3-D characterization of nanomaterials from a single 2-D STEM image

Date: 24 May 2019

Venue: UAntwerp, Campus Groenenborger, Room U.408 - Groenenborgerlaan 171 - 2020 Antwerp-Wilrijk (route: UAntwerpen, Campus Groenenborger)

Time: 11:30 AM - 12:30 PM

Organization / co-organization: EMAT

Short description: Friday Lecture by Ece Arslan Irmak (EMAT)

The investigation of the structural features of nanomaterials has great importance since there is a direct relationship between the properties and the arrangement of the atoms.  High angle annular dark field scanning transmission electron microscopy (HAADF-STEM) is a valuable method for the structural characterization of nanomaterials since it provides high-resolution 2D images. Nonetheless, these 2D images are usually inadequate to analyze the structural evolution of  (anisotropic) nanomaterials. One of the most known and robust methods to retrieve the 3D atomic structure is electron tomography, which can be used to reconstruct a nanomaterial based on 2D images, obtained from different tilting angles. However, this method has several limitations when studying dynamic processes, beam sensitive materials and for in situ heating or gas experiments since they require multiple exposures.

The main aim of this project is to retrieve the 3D atomic structure of nanomaterials from a single 2D scanning transmission electron microscopy image acquired along zone axis orientation. So far, we have implemented advanced statistical techniques and relaxation methods to carry out 3D characterization of nanomaterials. Although there is an excellent agreement between this method and electron tomography, it remains a challenging problem to obtain a complete 3D characterization of  asymmetrical nanomaterials.

Generally, molecular dynamics or ab-initio calculations are used as a relaxation method. Although ab-initio calculations give sufficiently reliable results, it requires high computational efforts for systems of a few tens of atoms. On the other hand, molecular dynamics is computationally efficient compared to ab initio approaches. However, the relaxation procedure ends up in a local energy minimum, instead of the global energy minimum, which is sensitive to the potential parametrization and initial atomic positions. Since the most stable structure corresponds to the global energy minimum, the inter-atomic potentials and starting atomic configurations play a significant role in the accuracy of the molecular dynamics simulations. In this project, we will develop a methodology to bridge the gap between accurate but computationally expensive methods and approximate but computationally convenient methods by optimizing the initialization of the molecular dynamics simulations. Our novel methodology will enable us to characterize and understand the structural evolution of anisotropic, beam sensitive and heterogeneous nanomaterials under either static conditions or real applications.

Link: https://www.uantwerpen.be/en/research-groups/emat/news-and-activities/friday-lectures/