPs have little innate chemical sensing ability and require pairing with organic fluorophores to act as biosensors, although the design of stable UCNP-fluorophore hybrids with efficient upconverted energy transfer (UET) has remained a challenge. Here, we report Yb3+- and Er3+-doped UCNP-fluorophore conjugates with UET efficiencies up to 88%, and photostabilities 100-fold greater by UET excitation than those of the free fluorophores under direct excitation. Despite adding distance between Er3+donors and organic acceptors, thin inert shells significantly enhance overall emission without compromising UET efficiency. This can be explained by the large increase in quantum yield of Er3+donors at the core/shell interface and the large number of fluorophore acceptors at the surface. Sensors excited by UET show increases in photostability well beyond those reported for other methods for increasing the longevity of organic fluorophores, and those covalently attached to UCNP surface polymers show greater chemical stability than those directly coordinated to the nanocrystal surface. By conjugating other fluorescent chemosensors to UCNPs, these hybrids may be extended to a series of NIR-responsive biosensors for quantifying the dynamic chemical populations critical for cell signaling.

© 2018 American Chemical Society. Transition metal dichalcogenides (TMDs) are particularly sensitive to mechanical strain because they are capable of experiencing high atomic displacements without nucleating defects to release excess energy. Being promising for photonic applications, it has been shown that as certain phases of layered TMDs MX2 (M = Mo or W; X = S, Se, or Te) are scaled to a thickness of one monolayer, the photoluminescence response is dramatically enhanced due to the emergence of a direct electronic band gap compared with their multilayer or bulk counterparts, which typically exhibit indirect band gaps. Recently, mechanical strain has also been predicted to enable direct excitonic recombination in these materials, in which large changes in the photoluminescence response will occur during an indirect-to-direct band gap transition brought on by elastic tensile strain. Here, we demonstrate an enhancement of 2 orders of magnitude in the photoluminescence emission intensity in uniaxially strained single crystalline WSe2 bilayers. Through a theoretical model that includes experimentally relevant system conditions, we determine this amplification to arise from a significant increase in direct excitonic recombination. Adding confidence to the high levels of elastic strain achieved in this report, we observe strain-independent, mode-dependent Grüneisen parameters over the entire range of tensile strain (1-3.59%), which were obtained as 1.149 ± 0.027, 0.307 ± 0.061, and 0.357 ± 0.103 for the E2g, A1g, and A21g optical phonon modes, respectively. These results can inform the predictive strain-engineered design of other atomically thin indirect semiconductors, in which a decrease in out-of-plane bonding strength may lead to an increase in the strength of strain-coupled optoelectronic effects.

Short-term oxidation exposures of an alumina-scale forming γ′-Ni3Al-based model alloy in air and O2 + 0.1%SO2 at 900 °C revealed that the presence of sulfur can affect the kinetic competition between the θ and α structural isomorphs of Al2O3. After 2 h exposure, metastable θ-Al2O3 growth predominated in air alone; whereas, a much larger percentage of stable α-Al2O3 formed during oxidation in O2 + 0.1%SO2. This promotion of α-Al2O3 establishment was due to sulfur enrichment on the alloy surface, which occurred even when samples were exposed to O2 + 0.1%SO2 in a low-temperature, pre-test position (∼150 °C), i.e., prior to insertion into the hot zone. It was determined from XPS measurements that the sulfur was mainly in the S6+ valence state and, correspondingly, in the form of NiSO4. Cross-sectional scanning transmission electron microscopy (STEM) using energy-dispersive X-ray spectroscopy (EDS) corroborated the XPS results by detecting that a ∼20 nm zone of sulfur enrichment within the surface region of a ∼90 nm oxygen-rich layer formed during the pre-test exposure. A systematic explanation for this intriguing observation of sulfur promoting α-Al2O3 establishment is provided from the perspective of kinetics competition between θ and α. This explanation was supported by kinetic calculations and complementary tests in a low p O 2 atmosphere.

