Microscopic mechanism of water-assisted diffusional phase transitions in inorganic metal halide perovskites.

The stability of perovskite materials is profoundly influenced by the presence of moisture in the surrounding environment. While it is well-established that water triggers and accelerates the black-yellow phase transition, leading to the degradation of the photovoltaic properties of perovskites, the underlying microscopic mechanism remains elusive. In this study, we employ classical molecular dynamics simulations to examine the role of water molecules in the yellow-black phase transition in a typical inorganic metal halide perovskite, CsPbI3.

Efficient Defect-Driven Cation Exchange beyond the Nanoscale Semiconductors toward Antibacterial Functionalization.

Defect engineering is an exciting tool for customizing semiconductors' structural and optoelectronic properties. Elaborating programmable methodologies to circumvent energy constraints in multievent inversions expands our understanding of the mechanisms governing the functionalization of nanomaterials. Herein, we introduce a novel strategy based on defect incorporation and solution rationalization, which triggers energetically unfavorable cation exchange reactions in extended solids.

Unraveling the Formation of Ternary AgCuSe Crystalline Nanophases and Their Potential as Antibacterial Agents.

AgCuSe nanoparticles could contribute to the growth of strongly light-absorbing thin films and solids with fast ion mobility, among other potential properties. Nevertheless, few methods have been developed so far for the synthesis of AgCuSe nanoparticles, and those reported deliver nanostructures with relatively large sizes and broad size and shape distributions. In this work, a colloidal cation exchange method is established for the easy synthesis of AgCuSe NPs with ca.

Unexpectedly high thermal stability of Au nanotriangle@mSiO yolk-shell nanoparticles.

The shape of Au nanoparticles (NPs) plays a crucial role for applications in, amongst others, catalysis, electronic devices, biomedicine, and sensing. Typically, the deformation of the morphology of Au NPs is the most significant cause of loss of functionality. Here, we systematically investigate the thermal stability of Au nanotriangles (NTs) coated with (mesoporous) silica shells with different morphologies (core-shell (CS): Au NT@mSiO/yolk-shell (YS): Au NT@mSiO) and compare these to 'bare' nanoparticles (Au NTs), by a combination of and/or TEM techniques and spectroscopy methods.

Thermal Reduction of MoO Particles and Formation of MoO Nanosheets Monitored by In Situ Transmission Electron Microscopy.

Nanoscale forms of molybdenum trioxide have found widespread use in optoelectronic, sensing, and battery applications. Here, we investigate the thermal evolution of micrometer-sized molybdenum trioxide particles during in situ heating in vacuum using transmission electron microscopy and observed drastic structural and chemical changes that are strongly dependent on the heating rate. Rapid heating (flash heating) of MoO particles to a temperature of 600 °C resulted in large-scale formation of MoO(001) nanosheets that were formed in a wide area around the reducing MoO particles, within a few minutes of time frame.

Reversible MnO to Mn O Oxidation in Manganese Oxide Nanoparticles.

Manganese is an attractive element for sustainable solutions. It is largely available in the earth's crust, making it ideal for cost-effective and large-scale applications. Especially MnO nanoparticles have recently received attention for applications in battery technology.

Morphology-Controlled Growth of Crystalline Ag-Pt-Alloyed Shells onto Au Nanotriangles and Their Plasmonic Properties.

The surface plasmon resonance of noble-metal nanoparticles depends on nanoscale size, morphology, and composition, and provides great opportunities for applications in biomedicine, optoelectronics, (photo)catalysis, photovoltaics, and sensing. Here, we present the results of synthesizing ternary metallic or trimetallic nanoparticles, Au nanotriangles (Au NTs) with crystalline Ag-Pt alloyed shells, the morphology of which can be adjusted from a yolk-shell to a core-shell structure by changing the concentration of AgNO or the concentration of Au NT seeds, while the shell thickness can be precisely controlled by adjusting the concentration of KPtCl. By monitoring the growth process with UV-vis spectra and scanning transmission electron microscopy (STEM), the shells on the Au NT-Ag-Pt yolk-shell nanoparticles were found to grow via a galvanic replacement synergistic route.

Thermolysis-Driven Growth of Vanadium Oxide Nanostructures Revealed by Transmission Electron Microscopy: Implications for Battery Applications.

