Insulator-to-metal transition in the black diamond from molecular-dynamics-Landauer method.

The critical condition and mechanism of the insulator-to-metal transition (IMT) for the black diamond were studied by the molecular-dynamics-Landauer method. The IMT will occur at sufficiently high contents of vacancies in the diamond. The critical concentration of vacancies for the IMT might be between V:C143 (0.69%) and V:C127 (0.78%). At a low concentration of vacancies (below 0.69%), the intermediate band (IB) consists of a filled band and a separate empty band, which makes the material to be an insulator. The IMT of the black diamond is due to the mergence between the two isolated IBs when the concentration of vacancies is high, and the merged IB is partially filled by electrons. The distribution of vacancies also influences the IMT of the black diamond.

Quantum dots as advanced nanomaterials for food quality and safety applications: A comprehensive review and future perspectives.

The importance of food quality and safety lies in ensuring the best product quality to meet consumer demands and public health. Advanced technologies play a crucial role in minimizing the risk of foodborne illnesses, contamination, drug residue, and other potential hazards in food. Significant materials and technological advancements have been made throughout the food supply chain. Among them, quantum dots (QDs), as a class of advanced nanomaterials with unique physicochemical properties, are progressively demonstrating their value in the field of food quality and safety. This review aims to explore cutting-edge research on the different applications of QDs in food quality and safety, including encapsulation of bioactive compounds, detection of food analytes, food preservation and packaging, and intelligent food freshness indicators. Moreover, the modification strategies and potential toxicities of diverse QDs are outlined, which can affect performance and hinder applications in the food industry. The findings suggested that QDs are mainly used in analyte detection and active/intelligent food packaging. Various food analytes can be detected using QD-based sensors, including heavy metal ions, pesticides, antibiotics, microorganisms, additives, and functional components. Moreover, QD incorporation aided in improving the antibacterial and antioxidant activities of film/coatings, resulting in extended shelf life for packaged food. Finally, the perspectives and critical challenges for the productivity, toxicity, and practical application of QDs are also summarized. By consolidating these essential aspects into this review, the way for developing high-performance QD-based nanomaterials is presented for researchers and food technologists to better capitalize upon this technology in food applications.

Computational design of a reliable intermediate-band photovoltaic absorber based on diamond.

To reduce the wide bandgap of diamond and expand its applications in the photovoltaic fields, a diamond-based intermediate-band (IB) material C-Ge-V alloy was designed by first-principles calculations. By replacing some C with Ge and V in the diamond, the wide bandgap of the diamond can be reduced sharply and a reliable IB, which is mainly formed by the d states of V, can be formed in the bandgap. With the increase of Ge content, the total bandgap of the C-Ge-V alloy will be reduced and close to the optimal value of an IB material. At a relatively low atomic concentration of Ge (below 6.25%), the IB formed in the bandgap is partially filled and varies little with the concentration of Ge. When further increasing the content of Ge, the IB moves close to the conduction band and the electron filling in the IB increases. The 18.75% content of Ge might be the limitation to form an IB material, and the optimal content of Ge should be between 12.5% and 18.75%. Compared with the content of Ge, the distribution of Ge has a minor effect on the band structure of the material. The C-Ge-V alloy shows strong absorption for the sub-bandgap energy photons, and the absorption band generates a red-shift with the increase of Ge. This work will further expand the applications of diamond and be helpful to develop an appropriate IB material.

Dynamic modulation of a surface-enhanced Raman scattering signal by a varying magnetic field.

Surface-enhanced Raman scattering (SERS) signals are fundamental for spectroscopy applications. However, existing substrates cannot perform a dynamically enhanced modulation of SERS signals. Herein, we developed a magnetically photonic chain-loading system (MPCLS) substrate by loading magnetically photonic nanochains of Fe3O4@SiO2 magnetic nanoparticles (MNPs) with Au nanoparticles (NPs). We achieved a dynamically enhanced modulation by applying an external stepwise magnetic field to the randomly dispersed magnetic photonic nanochains that gradually align in the analyte solution. The closely aligned nanochains create a higher number of hot spots by new neighboring Au NPs. Each chain represents a single SERS enhancement unit with both a surface plasmon resonance (SPR) effect and photonic property. The magnetic responsivity of MPCLS enables a rapid signal enhancement and tuning of the SERS enhancement factor.

Brillouin gain spectrum characterization in an acoustic anti-guided delivery fiber for high power narrow linewidth laser.