© 2014 Elsevier Inc. All rights reserved. Making connections between performance and structure in bimetallic catalysts requires knowledge of how the two elements are spatially associated. Elemental maps obtained by analytical TEM methods are an invaluable tool for identifying the location of different elements, but for many samples, visual inspection of elemental maps is insufficient for assessing the degree of element spatial correlation. This is particularly true for beam-sensitive materials where short mapping acquisition times lead to images with high noise and low color depth. In these situations, statistical analysis of elemental maps can be used to identify spatial correlations among the elements in a sample. In this work, the relationship between catalyst performance and bimetallic spatial association was explored using Mn-promoted Co-based Fischer-Tropsch synthesis catalysts prepared by different pretreatment methods. Mn was used as a catalyst additive to suppress methane formation. Catalysts that underwent calcination before reduction produced more methane and fewer long-chain hydrocarbons than catalysts that were directly reduced. The extent to which Co and Mn were spatially associated was assessed using correlation metrics, colocation plots, and histograms generated using data from STEM-EDS maps. Although both catalysts yielded visually similar elemental maps, the results of statistical analysis suggested that the calcined catalyst exhibited greater spatial segregation between the Co and Mn. These findings support the hypothesis that having Mn in close proximity to the Co is essential for the manifestation of Mn promotion effects in Co-based FTS catalysts.

Looking at teeny tiny platinum particles Electron microscopy is a powerful technique for taking snapshots of particles or images at near-atomic resolution. Park et al. studied free-floating platinum nanoparticles using electron microscopy and liquid cells (see the Perspective by Colliex). Using analytical techniques developed to study biological molecules, they reconstructed the threedimensional features of the Pt particles at near-atomic resolution. This approach has the scope to study a mixed population of particles one at a time and to study their synthesis as it occurs in solution. Science , this issue p. 290 ; see also p. 232

Diverse transition metal hydroxide nanostructures were synthesized by laser-induced hydrolysis in a liquid precursor solution for alkaline oxygen evolution reaction (OER). Several active OER catalysts with fine control of composition, structure, and valence state were obtained including (Li_x)[Ni_(0.66)Mn_(0.34)(OH)_2](NO_3)(CO_3) · mH_2O, Li_x[Ni_(0.67)Co_(0.33)(OH)_2](NO_3)_(0.25)(ORO)_(0.35) · mH_2O, etc. An operate overpotential less than 0.34 V at current density of 10 mA cm^(–2) was achieved. Such a controllable laser–chemical route for assessing complex nanostructures in liquids opens many opportunities to design novel functional materials for advanced applications.

© 2017 Elsevier Ltd Tungsten based support was prepared by polycondensation of resorcinol and formaldehyde from ammonium metatungstate, in the presence cetyltrimethylammonium bromide (CTABr) surfactant. Pd nanocatalyst on this support was synthesized by borohydride reduction method. The obtained materials were characterized by High Resolution Transmission Electron Microscopy (HRTEM), Electron Energy Loss Spectroscopy (EELS), X-ray Photoelectron Spectroscopy (XPS) and electrochemical measurements. TEM analysis revealed Pd nanoparticles size in the range of a few nanometers, even the clusters of single Pd atoms. X-Ray Photoelectron Spectroscopy was applied to determine surface composition of the substrates. It was found that tungsten based support consisted of W, WC and WO3species. The presence of metallic palladium – Pd(0) in the Pd/W@WCWO3catalyst was revealed, as well. The catalytic activity and stability for the oxygen reduction were investigated in acid and alkaline solutions, by cyclic voltammetry and linear sweep voltammetry at the rotating disc electrode. The catalystsʹ activities were compared to the carbon supported Pd nanoparticles (Vulcan XC 72). WC supported Pd nanoparticles have shown high activity and superior stability, comparable even to Pt based catalysts, especially in alkaline electrolytes.

