Metallic CoSb and Janus Co2AsSb monolayers as promising anode materials for metal-ion batteries.

Structural symmetry breaking plays a pivotal role in fine-tuning the properties of nano-layered materials. Here, based on the first-principles approaches we propose a Janus monolayer of metallic CoSb by breaking the out-of-plane structural symmetry. Specifically, within the CoSb monolayer by replacing the top-layer 'Sb' with 'As' atoms entirely, the Janus Co2AsSb monolayer can be formed, whose structure is confirmed via structural optimization and ab initio molecular dynamics simulations. Notably, the Janus Co2AsSb monolayer demonstrates stability at an elevated temperature of 1200 K, surpassing the stability of the CoSb monolayer, which remains stable only up to 900 K. We propose that both the CoSb and Janus Co2AsSb monolayers could serve as capable anode materials for power-driven metal-ion batteries, owing to their substantial theoretical capacity and robust binding strength. The theoretical specific capacities for Li/Na reach up to 1038.28/1186.60 mA h g-1 for CoSb, while Janus Co2AsSb demonstrates a marked improvement in electrochemical storage capacity of 3578.69/2215.38 mA h g-1 for Li/Na, representing a significant leap forward in this domain. The symmetry-breaking effect upgrades the CoSb monolayer, as a more viable contender for power-driven metal-ion batteries. Furthermore, electronic structure calculations indicate a notable charge transfer that augments the metallic nature, which would boost electrical conductivity. These simulations demonstrate that the CoSb and Janus Co2AsSb monolayers have immense potential for application in the design of metal-ion battery technologies.

Exploring the absolute yield curve of secondary electrons using machine learning methods.

Knowledge of absolute secondary electron yield (δ) is important for various applications of electron emission materials. Besides, it is also crucial to know the dependence of δ on primary electron energy Ep and material properties like atomic number Z. The available experimental database of δ reveals a large discrepancy among the measurement data, while the oversimplified semi-empirical theories of secondary electron emission can only present the general shape of the yield curve but not the absolute yield value. This limits not only the validation of a Monte Carlo model for theoretical simulations but also presents large uncertainties in the applications of different materials for various purposes. In applications, it is highly desirable to have the knowledge of the absolute yield of a material. Therefore, it is highly desirable to establish the relationship of the absolute yield with material and electron energy based on the available experimental data. Recently, machine learning (ML) methods have been increasingly used for the prediction of material properties mainly based on the atomistic calculations with the first-principles theory. We propose here the application of ML models to a material property study, starting with experimental observations and unfolding the relationship of δ with basic material properties and primary electron energy. Our ML models are able to predict δ(Ep)-curve covering a wide energy range of 10 eV-30 keV for unknown elements within the uncertainty range of the experimental data and can suggest more reliable data among the scattered experimental data.

Theoretical prediction and characterization of novel two-dimensional ternary tetradymite compounds La2X2Y (X = I, Br, Cl; Y = Ge, Te) as anode materials for metal-ion batteries.

Tetradymite compounds, such as Bi2Te3, crystallizing in rhombohedral structures have triggered tremendous research interest from the scientific community because of their intriguing properties. Herein, using the state-of-the-art first-principles calculations, we identify that La2X2Y (X = I, Br, Cl; Y = Ge, Te) nanosheets exhibit a ternary tetradymite-type structure with extraordinary electrical and electrochemical properties. It is first demonstrated that the layered La2X2Y compounds exhibit weak interlayer coupling with cleavage energies in the range of ∼0.28-0.38 J m-2, allowing the ready separation of monolayers that can be synthesized by mechanical exfoliation from their bulk counterparts. Next, we predict that La2X2Ge nanosheets exhibit a semiconducting nature, and upon physical realistic strain, a Dirac cone can be realized. These findings can be exploited in the transport properties. Furthermore, we comprehensively investigated the electrochemical properties of the predicted systems to evaluate their potential use in metal-ion (Li/Na) batteries. Our detailed analyses reveal that the Li (Na) adatoms are sufficiently mobile on the surface of the studied systems. For instance, the binding energy for the Li (Na) adatom on La2I2Ge is -2.24(-1.79) eV with a diffusion barrier of as small as ∼0.31(0.20) eV. Subsequently, the maximum theoretical specific capacity for Li (Na) reaches as high as 887(1064) mA h g-1, which can be attributed to a much higher storage capacity compared to previously identified 2D anode materials. These findings substantiate that the predicted nanosheets could be synthesized to explore their potential applications in future metal-ion batteries.

