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The coupled effects of pH and ionic strength impact a variety of geochemical processes in the subsurface. In this study, we investigate the interactions of H+ and major ions at the surface-solution interface of silica porous media under advection-dominated flow-through conditions. A series of 21 column experiments were performed by systematically injecting solutions of different pH and ionic strengths. Three types of porous media (i.e., two natural sands and quartz beads) were considered in order to explore differences in surface/solution interactions among quartz materials. Multiple lines of evidence were used to characterize the geochemical processes taking place during the flow-through experiments: (i) breakthrough curves of pH and major ions were measured at the column outlets; (ii) the natural sand surfaces were characterized by chemical extractions and scanning electron microscopy and the quartz structure was analyzed by XRD; (iii) reactive transport modeling was performed to quantitatively interpret the experimental results. We observed strong reactivity of the quartz surface characterized by significant release of protons when interacting with the major ions. The results also show significant differences in the quantity of protons emitted from the surfaces of the three silica porous media, as well as in the shape of the pH breakthrough curves. Reactive transport modeling was based on a multicomponent ionic transport formulation and on surface complexation description of the solid/solution interactions. The surface complexation model included the individual contributions of quartz and Fe/Al oxides present in the sand coatings with the component additive approach. For each medium, a single set of surface complexation parameters capable of reproducing the experimental dataset (i.e., 7 columns) was calibrated by parallelizing the simulations of the flow-through experiments. This approach allowed us to capture the pH and ionic species behavior within a large range of ionic strengths (i.e., [0–100] mM). The SCMs quantitatively show that H+ is released from quartz upon adsorption of Na+ and that the protonation of the oxides surfaces retards the pH front. Differences in acidity behavior between the silica surfaces seem to be primarily controlled by differences in surface topology, crystal structure of quartz and/or various presence of aluminosilicates. This study demonstrates that the reactivity and diversity of quartz surfaces in silica porous media and the complex interplay with oxide surfaces in the coatings control the transport of aqueous charged species in flow-through systems.

Fabricating smooth and contamination-free sub-10 nm thick gold layers on dielectric substrates is of interest for a number of applications, including plasmonics, metamaterials and nanoelectronics. Metallic adhesion layers are often used to facilitate good adhesion between gold and substrates but at the cost of interfacial alloying and subsequent deterioration of the optical and electrical properties of the thin films. Another approach for promoting adhesion between gold and SiO2 substrates is the use of self-assembled organosilane monolayer linkers, such as (3-aminopropyl)¬trimethoxysilane (APTMS). APTMS, however, is a corrosive chemical and its monolayer preparation is highly sensitive to ambient conditions. Here, we introduce an easy and fast immersion process using (3-aminopropyl)-silatrane (APS) for achieving smooth and high-purity gold films and compare its performance to APTMS. Our APS recipe is water based, does not require environmental considerations, and has approximately 6 times faster deposition time than APTMS (30min vs. 3hr). The results demonstrate that both organic molecules promote the formation of continuous and smooth 10 nm thick gold films, without leading to considerable chemical intermixing at the interface. Monitoring the growth evolution of the gold layer indicates a threshold thickness of 6-7 nm for obtaining continuous films. Overall, the ease of use, faster processing time and low toxicity of APS make it an attractive choice for fabricating high-quality ultrathin gold films on SiO2 substrates.

Ultrathin metallic films are important functional materials for optical and microelectronic devices. Dedicated characterization with high spatial resolution and sufficient field of view is key to the understanding of the relation between microstructure and optical and electrical properties of such thin films. Here, we have applied on-axis transmission Kikuchi diffraction (TKD) and scanning precession electron diffraction (SPED) to study the microstructure of 10 nm thick polycrystalline gold films. The study compares the results obtained from the same specimen region by the two techniques and provides insights on the limits of each diffraction technique. We compare the physical spatial resolution of on-axis TKD and SPED and discuss challenges due to the larger probe size in scanning electron microscopy (SEM). Moreover, we present an improvement for the physical spatial resolution (PSR) of on-axis TKD through acquisition in immersion mode. We show how this method extends the capabilities of SEM-based microstructure characterization of ultrathin films and achieve PSR comparable to semi-automated SPED.

