Lihua Wang

A High‐Rate and Ultralong‐Life Sodium‐Ion Battery Based on NaTi2(PO4)3 Nanocubes with Synergistic Coating of Carbon and Rutile TiO2

Highly regular NaTi2 (PO4 )3 nanocubes with synergistic nanocoatings of rutile TiO2 and carbon are prepared as an electrode material for sodium-ion batteries. It exhibits a high rate and ultralong life performance simultaneously, and a capacity retention of 89.3% after 10 000 cycles is achieved.

Facile synthesis of Ag3PO4 tetrapod microcrystals with an increased percentage of exposed {110} facets and highly efficient photocatalytic properties

Tetrapod-shaped Ag3PO4 microcrystals with an increased percentage of exposed {110} facets have been successfully prepared for the first time, and a possible growth mechanism is proposed. The as-prepared Ag3PO4 tetrapods exhibit excellent photocatalytic activities under visible light illumination, which may be ascribed to the relatively higher reactivity of {110} facets.

Transmission electron microscopy observations of dislocation annihilation and storage in nanograins

A detailed in situ investigation of dislocation processes has been rare for nanograined materials with grain sized near or less than 10 nm. Here, we report a time-resolved and atomic-scale in situ transmission electron microscopy observation of the nucleation, motion, annihilation, and storage of full dislocations in nanograins with diameters less than ∼10u2002nm. Annihilation of dislocation dipoles appears to be a major contributor to the reduction in dislocation density, in addition to annihilation at grain boundary sinks. The accumulation of a high density of dislocations inside nanograins is found to be possible when they are surrounded by neighboring grains.

In situ atomic scale mechanical microscopy discovering the atomistic mechanisms of plasticity in nano-single crystals and grain rotation in polycrystalline metals.

In this review, we briefly introduce our in situ atomic-scale mechanical experimental technique (ASMET) for transmission electron microscopy (TEM), which can observe the atomic-scale deformation dynamics of materials. This in situ mechanical testing technique allows the deformation of TEM samples through a simultaneous double-tilt function, making atomic-scale mechanical microscopy feasible. This methodology is generally applicable to thin films, nanowires (NWs), tubes and regular TEM samples to allow investigation of the dynamics of mechanically stressed samples at the atomic scale. We show several examples of this technique applied to Pt and Cu single/polycrystalline specimens. The in situ atomic-scale observation revealed that when the feature size of these materials approaches the nano-scale, they often exhibit unusual deformation behaviours compared to their bulk counterparts. For example, in Cu single-crystalline NWs, the elastic-plastic transition is size-dependent. An ultra-large elastic strain of 7.2%, which approaches the theoretical elasticity limit, can be achieved as the diameter of the NWs decreases to ∼6 nm. The crossover plasticity transition from full dislocations to partial dislocations and twins was also discovered as the diameter of the single-crystalline Cu NWs decreased. For Pt nanocrystals (NC), the long-standing uncertainties of atomic-scale plastic deformation mechanisms in NC materials (grain size G less than 15 nm) were clarified. For larger grains with G<∼10 nm, we frequently observed movements and interactions of cross-grain full dislocations. For G between 6 and 10 nm, stacking faults resulting from partial dislocations become more frequent. For G<∼6 nm, the plasticity mechanism transforms from a mode of cross-grain dislocation to a collective grain rotation mechanism. This grain rotation process is mediated by grain boundary (GB) dislocations with the assistance of GB diffusion and shuffling. These in situ atomic-scale images provide a direct demonstration that grain rotation, through the evolution of the misorientation angle between neighbouring grains, can be quantitatively assessed by the dislocation content within the grain boundaries. In combination with the revolutionary Cs-corrected sub-angstrom imaging technologies developed by Urban et al., the opportunities for experimental mechanics at the atomic scale are emerging.

Flower-shaped PdI2 nanomaterials with remarkable surface-enhanced Raman scattering activity

Uniform dispersed flower-shaped palladium iodide (PdI2) nanoparticles were prepared successfully by a simple wet chemical method. The as-synthesized products were structurally and morphologically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), as well as high resolution transmission electron microscopy (HRTEM). Large numbers of twin and stacking faults were observed at the tip of the petals of flower-shaped morphology. At the same time, a series of palladium iodide structures with different morphology and size were obtained through the manipulation of the concentration of KI and the reaction temperature. The formation of typical flower-shaped palladium iodide was correlated with their reaction conditions. The as-produced PdI2 nanoparticles exhibit high surface-enhanced Raman scattering (SERS) activities for malachite green (MG) probe molecules with 1.0 × 10−7 M concentration. As a result, the flower-shaped PdI2 nanostructures coupled with SERS hold a great potential as a rapid and ultra-sensitive agent for detecting trace amounts of prohibited substances in contaminated food samples.

