氟化氢溶液无电沉积法制备W掺杂Ag树枝晶

应用无电沉积在氟化氢溶液制备W掺杂Ag树枝晶,样品由XPS,XRD,SEM和TEM表征,结果表明在Ag-W二元体系中,Ag的生长起主导作用,不受钨酸根离子而改变。提出W元素的掺杂方式,即W元素的掺杂是在银的沉积过程中通过化学吸附—钨酸根二聚体的氧原子与银原子的化学作用力而实现的。循环伏安法用于检测银氧间的化学键能的强弱。     

Thermal fragmentation of the guanidinato aluminum amide precursor [Me2NC(NPr)2]Al(NMe2)2: An investigation of reactive species by matrix-isolation FTIR spectroscopy and time-of-flight mass spectrometry

The gas-phase thermolysis of the guanidinato aluminum amide precursor [Me₂NC(NⁱPr)₂]Al(NMe₂)₂ (1) in the oven temperature range of ambient temperatures to 600 °C has been investigated with matrix-isolation FTIR spectroscopy and time-of-flight mass spectrometry (argon as carrier gas). Precursor 1 fragments above 300 °C to form iPrCNCiPr (2) and monomeric Al(NMe₂)₃ (3m). Independent thermolysis series with 2 and the aluminum amide dimer 3d, [Al(NMe₂)₃]₂, were conducted and been used to interpret the results of the fragmentation of precursor 1. Compound 3m was present in the thermolysis range of 350–450 °C and has been identified for the first time. Through a comparison of measured FTIR spectra with the calculated spectrum of 3m (D₃ point group symmetry; B3LYP/6-31G(d) level of theory) all expected IR bands were found and could be assigned to normal modes. At thermolysis temperatures of ?500 °C signals indicative for H₂CNCH₃ (4) were found, showing that 3m fragments further at higher temperature. The thermolysis product 2 (iPrCNCiPr) withstands the higher thermolysis temperatures. From our study one can conclude that precursor 1 cleanly delivers the monomeric aluminum alane 3m, which then acts as the reactive material forming species.     

Characterization of nano-composite oxide ceramics and monitoring of oxide thin film growth by laser-induced breakdown spectroscopy

Multi-component oxide ceramics and epitaxial oxide thin films are analyzed by laser-induced breakdown spectroscopy (LIBS). Furthermore, pulsed-laser deposition (PLD) of thin films is investigated by long-term monitoring of the optical plasma emission. Both nano-composite high-temperature superconductors (HTS) consisting of YBa₂Cu₃O_7 − δ bulk and Y₂Ba₄MCuO_x (M-2411, M = Ag, Nb) nano-particles, and semiconducting ZnO doped with Aluminum and Lithium are ablated by nano-second laser pulses. The plasma emission is recorded using grating spectrometers with intensified gated detectors. The LIBS signals of nano-particles correlate with the nominal content of the M-2411 phase (0–15 mol%) and reveal a strong signal of Ytterbium impurity (3–35 ppm). In situ monitoring of the PLD process shows element signals that are stable for more than 10,000 laser pulses for both HTS and ZnO ceramics. The relative concentration of elements in thin films and ceramics as determined by LIBS is almost the same.     

Further conventions for NMR shielding and chemical shifts (IUPAC Recommendations 2008)

IUPAC has published a number of recommendations regarding the reporting of nuclear magnetic resonance (NMR) data, especially chemical shifts. The most recent publication [Pure Appl. Chem. 73, 1795 (2001)] recommended that tetramethylsilane (TMS) serve as a universal reference for reporting the shifts of all nuclides, but it deferred recommendations for several aspects of this subject. This document first examines the extent to which the (1)H shielding in TMS itself is subject to change by variation in temperature, concentration, and solvent. On the basis of recently published results, it has been established that the shielding of TMS in solution [along with that of sodium-3-(trimethylsilyl)propanesulfonate, DSS, often used as a reference for aqueous solutions] varies only slightly with temperature but is subject to solvent perturbations of a few tenths of a part per million (ppm). Recommendations are given for reporting chemical shifts under most routine experimental conditions and for quantifying effects of temperature and solvent variation, including the use of magnetic susceptibility corrections and of magic-angle spinning (MAS). This document provides the first IUPAC recommendations for referencing and reporting chemical shifts in solids, based on high-resolution MAS studies. Procedures are given for relating (13)C NMR chemical shifts in solids to the scales used for high-resolution studies in the liquid phase. The notation and terminology used for describing chemical shift and shielding tensors in solids are reviewed in some detail, and recommendations are given for best practice.     

Light-induced Photoswitching of 4-(Phenylazo)benzoic Acid on Au(111)

Photochromic molecules can undergo a reversible conversion between two isomeric forms upon exposure to external stimuli such as electromagnetic radiation. A significant physical transformation accompanying the photoisomerization process defines them as photoswitches, with potential applications in various molecular electronic devices. As such, a detailed understanding of the photoisomerization process on surfaces and the influence of the local chemical environment on switching efficiency is essential. Herein, we use scanning tunneling microscopy to observe the photoisomerization of 4-(phenylazo)benzoic acid (PABA) assembled on Au(111) in kinetically constrained metastable states guided by pulse deposition. Photoswitching is observed at low molecular density and is absent in tight-packed islands. Furthermore, switching events were noted in PABA molecules coadsorbed in a host octanethiol monolayer, suggesting an influence of the surrounding chemical environment on photoswitching efficiency.     

