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The development of patterning materials (“resists”) at the nanoscale involves two distinct trends: one is toward high sensitivity and resolution for miniaturization, the other aims at functionalization of the resists to realize bottom-up construction of distinct nanoarchitectures. Patterning of carbon nanostructures, a seemingly ideal application for organic functional resists, has been highly reliant on complicated pattern transfer processes because of a lack of patternable precursors. Herein, we present a fullerene–metal coordination complex as a fabrication material for direct functional patterning of sub-10 nm metal-containing carbon structures. The attachment of one platinum atom per fullerene molecule not only leads to significant improvement of sensitivity and resolution but also enables stable atomic dispersion of the platinum ions within the carbon matrix, which may gain fundamentally new interest in functional patterning of hierarchical carbon nanostructures.

Based on the four sets of faults data measured in the practical LCC-HVDC transmission project of China Southern Power Grid Tianshengqiao (Guangxi Province, China)–Guangzhou (Guangdong Province, China) HVDC transmission project, a fault diagnosis method based on the K-nearest neighbor (KNN) algorithm is proposed for an HVDC system. This method can effectively and accurately identify four different fault types, aiming to contribute to construction of a future HVDC system knowledge graph (KG). First, function and significance of fault diagnosis for KG are introduced, along with four specific fault scenarios. Then, the fault data are normalized, classified into a training set and a test set, and labeled. Based on this, the KNN fault diagnosis model is established and Euclidean distance (ED) is selected as the metric function of the KNN algorithm. Finally, the training data are conveyed to the model for training and testing, upon which the diagnosis result obtained by the KNN algorithm with a knowledge graph is compared with that of the support vector machine (SVM) algorithm and Bayesian classifier (BC). The simulation results show that the KNN algorithm can achieve the highest diagnosis accuracy, with more than 83.3% diagnostic accuracy under multiple test sets among all three diagnosis methods.

In order to restrain the spontaneous combustion of coal and ensure the safety of coal mine, an environment-friendly whole-process-inhibiting hydrogel-tea polyphenols-halloysite nanotubes (HNTs) phy...

This article reviewed the literature on gender differences in empathy(defined as someone’s emotional state causes one to experience what one perceive as a similar emotion). A total of five representative studies are examined according to the method they used to assess empathy, in which some studies used self-report questionnaires, others measured brain activities. All of the researches utilizing self-report questionnaires have consistent results favoring women in terms of empathetic abilities, while studies that measured brain activities concluded no discrepancies in initial empathetic abilities. It is suggested that the self-reports are influenced by social expectations, and discrepancy in results of researches in brain activities were impacted by the number of samples and the ongoing debate concerning the responsibility of particular brain areas for empathetic responses. To conclude, there is little discrepancy in the initial empathetic abilities between males and females. However, due to cultural and social factors, females may be more inclined to show more empathetic behavior.

The teaching buildings in colleges and universities are crowded and prone to accidents. The emergency evacuation capability of these buildings is evaluated by applying the methods of fault tree, entropy weight-logarithmic fuzzy multiobjective programming (E-LFMP) and fuzzy comprehensive evaluation. An index system was constructed using the basic event structure importance of the accident tree, and the influencing factors were more systematic. In order to improve the objectivity and rationality of the evaluation process and results, this study combines the entropy weight method and multi-objective fuzzy logarithmic programming (LFMP) method to form the entropy weight-logarithmic fuzzy multiobjective programming. Consequently, the weights of different levels of index factors were analyzed and calculated, and more comprehensive content was considered. The fuzzy comprehensive evaluation model is established to evaluate the emergency evacuation ability of a teaching building. The maximum membership degree is 0.4025, and the corresponding grade is “general”, indicating that its emergency evacuation ability must be improved. Based on the weight ratio and grade results of indicators in the evaluation model of emergency evacuation capability, safety rectification measures and suggestions were put forward from the aspects of improving information systems, widening evacuation channels and strengthening safety channel maintenance.