Dislocation "Bubble-Like-Effect" and the Ambient Temperature Super-plastic Elongation of Body-centred Cubic Single Crystalline Molybdenum.

With our recently developed deformation device, the in situ tensile tests of single crystal molybdenum nanowires with various size and aspect ratio were conducted inside a transmission electron microscope (TEM). We report an unusual ambient temperature (close to room temperature) super-plastic elongation above 127% on single crystal body-centred cubic (bcc) molybdenum nanowires with an optimized aspect ratio and size. A novel dislocation “bubble-like-effect” was uncovered for leading to the homogeneous, large and super-plastic elongation strain in the bcc Mo nanowires. The dislocation bubble-like-effect refers to the process of dislocation nucleation and annihilation, which likes the nucleation and annihilation process of the water bubbles. A significant plastic deformation dependence on the sample’s aspect ratio and size was revealed. The atomic scale TEM observations also demonstrated that a single crystal to poly-crystal transition and a bcc to face-centred cubic phase transformation took place, which assisted the plastic deformation of Mo in small scale.

Dynamic Atomic Mechanisms of Plasticity of Ni Nanowires and Nano Crystalline Ultra-Thin Films

Using our recently developed in situ transmission electron microscopy techniques, we revealed that the FCC structured Ni nanowires with diameter of about 30 nm possess ultra-large strain plasticity. Dynamic complex dislocation activities mediated the large strain bent-plasticity and they were monitored at atomic scale in real time. The bent-induced strain gradient allows studying the strain effects on dislocation mediated plasticity. We also explored the deformation techniques to more general cases, the nano thin films. An example of tensile Pt ultra-thin film is presented.

Atomic-Scale-Deformation-Dynamics (ASDS) of Nanowires and Nanofilms

Nanowires and nanofilms are fundamental building blocks of micro and nano-electronics for both of bottom-up and top-down technologies. Monitoring and recording the mechanical property dynamics at atomic scale are important to understand the atomic mechanism of new and surprising nano-phenomena and design new applications. Through years’ endeavors, we developed tensile and/or bending in-situ atomic-lattice resolution electron microscopy methods and equipments for nanowires and successfully conducted atomic-lattice resolution mechanical tests on individual nano-objects. With this, we observed the brittle materials SiC and Si nanowires (NWs) become highly ductile at room temperature. The crystalline structural evolution processes corresponding to the occurrence of unusual large strain plasticity includes the dislocation initiation, dislocation accumulation and amorphorization as well as the necking of the one dimensional nanowires were fully recorded at atomic scale and in real time. We also expand the experimental methods and equipments to two-dimensional nanofilms. An example of tensile experiment on nano-crystalline Au films is presented. The deformation mechanisms of nano-crystalline gold films were observed at the atomic scale and real-time. At the mean time, an atomic scale the crack blunting behavior was captured and the plastic deformation mechanism of the single nano-crystalline was revealed.

In situ atomic scale mechanisms of strain-induced twin boundary shear to high angle grain boundary in nanocrystalline Pt

Twin boundary can both strengthen and soften nanocrystalline metals and has been an important path for improving the strength and ductility of nano materials. Here, using in-lab developed double-tilt tensile stage in the transmission electron microscope, the atomic scale twin boundary shearing process was in situ observed in a twin-structured nanocrystalline Pt. It was revealed that the twin boundary shear was resulted from partial dislocation emissions on the intersected {111} planes, which accommodate as large as 47% shear strain. It is uncovered that the partial dislocations nucleated and glided on the two intersecting {111} slip planes lead to a transition of the original <110> symmetric tilt ∑3/(111) coherent twin boundary into a <110> symmetric tilt ∑9/(114) high angle grain boundary. These results provide insight of twin boundary strengthening mechanisms for accommodating plasticity strains in nanocrystalline metals.