Scanning transmission electron microscopy: A review of high angle annular dark field and annular bright field imaging and applications in lithium-ion batteries

Scanning transmission electron microscopy（STEM） has been shown as powerful tools for material characterization,especially after the appearance of aberration-corrector which greatly enhances the resolution of STEM. High angle annular dark field（HAADF） and annular bright field（ABF） imaging of the aberration-corrected STEM are widely used due to their high-resolution capabilities and easily interpretable image contrasts. However, HAADF mode of the STEM is still limited in detecting light elements due to the weak electron-scattering power. ABF mode of the STEM could detect light and heavy elements simultaneously, providing unprecedented opportunities for probing unknown structures of materials. Atomiclevel structure investigation of materials has been achieved by means of these imaging modes, which is invaluable in many fields for either improving properties of materials or developing new materials. This paper aims to provide a introduction of HAADF and ABF imaging techniques and reviews their applications in characterization of cathode materials, study of electrochemical reaction mechanisms, and exploring the effective design of lithium-ion batteries（LIBs）. The future prospects of the STEM are also discussed.

Spontaneous caving and gob-side entry retaining of thin seam with large inclined angle

Based on the research method of combining simulation analysis with field testing by distinct element process UDEC, we have analyzed the roof deformation and failure laws and roadway support technology of gob-side entry retaining in a thin seam with a large inclined angle. The results show that during exploitation in seams with large inclined angle, rotational subsidence of the main roof under the gob area is small and can maintain balance, so there is no need to provide artificial permanent support resistance for the main roof near the upper side to control rotational subsidence. Obstructed by the dense scrap rail,waste rock from the immediate roof caving slides from the upper gob area to the lower area and fills it,which strikes a balance between the immediate roof under the goaf after it fractures into large pieces and filling waste rocks.

Factor analysis of interceptor capture probability

The capture probability of interceptors has been deeply studied.Firstly,the definition of capture probability is analyzed.It is transformed into calculating the probability that the relative position vector between the target and the interceptor locates in a certain cone.The relative position vector and associated covariance matrix are projected in line-of-sight coordinates,and the 3-dimensional integral of a probability function in a cone is calculated to obtain the capture probability.The integral equation is a complicated expression of probability,and it is simplified to an explicit approximate expression according to some assumptions based on the characteristics of the engineering problems.The approximation precision is analyzed by comparative simulation difference,which indicates that approximate assumptions are reasonable.Utilizing the explicit expression,the characteristics of capture probability are analyzed respectively with the factors,such as the distance between the interceptor and the target,the precision of relative position vector,the maximum capture distance and the maximum field angle of interceptor seeker.

Correction Optimization of Lens Radial Distortion with Bending Measurement Function

In this paper, a distortion correction method with reduced complexity is proposed. With the singleparameter division model, the initial approximation of distortion parameters and the distortion center can be calibrated. Based on the distance from the image center to the fitting lines of the extracted curves, a bending measurement function with a weighted factor is proposed to optimize the initial value. Simulation and experiments verify the proposed method.

A technique of reconstructing field for measuring sound reflection coefficients at arbitrary angles of incidence

An improved reconstructing field method for measuring sound reflection coefficient of a large impedance surface at arbitrary incident angles is proposed in this paper. In order to get the reflection coefficient by the Spatial Transformation of Sound Fields (STSF), the complex pressure on two parallel planes near by the material surface or the reflection surface must be measured. By the acoustic intensity measurement, the phases of complex pressure on two parallel planes are given. The results of the numerical simulations are shown that the error due to the finite size of the measurement area, and it may be reduced by using a dipole sound source.

Self-accommodated defect structures modifying the growth of Laves phase

Laves phases,with the topologically close-packed structure and a chemical formula of Ab_(2),constitute the largest single class of intermetallics.Planar defects in Laves phases are widely investigated,especially for stacking behavior transformations through synchroshear.Here,we report the coexistence of C14,C36 and C15 structures in MgZn_2 precipitates by using atomic resolution scanning transmission electron microscopy,verifying the previously predicted Laves phase transformation sequence of C14→C36→C15 also applies to MgZn_2.One type of stacking fault couple in precipitates has been found to alone reduce the lattice mismatch with matrix,while some other stacking fault couples need to self-accommodate with irregular planar defects(rhombic units and flattened hexagonal units),or with five-fold symmetry structures to relieve the strain concentration.Precipitates thus grow towards an equiaxed or even round morphology,rather than the plate morphology as conventionally believed.Molecular dynamics calculations are performed to support our analysis.These findings reveal the principles governing the concurrent occurrence of various defects in laves structures,acting as an update of the widely accepted perception of random occurrence of defects during crystal growth.