With coexisting-cooperative-cognitive robots gradually appearing in daily life, an instinct and efficient human-robot interaction (HRI) is becoming more and more challenging and necessary. Surface electromyography (sEMG) signals, as one of mainstream manners of the interactions, are employed to predict human intentions. In this paper, to provide natural assistance for standing up and sitting down, sEMG signals acquired from active muscles of one’s lower limb are utilized to predict continuous movements. A temporally smoothed multilayer perceptron (MLP) regression scheme is proposed for continuous knee/ankle angles estimation by multi-channel sEMG signals. After correlation analyses of sEMG signals and movements, a series of linear and nonlinear regression models are trained to decode human intentions from pre-processed sEMG. Furthermore, to remove out local fluctuations of direct mappings, temporally smoothed techniques are further implemented as post-processings. In the experiments of standing up and sitting down, extensive results of ten healthy subjects show that a three-layer MLP with the Savitzky-Golay filter achieves the best performance on the mean squared error (MSE, testing: 59.58) and the $R^{2}$ score ( $R^{2}$ , testing: 0.948). The proposed regression scheme is compared with other methods and is also verified by measurements of a high-precision visual motion capture system.

Considering drawbacks such as the low inhibition efficiency and short inhibition life of an existing pure hydrogel, a new physicochemical composite hydrogel inhibitor was developed. First, tea polyphenol radicals were grafted and polymerized onto a hydrogel and then mixed with HNTs (halloysite nanotubes). Electron microscopy, Fourier transform infrared spectrometry and thermal gravimetric analysis were used to analyze the inhibiting effect and mechanism of the composite hydrogel inhibitor. Research shows that (i) the graft copolymerization of tea polyphenols with acrylate will increase the contact area between the grafted gels and the surroundings, thus improving the water absorption capability of the hydrogel; (ii) the added tea polyphenols reduce the content of hydroxyl in coal and the content of carboxyl and carbonyl generated during the oxidation of aliphatic groups and it also increase the content of stable ether bond; and (iii) by absorbing the combustible gases and producing water, HNTs can shorten the exothermic temperature range (From 120.22 ℃ to 572.22 ℃) of coal sample processed by composite hydrogel, and it can reduce the release of heat, which is 2536.73 J/mg. These results suggest that the composite hydrogel can distinctly inhibit the spontaneous combustion and oxidation of coal, achieving stable inhibition in many aspects such as its physics, chemistry and thermal stability during the whole process of spontaneous combustion.

The flotation performance of lignite is poor even if a high dosage of the collector is used. In this work, the lignite in the Huolinhe Coalfield of Inner Mongolia was used, and its physicochemical properties were determined by proximate analysis, particle size analysis and Fourier transform infrared spectroscopy. The flotation performances of lignite using six collectors were investigated. Moreover, the flotation responses of lignite with combined collector and two emulsified collectors were compared. It was found that the polar groups in the collector structure were helpful to improve the flotation of lignite through reducing the induction time to 15 ms, only 1/12 of that of the traditional collector (190 ms for diesel). The induction time was in the order of diesel> kerosene> emulsified kerosene> emulsified diesel> C1 (one of the nameless collectors), consistent with the flotation performance. C1 and emulsified collectors significantly improved the flotation performance of lignite by promoting the floating of coarse coal (−500 + 250 μm).

Controlled growth of far-from-equilibrium-shaped nanoparticles with size selection is essential for the exploration of their unique physical and chemical properties. Shape control by wet-chemistry preparation methods produces surfactant-covered surfaces with limited understanding due to the complexity of the processes involved. Here, we report the controlled production and transformation of octahedra to tetrahedra of size-selected platinum nanocrystals with clean surfaces in an inert gas environment. Molecular dynamics simulations of the growth reveal the key symmetry-breaking atomic mechanism for this autocatalytic shape transformation, confirming the experimental conditions required. In-situ heating experiments demonstrate the relative stability of both octahedral and tetrahedral Pt nanocrystals at least up to 700 °C and that the extended surface diffusion at higher temperature transforms the nanocrystals into equilibrium shape., Tetrahedral nanocrystals are out-of-equilibrium structures whose growth mechanism is a long-standing open problem. Here, the authors show that pure Pt tetrahedral nanocrystals grow in the gas phase and single out the defect-mediated mechanism leading to the symmetry-breaking for tetrahedral growth.

