Heterostructured materials combining metal oxides and transition metal dichalcogenides (TMDs) have emerged as promising candidates for advanced gas sensors. The WO₃/SnS₂ system remains scarcely explored despite the excellent individual gas sensing properties of both components. We report the synthesis and characterization of WO₃/SnS₂ heterostructures prepared via a two-step hydrothermal method, in which WO₃ nanostructures served as seeds for controlled SnS₂ growth. Stoichiometric control in the synthesis steps and subsequent partial oxidation by thermal treatments allowed fine-tuning of morphology and phase composition. The sample prepared with a Sn:W molar ratio of 10:1 in the synthesis precursor solution delivered the highest response to 10 ppm NO₂ (defined as the ratio of resistances in presence and absence of NO2, RNO2/R0), reaching 1149 after thermal treatment, while the 1:1 and 2:1 molar ratio samples reached responses of 188 and 223, respectively, outperforming similar oxide/TMD systems reported in the literature. This behavior was attributed to synergistic electronic sensitization across the n-n junction and chemical sensitization promoted by partial oxidation. The materials also displayed notable sensitivity to acetone, suggesting its potential for multi-analyte detection. These results highlight WO₃/SnS₂ heterostructures as a novel and effective platform for low-temperature gas sensing relevant to environmental and workplace safety monitoring.

We highlight recent advances in the controlled creation of single-photon emitters in van der Waals materials and in the understanding of their atomistic origin. We focus on quantum emitters created in monolayer transition-metal dichalcogenide semiconductors, which provide spectrally sharp single-photon emission at cryogenic temperatures, and the ones in insulating hBN, which provide bright and stable single-photon emission up to room temperature. After introducing the different classes of quantum emitters in terms of band-structure properties, we review the defect creation methods based on electron and ion irradiation as well as local strain engineering and plasma treatments. A main focus of the review is put on discussing the microscopic origin of the quantum emitters as revealed by various experimental platforms, including optical and scanning probe methods.

3D ice lithography (3DIL) is an emerging method for fabricating polymeric 3D objects with submicrometer patterns. However, there are no studies on 3DIL using metal-containing precursors. In addition, unlike numerous post-processing studies of two-photon polymerization (2PP) and focused electron beam-induced deposition (FEBID), there are no 3DIL post-processing investigations. Here, we present a 3DIL process using an organometallic precursor (gold dimethyl acetylacetonate, Au(acac)Me2), and its first post-processing study. We investigated 3D processing parameters and post-processing using Ar-, air annealing, and O2 plasma. X-ray photoelectron spectroscopy (XPS), atomic force microscopy, energy-dispersive X-ray spectroscopy, and transmission electron microscopy were used for materials analysis. Our results show (i) 3DIL processed materials exhibit thermoset properties, as they decompose rather than melt at elevated temperatures; (ii) free metal atoms diffuse and form clusters, here, gold nanoparticles with a diameter of around 10nm were formed; (iii) oxygen treatments remove carbon-based ligands while leaving noble metals behind. Also, Ar annealing leads to less material loss than air annealing, while O2 plasma generates oxidized Au states and efficiently removes carbon ligands. Ar annealing at 600 °C reduces the carbon XPS signals significantly and increases the gold XPS signal by ten times, giving a good purification effect but with a high material removal of around 95%. We printed large Au metalorganic 3D structures (>1000 times larger volume than FEBID), which suggests 3DIL bridges the gap between the capabilities of 2PP and FEBID. The unique capabilities of organometallic compounds to detect environmental changes can position 3DIL for sensing applications, and 3DIL is a safe and non-toxic technique to manufacture nanoparticle-containing 3D structures, which may have applications in many fields such as nanophotonics, drug delivery, and catalysis.

Pt nanoparticles supported on Al 2 O 3 reversibly change shape from 3D hemispheres at room temperature to flat rafts at 400 °C.