Watching platinum nanocube growth Size and shape drive the properties of metal nanoparticles. Understanding the factors that affect their growth is central to making use of the particles in a range of applications. Liao et al. tracked the growth of platinum nanoparticle shapes at high resolution using state-of-the-art liquid cells for in situ monitoring inside an electron microscope. The authors tracked changes in the growth rates at different crystal facets caused by differences in the mobility of the capping ligand. Science , this issue p. 916

The basal plane of graphene has been known to be less reactive than the edges, but some studies observed vacancies in the basal plane after reaction with oxygen gas. Observation of these vacancies has typically been limited to nanometer-scale resolution using microscopic techniques. This work demonstrates the introduction and observation of subnanometer vacancies in the basal plane of graphene by heat treatment in a flow of oxygen gas at low temperature such as 533 K or lower. High-resolution transmission electron microscopy was used to directly observe vacancy structures, which were compared with image simulations. These proposed structures contain C═O, pyran-like ether, and lactone-like groups.

At a basic level, materials properties depend on the three-dimensional arrangement of atoms, and it is necessary to determine their coordinates to make correlative measurements of structure and functionality from basic principles. Traditional 3D reconstruction techniques (such as X-ray crystallography and single-particle Cryo-Em) continue to provide critical insights into structure/property relationships but average over many identical structures. This will blur out the defects inherent to inhomogeneous nanoengineered materials important to their functionality. Aberration-corrected HR-TEM and HAADF-STEM are now indispensable techniques in materials science to examine the atomic structure of materials systems with sub-A resolution and single atom sensitivity. Combining these new tools with powerful iterative 3D reconstruction and peak finding algorithms for electron tomography is opening a new field with the ability to determine atomic coordinates of all atoms in a structure without the assumption of crystallinity. This talk will cover recent develops and future directions of Atomic Electron Tomography (AET), which will be critical to our understanding of the atomic structure of complex materials systems. HAADF-STEM and the equally sloped tomography method were recently used to determine the atomic coordinates of 3,769 atoms in 9 atomic layers at the apex of an etched tungsten needle (Figure 1) [1]. A tungsten point defect was unambiguously located in the material for the first time in three-dimensions. Comparing the experimental positions to the ideal bcc tungsten lattice produces the atomic displacement field with ±19 pm precision. Kernel density estimation applied to the differentiation of the displacement field was used to calculate the 6 components of the strain tensor with ~1 nm 3D spatial resolution indicating expansion along the [011] axis (x-axis) and compression along the [100] axis (y-axis). It was determined by experiments, DFT simulations and MD simulations that the strain in the lattice was due to a surface layer of tungsten carbide and sub-surface carbon. This result shows the capabilities of AET to measure atomic coordinates of inhomogeneous objects without the assumption of crystallinity providing and the capability of directly measuring materials properties. Measurements of material structure in their native environment are now being accomplished using in-situ TEM, but has been limited by the thickness of the SiN windows and the contained liquid volume. A recent advance in this field was the introduction of the graphene liquid cell (GLC) to minimize the combined window/liquid thickness allowing observation of the growth and coalescence of colloidal Pt nanoparticles at atomic resolution [2]. It was discovered that stable NPs in the GLC were randomly rotating thus providing many orientations that could be reconstructed using methods developed in single-particle Cryo-Em. A direct electron detector and aberration-corrected HR-TEM were combined with a GLC in a technique called 3D SINGLE (3D Structure Identification of Nanoparticles by Graphene Liquid Cell EM) to determine the atomic-scale facets, lattice plane orientations and multi-twinned grain structure of a Pt nanoparticle in liquid with 2.10 A resolution (Figure 2) [3]. The particle is constructed of three distinct regions: a central disk region of well-ordered {111} atomic planes with conical protrusions attached on each side connected by screw dislocations. Keywords: atomic electron tomography; STEM; TEM; graphene liquid cell; aberration-correction; electron tomography; in-situ