International audience; We report the first preparation of small gold–nickel (AuNi) bimetallic nanoparticles (

Biochar nanoparticles (BCN) derived from spruce wood and wheat straw were prepared, characterized and incorporated into zinc-rich epoxy coatings, with the aim of improving the zinc powder utilization and the anticorrosion performance. Formulations with different BCN and commercial carbon black dosages (0.4wt.%, 0.8wt.% and 1.6wt.%) were compared to a zinc-rich epoxy paint (ZRP) without carbon addition. After immersion and salt spray exposure, coated steel panels were characterized with optical, electrochemical and spectroscopy techniques to evaluate the anticorrosive performance. BCN and carbon black addition enhanced the local electrochemical reactions and the barrier effects were promoted by an increased amount of zinc corrosion products (Zn5(OH)8Cl2 and ZnCO3). The formulation with 0.8 wt.% of spruce wood BCN performed equivalently well compared to the ones with carbon black. The degraded area and rust accumulation around the artificial scribe for the formulation with 0.8 wt.% of spruce wood BCN were 29.8% and 27.8% less than ZRP, respectively, which is attributed to the good electrical conductivity and high specific surface area of spruce wood char. These results suggest a promising and sustainable option for improving the anticorrosive performance of zinc-rich epoxy coatings by the incorporation of BCN.

With the increasing exhaustion of high quality coals, it is important to utilize lignite efficiently, which is a resource with abundant reserves. Flotation, as an efficient method for fine particles separation, however, is making slow progress for use with lignite, which basically remains in the laboratory stage. In this article, we briefly describe the characteristics of lignite and explain why lignite is hard to separate. Meanwhile, we review progress in lignite flotation in recent years. In addition, we analysed lignite flotation methods, including grinding, reverse flotation, heating, microwaving, ultrasonic, oily-bubbles flotation and modification of collectors. The advantages and difficulties of the methods above are discussed from a molecular level. Finally, we provide an outlook for the future of lignite flotation.

Bimetallic nanoparticles with tailored structures constitute a desirable model system for catalysts, as crucial factors such as geometric and electronic effects can be readily controlled by tailoring the structure and alloy bonding of the catalytic site. Here we report a facile colloidal method to prepare a series of platinum–gold (PtAu) nanoparticles with tailored surface structures and particle diameters on the order of 7 nm. Samples with low Pt content, particularly Pt4Au96, exhibited unprecedented electrocatalytic activity for the oxidation of formic acid. A high forward current density of 3.77 A mgPt−1 was observed for Pt4Au96, a value two orders of magnitude greater than those observed for core–shell structured Pt78Au22 and a commercial Pt nanocatalyst. Extensive structural characterization and theoretical density functional theory simulations of the best-performing catalysts revealed densely packed single-atom Pt surface sites surrounded by Au atoms, which suggests that their superior catalytic activity and selectivity could be attributed to the unique structural and alloy-bonding properties of these single-atomic-site catalysts. Bimetallic nanoparticles with tailored structure constitute a desirable model system for catalysts. PtAu nanoparticles with Pt single-atom surface sites, prepared by a colloidal method, exhibit unprecedented electrocatalytic activity for formic acid oxidation.

