Stable mass-selected AuTiOx nanoparticles for CO oxidation.

Stability under reactive conditions poses a common challenge for cluster- and nanoparticle-based catalysts. Since the catalytic properties of <5 nm gold nanoparticles were first uncovered, optimizing their stability at elevated temperatures for CO oxidation has been a central theme. Here we report direct observations of improved stability of AuTiOx alloy nanoparticles for CO oxidation compared with pure Au nanoparticles on TiO2. The nanoparticles were synthesized using a magnetron sputtering, gas-phase aggregation cluster source, size-selected using a lateral time-of-flight mass filter and deposited onto TiO2-coated micro-reactors for thermocatalytic activity measurements of CO oxidation. The AuTiOx nanoparticles exhibited improved stability at elevated temperatures, which is attributed to a self-anchoring interaction with the TiO2 substrate. The structure of the AuTiOx nanoparticles was also investigated in detail using ion scattering spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. The measurements showed that the alloyed nanoparticles exhibited a core-shell structure with an Au core surrounded by an AuTiOx shell. The structure of these alloy nanoparticles appeared stable even at temperatures up to 320 °C under reactive conditions, for more than 140 hours. The work presented confirms the possibility of tuning catalytic activity and stability via nanoparticle alloying and self-anchoring on TiO2 substrates, and highlights the importance of complementary characterization techniques to investigate and optimize nanoparticle catalyst designs of this nature.

Broadband and Spectrally Selective Photothermal Conversion through Nanocluster Assembly of Disordered Plasmonic Metasurfaces.

Plasmonic metasurfaces have been realized for efficient light absorption, thereby leading to photothermal conversion through nonradiative decay of plasmonic modes. However, current plasmonic metasurfaces suffer from inaccessible spectral ranges, costly and time-consuming nanolithographic top-down techniques for fabrication, and difficulty of scale-up. Here, we demonstrate a new type of disordered metasurface created by densely packing plasmonic nanoclusters of ultrasmall size on a planar optical cavity. The system either operates as a broadband absorber or offers a reconfigurable absorption band right across the visible region, resulting in continuous wavelength-tunable photothermal conversion. We further present a method to measure the temperature of plasmonic metasurfaces via surface-enhanced Raman spectroscopy (SERS), by incorporating single-walled carbon nanotubes (SWCNTs) as an SERS probe within the metasurfaces. Our disordered plasmonic system, generated by a bottom-up process, offers excellent performance and compatibility with efficient photothermal conversion. Moreover, it also provides a novel platform for various hot-electron and energy-harvesting functionalities.

Metal Nanocluster-Metal Organic Framework-Polymer Hybrid Nanomaterials for Improved Hydrogen Detection.

The development of hydrogen sensors is of paramount importance for timely leak detection and remains a crucial unmet need. Palladium-based materials, well known as hydrogen sensors, still suffer from poisoning and deactivation. Here, a hybrid hydrogen sensor consisting of a Pd nanocluster (NC) film, a metal-organic framework (MOF), and a polymer, are proposed. The polymer coating, as a protection layer, endows the sensor with excellent H2 selectivity and CO-poisoning resistance. The MOF serves as an interface layer between the Pd NC film and the polymer layer, which alters the nature of the interaction with hydrogen and leads to significant sensing performance improvements, owing to the interfacial electronic coupling between Pd NCs and the MOF. The strategy overcomes the shortcomings of retarded response speed and degraded sensitivity induced by the polymer coating of a Pd NC film-polymer hybrid system. This is the first exhibition of a hydrogen-sensing enhancement mechanism achieved by engineering the electronic coupling between Pd and a MOF. The work establishes a deep understanding of the hydrogen-sensing enhancement mechanism at the nanoscale and provides a feasible strategy to engineer next-generation gas-sensing nanodevices with superior sensing figures of merit via hybrid material systems.

Molecular dynamics simulation of nanofilament breakage in neuromorphic nanoparticle networks.