A theoretical characterization method for non-spherical core-shell nanoparticles by XPS.

Core-shell nanoparticles (NPs) are active research areas for their unique properties and wide applications. By changing the elemental composition in the core and shell, a series of core-shell NPs with specific functions can be obtained, where the sizes of the core and shell also influence the properties. X-ray photoelectron spectroscopy (XPS) is useful in this context as a means of quantitatively analyzing such NPs. The empirical formula proposed by Shard [J. Phys. Chem. C, 2012, 116(31), 16806-16813] for calculating the shell thickness of the spherical core-shell NPs has been verified by Powell et al. [J. Phys. Chem. C, 2016, 120(39), 22730-22738] through a simulation of XPS with Simulation of Electron Spectra for Surface Analysis (SESSA) software. However, real core-shell NPs are not necessarily ideal spheres; such NPs can have rich shapes and uneven thicknesses. This work aims to extend the Shard formula to non-ideal core-shell NPs. We have used a Monte Carlo simulation method to study the XPS signal variation with the shell thickness for several modeled non-spherical shapes of core-shell NPs including some complex geometric structures which are numerically constructed with finite-element triangular meshes. Five types of non-spherical shapes, i.e. egg, ellipsoid, rod, rough-surface, and star shapes, are considered, while the size parameters are varied over a wide range. The equivalent radius and equivalent thickness are defined to characterize the average size of the nanoparticles for the use of the Shard formula. We have thus derived an extended Shard formula for the specific core-shell NPs, with which the relative error between the predicted shell thickness and the real thickness can be reduced to less than 10%.

Black phosphorene/blue phosphorene van der Waals heterostructure: a potential anode material for lithium-ion batteries.

Van der Waals (vdW) heterostructure-based electrodes have invoked tremendous research interest due to their intriguing properties and their capability to break the limitations of the restricted properties of single-material systems. Herein, based on first-principles approaches, we propose that the black phosphorene/blue phosphorene (BLK-P/BLE-P) vdW heterostructure can be a capable anode material for power-driving lithium-ion batteries (LIBs), as it exhibits a large theoretical capacity, together with a relatively strong binding strength compared with the individual BLK-P and BLE-P monolayers. Our calculation results show that the Li adatom prefers to intercalate into the interlayer of the BLK-P/BLE-P vdW heterostructure due to the synergistic interfacial effect, resulting in a high binding strength and a diffusivity comparable to the BLK-P and BLE-P monolayers. Subsequently, the theoretical specific capacity is found to be as high as 552.8 mA h g-1, which can be attributed to the much higher storage capacity of Li adatoms in the BLK-P/BLE-P vdW heterostructure. Furthermore, electronic structure calculations reveal that a large amount of charge transfer assists in semiconductor to metallic transition upon lithiation, which would ensure good electrical conductivity. These simulations prove that the BLK-P/BLE-P heterostructure has great potential in LIBs and is essential for future battery design.

Ensemble machine learning methods: predicting electron stopping powers from a small experimental database.

Electron stopping power (SP) is of great importance in theoretical and applied research areas specifically for Monte Carlo simulation studies in many microanalysis and surface analysis techniques, radiation dosimetry, and the design of particle detectors. However, experimental data are available for a dozen elemental materials only. On the other hand, the Bethe analytical expression of the SP is applicable at high energies only whereas no generally accepted formula exists at lower energies. We employed ensemble machine learning (ML) methods with the available experimental database for the prediction of SPs of electrons with energies from 100 keV down to 1 eV, in elements over the entire periodic table. With a small training database for electron SPs, we applied various algorithms individually as well as their ensembles, which have the credibility to enhance the prediction accuracy in the case of a small training database. Based on the model's performance evaluation tests, we concluded that the stacked generalization is more accurate than the individual algorithms. Using this method, we were able to predict the electron SPs for 54 elements (in total) including 12 elements that were present in the training database as well as for 42 elements beyond the training database over a wide energy range (1 eV to 100 keV). Compared to other theoretical approaches, the ML predicted SPs show very good agreement with the available experimental data at all energies. Moreover, unlike other theoretical approaches, the ML model does not need dielectric function data and other physical parameters which involve complex calculations. Using our ML model, we have predicted SPs for a further 14 elements for which no theoretical SPs are available because of the lack of good dielectric function data.

