In this work, we demonstrate the systematic and delicate geometry control of Cu 2 O nanocrystals by taking advantage of the selective surface stabilization effect. A variety of Cu 2 O architectures, evolved from cubes through truncated cubes, cubooctahedrons, truncated octahedrons and finally to octahedrons, were achieved by simply adjusting the added PVP. Based on the understanding of the intrinsic structural features of the cuprite Cu 2 O and PVP, we elucidated the underlying shape evolution mechanism. The as-prepared products demonstrated a crystallography-dependent adsorption ability with methyl orange (MeO) as the pollutant. With the advantage of a low cost, high yield and straightforward procedure without pre-formed crystals as sacrificial templates, this method may provide a good starting point for the study of shape construction and morphology-dependent properties of other nanocrystals.

We present an innovative approach to the production of single-crystal iron oxide nanorings employing a solution-based route. Single-crystal hematite (alpha-Fe2O3) nanorings were synthesized using a double anion-assisted hydrothermal method (involving phosphate and sulfate ions), which can be divided into two stages: (1) formation of capsule-shaped alpha-Fe2O3 nanoparticles and (2) preferential dissolution along the long dimension of the elongated nanoparticles (the c axis of alpha-Fe2O3) to form nanorings. The shape of the nanorings is mainly regulated by the adsorption of phosphate ions on faces parallel to c axis of alpha-Fe2O3 during the nanocrystal growth, and the hollow structure is given by the preferential dissolution of the alpha-Fe2O3 along the c axis due to the strong coordination of the sulfate ions. By varying the ratios of phosphate and sulfate ions to ferric ions, we were able to control the size, morphology, and surface architecture to produce a variety of three-dimensional hollow nanostructures. These can then be converted to magnetite (Fe3O4) and maghemite (gamma-Fe2O3) by a reduction or reduction-oxidation process while preserving the same morphology. The structures and magnetic properties of these single-crystal alpha-Fe2O3, Fe3O4, and gamma-Fe2O3 nanorings were characterized by various analytical techniques. Employing off-axis electron holography, we observed the classical single-vortex magnetic state in the thin magnetite nanorings, while the thicker rings displayed an intriguing three-dimensional magnetic configuration. This work provides an easily scaled-up method for preparing tailor-made iron oxide nanorings that could meet the demands of a variety of applications ranging from medicine to magnetoelectronics.

Elastic-plastic and fracture properties are key issues in characterizing materials' mechanical behavior, and they have been extensively studied for over a century for bulk structured materials. [1][2][3] Silicon is one of the most important and representative materials for these studies owing to its extremely important applications. [4,5] Silicon nanowires (NWs) are one of the most important nanostructures used for fabricating various electronic and optoelectronic nanodevices, [6,7] and they could be a building block for the construction and assembly of functional nanometer-scale systems. Although the electrical and optical properties of Si NWs have been extensively studied, only limited information is available about the structure-mechanical property correlations of Si NWs. This is likely due to the difficulty of carrying out in situ tensile or bending measurements on individual NWs. The elastic-plastic strains retained in NWs can significantly affect their electronic properties by perturbing the band structure or changing the Fermi energy of the nanostructures. [8] For example, the applied strains of continuous torsion on carbon NTs could result in chirality variation and therefore introduce a distinct conductance oscillation from metallic to semiconductor.[9] A straininduced giant piezoresistance effect has also been observed for Si NWs.[10]Results of studies of the elastic-plastic behavior of Si NWs are of technological importance. Silicon NWs are a potential candidate for building devices that are to be integrated with microelectronics and microelectromechanical systems (MEMS). They are also an outstanding candidate for constructing devices for flexible electronics. Several approaches have been developed to study the mechanical properties of NWs and nanotubes (NTs) based on atomic force microscopy (AFM) at nanometer-scale spatial resolution. [11,12] The major limitation of AFM measurements is that they are unable to reveal the atomic-scale structural evolution process during the in situ elastic-plastic-fracture process. Transmission electron microscopy (TEM) has been one of the most important and effective tools with a capability of atomic level imaging for investigating the in situ mechanical properties of single NWs and NTs, [13,14] although ex situ studies have to be carried out. [15,16] Direct and in situ atomic level imaging during tensile testing is fundamentally important to view and provide true physical insight into the elastic-plastic and fracture processes, [12,13] but this type of study is challenging experimentally.In this report, we present in situ TEM observation of the elastic-plastic-fracture processes of a single Si NW recorded at atomic resolution. The study directly shows the strain-induced structural evolution process of Si NWs and its largestrain plasticity (LSP). Our results indicate that the LSP of Si NWs via a brittle-ductile transition originates from a dislocation-initiated amorphization. This behavior is in contrast to the mechanical behavior of bulk Si. Our observation reveals a ...

