Numerical correction of anti-symmetric aberrations in single HRTEM images of weakly scattering 2D-objects

Here, we present a numerical post-processing method for removing the effect of anti-symmetric residual aberrations in high-resolution transmission electron microscopy (HRTEM) images of weakly scattering 2D-objects. The method is based on applying the same aberrations with the opposite phase to the Fourier transform of the recorded image intensity and subsequently inverting the Fourier transform. We present the theoretical justification of the method and its verification based on simulated images in the case of low-order anti-symmetric aberrations. Ultimately the method is applied to experimental hardware aberration-corrected HRTEM images of single-layer graphene and MoSe2 resulting in images with strongly reduced residual low-order aberrations, and consequently improved interpretability. Alternatively, this method can be used to estimate by trial and error the residual anti-symmetric aberrations in HRTEM images of weakly scattering objects

Efficient first principles simulation of electron scattering factors for transmission electron microscopy

Electron microscopy is a powerful tool for studying the properties of materials down to their atomic structure. In many cases, the quantitative interpretation of images requires simulations based on atomistic structure models. These typically use the independent atom approximation that neglects bonding effects, which may, however, be measurable and of physical interest. Since all electrons and the nuclear cores contribute to the scattering potential, simulations that go beyond this approximation have relied on computationally highly demanding all-electron calculations. Here, we describe a new method to generate ab initio electrostatic potentials when describing the core electrons by projector functions. Combined with an interface to quantitative image simulations, this implementation enables an easy and fast means to model electron microscopy images. We compare simulated transmission electron microscopy images and diffraction patterns to experimental data, showing an accuracy equivalent to earlier all-electron calculations at a much lower computational cost.Comment: 10 pages, 5 figures, 2 table

Bayesian Model for Matching the Radiometric Measurements of Aerospace and Field Ocean Color Sensors

A Bayesian model is developed to match aerospace ocean color observation to field measurements and derive the spatial variability of match-up sites. The performance of the model is tested against populations of synthesized spectra and full and reduced resolutions of MERIS data. The model derived the scale difference between synthesized satellite pixel and point measurements with R2 > 0.88 and relative error < 21% in the spectral range from 400 nm to 695 nm. The sub-pixel variabilities of reduced resolution MERIS image are derived with less than 12% of relative errors in heterogeneous region. The method is generic and applicable to different sensors

The RHIC SPIN Program: Achievements and Future Opportunities

Time and again, spin has been a key element in the exploration of fundamental physics. Spin-dependent observables have often revealed deficits in the assumed theoretical framework and have led to novel developments and concepts. Spin is exploited in many parity-violating experiments searching for physics beyond the Standard Model or studying the nature of nucleon-nucleon forces. The RHIC spin program plays a special role in this grand scheme: it uses spin to study how a complex many-body system such as the proton arises from the dynamics of QCD. Many exciting results from RHIC spin have emerged to date, most of them from RHIC running after the 2007 Long Range Plan. In this document we present highlights from the RHIC program to date and lay out the roadmap for the significant advances that are possible with future RHIC running

Incorporate elastic and inelastic scattering into image calculation for low-voltage transmission electron microscope

In this work, we have studied the dependence of image contrast on different parameters for low voltage TEM by means of image calculation. For pure elastic scattering, we have utilized a semi-experimental model which calculates the image by averaging over the energy distribution of the elastically scattered imaging electrons, derived from the experimental EELS data. The calculations were performed for graphene under the accelerating voltage of 80 kV and 20 kV. We have investigated the influence of geometrical aberrations, chromatic aberrations, energy distribution of the imaging electrons as well as other damping effects on the image contrast. Based on the calculations, we have shown the ways to obtain the optimum imaging conditions for low voltage TEMs and initiated the discussion of inelastic scattering under the accelerating voltage of 20 kV. For the calculation involving inelastic scattering, we have utilized the existing mutual coherence model. In order to improve the computational efficiency, we have derived a new approximation to factorize the mixed dynamic form factor, one of the key quantities for the image calculation involving inelastic scattering. The new approximation can be applied for different imaging conditions with enough accuracy. Experimental images are recorded with finite electron dose. We have explored the dependence of the signal-to-noise ratio, the atom contrast and the specimen resolution on the electron dose and the sampling of the detector. A modified definition of the atom contrast considering finite electron dose is introduced, and this definition is more reasonable for evaluating the object visibility in the experimental images than other existing contrast definitions. We have analyzed the 80 kV experimental HRTEM images of graphene based on the new definition of dose-dependent contrast and found good qualitative agreement between the experimental and calculated images

