Content of SPECIAL TOPIC — Stephen J. Pennycook: A research life in atomic-resolution STEM and EELS in our journal

Published in last 1 year |  In last 2 years |  In last 3 years |  All Please wait a minute... For selected: Download citations EndNote Ris BibTeX Toggle thumbnails Select A universal resist-assisted metal transfer method for 2D semiconductor contacts Xuanye Liu(刘轩冶), Linxuan Li(李林璇), Chijun Wei(尉驰俊), Peng Song(宋鹏), Hui Gao(高辉), Kang Wu(吴康), Nuertai Jiazila(努尔泰·加孜拉), Jiequn Sun(孙杰群), Hui Guo(郭辉), Haitao Yang(杨海涛), Wu Zhou(周武), Lihong Bao(鲍丽宏), and Hong-Jun Gao(高鸿钧) Chin. Phys. B, 2024, 33 (12): 127302.   DOI: 10.1088/1674-1056/ad8db4 Abstract （414）   HTML （4）    PDF （3611KB）（151）       Knowledge map    With the explosive exploration of two-dimensional (2D) semiconductors for device applications, ensuring effective electrical contacts has become critical for optimizing device performance. Here, we demonstrate a universal resist-assisted metal transfer method for creating nearly free-standing metal electrodes on the SiO$_{2}$/Si substrate, which can be easily transferred onto 2D semiconductors to form van der Waals (vdW) contacts. In this method, polymethyl methacrylate (PMMA) serves both as an electron resist for electrode patterning and as a sacrificial layer. Contacted with our transferred electrodes, MoS$_{2}$ exhibits tunable Schottky barrier heights and a transition from n-type dominated to ambipolar conduction with increasing metal work functions, while InSe shows pronounced ambipolarity. Additionally, using $\alpha$-In$_{2}$Se$_{3}$ as an example, we demonstrate that our transferred electrodes enhance resistance switching in ferroelectric memristors. Finally, the universality of our method is evidenced by the successful transfer of various metals with different adhesion forces and complex patterns. Select Making the link between ADF and 4D STEM: Resolution, transfer and coherence Peter D. Nellist and Timothy J. Pennycook Chin. Phys. B, 2024, 33 (11): 116803.   DOI: 10.1088/1674-1056/ad8554 Abstract （322）   HTML （7）    PDF （1608KB）（367）       Knowledge map    Steve Pennycook is a pioneer in the application of high-resolution scanning transmission electron microscopy (STEM) and in particular the use of annular dark-field (ADF) imaging. Here we show how a general framework for 4D STEM allows clear links to be made between ADF imaging and the emerging methods for reconstructing images from 4D STEM data sets. We show that both ADF imaging and ptychographical reconstruction can be thought of in terms of integrating over the overlap regions of diffracted discs in the detector plane. This approach allows the similarities in parts of their transfer functions to be understood, though we note that the transfer functions for ptychographic imaging cannot be used as a measure of information transfer. We also show that conditions of partial spatial and temporal coherence affect ADF imaging and ptychography similarly, showing that achromatic interference can always contribute to the image in both cases, leading to a robustness to partial temporal coherence that has enabled high-resolution imaging. Select Real-time four-dimensional scanning transmission electron microscopy through sparse sampling A W Robinson, J Wells, A Moshtaghpour, D Nicholls, C Huang, A Velazco-Torrejon, G Nicotra, A I Kirkland, and N D Browning Chin. Phys. B, 2024, 33 (11): 116804.   DOI: 10.1088/1674-1056/ad8a4a Abstract （299）   HTML （9）    PDF （2989KB）（296）       Knowledge map    Four-dimensional scanning transmission electron microscopy (4-D STEM) is a state-of-the-art image acquisition mode used to reveal high and low mass elements at atomic resolution. The acquisition of the electron momenta at each real space probe location allows for various analyses to be performed from a single dataset, including virtual imaging, electric field analysis, as well as analytical or iterative extraction of the object induced phase shift. However, the limiting factor in 4-D STEM is the speed of acquisition which is bottlenecked by the read-out speed of the camera, which must capture a convergent beam electron diffraction (CBED) pattern at each probe position in the scan. Recent developments in sparse sampling and image inpainting (a branch of compressive sensing) for STEM have allowed for real-time recovery of sparsely acquired data from fixed monolithic detectors, Further developments in compressive sensing for 4-D STEM have also demonstrated that acquisition speeds can be increased, i.e., live video rate 4-D imaging is now possible. In this work, we demonstrate the first practical implementations of compressive 4-D STEM for real-time inference on two different scanning transmission electron microscopes. Select Polarization pinning at antiphase boundaries in multiferroic YbFeO3 Guodong Ren, Pravan Omprakash, Xin Li, Yu Yun, Arashdeep S. Thind, Xiaoshan Xu, and Rohan Mishra Chin. Phys. B, 2024, 33 (11): 118502.   