Structured platinum nanoclusters Ptn (n = 5–30) capped by poly(N-vinylpyrrolidone) (PVP) have unique and highly attractive properties as potential selective catalysts. We show that the assembly of Pt mononuclear compounds in aqueous and tetrahydrofuran (THF) solutions under UV irradiation proceed via several steps: formation of linear Ptn clusters (n = 2–8), coalescence into mesocrystals, and transformation into Pt nanocrystals. The “quantum” size range of Ptn (n = 5–100) clusters is intermediate between those clusters with molecular properties and those with metallic properties. The PVP “cage” acts as a nano reactor and can hinder diffusion of photoexcited Pt atoms. The diffusion of the Pt from the polymer cage is strongly affected by the hydrophobic or hydrophilic property of the solution. An aqueous solution of [PtCl6]2– + PVP transforms into noncrystalline aggregates of molecules of less than 1.5–2 nm in diameter, whereas in THF solution Pt nanocrystals increase proportional to the UV irradiation time...

We describe the synthesis and three-dimensional structure of a new single-crystalline “hexameric” nanocrystal composed of six near-spherical PbSe nanocrystals arranged at the vertices of an octahed...

Block copolymer thin films with distinct morphologies are prepared by spin casting a nominally lamellar assay of poly(styrene-block-ethylene oxide) from a variety of solvents with and without salt doping. The 3-D morphologies of free-standing thin-film regions, which are obtained by casting directly onto holey substrates, are investigated in detail using various energy-filtering transmission electron microscopy techniques and by electron tomography. Surface characterization is achieved by atomic force microscopy. Our results demonstrate that in order to fully characterize the unique 3-D morphologies of the block copolymer thin films, a multi-method approach is required. When casting from a binary solvent, an unexpected layered honeycomb-type morphology is revealed, which likely results from an expansion of the poly(ethylene oxide) phase. A dramatic effect of selective cation coordination on the morphology of the as-cast block copolymer films is also directly observed.

The Cu migration behavior in PVD-CdS/PVD-Cu(In,Ga)Se2 (CIGS) heterojunctions is investigated by high-resolution electron microscopy (HREM) and energy dispersive X-ray spectroscopy (EDS). Incorporation of Cu into the CdS forms Cu-rich domains but has no effect on epitaxy of the CdS. Epitaxy is commonly observed in the CdS studied. Secondary ion mass spectroscopy depth profiles confirm the presence of Cu in the CdS. In some cases, Cd is completely replaced by Cu, resulting in a Cu–S binary compound epitaxially grown on the CIGS and fully coherent with the surrounding CdS. This is most likely to be cubic Cu2S, based on lattice spacing measurements from HREM images and EDS elemental quantification. In addition, we find that the buffer layer crystal structure influences the extent of Ga depletion at the CIGS surface, which is more pronounced adjacent to zinc-blende CdS than wurtzite CdS. Density functional theory calculations reveal that Cu clustering and different Ga depletion widths can be attributed to the inherent anisotropy of wurtzite CdS and differences in CIGS point-defect migration barriers. Understanding the influence of these effects on device properties is a critical step in developing more efficient CdS/CIGS-based photovoltaics.

© 2016 American Chemical Society. Nanoscale stress-sensing can be used across fields ranging from detection of incipient cracks in structural mechanics to monitoring forces in biological tissues. We demonstrate how tetrapod quantum dots (tQDs) embedded in block copolymers act as sensors of tensile/compressive stress. Remarkably, tQDs can detect their own composite dispersion and mechanical properties with a switch in optomechanical response when tQDs are in direct contact. Using experimental characterizations, atomistic simulations and finite-element analyses, we show that under tensile stress, densely packed tQDs exhibit a photoluminescence peak shifted to higher energies ("blue-shift") due to volumetric compressive stress in their core; loosely packed tQDs exhibit a peak shifted to lower energies ("red-shift") from tensile stress in the core. The stress shifts result from the tQD's unique branched morphology in which the CdS arms act as antennas that amplify the stress in the CdSe core. Our nanocomposites exhibit excellent cyclability and scalability with no degraded properties of the host polymer. Colloidal tQDs allow sensing in many materials to potentially enable autoresponsive, smart structural nanocomposites that self-predict impending fracture.

