A STEM tomographic multiplication nano-moiré method.

Heterojunction optoelectronic technology has extensive applications in modern optoelectronics. The lattice quality and mismatch strain near the heterojunction interface significantly affect the photoelectric performance of a photoelectronic device. Therefore, accurately characterizing the internal three-dimensional (3D) strain at the interface in a large field is essential to evaluate the heterojunction optoelectronic device quality. Here, we propose a tomographic multiplication nano-moiré method for internal 3D strain measurements in a large field. This method operates by combining the depth sectioning technique of scanning transmission electron microscopy (STEM) with the multiplication moiré method. A mutual overlapping analytical method based on spherical aberration correction is adopted in 3D reconstruction to achieve the nanometer resolution in the depth direction. The developed method overcomes the small measurement field of view (FOV) limitation of the conventional transmission electron microscope and provides high resolution and a large measurement volume, potentially facilitating the evaluation of the large-scale 3D internal lattice quality and strain field characterization. Using the proposed method, the 3D distribution of dislocations and strain fields in the [011] direction at the heterojunction interface of the InP/InGaAs nanomaterial is intuitively, clearly, and comprehensively revealed.

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Soil fauna play an important role in key functions of ecosystem such as material cycling. Litter quality and microenvironment of different tree species may regulate soil fauna community structure. In this study, we investigated soil fauna community structure, the differences of taxonomic and functional groups, and the regulatory factors under eight dominant tree species in August 2022. We captured 567 soil fauna (except for termites and ants), belonging to 3 phyla, 10 classes, 26 orders, and 99 families, with Achipteriidae, Trygoniidae, Poduridae, and Isotomidae as the dominant species. Tree species significantly affected soil fauna abundance, following an order: Michelia macclurei > Elaeocarpus decipiens > Castanopsis carlesii > Cunninghamia lanceolata > Lindera communis > Schima superba > Pinus massoniana > Liquidambar formosana. However, the richness, evenness, and diversity of soil fauna under different tree species were significantly different. Richness and diversity of M. macclurei, C. lanceolatas soil fauna were relatively high, while L. formosana, C. carlesii were relatively low. The evenness of meso-microfauna of L. formosana was the highest, which was significantly higher than that of M. macclureis and E. decipiens. The evenness of macrofauna and total soil fauna was not significantly different among the eight tree species. In addition, the abundance of omnivores and herbivores soil fauna was relatively high under M. macclurei, but relatively low under E. decipiens. The abundance of saprophages and predators soil fauna of E. decipiens, M. macclurei was higher than L. formosana, while saprophages was mainly meso-microfauna. Results of redundancy analysis showed that litter N, C:N, and K were the main factors affecting soil fauna community structure. The results indicated that the tree species with thicker litter layer and higher N and K contents may be conducive to enhancing the diversity of soil fauna community and affecting the distribution of different functional groups, thus contributing to the maintenance of forest biodiversity.

3D Strain Measurement of Heterostructures Using the Scanning Transmission Electron Microscopy Moiré Depth Sectioning Method.

The mechanical properties of micro- and nanoscale materials directly determine the reliability of heterostructures, microstructures, and microdevices. Therefore, an accurate evaluation of the 3D strain field at the nanoscale is important. In this study, a scanning transmission electron microscopy (STEM) moiré depth sectioning method is proposed. By optimizing the scanning parameters of electron probes at different depths of the material, the sequence STEM moiré fringes (STEM-MFs) with a large field of view, which can be hundreds of nanometers obtained. Then, the 3D STEM moiré information constructed. To some extent, multi-scale 3D strain field measurements from nanometer to the submicrometer scale actualized. The 3D strain field near the heterostructure interface and single dislocation accurately measured by the developed method.

High-Precision 3D-DIC Measurement Method Based on Improved Forward Newton Iteration.

To solve the problems of the traditional 3D-DIC algorithm based on feature information or FFT search at the expense of accuracy in exchange for time, such as error-point extraction, mismatching of feature points, poor robustness, and accuracy loss caused by poor anti-noise performance, an improved high-precision 3D-DIC measurement method was proposed. In this method, the exact initial value is obtained by an exhaustive search. Then, the forward Newton iteration method is used for pixel classification, and the first-order nine-point interpolation is designed, which can quickly obtain the elements of Jacobian and Hazen matrix, and achieve accurate sub-pixel positioning. The experimental results show that the improved method has high accuracy, and its mean error and standard deviation stability and extreme value are better than similar algorithms. Compared with the traditional forward Newton method, the total iteration time of the improved forward Newton method is reduced in the subpixel iteration stage, and the computational efficiency is 3.8 times that of the traditional NR algorithm. The whole process of the proposed algorithm is simple and efficient, and it has application value in the precision occasions requiring high precision.