The Brillouin gain spectrum (BGS) provides key information for stimulated Brillouin scattering (SBS), such as the Brillouin frequency shift (BFS), Brillouin spontaneous linewidth, and Brillouin gain coefficient. In this study, we theoretically investigate the field distributions and BGS characterization of Ge-doped, Al-doped, and Al/Ge co-doped fibers. Additionally, we analyzed and compared the relationship between the BGS and acoustic refractive index. In particular, we demonstrate the crucial role played by acoustic modes in anti-waveguide structures. The simulation results show that the Brillouin gain coefficient decreases with a decreasing acoustic index in the fiber core region. Furthermore, we experimentally measure the SBS threshold and BGS of the Al/Ge co-doped fiber to examine the validity of the numerical model. The simulated and experimental results are consistent.

Synthesis and modification mechanism of vanadium oxide coated LiFePO4cathode materials with excellent electrochemical performance.

In an era of rapid industrial development, such that the demand for energy is increasing daily, lithium-ion batteries are playing a dominant role in energy storage devices due to their high safety and low cost. However, it is still a challenge for the preparation of advanced cathodes, which can determine the battery performance, with stable structures and fast diffusion of Li+. This is especially the case for lithium iron phosphate (LFP), a cathode material with severe limitations due to its low conductive efficiency. To improve its conductivity, LFP was compounded with defect-modified V2O5to prepare LFP/V/C materials with excellent electrochemical properties, which exhibited an initial capacity of 138.85 mAh g-1and 95% retention after 500 charge/discharge cycles at a current density of 5 C. Also, the effect of defects on ionic diffusion was discussed in detail by means of density function theor (DFT) calculations, confirming that the improvement of electrochemical performance is closely related to the introduction of hybrid conductive layers of surface cladding.

A robust colorimetric aptasensor for the label-free detection of marine toxins based on tyrosine-capped gold nanoparticles.

PbTx-2 and okadaic acid (OA) are two typical marine toxins that are highly toxic and harmful to human health. The approach based on citrate-capped gold nanoparticles (Cit-AuNPs) and specific aptamers to construct label-free colorimetric sensors is a widely used method for marine toxin detection. However, the potential interactions between Cit-AuNPs and target molecules have always been ignored, which may result in wrong analytical results due to shortcomings in the Cit-AuNPs. To overcome these shortfalls, in this work, AuNPs were synthesized using tyrosine as a reducing and capping agent, and a robust colorimetric aptasensor based on tyrosine-capped AuNPs (Tyr-AuNPs) was constructed for the label-free detection of marine toxins. Tyr-AuNPs presented better stability compared to Cit-AuNPs due to the stronger binding of amine groups on tyrosine to AuNPs through the Au-N bond. Interactions between Tyr-AuNPs and PbTx-2 were analyzed through UV-vis and isothermal titration calorimetry methods and the results validated the robustness of the Tyr-AuNPs. Colorimetric aptasensors were established for PbTx-2 and OA detection with a linear range of 0.05-4 ppm and limits of detection of 2.25 ppb and 5.19 ppb, respectively. These results demonstrate that the developed colorimetric aptasensor can be a robust and promising method for marine toxin detection.

Gas adsorption effects of monolayer GeSe in terms of anisotropic transport properties.

Two-dimensional layered semiconducting material germanium selenide (GeSe) has attracted significant attention due to its environmental friendship, anisotropic electronic structures, and strong air-stability. To evaluate the candidacy of monolayer GeSe as a potential gas sensing material, the adsorption characteristics of various small gas molecules on monolayer GeSe are comprehensively studied combining density functional theory calculations and non-equilibrium Green's function formalism. The charge transfer reaction between gas molecules and monolayer GeSe leads to the marked change of the carrier density, which further affects the anisotropic transport characteristics of monolayer GeSe. The calculated band structures andI-Vcurves reveal distinctive responses of monolayer GeSe to the different gas molecules, and higher sensitivity of the monolayer GeSe in presence of SO2, NH3, NO2gas molecules along the zigzag direction is obtained. These results suggest that monolayer GeSe along the zigzag direction has promising application in gas detector.

Effects of p-d orbital mixings on magnetocrystalline anisotropy for D3d-symmetric ferromagnetic semiconducting monolayers.