Correlating 3D arrangements of atoms and defects with material properties and functionality forms the core of several scientific disciplines. Here, we determined the 3D coordinates of 6,569 iron and 16,627 platinum atoms in a model iron-platinum nanoparticle system to correlate 3D atomic arrangements and chemical order/disorder with material properties at the single-atom level. We identified rich structural variety and chemical order/disorder including 3D atomic composition, grain boundaries, anti-phase boundaries, anti-site point defects and swap defects. We show for the first time that experimentally measured 3D atomic coordinates and chemical species with 22 pm precision can be used as direct input for first-principles calculations of material properties such as atomic magnetic moments and local magnetocrystalline anisotropy. This work not only opens the door to determining 3D atomic arrangements and chemical order/disorder of a wide range of nanostructured materials with high precision, but also will transform our understanding of structure-property relationships at the most fundamental level., 21 pages, 4 figures

Platinum nanocatalysts on two tungsten based supports have been synthesized and characterized as catalysts for oxygen reduction reaction in 0.5 mol dm −3 HClO 4 solution, at 25 °C. Tungsten based support assigned WCctabr has been synthesized by polycondensation of resorcinol and formaldehyde in the presence of CTABr surfactant. Support assigned WC WO 3 was synthesized from resorcinol/formaldehyde gel, using WO 3 nanoparticles as starting material. Supporting materials have been characterized by BET (Brunauer, Emmett and Teller) technique and determined values of surface area were 80 m 2 g −1 for WCctabr and 175 m 2 g −1 for WC WO 3 . Platinum nanocatalysts (10% Pt) at tungsten based supports have been prepared by borohydride reduction method. Both synthesized supports and catalysts have been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) techniques. Cyclic voltammetry was applied for determination of electrochemically active surface area (40 m 2 g −1 for Pt/WC WO 3 and 55 m 2 g −1 for Pt/WCctabr). Oxygen reduction reaction has been studied by cyclic voltammetry and linear sweep voltammetry at rotating disc electrode (RDE). These catalysts exhibited better catalytic activity, expressed in terms of kinetic current density per real surface area at the constant potential and better stability, in comparison with Pt/C catalyst, as well as with already reported catalytic activity values for Pt catalysts on tungsten based supports.

Multicomponent nanocrystal superlattices represent an interesting class of material that derives emergent properties from mesoscale structure, yet their programmability can be limited by the alkyl-chain-based ligands decorating the surfaces of the constituent nanocrystals. Polymeric ligands offer distinct advantages, as they allow for more precise tuning of the effective size and ‘interaction softness' through changes to the polymer's molecular weight, chemical nature, architecture, persistence length and surrounding solvent. Here we show the formation of 10 different binary nanocrystal superlattices (BNSLs) with both two- and three-dimensional order through independent adjustment of the core size of spherical nanocrystals and the molecular weight of densely grafted polystyrene ligands. These polymer-brush-based ligands introduce new energetic contributions to the interparticle potential that stabilizes various BNSL phases across a range of length scales and interparticle spacings. Our study opens the door for nanocrystals to become modular elements in the design of functional particle brush solids with controlled nanoscale interfaces and mesostructures., Binary nanocrystal superlattice metamaterials are arousing significant interest due to their potential for use in functional devices. Here, the authors endow the nanoparticles with polymer brushes which enable control over their spacings and thus mesoscale structure and properties.

Atomic layer deposition (ALD) of titanium nitride, TiN, from the reaction of Ti[N(CH3)2]4 and NH3 on silicon dioxide, and silicon dioxide modified by interfacial organic layers with different structures (straight-chain vs branched) and functional terminations (−OH, −NH2, and −CH3), has been investigated employing molecular beam techniques, atomic force microscopy (AFM), X-ray photoelectron spectroscopy, and scanning transmission electron microscopy (STEM). We find that the interfacial organic layers have a profound effect on subsequent growth of TiN via ALD. For organic layers possessing unreactive end groups (−CH3), the initial rate of growth (thickness deposited per cycle) is strongly attenuated, and growth on these surfaces is 3-D and severely islanded, emanating from defects in the adlayer. Roughness builds quickest on the organic layers that are the thickest. For organic layers that possess reactive end groups (−NH2 and −OH), growth is also attenuated, but less so, and the degree of attenuation is es...