Off-axis electron holography was used to reveal remote doping in GaAs nanowires occurring during in situ annealing in a transmission electron microscope. Dynamic changes to the electrostatic potential caused by carbon dopant diffusion upon annealing were measured across GaAs nanowires with radial p-p+ core–shell junctions. Electrostatic potential profiles were extracted from holographic phase maps and built-in potentials (Vbi ) and depletion layer widths (DLWs) were estimated as function of temperature over 300–873 K. Simulations in absence of remote doping predict a significant increase of Vbi and DLWs with temperature. In contrast, we measured experimentally a nearly constant Vbi and a weak increase of DLWs. Moreover, we observed the appearance of a depression in the potential profile of the core upon annealing. We attribute these deviations from the predicted behavior to carbon diffusion from the shell to the core through the nanowire sidewalls, i.e. to remote doping, becoming significant at 673 K. The DLW in the p and p+ regions are in the 10–30 nm range.

Cellulose nanocrystals (CNCs) are promising bio-derived nanomaterials for the bottom-up fabrication of biomedical constructs. In this report, dicarboxylic acid-functionalized CNC (DCC) was functionalized with arginylglycylaspartic acid (RGD) tripeptide as a motif for improved cell adhesion and targeting. The product (DCC-RGD) self-assembled into a more elongated nanofibrillar structure through lateral and end-to-end association. When added into poly(ethylene imine) (PEI)/pDNA polyplex solution, nanocelluloses interacted electrostatically with positively charged polyplexes without affecting their integrity. The constructs were tested for their potentials as non-viral transfection reagents. Cell viability and transfection efficiency of fibroblast NIH3T3 cells were monitored as a function of CNC concentration where, in general, viability increased as the CNC concentration increased, and transfection efficiency could be optimized. Using wild-type MDCK and αV-knockout MDCK cells, the construct was able to provide targeted uptake of polyplexes. The findings have potential applications, for example, cell-selective in vitro or ex vivo transfection of autologous mesenchymal stem cells for cell therapy, or bottom-up design of future innovative biomaterials.

The synergistic combination of different nanomaterials for improved performance in environmental applications such as the removal of aqueous micropollutants has attracted increasing interest in recent years. This study demonstrates a novel sequential adsorption–aggregation concept that harnesses tubular halloysite nanotubes (HNTs) and flexible cellulose nanofibrils (CNFs) for the removal of a small, anionic dye molecule, chrome azurol S, from water. Hollow HNTs were first allowed to interact with the aqueous dye solution, after which the dye-loaded colloidal nanotubes were aggregated and separated from the water phase with cationized CNFs. The combination of 25 mg CNFs with 1 g HNTs at pH 7 resulted in efficient removal of dye (80%) and turbidity (~100%) and the removal of dye was further promoted in more acidic conditions (within the pH range of 6–8.5) because of the attractive electrostatic interactions. Cationic CNFs not only enabled the separation of dye-loaded clay particles from the water phase through a rapid aggregation but also participated in dye removal through adsorption (~20%). In comparison with nano-sized HNTs, the dye removal performance of micro-sized and chemically similar kaolin was poor (43%). Given the good availability of both HNTs and CNFs and the low consumption of the more expensive component (i.e., CNFs) in the process, the concept is straightforward, readily applicable, environmentally benign, and potentially cost-effective.

Hydrogen sensors are a prerequisite for the implementation of a hydrogen economy due to the high flammability of hydrogen-air mixtures. They are to comply with the increasingly stringent requirements set by stakeholders, such as the automotive industry and manufacturers of hydrogen safety systems, where sensor deactivation is a severe but widely unaddressed problem. In response, we report intrinsically deactivation-resistant nanoplasmonic hydrogen sensors enabled by a rationally designed ternary PdAuCu alloy nanomaterial, which combines the identified best intrinsic attributes of the constituent binary Pd alloys. This way, we achieve extraordinary hydrogen sensing metrics in synthetic air and poisoning gas background, simulating real application conditions. Specifically, we find a detection limit in the low ppm range, hysteresis-free response over 5 orders of magnitude hydrogen pressure, subsecond response time at room temperature, long-term stability, and, as the key, excellent resistance to deactivating species like carbon monoxide, notably without application of any protective coatings. This constitutes an important step forward for optical hydrogen sensor technology, as it enables application under demanding conditions and provides a blueprint for further material and performance optimization by combining and concerting intrinsic material assets in multicomponent nanoparticles. In a wider context, our findings highlight the potential of rational materials design through alloying of multiple elements for gas sensor development, as well as the potential of engineered metal alloy nanoparticles in nanoplasmonics and catalysis.