Electrostriction is the upsurge of strain under an electric field in any dielectric material. Oxygen-defective metal oxides, such as acceptor-doped ceria, exhibit high electrostriction 10-17 m2V-2 values, which can be further enhanced via interface engineering at the nanoscale. This effect in ceria is "non-classical" as it arises from an intricate relation between defect-induced polarisation and local elastic distortion in the lattice. Here, we investigate the impact of mismatch strain when epitaxial Gd-doped CeO2 thin films are grown on various single-crystal substrates. We demonstrate that varying the compressive and tensile strain can fine-tune the electromechanical response. The electrostriction coefficients achieve a large M11 ≈ 3.6·10-15 m2V-2 in lattices of in-plane compressed films, i.e., a positive tetragonality (c/a-1 > 0), with stress above 3 GPa at the film/substrate interface. Chemical and structural analysis suggests that the high electrostriction stems from anisotropic distortions in the local lattice strain, which lead to constructively oriented elastic dipoles and Ce3+ electronic defects. Non-classical electrostriction in fluorites arises from defect-induced polarization and lattice distortions. This study shows that mismatch strain in Gd-doped CeO2 thin films fine-tunes electromechanical responses, achieving high electrostriction above 10−15 m2V−2.

Large area graphene patterning is critical for applications. Current graphene patterning techniques, such as electron beam lithography and nano imprint lithography, are time consuming and can scale unfavorably with sample size. Resist-based masking and subsequent dry plasma etching can lead to high roughness edges with no alignment to the underlying graphene crystal orientations. In this study, we present hot punching as a novel and feasible method for patterning of chemical vapor deposition (CVD) graphene sheets supported by a polyvinylalcohol (PVA) layer. Additionally, we observe the effect of such hot punching on graphene supported by PVA via optical microscopy, Raman spectroscopy, AFM, and TEM, including wrinkling, strain and the formation of nanoribbons with crystallographically aligned and smooth edges due to fracturing. We present hot punching as a facile technique for the production of arrays of such nanoribbons.

Due to its excellent physical, chemical, and electrochemical characteristics, pyrolytic carbon has become a promising material for a wide range of advanced technologies. Pyrolytic carbon can be obtained through the pyrolysis of a polymeric carbon precursor at high temperatures and in inert atmosphere. By tuning the pyrolysis conditions, the hybridization of carbon atoms and thus the physicochemical properties of the derived carbon can be tailored. Advancing its development requires a deeper understanding of the graphitization process. In this context, an in situ microstructural analysis of the pyrolysis process is needed. This work presents the microfabrication of suspended polymer thin film structures on transmission electron microscopy heating chips, by twophoton polymerization 3D printing. We visualized graphitization of these films during in situ transmission electron microscopy heating studies. The favorable identified conditions are a thin film with a thickness of around 700 nm pre-pyrolysis, a pyrolysis profile reaching a maximum temperature of 1300 degrees C and a minimum of 2 h of dwell at this temperature. An increase in the number of stacked graphene layers was observed over dwell time. Overall, the developed method has the potential to enable the visualization of graphitization of different polymer precursors and thus help predict the microstructure and properties of pyrolytic carbon depending on its fabrication conditions.

Electromechanical metal oxides, such as piezoceramics, are often incompatible with soft polymers due to their crystallinity requirements, leading to high processing temperatures. This study explores the potential of ceria-based thin films as electromechanical actuators for flexible electronics. Oxygen-deficient fluorites, like cerium oxide, are centrosymmetric nonpiezoelectric crystalline metal oxides that demonstrate giant electrostriction. These films, deposited at low temperatures, integrate seamlessly with various soft substrates like polyimide and PET. Ceria thin films exhibit remarkable electrostriction (M-33 > 10(-16) m(2) V-2) and inverse pseudo-piezo coefficients (e(33) > 500 pmV(-1)), enabling large displacements in soft electromechanical systems. Our study explores resonant and off-resonant configurations in the low-frequency regime (<1 kHz), demonstrating versatility for three-dimensional and transparent electronics. This work advances the understanding of oxygen-defective metal oxide electromechanical properties and paves the way for developing versatile and efficient electromechanical systems for applications in biomedical devices, optical devices, and beyond.

