Atomically self-healing of structural defects in monolayer WSe_(2)

Minimizing disorder and defects is crucial for realizing the full potential of two-dimensional transition metal dichalcogenides(TMDs) materials and improving device performance to desired properties. However, the methods in defect controlcurrently face challenges with overly large operational areas and a lack of precision in targeting specific defects. Therefore,we propose a new method for the precise and universal defect healing of TMD materials, integrating real-time imaging withscanning transmission electron microscopy (STEM). This method employs electron beam irradiation to stimulate the diffusionmigration of surface-adsorbed adatoms on TMD materials grown by low-temperature molecular beam epitaxy (MBE),and heal defects within the diffusion range. This approach covers defect repairs ranging from zero-dimensional vacancydefects to two-dimensional grain orientation alignment, demonstrating its universality in terms of the types of samples anddefects. These findings offer insights into the use of atomic-level focused electron beams at appropriate voltages in STEMfor defect healing, providing valuable experience for achieving atomic-level precise fabrication of TMD materials.

Symmetry quantification and segmentation in STEM imaging through Zernike moments

We present a method using Zernike moments for quantifying rotational and reflectional symmetries in scanning transmission electron microscopy(STEM)images,aimed at improving structural analysis of materials at the atomic scale.This technique is effective against common imaging noises and is potentially suited for low-dose imaging and identifying quantum defects.We showcase its utility in the unsupervised segmentation of polytypes in a twisted bilayer TaS_(2),enabling accurate differentiation of structural phases and monitoring transitions caused by electron beam effects.This approach enhances the analysis of structural variations in crystalline materials,marking a notable advancement in the characterization of structures in materials science.

Visible-light driven room-temperature coupling of methane to ethane by atomically dispersed Au on WO_(3)

Gold(Au)as co-catalyst is remarkable for activating methane(CH4),especially atomically dispersed Au with maximized exposing active sites and specific electronic structure.Furthermore,singlet oxygen(^(1)O_(2))typically manifests a mild redox capacity with a high selectivity to attack organic substrates.Peroxomonosulfate(PMS)favors to produce oxidative species 102 during the photocatalytic reactions.Thus,combining atomic Au as co-catalyst and ^(1)O_(2) as oxidant is an effective strategy to selectively convert CH4.Herein,we synthesized atomically dispersed Au on WO_(3)(Au/WO_(3)),where Au was in the forms of single atoms and clusters.At room temperature,such Au/WO_(3) exhibited enhanced photocata lytic conversion of CH4 to CH3 CH3 with a selectivity,up to 94%,under visible light.The radicals-pathway mechanism of CH4 coupling has also been investigated through detection and trapping experiment of active species.Theoretical calculations further interpret the electronic structure of Au/WO_(3) and tip-enhanced local electric field at the Au sites for promoting CH4 conversion.

Epirubicin-gold nanoparticles suppress hepatocellular carcinoma xenograft growth in nude mice

We sought to investigate the effects of epirubicin-nanogold compounds （EPI-AuNP） on hepatocellular carcinoma xenograft growth in nude mice. EPI-AuNP was prepared and hepatoma xenograft model was established in nude mice. The mice were then randomly divided into four groups： the control group with injection of saline, the AuNP treatment group, the EPI treatment group and the EPI-AuNP treatment group. After two weeks, the hepatoma weight and volume of the xenografts were assessed. Our transmission electron microscopy revealed that epirubicin- gold nanoparticles caused significantly more structural changes of hepatocellular carcinoma cells HepG2. The tumor weight in the Epi-AuNP treatment group （0.80 ± 0.11 g） was significantly lower than that of the control group （2.48±0.15 g）, the AuNP treatment group （1.67±0.17 g）, and the EPI treatment group （1.39±0.10 g） （P〈0.01）. Furthermore, the tumor volume of mice in the EPI-AuNP treatment group （0.27 ± 0.06 cm3） was significantly smal- ler than that of the control group （2.23 ± 0.34 cm3）, the AuNP treatment group （1.21 ± 0.25 cm3） and the EPI treat- ment group （0.81 ± 0.11 cm3） （P〈0.01）. In conclusion, epirubicin-nanogold compounds （EPI-AuNP） have significant inhibitory effects on the growth of hepatocellular carcinoma cells in vivo.

