The covalent functionalization of few-layered MoTe2 thin films with iodonium salts

Covalent functionalization of 2D materials provides a tailored approach towards tuning of their chemical, optical, and electronic properties making the search for new ways to graft small molecules important. Herein, the reaction with (3,5-bis(trifluoromethyl)phenyl)iodonium salt is revealed as an effective strategy for functionalization of MoTe₂ thin films. Upon decomposition of the salt, the generated radicals graft covalently as aryl-(CF₃)₂ groups at the surface of both metallic (1T’) and semiconducting (2H) polymorphs of MoTe₂. Remarkably, the reactivity of the salt is governed by the electronic structure of the given polymorph. While the functionalization of the metallic MoTe₂ occurs spontaneously, the semiconducting MoTe₂ requires activation by light. The reaction proceeds with the elimination of oxide from the original films yielding the functionalized products that remain protected in ambient conditions, presenting a viable solution to the ageing of MoTe₂ in air.     

单斜氧化锆表面水合和脱水的动态模拟

常用的氧化物负载金属催化剂通常在水相中制备,且在使用前常常需要经过煅烧. 因此,氧化物载体表面的水合和脱水过程对于负载型金属催化剂的真实建模至关重要. 通过第一性原理分子动力学模拟,本文考察了温和温度下无水单斜氧化锆(111)表面在显式溶剂水中的演化. 在模拟过程中,所有的双重配位桥位氧位点很快被溶剂水质子化,形成酸性羟基(HO_L),并在锆原子上留下碱性羟基(HO^*). 这些碱性羟基(HO^*)可以与表面未解离的吸附水分子(H₂O^*$)进行活跃的质子交换,进而在表面自由扩散. 在273 K到373 K的温度范围下,第一性原理分子动力学水相模拟可以得到一种较为确定的、有代表性的平衡水合单斜氧化锆(111)表面,其表面锆原子上覆盖度(θ)为0.75. 随后,为了模拟低于800 K的温和煅烧温度下的表面脱水过程,本文使用密度泛函理论计算了表面水分子的逐步脱附自由能. 通过获得表面的脱水相图,总结了不同煅烧温度下有代表性的、部分水合的单斜氧化锆(111)表面(0.25≤θ<0.75). 这些水合单斜氧化锆(111)表面具有重要的理论意义,可以方便快捷地被应用于氧化锆催化剂及氧化锆负载金属催化剂的真实建模与模拟.     

非对称银纳米双环表面等离激元光谱特性

贵金属纳米材料在入射光激发下能够产生表面等离激元,即金属表面自由电子产生集体振荡.当其振荡频率与入射光频率相同时,发生表面等离激元共振,形成一种特殊的电磁场模式和光谱特性.利用该电磁场模式和光谱特性,能够调节金属纳米材料的光谱学行为,例如通过改变金属纳米结构的大小、形状以及周围介质介电常数等参数,在微纳尺度上实现光谱学...     

Measurement of refractive index variation of liquids by surface plasmon resonance and wavelength-modulated heterodyne interferometry

In this study an alternative method based on surface plasmon resonance is proposed for in-situ monitoring of variation in the refractive index of a test sample. A wavelength-modulated light source and an unequal-path-length optical configuration heterodyne interferometer are used to detect the phase difference change, which can then be used to estimate the change in the refractive index of a test sample. The experimental results demonstrate a phase stability of 0.02°. The resolution power of the refractive index is 1.5 × 10^− 6 RIU. This method has several advantages over previously used methods such as simple optical setup, easier operation in real time, and low cost.     

负偏压对磁控溅射Ti膜沉积速率和表面形貌的影响

 采用直流磁控溅射加负偏压的方法制备了Ti膜,研究了不同偏压条件对Ti膜沉积速率、密度、生长方式及表面形貌的影响。随着偏压逐渐增大,Ti膜沉积速率分三个阶段变化:0~ -40 V之间沉积速率基本不变; -40~ -80 V之间沉积速率迅速降低;超过-80 V后沉积速率随偏压的下降速度又放缓。Ti膜密度随偏压增加而增大,负偏压为-119.1 V时开始饱和并趋于块体Ti材密度。加负偏压能够抑制Ti膜的柱状生长方式;偏压可以改善Ti膜的表面形貌,对于40 W和100 W的溅射功率,负偏压分别在-100 V和-80 V左右时制备出表面光洁性能较佳的Ti膜。     

Densely-packed self-assembled monolayers on gold surfaces from a conformationally constrained helical hexapeptide

A novel hexapeptide was functionalized at the N-terminus by a lipoyl group for binding to gold substrates. Owing to the high content of α-aminoisobutyric acid residues, the peptide adopts a rigid helical conformation despite the shortness of its main chain. Binding of the peptide to gold was investigated by quartz crystal microbalance, cyclic voltammetry, X-ray photoelectron spectroscopy, and scanning tunneling microscopy under ultra-high vacuum conditions. Scanning tunneling microscopy experiments revealed that the peculiar self-assembly properties of this short helical peptide determine the complex morphology of the monolayer, showing ‘stripes’, i.e. peptide aggregates horizontally layered on the gold surface, and ‘holes’, i.e. Au vacancy islands coated by the peptide monolayer.     

Study of Si(0 0 1)4 × 2-Ga structure by scanning tunneling microscopy and ab initio calculation

We have studied Si(0 0 1)-Ga surface structures formed at Ga coverages of slightly above 0.50 monolayer (ML) at 250 °C by scanning tunneling microscopy (STM). 4 × 2-, 5 × 2-, and 6 × 2-Ga structures were observed in a local area on the surface. The 4 × 2-Ga structure consists of three protrusions, as observed in filled- and empty-state STM images. The characters of these structures are clearly different from those of other Si(0 0 1)-Ga structures. We also performed an ab initio calculation of the energetics for several possible models for the 4 × 2-Ga structure, and clarified that the three-orthogonal-Ga-dimer model is the most stable. Also, the results of comparing the simulated STM images and observation images at various bias voltages indicate that this structural model is the most favorable.     

Enhancement of light-emitting efficiency using combined plasmonic Ag grating and dielectric grating

Based on the analysis of the near-field evanescent wave in total internal reflection, the flip-chip light-emitting diode (LED) structure was proposed by placing a plasmonic Ag grating and a perforated sapphire grating in the substrate. The finite difference time domain (FDTD) method has been applied to study the spectral properties of the hybrid structure and the enhancement factor of light extraction efficiency of the LED model. From the computation examples, the effects of structure parameters on the extraction enhancement have been investigated. The results indicate that the plasmonic grating can enhance the near-field evanescent wave and couple it to propagation wave in the specific wavelength bands, which leads to the photons emitting out of the LED chip with high extraction efficiency. Due to the combined gratings used, the enhancement factor of the light extraction efficiency can reach approximately 4 times at a relatively longer wavelength.     

傅里叶红外光谱仪测定地表水中的石油类

傅里叶红外光谱仪测定地表水中石油类,用一次定量萃取代替两次萃取定容,用无水硫酸钠过滤吸水代替经过硅酸镁柱.方法的精密度和准确度均达到国家标准要求,减轻了工作量,提高了分析速度,可用于日常样品地表水中石油类的监测.