Optical properties of amorphous carbon determined by reflection electron energy loss spectroscopy spectra.

We present the combined experimental and theoretical investigations of the optical properties of amorphous carbon. The reflection electron energy loss spectra (REELS) spectra of carbon were measured using a cylindrical mirror analyzer under ultrahigh vacuum conditions at primary electron energies of 750, 1000 and 1300 eV. The energy loss function and thereby the refractive index n and the extinction coefficient k were determined from these REELS spectra in a wide loss energy range of 2-200 eV by applying our reverse Monte Carlo method. The high accuracy of the obtained optical constants is justified with the ps- and f-sum rules. We found that our present optical constants of amorphous carbon fulfill the sum rules with the highest accuracy compared with the previously published data. Therefore, we highly recommend to replace the previous data with the present ones for practical applications. Moreover, we present the atomic scattering factors of amorphous carbon obtained from the dielectric function to predict its optical constants at a given density.

Charging effect induced by electron beam irradiation: a review.

Charging effect frequently occurs when characterizing nonconductive materials using electrons as probes and/or signals and can impede the acquisition of useful information about the material under investigation. It is not adequate to investigate it merely by experiments, but theoretical investigations, for which the Monte Carlo method is a suitable tool, are also necessary. In this paper we review Monte Carlo simulations and selected experiments, intending to provide general insight into the charging effects induced by electron beam irradiation. We will introduce categories of the charging effect, the theoretical framework that is adopted in Monte Carlo modeling of the charging effect and present some typical simulation results. At last, with the knowledge on charging effect imparted by the above contents, we will discuss the measures that can be used for minimizing it.

[Correlation between elevation of brachial artery pulse pressure increased and coronary heart disease in different genders].

Objective: To explore the relationship between elevation of brachial pulse pressure and coronary heart disease in different genders. Methods: A total of 5 116 inpatients with suspected stable coronary heart disease were consecutively enrolled from December 2011 to June 2017 in the Affiliated Hospital of Chengde Medical College, and divided into coronary heart disease group (n=3 694) and non-coronary heart disease group (n=1 422). The clinical data of all inpatients were collected. A binary logistic regression model of coronary heart disease in different genders were separately established. Results: The morbidity of hypertension, dyslipidemia, type 2 diabetes, ischemic stroke and elevated pulse pressure were all higher in the coronary heart disease group than those in the non-coronary heart disease group (all P<0.05). The area under curve (AUC) of pulse pressure in the male group was 0.540, with an optimal diagnostic threshold of 50 mmHg. The AUC of pulse pressure in the female group was 0.612, with an optimal diagnostic threshold of 60 mmHg. Besides hypertension, type 2 diabetes, increase of low-density lipoprotein cholesterol, ischemic stroke, smoking, and aging, elevated pulse pressure was also an independent risk factor for coronary heart disease in both male and female groups (all P<0.05). Additionally, the risk of elevated pulse pressure for coronary heart disease was higher in female group than that of male group (odds ratio (OR): 1.741 vs 1.284, P<0.05). Conclusion: Elevated pulse pressure may be a new risk factor for coronary heart disease, and its risk for coronary heart disease is higher in women than in men.

[Epidemiological survey of mental disorders in the rural left behind elderly aged 60 years and older in Gansu].