Incorporate elastic and inelastic scattering into image calculation for low-voltage transmission electron microscope

In this work, we have studied the dependence of image contrast on different parameters for low voltage TEM by means of image calculation. For pure elastic scattering, we have utilized a semi-experimental model which calculates the image by averaging over the energy distribution of the elastically scattered imaging electrons, derived from the experimental EELS data. The calculations were performed for graphene under the accelerating voltage of 80 kV and 20 kV. We have investigated the influence of geometrical aberrations, chromatic aberrations, energy distribution of the imaging electrons as well as other damping effects on the image contrast. Based on the calculations, we have shown the ways to obtain the optimum imaging conditions for low voltage TEMs and initiated the discussion of inelastic scattering under the accelerating voltage of 20 kV. For the calculation involving inelastic scattering, we have utilized the existing mutual coherence model. In order to improve the computational efficiency, we have derived a new approximation to factorize the mixed dynamic form factor, one of the key quantities for the image calculation involving inelastic scattering. The new approximation can be applied for different imaging conditions with enough accuracy. Experimental images are recorded with finite electron dose. We have explored the dependence of the signal-to-noise ratio, the atom contrast and the specimen resolution on the electron dose and the sampling of the detector. A modified definition of the atom contrast considering finite electron dose is introduced, and this definition is more reasonable for evaluating the object visibility in the experimental images than other existing contrast definitions. We have analyzed the 80 kV experimental HRTEM images of graphene based on the new definition of dose-dependent contrast and found good qualitative agreement between the experimental and calculated images

Synthesis Method for Long Cycle Life Lithium-Ion Cathode Material: Nickel-Rich Core–Shell LiNi_0.8Co_0.1Mn_0.1O₂

High-nickel materials with core–shell structures, whose bulk is rich in nickel content and the outer shell is rich in manganese content, have been demonstrated to improve cycle stability. The high-nickel cathode material LiNi_0.8Co_0.1Mn_0.1O₂ is a very promising material for lithium-ion batteries; however, its low rate performance and especially cycle performance currently hamper further commercialization. This study presents a new synthesis method to prepare this core–shell material (LiNi_0.8Co_0.1Mn_0.1O₂@<i>x</i>[Li–Mn–O], <i>x</i> = 0.01, 0.03, 0.06). Electrochemical data show that LiNi_0.8Co_0.1Mn_0.1O₂@<i>x</i>[Li–Mn–O] (<i>x</i> = 0.03, CS-0.03) exhibits the best high-rate performance, cycle stability, and thermal stability. The initial discharge capacity of the core–shell sample CS-0.03 is 118 mAh g^–1, which is almost the same as the discharge capacity of pristine LiNi_0.8Mn_0.1Co_0.1O₂ (117 mAh g^–1) at the rate of 10 C in the voltage range of 3.0–4.3 V. Notably the capacity decay of CS-0.03 is 18.4% after 200 cycles compared to 27% decay in capacity of the pristine sample. Furthermore, CS-0.03 exhibits better thermal cycling stability. The capacity retention of the CS-0.03 sample reached 65.1% which is over 1.3 times than that of the pristine one, whose capacity retention is 49.2% after 105 cycles (55 °C). Evidently, the core–shell structured CS-0.03 sample has excellent cycle stability and this synthesis method can be applied to other cathode materials

