Papers by Keyword: Lattice Relaxation

Abstract: Thermal oxidation of 4H-SiC to grow native-oxide SiO₂ is always followed by the generation of crystal defects and lattice distortion. We studied the relaxation of this distorted lattice on thermally-oxidized 4H-SiC surface by performing annealing process with several conditions. The surface distortion could be relaxed partially by annealing under argon, nitrogen monoxide, and H₂O gases, confirmed by in-plane X-ray diffractometer. This surface relaxation is possibly induced by the release of oxygen-related defects, as confirmed by thermal desorption analysis. The surface distortion caused by thermal oxidation is due to the existence of oxygen in 4H-SiC lattice, while the relaxation is caused by the migration of the oxygen-related defect structure, and emitted from 4H-SiC surface region as CO molecule.

Abstract: In this work the magnetic and structural properties of quaternary Fe-Ni-Mn-Al Heusler alloys are studied. We use first principles calculations to investigate crystal lattice relaxation of alloys and their coupling to the magnetic order, with a particular focus on the tetragonal distortions characterized by the c/a ratio. It follows from our calculations that Fe-Ni-Mn-Al alloys have very interesting magnetic properties and can be good candidates as multifunctional magnetic materials.

Abstract: The structural and magnetic properties of Mn-based stoichiometric Heusler alloys have investigated by means of ab initio calculations in framework of the density functional theory. First principles electronic structure calculations have shown that Mn₂NiZ (Z = Ga, In, Sn, Sb) alloys are ferrimagnets with antiparallel alignment between the Mn atoms. The martensitic transition can be realized in Mn₂NiGa and Mn₂NiSn alloys with tetragonal ratio of 1.27 and 1.16, respectively. Calculated properties are in a good agreement with available experimental data.

Abstract: The defect evolution on 90 μm-thick heavily Al-doped 4H-SiC epilayers with Al doping level higher than 10²⁰ cm^-3 was studied by tracing back to initial growth stage to monitor major dislocations and their propagations in each growth stage. Results from X-ray topography and KOH etching demonstrate that all existing dislocations on the surface of 90 μm-thick epilayer can be identified as the defects originating from substrate. In other words, there seems no new dislocation generated after a long-term growth. Nevertheless, a high density of misfit dislocation was found appearing near the substrate/epilayer interface for epilayer with Al doping level of 3.5×10²⁰ cm^-3, while misfit dislocation cannot be seen on epilayer with Al doping level of 1.5×10²⁰ cm^-3.

Abstract: To clarify the origin of a characteristic fine grain structure formed under the high burn-up of the nuclear fuel, the comprehensive first-principles calculations for UO2 containing various types of point defect have been performed by the PAW-GGA+U with lattice relaxation for supercells containing 1, 2 and 8 unit cells of UO2. The electronic structure, the atomic displacement and the defect formation energies of defective systems are obtained, and the effects of supercell size on these properties are discussed. Based on this relatively high precise self-consistent formation energies dataset, thermodynamic properties of various types of point defects in UO2 are further investigated in the framework of the point defects model.