Noble metals are currently the most common building blocks in plasmonics and thus define the available range of optical properties. Their alloying provides a viable strategy to engineer new materials with a tunable range of optical responses. Despite this attractive prospect, the link between composition and optical properties of many noble metal alloys is still not well understood. Here, electron energy-loss spectroscopy is employed to systematically study AuAg and AuPd nanoparticles of varying compositions. The localized surface plasmons, the bulk plasmons, and the permittivity functions of these two sets of alloys are investigated as functions of their composition. In the case of the more widely studied AuAg alloy system, good agreement is found with previous experimental and theoretical studies. The results on the less scrutinized AuPd system provide highly valuable experimental data that complements other experimental investigations and supports the development of theoretical models.

Rotation during reaction Determining changes in heterogeneous catalysts under reaction conditions can provide insight into mechanisms. Under reaction conditions, not only can metal nanoparticles change shape but their interaction with the oxide support could also be affected. Yuan et al. used aberration-corrected environmental transmission electron microscopy to study gold nanoparticles on titanium surfaces at low electron beam doses. During carbon monoxide (CO) oxidation at total pressures of a few millibars and 500°C, they observed that gold nanoparticles rotated by about 10° but returned to their original position when CO was removed. Density function theory calculations indicated that rotation was induced by changes in the coverage of adsorbed molecular oxygen at the interface. Science , this issue p. 517

Preventing sintering of supported nanocatalysts is an important issue in nanocatalysis. A feasible way is to choose a suitable support. However, whether the metal–support interactions promote or prevent the sintering has not been fully identified. Now, completely different sintering behaviors of Au nanoparticles on distinct anatase TiO2 surfaces have been determined by in situ TEM. The full in situ sintering processes of Au nanoparticles were visualized on TiO2 (101) surface, which coupled the Ostwald ripening and particle migration coalescence. In contrast, no sintering of Au on TiO2 anatase (001) surface was observed under the same conditions. This facet‐dependent sintering mechanism is fully explained by the density function theory calculations. This work not only offers direct evidence of the important role of supports in the sintering process, but also provides insightful information for the design of sintering‐resistant nanocatalysts.

In the present work, the degradation of size-selected Pt nanoclusters is studied under electrochemical conditions. This model catalyst mimics carbon supported Pt nanoclusters and nanoparticles typically employed in proton exchange membrane fuel cells (PEMFCs). Insight into the early stage of degradation is given by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and confirmed by transmission electron microscopy (TEM). In contrast to common assumptions, it is demonstrated that even extremely small Pt clusters exhibit a remarkable stability under electrochemical conditions. Such nanoclusters are then relevant to develop electrodes for energy applications. Furthermore, applying mixed cluster samples of Pt22 and Pt68, no preferential dissolution of Pt22 by Ostwald ripening - usually held responsible to be the main mechanism for activity loss in Pt fuel cell catalysts - is observed. In light of the findings reported, developing highly-dispersed subnanometer Pt clusters as catalyst for PEMFCs is a realistic approach provided the operation conditions are suitably adjusted. Furthermore, mitigation strategies to improve the stability of few-atoms catalyst under electrochemical operation will benefit from addressing cluster-support interactions.

