Formation of Interfacial Layers in LaAlO3/Silicon during Film Deposition

We have studied the interracial reactions between amorphous LaAlO3 thin films and Si substrates, using high- resolution transmission electron microscopy and x-ray photoelectron spectroscopy. It has been shown that the interracial layer between LaAlO3 film and Si substrate chemical states show that the ratio of La 4d3/2 to Al 2p is SiLaxAlyOz. The depth distributions of La, Si and Al of the interfacial layer remains unchanged with the depth compared to that of the LaAlO3 film. Moreover, the Si content, in the interracial layer gradually decreases with increasing thickness of the interracial layer. These results strongly suggest that the Al element is not deficient in the interracial layer, as previously believed, and the formation of a SiLaxAlyOz interracial layer is mainly due to the diffusion of Si from the substrate during the LaAlO3 film deposition. With the understanding of the interracial layer formation, ones can control the interface characteristics to ensure the desired performances of devices using high-k oxides as gate dielectrics.     

Mechanically tunable broadband terahertz modulator based on high-aligned Ni nanowire arrays

We present a mechanically tunable broadband terahertz(THz) modulator based on the high-aligned Ni nanowire(NW)arrays. The modulator is a sandwich structure consisting of two polydimethylsiloxane layers and a central layer of highaligned Ni NW arrays. Our experimental measurements reveal the transmittance of THz wave can be effectively modulated by mechanical stretching. The NW density in arrays increases with the strain increasing, which induced an enhancement in the absorption of THz wave. When the strain increases from 0 to 6.5%, a linear relationship is observed for the variation of modulation depth(MD) of THz wave regarding the strain, and the modulated range is from 0 to 85% in a frequency range from 0.3 THz to 1.8 THz. Moreover, the detectable MD is about 15% regarding the 1% strain change resolution. This flexible Ni NW-based modulator can be promised many applications, such as remote strain sensing, and wearable devices.     

电子束诱导沉积钴微米线及其铁磁性

通过电子束诱导沉积的方法制备了钴(Co)微米线,并利用扫描电子显微镜(SEM)、原子力/磁力显微镜(AFM/MFM)以及物性测量系统(PPMS)等手段对Co微米线的沉积尺寸、微结构、铁磁性和电学性质进行了测试和分析。研究结果表明:Co微米线轮廓清晰、均匀性好。在不同的沉积条件下,微米线的实际长度与设定长度基本一致;实际宽度数据呈类梯形分布,半高宽是设定值的2~10倍;实际厚度低于设定厚度的60%。沉积电流对Co微米线的铁磁特性有重要影响。当沉积电流大于0.5 nA时,样品呈现出良好的铁磁特性。另外,电学性能测试结果显示Co微米线呈现绝缘特性。成功制备了室温铁磁绝缘Co微米线,这将有助于深入开展微纳尺度的结构与器件的研究和应用。     

新型路灯节能系统的设计

设计了一种新型的路灯节能照明控制系统。用发光二极管代替实际路灯,制备出了演示系统。该系统包括单片机、红外线感应器和光敏电阻等元器件。随着外界光照强度和人车流量等条件的改变该系统所控制的路灯可以自动调节灯光亮度,以达到节能的目的。如果该路灯控制系统能够投入使用,将会减少许多无谓的能源消耗,为我们国家所倡导的绿色、低碳、环保的生活添砖加瓦。     

薄膜材料杨氏模量测量方法的研究进展

基于国内外薄膜材料杨氏模量测试的最新研究进展,系统地综述了近年来薄膜材料杨氏模量的测量方法,包括共振法、纳米压痕法、动态膨胀法以及视觉图像跟踪系统与微拉伸复合法等,并对这些测试方法的基本原理、研究现状及存在的问题做了简要介绍。在这些方法中纳米压痕法和共振法是相对准确而且普及的测量方法。当薄膜厚度减小到纳米量级时,纳米压痕法将达到测试的极限。共振法对于器件的加工工艺有一定的依赖,但辅以其他相关纠正技术将来有望成为测试纳米级薄膜杨氏模量的标准方法。     