WOS: 000444554700003, PubMed ID: 29796531, The relative stabilities of different chemical arrangements of Pd-Ir and Au-Rh nanoalloys (and their pure metal equivalents) are studied, for a range of compositions, for fcc truncated octahedral 38- and 79-atom nanoparticles (NPs). For the 38-atom NPs, comparisons are made of pure and alloy NPs supported on a TiO2(110) slab. The relative energies of different chemical arrangements are found to be similar for Pd-Ir and Au-Rh nanoalloys, and depend on the cohesive and surface energies of the component metals. For supported nanoalloys on TiO2, the interaction with the surface is greater for Ir (Rh) than Pd (Au): most of the pure NPs and nanoalloys preferentially bind to the TiO2 surface in an edge-on configuration. When Au-Rh nanoalloys are bound to the surface through Au, the surface binding strength is lower than for the pure Au NP, while the Pd-surface interaction is found to be greater for Pd-Ir nanoalloys than for the pure Pd NP. However, alloying leads to very little difference in Ir-surface and Rh-surface binding strength. Comparing the relative stabilities of the TiO2-supported NPs, the results for Pd-Ir and Au-Rh nanoalloys are the same: supported Janus NPs, whose Ir (Rh) atoms bind to the TiO2 surface, bind most strongly to the surface, becoming closer in energy to the core-shell configurations (Ir@Pd and Rh@Au) which are favoured for the free particles., Xiamen University; EPSRC Critical Mass Grant TOUCAN [EP/J010804/1]; EPSRC [EP/L000202]; TOUCAN grant; Royal Society International Exchange Grant [IE140712], T-EF is grateful for funding from the Graduate School of Xiamen University. RLJ and ID acknowledge support through EPSRC Critical Mass Grant (EP/J010804/1) TOUCAN. Calculations were performed on the following HPC facilities: The University of Birmingham Bluebear HPC facility (see http://www.bear.bham.ac.uk/bluebear for more details) and the UK's national HPC facility, ARCHER, both via membership of the UK's HPC Materials Chemistry Consortium, which is funded by EPSRC (EP/L000202), and via the TOUCAN grant. ZYL acknowledges Royal Society International Exchange Grant IE140712. LP acknowledges the French METSA network and Corinne Ulhaq (IPCMS, Strasbourg) for STEM imaging of Pd-Ir nanoparticles.

The dynamics of oxidation of cobalt nanoparticles were directly revealed by in situ environmental transmission electron microscopy. Firstly, cobalt nanoparticles were oxidized to polycrystalline cobalt monoxide, then to polycrystalline tricobalt tetroxide, in the presence of oxygen with a low partial pressure. Numerous cavities (or voids) were formed during the oxidation, owing to the Kirkendall effect. Analysis of the oxides growth suggested that the oxidation of cobalt nanoparticles followed a parabolic rate law, which was consistent with diffusion-limited kinetics. In situ transmission electron microscopy allowed potential atomic oxidation pathways to be considered. The outward diffusion of cobalt atoms inside the oxide layer controlled the oxidation, and formed the hollow structure. Irradiation by the electron beam, which destroyed the sealing effect of graphite layer coated on the cobalt surface and resulted in fast oxidation rate, played an important role in activating and promoting the oxidations. These findings further our understanding on the microscopic kinetics of metal nanocrystal oxidation and knowledge of energetic electrons promoting oxidation reaction.

The surface oxidation of palladium nanocrystals plays an important role in changing the active sites and subsequently influencing the catalytic reactivity. Such a microscopy study on surface oxidation, down to the atomic scale, is essential for understanding the structure-property correlations of palladium nanocrystal based catalysts. Herein, we present an in situ atomic scale study on the surface oxidation behavior of palladium nanocrystals, which is induced by electron beam irradiation under low oxygen partial pressure and at room temperature inside an environmental transmission electron microscope. We found that: (i) surface oxidation initially started at the edge sites with atomic steps or vertex sites, which served as active sites for oxidation; (ii) the oxidation reaction proceeded with a much faster rate on the {111} surface, indicating a certain crystallography preference; (iii) nanometer-sized palladium monoxide islands were formed on the surfaces eventually. The results from our in situ studies provide insightful knowledge, and will be of certain importance for the design of improved functional catalysts in future.