DOI: 10.1088/1674-1056/ad8cbc Abstract （255）   HTML （7）    PDF （3024KB）（167）       Knowledge map    The switching characteristics of ferroelectrics and multiferroics are influenced by the interaction of topological defects with domain walls. We report on the pinning of polarization due to antiphase boundaries in thin films of the multiferroic hexagonal YbFeO$_{3}$. We have directly resolved the atomic structure of a sharp antiphase boundary (APB) in YbFeO$_{3}$ thin films using a combination of aberration-corrected scanning transmission electron microscopy (STEM) and total energy calculations based on density-functional theory (DFT). We find the presence of a layer of FeO$_{6}$ octahedra at the APB that bridges the adjacent domains. STEM imaging shows a reversal in the direction of polarization on moving across the APB, which DFT calculations confirm is structural in nature as the polarization reversal reduces the distortion of the FeO$_{6}$ octahedral layer at the APB. Such APBs in hexagonal perovskites are expected to serve as domain-wall pinning sites and hinder ferroelectric switching of the domains. Select Visualizing extended defects at the atomic level in a Bi2Sr2CaCu2O8+δ superconducting wire Kejun Hu(胡柯钧), Shuai Wang(王帅), Boyu Li(李泊玉), Ying Liu(刘影), Binghui Ge(葛炳辉), and Dongsheng Song(宋东升) Chin. Phys. B, 2024, 33 (9): 096101.   DOI: 10.1088/1674-1056/ad6ccd Abstract （276）   HTML （2）    PDF （2484KB）（294）       Knowledge map    The microstructure significantly influences the superconducting properties. Herein, the defect structures and atomic arrangements in high-temperature Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta }$ (Bi-2212) superconducting wire are directly characterized via state-of-the-art scanning transmission electron microscopy. Interstitial oxygen atoms are observed in both the charge reservoir layers and grain boundaries in the doped superconductor. Inclusion phases with varied numbers of CuO$_{2}$ layers are found, and twist interfaces with different angles are identified. This study provides insights into the structures of Bi-2212 wire and lays the groundwork for guiding the design of microstructures and optimizing the production methods to enhance superconducting performance. Select Controlled fabrication of freestanding monolayer SiC by electron irradiation Yunli Da(笪蕴力), Ruichun Luo(罗瑞春), Bao Lei(雷宝), Wei Ji(季威), and Wu Zhou(周武) Chin. Phys. B, 2024, 33 (8): 086802.   DOI: 10.1088/1674-1056/ad6132 Abstract （321）   HTML （5）    PDF （1273KB）（253）       Knowledge map    The design and preparation of novel quantum materials with atomic precision are crucial for exploring new physics and for device applications. Electron irradiation has been demonstrated as an effective method for preparing novel quantum materials and quantum structures that could be challenging to obtain otherwise. It features the advantages of precise control over the patterning of such new materials and their integration with other materials with different functionalities. Here, we present a new strategy for fabricating freestanding monolayer SiC within nanopores of a graphene membrane. By regulating the energy of the incident electron beam and the in-situ heating temperature in a scanning transmission electron microscope (STEM), we can effectively control the patterning of nanopores and subsequent growth of monolayer SiC within the graphene lattice. The resultant SiC monolayers seamlessly connect with the graphene lattice, forming a planar structure distinct by a wide direct bandgap. Our in-situ STEM observations further uncover that the growth of monolayer SiC within the graphene nanopore is driven by a combination of bond rotation and atom extrusion, providing new insights into the atom-by-atom self-assembly of freestanding two-dimensional (2D) monolayers. Select Symmetry quantification and segmentation in STEM imaging through Zernike moments Jiadong Dan, Cheng Zhang, Xiaoxu Zhao(赵晓续), and N. Duane Loh Chin. Phys. B, 2024, 33 (8): 086803.   DOI: 10.1088/1674-1056/ad51f4 Abstract （344）   HTML （9）    PDF （4251KB）（143）       Knowledge map    We present a method using Zernike moments for quantifying rotational and reflectional symmetries in scanning transmission electron microscopy (STEM) images, aimed at improving structural analysis of materials at the atomic scale. This technique is effective against common imaging noises and is potentially suited for low-dose imaging and identifying quantum defects. We showcase its utility in the unsupervised segmentation of polytypes in a twisted bilayer TaS$_2$, enabling accurate differentiation of structural phases and monitoring transitions caused by electron beam effects. This approach enhances the analysis of structural variations in crystalline materials, marking a notable advancement in the characterization of structures in materials science. Select Atomically self-healing of structural defects in monolayer WSe2 Kangshu Li(李康舒), Junxian Li(李俊贤), Xiaocang Han(韩小藏), Wu Zhou(周武), and Xiaoxu Zhao(赵晓续) Chin. Phys. B, 2024, 33 (9): 096804.   