At room temperature, glasses are known to be brittle and fracture upon deformation. Zheng et al. show that, by exposing amorphous silica nanostructures to a low-intensity electron beam, it is possible to achieve dramatic shape changes, including a superplastic elongation of 200% for nanowires.

Defect engineering modified graphite carbon nitride (g-C3N4) has been widely used in various photocatalytic systems due to the enhanced catalytic activity by multiple defect sites (such as vacancies or functional...

Large strain plasticity is phenomenologically defined as the ability of a material to exhibit an exceptionally large deformation rate during mechanical deformation. It is a property that is well established for metals and alloys but is rarely observed for ceramic materials especially at low temperature (∼300 K). With the reduction in dimensionality, however, unusual mechanical properties are shown by ceramic nanomaterials. In this Letter, we demonstrated unusually large strain plasticity of ceramic SiC nanowires (NWs) at temperatures close to room temperature that was directly observed in situ by a novel high-resolution transmission electron microscopy technique. The continuous plasticity of the SiC NWs is accompanied by a process of increased dislocation density at an early stage, followed by an obvious lattice distortion, and finally reaches an entire structure amorphization at the most strained region of the NW. These unusual phenomena for the SiC NWs are fundamentally important for understanding the nanoscale fracture and strain-induced band structure variation for high-temperature semiconductors. Our result may also provide useful information for further studying of nanoscale elastic−plastic and brittle−ductile transitions of ceramic materials with superplasticity.

In this work, we report a high figure of merit (ZT) of ~1.7 at 823 K in p-type polycrystalline Cd-doped SnSe by combining cation vacancies and localized-lattice engineering. It is observed that the introduction of Cd atoms in SnSe lattice induce Sn vacancies, which act as p-This article is protected by copyright. All rights reserved. type dopants. A combination of facile solvothermal synthesis and fast spark plasma sintering technique boosts the Sn vacancy to a high level of ~2.9 %, which results in an optimum hole concentration of ~2.6×10 19 cm -3 and an improved power factor of ~6.9 μW cm -1 K -2 . Simultaneously, a low thermal conductivity of ~0.33 W m -1 K -1 is achieved by effective phonon scattering at localized crystal imperfections, as observed by detailed structural characterizations.Density-functional-theory calculations reveal that the role of Cd atoms in the SnSe lattice is to reduce the formation energy of Sn vacancies, which in turn lower the Fermi level down into the valence bands, generating holes. This work explores the fundamental Cd-doping mechanisms at the nanoscale in a SnSe matrix and demonstrates vacancy and localized-lattice engineering as an effective approach to boosting thermoelectric performance. The work provides an avenue in achieving high-performance thermoelectric properties of materials.

We quantified the size-dependent energy bandgap modulation of ZnO nanowires under tensile strain by an in situ measurement system combining a uniaxial tensile setup with a cathodoluminescence spectroscope. The maximal strain and corresponding bandgap variation increased by decreasing the size of the nanowires. The adjustable bandgap for the 100 nm nanowire caused by a strain of 7.3% reached approximately 110 meV, which is nearly double the value of 59 meV for the 760 nm nanowire with a strain of 1.7%. A two-step linear feature involving bandgap reduction caused by straining and a corresponding critical strain was identified in ZnO nanowires with diameters less than 300 nm. The critical strain moved toward the high strain level with shrunken nanowires. The distinct size effect of strained nanowires on the bandgap variation reveals a competition between core-dominated and surface-dominated bandgap modulations. These results could facilitate potential applications involving nanowire-based optoelectronic devices and band-strain engineering.