Rational design of a two-dimensional high-temperature ferromagnet from HCP cobalt.

Cobalt has the highest Curie temperature (Tc) among the elemental ferromagnetic metals and has a hexagonal close-packed (HCP) structure at room temperature. In this study, HCP Co was thinned to the thickness of several (n) unit cells along the c-axis and then passivated by halogen atoms, thus being named Co2nX2 (X = F, Cl, Br and I). For Co2X2 and Co3X2, all of them are not only kinetically but also thermodynamically stable from the viewpoint of the phonon spectra and molecular dynamics. Similar to HCP Co, two-dimensional (2D) Co2F2, Co2Cl2 and Co3X2 (X = Cl, Br and I) are still ferromagnetic metals within the Stoner model but Co2X2 (X = Br and I) is a ferromagnetic half-metal with the coexistence of the metallic behavior for one spin and the insulating behavior for the other spin. Taking into account the spin-orbital coupling (SOC), the easy-magnetization axis is within the plane where the magnetization is isotropic, making it look like a 2D XY magnet. Applying a critical biaxial strain could lead to an easy-magnetization axis changing from the in-plane to the out-of-plane direction. Finally, we use classical Monte Carlo simulations to estimate the Curie temperature (Tc) which is as high as 957 and 510 K for Co2F2 and Co2Cl2, respectively, because of the strong direct exchange interaction. Different from being obtained by mechanical or liquid exfoliation from van der Waals layered structures, our study opens up new possibilities to search for novel 2D ferromagnets from the elemental ferromagnets and provides opportunities for realizing realistic ultra-thin spintronic devices.

Combining multivariate statistical analysis to characterize changes in amino acids and volatiles during growth of Lou onion pseudostems.

BACKGROUND: The main edible part of the Lou onion is the pseudostem, which is highly valued for its distinctive flavour. However, harvesting decisions for the pseudostem are often based on size and market price, with little consideration given to flavour. By clarifying the growth of flavour in pseudostems, farmers and consumers may benefit from evidence-based insights that help optimize harvesting time and maximize flavour quality. RESULTS: This study employed amino acid analysis and gas chromatography-ion migration spectroscopy (GC-IMS) to elucidate the compounds of the pseudostem across different growth phases, and 17 amino acids and 61 volatile substances. Subsequently, analysis revealed that 18 compounds, including arginine (Arg), aspartic acid (Asp), glutamic acid (Glu), valine (Val), (E)-2-nonenal, decanal, 2,4-nonadienal, 2-octenal, (Z)-4-decenal, 2,4-decadienal benzeneacetaldehyde, linalool, eugenol, (Z)-6-nonen-1-ol, methyl anthranilate, 2-acetylpyridine, 3-sec-butyl-2-methoxypyrazine, and 2,6-dichlorophenol, were the key compounds in determining the flavour characteristics of the pseudostems, as assessed by taste activity value and relative odour activity value calculations. In addition, correlation analysis, focusing on five amino acids and 38 volatile compounds with variable importance for predictive components scores of >1, identified anisaldehyde, eugenol, (Z)-6-nonen-1-ol, 2,4-decadienal, 3-sec-butyl-2-methoxypyrazine, Arg, Asp, and Val as the key differentiators and contributors to the pseudostems flavour profile. CONCLUSION: During the rapid growth of Lou onions just before the emergence of flower stems, the pseudostem exhibited the most prominent flavour, making this stage most suitable for harvesting compared to the regreening growth stage and the rapid growth period of the aerial bulbs. © 2024 Society of Chemical Industry.

Strain-driven phase transition and spin polarization of Re-doped transition-metal dichalcogenides.