Efficient adhesion of gold thin films on dielectric or semiconductor substrates is essential in applications and research within plasmonics, metamaterials, 2D materials, and nanoelectronics. As a consequence of the relentless downscaling in nanoscience and technology, the thicknesses of adhesion layer and overlayer have reached tens of nanometers, and it is unclear if our current understanding is sufficient. In this report, we investigated how Cr and Ti adhesion layers influence the nanostructure of 2-20 nm thin Au films by means of high-resolution electron microscopy, complemented with atomic force microscopy and X-ray photoelectron spectroscopy. Pure Au films were compared to Ti/Au and Cr/Au bilayer systems. Both Ti and Cr had a striking impact on grain size and crystal orientation of the Au overlayer, which we interpret as the adhesion layer-enhanced wetting of Au and the formation of chemical bonds between the layers. Ti formed a uniform layer under the Au overlayer. Cr interdiffused with the Au layer forming a Cr-Au alloy. The crystal orientation of the Au layers was mainly [111] for all thin-film systems. The results showed that both adhesion layers were partially oxidized, and oxidation sources were scrutinized and found. A difference in bilayer electrical resistivity between Ti/Au and Cr/Au systems was measured and compared. On the basis of these results, a revised and more detailed adhesion layer model for both Ti/Au and Cr/Au systems was proposed. Finally, the implications of the results were analyzed, and recommendations for the selection of adhesion layers for nano-optics and nanoelectronics applications are presented.

Structural evolution of iron nanoparticles involving the formation and growth of iron carbide nuclei in the iron nanoparticle was directly visualized at the atomic level, using environmental transmission electron microscopy (TEM) under reactive conditions mimicking Fischer-Tropsch synthesis. Formation of the iron carbide nuclei and surface reconstruction of the iron nanoparticle play an essential role in carburization of the iron nanoparticle and consequent formation of Fe5C2. Identification of carbide and oxide intermediates evidenced by high-resolution TEM images, electron diffraction patterns and electron energy-loss spectra provides a detailed picture from initial activation to final degradation of iron under synthesis gas. (Chemical Equation Presented).

International audience; In order to controllably grow single-wall carbon nanotubes (SWCNTs), a better understanding of the growth processes and how they are influenced by external parameters such as catalyst and gaseous environment is required. Here, we present direct evidence of growth termination of individual SWCNTs and successive growth of additional SWCNTs on Co catalyst particles supported on MgO by means of environmental transmission electron microscopy. Such in situ observations reveal the plethora of solid carbon formations at the local scale while it is happening and thereby elucidate the multitude of configurations resulting from identical external synthesis conditions, which should be considered in the quest for controlled SWCNT growth. Using CO and a mixture of CO and H2 as carbon sources, we show that the growth of SWCNTs terminates with a reduced tube−catalyst adhesion strength. Two main reasons for the cessation are proposed: insufficient active carbon species and a certain amount of stress exerted at the tube−catalyst interface. Interestingly, it was observed that catalyst particles stayed active in terms of nucleating additional solid carbon structures after growth termination of the first SWCNT. These observations elucidate the importance of an in-depth understanding of the role of catalysts and carbon sources in the continued growth of SWCNTs. Furthermore, it serves as a guide for further control of carbon nanostructure synthesis via catalyst engineering and synthesis optimization.

The activation of iron oxide Fischer–Tropsch Synthesis (FTS) catalysts was investigated during pretreatment: reduction in hydrogen followed by carburization in either CO or syngas mixture, or simultaneously reduction and carburization in syngas. A combination of different complementary in situ techniques was used to gain insight into the behavior of Fe-based FTS catalysts during activation. In situ XRD was used to identify the crystalline structures present during both reduction in hydrogen and carburization. An increase in reduction rate was established when increasing the temperature. A complete reduction was demonstrated in the ETEM and a grain size dependency was proven, i.e. bigger grains need higher temperature in order to reduce. XPS and XAS both indicate the formation of a small amount of carbonaceous species at the surface of the bulk metallic iron during carburization.

One of the biggest challenges for in situ heating transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) is the ability to measure the local temperature of the specimen accurately. Despite technological improvements in the construction of TEM/STEM heating holders, the problem of being able to measure the real sample temperature is still the subject of considerable discussion. In this study, we review the present literature on methodologies for temperature calibration. We analyze calibration methods that require the use of a thermometric material in addition to the specimen under study, as well as methods that can be performed directly on the specimen of interest without the need for a previous calibration. Finally, an overview of the most important characteristics of all the treated techniques, including temperature ranges and uncertainties, is provided in order to provide an accessory database to consult before an in situ TEM/STEM temperature calibration experiment.