Objective: To investigate the prevalence, demographic characteristics and social life function of mental disorders in the rural left behind elderly aged 60 years and older in Gansu. Methods: Between November 2017 and June 2018, a multi-stage stratified cluster sampling method was used to randomly select the rural left behind elderly aged 60 years and older in Gansu, and totally 6 000 elderly were enrolled. By using the extended general health questionnaire (GHQ-12) and the American Handbook for Diagnosis and Statistics of Mental Disorders (DSM-Ⅳ) Axis Ⅰ Disorders Formal Clinical Examination Patient Edition, all the included subjects were screened and diagnosed. Functional status was assessed by the Global Assessment Function scale (GAF). Statistical analysis of the prevalence of various mental illnesses, as well as the differences in the prevalence of different gender, marital status and age groups was performed. Results: Totally, 6 000 subjects completed the survey. The adjusted current prevalence of any mental disorder was 20.11% (95%CI 17.70%-22.85%). The six most prevalent specific disorders were major depressive disorder (9.20%), pain disorder (2.71%), mood disorder due to the body condition (2.08%), generalized anxiety disorder (1.99%), anxiety disorder not otherwise specified (1.15%) and dysthymic disorder (0.84%). The lifetime prevalence of mental disorders was 20.54% (95%CI 18.40%-23.39%). The overall current prevalence of mental disorders was higher in women (242.89‰) than in men (119.55‰), and the unmarried (248.37‰) was higher than those married (187.53‰). There was no significant difference in the prevalence of mental disorders among different age groups (P>0.05). The GAF score of mental disorders was 56±11, and 71.82% was moderate to severe functional impairment. Conclusions: The prevalence of mental disorders is high in rural left-behind population aged 60 years and over in Gansu Province. Major depression is a condition that deserves special attention.

Enhanced electronic and optical properties of three TMD heterobilayers.

The physical and chemical properties of monolayers can be tuned by selective combinations so as to be useful for device applications. Here we present a density functional theory study on the structural, electronic and optical properties of three transition metal dichalcogenide (TMD) heterobilayers, ZrS2/HfS2, ZrSe2/HfSe2 and SnS2/SnSe2. These heterobilayers are predicted to be energetically and dynamically stable structures. The band structure calculation result shows that ZrS2/HfS2, ZrSe2/HfSe2 and SnS2/SnSe2 heterobilayers are semiconductors with indirect band gaps. The efficient charge carrier separation in ZrS2/HfS2 and ZrSe2/HfSe2 heterobilayers indicates that they can be employed in energy harvesting devices. Contrary to the previous report on the ZrS2/HfS2 heterobilayer, we found it to have an intrinsic type-II band alignment which is required in p-n junction diodes and tunnel field effect transistors, and the same behavior was observed in ZrSe2/HfSe2 and SnS2/SnSe2 for the first time. The ZrS2/HfS2 and ZrSe2/HfSe2 heterobilayers reveal enhanced optical absorption both in the ultraviolet and visible regions as compared to their respective monolayers, whereas the parallel and perpendicular part of the optical absorption of the SnS2/SnSe2 heterobilayer revealed an anisotropic behavior; the perpendicular part is largely improved in the higher energy region, and the parallel part of the optical absorption is improved in the ultraviolet region.

Enhancement of the spin polarization of an Fe3O4(100) surface by nitric oxide adsorption.

The geometric, electronic and magnetic properties of a nitric oxide (NO) adsorbed Fe3O4(100) surface have been investigated using density functional theory (DFT) calculations. NO molecules preferentially bond with surface Fe(B) atoms via their N atoms. The generalized gradient approximation (GGA) is not recommended to be used in such a strongly correlated system since it provides not only an overestimation of the adsorption energy and an underestimation of the Fe(B)-N bond length, but also magnetic quenching of the adsorbate and the bonded Fe(B) atoms. In contrast, a tilted geometry and magnetization of the adsorbate and the bonded Fe(B) atom are obtained after including the strong on-site Coulomb interactions through a Hubbard term (GGA+U). The spin-down 2π* states of the NO molecule are filled and broadened due to the adsorbate-substrate interaction and the molecule-molecule interaction. The surface spin polarization close to the Fermi level is expected to be greatly enhanced by the NO adsorption which has significance for interface design in spintronic devices.

[Research Progress on Postmortem Interval Estimation by Vitreous Humor].

Postmortem interval （PMI） estimation is one of the most challenging problems in the field of forensic science. Vitreous humor is a hotspot which has been used for PMI estimation and postmortem chemical analysis in forensic pathology. In order to provide novel perspectives for the future research of PMI estimation using vitreous humor, the comparison between vitreous humor with other common body fluids, the effect of temperature on vitreous humor, vitreous humor detection method and data fitting method have been reviewed in this paper.

[Application of Mixed-effect Model in PMI Estimation by Vitreous Humor].