Understanding magnetic anisotropy based on electronic properties is vital for theoretical and applied research on ferromagnetic semiconductors. Here, for several representative D3d-symmetric ferromagnetic semiconducting monolayers, we investigate the effects of mixings between d-orbitals of central magnetic atoms and p-orbitals of ligands on magnetocrystalline anisotropy energy (MAE). For high-spin materials, the weakening of p-d mixing increases the electron occupation of spin-up bonding d-orbitals at the expense of the electron occupation in the corresponding spin-down orbitals, In contrast, the weakening of p-d mixing decreases the electron occupation of the spin-up antibonding d-orbitals and enhances the electron occupation in the corresponding spin-down orbitals. The weakening mixings also result in an overall shift of the spin-down band toward a higher energy with respect to the spin-up band. These changes are just the opposite in a low-spin material. More interestingly, we find that the transition point between the bonding and the antibonding spin-up bands plays a significant role in tuning the MAE. Its shift with strain is almost linearly related to the p-d bond strength and significantly affects both the electron occupation of occupied spin-up antibonding d-bands and the band shift of unoccupied spin-up d-bands. Furthermore, the correlation of these mixing-related changes in electronic structures with the MAE is qualitatively and quantitatively analyzed. Our findings can deepen the understanding of the correlation between MAE and p-d orbital mixings and provide theoretical guidance for modulating the MAE.

Steady semiconducting properties of monolayer PtSe2 with non-metal atom and transition metal atom doping.

Based on density functional theory, the electronic structure and magnetic properties of monolayer PtSe2 doped with different atoms were studied. The Pt and Se atoms are replaced by a transition metal atom (Mn) and a non-metal atom X (X = N, P, As), respectively. The pristine monolayer PtSe2 is a semiconductor with an indirect band gap of 1.352 eV. For one non-metal atom doping, the doped system exhibits indirect band gap magnetic semiconducting properties and the magnetic moment is less than 1 µB and mainly comes from the hybridization of Pt-5d and X-p orbitals. The N-Doped system still retains the magnetic semiconducting properties under strain (from -10% to 13%) and the band gap varies from 0.059 eV to 1.308 eV. For two X doped systems, three different configurations are considered. The doped systems retain the indirect band gap semiconducting properties except for the third nearest neighbor N-doped system (direct band gap). But, for all N-doped and the second nearest neighbor P-doped systems, the magnetic moment increases to more than double. Meanwhile, all X-doped monolayer PtSe2 systems exhibit p-type semiconducting characteristics. For (Mn, X) co-doped systems, the magnetic moments are mainly localized in the Mn 3d orbital and there is strong p-d hybridization between Mn atoms and X atoms. The (Mn, N/P) co-doped system still exhibits magnetic semiconducting properties. These results are important for designing semiconductor devices and electronic spin devices based on monolayer PtSe2.

Micro-joule level visible supercontinuum generation in seven-core photonic crystal fibers pumped by a 515 nm laser.

A visible supercontinuum (SC) with high energy is of vital importance to applications in remote sensing and hyperspectral light detection and ranging. A fiber laser with a wavelength of 1030 nm is frequency doubled through a LBO (LiB3O5) crystal, and a high-energy 515 nm laser is obtained after wavelength conversion. Two kinds of seven-core photonic crystal fibers (PCFs) are used in this Letter. One is a uniform seven-core PCF (USC-PCF), and the other is a tapered seven-core PCF (TSC-PCF). Pumped by a 515 nm laser with a pulse width in nanosecond level, an SC covering 400 to 900 nm is efficiently generated in both PCFs. A maximum energy of 4.24 µJ is obtained in a USC-PCF. To prevent fiber damage of the coupling fiber end, the TSC-PCF which contains a transition fiber and a meters-long small core fiber is fabricated. One end of the transition fiber possesses a larger core diameter, and the pump laser can be coupled into the TSC-PCF without fiber damage. The meters-long small core fiber has the same core size with a USC-PCF and is utilized as the nonlinear medium to generate an SC. The dispersive wave in the short wavelength band is excited when more energy is shed into a fiber anomalous dispersion region. Up to 15th-order Raman peaks are observed during the SC evolution process.

Citrus aurantium L. var. amara Engl. inhibited lipid accumulation in 3T3-L1 cells and Caenorhabditis elegans and prevented obesity in high-fat diet-fed mice.

