1
|
Li C, Mu X, Korytov M, Alexandrou I, Bosch EGT. Differential phase contrast (DPC) mapping electric fields: Optimising experimental conditions. J Microsc 2024; 293:177-188. [PMID: 38353282 DOI: 10.1111/jmi.13271] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2023] [Revised: 01/04/2024] [Accepted: 01/19/2024] [Indexed: 02/20/2024]
Abstract
DPC in Scanning Transmission Electron Microscopy (STEM) is a valuable method for mapping the electric fields in semiconductor materials. However, optimising the experimental conditions can be challenging. In this paper, we test and compare critical experimental parameters, including the convergence angle, camera length, acceleration voltage, sample configuration, and orientation using a four-quadrant segmented detector and a Si specimen containing layers of different As concentrations. The DPC measurements show a roughly linear correlation with the estimated electric fields, until the field gets close to the detection limitation, which is ∼0.5 mV/nm with a sample thickness of ∼145 nm. These results can help inform which technique to use for different user cases: When the electric field at a planar junction is above ∼0.5 mV/nm, DPC with a segmented detector is practical for electric field mapping. With a planar junction, the DPC signal-to-noise ratio can be increased by increasing the specimen thickness. However, for semiconductor devices with electric fields smaller than ∼0.5 mV/nm, or for devices containing curved junctions, DPC is unreliable and techniques with higher sensitivity will need to be explored, such as 4D STEM using a pixelated detector.
Collapse
Affiliation(s)
- Chen Li
- Thermo Fisher Scientific, Eindhoven, the Netherlands
| | - Xiaoke Mu
- Thermo Fisher Scientific, Eindhoven, the Netherlands
| | | | | | | |
Collapse
|
2
|
Heimes D, Chejarla VS, Ahmed S, Hüppe F, Beyer A, Volz K. Impact of beam size and diffraction effects in the measurement of long-range electric fields in crystalline samples via 4DSTEM. Ultramicroscopy 2023; 253:113821. [PMID: 37562100 DOI: 10.1016/j.ultramic.2023.113821] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2023] [Revised: 06/27/2023] [Accepted: 07/25/2023] [Indexed: 08/12/2023]
Abstract
Measuring long-range electric fields by 4-dimensional scanning transmission electron microscopy (4DSTEM) is on the verge to becoming an established method, though quantifying and understanding all underlying processes remains a challenge. To gain further insight into these processes, experimental studies employing the center-of-mass (COM) method of the model system of a GaAs p-n junction are carried out in which three ranges of the semi-convergence angle α are identified, with an intermediate one where measuring the built-in potential Vbi is not feasible. STEM multislice simulations including both atomic and nm-scale fields prove that this intermediate range begins once diffraction disks start overlapping with the undiffracted beam. The range ends when the diffraction disks' intensities become so low that they do not affect the measurement significantly anymore and when high-intensity diffractions overlap the center disk completely. From simulations without influence of atoms it is concluded that measuring Vbi has advantages over measuring the electric-field strength, as the potential difference does neither show a significant dependence on the beam size, nor on the specimen thickness.
Collapse
Affiliation(s)
- Damien Heimes
- Material Sciences Center and Department of Physics, Philipps-Universität Marburg, Germany
| | - Varun Shankar Chejarla
- Material Sciences Center and Department of Physics, Philipps-Universität Marburg, Germany
| | - Shamail Ahmed
- Material Sciences Center and Department of Physics, Philipps-Universität Marburg, Germany
| | - Franziska Hüppe
- Material Sciences Center and Department of Physics, Philipps-Universität Marburg, Germany
| | - Andreas Beyer
- Material Sciences Center and Department of Physics, Philipps-Universität Marburg, Germany
| | - Kerstin Volz
- Material Sciences Center and Department of Physics, Philipps-Universität Marburg, Germany.
