纳伏电压标准装置测量不确定度分析与评定

通过实验与经验分析,考虑零点漂移、环境温度、量程非线性、数据处理、信号衰减、信号传输、频率响应、噪声与干扰等因素的影响,对纳伏电压标准装置进行了测量不确定度分析与评定。给出了实验数据和评定结果,提出了提高纳伏级微弱信号测量准确度的建议。     

自制地温转接板引起测量误差偏移量的测定

本文通过实验方式,建立了测定自制地温转接板引起测量误差偏移量的测量模型,通过实验数据,计算出了自制地温转接板引起的被校传感器测量误差偏移量。     

医用超声诊断源检定过程中探头的识别

在检定医用超声诊断源的过程中,正确地识别所检医用超声诊断源的探头,是十分重要的一环,本文详细地分析了常见医用超声诊断源探头的特点,以及识别医用超声诊断源探头的方法。     

Experimental investigations on nanogrinding of RB-SiC wafers

Nanogrinding experiments are performed to investigate the processing characteristics and material removal mechanism of reaction-bonded silicon carbide (RB-SiC) wafers on an ultraprecision grinder using the cup wheel. #120, #600 diamond wheels are used as coarse and semifinished grinding wheels, while #2000 and #12000 diamond wheels are selected as fine and finish grinding wheels, respectively. The experimental results indicate that an ultrasmooth surface with roughness value R_a less than 3?nm and groove depth about 5?nm can be achieved using a diamond wheel whose mesh size exceeds 2000. In addition, R_a less than 1?nm and groove depth about 2?nm will be obtained with a #12000 diamond wheel. The present study reveals the feasibility of ultraprecision grinding RB-SiC materials in the ductile regime and provides technological insights into nanogrinding of hard materials with an ultrasmooth surface.     

Welding current influences on Inconel 625/X65 cladding interface

The pulsed gas tungsten arc welding with hot wire was used to clad Inconel 625 on the surface of X65 steel. The influences of welding current in horizontal welding position on the dilution, in further the composition, microstructure, and property of the Inconel 625/X65 cladding interface were investigated. Experimental results show that with the increase in welding current, namely, in heat input and arc force, dilution rate increased; the composition transition region in the cladding layer close to the fusion line, controlled by the cladding temperature, would be widen; in further, the microstructure would be different due to the heat transfer and composition change; the precipitates were niobium-rich MC carbide with a low welding current, but tended to be the intermetallic compounds, Laves phase, with a high welding current; the highest and lowest hardness values appeared on the heat-affected zone and cladding layer next to the bonding interface, respectively.     

Detwinning through migration of twin boundaries in nanotwinned Cu films under in situ ion irradiation

The mechanism of radiation-induced detwinning is different from that of deformation detwinning as the former is dominated by supersaturated radiation-induced defects while the latter is usually triggered by global stress. In situ Kr ion irradiation was performed to study the detwinning mechanism of nanotwinned Cu films with various twin thicknesses. Two types of incoherent twin boundaries (ITBs), so-called fixed ITBs and free ITBs, are characterized based on their structural features, and the difference in their migration behavior is investigated. It is observed that detwinning during radiation is attributed to the frequent migration of free ITBs, while the migration of fixed ITBs is absent. Statistics shows that the migration distance of free ITBs is thickness and dose dependent. Potential migration mechanisms are discussed.     

The Influence of Carbon Nitride Nanosheets Doping on the Crystalline Formation of MIL‐88B(Fe) and the Photocatalytic Activities

In this research, bulk graphitic carbon nitride (g‐C₃N₄) is exfoliated and transferred to the carbon nitride nanosheets (CNNSs), which are then coupled with MIL‐88B(Fe) to form the hybrid. From the results of the powder X‐ray diffraction, scanning electronic microscopy and thermogravimetric analysis, it is found that the doping of CNNSs on the surface of MIL‐88(Fe) could maintain the basic structure of MIL‐88B(Fe), and the smaller dimension of CNNSs might influence the crystallization process of metal‐organic frameworks (MOFs) compared to bulk g‐C₃N₄. Besides, the effects of the CNNSs incorporation on photocatalysis are also investigated. Through the photoluminescence spectra, electrochemical measurements, and photocatalytic experiments, the hybrid containing 6% CNNSs is certified to possess the highest catalytic activity to degrade methylene blue and reduce Cr(VI) under visible light. The improvement of the photocatalytic performance can be attributed to the matched energy level which favors the formation of the heterojunctions. Besides, it promotes the charge migration such that the contact between MOFs and CNNSs is more intimate, which can be inferred from the electronic microscopy images. Finally, a possible photocatalytic mechanism is put forward by the relative calculation and the employment of the scavengers to trap the active species.     

A Two‐Stage Annealing Strategy for Crystallization Control of CH3NH3PbI3 Films toward Highly Reproducible Perovskite Solar Cells

The solvent‐engineering method is widely used to fabricate top‐performing perovskite solar cells, which, however, usually exhibit inferior reproducibility. Herein, a two‐stage annealing (TSA) strategy is demonstrated for processing of perovskite films, namely, annealing the intermediate phase at 60 °C for the first stage then at 100 °C for the second stage. Compared to conventional direct annealing temperature (DHA) at 100 °C, using this strategy, MAPbI₃ films become more controllable, leading to superior film uniformity and device reproducibility with the champion device efficiency reaching 19.8%. More specifically, the coefficient of variation of efficiency for 49 cells is reduced to 5.9%, compared to 9.8% for that using DHA. The TSA process is carefully studied using Fourier transform infrared spectroscopy, X‐ray diffraction, and UV–vis absorption spectroscopy. It is found that in comparison with DHA the formation of hydrogen bonding and crystallization of perovskite are much slower and can be better controlled when using TSA. The improvements in film uniformity and device reproducibility are attributed to: 1) controllable MAPbI₃ crystal growth stemming from the progressive formation of hydrogen bonding between methylammonium and halide; 2) suppression of intermediate phase film dewetting, which is believed to be due to its decreased mobility at the initial low‐temperature annealing stage.