Imaging reactive surface water Recent developments in transmission electron microscopy (TEM) have enabled imaging of single atoms, but adsorbed gas molecules have proven more challenging because of a lack of sufficient image contrast. Yuan et al. adsorbed water and carbon monoxide (CO) on a reconstructed nanocrystalline anatase titanium dioxide (TiO 2 ) surface that has protruding TiO 3 ridges every four unit cells, which provide regions of distinct contrast. Water adsorption on this surface during environmental TEM experiments led to the formation of twinned protrusions. These structures developed dynamic contrast as the water reacted with coexposed CO to form hydrogen and carbon dioxide. Science , this issue p. 428

The growth kinetics play key roles in determining the chirality distribution of the grown single-walled carbon nanotubes (SWCNTs). However, the lack of comprehensive understandings on the SWCNT’s growth mechanism at the atomic scale greatly hinders SWCNT chirality-selective synthesis. Here, we establish a general model, where the dislocation theory is a specific case, to describe the etching agent–dependent growth kinetics of SWCNTs on solid catalyst particles. In particular, the growth kinetics of SWCNTs in the absence of etching agent is validated by both in situ environmental transmission electron microscopy and ex situ chemical vapor deposition growth of SWCNTs. On the basis of the new theory of SWCNT’s growth kinetics, we successfully explained the selective growth of (2n, n) SWCNTs. This study provides another degree of freedom for SWCNT controlled synthesis and opens a new strategy to achieve chirality-selective synthesis of (2n, n) SWCNTs using solid catalysts.

Oxide supported metal nanoparticles play an important role in heterogeneous catalysis. However, understanding the metal/oxide interface and their evolution under reaction conditions remains challenging. Herein, we investigate the interface between Au nanoparticles and a CeO2 substrate by environmental transmission electron microscopy with atomic resolution. We find that the Au nanoparticles have two preferential epitaxial relationships with the substrate, i.e. Type I (111)[-110]CeO2//(111)[-110]Au and Type II (111)[-110]CeO2//(111)[1-10]Au orientation relationships, where Type I is preferred. In situ observations in the presence of O-2 show that the gas can stimulate the supported Au nanoparticles to transform between these two orientations even at room temperature. Moreover, when increasing the temperature to 973 K, the transformation of an Au nanoparticle between the two orientation states and a non-crystalline state in the presence of O-2 is also observed. DFT calculations of the binding between Au and CeO2 in the two relationships are strongly influenced by the presence of oxygen vacancies. For a given position of a vacancy, there is a significant energy difference between the energy of the two types. However, for some positions, Type I is preferred, and for others, Type II, but the most favourable position of the vacancy for the two types has a very similar energy. This is consistent with the observation of both types of adhesion.

Structural changes of PtPd nanoparticles in a natural gas oxidation catalyst were studied at elevated temperatures in air and low-oxygen conditions and in situ using environmental transmission electron microscopy (ETEM). The fresh catalyst shows

This review article discusses the current and future possibilities for the application of in situ transmission electron microscopy to reveal synthesis pathways and functional mechanisms in complex and nanoscale materials. The findings of a group of scientists, representing academia, government labs and private sector entities (predominantly commercial vendors) during a workshop, held at the Center for Nanoscale Science and Technology-National Institute of Science and Technology (CNST-NIST), are discussed. We provide a comprehensive review of the scientific needs and future instrument and technique developments required to meet them. Published by Elsevier B.V.

