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Nanophotonics ◽  
2022 ◽  
Vol 0 (0) ◽  
Dung Thi Vu ◽  
Nikolaos Matthaiakakis ◽  
Hikaru Saito ◽  
Takumi Sannomiya

Abstract Two-dimensional (2D) transition metal dichalcogenides (TMDCs), possessing unique exciton luminescence properties, have attracted significant attention for use in optical and electrical devices. TMDCs are also high refractive index materials that can strongly confine the electromagnetic field in nanoscale dimensions when patterned into nanostructures, thus resulting in complex light emission that includes exciton and dielectric resonances. Here, we use cathodoluminescence (CL) to experimentally visualize the emission modes of single molybdenum disulfide (MoS2) nanoflakes and to investigate luminescence enhancement due to dielectric resonances in nanoscale dimensions, by using a scanning transmission electron microscope. Specifically, we identify dielectric modes whose resonant wavelength is sensitive to the shape and size of the nanoflake, and exciton emission peaks whose energies are insensitive to the geometry of the flakes. Using a four-dimensional CL method and boundary element method simulations, we further theoretically and experimentally visualize the emission polarization and angular emission patterns, revealing the coupling of the exciton and dielectric resonant modes. Such nanoscopic observation provides a detailed understanding of the optical responses of MoS2 including modal couplings of excitons and dielectric resonances which play a crucial role in the development of energy conversion devices, single-photon emitters, and nanophotonic circuits with enhanced light-matter interactions.

2022 ◽  
pp. 1-9
Tiarnan Mullarkey ◽  
Jonathan J. P. Peters ◽  
Clive Downing ◽  
Lewys Jones

In the scanning transmission electron microscope, fast-scanning and frame-averaging are two widely used approaches for reducing electron-beam damage and increasing image signal noise ratio which require no additional specialized hardware. Unfortunately, for scans with short pixel dwell-times (less than 5 μs), line flyback time represents an increasingly wasteful overhead. Although beam exposure during flyback causes damage while yielding no useful information, scan coil hysteresis means that eliminating it entirely leads to unacceptably distorted images. In this work, we reduce this flyback to an absolute minimum by calibrating and correcting for this hysteresis in postprocessing. Substantial improvements in dose efficiency can be realized (up to 20%), while crystallographic and spatial fidelity is maintained for displacement/strain measurement.

2022 ◽  
Vol 13 (1) ◽  
Binbin Chen ◽  
Nicolas Gauquelin ◽  
Nives Strkalj ◽  
Sizhao Huang ◽  
Ufuk Halisdemir ◽  

AbstractIn order to bring the diverse functionalities of transition metal oxides into modern electronics, it is imperative to integrate oxide films with controllable properties onto the silicon platform. Here, we present asymmetric LaMnO3/BaTiO3/SrTiO3 superlattices fabricated on silicon with layer thickness control at the unit-cell level. By harnessing the coherent strain between the constituent layers, we overcome the biaxial thermal tension from silicon and stabilize c-axis oriented BaTiO3 layers with substantially enhanced tetragonality, as revealed by atomically resolved scanning transmission electron microscopy. Optical second harmonic generation measurements signify a predominant out-of-plane polarized state with strongly enhanced net polarization in the tricolor superlattices, as compared to the BaTiO3 single film and conventional BaTiO3/SrTiO3 superlattice grown on silicon. Meanwhile, this coherent strain in turn suppresses the magnetism of LaMnO3 as the thickness of BaTiO3 increases. Our study raises the prospect of designing artificial oxide superlattices on silicon with tailored functionalities.

2022 ◽  
Vol 12 (1) ◽  
Yalin Zhang ◽  
Tong Wang ◽  
Zhihe Wang ◽  
Zhongwen Xing

AbstractHigh quality FeySe1−xTex epitaxial thin films have been fabricated on TiO2-buffered SrTiO3 substrates by pulsed laser deposition technology. There is a significant composition deviation between the nominal target and the thin film. Te doping can affect the Se/Te ratio and Fe content in chemical composition. The superconducting transition temperature Tc is closely related to the chemical composition. Fe vacancies are beneficial for the FeySe1−xTex films to exhibit the higher Tc. A 3D phase diagram is given that the optimize range is x = 0.13–0.15 and y = 0.73–0.78 for FeySe1−xTex films. The anisotropic, effective pining energy, and critical current density for the Fe0.72Se0.94Te0.06, Fe0.76Se0.87Te0.13 and Fe0.91Se0.77Te0.23 films were studied in detail. The scanning transmission electron microscopy images display a regular atomic arrangement at the interfacial structure.