Recent development of liquid phase transmission electron microscopy (TEM) enables the study of specimens in wet ambient conditions within a liquid cell; however, direct structural observation of biological samples in their native solution using TEM is challenging since low-mass biomaterials embedded in a thick liquid layer of the host cell demonstrate low contrast. Furthermore, the integrity of delicate wet samples is easily compromised during typical sample preparation and TEM imaging. To overcome these limitations, we introduce a graphene liquid cell (GLC) using multilayer graphene sheets to reliably encapsulate and preserve biological samples in a liquid for TEM observation. We achieve nanometer scale spatial resolution with high contrast using low-dose TEM at room temperature, and we use the GLC to directly observe the structure of influenza viruses in their native buffer solution at room temperature. The GLC is further extended to investigate whole cells in wet conditions using TEM. We also demonstrate the potential of the GLC for correlative studies by TEM and fluorescence light microscopy imaging.

The Cu migration behavior in PVD-CdS/PVD-Cu(In,Ga)Se2 (CIGS) heterojunctions is investigated by high resolution electron microscopy and energy dispersive X-ray spectroscopy (EDS) mapping. The incorporation of Cu into CdS forms Cu-rich domains in the CdS across the heterojunction and has no effect on epitaxy of the CdS film, which is commonly observed in the materials studied. In some cases Cd is completely replaced by Cu, resulting in a Cu-S binary compound epitaxially grown on the CIGS and fully coherent with the surrounding CdS, which is most likely cubic Cu2S by lattice spacing measurement from HREM images and EDS elemental quantification. The presence of a binary Cu-S phase as a heterojunction partner material may have significant impact on the resulting device performance although only modest loss of Voc occurs in the devices studied.

Two binary Ru-Ti oxides, Rum Ti0.9O2 and Ru0.7Ti0.3O2, were synthesized by the sol-gel method and used as an electrocatalyst support. The system was characterized by XRD, EDS, TEM and cyclic voltammetry. The Rum Ti0.9O2 and Ru0.7Ti0.3O2 consist of two phases of anatase and rutile structure. An average size of the Pt nanoparticles supported on them is similar to 3.5 nm and they are deposited on both Ru and Ti-rich domains. The supports exhibited good conductivity and electrochemical stability. The onset potentials of COads oxidation on the synthesized catalysts and on commercial PtRu/C are similar to each other and lower than that on Pt/C. This suggests that in Pt/Rum Ti0.9O2 and Pt/Ru0(.7)Ti(0.3)O(2) the Pt nanoparticles are in close contact with Ru atoms from the support, which enables the bifunctional mechanism. The activity and stability of the catalysts for methanol oxidation were examined under potentiodynamic and potentiostatic conditions. While the activity of Pt/Rum Ti0.9O2 is unsatisfactory, the performance of Pt/Ru0.7Ti0.3O2 is comparable to PtRu/C. For example, in the potentiostatic test at 0.5 V the activities after 25 min are 0.035 mA cm(-2) and 0.022 mA cm(-2) for Pt/Ru0.7Ti0.3O2 and PtRu/C, respectively. In potentiodynamic test the activities at 0.5V after 250 cycles are around 0.02 mA cm(-2) for both catalysts. (C) 2015 Elsevier B.V. All rights reserved.