The preparation of inorganic nanomaterials with a desired structure and specific properties requires the ability to strictly control their size, shape and composition. A series of chemical reactions with platinum compounds carried out within the 1.5 nm wide channel of single-walled carbon nanotubes (SWNTs) have demonstrated the ability of SWNTs to act as both a very effective reaction vessel and a template for the formation of nanocrystals of platinum di-iodide and platinum di-sulphide, materials that are difficult to synthesise in the form of nanoparticles by traditional synthetic methods. The stepwise synthesis inside nanotubes has enabled the formation of Pt compounds to be monitored at each step of the reaction by aberration-corrected high resolution transmission electron microscopy (AC-HRTEM), verifying the atomic structures of the products, and by an innovative combination of fluorescence-detected X-ray absorption spectroscopy (FD-XAS) and Raman spectroscopy, monitoring the oxidation states of the platinum guest-compounds within the nanotube and the vibrational properties of the host-SWNT, respectively. This coupling of complementary spectroscopies reveals that electron transfer between the guest-compound and the host-SWNT can occur in either direction depending on the composition and structure of the guest. A new approach for nanoscale synthesis in nanotubes developed in this study utilises the versatile coordination chemistry of Pt which has enabled the insertion of the required chemical elements (e.g. metal and halogens or chalcogens) into the nanoreactor in the correct proportions for the controlled formation of PtI2 and PtS2 with the correct stoichiometry.

Density functional theory calculations are performed to investigate both mixing and adsorption properties of 38-atom and 79-atom Au–Rh nanoalloys at the nanoscale. The RhcoreAushell and RhballAucup isomers are found to be energetically favourable with respect to other isomers. The adsorption strengths of reactive species such as H2, O2 and CO are found to be greater on the Rh part than on the Au part of the nanoalloys and therefore a core–shell inversion is found to be feasible under a molecular environment. It is also found that underlying Rh atoms decrease the adsorption strength on the Au part whereas underlying Au atoms increase it on the Rh part of the nanoalloys. The strain, alloying and relaxation effects on adsorption strength are characterized using a sequential approach and their competing nature is demonstrated for the Au–Rh bimetallic system.

The high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) has been widely used in nanoparticle characterization due to its relatively straightforward interpretability, although multislice simulation is often required in order to take into account the strong dynamical screening effect if quantitative structure information is needed. The multislice simulation is very time-consuming, which can be a hurdle in cases when one has to deal with a large set of images. In this paper, we introduce a simple computer program, based on kinematic-scattering method, which allows users to simulate HAADF-STEM images of small nanoparticles, in ‘real time’ on a standard desktop computer. By comparing with the sophisticated multislice simulation, we demonstrate that such an approach is adequate for nanoparticles of ∼3 nm in diameter (assuming an approximately spherical shape), particularly away from strict zone axis conditions. As an application, we show that the efficient kinematic simulation allows quick identification of orientation of nanoparticles.

In this work, we reported our experimental approach to reveal the detailed growth behavior of platinum (Pt)–copper (Cu) bimetallic multipod nanostructures in a one-pot synthesis by analyzing the intermediate products from different stages by using aberration-corrected scanning transmission electron microscopy and associated energy-dispersive X-ray spectroscopy. An element-specific growth trajectory of Pt–Cu multipod nanostructures with compositional variation couples to geometric morphologies was observed: Ptx–Cu1−x multipods start from Pt-rich seeds (x > 0.6), evolve into a Pt–Cu alloy phase (x ≈ 0.5), and then form Pt-rich branches (with x > 0.8). This could be further explained on considering the different redox potentials of two metals and their interactions through underpotential deposition, galvanic replacement, and phase segregation. The observed combination of geometric morphologies and compositional variations may provide new strategies to potentially aid rational synthesis of alloy catalysts.

Electromyography (EMG) has been popularly used as interface command to achieve a natural control for myoelectric prosthetic-hands. Traditional EMG-based recognition methods always only focus on the classification of target motion classes that were defined in the training phase, but have no ability to reject outlier motion interferences that did not present before. In this paper, a hybrid classifier that combines one one-class Gaussian classifiers and a multi-class LDA was constructed to achieve EMG-based motion classification, in which Gaussian classifiers were used to reject outlier interferences, while LDA was used to classify target motion samples. The robust hybrid classifier is easily built and has low run-time complexity. Extensive experiments were conducted to verify the performance of the proposed hybrid classifier, where 91.6% of target motion recognition accuracy and 96.5% of outlier motion rejection accuracy were respectively obtained. Finally, the hybrid classifier was involved to achieve a robust and real-time control of a myoelectric prosthetic-hand.