| |
Collapse
|
3
|
Chejarla VS, Ahmed S, Belz J, Scheunert J, Beyer A, Volz K. Measuring Spatially-Resolved Potential Drops at Semiconductor Hetero-Interfaces Using 4D-STEM. SMALL METHODS 2023; 7:e2300453. [PMID: 37246264 DOI: 10.1002/smtd.202300453] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/05/2023] [Indexed: 05/30/2023]
Abstract
Characterizing long-range electric fields and built-in potentials in functional materials at nano to micrometer scales is of supreme importance for optimizing devices, e.g., the functionality of semiconductor hetero-structures or battery materials is determined by the electric fields established at interfaces which can also vary spatially. In this study, momentum-resolved four-dimensional scanning transmission electron microscopy (4D-STEM) is proposed for the quantification of these potentials and the optimization steps required to reach quantitative agreement with simulations for the GaAs/AlAs hetero-junction model system are shown. Using STEM the differences in the mean inner potentials (∆MIP) of two materials forming an interface and resulting dynamic diffraction effects have to be considered. This study shows that the measurement quality is significantly improved by precession, energy filtering and a off-zone-axis alignment of the specimen. Complementary simulations yielding a ∆MIP of 1.3 V confirm that the potential drop due to charge transfer at the intrinsic interface is ≈0.1 V, in agreement with experimental and theoretical values found in literture. These results show the feasibility of accurately measuring built-in potentials across hetero-interfaces of real device structures and its promising application for more complex interfaces of other polycrystalline materials on the nanometer scale.
Collapse
Affiliation(s)
- Varun Shankar Chejarla
- Department of Physics and Materials Science Center, Philipps-University Marburg, Hans-Meerwein Str. 6, 35032, Marburg, Germany
| | - Shamail Ahmed
- Department of Physics and Materials Science Center, Philipps-University Marburg, Hans-Meerwein Str. 6, 35032, Marburg, Germany
| | - Jürgen Belz
- Department of Physics and Materials Science Center, Philipps-University Marburg, Hans-Meerwein Str. 6, 35032, Marburg, Germany
| | - Jonas Scheunert
- Department of Physics and Materials Science Center, Philipps-University Marburg, Hans-Meerwein Str. 6, 35032, Marburg, Germany
| | - Andreas Beyer
- Department of Physics and Materials Science Center, Philipps-University Marburg, Hans-Meerwein Str. 6, 35032, Marburg, Germany
| | - Kerstin Volz
- Department of Physics and Materials Science Center, Philipps-University Marburg, Hans-Meerwein Str. 6, 35032, Marburg, Germany
| |
Collapse
|
4
|
Chen L, Liang Z, Shao S, Huang Q, Tang K, Huang R. First direct observation of the built-in electric field and oxygen vacancy migration in ferroelectric Hf 0.5Zr 0.5O 2 film during electrical cycling. NANOSCALE 2023; 15:7014-7022. [PMID: 36970751 DOI: 10.1039/d2nr06582g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
The wake-up and fatigue effects exhibited by ferroelectric hafnium oxide (HfO2) during electrical cycling are two of the most significant obstacles limiting its development and application. Despite a mainstream theory relating these phenomena to the migration of oxygen vacancies and the evolution of the built-in field, no supportive experimental observations from a nanoscale perspective have been reported so far. By combining differential phase contrast scanning transmission electron microscopy (DPC-STEM) and energy dispersive spectroscopy (EDS) analysis, we directly observe the migration of oxygen vacancies and the evolution of the built-in field in ferroelectric HfO2 for the first time. These solid results indicate that the wake-up effect is caused by the homogenization of oxygen vacancy distribution and weakening of the vertical built-in field whereas the fatigue effect is related to charge injection and transverse local electric field enhancement. In addition, using a low-amplitude electrical cycling scheme, we exclude field-induced phase transition from the root cause of the wake-up and fatigue in Hf0.5Zr0.5O2. With direct experimental evidence, this work clarifies the core mechanism of the wake-up and fatigue effects, which is important for the optimization of ferroelectric memory devices.