First Assessment of Sentinel-1A Data for Surface Soil Moisture Estimations Using a Coupled Water Cloud Model and Advanced Integral Equation Model over the Tibetan Plateau

The spatiotemporal distribution of soil moisture over the Tibetan Plateau is important for understanding the regional water cycle and climate change. In this paper, the surface soil moisture in the northeastern Tibetan Plateau is estimated from time-series VV-polarized Sentinel-1A observations by coupling the water cloud model (WCM) and the advanced integral equation model (AIEM). The vegetation indicator in the WCM is represented by the leaf area index (LAI), which is smoothed and interpolated from Terra Moderate Resolution Imaging Spectroradiometer (MODIS) LAI eight-day products. The AIEM requires accurate roughness parameters, which are parameterized by the effective roughness parameters. The first halves of the Sentinel-1A observations from October 2014 to May 2016 are adopted for the model calibration. The calibration results show that the backscattering coefficient (σ°) simulated from the coupled model are consistent with those of the Sentinel-1A with integrated Pearson’s correlation coefficients R of 0.80 and 0.92 for the ascending and descending data, respectively. The variability of soil moisture is correctly modeled by the coupled model. Based on the calibrated model, the soil moisture is retrieved using a look-up table method. The results show that the trends of the in situ soil moisture are effectively captured by the retrieved soil moisture with an integrated R of 0.60 and 0.82 for the ascending and descending data, respectively. The integrated bias, mean absolute error, and root mean square error are 0.006, 0.048, and 0.073 m3/m3 for the ascending data, and are 0.012, 0.026, and 0.055 m3/m3 for the descending data, respectively. Discussions of the effective roughness parameters and uncertainties in the LAI demonstrate the importance of accurate parameterizations of the surface roughness parameters and vegetation for the soil moisture retrieval. These results demonstrate the capability and reliability of Sentinel-1A data for estimating the soil moisture over the Tibetan Plateau. It is expected that our results can contribute to developing operational methods for soil moisture retrieval using the Sentinel-1A and Sentinel-1B satellites

Enhancing the Catalytic Activity of Co₃O₄ for Li–O₂ Batteries through the Synergy of Surface/Interface/Doping Engineering

Efficient bifunctional catalysts are highly desirable for Li–O₂ batteries to accerlerate the oxygen reduction and oxygen evolution reactions. Surface/interface regulation or doping has been used to enhance the activity of the catalysts. Herein, we propose a facile synchronous reduction strategy to fabricate a yolk–shell Co₃O₄@Co₃O₄/Ag hybrid which integrates the advantages of surface, interface, and doping engineering as a highly active catalyst for Li-O₂ batteries. The Co₃O₄@Co₃O₄/Ag-based cathode shows a high initial capacity (12000 mAh g^–1@200 mA g^–1), high rate capability (4700 mAh g^–1@800 mA g^–1), low overpotential, and long cycle life due to the synergetic interactions of surface, interface, and doping engineering. The underling synergetic mechanism has been uncovered by X-ray diffraction, X-ray photoelectron spectroscopy, X-ray absorption near-edge structure spectra, aberration-corrected scanning transmission electron microscopy, electrochemical impedance spectra, and ex situ scanning electron microscopy. For Co₃O₄@Co₃O₄/Ag, part of Ag has formed on the surface of Co₃O₄ shell as single atoms or clusters and a fraction of Ag has been doped into the crystal lattice of Co₃O₄ at the same time, which not only strengthens the Ag–Co₃O₄ interface binding but also tailors the valence electronic structure of Ag and Co species as well as improves the electronic conductivity. This particular architecture provides more active sites for the ORR/OER and also enhances the catalytic activity. In addition, flowerlike Li₂O₂ forms on the Co₃O₄@Co₃O₄/Ag cathode, which is more feasible to decompose in comparison to toroidal-like Li₂O₂. This study offers some insights into designing efficient cathode catalysts through a synergetic surface/interface/doping engineering strategy