Assembly of Three-Dimensional Hetero-Epitaxial ZnO/ZnS Core/Shell Nanorod and Single Crystalline Hollow ZnS Nanotube Arrays

Hetero-epitaxial growth along three-dimensional (3D) interfaces from materials with an intrinsic large lattice mismatch is a key challenge today. In this work we report, for the first time, the controlled synthesis of vertically aligned ZnO/ZnS core/shell nanorod arrays composed of single crystalline wurtzite (WZ) ZnS conformally grown on ZnO rods along 3D interfaces through a simple two-step thermal evaporation method. Structural characterization reveals a “(01–10)_ZnO//(01–10)_ZnS and [0001]_ZnO//[0001]_ZnS” epitaxial relationship between the ZnO core and the ZnS shell. It is exciting that arrays of single crystalline hollow ZnS nanotubes are also innovatively obtained by simply etching away the inner ZnO cores. On the basis of systematic structural analysis, a rational growth mechanism for the formation of hetero-epitaxial core/shell nanorods is proposed. Optical properties are also investigated <i>via</i> cathodoluminescence and photoluminescence measurements. Remarkably, the synthesized ZnO/ZnS core/shell heterostructures exhibit a greatly reduced ultraviolet emission and dramatically enhanced green emission compared to the pure ZnO nanorods. The present single-crystalline heterostructure and hollow nanotube arrays are envisaged to be highly promising for applications in novel nanoscale optoelectronic devices, such as UV-A photodetectors, lasers, solar cells, and nanogenerators

Polarity-Free Epitaxial Growth of Heterostructured ZnO/ZnS Core/Shell Nanobelts

Surface-polarity-induced formation of ZnO/ZnS heterojunctions has a common characteristic that ZnS (or ZnO) is exclusively decorated on a Zn-terminated (0001) surface of ZnO (or ZnS) due to its comparatively chemically active nature to an O (or S)-terminated (000–1) surface. Here, we report a polarity-free and symmetrical growth of ZnS on both ZnO±(0001) surfaces to form a new heterostructured ZnO/ZnS core/shell nanobelt via a thermal evaporation method. Remarkably, the ZnS shell is single-crystalline and preserves the structure and orientation of the inner ZnO nanobelt with an epitaxial relationship of (0001)_ZnO//(0001)_ZnS; [2–1–10]_ZnO//[2–1–10]_ZnS. Through this case, we demonstrate that an anion-terminated polar surface could also drive the nucleation and growth of nanostructures as the cation-terminated surface by controlling the growth kinetics. Considering high-performance devices based on ZnO/ZnS heterojunctions, the current ZnO/ZnS nanobelt is advantageous for optoelectronic applications due to its single-crystalline nature and relatively more efficient charge separation along 3D heterointerfaces

Nanodomains Coupled to Ferroelectric Domains Induced by Lattice Distortion in Self-Doped LuMn_<i>x</i>O_3±δ Hexagonal Ceramics

Self-doped h-LuMn_<i>x</i>O_3±δ multiferroic ceramics with 0.92 ≤ <i>x</i> ≤ 1.12 were studied for the dependence of magnetic properties on <i>x</i>. Interlocking of lattice distortion at the nanoscale with ferroelectric (FE) domains in bulk RMnO₃ materials is mostly unknown. Here we report occurrence of nanodomains in transmission electron microscopy (TEM) images with the presence of antiphase boundaries/ferroelectric domain walls separating nano-FE domains. Observed chemical inhomogeneity across the crystalline grains of the ceramics causes distortion in the lattice. Formation of nanostructural domains revealed across particles of Mn deficient or Lu deficient samples includes bands of strained atomic planes, structural antiphase boundaries, and planar defects similar to stacking fault ribbons. Nanotwins exist in the basal plane, the twin boundary representing disorder of the stacking of atomic planes along the [110] direction. Image contrast in high resolution HRTEM images and TEM image simulation confirm the role of planar defects on switching of electrical polarization, which cause topology breaking of sixfold vortices of FE domains in h-RMnO₃ oxides. The local orbital arrangements of ions are investigated by EELS spectroscopy of O K-edge supported by theoretical analysis. Irreversibility in magnetization below the Néel temperature of antiferromagnetic ordering of the h-LuMn_<i>x</i>O_3±δ multiferroic solid solution is found for all ceramics showing dependence on cation vacancy type and nominal content. The main features observed in the irreversibility of magnetization were correlated to defects and inhomogeneity in the nanoscale images of the lattice of ceramics. The interplay of lattice distortion linked to extended defects and magnetic/ferroelectric properties of multiferroic ceramics is further discussed

<i>In Situ</i> Atomic-Scale Observation of Surface-Tension-Induced Structural Transformation of Ag-NiP_<i>x</i> Core–Shell Nanocrystals