OBJECTIVES: To test the changes of the potassium （K⁺） and magnesium （Mg²âºï¼‰ concentrations in vitreous humor of rabbits along with postmortem interval （PMI） under different temperatures, and explore the feasibility of PMI estimation using mixed-effect model. METHODS: After sacrifice, rabbit carcasses were preserved at 5 ℃, 15 ℃, 25 ℃ and 35 ℃, and 80-100 µL of vitreous humor was collected by the double-eye alternating micro-sampling method at every 12 h. The concentrations of K⁺ and Mg²âº in vitreous humor were measured by a biochemical-immune analyser. The mixed-effect model was used to perform analysis and fitting, and established the equations for PMI estimation. The data detected from the samples that were stoned at 10 ℃, 20 ℃ and 30 ℃ with 20, 40 and 65 h were used to validate the equations of PMI estimation. RESULTS: The concentrations of K⁺ and Mg²âº [f（x,y）] in vitreous humor of rabbits under different temperature increased along with PMI （x）. The relative equations of K⁺ and Mg²âº concentration with PMI and temperature under 5 ℃~35 ℃ were fK⁺（x,y）=3.413 0+0.309 2 x+0.337 6 y+0.010 83 xy-0.002 47 x² （P<0.000 1）, and fMg²âºï¼ˆx,y）=0.745 6+0.006 432 x+0.033 8 y （P<0.000 1）, respectively. It was proved that the time of deviation for PMI estimation by K⁺ and Mg²âº was in 10 h when PMI was between 0 to 40 h, and the time of deviation was in 21 h when PMI was between 40 to 65 h. CONCLUSIONS: the ambient temperature range of 5 ℃-35 ℃, the mixed-effect model based on temperature and vitreous humor substance concentrations can provide a new method for the practical application of vitreous humor chemicals for PMI estimation.

[Propensity score matching-based analysis of short-term outcomes of Laparoscopic-assisted Natural Orifice Specimen Extraction for left colorectal cancer radical resection].

OBJECTIVE: To explore short-term outcomes obtained with Laparoscopic-assisted Natural Orifice Specimen Extraction for left colorectal cancer radical resection. METHODS: A total of 123 patients with left colorectal tumor who had undergone laparoscopic surgery between Jan.2014 and Jun.2015 were reviewed. According to surgical approach, transanal specimen extraction using the Cai Tube (study group, n=29) and trans-abdominal incision specimen extraction (control group, n=123) were studied. Propensity score matching was applied at a ratio of 1∶1 comparing the study (n=23) and control (n=23) groups. RESULTS: The two matched groups had similar baseline characteristics. There was no significant difference in the length of distal or proximal resection margin, the rate of circumferential resection negative margin, the estimated blood loss, the levels of C-reactive protein on 2nd day after surgery, the postoperative time to take liquid, the postoperative hospital day, the hospital fee and the postoperative anal function. The study group presented longer operative time[(237.8±68.1)min vs (168.9±47.5)min, P<0.05], less number of lymph nodes dissected (12.4±5.4 vs 16.4±7.2, P<0.05), higher white cell count on 2nd day after surgery[(11.7±3.4)×10(9)/L vs (9.4±2.6)×10(9)/L, P<0.05], but quicker postoperative recovery of bowel function[(2.6±0.7)d vs (3.4±0.7)d, P<0.05], shorter postoperative ambulation time[(2.3±0.6)d vs (3.6±0.7)d, P<0.05], lower rate of postoperative complications (0/23 vs 6/23, P<0.05) and lower rate of utilization of painkillers in addition to postoperative analgesia pump (1/20 vs 9/23, P<0.05). CONCLUSION: Laparoscopic-assisted left colorectal cancer radical resection using the Cai Tube is in line with oncologic principle, less pain, quicker recovery and better cosmetic results.

Calculation of Bohmian quantum trajectories for STEM.

We present in this work the calculation of Bohmian quantum trajectories representing the wave function propagation in a crystal for a focused electron probe in a scanning transmission electron microscope (STEM). The wave function and quantum trajectories are obtained from the calculation of time-dependent Schrödinger equation by fast Fourier transformation multislice algorithm. In our work, the Bohmian quantum trajectories of a scanning probe penetrating a Cu crystal are studied as an example of this calculation scheme. The results help us to better understand the electron diffraction process in a microscopic imaging from a trajectory-based point of view. This Bohmian quantum trajectory method can be used to extend the application of classical Monte Carlo method from the study of electron interaction with amorphous solid to crystalline structure.