Here we report on the synthesis of novel dendritic Pt3Cu triangular pyramid caps via a solvothermal coreduction method. These caps had three-dimensional caved structures with ultrathin branches, as evidenced by high-resolution transmission electron microscopy (HRTEM) and HAADF-STEM characterization. Tuning the reduction kinetics of two metal precursors by an iodide ion was believed to be the key for the formation of an alloyed nanostructure. Electro-oxidation of methanol and formic acid showed dramatically improved electrocatalytic activities and poison-tolerance for these nanoalloys as compared to commercial Pt/C catalysts, which was attributed to their unique open porous structure with interconnected network, ultrahigh surface areas, as well as synergetic effect of the two metallic components.

In order to overcome the short inhibition duration of physical inhibitor, the environmentally friendly chemical inhibitors of polyethylene glycol (PEG) and proanthocyanidin (OPC) were selected to conduct the experimental study for coal spontaneous combustion prevention. Through temperature programmed experiment, electron spin resonance experiment and Fourier infrared spectroscopy experiment, it was found that for the coal sample after treated by PEG and OPC, crossing point temperature increased by 17.6 °C and 14.3 °C, free radical concentration decreased to 0.1512 Ng/1017 g−1 and 0.1178 Ng/1017 g−1, association and hydroxyl free hydroxyl groups decreased by 59.72% and 24.37%, and the stability of the C O C ether bond increased by 42.71% and 18.41%, respectively, which showed the inhibition effects of both inhibitors are obvious and OPC is better. For the sample treated by OPC and PEG (ratio 1:2), crossing point temperature increased 25 °C, which indicated that the collaborative effect was remarkable. The analysis shows that PEG and OPC contain a large number of hydroxyl groups, which react with the oxide intermediate product alcohol to form ether bonds with relatively stable chemical properties, thus mitigating the rate of coal spontaneous combustion; PEG and OPC are linked by hydrogen bonds to synthesize larger hydrogen proton donors, which improved antioxidant activity. PEG is a viscous liquid, when carrying proanthocyanidin, can cover the surface of coal, isolating coal surface from oxygen, keeping moisture and cooling. The combination of the two inhibitors has significant synergistic inhibition effect, which can greatly suppress the coal spontaneous combustion.

We present a comparative study of the activity and selectivity of Rh/C nanoparticles and Sn-modified Rh/C nanoparticles towards electrocatalytic nitrate reduction in sulfuric acid. Electrochemical techniques, combined with more direct analytical techniques such as mass spectrometry and ion chromatography, were applied to analyse the products obtained during the reaction. Online electrochemical mass spectrometry was employed to detect volatile products, such as nitric oxide (NO), nitrous oxide (N2O) and dinitrogen (N2). The combination of online sample collection to the electrochemical cell and offline ion chromatography allows the quantitative analysis of non-volatile products, such as ammonium () and hydroxylamine (NH3OH+). Non-volatile products can be detected during nitrate reduction at Rh/C electrodes. The catalytic activity of Rh/C electrodes can be enhanced by Sn modification. N2O is the dominant volatile product at SnRh/C electrodes. is the main ionic product at the Rh/C electrodes, whereas modification by Sn also leads to the formation of NH3OH+.

The energetics, structures and segregation of 98-atom AuPd nanoclusters are investigated using a genetic algorithm global optimization technique with the Gupta empirical potential (comparing three different potential parameterisations) followed by local minimizations using Density Functional Theory (DFT) calculations. A shell optimization program algorithm is employed in order to study the energetics of the highly symmetric Leary Tetrahedron (LT) structure and optimization of the chemical ordering of a number of structural motifs is carried out using the Basin Hopping Monte Carlo approach. Although one of the empirical potentials is found to favour the LT structure, it is shown that Marks Decahedral and mixed FCC-HCP motifs are lowest in energy at the DFT level. © The Royal Society of Chemistry.