Two-dimensional transition metal dichalcogenides (TMDCs) are promising in spintronics due to their spin-orbit coupling, but their intrinsic non-magnetic properties limit their further development. Here, we focus on the energy landscapes of TMDC (MX2, M = Mo, W and X = S, Se, Te) monolayers by rhenium (Re) substitution doping under axial strains, which controllably drive 1H ↔ 1Td structural transformations. For both 1H and 1Td phases without strain, Re-doped TMDCs have an n-type character and are non-magnetic, but the tensile strain could effectively induce and modulate the magnetism. Specifically, 1H-Re0.5Mo0.5S2 gets a maximum magnetic moment of 0.69 µB at a 6% uniaxial tensile strain along the armchair direction; along the zigzag direction it exhibits a significant magnetic moment (0.49 µB) at a 2.04% uniaxial tensile strain but then exhibits no magnetism in the range of [5.10%, 7.14%]. By contrast, for 1Td-Re0.5Mo0.5S2 a critical uniaxial tensile strain along the zigzag direction reaches up to ∼9.18%, and a smaller uniaxial tensile strain (∼5.10%) along the zigzag direction is needed to induce the magnetism in 1Td-Re0.5M0.5Te2. The results reveal that the magnetism of Re-doped TMDCs could be effectively induced and modulated by the tensile strain, suggesting that strain engineering could have significant applications in doped TMDCs.

Temperature-dependent LITT effect in c axis inclined BiCuSeO thin films.

Light-induced transverse thermoelectric (LITT) effect in c axis inclined BiCuSeO thin films was investigated in the temperature range of 80-300 K by using three different lasers with the wavelength changing from visible to mid-IR. Obvious open-circuit voltage signals were all detected when the film surface was illuminated by these lasers, and the amplitude Vp of the induced voltage signals was found to increase with the measured temperature. The improvement of Vp at a higher temperature can be explained by the enhanced anisotropy of the Seebeck coefficient as well as the reduced thermal conductivity of the film. This work demonstrates the potential application of BiCuSeO thin film as a broadband light detector working at wide temperature ranges, including a very low temperature environment.

Variations of thermoelectric performance by electric fields in bilayer MX2 (M = W, Mo; X = S, Se).

A gate electrode is usually used to controllably tune the carrier concentrations, further modulating the electrical conductivity and the Seebeck coefficient to obtain the optimum thermoelectric figure of merit (ZT) in two-dimensional materials. On the other hand, it is necessary to investigate how an electric field induced by a gate voltage affects the electronic structures, further determining the thermoelectric properties. Therefore, by using density functional calculations in combination with Boltzmann theory, the thermoelectric properties of bilayer MX2 (M = W, Mo; X = S, Se) with or without a 1 V nm-1 perpendicular electric field are comparatively investigated. First of all, the variations of the electrical conductivity (σ), electron thermal conductivity and Seebeck coefficient (S) with the carrier concentration are studied. Due to the trade-off relationship between S and σ, there is an optimum concentration to obtain the maximum ZT, which increases with the temperature due to the enhancement of the Seebeck coefficient. Moreover, N-type bilayers have larger optimum ZTs than P-type bilayers. In addition, the electric field results in the increase of the Seebeck coefficient in low hole-doped MS2 bilayers and high hole-doped MSe2 bilayers, thus leading to similar variations in ZT. The optimum ZTs are reduced from 2.11 × 10-2, 3.19 × 10-2, 2.47 × 10-2, and 2.58 × 10-2 to 1.57 × 10-2, 1.51 × 10-2, 2.08 × 10-2, and 1.43 × 10-2 for the hole-doped MoS2, MoSe2, and WSe2 bilayers, respectively. For N-type bilayers, the electric field shows a destructive effect, resulting in the obvious reduction of the Seebeck coefficient in the MSe2 layers and the low electron-doped MS2 bilayers. In electron-doped bilayers, the optimum ZTs will decrease from 3.03 × 10-2, 6.64 × 10-2, and 6.69 × 10-2 to 2.81 × 10-2, 3.59 × 10-2, and 4.39 × 10-2 for the MoS2, MoSe2, and WSe2 bilayers, respectively.

Thermoelectric properties of fullerene-based junctions: a first-principles study.