Selective substitution induced anomalous phonon stiffening within quasi-one-dimensional P–P chains in SiP2

Light-matter interactions in low-dimensional quantum-confined structures can dominate the optical properties of the materials and lead to optoelectronic applications.In anisotropic layered silicon diphosphide(SiP2)crystal,the embedded quasi-onedimensional(1D)phosphorus–phosphorus(P–P)chains directly result in an unconventional quasi-1D excitonic state,and a special phonon mode vibrating along the P–P chains,establishing a unique 1D quantum-confined system.Alloying SiP2 with the homologous element serves as an effective way to study the properties of these excitons and phonons associated with the quasi-1D P–P chains,as well as the strong interaction between these quasiparticles.However,the experimental observation and the related optical spectral understanding of SiP2 with isoelectronic dopants remain elusive.Herein,with the photoluminescence and Raman spectroscopy measurements,we demonstrate the redshift of the confined excitonic peak and the stiffening of the phonon vibration mode■of a series of Si(P1−xAsx)2 alloys with increasing arsenic(As)compositions.This anomalous stiffening of■is attributed to the selective substitution of As atoms for P atoms within the P–P chains,which is confirmed via our scanning transmission electron microscopy investigation.Such optical spectra evolutions with selective substitution pave a new way to understand the 1D quantum confinement in semiconductors,offering opportunities to explore quasi-1D characteristics in SiP2 and the resulting photonic device application.

Physics through the microscope

The electron microscope provides numerous insights into physics, from demonstrations of fundamental quantummechanical principles to the physics of imaging and materials. It reveals the atomic and electronic structure of key regionssuch as defects and interfaces. We can learn the underlying physics governing properties, and gain insight into how tosynthesize new materials with improved properties. Some recent advances and possible future directions are discussed.

A machine perspective of atomic defects in scanning transmission electron microscopy

Enabled by the advances in aberration-corrected scanning transmission electron microscopy(STEM),atomic-resolution real space imaging of materials has allowed a direct structure-property investigation.Traditional ways of quantitative data analysis suffer from low yield and poor accuracy.New ideas in the field of computer vision and machine learning have provided more momentum to harness the wealth of big data and sophisticated information in STEM data analytics,which has transformed STEM from a localized characterization technique to a macroscopic tool with intelligence.In this review article,we discuss the prime significance of defect topology and density in two-dimensional(2D)materials,which have proved to be a powerful means to tune a wide range of properties.Subsequently,we systematically review advanced data analysis methods that have demonstrated promising prospects in analyzing STEM data,particularly for identifying structural defects,with high throughput and veracity.A unified framework for atomic structure identification is also summarized.

Space-confined microwave synthesis of ternary-layered BiOCl crystals with high-performance ultraviolet photodetection

In recent years,two-dimensional(2D)ternary materials have attracted wide attention due to their novel properties which can be achieved by regulating their chemical composition with a very great degree of freedom and adjustable space.However,as for the precise synthesis of 2D ternary materials,great challenges still lie ahead that hinder their further development.In this work,we demonstrated a simple and reliable approach to synthesize 2D ternary-layered BiOCl crystals through a microwave-assisted space-confined process in a short time(<3 minutes).Their ultraviolet(UV)detection performance was analyzed systematically.The photodetectors based on the as-obtained BiOCl platelets demonstrate high sensitivity to 266-nm laser illumination.The responsivity is calculated to be8 A/W and the response time is up to be18 ps.On the other hand,the device is quite stable after being exposed in the ambient air within 3 weeks and the response is almost unchanged during the measurement.The facile and fast synthesis of single crystalline BiOCl platelets and its high sensitivity to UV light irradiation indicate the potential optoelectronic applications of 2D BiOCl photodetectors.