Experimental Study at the Phase Interface of a Single-Crystal Ni-Based Superalloy Using TEM.

The single-crystal Ni-based superalloys, which have excellent mechanical properties at high temperatures, are commonly used for turbine blades in a variety of aero engines and industrial gas turbines. Focusing on the phase interface of a second-generation single-crystal Ni-based superalloy, in-situ TEM observation was conducted at room temperature and high temperatures. Intensity ratio analysis was conducted for the measurement of two-phase interface width. The improved geometric phase analysis method, where the adaptive mask selection method is introduced, was used for the measurement of the strain field near the phase interface. The strained irregular transition region is consistent with the calculated interface width using intensity ratio analysis. An intensity ratio analysis and strain measurement near the interface can corroborate and complement each other, contributing to the interface structure evaluation. Using TEM in-situ heating and Fourier transform, the change of dislocation density in the γ phase near the two-phase interface of the single-crystal Ni-based superalloy was analyzed. The dislocation density decreases first with the increase in temperature, consistent with the characteristics of metal quenching, and increases sharply at 450 °C. The correlation between the variation of dislocation density at high temperatures and the intermediate temperature brittleness was also investigated.

A hybrid method for lattice image reconstruction and deformation analysis.

Geometric phase analysis (GPA) is a powerful tool to investigate the deformation in nanoscale measurement, especially in dealing with high-resolution transmission electron microscopy images. The traditional GPA method using the fast Fourier transform is built on the relationship between the displacement and the phase difference. In this paper, a nano-grid method based on real-space lattice image processing was firstly proposed to enable the measurement of nanoscale interface flatness, and the thickness of different components. Then, a hybrid method for lattice image reconstruction and deformation analysis was developed. The hybrid method enables simultaneous real-space and frequency-domain processing, thus, compensating for the shortcomings of the GPA method when measuring samples with large deformations or containing cracks while retaining its measurement accuracy.

Evaluation of interfacial misfit strain field of heterostructures using STEM nano secondary moiré method.

STEM nano-moiré can achieve high-precision deformation measurement in a large field of view. In scanning moiré fringe technology, the scanning line and magnification of the existing transmission electron microscope (TEM) cannot be changed continuously. The frequency of the crystal lattice is often difficult to match with the fixed frequency of the scanning line, resulting in mostly too dense fringes that cannot be directly observed; thus, the calculation error is relatively large. This problem exists in both the STEM moiré method and the multiplication moiré method. Herein, we propose the STEM secondary nano-moiré method, i.e., a digital grating of similar frequency is superimposed on or sampling the primary moiré fringe or multiplication moiré to form the secondary moiré. The formation principle of the secondary moiré is analyzed in detail, with deduced theoretical relations for measuring the strain of STEM secondary nano-moiré fringe. The advantages of sampling secondary moiré and digital secondary moiré are compared. The optimal sampling interpolation function is obtained through error analysis. This method expands the application range of the STEM moiré method and has better practicability. Finally, the STEM secondary nano-moiré is used to accurately measure the strain field at the Si/Ge heterostructure interface, and the theoretical strain field calculated by the dislocation model is analyzed and compared. The obtained results are more compatible with the P-N dislocation model. Our work provides a practical method for the accurate evaluation of the interface characteristics of heterostructures, which is an important basis for judging the photoelectric performance of the entire device and the optimal design of the heterostructures.

Interphase interface structure and evolution of a single crystal Ni-based superalloy based on HRTEM image analysis.

Interface plays an important role in determining several properties in multiphase systems. It is also essential for the accurate measurement of the interface structure in a single crystal Ni-based superalloy (SCNBS) under different conditions. In this work, a subpixel accuracy transform method is introduced in detail to measure SCNBS lattice spacing at high temperatures. An intensity ratio analysis based on a high-resolution transmission electron microscopy image is employed for SCNBS interface width analysis. In this particular sample, the interface width is about 2 nm. The evolution of the lattice spacing of an ordered γ' phase and a solid solution γ matrix is also obtained at high temperatures. The lattice misfit between the matrix γ phase and the γ' precipitation increases with the temperature, with values of -0.39% and -0.21% at 20°C and 600°C. In addition, the coefficient of the SCNBS thermal expansion at high temperatures is discussed.

STEM multiplication nano-moiré method with large field of view and high sensitivity.

