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Observing Individual Atoms in 3D Nanomaterials and Their Surfaces
Atoms are the basic building blocks for all materials. To tailor functional properties, it is essential to accurately determine their atomic structures. KAIST researchers observed the 3D atomic structure of a nanoparticle at the atom level via neural network-assisted atomic electron tomography.
Using a platinum nanoparticle as a model system, a research team led by Professor Yongsoo Yang demonstrated that an atomicity-based deep learning approach can reliably identify the 3D surface atomic structure with a precision of 15 picometers (only about 1/3 of a hydrogen atom’s radius). The atomic displacement, strain, and facet analysis revealed that the surface atomic structure and strain are related to both the shape of the nanoparticle and the particle-substrate interface.
Combined with quantum mechanical calculations such as density functional theory, the ability to precisely identify surface atomic structure will serve as a powerful key for understanding catalytic performance and oxidation effect.
“We solved the problem of determining the 3D surface atomic structure of nanomaterials in a reliable manner. It has been difficult to accurately measure the surface atomic structures due to the ‘missing wedge problem’ in electron tomography, which arises from geometrical limitations, allowing only part of a full tomographic angular range to be measured. We resolved the problem using a deep learning-based approach,” explained Professor Yang.
The missing wedge problem results in elongation and ringing artifacts, negatively affecting the accuracy of the atomic structure determined from the tomogram, especially for identifying the surface structures. The missing wedge problem has been the main roadblock for the precise determination of the 3D surface atomic structures of nanomaterials.
The team used atomic electron tomography (AET), which is basically a very high-resolution CT scan for nanomaterials using transmission electron microscopes. AET allows individual atom level 3D atomic structural determination.
“The main idea behind this deep learning-based approach is atomicity—the fact that all matter is composed of atoms. This means that true atomic resolution electron tomogram should only contain sharp 3D atomic potentials convolved with the electron beam profile,” said Professor Yang.
“A deep neural network can be trained using simulated tomograms that suffer from missing wedges as inputs, and the ground truth 3D atomic volumes as targets. The trained deep learning network effectively augments the imperfect tomograms and removes the artifacts resulting from the missing wedge problem.”
The precision of 3D atomic structure can be enhanced by nearly 70% by applying the deep learning-based augmentation. The accuracy of surface atom identification was also significantly improved.
Structure-property relationships of functional nanomaterials, especially the ones that strongly depend on the surface structures, such as catalytic properties for fuel-cell applications, can now be revealed at one of the most fundamental scales: the atomic scale.
Professor Yang concluded, “We would like to fully map out the 3D atomic structure with higher precision and better elemental specificity. And not being limited to atomic structures, we aim to measure the physical, chemical, and functional properties of nanomaterials at the 3D atomic scale by further advancing electron tomography techniques.”
This research, reported at Nature Communications, was funded by the National Research Foundation of Korea and the KAIST Global Singularity Research M3I3 Project.
-Publication
Juhyeok Lee, Chaehwa Jeong & Yongsoo Yang
“Single-atom level determination of 3-dimensional surface atomic structure via neural network-assisted atomic electron tomography”
Nature Communications
-Profile
Professor Yongsoo Yang
Department of Physics
Multi-Dimensional Atomic Imaging Lab (MDAIL)
http://mdail.kaist.ac.kr
KAIST
2021.05.12 View 18275 -
New Text Book on Chemistry Published by KAIST Professor and Student
A chemistry textbook written in English and Korean will aid Korean students to learn General Chemistry in a global academic setting.
Korean students majoring in chemistry and looking for an opportunity to study abroad will have a new, handy textbook that presents them with a practical introduction to an English speaking lecture on general chemistry.
Aiming for advanced Korean high school and college/university students, the inter-language textbook is written by two incumbent professors teaching chemistry at a university in Korea and the US. The book will help Korean students prepare for a classroom where various topics of general chemistry are presented and discussed in English. Clear, collated sections of English and Korean text provide the student with sufficient explanation of the rudimentary topics and concepts.
Composed of 15 chapters on the core subjects of General Chemistry, i.e., Stoichiometry and Chemical Reactions, Thermochemistry, Atomic Structure, and Bonding, the textbook includes essential English vocabulary and usage sections for each chapter; it also contains a pre-reading study guide on the subject that prepares the student for listening to a lecture. This section includes view-graph type slides, audio files, and follow-up questions the student can use to prepare for an English-speaking course. The various accompanying audio files are prepared to expose the student to English scientific dialogue and serve as examples for instruction at Korean secondary and tertiary schools.
The book was coauthored by Korean and American scientists: A father and son, who have taught chemistry at an American and Korean university, wrote the book. Professor Melvyn R. Churchill at the State University of New York at Buffalo and Professor David G. Churchill at KAIST prepared all of the technical English text which was adapted from General Chemistry course lecture notes; the text was further shaped by original perspectives arising from many student interactions and questions.
This English text was translated into Korean by Professor Kwanhee Lee from the Department of Life and Food Science at Handong Global University, who coauthored a previous preparatory book for Korean students in a different subject. He also supplied an important introductory section which serves as a general guide to the classroom student. Kibong Kim, a doctoral student in the Department of Chemistry at KAIST, helped in preparing the book as well.
“This has been definitely a collaborative undertaking with an international academic crew and it underscores that the Korean internationalization in science is mainstream. Professors and a Korean student created a new book for Korean consumption and benefit,” Professor David G. Churchill says.
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Bibliography: “How to Prepare for General Chemistry Taught in English” by David George Churchill, Melvyn Rowen Churchill, Kwanhee Lee & Kibong Kim, Darakwon Publishing, Paju, Republic of Korea, 2010, 400 pp, ISBN 978-89-5995-730-9 (1 Audio CD included)
2010.04.02 View 21777