This study is built on density functional calculations in combination with the non-equilibrium Green's function, and we probe the thermoelectric transport mechanisms through C60 molecules anchored to Al nano-electrodes in three different ways, such as, the planar, pyramidal, and asymmetric surfaces. When the electrode is switched from the planar and pyramidal surfaces, the electrical conductance (σ) and electron's thermal conductance (κel) decrease almost two orders of magnitude due to the reduction of the molecule-electrode contact coupling, whereas the Seebeck coefficients (S) are reduced by ∼55%. Furthermore, the maximum electron's thermoelectric figure of merit (ZelT = S2σT/κel, assuming a vanishing phonon's thermal conductance) is about 0.12 in the asymmetric junction. In particular, all σ, S, κel, and ZelT increase along with the average temperature (T) in all C60-junctions, although their growth is really quite negligible in the pyramidal junction because the Fermi level is far away from the frontier orbitals. In addition, when the strain increases from the compressive (-1.0 Å) to tensile (1.0 Å) strain, the Seebeck coefficient in the planar junction increases drastically, while the Seebeck coefficients in the asymmetric and pyramidal junctions reach their maximum values at 0.2 Å tensile and -0.4 Å compressive strains, respectively. This is because the Seebeck coefficient is inversely proportional to the magnitudes and proportional to the slopes of the transmission spectrum around the Fermi level. Finally, it is found that the shift of the Fermi level is an effective scheme to obtain the maximum ZelT of any molecular junction, including fullerene-based junctions.

Flatbands in 2D boroxine-linked covalent organic frameworks.

Density functional calculations have been performed to analyze the electronic and mechanical properties of a number of 2D boroxine-linked covalent organic frameworks (COFs), which are experimentally fabricated from di-borate aromatic molecules. Furthermore, the band structures are surprising and show flat-band characteristics which are mainly attributed to the delocalized π-conjugated electrons around the phenyl rings and can be better understood within aromaticity theories. Next, the effects of branch sizes and hydrostatic strains on their band structures are systematically considered within generalized gradient approximations. It is found that their band gaps will start to saturate when the branch size reaches 9. For boroxine-linked COFs with only one benzene ring in the branch, the band gap is robust under compressive strain while it decreases with the tensile strain increasing. When the branch size is equal or greater than 2, their band gaps will monotonously increase with the strain increasing in the range of [-1.0, 2.0] Å. All boroxine-linked COFs are semiconductors with controllable band gaps, depending on the branch length and the applied strain. In comparison with other 2D materials, such as graphene, hexagonal boron nitride, and even γ-graphyne, all boroxine-linked COFs are much softer and even more stable. That is, they can maintain the planar features under a larger compressive strain, which means that they are good candidates in flexible electronics.

Enhanced thermoelectric performance in CdO by nano-SiO2 inclusions.

We report enhanced thermoelectric (TE) performance in CdO by using thermally insulating nano-particles to mimic nano pores in the composite. Through simply mechanical alloying, we fabricated CdO-SiO2 composites with varying nano-SiO2 concentration from 0.1 to 3 at%. Due to the very low thermal conductivity of nano-SiO2 distributed in the CdO matrix, the thermal conductivity of the composite was substantially reduced by about 80%, which lead to the dimensionless figure of merit (ZT) value increment about 28% (from 0.32 to 0.41) at 1000 K. TEM shows the nano inclusions formed within the CdO matrix and grain boundaries as well, which is thought to contribute to the reduction of thermal conductivity of the composite by additional scattering mechanism for the mid- to long-wavelength phonons. This facile and low-cost approach might be widely adopted and synergized to other TE materials systems to further improve their performance.

Dependence of oxygen content on transverse thermoelectric effect in tilted Bi2Sr2Co2Oy thin films.

The transverse thermoelectric (TE) effect has been investigated in c axis tilted Bi2Sr2Co2Oy thin films with different oxygen content. The film samples were fabricated by a chemical solution deposition method annealed under different atmospheres of O2, air, and N2, respectively. Open-circuit transverse voltage signals were observed when the surface of the films was heated by a pulsed laser as well as a continuous thermal source. With the increase of oxygen content in the films, the amplitude of the observed voltage signals increased while the response time decreased. The experimental results can be explained by a mechanism involving the transverse TE effect as well as the transport theory of TE materials.

Effects of intravenous pulse methylprednisolone in neuromyelitis optica during the acute phase.