International audience; Catalyst selection is very crucial for controlled growth of single-walled carbon nanotubes (SWNTs). Here we introduce a well-designed Fesingle bondTisingle bondO solid solution for SWNT growth with a high preference to large chiral angles. The Fesingle bondTisingle bondO catalyst was prepared by combining Ti layer deposition onto premade Fe nanoparticles with subsequent high-temperature air calcination, which favours the formation of a homogeneous Fesingle bondTisingle bondO solid solution. Using CO as the carbon feedstock, chemical vapour deposition growth of SWNTs at 800 °C was demonstrated on the Fesingle bondTisingle bondO catalyst. Nanobeam electron diffraction characterization on a number of individual SWNTs revealed that more than 94% of SWNTs have chiral angles larger than 15°. In situ environmental transmission electron microscopy study was carried out to reveal the catalyst dynamics upon reduction. Our results identify that the phase segregation through reducing Fesingle bondTisingle bondO catalyst leads to the formation of TiOx-supported small Fe nanoparticles for SWNT growth. The strong metal-support interactions induced by partial reduction of TiOx support promote the wettability of Fe nanoparticle, accounting for the preferential growth of large-chiral-angle SWNTs. This work opens a new avenue for chiral angle selective growth of SWNTs.

The stability of Ni-MoS2/ZrO2 toward water, potassium, and chlorine containing compounds during hydrodeoxygenation (HDO) of a mixture of phenol and 1-octanol was investigated in a high pressure gas and liquid continuous flow fixed bed setup at 280 °C and 100 bar. To maintain the stability of the catalyst, sufficient co-feeding of a sulfur source was necessary to avoid oxidation of the sulfide phase by oxygen replacement of the edge sulfur atoms in the MoS2 structure. However, the addition of sulfur to the feed gas resulted in the formation of sulfur containing compounds, mainly thiols, in the oil product if the residence time was too low. At a weight hourly space velocity (WHSV) of 4.9 h−1 the sulfur content in the liquid product was 980 ppm by weight, but this could be decreased to 5 ppm at a WHSV of 1.4 h−1. A high co-feed of sulfur was needed when water was present in the feed and the H2O/H2S molar ratio should be below ca. 10 to maintain a decent stability of the catalyst. Chlorine containing compounds caused a reversible deactivation of the catalyst when co-fed to the reactor, where the catalytic activity could be completely regained when removing it from the feed. Commonly, chlorine, H2O, and H2S all inhibited the activity of the catalyst by competing for the active sites, with chlorine being by far the strongest inhibitor and H2S and H2O of roughly the same strength. Dissimilar, potassium was a severe poison and irreversibly deactivated the catalyst to 2 slabs.

Traditionally, direct imaging of atom diffusion is only available by scanning tunneling microscopy and field ion microscopy on geometry-constrained samples: flat surfaces for STM and needle tips for FIM. Here we show time-resolved atomic-scale HRTEM investigations of CeO2-supported Au nanoparticle surfaces to characterize the surface dynamics of atom columns on gold nanoparticles. The observed surface dynamics have been categorized into four types: layer jumping, layer gliding, re-orientation and surface reconstruction. We successfully captured atoms moving in a concerted manner with a time resolution of 0.1 s. A quantitative approach for measuring the dynamics in various gaseous surroundings at elevated temperatures is presented. An approach for measuring quantitative electron beam effects on the surface dynamics is presented by counting atom column occupation as a function of time under a range of dose rates in high vacuum.

Tuning and tailoring of surface terminating functional species hold the key to unlock unprecedented properties for a wide range of applications of the largest 2D family known as MXenes. However, a few routes for surface tailoring are explored and little is known about the extent to which the terminating species can saturate the MXene surfaces. Among available terminations, atomic oxygen is of interest for electrochemical energy storage, hydrogen evolution reaction, photocatalysis, etc. However, controlled oxidation of the surfaces is not trivial due to the favored formation of oxides. In the present contribution, single sheets of Ti3C2Tx MXene, inherently terminated by F and O, are defluorinated by heating in vacuum and subsequentially exposed to O-2 gas at temperatures up to 450 degrees C in situ, in an environmental transmission electron microscope. Results include exclusive termination by O on the MXene surfaces and eventual supersaturation (x amp;gt; 2) with a retained MXene sheet structure. Upon extended O exposure, the MXene structure transforms into TiO2 and desorbs surface bound H2O and CO2 reaction products. These results are fundamental for understanding the oxidation, the presence of water on MXene surfaces, and the degradation of MXenes, and pave way for further tailoring of MXene surfaces. Funding Agencies|Swedish Research CouncilSwedish Research Council [2016-04412, 2016-00889, 642-2013-8020]; Knut and Alice Wallenbergs FoundationKnut & Alice Wallenberg Foundation [KAW 2015.0043]; Swedish Foundation for Strategic Research (SSF)Swedish Foundation for Strategic Research [RIF 14-0074, FL12-0181]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]