Collapse
Affiliation(s)
- Liang Chen
- School of Integrated Circuits, Peking University, Beijing 100871, China.
| | - Zhongxin Liang
- School of Integrated Circuits, Peking University, Beijing 100871, China.
| | - Shixuan Shao
- State Key Laboratory for Turbulence and Complex Systems, Department of Mechanics and Engineering Science, College of Engineering, Peking University, Beijing 100871, China
| | - Qianqian Huang
- School of Integrated Circuits, Peking University, Beijing 100871, China.
- Beijing Advanced Innovation Center for Integrated Circuits, Beijing 100871, China
| | - Kechao Tang
- School of Integrated Circuits, Peking University, Beijing 100871, China.
- Beijing Advanced Innovation Center for Integrated Circuits, Beijing 100871, China
| | - Ru Huang
- School of Integrated Circuits, Peking University, Beijing 100871, China.
- Beijing Advanced Innovation Center for Integrated Circuits, Beijing 100871, China
| |
Collapse
|
5
|
Seki T, Khare K, Murakami YO, Toyama S, Sánchez-Santolino G, Sasaki H, Findlay SD, Petersen TC, Ikuhara Y, Shibata N. Linear imaging theory for differential phase contrast and other phase imaging modes in scanning transmission electron microscopy. Ultramicroscopy 2022; 240:113580. [DOI: 10.1016/j.ultramic.2022.113580] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2022] [Revised: 06/13/2022] [Accepted: 06/21/2022] [Indexed: 11/17/2022]
|
6
|
Liu JJ. Advances and Applications of Atomic-Resolution Scanning Transmission Electron Microscopy. MICROSCOPY AND MICROANALYSIS : THE OFFICIAL JOURNAL OF MICROSCOPY SOCIETY OF AMERICA, MICROBEAM ANALYSIS SOCIETY, MICROSCOPICAL SOCIETY OF CANADA 2021; 27:1-53. [PMID: 34414878 DOI: 10.1017/s1431927621012125] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Although scanning transmission electron microscopy (STEM) images of individual heavy atoms were reported 50 years ago, the applications of atomic-resolution STEM imaging became wide spread only after the practical realization of aberration correctors on field-emission STEM/TEM instruments to form sub-Ångstrom electron probes. The innovative designs and advances of electron optical systems, the fundamental understanding of electron–specimen interaction processes, and the advances in detector technology all played a major role in achieving the goal of atomic-resolution STEM imaging of practical materials. It is clear that tremendous advances in computer technology and electronics, image acquisition and processing algorithms, image simulations, and precision machining synergistically made atomic-resolution STEM imaging routinely accessible. It is anticipated that further hardware/software development is needed to achieve three-dimensional atomic-resolution STEM imaging with single-atom chemical sensitivity, even for electron-beam-sensitive materials. Artificial intelligence, machine learning, and big-data science are expected to significantly enhance the impact of STEM and associated techniques on many research fields such as materials science and engineering, quantum and nanoscale science, physics and chemistry, and biology and medicine. This review focuses on advances of STEM imaging from the invention of the field-emission electron gun to the realization of aberration-corrected and monochromated atomic-resolution STEM and its broad applications.
Collapse
Affiliation(s)
- Jingyue Jimmy Liu
- Department of Physics, Arizona State University, Tempe, AZ85287, USA
| |
Collapse
|
7
|
Beyer A, Munde MS, Firoozabadi S, Heimes D, Grieb T, Rosenauer A, Müller-Caspary K, Volz K. Quantitative Characterization of Nanometer-Scale Electric Fields via Momentum-Resolved STEM. NANO LETTERS 2021; 21:2018-2025. [PMID: 33621104 DOI: 10.1021/acs.nanolett.0c04544] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Most of today's electronic devices, like solar cells and batteries, are based on nanometer-scale built-in electric fields. Accordingly, characterization of fields at such small scales has become an important task in the optimization of these devices. In this study, with GaAs-based p-n junctions as the example, key characteristics such as doping concentrations, polarity, and the depletion width are derived quantitatively using four-dimensional scanning transmission electron microscopy (4DSTEM). The built-in electric fields are determined by the shift they introduce to the center-of-mass of electron diffraction patterns at subnanometer spatial resolution. The method is applied successfully to characterize two p-n junctions with different doping concentrations. This highlights the potential of this method to directly visualize intentional or unintentional nanoscale electric fields in real-life devices, e.g., batteries, transistors, and solar cells.