Neuromorphic computing systems may be the future of computing and cluster-based networks are a promising architecture for the realization of these systems. The creation and dissolution of synapses between the clusters are of great importance for their function. In this work, we model the thermal breakage of a gold nanofilament located between two gold nanoparticles via molecular dynamics simulations to study on the mechanisms of neuromorphic nanoparticle-based devices. We employ simulations of Au nanowires of different lengths (20-80 Å), widths (4-8 Å) and shapes connecting two Au1415nanoparticles (NPs) and monitor the evolution of the system via a detailed structural identification analysis. We found that atoms of the nanofilament gradually aggregate towards the clusters, causing the middle of wire to gradually thin and then break. Most of the system remains crystalline during this process but the center is molten. The terminal NPs increase the melting point of the NWs by fixing the middle wire and act as recrystallization areas. We report a strong dependence on the width of the NWs, but also their length and structure. These results may serve as guidelines for the realization of cluster-based neuromorphic computing systems.

An ab initio study of size-selected Pd nanocluster catalysts for the hydrogenation of 1-pentyne.

The hydrogenation of alkynes is an important reaction in the synthesis of both fine and bulk chemicals. Palladium-based catalysts are widely used and therefore size-selected Pd nanoclusters may provide enhanced performance. An investigation of the adsorption and desorption of the molecules involved in the reaction can shed light on the activity and selectivity of the catalysts. We employ ab initio calculations to investigate the binding energies of all the molecules related to the hydrogenation of 1-pentyne (1-pentyne, 1-pentene, cis-2-pentene, trans-2-pentene and pentane) on a comprehensive set of possible binding sites of two Pd147 and Pd561 cuboctahedral nanoclusters. We extract the site and size dependence of these binding energies. We find that the adsorption of 1-pentyne occurs preferably on the (100) facets of the nanoclusters, followed by their (111) facets, their edges and their vertices. The molecule binds more strongly on the larger nanoclusters, which are therefore expected to display higher activity. The binding energies of the pentenes are found to be lower on the smaller nanoclusters. Therefore, these molecules are expected to desorb more easily and the small clusters should display better selectivity, i.e., partial hydrogenation to 1-pentene, compared with large clusters. Our results provide guidelines for the optimal design of Pd nanocatalysts.

Expansion of the Human Phenotype Ontology (HPO) knowledge base and resources.

The Human Phenotype Ontology (HPO)-a standardized vocabulary of phenotypic abnormalities associated with 7000+ diseases-is used by thousands of researchers, clinicians, informaticians and electronic health record systems around the world. Its detailed descriptions of clinical abnormalities and computable disease definitions have made HPO the de facto standard for deep phenotyping in the field of rare disease. The HPO's interoperability with other ontologies has enabled it to be used to improve diagnostic accuracy by incorporating model organism data. It also plays a key role in the popular Exomiser tool, which identifies potential disease-causing variants from whole-exome or whole-genome sequencing data. Since the HPO was first introduced in 2008, its users have become both more numerous and more diverse. To meet these emerging needs, the project has added new content, language translations, mappings and computational tooling, as well as integrations with external community data. The HPO continues to collaborate with clinical adopters to improve specific areas of the ontology and extend standardized disease descriptions. The newly redesigned HPO website (www.human-phenotype-ontology.org) simplifies browsing terms and exploring clinical features, diseases, and human genes.

Absence of Nonlocal Manipulation of Oxygen Atoms Inserted below the Si(111)-7×7 Surface.

The injection of electrons from the scanning tunneling microscope tip can be used to perform nanoscale chemistry and study hot electron transport through surfaces. While nonlocal manipulation has been demonstrated primarily for aromatic adsorbates, here we confirm that oxygen atoms bonded to the Si(111) surface can also be nonlocally manipulated, and we fit the measured manipulation data to a single channel decay model. Unlike aromatic adsorption systems, oxygen atoms also insert below the surface of silicon. Although the inserted oxygen can be manipulated when the tip is directly over the relevant silicon adatom, it is not possible to induce nonlocal manipulation of inserted oxygen atoms at the same bias. We attribute this to the electrons injected at +4 eV initially relaxing to couple to the highest available surface state at +3.4 eV before laterally transporting through the surface. With a manipulation threshold of 3.8 eV for oxygen inserted into silicon, once carriers have undergone lateral transport, they do not possess enough energy to manipulate and remove oxygen atoms inserted beneath the surface of silicon. This result confirms that nonlocal nanoscale chemistry using the scanning tunneling microscope tip is dependent not only on the energy required for atomic manipulation, but also on the energy of the available surface states to carry the electrons to the manipulation site.

Optimization of sol-immobilized bimetallic Au-Pd/TiO2 catalysts: reduction of 4-nitrophenol to 4-aminophenol for wastewater remediation.

