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Two-Dimensional Fluorine Distribution in a Heavily Distorted Perovskite Nickel Oxyfluoride Revealed by First-Principles Calculation
摘要： Most perovskite oxyfluorides synthesized to date have cubic structures, wherein fluorine atoms tend to reside at every oxygen site randomly. In this theoretical study, we show a two-dimensional fluorine arrangement in a perovskite nickel oxyfluoride (NdNiO2F) with a large orthorhombic distortion. The site selectivity in the perovskite lattice is due to the orthorhombicity, which stabilizes the two-dimensional cis configurations with shorter Ni?O and longer Ni?F bonds to minimize the electrostatic energy. The electronic structure of NdNiO2F is characterized by its large octahedral rotation and the higher electronegativity of fluorine than oxygen. We also observed how the anion arrangement was affected by the biaxial strain by modeling epitaxial strained thin film on substrate and found that the 2D cis structure remains the most stable. However, the orientation of the two-dimensional structure containing F depends on the magnitude of the biaxial strain. Our findings suggest that fluorine doping in orthorhombic perovskite oxides effectively yields oxyfluorides with anisotropic anion ordering.
关键词： electronic structure,orthorhombic distortion,perovskite oxyfluorides,two-dimensional fluorine arrangement,biaxial strain
更新于2025-09-12 10:27:22
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Equi-biaxial compressive strain in graphene: Grüneisen parameter and buckling ridges
摘要： Here we report equi-biaxial compressive strain in monolayer graphene on SiO2 and Si3N4 substrates induced by thermal cycling in vacuum. The equi-biaxial strain is attributed to the mismatch in coefficient of thermal expansion between graphene and the substrate and sliding of graphene on the substrate. Importantly, the induced buckling ridges in graphene exhibit a pattern representing the symmetry of graphene crystal structure, which agreed well with our molecular dynamics (MD) simulations. Furthermore, these thermally-induced buckling ridges were found reminiscent of those in graphene synthesized by the CVD and SiC sublimation methods, suggesting the same origin of formation of the buckling ridges.
关键词： biaxial strain,thermal cycling,graphene,buckling ridges,molecular dynamics simulation,Grüneisen parameter
更新于2025-09-09 09:28:46
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The formation mechanism of globally biaxial strain in He <sup>+</sup> implanted silicon-on-insulator wafer based on the plastic deformation and smooth sliding of buried SiO <sub/>2</sub> film
摘要： In this paper, we proposed an approach to obtain a globally biaxially strained silicon-on-insulator (SOI) wafer, and the strain mechanism was discussed. By this process, both biaxially tensile and compressive strained SOI (sSOI) can be obtained. The strain introduced into the SOI layer is mainly contributed by the plastic deformation of the buried SiO2 film caused by annealing with the deposition of a high-stress SiN film. Furthermore, He+ implantation at the interface between SiO2 and the substrate Si layer is confirmed to effectively enhance the strain by the sliding of the buried SiO2 at the SiO2-substrate Si interface. Raman spectroscopy shows that the strain of the He+ implanted sSOI has a significant enhancement of more than 300% compared with the unimplanted sSOI.
关键词： silicon-on-insulator,biaxial strain,plastic deformation,He implantation,SiO2 film
更新于2025-09-09 09:28:46
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with pentagonal structure
摘要： Structure-property relationships have always been guiding principles for materials discovery. Here we explore the relationships to discover two-dimensional (2D) materials with the goal of identifying 2D magnetic semiconductors for spintronics applications. In particular, we report a density functional theory + U study of single-layer antiferromagnetic (AFM) semiconductor CoS2 with the pentagonal structure forming the so-called Cairo tessellation. We ?nd that this single-layer magnet exhibits an indirect band gap of 1.06 eV with electron and hole effective masses of 0.52 and 1.93 m0, respectively, which may lead to relatively high electron mobility. The hybrid density functional theory calculations correct the band gap to 2.24 eV. We also compute the magnetocrystalline anisotropy energy (MAE), showing that the easy axis of the AFM ordering is along the b axis with a sizable MAE of 153 μeV per Co ion. We further calculate the magnon frequencies at different spin-spiral vectors, based on which we estimate the N′eel temperatures to be 20.4 and 13.3 K using the mean ?eld and random phase approximations, respectively. We then apply biaxial strains to tune the band gap of single-layer pentagonal CoS2. We ?nd that the energy difference between the ferromagnetic and AFM structures strongly depends on the biaxial strain, but the ground state remains the AFM ordering. Although the low critical temperature prohibits the magnetic applications of single-layer pentagonal CoS2 at room temperature, the excellent electrical properties may ?nd single-layer semiconductor applications in optoelectronic nanodevices.
关键词： two-dimensional materials,magnon frequencies,N′eel temperature,biaxial strain,Cairo tessellation,antiferromagnetic semiconductor,density functional theory,band gap,magnetocrystalline anisotropy energy,pentagonal structure,spintronics
更新于2025-09-09 09:28:46