Ruthenium oxide/titanium oxide, with a Ru:Ti atomic ratio of 7:3 was synthesized by modified sol-gel procedure and used as a support for platinum nanocatalyst for oxygen reduction reaction. The synthesized materials were characterized in terms of morphology, particle size distribution, chemical and phase composition by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high angle annular dark filed scanning transmission electron microscopy (HAADF, STEM) and electron energy loss spectroscopy (EELS). XPS spectra revealed that Ru atoms were in mainly in Ru(4+) oxidation state, the Ti atoms in Ti(4+) oxidation state, whereas the Pt-atoms were in metallic state. TEM analysis proved that platinum nanoparticles nucleated at both oxide species and homogeneous distribution was observed. The average platinum nanoparticle size was 3.05 nm. Electrochemically active surface area of platinum was 32 m(2) g(-1). Kinetics of the oxygen reduction was studied at rotating disc electrode in 0.5 mol dm(-3) HClO4 solution, at 25 degrees C. The catalytic activities expressed in terms of specific activity (per electrochemically active surface area of platinum) and mass activity (per mass of platinum) were determined and compared to Pt catalyst on carbon support. The high catalytic activity was proven by electrochemical characterization. (C) 2014 Elsevier B.V. All rights reserved.

Monochromated electron energy-loss spectroscopy (EELS) is employed to determine the optical properties of carbonaceous aerosols from the infrared to the ultraviolet region of the spectrum. It is essential to determine their optical properties to understand their accurate contribution to radiative forcing for climate change. The influence of surface and interface plasmon effects on the accuracy of dielectric data determined from EELS is discussed. Our measurements show that the standard thin film formulation of Kramers−Kronig analysis can be employed to make accurate determination of the dielectric function for carbonaceous particles down to about 40 nm in size. The complex refractive indices of graphitic and amorphous carbon spherules found in the atmosphere were determined over the wavelength range 200–1,200 nm. The graphitic carbon was strongly absorbing black carbon, whereas the amorphous carbon shows a more weakly absorbing brown carbon profile. The EELS approach provides an important tool for exploring the variation in optical properties of atmospheric carbon.

Dislocations have a significant effect on mechanical, electronic, magnetic and optical properties of crystals. For a dislocation to migrate in bulk crystals, collective and simultaneous movement of several atoms is needed. In two-dimensional crystals, in contrast, dislocations occur on the surface and can exhibit unique migration dynamics. Dislocation migration has recently been studied in graphene, but no studies have been reported on dislocation dynamics for two-dimensional transition metal dichalcogenides with unique metal-ligand bonding and a three-atom thickness. This study presents dislocation motion, glide and climb, leading to grain boundary migration in a tungsten disulphide monolayer. Direct atomic-scale imaging coupled with atomistic simulations reveals a strikingly low-energy barrier for glide, leading to significant grain boundary reconstruction in tungsten disulphide. The observed dynamics are unique and different from those reported for graphene. Through strain field mapping, we also demonstrate how dislocations introduce considerable strain along the grain boundaries and at the dislocation cores.

There has been considerable interest in chalcogenide alloys with high concentrations of native vacancies that lead to properties desirable for thermoelectric and phase-change materials. Recently, vacancy ordering has been identified as the mechanism for metal-insulator transitions observed in GeSb2Te4 and an unexpectedly low thermal conductivity in Ga2Te3. Here, we report the direct observation of vacancy ordering in Ga2SeTe2 utilizing aberration-corrected electron microscopy. Images reveal a cation-anion dumbbell inversion associated with the accommodation of vacancy ordering across the entire crystal. The result is a striking example of the interplay between native defects and local structure., 9 pages, 5 figures

Recently, silicon-based lithium-ion battery anodes have shown encouraging results, as they can offer high capacities and long cyclic lifetimes. The applications of this technology are largely impeded by the complicated and expensive approaches in producing Si with desired nanostructures. We report a cost-efficient method to produce nanoporous Si particles from metallurgical Si through ball-milling and inexpensive stain-etching. The porosity of porous Si is derived from particle's three-dimensional reconstructions by scanning transmission electron microscopy (STEM) tomography, which shows the particles' highly porous structure when etched under proper conditions. Nanoporous Si anodes with a reversible capacity of 2900 mAh/g was attained at a charging rate of 400 mA/g, and a stable capacity above 1100 mAh/g was retained for extended 600 cycles tested at 2000 mA/g. The synthetic route is low-cost and scalable for mass production, promising Si as a potential anode material for the next-generation lithium-ion batteries with enhanced capacity and energy density.