Current Density-Dependent Thermal Stability of ZnSe Nanowire in M-S-M NanostructureD

Due to semiconductor nanowire （NW） having a very tiny diameter, the electronic devices based on metal-semiconductor NW-metal （M-S-M） nanostruc- ture can carry a very large current density com- pared to electronics based on bulk semiconductors. A small mass of a NW also means a small heat capacitance. In this case, any small energy trans- fer from the current-carry electrons to local ionic or/and lattice vibrations in NWs may cause a sub- stantial self-heating of the NWs. Thus thermal insta- bility of NWs in M-S-M nanostructure due to Joule heating has become a fundamentally and technolog- ically important issue concerning the performance of semiconductor NW-based nanoelectronics and has at- tracted a lot of attention. The failure behaviors of various semiconductor and metallic NWs inves- tigated by in situ transmission electron microscopy （TEM） and confocal micro-Raman spectroscopy re- spectively have confirmed semiconductor NWs includ- ing Si, Ge, GaN, ZnO, Sn02, Ti02, ZnSe and ZnTe NWs electrically broken by thermal evaporation due to Joule heating and metallic NWs electrically de- stroyed by electromigration. Electron-phonon in- teraction that transfers energy from conduction elec- trons to the ions in the material causes Joule heating. Electromigration due to the transfer of the momentum of conduction electrons to the ions causes migration of atoms in the material when high current density flows through a circuit. The different failure mechanisms of these NWs are significantly materials-dependent due to the difference of their chemical and physical prop- erties and have a very close relation with the param- eters governing the electron transport mechanism at the metal-semiconductor （M-S） nanocontact such as Schottky barrier and bias polarity .     

Determination of the Potential Barrier at the Metal／Oxide Interface in a Specular Spin Valve Structure with Nano—oxide Layers Using Electron Holography

The local potential distribution in a specular spin valve structure with nano-oxide layers has been mapped by using off-axis electron holography in a field emission gun transmission electron microscope.A potential jump of 3-4 V across the metal/oxide interface was detected for the first time.The presence of the potential barrier confirms the formation of the metal/insulator/metal structure,which contributes to the increasing mean free path of spin-polarized elecrons via the specular reflection of spin-polarized electrons at the metal/oxide interface.It leads to nearly double enhancement of the magnetoresistance ratio from 8% to 15%.     

无烟煤结构的高分辨电镜研究

镜质组不仅是煤结构变化最具规律性，也是影响煤质的主要微成分。用点分辨率为２．１Ａ的高分辨电镜对几种不同煤化程度的无烟煤大分子结构进行了研究。结果表明：电镜图像直接表征了无烟煤分子的非均匀性孔隙结构。京西煤分子方向化程度强，主要以芳层平行堆或有序化前结构为主；晋城煤方向化程度弱，主要以粒状嵌晶结构为主。高分辨电镜技术是研究煤分子结构和煤化作用实质的有效方法。     

碳纳米管阵列、捆束的三步升温工艺制备及其形貌与结构

使用结构简单的单温炉设备，通过三步升温热解二茂铁、三聚氰氨混合物方法，在二氧化硅、多晶陶瓷基底上分别合成了碳纳米管阵列、碳纳米管捆束.使用扫描电子显微镜、透射电子显微镜、电子能量损失谱和x射线光电子能谱对合成样品进行了结构和成分分析.结果显示：两种基底上合成的纳米管均为多壁纯碳管；生长于光滑二氧化硅表面的碳纳米管具有高度取向性和一致的外径，长度为10—40μm.碳纳米管采取催化剂顶端生长模式并展示出类杯状形貌；生长于粗糙多晶陶瓷表面的碳纳米管捆束随机取向，碳纳米管直径为15—80nm，长度在几百微米，展示 关键词： 碳纳米管 热解法 三步升温工艺     

钴纳米粒子自组装有序阵列与磁性

采用高温液相分解法制备出平均粒径不同的单分散的钴纳米粒子.用自组装的方法得到二维和三维的钴纳米粒子有序阵列，用透射电子显微镜研究了粒径、温度、有机溶剂以及浓度对钴纳米粒子的自组装的影响.用超导量子干涉仪研究了钴纳米粒子的超顺磁性.这些研究结果为深入研究磁性纳米粒子的物性和在纳米器件中的应用奠定了良好的基础. 关键词： 钴纳米粒子 自组装 超顺磁性     

基于FPGA的自适应调节光栅光谱仪

采用FPGA作驱动和控制电路的核心,以简单的逻辑电路实现了CCD曝光时间和可编程放大器增益的自适应控制.在此基础上开发了能将信号幅度自动调节到合适范围的光栅光谱仪,采用USB总线实现系统与上位机的通讯,由LabVIEW平台开发出的应用程序进行光谱数据存储、谱图显示和处理.     

Measurement of Specimen Thickness by Using Electron Holography and Electron Dynamic Calculation with a Transmission Electron Microscope

A method of transmission-electron microscopy for accurate measurement of specimen thickness has been proposed based on off-axis electron holography along with the dynamic electron diffraction simulation.The phase shift of the exit object wave with respect to the reference wave in vacuum,resulting from the scattering within the specimen,has been simulated versus the specimen thickness by the dynamic electron diffraction formula.Offaxis electron holography in a field emission gun transmission-electron microscope has been used to determine the phase shift of the exit wave.The specimen thickness can be obtained by match of the experimental and simulated phase shift.Based on the measured phase shift of the [110] oriented copper foil,the thickness can be determined at a good level of accuracy with an error less than-10%.     

Determination of Mean Inner Potential by Electron Holography Along with Electron Dynamic Simulation

Off-axis electron holography in a field-emission-gun transmission electron microscope and electron dynamic simulation is used to determine the mean inner potential of copper.The phase shift of object wave versus specimen thickness is calculated up to 30 nm using electron dynamic formula,and the sample thickness is decided by match of the experimental and calculated phase shift.Based on the measured phase shift the calculated mean inner potential of Cu is 21.2V,which agrees with the reported values within the experimental error.     

Enhanced Current Carrying Capability of Au-ZnSe Nanowire-Au Nanostructure via High Energy Electron Irradiation

To enhance the performance of nanoelectronics based on Au-ZnSe nanowire （NW）-Au （M-S-M） nanostructure, the effect of irradiation of the high energy electron beam emitted from the electron gun of a transmission electron microscope operated at 200kV on the current carrying capability of M-S-M nanostructure is investigated in sftu. Focusing the high energy electron beam on a Au electrode, the current carrying capability of the M-S-M nanostructure can be enhanced significantly with respect to the case of the electron beam being switched off. In this case, the electrons in the electrode are excited by the incident high energy electron and can freely tunnel through the Schottky barriers at the metal-semiconductor NW （M-S） nanocontacts, which can effectively reduce Joule heat dissipation and remarkably improve the current carrying capability of M-S-M nanostructure due to the fact that the current carrying capability highly depends on the Joule heating effect of Schottky barriers at M-S nanocontacts.     

Low-field electron emission from pinaster-like MoO2 nanoarrays as two-stage emitters

Low-field electron emission is obtained from the pinaster-like MoO2 nanoarrays. The turn-on field of the pinasterlike MoO2 nanoarrays is found to be as low as 2.39 V/μm with the current density of 10μA/cm2. The enhancement factor is extracted to be 3590 from the Fowler-Nordheim plot. These excellent emission properties are attributed to the special structure of the pinaster-like MoO2 nanoarrays and confirmed by the calculation in the frame of the two -stage model. Our results show that the pinaster-like MoO2 nanoarrays are promising candidate in realizing field emission displays.