BACKGROUND: Neuromyelitis optica spectrum disorder (NMOSD) is an anti-aquaporin 4 (anti-AQP4) autoantibodies-mediated idiopathic inflammatory demyelinating disease of the central nervous system. While intravenous pulse methylprednisolone (IVMP) is the recommended initial treatment option for acute onset NMOSD, its therapeutic mechanism remains unclear. We hypothesized that IVMP would reduce the expression of pro-inflammatory factors and increase the resolution of inflammation in patients with NMOSD. METHODS: Mendelian randomization (MR) analysis was used to screen meaningful inflammatory and resolution factors for inclusion. Three MR methods with inverse variance weighting (IVW) were primarily used to identify positive results. Interleukin (IL)-10, IL-1ß, IL-6, C-X-C motif chemokine ligand 12 (CXCL12), and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) were screened from 41 inflammatory factors, and resolvin D1 (RvD1), maresin 1 (MaR1), and lipoxin A4 (LXA4) were screened from 6 resolution markers for inclusion. Subsequently, 12 patients with NMOSD were enrolled and treated with IVMP. Serum levels of the aforementioned inflammatory and resolution markers were measured by enzyme-linked immunosorbent assay before and after IVMP treatment. RESULTS: High levels of TRAIL, CXCL12, and IL-1ß were associated with an increased risk of NMOSD (TRAIL: odds ratio [OR], 1.582; 95% confidence interval [CI], 1.003-2.495; CXCL12: OR, 3.610; 95% CI, 1.011-12.889; IL-1ß: OR, 4.500; 95% CI, 1.129-17.927). High levels of RvD1, MaR1, and LXA4 were associated with a reduced risk of NMOSD (RvD1: OR, 0.725; 95% CI, 0.538-0.976; MaR1: OR, 0.985; 95% CI, 0.970-0.999; LXA4: OR, 0.849; 95% CI, 0.727-0.993). Among patients with NMOSD, serum levels of IL-6, CXCL12, and TRAIL significantly decreased following IVMP treatment, compared with pretreatment levels, while levels of IL-1ß, LXA4, and MaR1 significantly increased after IVMP treatment (p < 0.05). A significant positive correlation was observed between CXCL12 levels and Expanded Disability Status Scale (EDSS) scores (r = 0.451, p < 0.05). CONCLUSION: Several systemic inflammatory regulators associated with the pathogenesis of NMOSD were identified. The protective roles of LXA4 and MaR1 may be indispensable components of glucocorticoid treatment. Therefore, the use of resolution markers may be a potential strategy for improving central nervous system injury in individuals with NMOSD.

A bidirectional Mendelian randomization study investigating the relationship between genetically predicted systemic inflammatory regulators and chronic obstructive pulmonary disease.

Research has shown a connection between inflammation and chronic obstructive pulmonary disease (COPD), however the relationship between inflammation mediators and COPD causation remains unknown. To investigate the causal relationship of mediators of inflammation and COPD, we conducted a two-sample Mendelian randomization (MR) study. In our study, we incorporated 41 regulators of inflammation from 8293 Finnish individuals from genome-wide association studies (GWASs) of COPD corresponding to GWAS summary data for 2115 cases and 454,233 healthy individuals in Europe. Our research validated that higher levels of interleukin 8 (IL-8) are related with a decrease occurrence of COPD (OR = 0.795, 95 % CI = 0.642-0.984, p = 0.035) but that elevated levels of interleukin 18(IL-18) and interleukin 2 (IL-2) may be connected to an amplified risk of COPD (OR = 1.247, 95 % CI = 1.011-1.538; p = 0.039; OR = 1.257, 95 % CI = 1.037-1.523, p = 0.020, respectively). According to our research, cytokines play a crucial role in the development of COPD, and further investigation is necessary to explore the potential of utilizing these cytokines as targets for treatment and prevention of COPD.

The enhancement of photo-thermo-electric conversion in tilted Bi2Sr2Co2O(y) thin films through coating a layer of single-wall carbon nanotubes light absorber.

Light-induced transverse thermoelectric effect has been investigated in c-axis tilted Bi(2)Sr(2)Co(2)O(y) thin films coated with a single-wall carbon nanotubes light absorption layer. Open-circuit voltage signals were detected when the sample surface was irradiated by different lasers with wavelengths ranging from ultraviolet to near-infrared and the voltage sensitivity was enhanced as a result of the increased light absorption at the carbon nanotubes layer. Moreover, the enhancement degree was found to be dependent on the laser wavelength as well as the absorption coating size. This work opens up new strategy toward the practical applications of layered cobaltites in photo-thermo-electric conversion devices.