Nb doping effect on TiO2−x films for bolometer applications

Nb-doped TiO_2−x thin films were deposited using a 1 at% niobium doped titanium target by RF reactive magnetron sputtering at various oxygen partial pressures (pO₂). The films appeared amorphous in the pO₂ range of 4.4–4.7% with resistivity ranging from 0.39 Ω cm to 2.48 Ω cm. Compared to pure TiO_2−x films, the resistivity of the Nb-doped TiO_2−x films did not change sensitively with the oxygen partial pressure, indicating that the resistivity of the films can be accurately controlled. 1/f noise parameter of Nb-doped TiO_2−x films were found to decrease largely while the measured temperature coefficient of resistance (TCR) of the films was still high. The obtained results indicate that Nb-doped TiO_2−x films have great potential as an alternative bolometric material.     

Solid–Vapor Reaction Growth of Transition‐Metal Dichalcogenide Monolayers

Two‐dimensional (2D) layered semiconducting transition‐metal dichalcogenides (TMDCs) are promising candidates for next‐generation ultrathin, flexible, and transparent electronics. Chemical vapor deposition (CVD) is a promising method for their controllable, scalable synthesis but the growth mechanism is poorly understood. Herein, we present systematic studies to understand the CVD growth mechanism of monolayer MoSe₂, showing reaction pathways for growth from solid and vapor precursors. Examination of metastable nanoparticles deposited on the substrate during growth shows intermediate growth stages and conversion of non‐stoichiometric nanoparticles into stoichiometric 2D MoSe₂ monolayers. The growth steps involve the evaporation and reduction of MoO₃ solid precursors to sub‐oxides and stepwise reactions with Se vapor to finally form MoSe₂. The experimental results and proposed model were corroborated by ab initio Car–Parrinello molecular dynamics studies.     

A diffuse‐interface modeling for liquid solution–solid gel phase transition of physical hydrogel with nonlinear deformation

A diffuse‐interface model is presented in this paper for simulation of the evolution of phase transition between the liquid solution and solid gel states for physical hydrogel with nonlinear deformation. The present domain covers the gel and solution states as well as a diffuse interface between them. They are indicated by the crosslink density in such a way that the solution phase is identified as the state when the crosslink density is small, while the gel as the state if the crosslink density becomes large. In this work, a novel order parameter is thus defined as the crosslink density, which is homogeneous in each distinct phase and smoothly varies over the interface from one phase to another. In this model, the constitutive equations, imposed on the two distinct phases and the interface, are formulated by the second law of thermodynamics, which are in the same form as those derived by a different approach. The present constitutive equations include a novel Ginzburg–Landau type of free energy with a double‐well profile, which accounts for the effect of crosslink density. The present governing equations include the equilibrium of forces, the conservations of mass and energy, and an additional kinetic equation imposed for phase transition, in which nonlinear deformation is considered. The equilibrium state is investigated numerically, where two stable phases are observed in the free energy profile. As case studies, a spherically symmetrical solution‐gel phase transition is simulated numerically for analysis of the phase transition of physical hydrogel.     

Underpotential Deposition Preparation of Pt‐loading AuNPs/Reduced Graphene Oxide and Its Catalytic Detection of Catechol

Ultralow Pt‐loading Au nanoparticles have been fabricated on the surface of reduced graphene oxide (RGO) by using underpotential deposition (UPD) monolayer redox replacement process. The Pt/Au/RGO modified electrode exhibits an excellent electrocatalytic activity toward catechol and hydroquinone. Under the optimized condition, the separation of peak‐to‐peak between hydroquinone and catechol is 197 mV, which is wide enough to distinguish the isomers of benzenediol. Catechol is detected by the Pt/Au/RGO/GCE with a low detection limit in the presence of hydroquinone.     

体力活动对围绝经期女性更年期综合征影响的研究

目的研究体力活动对围绝经期女性更年期综合征的影响。方法2013年8月至2014年8月通过院内调查及社会调查两种模式共调查杭州市余杭区472例围绝经期女性,调查资料完整者401例,其中符合纳入标准者223例,通过问卷形式收集患者一般情况（包括年龄、身高、体重、吸烟饮酒情况、生育情况等）、更年期综合征症状、体力活动强度。分析患者体力活动与更年期综合征的关系。结果在文化水平、初次月经、年龄等方面,轻、中、重体力活动组之间无统计学差异（均P＞0.05）;轻度体力活动组BMI＞25的比例为26.5%,吸烟比例为32.5%,饮酒比例为27.7%,均高于中、重度体力活动组的相应比例（均P＜0.05）。轻度及重度体力活动组血管舒缩分值高于中度体力活动组（P＜0.05）,但轻度体力活动组与重度体力活动组比较差异无统计学意义（P＞0.05）,在心理社会、性生活、生理状态上,轻度体力活动组分值均高于中度及重度体力活动组,差异均有统计学意义（均P＜0.05）,中度体力活动组与重度体力活动组间比较均无统计学差异（均P＞0.05）。采用多元logistic回归分析绝经期生存质量状况与体力活动的关系,在校正BMI、文化水平、吸烟、饮酒、初次月经、婚姻状况、生育情况、工作状态、年龄等因素后,血管舒缩症状在中度体力活动组症状轻于轻度及重度体力活动组（P＜0.05）,重度体力活动组与轻度体力活动组无统计学统计学意义（P＞0.05）;心理社会、性生活及生理状态症状,中度及重度体力活动组症状均要轻于轻度体力组（P＜0.05）,中度与重度体力活动组间比较无统计学意义（P＞0.05）。结论体力活动的增加对围绝经期女性是潜在有意义的替代治疗方法,尤其是中度的体力活动可以在一定程度上预防或改善更年期综合征症状。