A sol-immobilization method is used to synthesize a series of highly active and stable AuxPd1-x/TiO2 catalysts (where x = 0, 0.13, 0.25, 0.5, 0.75, 0.87 and 1) for wastewater remediation. The catalytic performance of the materials was evaluated for the catalytic reduction of 4-nitrophenol, a model wastewater contaminant, using NaBH4 as the reducing agent under mild reaction conditions. Reaction parameters such as substrate/metal and substrate/reducing agent molar ratios, reaction temperature and stirring rate were investigated. Structure-activity correlations were studied using a number of complementary techniques including X-ray powder diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy. The sol-immobilization route provides very small Au-Pd alloyed nanoparticles, with the highest catalytic performance shown by the Au0.5Pd0.5/TiO2 catalyst. This article is part of a discussion meeting issue 'Science to enable the circular economy'.

Synthesis without Solvents: The Cluster (Nanoparticle) Beam Route to Catalysts and Sensors.

It is hard to predict the future of science. For example, when C60 and its structure were identified from the mass spectra of gas phase carbon clusters, few could have predicted the era of carbon nanotechnology which the discovery introduced. The solubilization and functionalization of C60, the identification and then synthesis of carbon nanotubes, and the generation and physics of graphene have made a scale of impact on the international R&D (and to some extent industrial) landscape which could not have been foreseen. Technology emerged from a search for molecules of astrochemical interest in the interstellar gas. This little sketch provides the authors with the confidence to present here a status report on progress toward another radical future-the synthesis of nanoparticles (typically metals) on an industrial scale without solvents and consequently effluents, without salts and their sometimes accompanying toxicity, with minimal prospects for unwanted nanoparticle escape into the environment, with a high degree of precision in the control of the size, shape and composition of the nanoparticles produced and with applications from catalysts and sensors to photonics, electronics and theranostics. In fact, our story begins in exactly the same place as the origin of the nanocarbon era-the generation and mass selection of free atomic clusters in a vacuum chamber. The steps along the path so far include deposition of such beams of clusters onto surfaces in vacuum, elucidation of the key elements of the cluster-surface interaction, and demonstrations of the potential applications of deposited clusters. The principal present challenges, formidable but solvable, are the necessary scale-up of cluster beam deposition from the nanogram to the gram scale and beyond, and the processing and integration of the nanoclusters into appropriate functional architectures, such as powders for heterogeneous catalysis, i.e., the formulation engineering problem. The research which is addressing these challenges is illustrated in this Account by examples of cluster production (on the traditional nanogram scale), emphasizing self-selection of size, controlled generation of nonspherical shapes, and nonspherical binary nanoparticles; by the scale-up of cluster beam production by orders of magnitude with the magnetron sputtering, gas condensation cluster source, and especially the Matrix Assembly Cluster Source (MACS); and by promising demonstrations of deposited clusters in gas sensing and in heterogeneous catalysis (this on the gram scale) in relevant environments (both liquid and vapor phases). The impact on manufacturing engineering of the new paradigm described here is undoubtedly radical; the prospects for economic success are, as usual, full of uncertainties. Let the readers form their own judgements.

Advancing Health Services Research to Eliminate Health Care Disparities.

Findings from health services research highlight continuing health care disparities in the United States, especially in the areas of access to health care and quality of care. Although attention to health care disparities has increased, considerable knowledge gaps still exist. A better understanding of how cultural, behavioral, and health system factors converge and contribute to unequal access and differential care is needed. Research-informed approaches for reducing health care disparities that are feasible and capable of sustained implementation are needed to inform policymakers. More important, for health equity to be achieved, it is essential to create a health care system that provides access, removes barriers to care, and provides equally effective treatment to all persons living in the United States.

Methodological Approaches to Understanding Causes of Health Disparities.

Understanding health disparity causes is an important first step toward developing policies or interventions to eliminate disparities, but their nature makes identifying and addressing their causes challenging. Potential causal factors are often correlated, making it difficult to distinguish their effects. These factors may exist at different organizational levels (e.g., individual, family, neighborhood), each of which needs to be appropriately conceptualized and measured. The processes that generate health disparities may include complex relationships with feedback loops and dynamic properties that traditional statistical models represent poorly. Because of this complexity, identifying disparities' causes and remedies requires integrating findings from multiple methodologies. We highlight analytic methods and designs, multilevel approaches, complex systems modeling techniques, and qualitative methods that should be more broadly employed and adapted to advance health disparities research and identify approaches to mitigate them.

