金刚石复合界面扩散系数的电子探针研究

结合金刚石与硬质合金复合材料的研究，对含轻元素的界面扩散问题提出了能谱仪与波谱仪原位互补分析研究的方法，从扩散深度和扩散浓度分布两种角度探讨了扩散系数的电子探针测定；同时讨论了该方法在金刚石与硬质合金复合钻头上的应用。     

氧含量对钕铁硼镝扩散梯度的影响研究

主要对不同厚度烧结钕铁硼磁体进行Dy晶界扩散,主要研究了磁体氧含量的高、低对成分及磁性能梯度分布的影响。研究发现:高、低氧磁体方形度均会随着厚度增加而下降,其中前者的下降幅度尤为显著。将磁体沿着厚度方向切片进行分析发现,低氧磁体成分及矫顽力的纵深梯度分布较为均匀。电子探针微观分析结果显示:高氧样品中O, Dy元素均集中富集在团块状的富Nd相之中;而低氧样品中这种团块稀少, Dy分布在其他微细晶界形成连续条纹。低氧磁体为Dy扩散提供了连续的通道,最终能使Dy扩散饱和度及矫顽力饱和度更大于高氧磁体。     

金属基复合材料的界面分析

用透射电镜、扫描电镜、Ｘ射线能谱仪和电子探针研究了碳化硅颗粒（ＳｉＣｐ）增强Ａｌ２０１４复合材料的微观结构和界面。鉴定了界面上和基体中三种主要的沉淀相：ＣｕＡｌ２、Ｃｕ２Ｍｇ８Ｓｉ６Ａｌ５、（Ｍｎ，Ｆｅ）３ＳｉＡｌ１２和高温下形成的条状Ａｌ４Ｃ３。试验指出，碳化硅和基体间的界面上没有Ｓｉ和Ａｌ的相互扩散，并观察分析了ＳｉＣｐ／Ａｌ２０１４界面周围的无析出带和高密度位错     

双主相(Nd,Dy)-Fe-B磁体矫顽力再提高机制的探究

研究了双主相(Nd, Dy)-Fe-B烧结磁体晶界扩散TbF_3的热处理工艺、微观结构及矫顽力再提升的技术机制。晶界扩散最佳的一级、二级热处理温度为900, 490℃。经过扩散工艺的综合优化磁体的矫顽力由20.00 kOe增加到29.49 kOe。利用电子探针微区分析仪(EPMA)对其元素分布进行分析,F扩散进入磁体表层,而Tb扩散进入磁体的几何中心;Tb更容易替代磁性相中的Nd元素而不是Dy; Tb在主相晶粒间的晶界相中不存在浓度梯度,说明主相晶粒之间的类似毛细吸力也是Tb扩散的驱动力之一。X射线衍射分析表明,扩散后磁体的取向度略微降低。综合来看晶界扩散明显改善了磁体的温度稳定性,在20～150℃之间,扩散工艺使磁体剩磁温度系数α由-0.107%·℃~(-1)提升到-0.093%·℃~(-1),矫顽力温度系数β由-0.539%·℃~(-1)增加到-0.483%·℃~(-1)。     

三元扩散偶Y—Zr—Hf,Y—Zr—Nb的制备及相图研究

本文对含稀土三元扩散偶的制备进行了一些摸索。根据稀土元素性质活泼的特点,采取一定措施,成功地制备了包括有稀土元素钇的Y-Zr-Hf、Y-Zr-Nb三元稀土扩散偶。采用电子探针微区成分分析方法,确定了Y-Zr-Hf、Y-Zr-Nb两个三元系在1000℃时的等温截面。结果表明,Y-Zr-Hf截面包括三个单相区(α-Y、β-Zr、α-Hf),三个两相区和一个三相区;Y-Zr-Nb截面只有两个单相区(α-Y,β(Zr、Nb))和一个两相区。同时对电子探针测量精度的影响因素进行了初步讨论。     

氧化锌颗粒脱硫中固体扩散的动力学分析

用电子探针显微分析 (EPMA)对ZnO基脱硫剂的脱硫颗粒径向硫分布行为进行了考查 ,对颗粒最外层粒子的实验结果分别用未反应收缩核模型及改良收缩核模型进行了动力学处理 ,给出了固体扩散活化能的参数估值。通过与热重研究的比较 ,进一步证实了固体粒子扩散的作用。     

C/C,C/C-SiC梯度基、纳米基、双元基复合材料微观结构特征

采用C和SiC共沉积的CVI技术制备了C/C ,C/C SiC梯度基、纳米基和双元基复合材料 .用光学显微镜、电子探针微观分析、透射电子显微镜和扫描电子显微镜观察了各种材料微观结构 .结果表明 ,SiC加入到碳基体里改变了热解碳的微观结构并导致了C/C复合材料性能的改善 .每种材料都各具特点 .由于它们密度低、良好的力学性能和抗氧化性能使得这些材料成为很有希望的热结构复合材料     

基于随机行走的二维空间扩散模拟研究

分子的扩散行为是微观化学的重要研究领域. 影响扩散行为的因素很多,但是目前各个因素的具体影响效果还不明确. 作者基于随机行走理论建立了分子在二维空间的扩散模型,依据此模型自主开发了模拟软件以及数据分析系统,并利用该模拟软件系统研究了势垒尧横向速度等因素对扩散行为的影响,验证了该模型的可靠性,证明根据该模型可以得到和实验尧理论相吻合的结果. 该软件有望成为模拟微观化学扩散行为的潜在平台,如电化学以及膜过滤过程中的扩散.     

