Janus Monolayer Transition Metal Dichalcogenides

A novel crystal configuration of sandwiched S-Mo-Se structure (Janus SMoSe) at the monolayer limit has been synthesized and carefully characterized in this work. By controlled sulfurization of monolayer MoSe2 the top layer of selenium atoms are substituted by sulfur atoms while the bottom selenium layer remains intact. The peculiar structure of this new material is systematically investigated by Raman, photoluminescence and X-ray photoelectron spectroscopy and confirmed by transmission-electron microscopy and time-of-flight secondary ion mass spectrometry. Density-functional theory calculations are performed to better understand the Raman vibration modes and electronic structures of the Janus SMoSe monolayer, which are found to correlate well with corresponding experimental results. Finally, high basal plane hydrogen evolution reaction (HER) activity is discovered for the Janus monolayer and DFT calculation implies that the activity originates from the synergistic effect of the intrinsic defects and structural strain inherent in the Janus structure.Comment: 22 pages, 12 figure

Influence of intermittent water releases on groundwater chemistry at the lower reaches of the Tarim River, China

Based on the data of the depths and the chemical properties of groundwater, salinity in the soil profile, and the basic information on each delivery of water collected from the years 2000 to 2006, the varied character of groundwater chemistry and related factors were studied. The results confirmed the three stages of the variations in groundwater chemistry influenced by the intermittent water deliveries. The factors that had close relations to the variations in groundwater chemistry were the distances of monitoring wells from the water channel, the depths of the groundwater, water flux in watercourse, and the salinities in soils. The relations between chemical variation and groundwater depths indicated that the water quality was the best with the groundwater varying from 5 to 6 m. In addition, the constructive species in the study area can survive well with the depth of groundwater varying from 5 to 6 m, so the rational depth of groundwater in the lower reaches of the Tarim River should be 5 m or so. The redistribution of salts in the soil profile and its relations to the chemical properties and depths of groundwater revealed the linear water delivery at present combining with surface water supply in proper sections would promote water quality optimized and speed up the pace of ecological restoration in the study area

Dimensionality-confined superconductivity within SrNbO3-SrTiO3 heterostructures

Interfaces between transition-metal oxides are able to host two-dimensional electron gases (2DEGs) and exhibit exotic quantum phenomena. Here we report the observation of superconductivity below 230 mK for the heterostructure composed of SrNbO3 (SNO) and SrTiO3 (STO). Different from some other counterparts with two insulators, the metallic SNO provides a novel mechanism to form a quasi 2DEG by charge transfer from bulk towards interface under strain. The superconductivity, residing within the strained SNO layer near the interface, is contributed by an electron system with record-low carrier density. Notably, although embedded in a normal metallic layer with a carrier density 4 to 5 orders higher, the electron system is still uniquely well-protected to retain high mobility and lies deep in extreme quantum regime

Rural-urban disparities in Oral Health-related Quality of Life for middle-aged and older adults with diabetes in Taiwan

BackgroundPublic health faces a significant challenge in reducing rural–urban disparities in diabetes. Since dietary control is part of the medical regimen for diabetes management, how diabetic patients perceive the impact of oral health on their quality of life is critical. The present study aimed to compare the Oral Health-related Quality of Life (OHRQoL) between rural and urban diabetic patients.MethodsThe study design was cross-sectional. The study sample included 831 self-reported diabetic patients, extracted from the first wave of the new-cohort Taiwan Longitudinal Study on Aging survey (NC_TLSA) that comprised a nationally representative sample of community-dwelling adults aged 50 and above in Taiwan. The composite score generated from the Oral Health Impact Profile-7 (OHIP-7), which has seven questions, was used to construct two OHRQoL measures, the severity of perceived poor OHRQoL and the prevalence of poor OHRQoL. These two OHRQoL measures were treated as dichotomous variables. Multivariate logistic regression models were applied for analysis.ResultsRural diabetic patients had a higher likelihood of experiencing the severity of perceived poor OHRQoL than those in urban areas (OR = 2.40, 95% CI: 1.30–4.40). Although rural diabetic patients also had a higher prevalence of poor OHRQoL than urban diabetic patients, the difference was not significant (OR = 1.47, 95% CI: 0.95–2.28). Social determinants, such as education, are essential factors attributed to both OHRQoL measures.ConclusionOverall, rural diabetes community-dwelling patients had a poorer OHRQoL than those in urban areas. Given a bidirectional relationship between oral health and diabetes, improving oral health in rural areas may be a critical avenue to improve the quality of diabetes care in rural areas

Strain mediated phase crossover in Ruddlesden Popper nickelates

Recent progress on the signatures of pressure-induced high temperature superconductivity in Ruddlesden Popper (RP) nickelates (Lan+1NinO3n+1) has attracted growing interest in both theoretical calculations and experimental efforts. The fabrication of high-quality single crystalline RP nickelate thin films is critical for possible reducing the superconducting transition pressure and advancing applications in microelectronics in the future. In this study, we report the observations of an active phase transition in RP nickelate films induced by misfit strain. We found that RP nickelate films favor the perovskite structure (n = infinite) under tensile strains, while compressive strains stabilize the La3Ni2O7 (n = 2) phase. The selection of distinct phases is governed by the strain dependent formation energy and electronic configuration. In compressively strained La3Ni2O7, we experimentally determined splitting energy is ~0.2 eV and electrons prefer to occupy in-plane orbitals. First principles calculations unveil a robust coupling between strain effects and the valence state of Ni ions in RP nickelates, suggesting a dual driving force for the inevitable phase co-existence transition in RP nickelates. Our work underscores the sensitivity of RP nickelate formation to epitaxial strain, presenting a significant challenge in fabricating pure-phase RP nickelate films. Therefore, special attention to stacking defects and grain boundaries between different RP phases is essential when discussing the pressure-induced superconductivity in RP nickelates.Comment: 29 pages, 5 figures, one supplementary material

Spin State Disproportionation in Insulating Ferromagnetic LaCoO3 Epitaxial Thin Films

The origin of insulating ferromagnetism in epitaxial LaCoO3 films under tensile strain remains elusive despite extensive research efforts have been devoted. Surprisingly, the spin state of its Co ions, the main parameter of its ferromagnetism, is still to be determined. Here, we have systematically investigated the spin state in epitaxial LaCoO3 thin films to clarify the mechanism of strain induced ferromagnetism using element-specific x-ray absorption spectroscopy and dichroism. Combining with the configuration interaction cluster calculations, we unambiguously demonstrate that Co3+ in LaCoO3 films under compressive strain (on LaAlO3 substrate) are practically a low spin state, whereas Co3+ in LaCoO3 films under tensile strain (on SrTiO3 substrate) have mixed high spin and low spin states with a ratio close to 1:3. From the identification of this spin state ratio, we infer that the dark strips observed by high-resolution scanning transmission electron microscopy indicate the position of Co3+ high spin state, i.e., an observation of a spin state disproportionation in tensile-strained LaCoO3 films. This consequently explains the nature of ferromagnetism in LaCoO3 films