Orientational Epitaxy of van der Waals Molecular Heterostructures.

The shape of individual building blocks is an important parameter in bottom-up self-assembly of nanostructured materials. A simple shape change from sphere to spheroid can significantly affect the assembly process due to the modification to the orientational degrees of freedom. When a layer of spheres is placed upon a layer of spheroids, the strain at the interface can be minimized by the spheroid taking a special orientation. C70 fullerenes represent the smallest spheroids, and their interaction with a sphere-like C60 is investigated. We find that the orientation of the C70 within a close-packed C70 layer can be steered by contacting a layer of C60. This orientational steering phenomenon is potentially useful for epitaxial growth of multilayer van der Waals molecular heterostructures.

Determining the Long-Term Effectiveness of a Group-Based Physical Activity Program.

OBJECTIVE: In 2015, only half (48%) of older adults in the United States (≥60 years) reported engaging in any kind of physical activity. Few studies examine the impact of evidence-based programs when adopted in community-based settings. The purpose of this study is to assess the effectiveness of EnhanceFitness (EF) upto 12-months. METHOD: EF was offered to older adults in South Florida. A total of 222 EF classes were offered between October 2008 and December 2014. Program consisted of a 1-hour session held three times a week. Even though participation was required for 4 months, 1,295 participants continued the program for at least 1 year. RESULTS: All participants showed significant improvement in outcome measures. A mean change of 1.5, 1.7, and 1.9 was seen in number of chair stands at 4, 8, and 12 months (p < .001), respectively. The number of arm curls performed improved from 16.8 at baseline to 18.8, 18.8, and 19.2 at 4-, 8-, and 12-months, respectively. Participants improved their up-and-go time by decreasing from 9.1 (baseline) to 8.7 (4 months) to 8.6 (12 months; p = .001). DISCUSSION: Randomized controlled trials are commonly used to determine the efficacy of an intervention. These interventions when disseminated at the population level have the potential to benefit large masses. EF is currently offered at more than 700 locations. This tremendous success of EF brings attention to an important question of continuous monitoring of these programs to ensure program consistency and intended outcomes. The model used by the Healthy Aging Regional Collaborative could be replicated by other communities.

Performance of Preformed Au/Cu Nanoclusters Deposited on MgO Powders in the Catalytic Reduction of 4-Nitrophenol in Solution.

The deposition of preformed nanocluster beams onto suitable supports represents a new paradigm for the precise preparation of heterogeneous catalysts. The performance of the new materials must be validated in model catalytic reactions. It is shown that gold/copper (Au/Cu) nanoalloy clusters (nanoparticles) of variable composition, created by sputtering and gas phase condensation before deposition onto magnesium oxide powders, are highly active for the catalytic reduction of 4-nitrophenol in solution at room temperature. Au/Cu bimetallic clusters offer decreased catalyst cost compared with pure Au and the prospect of beneficial synergistic effects. Energy-dispersive X-ray spectroscopy coupled with aberration-corrected scanning transmission electron microscopy imaging confirms that the Au/Cu bimetallic clusters have an alloy structure with Au and Cu atoms randomly located. Reaction rate analysis shows that catalysts with approximately equal amounts of Au and Cu are much more active than Au-rich or Cu-rich clusters. Thus, the interplay between the Au and Cu atoms at the cluster surface appears to enhance the catalytic activity substantially, consistent with model density functional theory calculations of molecular binding energies. Moreover, the physically deposited clusters with Au/Cu ratio close to 1 show a 25-fold higher activity than an Au/Cu reference sample made by chemical impregnation.

Silver Russel syndrome in an aboriginal patient from Australia.

Silver-Russell syndrome (SRS OMIM 180860) is a rare, albeit well-recognized disorder characterized by severe intrauterine and postnatal growth retardation. It remains a clinical diagnosis with a molecular cause identifiable in approximately 60%-70% of patients. We report a 4-year-old Australian Aboriginal girl who was born at 32 weeks gestation with features strongly suggestive of SRS, after extensive investigation she was referred to our undiagnosed disease program (UDP). Genomic sequencing was performed which identified a heterozygous splice site variant in IGF2 which is predicted to be pathogenic by in-silico studies, paternal allelic origin, de novo status, and RNA studies on fibroblasts. We compare clinical findings with reported patients to add to the knowledge base on IGF2 variants and to promote the engagement of other Australian Aboriginal families in genomic medicine.