Gold nanoparticles on solid supports are of particular interest for their high catalytic activity for low-temperature CO oxidation.1 Although a number of factors influencing the catalytic properties have been recognized, including method of synthesis, size, shape, and interaction with support, the origin of the reactivity is still much of a debate.2 By way of example, Lopez et al. pointed out that, among these factors, the availability of a high concentration of low-coordination sites on small Au particles, particularly those at corners, is the most important.2b In contrast, Valden et al. showed that the catalytic rate of Au nanoparticles decreases with decreasing particle size when they are smaller than 3 nm, despite an increase in the amount of low-coordination atoms.3 In the later articles, the same group demonstrated that the catalytic activity of the bilayer Au films is the highest as compared with those of the bilayer and hemispherical Au particles.4 This further suggested that low-coordination corner or edge Au sites may not be so crucial as they were previously considered. More recently, based on the scanning transmission electron microscopy (STEM) analysis, a high catalytic activity for carbon monoxide oxidation is associated with the presence of bilayer Au nanoparticles of 0.5 nm on iron oxide.5 However, this is not supported in a subsequent article, in which the absolute necessity of monolayer or bilayer structure for high catalytic performance is ruled out.6 These distinct reports indicate that more in-depth research is needed in order to establish a clear link among these identified factors and any combination of them should be treated on a case-by-case basis. Measuring size and shape of nanometer catalytic clusters is a challenging task. In particular, real catalyst samples are often characterized by a distribution of size and shape. Although the capability of STEM, with or without an aberration corrector, as a structural probe has been demonstrated,7–11 there have been few reports on viability of the technique as an effective tool for obtaining size and shape information of real nanocatalysts. Here, we apply this technique to size-selected model catalysts, Au25 and Au39 (clusters containing nominal 25 and 39 gold atoms, respectively). We show, by optimizing imaging conditions of a STEM equipped with a high-angle annular dark-field (HAADF) detector, that the size and shape of the clusters can be obtained from the STEM-HAADF intensity profile through single-shot imaging. The quantitative analysis of STEM-HAADF intensity allows us to derive that the deposited and then calcined Au clusters maintained discrete sizes being multiples of either Au25 or Au39. The overall shape of the clusters can be modelled as hemispherical-like, suggesting a strong cluster–support interaction. Figure ​1a,b1a,b show two high-resolution images taken from samples of Au25 and Au29 supported on hydroxyapatite (HAP), respectively. Each cluster was analysed with the background subtracted with reference to its surrounding areas. The histograms of the integrated intensities for the samples Au25 and Au39 are shown in Figure ​2a,b,2a,b, respectively. To determine the number of peaks (k) and the associated peak positions in each case, the Integrated Complete Likelihood (ICL) criterion was employed based on Gaussian distributions.12 The intensities larger than 120 × 104 for Au25 and 95 × 104 for Au39 were not included in the ICL calculation due to a small number of data points. The best fits were achieved when k = 8 for Au25 and k = 4 for Au39, corresponding the existence of 8 and 4 mixed Gaussian functions, respectively, as shown in Figure 2. Figure 1 High resolution HAADF-STEM images taken from: a) Au25, and b) Au39 samples, respectively. The mass of the clusters were labeled as times of either Au25 or Au39 monometers in each case. Figure 2 Histograms of integrated intensity and the corresponding Integrated Complete Likelihood (ICL) criteria evaluated as a function of the number of Gaussian functions for: a) the Au25, and b) the Au39 clusters on hydroxyapatite, respectively. The solid curves ... There are several features of interest in Figure 2 that relate to the nature of the size-controlled Au clusters. The fitted Gaussian functions are evenly spaced in both cases. The spacing between the neighboring peaks for the Au25 sample is (136 ± 11) × 102, with that for the Au39 sample being (208 ± 22) × 102. The ratio of these two values is 1.53, being very close to the expected ratio of numbers of atoms in Au39 and Au25 monomers, i.e., 39/25 = 1.56. Therefore, the first peaks in each case are attributed to the corresponding monomers, with the rest of peaks being the multiples. The multiples of the Au25 and Au39 monomers are labeled in Figure 1 according to the above analysis. Here, the size-controlled Au25 and Au39 nanoclusters were acting as mutual mass calibrators. In the quantitative analysis of the cluster intensities, a number of factors