Paschen-Back Ferromagnetism in Strained Oxide Heterostructures

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Anti-phase boundary accelerated exsolution of nanoparticles in non-stoichiometric perovskite thin films

Exsolution of excess transition metal cations from a non-stoichiometric perovskite oxide has sparked interest as a facile route for the formation of stable nanoparticles on the oxide surface. However, the atomic-scale mechanism of this nanoparticle formation remains largely unknown. The present in situ scanning transmission electron microscopy combined with density functional theory calculation revealed that the anti-phase boundaries (APBs) characterized by the a/2 < 011> type lattice displacement accommodate the excess B-site cation (Ni) through the edge-sharing of BO6 octahedra in a non-stoichiometric ABO3 perovskite oxide (La0.2Sr0.7Ni0.1Ti0.9O3-δ) and provide the fast diffusion pathways for nanoparticle formation by exsolution. Moreover, the APBs further promote the outward diffusion of the excess Ni toward the surface as the segregation energy of Ni is lower at the APB/surface intersection. The formation of nanoparticles occurs through the two-step crystallization mechanism, i.e., the nucleation of an amorphous phase followed by crystallization, and via reactive wetting on the oxide support, which facilitates the formation of a stable triple junction and coherent interface, leading to the distinct socketing of nanoparticles to the oxide support. The atomic-scale mechanism unveiled in this study can provide insights into the design of highly stable nanostructures

Controlling Magnetocrystalline Anisotropy by Strain in Double Perovskite Sr2FeReO6 Films

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Anti-phase boundary accelerated exsolution of nanoparticles in non-stoichiometric perovskite thin films

This work was supported by National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. NRF-2020R1A2C2101735), Creative Materials Discovery Program (NRF-2019M3D1A1078299), the Samsung Research Funding & Incubation Center of Samsung Electronics under Project Number SRFC-MA1702-01, and the KENTECH Research Grant (KRG2022-01-019). D.I.B. acknowledges the financial support from Russian Foundation for Basic Research under Grant No. 19-29-03051MK. The first-principle calculations were performed using the facilities of the Joint Supercomputer Center of the Russian Academy of Sciences (JSCC RAS). J.L. acknowledges the support of an NRF grant funded by the Korean government (NRF-2018R1A2B6004394). J.T.S.I. thanks the EPSRC for support on emergent nanomaterials through Grant EP/R023522/1. Y.X. and S.H.O. acknowledge the support from Advanced Facility Center for Quantum Technology.Exsolution of excess transition metal cations from a non-stoichiometric perovskite oxide has sparked interest as a facile route for the formation of stable nanoparticles on the oxide surface. However, the atomic-scale mechanism of this nanoparticle formation remains largely unknown. The present in situ scanning transmission electron microscopy combined with density functional theory calculation revealed that the anti-phase boundaries (APBs) characterized by the a/2 type lattice displacement accommodate the excess B-site cation (Ni) through the edge-sharing of BO6 octahedra in a non-stoichiometric ABO3 perovskite oxide (La0.2Sr0.7Ni0.1Ti0.9O3-δ) and provide the fast diffusion pathways for nanoparticle formation by exsolution. Moreover, the APBs further promote the outward diffusion of the excess Ni toward the surface as the segregation energy of Ni is lower at the APB/surface intersection. The formation of nanoparticles occurs through the two-step crystallization mechanism, i.e., the nucleation of an amorphous phase followed by crystallization, and via reactive wetting on the oxide support, which facilitates the formation of a stable triple junction and coherent interface, leading to the distinct socketing of nanoparticles to the oxide support. The atomic-scale mechanism unveiled in this study can provide insights into the design of highly stable nanostructures.Publisher PDFPeer reviewe

Ferromagnetic semiconductor with perpendicular magnetic anisotropy by strain

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Decoupled Phonon-induced Unit Cell Width Ferroelectricity in Brownmillerite Oxides

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Site-selective doping mechanisms for the enhanced photocatalytic activity of tin oxide nanoparticles

© 2022 Elsevier B.V.The addition of transition metal dopants into metal oxide nanoparticles (MO NPs) is an universal strategy to engineer the electronic and chemical properties of NPs. Although doping phenomena strongly rely on interactions with compositional and electronic degrees of freedom, fully understanding the site-specific doping behavior in the lattice framework of MO NP on atomic scale remains challenging. Here, we directly resolve the atomic site-selective (substitutional or interstitial) doping behaviors of Cr and Fe in SnO2, revealing their different roles in photocatalytic activities. Atomic-resolution microscopy combined with spectroscopy reveals two contrasting doping behaviors: Cr3+ substitutes for Sn4+ associated with the formation of oxygen vacancies, whereas Fe3+ occupies interstitial sites accompanied by lattice strain. Theoretical calculations indicate that substitutional dopant-vacancy cooperation and interstitial dopant-strain coupling can be energetically favorable routes for enhancing catalytic properties. Our results provide fundamental insights into atomic-scale doping mechanisms and engineering strategies for high-performance doped MO NPs.11Nsciescopu

A Novel 1919\sqrt {19} × 1919\sqrt {19} Superstructure in Epitaxially Grown 1T-TaTe2.

The spontaneous formation of electronic orders is a crucial element for understanding complex quantum states and engineering heterostructures in 2D materials. A novel 19$\sqrt {19}$ × 19$\sqrt {19}$ charge order in few-layer-thick 1T-TaTe2 transition metal dichalcogenide films grown by molecular beam epitaxy, which has not been realized, is report. The photoemission and scanning probe measurements demonstrate that monolayer 1T-TaTe2 exhibits a variety of metastable charge density wave orders, including the 19$\sqrt {19}$ × 19$\sqrt {19}$ superstructure, which can be selectively stabilized by controlling the post-growth annealing temperature. Moreover, it is found that only the 19$\sqrt {19}$ × 19$\sqrt {19}$ order persists in 1T-TaTe2 films thicker than a monolayer, up to 8 layers. The findings identify the previously unrealized novel electronic order in a much-studied transition metal dichalcogenide and provide a viable route to control it within the epitaxial growth process

Selective patterning of out-of-plane piezoelectricity in MoTe2 via focused ion beam

© 2020 Elsevier Ltd. Two-dimensional transition-metal dichalcogenides (TMDs) have a strain-sensitive nature and can only exhibit in-plane piezoelectricity, owing to their in-plane inversion symmetry breaking, which limits their practical applications for vertical stimulations. In this study, we demonstrated the capability of focused ion beams to create out-of-plane piezoelectricity on multi-layered MoTe2. We utilized a focused helium ion beam to selectively pattern the out-of-plane piezoelectricity via defect engineering in a layered MoTe2 flake. The generated out-of-plane piezoelectricity in the desired area was quantitatively examined using atomic force microscopy, and ion beam irradiation-induced defect formation that gave rise to inversion symmetry breaking was confirmed. These results indicated that the out-of-plane piezoelectricity can be selectively patterned through a focused helium ion beam, and it is expected that this approach can also be applied to other classes of TMDs and can expand the application fields of TMD-based devices.11Nsciescopu