Microbial community structure and diversity in fish-flower (mint) symbiosis.

The fish-flower symbiosis model is an eco-friendly sustainable farming technology combining plants, fish and microorganisms in a recirculating aquaculture system. However, there are few studies on the structure and diversity of microbial communities in fish intestines, culture water and plant roots during fish-flower symbiosis. Here, we cultured carp (Cyprinus carpio), crucian carp (Carassius auratus) and grass carp (Ctenopharyngodon idella) with mint (Mentha spicala L.) and extracted total genomic DNA from intestinal microorganisms, culture-water microorganisms and root microorganisms for each fish species for high-throughput sequencing of 16S rRNA genes. Analysis of microbial community structure and diversity revealed changes in abundance of microbial genera in the intestines and culture water of each fish species, including changes in the dominant taxa. Pirellula, Truepera, Aquincola, Cetobacterium and Luteolibacter were widespread in the fish intestine, culture water and mint root system. This study revealed the effects of mint feeding on the structure and diversity of microbial communities of fish, water bodies and the mint root system during fish-flower symbiosis, providing a theoretical reference for the promotion and application of fish-flower (mint) symbiosis technology and healthy fish culture technology.

Causal relationships between susceptibility and severity of COVID-19 and neuromyelitis optica spectrum disorder (NMOSD) in European population: a bidirectional Mendelian randomized study.

Background: Neurological disorders can be caused by viral infections. The association between viral infections and neuromyelitis optica spectrum disorder (NMOSD) has been well-documented for a long time, and this connection has recently come to attention with the occurrence of SARS-CoV-2 infection. However, the precise nature of the causal connection between NMOSD and COVID-19 infection remains uncertain. Methods: To investigate the causal relationship between COVID-19 and NMOSD, we utilized a two-sample Mendelian randomization (MR) approach. This analysis was based on the most extensive and recent genome-wide association study (GWAS) that included SARS-CoV-2 infection data (122616 cases and 2475240 controls), hospitalized COVID-19 data (32519 cases and 2062805 controls), and data on severe respiratory confirmed COVID-19 cases (13769 cases and 1072442 controls). Additionally, we incorporated a GWAS meta-analysis comprising 132 cases of AQP4-IgG-seropositive NMOSD (NMO-IgG+), 83 cases of AQP4-IgG-seronegative NMOSD (NMO-IgG-), and 1244 controls. Results: The findings of our study indicate that the risk of developing NMO-IgG+ is elevated when there is a genetic predisposition to SARS-CoV-2 infection (OR = 5.512, 95% CI = 1.403-21.657, P = 0.014). Furthermore, patients with genetically predicted NMOSD did not exhibit any heightened susceptibility to SARS-CoV2 infection, COVID-19 hospitalization, or severity. Conclusion: our study using Mendelian randomization (MR) revealed, for the first time, that the presence of genetically predicted SARS-CoV2 infection was identified as a contributing factor for NMO-IgG+ relapses.

Assessment of the relationship between generalized convulsive epilepsy and systemic inflammatory regulators: a bidirectional Mendelian randomization study.