The properties of nanocrystals are highly dependent on their morphology, composition, and structure. Tailored synthesis over these parameters is successfully applied for the production of nanocrystals with desired properties for specific applications. However, in order to obtain full control over the properties, the behavior of nanocrystals under external stimuli and application conditions needs to be understood. Herein, using Ag-NiP_<i>x</i> nanocrystals as a model system, we investigate the structural evolution upon thermal treatment by <i>in situ</i> aberration-corrected scanning transmission electron microscopy. A combination of real-time imaging with elemental analysis enables the observation of the transformation from a Ag-NiP_<i>x</i> core–shell configuration to a Janus structure at the atomic scale. The transformation occurs through dewetting and crystallization of the NiP_<i>x</i> shell and is accompanied by surface segregation of Ag. Further temperature increase leads to a complete sublimation of Ag and formation of individual Ni₁₂P₅ nanocrystals. The transformation is rationalized by theoretical modeling based on density functional theory calculations. Our model suggests that the transformation is driven by changes of the surface energy of NiP_<i>x</i> and the interfacial energy between NiP_<i>x</i> and Ag. The direct observation of atomistic dynamics during thermal-treatment-induced structural modification will help to understand more complex transformations that are induced by aging over time or the interaction with a reactive gas phase in applications such as catalysis

<i>In Situ</i> Atomic-Scale Observation of Surface-Tension-Induced Structural Transformation of Ag-NiP_<i>x</i> Core–Shell Nanocrystals

The properties of nanocrystals are highly dependent on their morphology, composition, and structure. Tailored synthesis over these parameters is successfully applied for the production of nanocrystals with desired properties for specific applications. However, in order to obtain full control over the properties, the behavior of nanocrystals under external stimuli and application conditions needs to be understood. Herein, using Ag-NiP_<i>x</i> nanocrystals as a model system, we investigate the structural evolution upon thermal treatment by <i>in situ</i> aberration-corrected scanning transmission electron microscopy. A combination of real-time imaging with elemental analysis enables the observation of the transformation from a Ag-NiP_<i>x</i> core–shell configuration to a Janus structure at the atomic scale. The transformation occurs through dewetting and crystallization of the NiP_<i>x</i> shell and is accompanied by surface segregation of Ag. Further temperature increase leads to a complete sublimation of Ag and formation of individual Ni₁₂P₅ nanocrystals. The transformation is rationalized by theoretical modeling based on density functional theory calculations. Our model suggests that the transformation is driven by changes of the surface energy of NiP_<i>x</i> and the interfacial energy between NiP_<i>x</i> and Ag. The direct observation of atomistic dynamics during thermal-treatment-induced structural modification will help to understand more complex transformations that are induced by aging over time or the interaction with a reactive gas phase in applications such as catalysis

<i>In Situ</i> Atomic-Scale Observation of Surface-Tension-Induced Structural Transformation of Ag-NiP_<i>x</i> Core–Shell Nanocrystals

The properties of nanocrystals are highly dependent on their morphology, composition, and structure. Tailored synthesis over these parameters is successfully applied for the production of nanocrystals with desired properties for specific applications. However, in order to obtain full control over the properties, the behavior of nanocrystals under external stimuli and application conditions needs to be understood. Herein, using Ag-NiP_<i>x</i> nanocrystals as a model system, we investigate the structural evolution upon thermal treatment by <i>in situ</i> aberration-corrected scanning transmission electron microscopy. A combination of real-time imaging with elemental analysis enables the observation of the transformation from a Ag-NiP_<i>x</i> core–shell configuration to a Janus structure at the atomic scale. The transformation occurs through dewetting and crystallization of the NiP_<i>x</i> shell and is accompanied by surface segregation of Ag. Further temperature increase leads to a complete sublimation of Ag and formation of individual Ni₁₂P₅ nanocrystals. The transformation is rationalized by theoretical modeling based on density functional theory calculations. Our model suggests that the transformation is driven by changes of the surface energy of NiP_<i>x</i> and the interfacial energy between NiP_<i>x</i> and Ag. The direct observation of atomistic dynamics during thermal-treatment-induced structural modification will help to understand more complex transformations that are induced by aging over time or the interaction with a reactive gas phase in applications such as catalysis

<i>In Situ</i> Atomic-Scale Observation of Surface-Tension-Induced Structural Transformation of Ag-NiP_<i>x</i> Core–Shell Nanocrystals