Natural products with anti-obesity effects and few side effects have attracted great attention recently. Citrus aurantium L. var. amara Engl. (CAVA) is popularly consumed as an edible and medicinal resource in China. However, its anti-obesity effects were poorly understood. The anti-obesity effects of CAVA extracts were systematically evaluated using 3T3-L1 cells, Caenorhabditis elegans (C. elegans) and high fat diet (HFD)-fed mice. Flavonoid-rich (EA) extracts with neohesperidin, hesperidin and naringin comprising 32.15%, were isolated from CAVA. EA extracts treatment significantly inhibited differentiation of 3T3-L1 preadipocytes by modulating lipid metabolism-related mediators. EA extracts supplementation also inhibited antioxidant responses in C. elegans by decreasing reactive oxygen species generation and malonaldehyde value, and increasing superoxide dismutase content. EA extracts feeding markedly decreased triglyceride (TG) content, and affected expression of genes involved in lipid and glucose metabolism in wild type C. elegans. TG content in mdt-15 (XA7702) mutants was not decreased by EA extracts administration, suggesting that EA extracts treatment might inhibit lipid accumulation in C. elegans dependent on mdt-15. EA extracts intervention further reduced body weight gain and modulated plasma biochemical parameters in HFD-fed mice. EA extracts treatment prevented HFD-induced epididymal adipose hypertrophy, liver oxidative injuries and steatosis. EA extracts administration also strongly prevented HFD-induced reduction of gut microbial diversity, decreased the Firmicutes-to-Bacteroidetes ratio and the Erysipelotrichaceae abundance, and enhanced the Bifidobacteriace abundance in HFD-fed mice. EA extracts from blossoms of CAVA were excellent antiobesogenic candidates that acted through multiple mechanisms that acted simultaneously.

Band structure engineering of SnS2/polyphenylene van der Waals heterostructure via interlayer distance and electric field.

Constructing a van der Waals heterostructure (vdWH) by stacking different two-dimensional (2D) materials has been considered to be an effective strategy to obtain the desired properties. Here, based on first-principle methods, we systematically explored the electronic structures of 2D SnS2/polyphenylene vdWH. The theoretical results predicted that vdWH exhibited type-II band alignment, which realized effective separation of carriers. The band gap values could be tuned effectively by interlayer coupling effects. Moreover, the vertical electric field not only modulated the band gap, but also transformed the type-II band alignment to type-I or type-III band alignment, realizing multi-functional device applications. Thus, these predicted results reveal the possibility of realizing next-generation electronic applications for 2D SnS2/polyphenylene-based materials.

Modulation of the electronic properties and spin polarization of 2H VS2 nanoribbons by tuning ribbon widths and edge decoration.

The band structures and spin-polarization characteristics of armchair and zigzag VS2 nanoribbons with different terminated edges are investigated based on density functional theory (DFT) calculations with a spin polarized meta-GGA. The results reveal that zigzag 2H VS2 nanoribbons exhibit metal, half-metal, or semiconductor electrical characteristics with different edge decorations or ribbon widths. And the spin polarized ratio can achieve 100% self-polarization for the zigzag VS2 nanoribbons with V atom edges. The Curie temperatures (TC) estimated by mean field approximation simulations for the zigzag 2H VS2 nanoribbons with terminated edges of V systems are 276 K. These preliminary findings offer an effective treatment option for controllable and adjustable spintronic devices.

Type-I Transition Metal Dichalcogenides Lateral Homojunctions: Layer Thickness and External Electric Field Effects.

Transition metal dichalcogenide (TMD) heterostructures have been widely explored due to the formation of type-II band alignment and interlayer exciton. However, the studies of type-I TMD heterostructures are still lacking, which limit their applications in luminescence devices. Here, the 1L/nL MX2 (n = 2, 3, 4; M = Mo, W; X = S, Se) lateral homojunction based on the layer-dependent band gaps of TMD nanosheets is theoretically simulated. The studies show that the TMD homojunction presents with high thermal stability and type-I band alignment. The band offset and quantum confinement of carriers can be easily tuned by controlling the thickness of the multilayer region. Moreover, the electric field can decrease the band gaps of 1L/3L and 1L/4L homojunctions linearly. Interestingly, for the 1L/2L MX2 homojunction, the gap value is robust to the weak electric field, while it drops sharply under a strong electric field. This study sheds light on the physical pictures in the TMD lateral homojunction, and provides a practicable and general approach to engineer a type-I homojunction based 2D semiconductor materials.

Single/dual-wavelength switchable bidirectional Q-switched all-fiber laser using a bidirectional fiber polarizer.