Quantum-trajectory Monte Carlo method for study of electron-crystal interaction in STEM.

In this paper, a novel quantum-trajectory Monte Carlo simulation method is developed to study electron beam interaction with a crystalline solid for application to electron microscopy and spectroscopy. The method combines the Bohmian quantum trajectory method, which treats electron elastic scattering and diffraction in a crystal, with a Monte Carlo sampling of electron inelastic scattering events along quantum trajectory paths. We study in this work the electron scattering and secondary electron generation process in crystals for a focused incident electron beam, leading to understanding of the imaging mechanism behind the atomic resolution secondary electron image that has been recently achieved in experiment with a scanning transmission electron microscope. According to this method, the Bohmian quantum trajectories have been calculated at first through a wave function obtained via a numerical solution of the time-dependent Schrödinger equation with a multislice method. The impact parameter-dependent inner-shell excitation cross section then enables the Monte Carlo sampling of ionization events produced by incident electron trajectories travelling along atom columns for excitation of high energy knock-on secondary electrons. Following cascade production, transportation and emission processes of true secondary electrons of very low energies are traced by a conventional Monte Carlo simulation method to present image signals. Comparison of the simulated image for a Si(110) crystal with the experimental image indicates that the dominant mechanism of atomic resolution of secondary electron image is the inner-shell ionization events generated by a high-energy electron beam.

Extended Mermin method for calculating the electron inelastic mean free path.

We propose an improved method for calculating electron inelastic mean free paths (IMFPs) in solids from experimental energy-loss functions based on the Mermin dielectric function. The "extended Mermin" method employs a nonlimited number of Mermin oscillators and allows negative oscillators to take into account not only electronic transitions, as is common in the traditional approaches, but also infrared transitions and inner shell electron excitations. The use of only Mermin oscillators naturally preserves two important sum rules when extending to infinite momentum transfer. Excellent agreement is found between calculated IMFPs for Cu and experimental measurements from elastic peak electron spectroscopy. Notably improved fits to the IMFPs derived from analyses of x-ray absorption fine structure measurements for Cu and Mo illustrate the importance of the contribution of infrared transitions in IMFP calculations at low energies.

Black phosphorene/SnSe van der Waals heterostructure as a promising anchoring anode material for metal-ion batteries.

Black phosphorene (BP) is a glowing two-dimensional semiconducting layer material for cutting-edge microelectronics, with high carrier mobility and thickness-dependent band gap. Here, based on van der Waals (vdW)-corrected first-principles approaches, we investigated stacked BP/tin selenide (BP/SnSe) vdW heterostructure as an anode material for metal ion batteries, which exhibits a significant theoretical capacity, along with relatively durable binding strength compared to the constituent BP and SnSe monolayers. Our calculations demonstrated that the Li/Na adatom favors insertion into the interlayer region of BP/SnSe vdW heterostructure owing to synergistic interfacial effect, resulting in comparable diffusivity to the BP and SnSe monolayers. Subsequently, the theoretical specific capacities for Li/Na are found to be as high as 956.30 mAhg-1and 828.79 mAhg-1, respectively, which could be attributed to the much higher storage capacity of Li/Na adatoms in the BP/SnSe vdW heterostructure. Moreover, the electronic structure calculations reveal that a large amount of charge transfer assists in semiconductor-to-metallic transition upon lithiation/sodiation, ensuring good electrical conductivity. These simulations verify that the BP/SnSe vdW heterostructure has immense potential for application in the design of metal-ion battery technologies.

Improved reverse Monte Carlo analysis of optical property of Fe and Ni from reflection electron energy loss spectroscopy spectra.

The energy loss functions (ELFs) of Fe and Ni have been derived from measured reflection electron energy loss spectroscopy (REELS) spectra by a reverse Monte Carlo analysis in our previous work. In this work, we present further improvements of ELFs for these metals. For Fe, we have updated ELFs at primary electron energies of 2 keV and 3 keV in a wider photon energy region (0-180 eV) with a better accuracy, which is verified by sum rules. Regarding to Ni, we supplement the ELF at primary energy of 5 keV and we also improve the data accuracy at 3 keV. Applying these new and more accurate ELFs we present the optical constants and dielectric functions for the two metals. The improvements were highlighted by comparing our present results with the previous data.