Global warming caused by burning of fossil fuels is indisputably one of mankinds greatest challenges in the 21st century. To reduce the ever-increasing CO2 emissions released into the atmosphere, dry solid adsorbents with large surface-to-volume ratio such as carbonaceous materials, zeolites, and metal-organic frameworks have emerged as promising material candidates for capturing CO2. However, challenges remain because of limited CO2/N-2 selectivity and long-term stability. The effective adsorption of CO2 gas (approximate to 12 mol kg(-1)) on individual sheets of 2D transition metal carbides (referred to as MXenes) is reported here. It is shown that exposure to N-2 gas results in no adsorption, consistent with first-principles calculations. The adsorption efficiency combined with the CO2/N-2 selectivity, together with a chemical and thermal stability, identifies the archetype Ti3C2 MXene as a new material for carbon capture (CC) applications. Funding Agencies|Swedish Research Council [2016-04412, 2016-00889, 642-2013-8020]; Knut and Alice Wallenbergs Foundation [KAW 2015.0043]; Swedish Foundation for Strategic Research (SSF) [EM16-0004, RIF 14-0074, FL12-0181]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]

Hydrogen–air mixtures are highly flammable. Hydrogen sensors are therefore of paramount importance for timely leak detection during handling. However, existing solutions do not meet the stringent performance targets set by stakeholders, while deactivation due to poisoning, for example by carbon monoxide, is a widely unsolved problem. Here we present a plasmonic metal–polymer hybrid nanomaterial concept, where the polymer coating reduces the apparent activation energy for hydrogen transport into and out of the plasmonic nanoparticles, while deactivation resistance is provided via a tailored tandem polymer membrane. In concert with an optimized volume-to-surface ratio of the signal transducer uniquely offered by nanoparticles, this enables subsecond sensor response times. Simultaneously, hydrogen sorption hysteresis is suppressed, sensor limit of detection is enhanced, and sensor operation in demanding chemical environments is enabled, without signs of long-term deactivation. In a wider perspective, our work suggests strategies for next-generation optical gas sensors with functionalities optimized by hybrid material engineering. Sensing hydrogen by the change in plasmonic response upon metal hydride formation is safe, but trace gas poisoning and low sensitivity can occur. Here, a PdAu alloy/polymer sensor is poison resistant and can sense 3 ppm H2 with a response time of 1 s.

Micro-supercapacitors (MSCs) hold great promise as highly competitive miniaturized power sources satisfying the increased demand in microelectronics; however, simultaneously achieving high areal and volumetric capacitances is still a great challenge. Here we demonstrated the designed construction of binder-free, electrically conductive, nanoporous activated graphene (AG) compact films for high-performance MSCs. The binder-free AG films are fabricated by alternating deposition of electrochemically exfoliated graphene (EG) and nanoporous AG with a high specific surface area of 2920 m2/g, and then dry transferring onto the target substrates with a high-pressure mechanical densification process. Remarkably, the resulting compressed AG films showed uniform morphology in lateral dimensions, high conductivity (60 S/cm), nanoporous feature ( 99.6% after 10,000 cycles). Our results suggested that AG-MSCs are competitive for prospective applications of miniaturized energy storage devices.