can introduce errors, including, for example, the emission current, the aberrations of the magnetic lenses, the position of the objective aperture to the Ronchigram, the position of the electron beam with regards to the ADF detector and the offset and gain values of the ADF preamplifier. In particular, to assess the microscopy conditions on quantification of mass of a cluster, two specimens, both containing single Au atoms supported on carbon films (images not shown in this paper), were used as an independent check between two different runs. The difference in the mean integrated intensity for a single atom is ∼5%, far smaller than the integrated intensity difference, ∼56%, between the Au25 and Au39 cluster samples. Whenever possible, both Au25 and Au39 samples were always imaged in the same session to compare. The results in Figure 2 show that a large fraction of the clusters in both samples had aggregated, consisting several clusters of initial sizes. The clear integer multiples in the intensity histograms suggest that the aggregation is not via an Ostwald ripening process, rather it may be through cluster fusion, in which clusters retained their original identities. This is consistent with the broad cluster diameter distribution (full-width-half-maximum) in each case, 1.25 nm for Au25 and 1.5 nm for Au39, with the mean diameter of around 1.7–1.9 nm (See Figure ​33). Figure 3 Histograms showing the diameters of the Au25 (a) and the Au39 (b) clusters on hydroxyapatite. The above result should be compared with the previous published data for the same set of samples when they were imaged immediately after the synthesis, in which both types of the clusters had been shown to be 1.1 ± 0.5 nm in diameter.13 The large discrepancy in diameter distribution between the two studies cannot be completely attributed to the limited resolution and low sensitivity of the STEM without a probe corrector used in the previous study. One possibility is that the aggregation had occurred during the time span over two months from the sample preparation in Japan to the STEM observations in the UK. Further investigation is planned to see if these aggregated clusters, which have retained the memory of their initial sizes, still maintain their size-dependent catalytic performance. To gain insight of the bonding strength between clusters and the HAP support, we plot in Figure ​44 the integrated HAADF intensity of each cluster as a function of its diameter, together with the relationship generated from the idealized spherical and hemispherical models (shown with solid and dashed lines). In the geometric models, the Wigner-Seitz radius of gold, rws = 0.165 nm, is used.10, 14 It is clear from Figure 4 that majority data points, though scattered, follow the trend of the hemispherical model, when the diameter is less than ∼2 nm. The result suggests that the clusters are flattened on the support, likely as a result of the strong interaction between the Au and PO43− moieties of HAP.15 Figure 4 Integrated HAADF intensity of clusters as a function of corresponding diameter. The solid and dashed lines represent idealized spherical and hemispherical models, respectively. In summary, Au25 and Au39 nanoclusters supported on hydroxyapatite (HAP) were investigated using aberration corrected scanning transmission electron microscopy. We demonstrate that the quantitative analysis of the HAADF intensities of the nanoclusters provide an invaluable tool in obtaining direct information of cluster size in terms of the number of atoms within. We show that the well size-controlled clusters, as in this work, can act as ideal mass calibrators, similar as those prepared in the gas phase and mass selected.9, 10, 16 We have associated the evenly spaced peaks in the histograms with multiples of single clusters of either Au25 or Au39 in each case, from which Oswald ripening mechanism for the observed cluster aggregation can be ruled out. There is a clear sign indicating that the aggregated clusters retained their original identity. This feature together with the strong interaction with the hydroxyapatite support based on the 3D shape analysis suggests new opportunities in the development of stable Au catalysts with size-dependent reactivity.

We identify and report on UV−vis spectral features of AucorePdshell nanoparticles. Chains of conjoined nanospheres are formed with clear core/shell segregation and identified via experimental spectral red shifts of λmax and scanning transmission electron microscopy (STEM) imaging. Theoretical calculations performed using the discrete dipole approximation (DDA) validate our findings. The DDA simulation method is then used to delve further into possible spectroscopic implications of geometric and environmental changes. Structural configurations including extended chains of nanospheres, differing levels of nanosphere conjoinment, and increased Pd shell thickness are investigated, as well as variations of the surrounding dielectric medium.