Collapse
Affiliation(s)
- Andreas Beyer
- Materials Science Centre and Department of Physics, Philipps University Marburg, Hans-Meerwein-Straße 6, Marburg 35032, Germany
| | - Manveer Singh Munde
- Materials Science Centre and Department of Physics, Philipps University Marburg, Hans-Meerwein-Straße 6, Marburg 35032, Germany
| | - Saleh Firoozabadi
- Materials Science Centre and Department of Physics, Philipps University Marburg, Hans-Meerwein-Straße 6, Marburg 35032, Germany
| | - Damien Heimes
- Materials Science Centre and Department of Physics, Philipps University Marburg, Hans-Meerwein-Straße 6, Marburg 35032, Germany
| | - Tim Grieb
- Institut für Festkörperphysik, Universität Bremen, Otto-Hahn-Allee 1, Bremen 28359, Germany
| | - Andreas Rosenauer
- Institut für Festkörperphysik, Universität Bremen, Otto-Hahn-Allee 1, Bremen 28359, Germany
| | - Knut Müller-Caspary
- Ernst Ruska-Center for Microscopy and Spectroscopy with Electrons, Forschungszentrum Jülich, Wilhelm-Johnen-Straße, RWTH Aachen University, II. Institute of Physics, Otto-Blumenthal-Straße, Aachen 52074, Germany
| | - Kerstin Volz
- Materials Science Centre and Department of Physics, Philipps University Marburg, Hans-Meerwein-Straße 6, Marburg 35032, Germany
| |
Collapse
|
8
|
Seki T, Ikuhara Y, Shibata N. Toward quantitative electromagnetic field imaging by differential-phase-contrast scanning transmission electron microscopy. Microscopy (Oxf) 2021; 70:148-160. [PMID: 33150939 DOI: 10.1093/jmicro/dfaa065] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2020] [Revised: 10/26/2020] [Accepted: 10/30/2020] [Indexed: 11/14/2022] Open
Abstract
Differential-phase-contrast scanning transmission electron microscopy (DPC STEM) is a technique to directly visualize local electromagnetic field distribution inside materials and devices at very high spatial resolution. Owing to the recent progress in the development of high-speed segmented and pixelated detectors, DPC STEM now constitutes one of the major imaging modes in modern aberration-corrected STEM. While qualitative imaging of electromagnetic fields by DPC STEM is readily possible, quantitative imaging by DPC STEM is still under development because of the several fundamental issues inherent in the technique. In this report, we review the current status and future prospects of DPC STEM for quantitative electromagnetic field imaging from atomic scale to mesoscopic scale.
Collapse
Affiliation(s)
- Takehito Seki
- Institute of Engineering Innovation, School of Engineering, The University of Tokyo, Yayoi 2-11-16, Bunkyo-ku, Tokyo 113-8656, Japan
| | - Yuichi Ikuhara
- Institute of Engineering Innovation, School of Engineering, The University of Tokyo, Yayoi 2-11-16, Bunkyo-ku, Tokyo 113-8656, Japan.,Nanostructures Research Laboratory, Japan Fine Ceramics Center, 2-4-1 Mutsuno, Atsuta-ku, Nagoya 456-8587, Japan
| | - Naoya Shibata
- Institute of Engineering Innovation, School of Engineering, The University of Tokyo, Yayoi 2-11-16, Bunkyo-ku, Tokyo 113-8656, Japan.,Nanostructures Research Laboratory, Japan Fine Ceramics Center, 2-4-1 Mutsuno, Atsuta-ku, Nagoya 456-8587, Japan.,Quantum-Phase Electronics Center (QPEC), The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8656, Japan
| |
Collapse
|