Background: Generalized convulsive epilepsy (GCE), an important subtype of epilepsy, is a syndrome of neuronal dysfunction characterized by diffuse abnormal discharge of neurons within the brain. Compounding evidence suggests a correlation between epilepsy and inflammatory factors, for instance, cyclooxygenase-2, interleukin-1ß, and interleukin-6. Elevated levels of inflammatory factors have been observed in patients with epilepsy and several animal models. Therefore, inflammation may be closely associated with the pathogenesis and progression of GCE. However, the cause-and-effect relationship between the two is difficult to determine because of small sample sizes and confounding factors. Methods: To test for causality of the 41 cytokines on GCE, we conducted a two-sample Mendelian randomization (MR) based on the largest and latest genome-wide association study (GWAS) involving 290 cases and 453,521 European controls and a GWAS meta-analysis consisting of 41 cytokines from 8,293 individuals. Results: R confirmed a bidirectional causal link between cytokines and GCE. Genetically predicted increased levels of hepatocyte growth factor and decreased levels of eotaxin and interleukin-18 are associated with an increased risk of GCE (OR = 1.904, 95% CI = 1.019-3.561, p = 0.044; OR = 0.641, 95% CI = 0.417-0.984, p = 0.042; OR = 0.482, 95% CI = 0.251-0.927, p = 0.046). Furthermore, the presence of GCE is related to an increase in levels of multiple cytokines, such as macrophage inflammatory protein-1α, interleukin-12p70, interleukin-17, interleukin-1 receptor antagonist, and basic fibroblast growth factor (OR = 1.038, 95% CI = 1.005-1.073, p = 0.024; OR = 1.031, 95% CI = 1.009-1.054, p = 0.006; OR = 1.027, 95% CI = 1.002-1.053, p = 0.037; OR = 1.037, 95% CI = 1.003-1.072, p = 0.032; OR = 1.032, 95% CI = 1.000-1.066, p = 0.048; OR = 1.025, 95% CI = 1.003-1.048, p = 0026). Conclusion: A bidirectional causal link existed between inflammation and GCE. Detecting significantly altered factor concentrations may be of great significance for screening GCE and predicting their occurrence. Moreover, available pharmacological treatments for GCE are focused primarily on suppressing seizures. In future, altering the concentration of these cytokines in the body through targeted anti-inflammatory therapy to modify the epileptogenic mechanism and prevent the recurrence and refractoriness of GCE may become the key to new treatments.

Constructing quasi-layered and self-hole doped SnSe oriented films to achieve excellent thermoelectric power factor and output power density.

Thermoelectric (TE) technology can achieve the mutual conversion between electric energy and waste heat, and it has exhibited great prospects in multifunctional energy applications to alleviate the energy crisis. In the recent decade, SnSe has been explored widely because of its potentially high energy harvesting efficiency, green nature, and low cost. However, the relatively poor power factor (PF) derived from the intrinsic low carrier concentration (∼1017 cm-3) limits the output power density of the stoichiometric SnSe devices. Therefore, the advancement of novel optimization strategies for controlling carrier concentration is of utmost importance. Besides, compared with 3D bulks, 2D thin films are more compatible with modern semiconductor technology and have unique advantages in the construction and application of TE micro- and nano-devices. In this study, post-selenization technology were applied to increase the carrier concentration of the a-axis oriented SnSe epitaxial films utilizing the charge transfer and self-hole doped effects. The quasi-layered and self-hole doped films exhibited a high power factor of ∼5.9 µW cm-1 K-2 at 600 K along the in-plane direction when the carrier concentration is enhanced to ∼1018 cm-3 by increasing the selenization time to ∼20 min. The TE generator composed of four P-type film legs demonstrated the ultrahigh maximum power density of ∼83, ∼838 µW cm-2 at the temperature difference of ∼50 and ∼90 K, respectively. Post-selenization can effectively optimize the carrier concentration of SnSe-based materials, which is also feasible to other anion deficient TE films.

Factors influencing the surveillance of re-emerging intracranial infections in elective neurosurgical patients: A single-center retrospective study.

BACKGROUND: At present, many studies have reported the risk factors for postoperative intracranial reinfection, including age, sex, time to surgery, duration of postoperative catheterization, emergency procedures, type of disease and cerebrospinal fluid leakage, but the academic community has not reached a unified conclusion. AIM: To find factors influencing the surveillance of re-emerging intracranial infections in elective neurosurgical patients. METHODS: Ninety-four patients who underwent elective craniotomy from January 1, 2015 to December 31, 2022 in the Department of Neurosurgery, First Hospital of Jilin University, were included in this study. Of those, 45 patients were enrolled in the infection group, and 49 were enrolled in the control group. The clinical data of the patients were collected and divided into three categories, including preoperative baseline conditions, intraoperative characteristics and postoperative infection prevention. The data were analyzed using SPSS 26.0 software. RESULTS: There were 23 males and 22 females in the infection group with a mean age of 52.8 ± 15.1 years and 17 males and 32 females in the control group with a mean age of 48.9 ± 15.2 years. The univariate analysis showed that the infection group had higher systolic blood pressures and postoperative temperatures, fewer patients who underwent a supratentorial craniotomy, more patients with a history of hypertension and higher initial postoperative white blood cell counts than the control group, with statistically significant differences (P < 0.05). The multifactorial logistic regression analysis showed that a history of hypertension and a high postoperative body temperature were independent risk factors for postoperative infection in neurosurgical patients. CONCLUSION: The results obtained in this study indicated that a history of hypertension and a high postoperative body temperature were independent risk factors for postoperative neurological symptoms.

