激光能量对反钙钛矿GaCMn_3薄膜结构与物性的影响

本文采用脉冲激光沉积方法在LaAlO3(001)单晶衬底上制备了反钙钛矿GaCMn3薄膜,通过控制制备过程中脉冲激光的能量,研究了不同激光能量条件对GaCMn3薄膜结构与物理性能的影响.分别利用X射线衍射仪、原子力显微镜、超导量子干涉仪和物理性能测试系统,对所制备的薄膜的晶体结构、表面形貌和磁性、电输运性质进行了研究.结果表明,制备的样品均为具有多个晶面取向的反钙钛矿薄膜,且薄膜结构和物性明显随制备激光能量的变化而变化.当激光能量为450mJ时,制备的薄膜多晶面取向性最弱,结晶性和表面形貌最优良.实验所得的薄膜均表现出顺磁-铁磁-反铁磁相转变,然而转变过程比块材较平缓,同时薄膜的电阻率并未表现出块材中的突变特征,我们推测该现象很可能是由衬底的应力及衬底的晶格膨胀对薄膜反常晶格变化的抑制作用造成的.     

基于NICE-OHMS技术进行大气压气样直接检测的理论分析

噪声免疫腔增强光外差分子光谱技术(NICE-OHMS)是目前世界上最灵敏的激光吸收光谱技术,其在低压环境中具有极高的探测灵敏度。然而当测量样品处于大气压时,NICE-OHMS系统的探测灵敏度会大幅下降。主要原因之一是大气压下获取最大NICE-OHMS信号幅度的条件与低气压下不同。通过对大气压NICE-OHMS理论进行分析,分析了影响信号幅度的参数,并通过数值模拟来寻找最佳的实验条件。本文着重讨论影响信号的主要参数包括光学腔腔长L,调制系数β,探测相位θ。其中,由于在NICE-OHMS中使用DeVoe-Brewer技术将调制频率ν_m锁定到Fabry-Parot(FP)腔的自由光谱区(FSR)。因此FP腔的腔长决定了ν_m,同时还作用于信号幅度S■。模拟结果显示,当腔长增大时,由于ν_m随之减小,载波和边带的光谱成分相互重叠部分增大,因此线型函数的幅度逐渐减小。而吸收信号幅度随着腔长的增加而逐渐增加,色散信号幅度先增大后减小,并且在腔长等于8 cm时达到最大值。调制系数β会影响频率调制后激光载波和边带的幅度大小,并且影响信号线型。随着腔长的增加,最大信号幅度对应的β值也随之增加。在相同腔长下,色散信号的最佳β值小于吸收信号,更容易使用电光调制器实现。最后分析了参数的可实现性,分析了不同种类激光器的频率调谐能力,压电陶瓷的扫描宽度等。以乙炔气体为例,大气压下NICE-OHMS的谱线半宽达到~3 GHz,而光谱覆盖范围大于10 GHz。分布反馈式半导体激光器(DFB)与外腔二极管激光器(ECDL)的频率调谐范围可以达到30 GHz以上,但是由于激光线宽宽,得到的PDH锁定性能欠佳。回音壁模式激光器(WGM)和掺饵光纤激光器(EDFL)线宽为百Hz量级,是目前高灵敏NICE-OHMS系统中常用的光源。但是WGM目前可以实现了5 GHz的激光频率调谐范围,而EDFL的外部电压可控制的调谐范围仅为3 GHz。使用精细度为55000的腔进行模拟,调制系数β=1,腔长大于8 cm时,可使用WGM激光器实现,腔长大于25 cm时,可以使用EDFL激光器实现。而对于在设计光学腔中常用的伸缩长度为25μm的PZT,随着腔长的增加,对应的腔模频移范围逐渐减小,在腔长为典型的40 cm时,扫描范围大于12 GHz。     

Monitoring the Thiol/Thiophenol Molecule-Modulated Plasmon-Mediated Silver Oxidation with Dark-Field Optical Microscopy

Surface plasmon can trigger or accelerate many photochemical reactions, especially useful in energy and environmental industries. Recently, molecular adsorption has proven effective in modulating plasmon-mediated photochemistry, however the realized chemical reactions are limited and the underlying mechanism is still unclear. Herein, by using in situ dark-field optical microscopy, the plasmon-mediated oxidative etching of silver nanoparticles (Ag NPs), a typical hot-hole-driven reaction, is monitored continuously and quantitatively. The presence of thiol or thiophenol molecules is found essential in the silver oxidation. In addition, the rate of silver oxidation is modulated by the choice of different thiol or thiophenol molecules. Compared with the molecules having electron donating groups, the ones having electron accepting groups accelerate the silver oxidation dramatically. The thiol/thiophenol modulation is attributed to the modulation of the charge separation between the Ag NPs and the adsorbed thiol or thiophenol molecules. This work demonstrates the great potential of molecular adsorption in modulating the plasmon-mediated photochemistry, which will pave a new way for developing highly efficient plasmonic photocatalysts.     