微波合成SrTiO~3的反应机理

研究了微波合成SrTiO~3的合成过程,XRD及电子探针的结果表明这一反应过程是由扩散控制,微波场的存在使扩散过程明显增强,存在有Sr和Ti元素的相互扩散,与常规合成有较大不同。从微波合成和常规合成反应产物的组成及显微结构等方面说明微波合成与常规合成具有不同的反应机理,微波合成在反应过程中没有出现其他的中间相,反应动力学计算表明反应过程的动力学符合Carter方程,反应的活化能为129kJ/mol,约为常规合成的1/2～1/3。     

特高综合磁性能晶界扩散磁体的研究

采用Tb_4O_7, TbH_x和Nd_2O_3+Tb_4O_7三种扩散源,通过晶界扩散技术制备出特高综合磁性能的钕铁硼磁体,对不同扩散源的扩散效果及扩散机制进行研究。采用TbH_x进行晶界扩散,获得综合磁性能(BH)_(max)+H_(cj)=84.26,矫顽力温度系数为-0.361%·℃~(-1)的最佳钕铁硼磁体,SEM微观结构分析表明TbH_x扩散源制备磁体在靠近磁体的表层晶粒形态与中心晶粒一致,晶粒表面平整。     

Signal-on electrochemical Y or junction probe detection of nucleic acid

A methylene-blue (MB)-labeled molecular beacon junction probe allows for a signal-on electrochemical detection of nucleic acids via target recycling using endonucleases. Electron transfer is reduced when the MB is intercalated in the stem of the molecular beacon, but then electron transfer from MB to a gold electrode is enhanced upon cleavage of the junction probe due to increased probability of MB approaching the electrode when attached to the more flexible ssDNA.     

从分子水平研究电子传递

有机分子中电子传递受到诸多因素的影响, 纳米电极、界面、环境和分子本身都是必须要系统考察的因素. 本文从理论模拟和实验研究两个方面总结了在分子尺度上电子传递研究的最新进展. 着重讨论了分子动力学方法模拟纳米电极的制备, 量子化学方法研究电场作用下的分子构象及分子电导, 另外还讨论了扫描隧道显微术和电化学方法研究单分子结的电子传递. 分子电子传递的研究不仅涉及微观的实验测量, 从宏观的实验结果通过合理的分析推导, 也可以得到微观的信息.     

电子在有机单分子膜中传递研究的新进展

随着分子电子器件研究的兴起,人们广泛使用诸如表面电化学、微接触滴汞电极、导电探针显微术和“Break-junction”等各种电化学或电学手段,对电子传递过程进行了深人研究。本文评述了有关电子在有机单分子膜传递研究的最新进展,同时介绍了与此相关的理论。     

Molecularly resolved protein electromechanical properties

Previous work has shown that protein molecules can be trapped between the conductive surfaces presented by a metal-coated AFM probe and an underlying planar substrate where their molecule-specific conductance characteristics can be assayed. Herein, we demonstrate that transport across such a derived metal-protein-electrode junction falls within three, pressure-dependent, regimes and, further, that pressure-dependent conductance can be utilized in analyzing temporal variations of protein fold. Specifically, the electronic and mechanical properties of the metalloprotein azurin have been characterized under conditions of anisotropic vertical compression through the use of a conducting atomic force microscope (CP-AFM). By utilizing the ability of azurin to chemically self-assemble on the gold surface presented either by the apex of a suitably coated AFM probe or a planar metallic surface, molecular-level transport characteristics are assayable. Under conditions of low force, typically less than 2 nN, the weak physical and electronic coupling between the protein and the conducting contacts impedes tunneling and leads to charge buildup followed by dielectric breakdown. At slightly increased force, 3-5 nN, the copper protein exhibits temporal electron occupation with observable negative differential resistance, while the redox-inactive zinc mutant does not. At imposed loads greater than 5 nN, appreciable electron tunneling can be detected even at low bias for both the redox-active and -inactive species. Dynamic current-voltage characteristics have been recorded and are well-described by a modified Simmons tunneling model. Subsequent analyses enable the electron tunneling barrier height and barrier length to be determined under conditions of quantified vertical stress. The variance observed describes, in essence, the protein's mechanical properties within the confines of the tunnel junction.     

Electrochemically driven transfer of carboxyl-terminated PAMAM dendrimers at the water/dichloroethane interface

The transfer of PAMAM dendrimers bearing carboxylic acid peripheral groups between two immiscible liquids was studied by means of the three phase junction system, using a gold wire vertically crossing the interface and decamethyl ferrocene as the redox probe in the organic phase. While the voltammetric behavior indicates kinetic limitations of the overall ion–electron transfer process, thermodynamic data shows that the phase transfer process is entropically controlled. Four dendrimer generations were analyzed and it was found that the kinetics as well as the thermodynamics of the phase transfer reaction are size dependent.     

