Structure prediction in materials science and characterisation with EELS in the low-loss regime

Thesis

Electron Energy Loss (EEL) spectroscopy is a complementary spectroscopic method that is adopted in (scanning) transmission electron microscope ((S)TEM). The low-loss region of the corresponding Electron Energy Loss spectrum (EELS) is associated with plasmon excitation. It is closely related to the optical properties of the sample and can reveal a wealth of crystallographic information, such as structures and bondings. To fully interpret experimental EELS, it is vital to develop a protocol to accurately simulate EELS.

This thesis focuses on enhancing the accuracy of computationally modelled EELS, especially in the low-loss region. Within the density functional theory (DFT), several functionals are tested: the Becke-Johnson functional (BJ), the Tran-Blaha functional (TB), and the SCAN functional. The functionals are reported to provide better descriptions of the excited properties of materials but have not been thoroughly studied in the context of EELS modelling. Beyond DFT, we employ the time-dependent DFT (TDDFT) and state-of-art GW method combined with the Bethe-Salpeter Equation (BSE) method. In addition, we also apply the method to a case study of the corrosion products of beryllium tiles from nuclear reactors. During this study, we have found a new approach to simulate the coreloss spectrum of beryllium. The approach could potentially be applied to other elements with semi-core electrons, such as lithium.

Authors: Liu, X

• DOI: 10.5287/ora-o52rebge0
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: EELS; DFT; GW
• Subjects: Materials science; Physics