Strain is one of the important factors that determine the photoelectric and mechanical properties of semiconductor materials and devices. In this paper, the scanning transmission electron microscopy multiplication nano-moiré method is proposed to increase the measurement range and sensitivity for strain field. The formation principle, condition, and measurement range of positive and negative multiplication moiré fringes (PMMFs and NMMFs) are analysed in detail here. PMMF generally refers to the multiplication of field of view, NMMF generally refers to the multiplication of displacement measurement sensitivity. Based on the principle of multiplication nano-moiré, Theoretical formulas of the fringe spacing and strain field are derived. Compared with geometric phase analysis of deformation measurements based on high-resolution atom images, both the range of field of view and the sensitivity of displacement measurements of the multiplication moiré method are significantly improved. Most importantly, the area of field of view of the PMMF method is increased by about two orders of magnitude, which is close to micrometre-scale with strain measurement sensitivity of 2 × 10-5. In addition, In order to improve the quality of moiré fringe and the accuracy of strain measurement, the secondary moiré method is developed.The strain laws at the interface of the InP/InGaAs superlattice materials are characterised using the developed method.

Geometric phase analysis method using a subpixel displacement match algorithm.

The geometrical phase analysis (GPA) method, which is an efficient and powerful noncontact method to obtain the strain field, has already been widely applied in deformation measurement in micro- and nano-scale. It is easy to get the strain field accurately; however, the displacement field is unreliable in some cases. Therefore, a subpixel displacement match method hereby is applied in the GPA method for the first time, to the best of our knowledge, to overcome this defect. The presented algorithm's limit error of 0.01 pixel under ideal conditions can match two corresponding local areas in reference and deformation image, and, thus, the displacement with subpixel precision of this point can be established. Owing to the continuity of the displacement field, the displacements of other points can be obtained subsequently. The error that is associated with the existing method will be dealt with in detail and verified by simulation further. Combined with simulation, the performance of the presented method is demonstrated; furthermore, the noise introduced by the imaging system is taken into consideration. Finally, a typical bending test was performed, and the result agrees well with the theoretical analysis. Both the simulation and experiment results prove that the presented method is effective and robust.

Application of digital phase shifting moiré method in interface and dislocation location recognition and real strain characterization from HRTEM images.

In high-resolution transmission electron microscopy (HRTEM) images of heterostructures, it is always difficult to accurately determine the interface position and identify dislocations in a large field of view at tens to hundreds of nanometers due to the small lattice differences. However, in the heterostructure, the determination of the interface position is the key to obtain the true mismatch stress/strain field of the interface. Due to the magnifying effect of the digital moiré method on small differences, digital moiré technology was applied to determine Ge/Si heterostructure interfaces and large-area identification interface dislocations in HRTEM lattice diagrams in this study. By optimizing the frequency and angle of the reference lattice, the interface and dislocation position are clearly and intuitively displayed. How to accurately determine the position of the heterostructure interface and the dislocation of the large-area recognition interface from HRTEM images are studied through simulation experiments. The results show that when the frequency of the reference lattice and the specimen lattice are close, and the angle between them is within 10°, the position of the heterostructure interface can be accurately and intuitively determined by the naked eye according to the distortion characteristics of the moiré fringe. When the frequency of the reference lattice is 0.7 to 0.9 times of the specimen lattice, and the rotation angle is within 8°, the visually clear crossover phenomenon of the moiré fringes is used for large-area identification of interface dislocations. Using the phase measurement interface position sensitivity can reach the Å level. Using the phase-shifting digital moiré method the strain field on the dislocation core at the Ge/Si heterostructure interface and the interface stress distribution were quantitatively analyzed. Compared with the Peierls-Nabarro dislocation model and the Foreman dislocation model, Foreman's variable factor α = 4 is more suitable for describing the strain field of misfit dislocations on the Ge/Si heterostructure interface.

Analyzing the Transcriptome Profile of Human Cumulus Cells Related to Embryo Quality via RNA Sequencing.

Selecting excellent oocytes is required to improve the outcomes of in vitro fertilization (IVF). Cumulus cells (CCs) are an integral part of the oocyte maturation process. Therefore, we sought to identify differentially expressed genes in CCs to assess oocyte quality and embryo development potential. We divided the participants' embryos into the high-quality embryo group and low-quality embryo group by the information including age, body mass index, and the levels of luteinizing hormone, follicle-stimulating hormone, estradiol, and progesterone. We analyzed a total of 7 CC samples after the quality control in RNA sequencing. We found that 2499 genes were unregulated and 5739 genes were downregulated in high-quality embryo group compared to the low-quality embryo group (Padj < 0.05). Interestingly, MSTN, CTGF, NDUFA1, VCAN, SCD5, and STAR were significantly associated with the quality of embryo. In accordance with the results of RNA sequencing, the association of the expression levels of MSTN, CTGF, NDUFA1, VCAN, SCD5, and STAR with the embryo quality was verified by quantitative reverse-transcription polymerase chain reaction (RT-qPCR) in 50 CC samples. Despite the small sample size and lack of validation in animal models, our study supports the fact that differential gene expression profile of human CCs, including MSTN, CTGF, NDUFA1, VCAN, SCD5, and STAR, can serve as potential indicator for embryo quality.