用于长城等古建筑探测的NMR探测器的磁体设计

以万里长城为代表的古建筑是世界瑰宝,更是中华民族的象征和骄傲.本文提出利用便携式核磁共振（NMR）装置来探测研究这类古建筑的建筑材料,在不对其造成损伤的基础上,发掘其隐含的科学、技术和工程相关的丰富信息.为此,作为第一步,设计了适合于探测这类古建筑的便携式单边NMR探测器组合式磁体.该探测器的磁体结构以semi-Halbach为基础,通过不同磁体模块间的组合得到对应移动探测模式、长距离探测模式和均匀磁场探测模式的磁体结构.随后根据优化结果,设计加工了磁体组件,并采用该磁体进行了流体、长城城砖和现代红砖的NMR实验,实测结果与模拟一致.该组合式磁体的优点在于通过不同磁体模块组合,实现了多种探测方式,适用于探测长城等这类古建筑物需要多种探测模式的科学研究.     

原子尺度控制钙钛矿氧化物薄膜的异质外延生长和特性研究

用激光分子束外延,原子尺度控制的外延生长出多种钙钛矿氧化物异质结.X射线衍射和原子力显微镜测量结果表明,在Si基底上生长的SrTiO3和LaAlO3薄膜具有很好的外延结构和取向,其表面达到原子尺度的光滑.YBCO/SrNb0.01Ti0.99O3、La0.9Sr0.1MnO3/SrNb0.01Ti0.99O3(LSMO/SNTO)等异质结,均观测到较好的p-n结I-V特性.首次观测到钙钛矿结构氧化物p-n结电流的磁调制和正巨磁电阻效应,在255K条件下,当外加磁场分别为5×10-4T、1×10-3T、1×10-2T和0.1T时,LSMO/SNTO p-n结的磁电阻变化率ΔR/R0达到:46.7%、59.7%、70.5%和83.4%;当外加磁场为3T时,在100K条件下,在LSMO/SNTO多层p-n异质结上观测465%的正磁电阻变化率.     

一维纳米材料排列方法的研究进展

基于国内外一维纳米材料器件的最新研究进展,系统综述了近年来一维纳米材料的排列方法,并介绍了磁场排列法、电场排列法、微流法、Langmiur-Blodgett等方法的原理和优缺点。同时,指出了一维纳米材料器件集成所面临的挑战,例如无法兼顾大规模有序排列与单一纳米材料精确定位排列等。最后,简单展望了一维纳米材料排列方法的发展趋势,传统排列方法,包括磁学方法和电学方法等的发展已经遇到了技术瓶颈,短时间内难以得到本质性的优化,生物技术也许会成为一维纳米材料有序排列的一个发展方向。     

Ni(Pt) 锗硅化合物/Si1-xGex 接触电阻的测试

The electrical properties of Ni0.95Pt0.05-germanosilicide/Si1_xGex contacts on heavily doped p-type strained Sil-xGex layers as a function of composition and doping concentration for a given composition have been investigated. A four-terminal Kelvin-resistor structure has been fabricated by using the conventional com- plementary metal-oxide-semiconductor （CMOS） process to measure contact resistance. The results showed that the contact resistance of the Ni0.95Pt0.05-germanosilicide/Sil-xGex contacts slightly reduced with increasing the Ge fraction. The higher the doping concentration, the lower the contact resistivity. The contact resistance of the samples with doping concentration of 4×10^19 cm^-3 is nearly one order of magnitude lower than that of the sam- ples with doping concentration of 5 × 10^17 cm^-3. In addition, the influence of dopant segregation on the contact resistance for the lower doped samples is larger than that for the higher doped samples.     

Ni纳米线的化学还原法可控制备北大核心

利用化学还原法制备了Ni纳米线,通过扫描电子显微镜（SEM）研究了制备参数（磁场强度、Ni 2＋离子浓度和反应温度）对Ni纳米线合成以及结构的影响。实验结果表明：磁场强度是影响Ni纳米线直径均匀性的关键因素。无外加磁场时所制得的产物为Ni纳米颗粒;当磁场强度达到0.25 T时,纳米线的长度较长,直径较均匀。Ni 2＋离子浓度决定着纳米线直径的大小。Ni 2＋浓度越低,直径越小。反应温度影响成核以及纳米线的表面形貌。当温度低于50℃时,溶液中没有纳米线生成,说明溶液没有反应;当反应温度在60~80℃范围内时,纳米线的表面均有明显的刺状结构;当温度高于85℃时,纳米线表面的刺状结构数目明显减少,形成了光滑的表面。