Recent Highlights

Structure Instability and Decomposition Pathway of CH3NH3PbI3
We probe the stability of CH3NH3PbI3 films in a transmission electron microscope, defining the threshold conditions to avoid damage under the electron beam, and describing a decomposition pathway. We discover that the decomposition of MAPbI3 is likely initiated with the loss of I iodine ions, to subsequently form the superstructure MAPbI2.5 with ordered I vacancies, which is followed by the loss of MA and additional I to form MAyPbI2.5-z (0≤y≤1 and 0≤z≤0.5), and finally resulting in eventual collapse of perovskite structure and its decomposition into PbI2. (Nature Communications 9:4807(2018))
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Surface phonon intensity decaying measurement and fast fitting
Based on the Nion U-HERMES200 with 8 meV energy resolution and 60pm space resolution, the phonon of the hexagonal–boron nitride (h-BN) nanosheet is measured and various fitting methods are used to quantitatively study the intensity distribution behavior of the aloof mode. Meanwhile, a simple empirical formula is proposed to fit the decaying of phonon intensity in vacuum and the underlying mechanism is discussed.
(Journal of Chinese Electron Microscopy Society 37(5):508-514 (2018))   
Graphene enables the fast growth of strain-free AlN
Graphene can reduce the density of AlN nuclei but increase the growth rate for individual nucleus at the initial growth stage. This can lead to the reduction of threading dislocations evolved at the coalescence boundaries. The graphene interlayer also weakens the interaction between AlN and sapphire and accommodates their large mismatch in lattice and thermal expansion coefficient, thus the compressive strain in AlN and tensile strain in sapphire is largely relaxed. The effective relaxation of strain further leads to low density of defects in AlN films.
(J. Am. Chem. Soc. DOI:10.1021/jacs.8b03871 (2018))   
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Reversible phase transition of 1T-V1+xSe2
By in situ transmission electron microscopy technique we directly track the structural evolution during Li ions insertion and extraction in transition metal dichalcogenide 1TV1+xSe2 nanostructures which feature spontaneous localized superstructures due to the periodical interstitial V atoms within the van der Waals interlayers. We find that lithium ion migration destroys the cationic orderings and leads to a reversible phase transition from superstructure to nonsuperstructure.
(Nano Letters DOI: 10.1021/acs.nanolett.8b03154 (2018))   
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Polarized dislocation cores
Due to the broken translation symmetry at the dislocations, the naturally existed inhomogeneous strain is expected to generate flexoelectric polarization. By using the quantitative ABF analysis, for the first time we directly confirm this phenomenon at the dislocations of SrTiO3, and precisely measure the value of polarization.
(Physical Review Letters 120, 267601 (2018))   
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Structural Relaxation Screening at Polar Interfaces
By combining the annular bright field imaging and electron energy-loss spectroscopy (EELS) in aberration-corrected scanning transmission electron microscope with phase-field simulations, we investigate the screening mechanism by quantitatively measuring the structural relaxation at Pb(Zr0.2Ti0.8)O3/SrTiO3 interfaces. We find that the thickness of the interfacial layer is ~3.5 unit cells (~1.4 nm) in a domain with upward polarization and ~5.5 unit cells (~2.2 nm) in a domain with downward polarization. The existence of interfacial oxygen vacancies accounts for the narrower interfacial layer in the domain with upward polarization.
(Physical Review B 97(18):180103 (2018))   
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Graphene promote High performance LED devices
Gr films were directly grown on sapphire substrate to avoid the tedious transfer process and GaN was grown by metal-organic chemical vapor deposition (MOCVD). The introduced Gr buffer layer greatly releases biaxial stress and reduces the density of dislocations in GaN film and InxGa1-xN/GaN multiple quantum well structures.The as-fabricated LED devices therefore deliver much higher light output power of compared to that on bare sapphire substrate, which even outperforms its mature process derived counterpart.
(Advanced Materials 30(30):1801608 (2018))   
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The ‘true’ atomic structure of dislocation cores in SrTiO3
By using the state-of-the-art microscopy and spectroscopy in aberration-corrected scanning transmission electron microscopes, we determine the ‘true’ atomic structure of dislocation cores in the 10°tilted SrTiO3 bicrystal, i.e., the SrO plane terminated Sr0.82Ti0.85O3-x (Ti3.67+, 0.48≤x≤0.91) and TiO2 plane terminated Sr0.63Ti0.90O3-y (Ti3.60+, 0.57≤y≤1). (Ultramicroscopy 184 (2018) 217–224)
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The thinnest perovskite ferroelectric film
Understanding ferroelectricity at reduced dimensions will be important for future sub-nanoscale devices based on ferroelectrics. Using quantitative annular bright field imaging analysis in aberration corrected electron microscopy; we observe the existence of a measurable polarization at a thickness of just 1.5 unit cells, indicating possible absence of critical thickness in perovskite ferroelectric thin films. (Nature Communications 8, 15549 (2017))
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Reversible Na insertion and extraction
Reversible Na insertion and extraction in SnS2 is tracked by in situ TEM. Na insertion occurs via two-phase reaction, while Na extraction involves intermediate phase Na0.5SnS2, being solid-solution-like. The Na0.5SnS2 phase has row ordering within (001) planes, rather than the widely observed staging phase (i.e. (001) plane ordering). (Nano energy 10.1016.(2017))

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Tracking Asymetric reaction pathways
We find that the reaction pathways during lithium insertion and extraction in the SnS2 nanostructures are significantly different, i.e., the lithium insertion occurs via a fast two-phase reaction to form expanded and defective LiSnS2, while the lithium extraction initially involves heterogeneous nucleation of intermediate superstructure Li0.5SnS2 domains with a 1–4 nm size. These results suggest possible alternatives to the accepted explanation of the origins of voltage hysteresis in the intercalation electrode materials. (Nano Letters 10.1021/acs.nanolett.6b02136 (2016))
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Atomic structure of oxide skin
Miniature of electronic devices are attractive yet challenging due to spatial structural variation at nanoscale. Here, Gao et al. report atomic imaging of reconstruction and unusual domain walls on Pb(Zr0.2Ti0.8)O3 surface, revealing atomic information towards understanding and control of structural change for nanoscale engineering (Nature Communications 7, 11318 (2016))
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