Understanding the growth modes of 2D transition-metal oxides through direct observation is of vital importance to tailor these materials to desired structures. Here, we demonstrate thermolysis-driven growth of 2D VO nanostructures via transmission electron microscopy (TEM). Various growth stages in the formation of 2D VO nanostructures through thermal decomposition of a single solid-state NHVO precursor are unveiled during the TEM heating.

Thermal Stability and Sublimation of Two-Dimensional CoSe Nanosheets for Ultrathin and Flexible Nanoelectronic Devices.

An understanding of the structural and compositional stability of nanomaterials is significant from both fundamental and technological points of view. Here, we investigate the thermal stability of half-unit-cell thick two-dimensional (2D) CoSe nanosheets that are exceptionally interesting because of their half-metallic ferromagnetic properties. By employing heating in the transmission electron microscope (TEM), we find that the nanosheets show good structural and chemical stability without changes to the cubic crystal structure until sublimation of the nanosheets starts at temperatures between 460 and 520 °C.

Formation Pathways of Lath-Shaped WO Nanosheets and Elemental W Nanoparticles from Heating of WO Nanocrystals Studied via In Situ TEM.

WO is a versatile material occurring in many polymorphs, and is used in nanostructured form in many applications, including photocatalysis, gas sensing, and energy storage. We investigated the thermal evolution of cubic-phase nanocrystals with a size range of 5-25 nm by means of in situ heating in the transmission electron microscope (TEM), and found distinct pathways for the formation of either 2D WO nanosheets or elemental W nanoparticles, depending on the initial concentration of deposited WO nanoparticles. These pristine particles were stable up to 600 °C, after which coalescence and fusion of the nanocrystals were observed.

In situ single particle characterization of the themoresponsive and co-nonsolvent behavior of PNIPAM microgels and silica@PNIPAM core-shell colloids.

Poly(N-isopropylacrylamide) (PNIPAM) microgels and PNIPAM colloidal shells attract continuous strong interest due to their thermoresponsive behavior, as their size and properties can be tuned by temperature. The direct single particle observation and characterization of pure, unlabeled PNIPAM microgels in their native aqueous environment relies on imaging techniques that operate either at interfaces or in cryogenic conditions, thus limiting the observation of their dynamic nature. Liquid Cell (Scanning) Transmission Electron Microscopy (LC-(S) TEM) imaging allows the characterization of materials and dynamic processes such as nanoparticle growth, etching, and diffusion, at nanometric resolution in liquids.

Solution-Mediated Inversion of SnSe to SbSe Thin-Films.

New facile and controllable approaches to fabricating metal chalcogenide thin films with adjustable properties can significantly expand the scope of these materials in numerous optoelectronic and photovoltaic devices. Most traditional and especially wet-chemical synthetic pathways suffer from a sluggish ability to regulate the composition and have difficulty achieving the high-quality structural properties of the sought-after metal chalcogenides, especially at large 2D length scales. In this effort, and for the first time, we illustrated the fast and complete inversion of continuous SnSe thin-films to SbSe using a scalable top-down ion-exchange approach.

Frequency-controlled electrophoretic mobility of a particle within a porous, hollow shell.

Unlabelled: The unique properties of yolk-shell or rattle-type particles make them promising candidates for applications ranging from switchable photonic crystals, to catalysts, to sensors. To realize many of these applications it is important to gain control over the dynamics of the core particle independently of the shell.

Hypothesis: The core particle may be manipulated by an AC electric field with rich frequency-dependent behavior.

Heating-Induced Transformation of Anatase TiO Nanorods into Rock-Salt TiO Nanoparticles: Implications for Photocatalytic and Gas-Sensing Applications.

Anatase TiO nanocrystals (NCs) play a vital role in photocatalytic applications due to their high catalytic activity and in gas-sensing applications due to their high chemical sensitivity. Here, we report the transformation at elevated temperature of anatase nanorods (NRs) with a length of 25 nm into rock-salt TiO nanoparticles with an average size of 9.2 ± 2.

Tandem catalysis with double-shelled hollow spheres.

Metal-zeolite composites with metal (oxide) and acid sites are promising catalysts for integrating multiple reactions in tandem to produce a wide variety of wanted products without separating or purifying the intermediates. However, the conventional design of such materials often leads to uncontrolled and non-ideal spatial distributions of the metal inside/on the zeolites, limiting their catalytic performance. Here we demonstrate a simple strategy for synthesizing double-shelled, contiguous metal oxide@zeolite hollow spheres (denoted as MO@ZEO DSHSs) with controllable structural parameters and chemical compositions.