A single/dual-wavelength switchable bidirectional Q-switched fiber laser using a bidirectional fiber polarizer is demonstrated. A 45° tilted fiber grating is used as a bidirectional fiber polarizer to induce a bidirectional intracavity birefringence filter in both clockwise (CW) and counter-clockwise (CCW) directions. A carbon nanotube saturable absorber is employed to produce Q-switched pulses. Through adjusting polarization states, switchable single/dual-wavelength lasing at 1551 and 1560 nm can be achieved in both CW and CCW directions. To the best of our knowledge, this is the first demonstration of a wavelength switchable bidirectional passively Q-switched fiber laser.

PtSe2/graphene hetero-multilayer: gate-tunable Schottky barrier height and contact type.

Graphene-based two-dimensional hybrid materials are attracting significant attention because they can preserve novel characteristics of Dirac cone. Here, based on first-principles methods, we focus on the electronic characteristics of PtSe2/graphene hetero-multilayer. The negative binding energies indicate that the hybrid materials can be fabricated easily in practice. Also, the n-type Schottky contact is formed and its barrier height is robust to the number of graphene layer. Moreover, the gate-voltage can effectively induce the Schottky barrier transformation from n-type to p-type and contact type transformation from Schottky to Ohmic in the PtSe2/graphene hetero-multilayer. Thus, the work demonstrates that the graphene stacking configuration and gate-voltage will tune the electronic characteristics of PtSe2/graphene-based nanodevices.

How does the electric current propagate through fully-hydrogenated borophene?

We study the electronic transport properties of two-dimensional (2D) fully-hydrogenated borophene (namely, borophane), using density functional theory and non-equilibrium Green's function approaches. Borophane shows a perfect electrical transport anisotropy and is promising for applications. Along the peak- or equivalently the valley-parallel direction, 2D borophane exhibits a metallic characteristic and its current-voltage (I-V) curve shows a linear behavior, corresponding to the ON state in borophane-based nano-switches. In this case, electrons mainly propagate via the B-B bonds along the linear boron chains. In contrast, electron transmission is almost forbidden along the perpendicular buckled direction (i.e., the OFF state), due to its semi-conductor property. Our work demonstrates that 2D borophane could combine metal and semiconductor features and may be a promising candidate for nano-switching materials with a stable structure and high ON/OFF ratio.

Stable passively Q-switched erbium-doped fiber laser incorporating a PbS quantum dots polystyrene composite film based saturable absorber.

We demonstrated a passively Q-switched erbium-doped fiber laser (EDFL) using PbS quantum dots in polystyrene films (QDPFs) as saturable absorbers (SAs). Compared to other SAs, PbS QDPFs have advantages of broad absorption range, high quantum yield, low cost, and facile preparation. We have successfully generated stable Q-switched pulses with an average output power of 40.19 mW, a single pulse energy of 586.1 nJ, a repetition rate of 68.04 kHz, a pulse width of 3.9 µs, and a signal-to-noise ratio of 50.5 dB under 660 mW pump power. The output of the EDFL has been monitored for 5 consecutive hours under laboratory conditions to show stable operation of the laser system.

Effect of Low Molecular Weight Oligopeptides Isolated from Sea Cucumber on Diabetic Wound Healing in db/db Mice.

Impaired wound healing is a major clinical problem in patients with diabetes and is the leading cause of lower limb amputation. This study is aimed to observe the effects of small molecule oligopeptides isolated from sea cucumber (SCCOPs) on the wound healing process in diabetic mice. Ninety db/db male mice were divided into five groups, including the model control group, whey protein group (0.50 g/kg) and three SCCOPs dose groups (0.25 g/kg, 0.50 g/kg and 1.00 g/kg). Additionally, 18 db/m male mice were used as normal control group. After full-thickness incisions on the dorsum, mice in SCCOPs-treated groups were intragastrically administered SCCOPs, while others were administered vehicle or whey protein. Mice were sacrificed on days 4, 7 and 14. The wound healing condition, inflammatory response, angiogenesis, collagen deposition, oxidative stress and nutritional status were evaluated. A pathological report showed increased vascularisation, collagen deposition and epithelialisation in SCCOPs-treated groups. SCCOPs-treated mice showed decreased C-reactive protein (CRP), interleukin (IL)-6, IL-8, tumor necrosis factor (TNF)-α, chemokine (C-C motif) ligand 2 (CCL2) and reactive oxygen species (ROS) contents, and increased IL-10, stromal cell-derived factor-1 alpha (SDF-1α), nitric oxide (NO), albumin (ALB), prealbumin (PA) and transferrin (TRF) levels and vascular endothelial growth factor (VEGF) expression. All parameters were significant (p < 0.05) in comparison to model control group. These results suggest that treatment with SCCOPs can promote significant wound healing in diabetic mice.