Quantitative evaluation of the interface lattice quality of a strain superlattice by strain analysis.

The lattice quality of strain superlattice structures in Quantum Cascade Lasers (QCLs) directly influences the photoelectric properties and service life of the lasers. However, the evaluation method for lattice quality on the nanoscale is not very well developed at present, especially for interface lattice quality assessment. In this investigation, all atoms positioned in the multiple interface layers can be simultaneously and accurately determined through Subset Geometric Phase Analysis (S-GPA) combined with a Peak Finding (PF) method and an Optimal Approximation Algorithm (OAA) with a sensitivity of about 0.04 Å. Based on the determined interface location, the strain distribution in all layers of the superlattice structure was simultaneously measured using the improved S-GPA by means of the optimal selection of multiple reference areas. A quantitative evaluation of the strain/stress compensation effect was then carried out based on the theoretical model of elastic mechanics. The proposed method was successfully applied to evaluating the lattice quality of an In0.6Ga0.4As/In0.44Al0.56As superlattice structure grown by Molecular Beam Epitaxy (MBE). The obtained results show that the interface lattices are almost perfect with a uniform thickness of layers, without any defects and stress concentration. Each In0.44Al0.56As layer and adjacent In0.6Ga0.4As layers provided effective strain/stress compensation for each other, reducing the possibility of forming dislocations. In one period, the active region has been properly strain-balanced to give a nearly net zero strain. The proposed method can not only be applied in evaluating the growth quality of the superlattice structure with a large field of view, but also provide quantitative experimental data for further improving the superlattice design.

TEM nano-Moiré evaluation for an invisible lattice structure near the grain interface.

Moiré technique is a powerful, important and effective tool for scientific research, from the nano-scale to the macro-scale, which is essentially the interference between two or more periodic structures with a similar frequency. In this study, an inverse transmission electron microscopy (TEM) nano-Moiré method has been proposed, for the first time, to reconstruct an invisible lattice structure near the grain interface, where only one kind of lattice structure and Moiré fringe were visible in a high resolution TEM (HRTEM) image simultaneously. The inversion process was performed in detail. Three rules were put forward to ensure the uniqueness of the inversion result. The HRTEM image of a top-coat/thermally grown oxide interface in a thermal barrier coating (TBC) structure was observed with coexisting visible lattice and Moiré fringes. Using the inverse TEM nano-Moiré method, the invisible lower layer lattice was inversed and a 3-dimensional structure near the interface was also reconstructed to some degree. The real strain field of oriented invisible and visible lattices and the relative strain field of the Moiré fringe in the grain and near the grain boundary were obtained simultaneously through the subset geometric phase analysis method. The possible failure mechanism and position of the TBC spallation from the nano-scale to the micro-scale were discussed.

Subset geometric phase analysis method for deformation evaluation of HRTEM images.

Geometrical phase analysis (GPA) is typically a powerful tool to investigate the deformation in high resolution transmission electron microscopy images and has been used in various fields. The traditional GPA method using the fast Fourier transform, referred to as global-GPA (G-GPA) here, is based on the relationship between the displacement and the phase difference. In this paper, a subset-GPA (S-GPA) is introduced for further improvement. The S-GPA performs the windowed Fourier transform block by block in the image. The maximum strain measurement scale of the GPA method is theoretically analyzed on the basic of the phase spectrum extraction process. The upper limit is one third of the atomic spacing. The results of various numerical simulations verified that the S-GPA method performs better than the traditional G-GPA method in both the homogeneous and inhomogeneous deformation conditions, with the evaluation parameter of calculation reliability of S-GPA 10% higher than G-GPA. Specifically, the measurement accuracy of S-GPA is about three times higher than the G-GPA when calculating small strain (less than 2000µÎµ). For the large strain (greater than 150000µÎµ), the measurement accuracy of S-GPA is about 50% higher than that of the G-GPA. Besides, the S-GPA method can significantly eliminate the phase filling effect, while the G-GPA cannot. The S-GPA method has been successfully applied to analyze the strain field distribution in an lnGaAs/InAlAs supperlattice heterostructure.