Luminescent Thin Films Enabled by CsPbX3 (X=Cl,Br, I) Precursor Solution

Inorganic cesium lead halide perovskite nanocrystals are candidates for lighting and display materials due to their outstanding optoelectronic properties. However, the dissolution issue of perovskite nanocrystals in polar solvents remains a challenge for practical applications. Herein, we present a newly designed one-step spin-coating strategy to prepare a novel multicolor-tunable CsPbX₃ (X=Cl, Br, I) nanocrystal film, where the CsPbX₃ precursor solution was formed by dissolving PbO, Cs₂CO₃, and CH₃NH₃X into the ionic liquid n-butylammonium butyrate. The as-designed CsPbX₃ nanocrystal films show high color purity with a narrow emission width. Also, the blue CsPb(Cl/Br)₃ film demonstrates an absolute photoluminescence quantum yields (PLQY) of 15.6 %, which is higher than 11.7 % of green CsPbBr₃ and 8.3 % of red CsPb(Br/I)₃ film. This study develops an effective approach to preparing CsPbX₃ nanocrystal thin films, opening a new avenue to design perovskite nanocrystals-based devices for lighting and display applications.     

Transition Metal Doping Induces Ti3+ to Promote the Performance of SrTiO3@TiO2 Visible Light Photocatalytic Reduction of CO2 to Prepare C1 Product.

Transition metal Fe, Co, Ni and Cu doped strontium titanate-rich SrTiO₃@TiO₂ (STO@T) materials were prepared by hydrothermal method. The prepared doped materials exhibit better photocatalytic CO₂ reduction to CH₄ ability under visible light conditions. Among them, Fe-doped and undoped SrTiO₃@TiO₂ under visible light conditions CO₂ reduction products only CO, while M-STO@T (M=Co, Ni, Cu) samples converted CO₂ to CH₄. The average methane yield of Ni-doped STO@T samples are as high as 73.85 μmol g⁻¹ h⁻¹. The production of methane is mainly due to the increase in the response of the doped samples to visible light. And the increase in the separation rate of photogenerated electrons and holes and the efficiency of electron transport caused by the generation of impurity levels. The impurity level caused by Ti³⁺ plays an important role in the production of methane by CO₂ visible light reduction. Ni doping effectively improves the photocatalytic performance of STO@T and CO₂ reduction mechanism were explained.     

枝晶生长理论中的热-动力学协同

随加工工艺趋于复杂化和极端化,基于热力学驱动力和动力学能垒相对独立的枝晶生长理论已无法精确描述多种机制共同作用的非平衡凝固过程,大大限制了该理论与工业应用的结合。首先,本文综述基于热-动力学相对独立的枝晶生长理论的发展,分析其内涵的本征热-动力学相关性,并集成于以双辊薄带连铸技术为背景的基于热-动力学相关性的枝晶生长模型。其次,定量证明了热力学驱动力和动力学能垒的相关性,通过选择不同的驱动力-能垒组合,试图在双辊薄带连铸技术中实现合金设计和工艺优化。最后,通过分析现有模型的不足,对进一步枝晶生长模型的发展以及与工艺的结合进行展望。     

静电纺丝法制备柔性SERS基底及性能研究

利用静电纺丝技术制备了聚乙烯醇(PVA)/银纳米粒子高活性SERS柔性基底.将硝酸银、聚乙烯醇按照一定比例混合配置纺丝溶液,纺丝成膜后采用紫外光照射还原法得到纳米纤维基底.采用扫描电子显微镜(SEM),透射电子显微镜(TEM),傅立叶红外光谱(FT-IR),拉曼光谱(Raman),紫外可见光谱(UV-Vis)等技术,对合成的纳米纤维基底进行表征.研究表明,银纳米颗粒呈球形分布在复合纤维中,粒径小于10 nm.以罗丹明为探针分子,硝酸银含量16 wt;,紫外光照射3 h制备的基底具备最优的SERS性能.同时将此基底应用于烟酸药品检测,拉曼检测极限可达10-5 mol·L-1.     

基于级联卷积神经网络的前列腺磁共振图像分类

针对深度学习训练成本高，以及基于磁共振图像的前列腺癌临床诊断需要大量医学常识且极为耗时的问题，本文提出了一种基于级联卷积神经网络（Convolutional Neural Network，CNN）和磁共振图像的前列腺癌（Prostate Cancer，PCa）自动分类诊断方法，该网络以Faster-RCNN作为前网络，对前列腺区域进行提取分割，用于排除前列腺附近组织器官的干扰；以基于ResNet改进的网络结构CNN40_bottleneck作为后网络，用于对前列腺区域病变进行分类.后网络由瓶颈结构串联组成，其中使用批量标准化（Batch Normalization，BN）、全局平均池化（Global Average Pooling，GAP）进行优化.实验结果证明，本文方法对前列腺癌诊断结果较好，而且缩减了训练时间和参数量，有效降低了训练成本.     

高分辨率微型星载相机光学系统的设计及应用

为了克服太空环境的复杂性，满足航天工程的空间使用要求，研制一款2 500万像素宽光谱共焦成像的微型星载相机光学系统。该系统适应卫星发射和在轨道运行的恶劣环境，具有抗冲击震动、耐太空高温差强辐射，体积小，质量轻等优点。设计的系统可在450 nm～800 nm的谱段内清晰成像，焦距181 mm，入瞳口径45 mm，视场角10.4°，边缘相对照度0.81，轴上点MTF:0.57@55 lp/mm，0.33@110 lp/mm，畸变1.2%，镜头质量622 g，外形尺寸Φ58.3 mm×117 mm，抗辐照性能≥5 krad。通过温度适应性的模拟和优化，用户进行?30 ℃～+70 ℃光学镜头热真空试验，可正常工作。该系统已成功应用于天宫二号伴飞卫星相机中，获得的图像清晰稳定，为空间遥感实验观测发挥了重要的作用。