Interlayer Quasi-Bonding Interactions in 2D Layered Materials: A Classification According to the Occupancy of Involved Energy Bands.

Recent studies have revealed that the interlayer interaction in two-dimensional (2D) layered materials is not simply of van der Waals character but could coexist with quasi-bonding character. Herein, we classify the interlayer quasi-bonding interactions into two main categories (I: homo-occupancy interaction; II: hetero-occupancy interaction) according to the occupancy of the involved energy bands near the Fermi level. We then investigate the quasi-bonding-interaction-induced band structure evolution of several representative 2D materials based on density functional theory calculations. Further calculations confirm that this classification is applicable to generic 2D layered materials and provide a unified understanding of the total strength of interlayer interaction, which is a synergetic effect of the van der Waals attraction and the quasi-bonding interaction. The latter is stabilizing in main category II and destabilizing in main category I. Thus, the total interlayer interaction strength is relatively stronger in category II and weaker in category I.

Fracture toughness of bone at the microscale.

Bone's hierarchical arrangement of collagen and mineral generates a confluence of toughening mechanisms acting at every length scale from the molecular to the macroscopic level. Molecular defects, disease, and age alter bone structure at different levels and diminish its fracture resistance. However, the inability to isolate and quantify the influence of specific features hampers our understanding and the development of new therapies. Here, we combine in situ micromechanical testing, transmission electron microscopy and phase-field modelling to quantify intrinsic deformation and toughening at the fibrillar level and unveil the critical role of fibril orientation on crack deflection. At this level dry bone is highly anisotropic, with fracture energies ranging between 5 and 30 J/m2 depending on the direction of crack propagation. These values are lower than previously calculated for dehydrated samples from large-scale tests. However, they still suggest a significant amount of energy dissipation. This approach provides a new tool to uncouple and quantify, from the bottom up, the roles played by the structural features and constituents of bone on fracture and how can they be affected by different pathologies. The methodology can be extended to support the rational development of new structural composites.

Fluorescence and Optical Activity of Chiral CdTe Quantum Dots in Their Interaction with Amino Acids.

Ligand-induced chirality in semiconducting nanocrystals has been the subject of extensive study in the past few years and shows potential applications in optics and biology. Yet, the origin of the chiroptical effect in semiconductor nanoparticles is still not fully understood. Here, we examine the effect of the interaction with amino acids on both the fluorescence and the optical activity of chiral semiconductor quantum dots (QDs). A significant fluorescence enhancement is observed for l/d-Cys-CdTe QDs upon interaction with all the tested amino acids, indicating suppression of nonradiative pathways as well as the passivation of surface trap sites brought via the interaction of the amino group with the CdTe QDs' surface. Heterochiral amino acids are shown to weaken the circular dichroism (CD) signal, which may be attributed to a different binding configuration of cysteine molecules on the QDs' surface. Furthermore, a red shift of both CD and fluorescence signals in l/d-Cys-CdTe QDs is only observed upon adding cysteine, while other tested amino acids do not exhibit such an effect. We speculate that the thiol group induces orbital hybridization of the highest occupied molecular orbital (HOMOs) of cysteine and the valence band of CdTe QDs, leading to the decrease of the energy band gap and a concomitant red shift of CD and fluorescence spectra. This is further verified by density functional theory calculations. Both the experimental and theoretical findings indicate that the addition of ligands that do not "directly" interact with the valence band (VB) of the QD (noncysteine moieties) changes the QD photophysical properties, as it probably modifies the way cysteine is bound to the surface. Hence, we conclude that it is not only the chemistry of the amino acid ligand that affects both CD and PL but also the exact geometry of binding that modifies these properties. Understanding the relationship between the QD's surface and chiral amino acid thus provides an additional perspective on the fundamental origin of induced chiroptical effects in semiconductor nanoparticles, potentially enabling us to optimize the design of chiral semiconductor QDs for chiroptic applications.