Effects of vacancy defects on the magnetic properties of vanadium diselenide monolayers: a first principle investigation.

Long-range ferromagnetic (FM) order in vanadium diselenide (VSe2) monolayers (MLs) remains a controversial subject. In this theoretical study, we examined the effect of vacancy defects on the magnetic properties of octahedrally coordinated 1T-VSe2 MLs using spin-polarized density functional theory (DFT). In total, 45 different kinds of defects with various concentrations were introduced, including two single vacancies (S), 27 double vacancies (D), nine triple vacancies (T), and seven quadruple vacancies (Q). To understand the magnetic properties, SSe, DSe-(10), TSe-(10)(10), and QSe-(21)(10)(10) were selected to be analyzed because they had low formation energies and large variations in magnetic moments (M). Compared with the perfect VSe2 ML, the values of the M of vanadium (V) decreased from 0.675 to 0.466, 0.183, 0.213, and 0.208 µB with increasing vacancy concentration. The same trend was also found for the energy differences between FM and antiferromagnetic (AFM) ordering. These results generally indicated weaker FM coupling and a lower Curie temperature in defective VSe2. Vacancy-induced lattice distortion, d orbital shifting, electronic occupation, and spin density redistribution were discussed in order to explain the above observations. Our investigation demonstrated a strong dependence of M and the magnetic interaction of VSe2 on the concentration and types of Se vacancies, which would explain the uncertainties encountered in magnetic experiments.

Isolation, purification, and structural elucidation of Stropharia rugosoannulata polysaccharides with hypolipidemic effect.

Stropharia rugosoannulata is a widely grown edible mushroom with a high nutritional value. S. rugosoannulata polysaccharides is one of the most important bioactive components of S. rugosoannulata and has a wide range of activities. A S. rugosoannulata polysaccharides, named SRF-3, was derived from the S. rugosoannulata extraction by freeze-thaw combine with hot water extraction method, then prepareed with DEAE-cellulose column and Sephacryl S-200 HR gel column, and its hypolipidemic activity was determined. The structural characteristics of SRF-3 were analyzed by infrared spectral scanning (FT-IR), ultra-high performance liquid chromatography (UHPLC), acid hydrolysis, methylation analysis, nuclear magnetic resonance (NMR), and Gas Chromatography-Mass Spectrometer (GC-MS). SRF-3 is composed of mannose, galactose, methyl galactose and fructose with ratios of 16, 12, 58 and 12, respectively. In addition, the average relative molecular mass of SRF-3 is approximately 24 kDa. The main chain of SRF-3 is mainly composed of repeating α-D-1,6-Galp and α-D-1,6-Me-Galp units, with branches in the O-2 position of Gal. The structure is presumed to be a mannogalactan, with a small amount of t-ß-D-Manp present as a side chain. Hypolipidemic activity assay showed that SRF-3 had good antioxidant and hypolipidemic effects in vitro, suggesting that SRF-3 have potential application in reducing liver fat accumulation.

Current trends in smart mesoporous silica-based nanovehicles for photoactivated cancer therapy.

Photoactivated therapeutic strategies (photothermal therapy and photodynamic therapy), due to the adjusted therapeutic area, time and light dosage, have prevailed for the fight against tumors. Currently, the monotherapy with limited treatment effect and undesired side effects is gradually replaced by multimodal and multifunctional nanosystems. Mesoporous silica nanoparticles (MSNs) with unique physicochemical advantages, such as huge specific surface area, controllable pore size and morphology, functionalized modification, satisfying biocompatibility and biodegradability, are considered as promising candidates for multimodal photoactivated cancer therapy. Excitingly, the innovative nanoplatforms based on the mesoporous silica nanoparticles provide more and more effective treatment strategies and display excellent antitumor potential. Given the rapid development of antitumor strategies based on MSNs, this review summarizes the current progress in MSNs-based photoactivated cancer therapy, mainly consists of (1) photothermal therapy-related theranostics; (2) photodynamic therapy-related theranostics; (3) multimodal synergistic therapy, such as chemo-photothermal-photodynamic therapy, phototherapy-immunotherapy and phototherapy-radio therapy. Based on the limited penetration of irradiation light in photoactivated therapy, the challenges faced by deep-seated tumor therapy are fully discussed, and future clinical translation of MSNs-based photoactivated cancer therapy are highlighted.