A nanodispersed intermetallic GaPd2/SiO2 catalyst is prepared by simple impregnation of industrially relevant high-surface-area SiO2 with Pd and Ga nitrates, followed by drying, calcination, and reduction in hydrogen. The catalyst is tested for CO2 hydrogenation to methanol at ambient pressure, revealing that the intrinsic activity of the GaPd2/SiO2 is higher than that of the conventional Cu/ZnO/Al2O3, while the production of the undesired CO is lower. A combination of complementary in situ and ex situ techniques are used to investigate the GaPd2/SiO2 catalyst. In situ X-ray diffraction and in situ extended X-ray absorption fine structure spectroscopy show that the GaPd2 intermetallic phase is formed upon activation of the catalyst via reduction and remains stable during CO2 hydrogenation. Identical location–transmission electron microscopy images acquired ex situ (i.e., micrographs of exactly the same catalyst area recorded at the different steps of activation and reaction procedure) show that nanopartic...

Platinum-yttrium alloy nanoparticles show both a high activity and stability for the oxygen reduction reaction. The catalysts were prepared by magnetron sputter aggregation and mass filtration providing a model catalyst system with a narrow size distribution. The structure and stability of nanostructured Pt-Y alloy catalysts were studied using transmission electron microscopy techniques. Using elemental X-ray mapping and high-resolution electron microscopy, the specific compositional structure and distribution of the individual nanoparticles was unraveled and the stability assessed. Studying the catalyst after reaction and after aging tests shows the development of a core-shell type structure after being exposed to reaction conditions.

Environmental transmission electron microscopy (ETEM) studies offer great potential for gathering atomic scale information on the electronic state of electrodes in contact with reactants. It also poses big challenges due to the impact of the high energy electron beam. In this article, we present an ETEM study of a Pr0.64Ca0.36MnO3 (PCMO) thin film electrocatalyst for water splitting and oxygen evolution in contact with water vapor. We show by means of off-axis electron holography and electrostatic modeling that the electron beam gives rise to a positive electric sample potential due to secondary electron emission. The value of the electric potential depends on the primary electron flux, the sample’s electric conductivity and grounding, and gas properties. We present evidence that two observed electrochemical reactions are driven by a beam induced electrostatic potential of the order of a volt. The first reaction is an anodic oxidation of oxygen depleted amorphous PCMO which results in recrystallization of...

The doping process in GaP core-shell nanowire pn-junctions using different precursors is evaluated by mapping the nanowires' electrostatic potential distribution by means of off-axis electron holography. Three precursors, triethyltin (TESn), ditertiarybutylselenide, and silane are investigated for n-type doping of nanowire shells; among them, TESn is shown to be the most efficient precursor. Off-axis electron holography reveals higher electrostatic potentials in the regions of nanowire cores grown by the vapor-liquid-solid (VLS) mechanism (axial growth) than the regions grown parasitically by the vapor-solid (VS) mechanism (radial growth), attributed to different incorporation efficiency between VLS and VS of unintentional p-type carbon doping originating from the trimethylgallium precursor. This study shows that off-axis electron holography of doped nanowires is unique in terms of the ability to map the electrostatic potential and thereby the active dopant distribution with high spatial resolution.

Transmission Kikuchi diffraction (TKD) facilitates automated orientation mapping of thin films in scanning electron microscopes (SEM). In this study TKD is applied for the first time to perform in-situ annealing experiments on gold thin films deposited on a MEMS-based heating system. The very local heating associated with this system enables reliable TKD measurements at elevated temperatures without notable disturbance from infrared radiation. The dewetting of an Au thin film into Au nanoparticles upon heating is followed with orientation mapping in a temperature range between 20 °C and 900 °C. The local thickness variation associated with the dewetting is observed qualitatively by observing the intensity of the transmitted beam, which decreases as the film thickness increases locally. The results of this study reveal that TKD is a well suited technique to study thin-film stability and solid state dewetting. Moreover, the outcome of this methodological study provides a baseline for further in-situ crystallographic studies of electron transparent samples in the SEM.

Recording atomic-resolution transmission electron microscopy (TEM) images is becoming increasingly routine. A new bottleneck is then analyzing this information, which often involves time-consuming manual structural identification. We have developed a deep learning-based algorithm for recognition of the local structure in TEM images, which is stable to microscope parameters and noise. The neural network is trained entirely from simulation but is capable of making reliable predictions on experimental images. We apply the method to single sheets of defected graphene, and to metallic nanoparticles on an oxide support., Comment: v2: Typo in author list corrected