DOI: 10.1088/1674-1056/ad641f Abstract （275）   HTML （0）    PDF （1554KB）（446）       Knowledge map    Minimizing disorder and defects is crucial for realizing the full potential of two-dimensional transition metal dichalcogenides (TMDs) materials and improving device performance to desired properties. However, the methods in defect control currently face challenges with overly large operational areas and a lack of precision in targeting specific defects. Therefore, we propose a new method for the precise and universal defect healing of TMD materials, integrating real-time imaging with scanning transmission electron microscopy (STEM). This method employs electron beam irradiation to stimulate the diffusion migration of surface-adsorbed adatoms on TMD materials grown by low-temperature molecular beam epitaxy (MBE), and heal defects within the diffusion range. This approach covers defect repairs ranging from zero-dimensional vacancy defects to two-dimensional grain orientation alignment, demonstrating its universality in terms of the types of samples and defects. These findings offer insights into the use of atomic-level focused electron beams at appropriate voltages in STEM for defect healing, providing valuable experience for achieving atomic-level precise fabrication of TMD materials. Select Multiphase cooperation for multilevel strain accommodation in a single-crystalline BiFeO3 thin film Wooseon Choi, Bumsu Park, Jaejin Hwang, Gyeongtak Han, Sang-Hyeok Yang, Hyeon Jun Lee, Sung Su Lee, Ji Young Jo, Albina Y. Borisevich, Hu Young Jeong, Sang Ho Oh, Jaekwang Lee, and Young-Min Kim Chin. Phys. B, 2024, 33 (9): 096805.   DOI: 10.1088/1674-1056/ad62e0 Abstract （310）   HTML （0）    PDF （2024KB）（166）       Knowledge map    The functionalities and diverse metastable phases of multiferroic BiFeO$_{3}$ (BFO) thin films depend on the misfit strain. Although mixed phase-induced strain relaxation in multiphase BFO thin films is well known, it is unclear whether a single-crystalline BFO thin film can accommodate misfit strain without the involvement of its polymorphs. Thus, understanding the strain relaxation behavior is key to elucidating the lattice strain-property relationship. In this study, a correlative strain analysis based on dark-field inline electron holography (DIH) and quantitative scanning transmission electron microscopy (STEM) was performed to reveal the structural mechanism for strain accommodation of a single-crystalline BFO thin film. The nanoscale DIH strain analysis results indicated a random combination of multiple strain states that acted as a primary strain relief, forming irregularly strained nanodomains. The STEM-based bond length measurement of the corresponding strained nanodomains revealed a unique strain accommodation behavior achieved by a statistical combination of multiple modes of distorted structures on the unit-cell scale. The globally integrated strain for each nanodomain was estimated to be close to $-1.5%$, irrespective of the nanoscale strain states, which was consistent with the fully strained BFO film on the SrTiO$_{3}$ substrate. Density functional theory calculations suggested that strain accommodation by the combination of metastable phases was energetically favored compared to single-phase-mediated relaxation. This discovery allows a comprehensive understanding of strain accommodation behavior in ferroelectric oxide films, such as BFO, with various low-symmetry polymorphs. Select Multidimensional images and aberrations in STEM Eric R. Hoglund and Andrew R. Lupini Chin. Phys. B, 2024, 33 (9): 096807.   DOI: 10.1088/1674-1056/ad73b2 Abstract （272）   HTML （4）    PDF （2083KB）（190）       Knowledge map    Recent advances in scanning transmission electron microscopy (STEM) have led to increased development of multi-dimensional STEM imaging modalities and novel image reconstruction methods. This interest arises because the main electron lens in a modern transmission electron microscope usually has a diffraction-space information limit that is significantly better than the real-space resolution of the same lens. This state-of-affairs is sometimes shared by other scattering methods in modern physics and contributes to a broader excitement surrounding multidimensional techniques that scan a probe while recording diffraction-space images, such as ptychography and scanning nano-beam diffraction. However, the contrasting resolution in the two spaces raises the question as to what is limiting their effective performance. Here, we examine this paradox by considering the effects of aberrations in both image and diffraction planes, and likewise separate the contributions of pre- and post-sample aberrations. This consideration provides insight into aberration-measurement techniques and might also indicate improvements for super-resolution techniques. Select A large language model-powered literature review for high-angle annular dark field imaging Wenhao Yuan(袁文浩), Cheng Peng(彭程), and Qian He(何迁) Chin. Phys. B, 2024, 33 (9): 098703.   DOI: 10.1088/1674-1056/ad625c Abstract （343）   HTML （1）    PDF （1248KB）（400）       Knowledge map    High-angle annular dark field (HAADF) imaging in scanning transmission electron microscopy (STEM) has become an indispensable tool in materials science due to its ability to offer sub-Å resolution and provide chemical information through Z-contrast. This study leverages large language models (LLMs) to conduct a comprehensive bibliometric analysis of a large amount of HAADF-related literature (more than 41000 papers). By using LLMs, specifically ChatGPT, we were able to extract detailed information on applications, sample preparation methods, instruments used, and study conclusions. The findings highlight the capability of LLMs to provide a new perspective into HAADF imaging, underscoring its increasingly important role in materials science. Moreover, the rich information extracted from these publications can be harnessed to develop AI models that enhance the automation and intelligence of electron microscopes.