Ab initioanalytic calculation of point defects in AlGaN/GaN heterointerfaces.

One of the major challenges for the GaN-based high-electron-mobility transistors (HEMTs) used as high power devices is to understand the effect of defects, especially on the band alignment. Usingab initiocalculation, herein we investigate the variations of band offsets with interfacial structure, defect position, interface states and Al content in AlxGa1-xN/GaN heterostructures (x= 0.06, 0.13, 0.19, 0.25). It was found that N vacancy (VN) and Ga anti-site (GaN) introduce nonlocal interface states and the change of valence band offset (VBO) depends on the defect location. While the interface states induced by Ga vacancy (VGa) and N anti-site (NGa) show strong localization behavior, and their impact on VBO is independent on the defect position. The low symmetry of wurtzite nitride and the lattice mismatch between AlGaN and GaN will generate polarization charge (spontaneous polarization and piezoelectric polarization) at the interface. Along the direction of polarization field, VNand GaNlying in the AlGaN side change the VBO most pronouncedly. These theoretical results provide useful guidance for control of point defects in AlGaN/GaN HEMTs, which have profound impact on the performance and reliability of GaN-based devices.

Two-Dimensional Metallic NiTe2 with Ultrahigh Environmental Stability, Conductivity, and Electrocatalytic Activity.

Two-dimensional (2D) metallic transition metal dichalcogenides (MTMDCs) supply a versatile platform for investigating newfangled physical issues and developing potential applications in electronics/spintronics/electrocatalysis. Among these, NiTe2 (a type-II Dirac semimetal) possesses a Dirac point near its Fermi level. However, as-prepared 2D MTMDCs are mostly environmentally unstable, and little attention has been paid to synthesizing such materials. Herein, a general chemical vapor deposition (CVD) approach has been designed to prepare thickness-tunable and large-domain (∼1.5 mm) 1T-NiTe2 on an atomically flat mica substrate. Significantly, ultrahigh conductivity (∼1.15 × 106 S m-1) of CVD-synthesized 1T-NiTe2 and high catalytic activity in pH-universal hydrogen evolution reaction have been uncovered. More interestingly, the 2D 1T-NiTe2 maintains robust environmental stability for more than one year and even after a variety of harsh treatments. These results hereby fill an existing research gap in synthesizing environmentally stable 2D MTMDCs, making fundamental progress in developing 2D MTMDC-based devices/catalysts.

Giant Thickness-Tunable Bandgap and Robust Air Stability of 2D Palladium Diselenide.

Uncovering the thickness-dependent electronic property and environmental stability for 2D materials are crucial issues for promoting their applications in high-performance electronic and optoelectronic devices. Herein, the extrahigh air stability and giant tunable electronic bandgap of chemical vapor deposition (CVD)-derived few-layer PdSe2 on Au foils, by using scanning tunneling microscope/spectroscopy (STM/STS), are reported. The robust stability of 2D PdSe2 is uncovered by the observation of nearly defect/adsorption-free atomic lattices on long-time air-exposed samples. A one-to-one correspondence between the electronic bandgap (from ≈1.15 to ≈0 eV) and thickness of PdSe2 /Au (from bilayer to bulk) is established. It is also revealed that few-layer semiconducting PdSe2 flakes present zero-gap edges, induced by hybridization of Pd 4d and Se 4p orbitals. This work hereby provides straightforward evidence for the thickness-tunable electronic property and air stability of 2D semiconductors, thus shedding light on their applications in next-generation electronic devices.