Simultaneous nanoindentation and electron tunneling through alkanethiol self-assembled monolayers

Electrical tunnel junctions consisting of alkanethiol molecules self-assembled on Au-coated Si substrates and contacted with Au-coated atomic force microscopy tips were characterized under varying junction loads in a conducting-probe atomic force microscopy configuration. Junction load was cycled in the fashion of a standard nanoindentation experiment; however, junction conductance rather than probe depth was measured directly. The junction conductance data have been analyzed with typical contact mechanics (Derjaguin-Müller-Toporov) and tunneling equations to extract the monolayer modulus (approximately 50 GPa), the contact transmission (approximately 2 x 10(-6)), contact area, and probe depth as a function of load. The monolayers are shown to undergo significant plastic deformation under compression, yielding indentations approximately 7 Angstroms deep for maximum junction loads of approximately 50 nN. Comparison of mechanical properties for different chain lengths was also performed. The film modulus decreased with the number of carbons in the molecular chain for shorter-chain films. This trend abruptly reversed once 12 carbons were present along the backbone.     

Highly sensitive electrochemical detection of mercury (II) via single ion-induced three-way junction of DNA

A “signal-on” electrochemical sensing strategy was designed for highly sensitive and selective detection of mercury (II) via its induction to three-way junction of DNA (DNA-TWJ). The TWJ consisted of the capture probe that was self-assembled on a gold electrode surface through SAu bond, the signal probe that was labeled with ferrocene (Fc) and contained single T–T mismatch to capture probe, and an assistant probe for the formation of DNA-TWJ upon the presence of mercury (II). This process caused the Fc tag approaching the electrode for fast electron transfer and thus increased the oxidation current. The “signal-on” sensing method could detect Hg^2 + ranging from 0.005 to 100 nM. The assay was simple and fast. It showed potential application in on-site and real-time Hg^2 + detection.     

Grazing-exit electron probe X-ray microanalysis (GE-EPMA): Fundamental and applications

Electron probe microanalysis (or Scanning electron microscope-energy dispersive X-ray spectrometry) has been studied under grazing-exit conditions. That is, characteristic X-rays are detected at a very small take-off (exit) angle; the technique is known as grazing-exit electron probe microanalysis (GE-EPMA). Fundamental aspects, instrumentation, and characteristics of grazing-exit electron probe X-ray microanalysis method are described here. Since the observation depth decreases as the exit angle decreases, theoretically to a few nanometers, surface analysis is possible in grazing-exit electron probe X-ray microanalysis. Of course, the size of the electron beam is also small—less than 1 μm, enabling localized surface analysis. In the case of total reflection X-ray spectrometry that allows surface analysis, the whole sample surface must be flat. However, the requirement for flatness is not as strict in grazing-exit electron probe X-ray microanalysis. Grazing-exit electron probe X-ray microanalysis measurements can easily be applied using a commercially available electron probe microanalysis (or Scanning electron microscope-energy dispersive X-ray spectrometry) instrument. To change and control the exit angle in grazing-exit electron probe X-ray microanalysis, the inclination of the sample stage or movement of the X-ray detector is all that is required. Theoretically, this study shows that grazing-exit electron probe X-ray microanalysis would be useful in improving the lateral resolution of the sample surface. In addition, the study demonstrates that grazing-exit electron probe X-ray microanalysis can be applied successfully for surface, thin-film, and particle analyses. As an optional method of electron probe microanalysis, grazing-exit electron probe X-ray microanalysis will be useful in expanding the research fields of normal electron probe microanalysis.     

Correlation between HOMO alignment and contact resistance in molecular junctions: aromatic thiols versus aromatic isocyanides

Understanding electron transport in metal-molecule-metal (MMM) junctions is of great importance for the advancement of molecular electronics. Critical factors that determine conductivity in a MMM junction include the nature of metal-molecule contacts and the electronic structure of the molecular backbone. We have studied the electronic transport property and the valence electronic structure on rigid, conjugated oligoacenes of increasing length with either thiol (-S) or isocyanide (-CN) linkers using conducting probe atomic force microscopy (CP-AFM) and ultraviolet photoelectron spectroscopy (UPS). We find that for these conjugated systems the Au-CN contact is more resistive than Au-S. The difference in contact resistance correlates with UPS measurements that show the highest-occupied molecular orbital (HOMO) of the isocyanide series is lower in energy (relative to the Fermi level of Au) than the HOMO of the thiol series, indicating the presence of a higher tunneling barrier at the contact for the isocyanide-linked molecules. By contrast, the difference in the HOMO positions for the two series of molecules does not appear to affect the length dependence of the junction resistance (i.e., the beta value = 0.5 A-1).     

Observation of Quantum Interference at Room Temperature in a Single Perovskite Quantum Dot

Break junction technique allows researchers to probe charge transport properties in a single Perovskite quantum dot(QD)with anÅngstrom scale resolution,and observe signatures of quantum interference effects at room temperature.