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Synthesis of Perovskite Oxides
Published in Gibin George, Sivasankara Rao Ede, Zhiping Luo, Fundamentals of Perovskite Oxides, 2020
Gibin George, Sivasankara Rao Ede, Zhiping Luo
RHEED accompanies the MBE set up for the continuous monitoring of the film growth. The shutters control the release of vaporized elements from the effusion cell. The oxide or nitride films are achieved by injecting the respective reactive gases into the chamber, as in the case of any other reactive deposition technique. In reactive MBE, the pressure is maintained sufficiently low to guarantee the reaction between the vaporized atoms and the reactive gases. A hybrid MBE technique is also used for the deposition of perovskite oxide films. In a hybrid MBE, A-site element is evaporated in the effusion cells, and a chemical beam produced by the thermal evaporation of the respective precursor is used as the source for the B-site element, which also acts as the source of the anion (Jalan et al. 2009). In reactive MBE, the pressure is reduced to 10–3 Pa; thus, the path of the atoms evaporated from the cells is much larger than the source–substrate distance. For the effective deposition of perovskite oxides, it is essential to retain the stoichiometric ratios of the molecular beams of the different constituent elements and the corresponding fluxes. To do the same spectroscopic techniques, such as atomic absorption spectroscopy, mass spectroscopy, quartz-crystal monitors, and electron microscopy, are often employed.
Applications
Published in Pramod K. Naik, Vacuum, 2018
Oura et al 10 have discussed the modern surface analytical techniques including LEED. In LEED, low energy electrons are used to provide large elastic scattering cross-section for back-scattered electrons and to keep the penetration depth of the electrons short. Reflected High Energy Electron Diffraction (RHEED) employs large elastic scattering cross-sections of forward-scattered high energy electrons. The small penetration depth is achieved by using the grazing angle incidence of the incident electrons. In RHEED, a high-energy (5 to 100 keV) electron beam is incident on the surface at a very small angle relative to the sample surface. Incident electrons diffract from atoms at the surface of the sample, and a
Characterization of Heteroepitaxial Layers
Published in John E. Ayers, Heteroepitaxy of Semiconductors, 2018
In a typical RHEED experiment, a high-energy (10- to 100-keV) beam of electrons is incident on the sample surface at a shallow angle of 1 to 2°. Diffraction of the electrons is governed by the Bragg law, as with x-ray diffraction. However, there are two important differences between RHEED and the x-ray case. First, the electrons do not penetrate significantly into the sample, so diffraction is essentially from the two-dimensional lattice on the surface. Second, for the high-energy electrons used in RHEED, the Ewald sphere is large in diameter, so many reflections are excited at once.
A critical overview of thin films coating technologies for energy applications
Published in Cogent Engineering, 2023
Mohammad Istiaque Hossain, Said Mansour
The article has been arranged in a way to provide an in-depth knowledge to the wide range of readers where both theoretical and basic mechanism of PVD methods are considered. Such techniques are the best due to the technological adaptability to fabricate inorganic, hybrid, and nanocomposite thin films. MBE is a significant deposition technique to grow epitaxial, layered structures under ultrahigh vacuum conditions on different substrate materials (Kim et al., 2022; Richards et al., 2022; Yao et al., 2022; Zhao et al., 2022; Zhu et al., 2022). In general, chemical reaction occurs through molecular beam impinging on the surface, where this chemical reaction is the material transition from the gas phase in the molecular beam to the solid state on top of the substrate. MBE tool allows higher qualities of the deposited films through heating and rotation capabilities. In-situ reflection high energy electron diffraction (RHEED) can be used to check the quality of the deposited films, which is an added advantage. In this tool, growth process involves controlling molecular and/or atomic beams via shutters and source temperature, deposited on mono-crystal substrate for epitaxial growth.
Skill-Agnostic analysis of reflection high-energy electron diffraction patterns for Si(111) surface superstructures using machine learning
Published in Science and Technology of Advanced Materials: Methods, 2022
Asako Yoshinari, Yuma Iwasaki, Masato Kotsugi, Shunsuke Sato, Naoka Nagamura
Clean semiconductor surfaces with well-controlled atomic structures provide attractive stages for various low-dimensional systems such as atomic-layer materials [1–4], heteroepitaxial multi-layers [5–7], topological materials [8–10], and Rashba films [11–13]. These surfaces and thin films are fabricated by physical vapor deposition (PVD). Reflection high-energy electron diffraction (RHEED) is a widely used technique for structural analysis of surfaces obtained by PVD growth. RHEED enables researchers to observe surface structures in situ during film fabrication because the deposition rate can be evaluated by monitoring the dynamic changes in the diffraction patterns and intensity oscillations of the selected diffraction spots. Thus, RHEED has been used in the process optimization for sample preparation. However, the intensity of the diffraction spot is affected by the background, neighboring spots, incident electron beam intensity fluctuations, and sample temperature, among other factors. Moreover, expert knowledge is required to interpret diffraction patterns. RHEED images contain a lot of surface information, including surface atomic structural and film quality information, such as step density, growth mode, and strain [14–17]. Therefore, an appropriate data processing technique is required to extract the necessary information and perform a high-accuracy analysis.
Optical phase change in bismuth through structural distortions induced by laser irradiation
Published in Radiation Effects and Defects in Solids, 2020
Ørjan S. Handegård, Masahiro Kitajima, Tadaaki Nagao
A schematic of Bi droplets formation with characterisation by RHEED and SEM is shown in Figure 6(a). The high surface sensitivity of RHEED technique provides detailed insight into sample crystallinity by observation of diffraction lines and spots on a fluorescent screen. The streaky lines seen in the RHEED pattern (Figure 6(b)) are recognised as Bi single crystalline thin films with its trigonal axis normal to the surface plane ([001] orientation) (34,35). When applying current across the Si substrate to initiate resistive heating, the thin film integrity and geometry became disrupted, and went from a continuous 2D film to disconnected 3D droplets. This process was tracked by monitoring the RHEED pattern, which changed from its streaky lines to a spotty transmission pattern as 3D structures formed (Figure 6(d)). The formation of 3D structures in the form of droplets from the thin film was confirmed by SEM, after the resistive heating, droplet shapes of Bi were clearly visible (Figure 6(c,e)). The resistive heating process resulted in a thermal dewetting of Bi, as the film spontaneous develops into droplets on the Si surface to minimise contact area, which can typically occur when a molten film with high surface tension resolidifies (37,38).