Controlled Manipulation of Magic Number Gold-Fullerene Clusters Using Scanning Tunneling Microscopy.

We report controlled manipulation of magic number gold-fullerene clusters, (C60) m-(Au) n, on a Au(111) substrate at 110 K using scanning tunneling microscopy (STM). Each cluster consists of a two-dimensional gold island of nAu atoms confined by a frame of mC60 molecules. Using STM, C60 molecules are extracted from the molecular frame one at a time. The extraction is conducted by driving the STM tip into the cluster, leading to one of the molecules being squeezed out of the frame. Unlike at room temperature, the extracted molecules do not move away from the cluster because of the lack of thermal energy at 110 K; they are found to be attached to the outside of the frame. Reversible manipulation is also possible by pushing an extracted molecule back into the frame. This reversible manipulation is possible only for molecules from the edge of the cluster.

Bridge-bonded methylthiolate on Au(111) observed with the scanning tunneling microscope.

We report the discovery of bridge-bonded methylthiolate, SCH3, along the step edges of the Au(111) surface. Real-space imaging with a scanning tunnelling microscope reveals the presence of bridge-bonded SCH3 along both the [11[combining macron]0] and the [112[combining macron]] oriented step edges. The nearest neighbour distances of SCH3 along these steps are 2a and , respectively. The Au(111) terrace is covered with the usual CH3SAuSCH3 staples. The bridge-bonded alkanethiolate is expected to play a rather significant role in the formation of thiol-passivated Au nanoclusters because of the high fraction of atoms in similar low-coordination sites.

Tip-triggered Thermal Cascade Manipulation of Magic Number Gold-Fullerene Clusters in the Scanning Tunnelling Microscope.

We demonstrate cascade manipulation between magic number gold-fullerene hybrid clusters by channelling thermal energy into a specific reaction pathway with a trigger from the tip of a scanning tunnelling microscope (STM). The (C60)m-Aun clusters, formed via self-assembly on the Au(111) surface, consist of n Au atoms and m C60 molecules; the three smallest stable clusters are (C60)7-Au19, (C60)10-Au35, and (C60)12-Au49. The manipulation cascade was initiated by driving the STM tip into the cluster followed by tip retraction. Temporary, partial fragmentation of the cluster was followed by reorganization. Self-selection of the correct numbers of Au atoms and C60 molecules led to the formation of the next magic number cluster. This cascade manipulation is efficient and facile with an extremely high selectivity. It offers a way to perform on-surface tailoring of atomic and molecular clusters by harnessing thermal energy, which is known as the principal enemy of the quest to achieve ultimate structural control with the STM.

Towards production of novel catalyst powders from supported size-selected clusters by multilayer deposition and dicing.

A multilayer deposition method has been developed with the potential to capture and process atomic clusters generated by a high flux cluster beam source. In this deposition mode a series of sandwich structures each consisting of three layers-a carbon support layer, cluster layer and polymer release layer-is sequentially deposited to form a stack of isolated cluster layers, as confirmed by through-focal aberration-corrected HAADF STEM analysis. The stack can then be diced into small pieces by a mechanical saw. The diced pieces are immersed in solvent to dissolve the polymer release layer and form small platelets of supported clusters.

A proximal retarding field analyzer for scanning probe energy loss spectroscopy.

A compact proximal retarding field analyzer for scanning probe energy loss spectroscopy measurements is described. Using the scanning tunneling microscope (STM) tip as a field emission (FE) electron source in conjunction with this analyzer, which is placed at a glancing angle to the surface plane, FE sample current and electron reflectivity imaging may be performed simultaneously. This is demonstrated in measurements of Ag nanostructures prepared on graphite by electron-beam lithography, where a material contrast of 13% is observed, with a lateral resolution of 25 nm, between the silver and graphite in electron reflectivity images. Topological contrast mechanisms such as edge enhancement and shadowing are also observed, giving rise to additional features in the electron reflectivity images. The same instrument configuration has been used to measure electron energy loss spectra on bare graphite, where the zero loss peak, π band plasmon loss peak and secondary electron peaks are observed. Using this simple and compact analyzer an STM, with sufficient open access to the tip-sample junction, may easily be augmented to provide simultaneous elemental and topographic mapping, supplementing STM image measurements with FE sample current and electron reflectivity images, as well as electron energy loss spectroscopy measurements, in the same instrument.