Materials ◽  
2022 ◽  
Vol 15 (2) ◽  
pp. 487
Yang Zhang ◽  
Wanbo Qu ◽  
Guyang Peng ◽  
Chenglong Zhang ◽  
Ziyu Liu ◽  

Aberration-corrected scanning transmission electron microscopy (AC-STEM) has evolved into the most powerful characterization and manufacturing platform for all materials, especially functional materials with complex structural characteristics that respond dynamically to external fields. It has become possible to directly observe and tune all kinds of defects, including those at the crucial atomic scale. In-depth understanding and technically tailoring structural defects will be of great significance for revealing the structure-performance relation of existing high-property materials, as well as for foreseeing paths to the design of high-performance materials. Insights would be gained from piezoelectrics and thermoelectrics, two representative functional materials. A general strategy is highlighted for optimizing these functional materials’ properties, namely defect engineering at the atomic scale.

Xu Lu ◽  
Dong Wang ◽  
Di Wan ◽  
Xiaofei Guo ◽  
Roy Johnsen

AbstractIn this study, the effect of hydrogen on dislocation and twinning behavior along various grain boundaries in a high-manganese twinning-induced plasticity steel was investigated using an in situ micropillar compression test. The compressive stress in both elastic and plastic regimes was increased with the presence of hydrogen. Further investigation by transmission electron backscatter diffraction and scanning transmission electron microscope demonstrated that hydrogen promoted both dislocation multiplication and twin formation, which resulted in higher stress concentration at twin–twin and twin–grain boundary intersections.

Yuta ITOH ◽  
Hirotaka Watanabe ◽  
Yuto Ando ◽  
Emi Kano ◽  
Manato Deki ◽  

Abstract We evaluated the beam current dependence of defect formation during Mg ion implantation into GaN at a high temperature of 1100℃ with two beam currents. Photoluminescence spectra suggested that low-beam-current ion implantation reduced the vacancy concentration and activated Mg to a greater extent. Moreover, scanning transmission electron microscopy analysis showed that low-beam-current implantation reduced the density of Mg segregation defects with inactive Mg and increased the number of intrinsic dislocation loops, suggesting a decrease in the density of Ga and N vacancies. The formation of these defects depended on beam current, which is an important parameter for defect suppression.

2022 ◽  
Vol 2 ◽  
pp. 1
Oskar Ronan ◽  
Clive Downing ◽  
Valeria Nicolosi

Lithium-sulfur battery is one of promising candidates for next-generation energy storage device due to the sulfur cathode material with low cost and nontoxicity, and super high theoretical energy density (nearly 2600Wh kg−1) and specific energy (2567Wh kg−1). Sulphur, however, poses a few interesting challenges before it can gain widespread utilisation. The biggest issue is known as the polysulphide shuttling effect which contributes to rapid capacity loss after cycling. Accurate characterisation of sulphur cathodic materials becomes critical to our understanding polysulphide shuttling effect in the quest of finding mitigating solutions. Electron microscopy is playing a crucial role in battery research in determining structure–property–function relations. However, sulphur undergoes sublimation at a point above the typical pressures found in the column of a transmission electron microscope (TEM) at room temperature. This makes the imaging and characterisation of any sort of nanostructured sulphur samples challenging, as the material will be modified or even disappear rapidly as soon as it is inserted into the TEM vacuum. As a result, materials characterised by such methods are prone to deviation from normal conditions to a great extent. To prevent this, a novel method of encapsulating sulphur particles between silicon nitride (SiNx) membranes is demonstrated in this work.

2022 ◽  
pp. 1-12
Murilo Moreira ◽  
Matthias Hillenkamp ◽  
Giorgio Divitini ◽  
Luiz H. G. Tizei ◽  
Caterina Ducati ◽  

Scanning transmission electron microscopy is a crucial tool for nanoscience, achieving sub-nanometric spatial resolution in both image and spectroscopic studies. This generates large datasets that cannot be analyzed without computational assistance. The so-called machine learning procedures can exploit redundancies and find hidden correlations. Principal component analysis (PCA) is the most popular approach to denoise data by reducing data dimensionality and extracting meaningful information; however, there are many open questions on the accuracy of reconstructions. We have used experiments and simulations to analyze the effect of PCA on quantitative chemical analysis of binary alloy (AuAg) nanoparticles using energy-dispersive X-ray spectroscopy. Our results demonstrate that it is possible to obtain very good fidelity of chemical composition distribution when the signal-to-noise ratio exceeds a certain minimal level. Accurate denoising derives from a complex interplay between redundancy (data matrix size), counting noise, and noiseless data intensity variance (associated with sample chemical composition dispersion). We have suggested several quantitative bias estimators and noise evaluation procedures to help in the analysis and design of experiments. This work demonstrates the high potential of PCA denoising, but it also highlights the limitations and pitfalls that need to be avoided to minimize artifacts and perform reliable quantification.

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