We develop a combined theoretical and experimental method for estimating the amount of heating that occurs in metallic nanoparticles that are being imaged in an electron microscope. We model the thermal transport between the nanoparticle and the supporting material using molecular dynamics and equivariant neural network potentials. The potentials are trained to Density Functional Theory (DFT) calculations, and we show that an ensemble of potentials can be used as an estimate of the errors the neural network make in predicting energies and forces. This can be used both to improve the networks during the training phase, and to validate the performance when simulating systems too big to be described by DFT. The energy deposited into the nanoparticle by the electron beam is estimated by measuring the mean free path of the electrons and the average energy loss, both are done with Electron Energy Loss Spectroscopy (EELS) within the microscope. In combination, this allows us to predict the heating incurred by a nanoparticle as a function of its size, its shape, the support material, and the electron beam energy and intensity.

High-resolution electron microscopy is a well-suited tool for characterizing the nanoscale structure of materials. However, the interaction of the sample and the high-energy electrons of the beam can often have a detrimental impact on the sample structure. This effect can only be alleviated by decreasing the number of electrons to which the sample is exposed but will come at the cost of a decreased signal-to-noise ratio in the resulting image. Images with low signal to noise ratios are often challenging to interpret as parts of the sample with a low interaction with the electron beam are reproduced with very low contrast. Here we suggest simple measures as alternatives to the conventional signal-to-noise ratio and investigate how these can be used to predict the interpretability of the electron microscopy images. We test the models on a sample consisting of gold nanoparticles supported on a cerium dioxide substrate. The models are evaluated based on series of images acquired at varying electron dose.

Journal Article Nanoparticle Mobility and Coalescence During Sintering of a Ni/MgAl2O4 Methane Steam Reforming Catalyst Get access Thomas W Hansen, Thomas W Hansen National Centre for Nanofabrication and Characterization, DTU Nanolab, Technical University of Denmark, Kongens Lyngby, Denmark Search for other works by this author on: Oxford Academic Google Scholar Andrew DeLaRiva, Andrew DeLaRiva University of New Mexico, Department of Chemical Biological Engineering and Center for Microengineered Materials, Albuquerque, NM, USA Search for other works by this author on: Oxford Academic Google Scholar Abhaya K Datye Abhaya K Datye University of New Mexico, Department of Chemical Biological Engineering and Center for Microengineered Materials, Albuquerque, NM, USA Corresponding author: datye@unm.edu Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 29, Issue Supplement_1, 1 August 2023, Pages 1618–1619, https://doi.org/10.1093/micmic/ozad067.831 Published: 22 July 2023

High-density dispersion and efficient exposure of active metal sites are crucial for enhancing the catalytic activity of metal-based heterogeneous catalysts and improving the utilization of precious metal atoms. Increasing the surface to volume ratio by decreasing the size of metal nanoparticles is considered an ideal and straightforward strategy to increase catalytic activity. However, the generation of stable metal clusters or even single-atom metal species on supports is challenging since metal atoms are prone to agglomerate. In this work, we report a facile and practical method to anchor atomically dispersed Pd on an N-doped holey carbon nanotube (Pd/NHCNT) by efficiently strengthening metal-support interaction. Due to the unique characteristics of defected NHCNT sup-port, highly dispersed Pd clusters and single atoms can be facilely introduced and anchored onto NHCNT. The resultant Pd/NHCNT catalyst exhibits a remarkable activity for nitroarenes hydrogenation with a turnover fre-quency as high as 1091.49 min-1, which surpasses the reported noble metal-based catalysts. Furthermore, theoretical simulations are applied for the understanding of the defect anchoring of atomically Pd and the interaction between active sites and substrate. The defect-induced anchoring approach provides a new avenue for designing and preparing other highly active atomic metal catalysts with high metal dispersion and can be applied to diverse organic reactions.