Tunability of Interactions between the Core and Shell in Rattle-Type Particles Studied with Liquid-Cell Electron Microscopy.

Yolk-shell or rattle-type particles consist of a core particle that is free to move inside a thin shell. A stable core with a fully accessible surface is of interest in fields such as catalysis and sensing. However, the stability of a charged nanoparticle core within the cavity of a charged thin shell remains largely unexplored.

Single-step coating of mesoporous SiO onto nanoparticles: growth of yolk-shell structures from core-shell structures.

Yolk-shell nanoparticles based on mesoporous SiO (mSiO) coating of Au nanoparticles (Au NPs) hold great promise for many applications in e.g., catalysis, biomedicine, and sensing.

Transformation of CoO nanoparticles to CoO monitored by TEM and predicted ferromagnetism at the CoO/CoO interface from first principles.

Nanoparticles of CoO and CoO are of paramount importance because of their chemical properties propelling their applications in catalysis and battery materials, and because of their intriguing magnetic properties. Here we elucidate the transformation of CoO nanoparticles to CoO into nanoscale detail by heating in the transmission electron microscope (TEM), and we decipher the energetics and magnetic properties of the CoO/CoO interface from first principles calculations. The transformation was found to start at a temperature of 350 °C, and full conversion of all particles was achieved after heating to 400 °C for 10 minutes.

Structural Control over Bimetallic Core-Shell Nanorods for Surface-Enhanced Raman Spectroscopy.

Bimetallic nanorods are important colloidal nanoparticles for optical applications, sensing, and light-enhanced catalysis due to their versatile plasmonic properties. However, tuning the plasmonic resonances is challenging as it requires a simultaneous control over the particle shape, shell thickness, and morphology. Here, we show that we have full control over these parameters by performing metal overgrowth on gold nanorods within a mesoporous silica shell, resulting in Au-Ag, Au-Pd, and Au-Pt core-shell nanorods with precisely tunable plasmonic properties.

Symmetric and asymmetric epitaxial growth of metals (Ag, Pd, and Pt) onto Au nanotriangles: effects of reductants and plasmonic properties.

The surface plasmon resonance of noble metals can be tuned by morphology and composition, offering interesting opportunities for applications in biomedicine, optoelectronics, photocatalysis, photovoltaics, and sensing. Here, we present the results of the symmetrical and asymmetrical overgrowth of metals (Ag, Pd, and Pt) onto triangular Au nanoplates using l-ascorbic acid (AA) and/or salicylic acid (SA) as reductants. By varying the reaction conditions, various types of Au nanotriangle-metal (Au NT-M) hetero-nanostructures were easily prepared.

Compartmentalization of gold nanoparticle clusters in hollow silica spheres and their assembly induced by an external electric field.

Assembly of plasmonic nanoparticle clusters having hotspots in a specific space is an effective way to efficiently utilize their plasmonic properties. In the assembly, however, bulk-like aggregates of the nanoparticles are readily formed by strong van der Waals forces, inducing a decrease of the properties. The present work proposes an advanced method to avoid aggregation of the clusters by encapsulating into a confined space of hollow silica interior.

Thermal enhancement and quenching of upconversion emission in nanocrystals.

Photoluminescence is a powerful tool in temperature sensing. Recently, the application of upconversion (UC) nanocrystals (NCs) has shown great potential for nanothermometry due to high spatial resolution, superior accuracy, and its non-invasive nature. In addition to spectral changes upon heating, anomalous thermal enhancement of UC emission has been reported for UC NCs, but the underlying mechanism remains unclear.

Bridging the gap: 3D real-space characterization of colloidal assemblies via FIB-SEM tomography.

Insight in the structure of nanoparticle assemblies up to a single particle level is key to understand the collective properties of these assemblies, which critically depend on the individual particle positions and orientations. However, the characterization of large, micron sized assemblies containing small, 10-500 nanometer, sized colloids is highly challenging and cannot easily be done with the conventional light, electron or X-ray microscopy techniques. Here, we demonstrate that focused ion beam-scanning electron microscopy (FIB-SEM) tomography in combination with image processing enables quantitative real-space studies of ordered and disordered particle assemblies too large for conventional transmission electron tomography, containing particles too small for confocal microscopy.