The properties of nanocrystals are highly dependent on their morphology, composition, and structure. Tailored synthesis over these parameters is successfully applied for the production of nanocrystals with desired properties for specific applications. However, in order to obtain full control over the properties, the behavior of nanocrystals under external stimuli and application conditions needs to be understood. Herein, using Ag-NiP_<i>x</i> nanocrystals as a model system, we investigate the structural evolution upon thermal treatment by <i>in situ</i> aberration-corrected scanning transmission electron microscopy. A combination of real-time imaging with elemental analysis enables the observation of the transformation from a Ag-NiP_<i>x</i> core–shell configuration to a Janus structure at the atomic scale. The transformation occurs through dewetting and crystallization of the NiP_<i>x</i> shell and is accompanied by surface segregation of Ag. Further temperature increase leads to a complete sublimation of Ag and formation of individual Ni₁₂P₅ nanocrystals. The transformation is rationalized by theoretical modeling based on density functional theory calculations. Our model suggests that the transformation is driven by changes of the surface energy of NiP_<i>x</i> and the interfacial energy between NiP_<i>x</i> and Ag. The direct observation of atomistic dynamics during thermal-treatment-induced structural modification will help to understand more complex transformations that are induced by aging over time or the interaction with a reactive gas phase in applications such as catalysis

One-Step Synthesis and Self-Assembly of Metal Oxide Nanoparticles into 3D Superlattices

A simple one-pot approach based on the “benzyl alcohol route” is introduced for the fabrication of highly ordered supercrystals composed of highly uniform 3–4 nm zirconia and rare-earth stabilized zirconia nanoparticles. The as-fabricated supercrystals reach sizes larger than 10 μm and present well-defined 3D morphologies such as flower-like, rhombic dodecahedron, and bipyramids. This system is unique in that the supercrystals are formed in one-step directly in the reaction medium where the nanoparticles are synthesized. The uniformity in nanocrystal shape and size is attributed to the <i>in situ</i> formation of benzoate species that directs the nanoparticle growth and assembly. The low colloidal stabilization of the benzoate-capped nanoparticles in benzyl alcohol promotes the formation of supercrystals in solution by π–π interaction between the <i>in situ</i> formed benzoate ligands attached to neighboring particles. By varying the reaction temperature and the nature of the doping the way the nanobulding blocks assemble in the supercrystals could be controlled. Standard FCC superlattice packings were found together with more unusual ones with <i>P</i>6<i>/mmm</i> and <i>R</i>3̅<i>m</i> symmetries

<i>In Situ</i> Atomic-Scale Observation of Surface-Tension-Induced Structural Transformation of Ag-NiP_<i>x</i> Core–Shell Nanocrystals

The properties of nanocrystals are highly dependent on their morphology, composition, and structure. Tailored synthesis over these parameters is successfully applied for the production of nanocrystals with desired properties for specific applications. However, in order to obtain full control over the properties, the behavior of nanocrystals under external stimuli and application conditions needs to be understood. Herein, using Ag-NiP_<i>x</i> nanocrystals as a model system, we investigate the structural evolution upon thermal treatment by <i>in situ</i> aberration-corrected scanning transmission electron microscopy. A combination of real-time imaging with elemental analysis enables the observation of the transformation from a Ag-NiP_<i>x</i> core–shell configuration to a Janus structure at the atomic scale. The transformation occurs through dewetting and crystallization of the NiP_<i>x</i> shell and is accompanied by surface segregation of Ag. Further temperature increase leads to a complete sublimation of Ag and formation of individual Ni₁₂P₅ nanocrystals. The transformation is rationalized by theoretical modeling based on density functional theory calculations. Our model suggests that the transformation is driven by changes of the surface energy of NiP_<i>x</i> and the interfacial energy between NiP_<i>x</i> and Ag. The direct observation of atomistic dynamics during thermal-treatment-induced structural modification will help to understand more complex transformations that are induced by aging over time or the interaction with a reactive gas phase in applications such as catalysis

The Extent of Platinum-Induced Hydrogen Spillover on Cerium Dioxide

Hydrogen spillover from metal nanoparticles to oxides is an essential process in hydrogenation catalysis and other applications such as hydrogen storage. It is important to understand how far this process is reaching over the surface of the oxide. Here, we present a combination of advanced sample fabrication of a model system and in situ X-ray photoelectron spectroscopy to disentangle local and far-reaching effects of hydrogen spillover in a platinum–ceria catalyst. At low temperatures (25–100 °C and 1 mbar H2) surface O–H formed by hydrogen spillover on the whole ceria surface extending microns away from the platinum, leading to a reduction of Ce4+ to Ce3+. This process and structures were strongly temperature dependent. At temperatures above 150 °C (at 1 mbar H2), O–H partially disappeared from the surface due to its decreasing thermodynamic stability. This resulted in a ceria reoxidation. Higher hydrogen pressures are likely to shift these transition temperatures upward due to the increasing chemical potential. The findings reveal that on a catalyst containing a structure capable to promote spillover, hydrogen can affect the whole catalyst surface and be involved in catalysis and restructuring