Catalysis is a highly complex phenomenon involving fundamental processes on multiple length scales. The full-scale complexity of catalysis is only poorly understood, and how atomic-scale processes influence long-range order in the materials is not well documented experimentally. The result is that we still, to a large degree, develop new catalysts on the basis of iterative trial-and-error approaches. Elucidating the link between atomic-scale structural dynamics, feedback mechanisms, and collective behavior could be the key to a deeper understanding and further optimization of catalysts and processes. From imaging of quasi-static low-energy configurations through gas-phase-induced state switching to observation of complex nonequilibrium dynamics and oscillatory behavior, electron microscopy has provided novel insights over several length and time scales and has meanwhile matured from a service tool for catalyst researchers to a driving force in catalysis research. Here, we discuss new insights provided by novel instrumentation and the extension from in situ to operando investigations, enabling the study of mechanisms and kinetics of catalytic processes.

Motivated by the need for low electron dose transmission electron microscopy imaging, we report the optimal frame dose (i.e.e-/Å2) range for object detection and segmentation tasks with neural networks. The MSD-net architecture shows promising abilities over the industry standard U-net architecture in generalising to frame doses below the range included in the training set, for both simulated and experimental images. It also presents a heightened ability to learn from lower dose images. The MSD-net displays mild visibility of a Au nanoparticle at 20-30 e-/Å2, and converges at 200 e-/Å2 where a full segmentation of the nanoparticle is achieved. Between 30 and 200 e-/Å2 object detection applications are still possible. This work also highlights the importance of modelling the modulation transfer function when training with simulated images for applications on images acquired with scintillator based detectors such as the Gatan Oneview camera. A parametric form of the modulation transfer function is applied with varying ranges of parameters, and the effects on low electron dose segmentation is presented.

The asymmetrical growth of a single-wall carbon nanotube (SWCNT) by introducing a change of a local atomic structure, is usually inevitable and supposed to have a profound effect on the chirality control and property tailor. However, the breaking of the symmetry during SWCNT growth remains unexplored and its origins at the atomic-scale are elusive. Here, environmental transmission electron microscopy is used to capture the process of breaking the symmetry of a growing SWCNT from a sub-2-nm platinum catalyst nanoparticle in real-time, demonstrating that topological defects formed on the side of a SWCNT can serve as a buffer for stress release and inherently break its axis-symmetrical growth. Atomic-level details reveal the importance of the tube-catalyst interface and how the atom rearrangement of the solid-state platinum catalyst around the interface influences the final tubular structure. The active sites responsible for trapping carbon dimers and providing enough driving force for carbon incorporation and asymmetric growth are shown to be low-coordination step edges, as confirmed by theoretical simulations.

The use of metal-based heterogeneous catalysts for the degradation of N-containing organic dyes has attracted much attention due to their excellent treatment efficiency and capability. Here, we report the synthesis of heterometals (Ni and Pd)-incorporated Fe3O4 (Ni-Pd/Fe3O4) yolk-shelled nanospheres for the catalytic reduction of N-containing organic dyes using a facile combination of solvothermal treatment and high-temperature annealing steps. Benefiting from the magnetic properties and the yolk-shelled structure of the Fe3O4 support, as well as the uniformly dispersed active heterometals incorporated in the shell and yolk of spherical Fe3O4 nanoparticles, the as-prepared Ni-Pd/Fe3O4 composite shows excellent recyclability and enhanced catalytic activity for three N-containing organic dyes (e.g., 4-nitrophenol, Congo red, and methyl orange) compared with its mono metal counterparts (e.g., Ni/Fe3O4 and Pd/Fe3O4). In the 4-nitrophenol reduction reaction, the catalytic activity of Ni-Pd/Fe3O4 was superior to many Fe3O4-supported nanocatalysts reported within the last five years. This work provides an effective strategy to boost the activity of iron oxide-based catalytic materials via dual or even multiple heterometallic incorporation strategy and sheds new light on environmental catalysis.