Research Annick De Backer

Abstract

In order to fully understand the structure-property relationship of materials, it is important to reliably quantify structure parameters such as the position of the atoms, the type of the atoms, and the number of atoms. The starting point of a quantitative analysis is the availability of a correct physics-based model depending on those structure parameters. My research focuses on quantifying these parameters from atomic resolution electron microscopy images.

Researcher(s)

• Promoter: De Backer Annick

Research team(s)

• Electron microscopy for materials research (EMAT)

Project type(s)

• Research Project

Abstract

The goal of my proposal is to develop a powerful method in order to evolve toward four-dimensional (4D=3D+time) quantification of nanostructures of arbitrary shape, size and atom type at the atomic scale. Therefore, novel quantitative measurement tools will be combined with aberration-corrected scanning transmission electron microscopy (STEM). Quantitative 3D characterisation of nanostructures can nowadays be achieved with high reliability for model-like systems with 1 type of chemical element present. Also for some heteronanostructures, a 3D visualisation at the atomic scale is possible using state-of-the-art STEM. However, high-precision quantification often involves a meticulous analysis using advanced methods. This impedes high-throughput analyses which are increasingly important for the study of dynamical processes induced by heating, under de flow of a selected gas, or by the electron beam. In this project, the initiation of real-time image simulations will be a giant leap forward for the 4D characterisation of nanomaterials. This highly challenging and innovative objective will be reached by introducing deep learning architectures into quantitative STEM. This unique approach will allow simulating images in real time using a fully physics-based description of the experimental intensities. The outcome of this project will deliver all necessary input for understanding and predicting the properties in complex nanostructures and their dynamical processes.

Researcher(s)

• Promoter: Van Aert Sandra
• Fellow: De Backer Annick

Research team(s)

• Electron microscopy for materials research (EMAT)

Project type(s)

• Research Project

Abstract

The properties of nanomaterials are controlled by their three-dimensional (3D) atomic structure. Nowadays, quantitative methods can be used to retrieve 3D atomic structural information from two-dimensional (2D) scanning transmission electron microscopy (STEM) images of materials which can withstand high electron doses. The goal of this project is to develop quantitative methods to estimate the atomic positions, atom types, and number of atoms from 2D STEM images recorded using a low electron dose.

Researcher(s)

• Promoter: Van Aert Sandra
• Co-promoter: De Backer Annick
• Fellow: De wael Annelies

Research team(s)

• Electron microscopy for materials research (EMAT)

Project type(s)

• Research Project

Abstract

The properties of nanomaterials are controlled by their three-dimensional (3D) atomic structure. Nowadays, quantitative methods can be used to retrieve 3D atomic structural information from two-dimensional (2D) scanning transmission electron microscopy (STEM) images of materials which can withstand high electron doses. The goal of this project is to develop quantitative methods to estimate the atomic positions, atom types, and number of atoms from 2D STEM images recorded using a low electron dose.

Researcher(s)

• Promoter: Van Aert Sandra
• Co-promoter: De Backer Annick
• Fellow: De wael Annelies

Research team(s)

• Electron microscopy for materials research (EMAT)

Project type(s)

• Research Project

Abstract

The goal of this project is to develop and design a powerful method in order to unscramble mixed element nanostructures at the atomic scale in three dimensions (3D). Therefore, novel quantitative measurement tools will be combined with aberration corrected scanning transmission electron microscopy (STEM). Visualisation at the atomic scale in 3D using state-of-the-art STEM is nowadays possible for modellike systems with 1 type of chemical element present. For this purpose counting the number of atoms in each projected atomic column is of great help. However, precise determination of the atomic structure in 3D of hetero-nanostructures is currently limited because of the lack of methods to quantitatively unscramble mixed elements. In this project, atom-counting will be performed for technologically important nanostructures that are more complex than model systems, including systems with adjacent atomic number Z such as Pt-Au, Fe-Co, and Ge-Ga-As. The aim is to quantitatively characterise the number of atoms and atom types of mixed element nanostructures with single atom sensitivity. This highly challenging objective will be reached by a unique combination of physics-based modelling and advanced statistical methods. The outcome of this project will deliver the necessary input for understanding and predicting the properties of complex hetero-nanostructures and to guide the development of new nanomaterials.

Researcher(s)

• Promoter: Van Aert Sandra
• Co-promoter: Van Tendeloo Staf
• Fellow: De Backer Annick

Research team(s)

• Electron microscopy for materials research (EMAT)

Project type(s)

• Research Project

Abstract

The main objective of this proposal is to push aberration corrected transmission electron microscopy (TEM) toward precise measurements of unknown structure parameters. Although the resolution of these state-of-the-art instruments has greatly been improved by optimizing the lens design, equally fundamental changes in the image processing and acquisition methods are required in order to have the instrument performing at the limits of its capabilities. Therefore, use will be made of statistical parameter estimation theory. The starting-point is the availability of a parametric model describing the expectations of the images. This is a physics-based model depending on the unknown structure parameters. It describes the interaction of the electrons with the object, the transfer in the microscope, and the detection. Next, the unknown parameters are estimated by fitting this model to the experimental images using a criterion of goodness of fit. Through a combination of available techniques in TEM, the focus in this project will be to determine atom positions with picometer precision for heavy as well as for light atoms, precise chemical composition analysis, and detection of single atoms. Finally, in order to study beam sensitive matter without radiation damage, the principles of statistical experimental design will be used to determine the minimally required electron dose in order to attain a pre-specified precision.

Researcher(s)

• Promoter: Van Aert Sandra
• Fellow: De Backer Annick

Research team(s)

• Electron microscopy for materials research (EMAT)

Project type(s)

• Research Project

Abstract

The main objective of this proposal is to push aberration corrected transmission electron microscopy (TEM) toward precise measurements of unknown structure parameters. Although the resolution of these state-of-the-art instruments has greatly been improved by optimizing the lens design, equally fundamental changes in the image processing and acquisition methods are required in order to have the instrument performing at the limits of its capabilities. Therefore, use will be made of statistical parameter estimation theory. The starting-point is the availability of a parametric model describing the expectations of the images. This is a physics-based model depending on the unknown structure parameters. It describes the interaction of the electrons with the object, the transfer in the microscope, and the detection. Next, the unknown parameters are estimated by fitting this model to the experimental images using a criterion of goodness of fit. Through a combination of available techniques in TEM, the focus in this project will be to determine atom positions with picometer precision for heavy as well as for light atoms, precise chemical composition analysis, and detection of single atoms. Finally, in order to study beam sensitive matter without radiation damage, the principles of statistical experimental design will be used to determine the minimally required electron dose in order to attain a pre-specified precision.

Researcher(s)

• Promoter: Van Aert Sandra
• Fellow: De Backer Annick

Research team(s)

• Electron microscopy for materials research (EMAT)

Project type(s)

• Research Project