氮离子注入形成SOI结构的外延研究

用大束流(50μA/cm~2)、高剂量(1.8×10~(18)/cm~2)的190keV N~+注入Si〈100〉中,然后在SiO_2覆盖保护下于1220℃退火二小时形成SOI结构.为了增加SOI材料上层单晶Si的厚度以应用于器件制作,将退火得到的SOI样品经化学处理后作外延生长.外延后获得的SOI材料,上层单晶Si厚度为0.8-1.0μm;Si_3N_4埋层的厚度为2800A;上、下Si-Si_3N_4界面陡峭.测试分析结果表明,利用N~+注入与气相外延生长能获得质量好的SOI材料.     

大剂量氧离子注入形成SOI结构的研究

本文利用背散射分析技术、扩展电阻测量、高能电子衍射及超高压透射电镜研究了注氧后埋SiO_2层的形成过程以及顶部剩余硅的退火行为,通过沟道背散射分析技术与霍尔测量,给出了在不同退火条件下顶部剩余硅的单晶结晶度及霍尔迁移率.结果表明:150keV下注入1.8×10~(13)O~+/cm~(?),经1250℃2h退火后,表面剩余单晶硅厚度约为1600-1900A,埋SiO_2层厚度为3000-3500A.同时,采用高温注入对于埋SiO_2层性能的改善以及顶部剩余硅的单晶恢复均是非常必要的.     

氧离子注入硅SOI结构的椭偏谱研究

本文利用椭偏光谱法测量了能量为200keV、剂量为2×10~(18)cm~(-2)的~(16)O~+注入Si以及退火样品.应用多层介质膜模型和有效介质近似,分析了这些样品的SIMOX结构的各层厚度以及各层中的主要组份.提出了从椭偏谱粗略估算表层Si及埋层SiO_2厚度的简单方法.研究结果表明,这种条件下的O~+注入Si可以形成SIMOX结构,经高温退火后,表层Si是较完整的单晶层,埋层SiO_2基本没有Si聚积物.椭偏谱的结果与背散射、扩展电阻测量和红外吸收光谱等结果作了比较.     

用高分辨电子能量损失谱和紫外光电子谱研究多孔硅的电子结构

本文首次使用分辨电子能量损失谱（ＨＲＥＥＬＳ）和紫外光电子能谱（ＵＰＳ）研究新腐蚀的多孔硅样品（ＰＳ）的电子结构．实验结果发现,从ＨＲＥＥＬＳ谱中能量损失阈值测得的多孔硅的能隙最可几值移到２．９ｅＶ左右,与文献报道的光激发谱（ＰＬＥ）的结果相近．ＵＰＳ结果发现多孔硅费米能级到价带顶的距离不同于单晶硅,结合ＨＲＥＥＬＳ和ＵＰＳ结果可以初步得出多孔硅与硅界面的能带排列．     

生长于Si(111)上的氮化硅薄膜表面结构

利用扫描隧道显微镜 ( STM)等分析手段 ,我们对 Si( 1 1 1 )在 NH3气氛下氮化后的表面结构进行了研究 .Si( 1 1 1 )在 1 0 75K暴露于 NH3后 ,表现所形成的氮化硅存在周期为 1 .0 2 nm的(“8/3× 8/3”)再构 ,当温度提高到 1 1 2 5K以上时 ,表面出现周期为 3.0 7nm的超结构 .这两种表面超结构都可以形成“8× 8”低能电子衍射花样 .系统的研究证明 3.0 7nm超结构是在 Si( 1 1 1 )表面形成晶态 β- Si3N4 薄膜 ( 0 0 0 1 )表面的 4× 4再构 ,而 1 .0 2 nm周期是 Si( 1 1 1 )表面未获得有效氮化的一种结构     

耦合双纳米颗粒的表面等离激元计算

本文以耦合的Au纳米双颗粒以及Au/CdS核壳双颗粒为例,介绍了利用有限元多物理场耦合软件COMSOL计算电子能量损失谱的方法.计算结果不仅证实了实验中观察到的共振吸收峰随电子束入射点远离颗粒而红移的结果,也揭示出高能电子所激发的振荡模式和系统本征模式之间的差异,表明所获取的电子能量损失谱的振荡模式并非是单一的本征振荡,而是几种本征模式组合而成的混合模式.     

生长于Si(111)上的氮化硅薄膜表面结构

利用扫描隧道显微镜(STM)等分析手段,我们对Si(111)在NH3气氛下氮化后的表面结构进行了研究.Si(111)在1075K暴露于NH3后,表现所形成的氮化硅存在周期为1.02nm的(“8/3×8/3”)再构,当温度提高到1125K以上时,表面出现周期为3.07nm的超结构.这两种表面超结构都可以形成“8×8”低能电子衍射花样.系统的研究证明3.07nm超结构是在Si(111)表面形成晶态β-Si3N4薄膜(0001)表面的4×4再构,而1.02nm周期是Si(111)表面未获得有效氮化的一种结构.     

低电压STEM-EELS在纳米催化剂结构表征中的应用

低电压球差校正扫描透射电子显微学和电子能量损失谱(STEM-EELS)由于能够有效地避免撞击位移损伤(knock-on damage)和提高电子束与样品的非弹性散射截面,从而在低维纳米催化剂的结构表征方面具有广阔的应用前景。作者以最近在CrNi氧化物和Ni-N-C单原子催化剂上的工作为例,展示利用低电压STEM-EELS表征不同元素不同化合价态在空间上的分布以及在单原子敏感度下进行化学键合的分析。这些基于低加速电压下的STEM-EELS结果为理解纳米催化剂的构效关系提供了更全面的认识以及为材料设计提供了进一步指导。     

空间分辨电子能量损失谱对合金高温氧化的研究

空间分辨电子能量损失谱（Spatially-resolved EELS）是指在利用配备有能量过滤系统的透射电子显微镜（Energy filter coupled TEM）采集电子能量损失谱时，通过调整样品取向使得样品表面与EELS能量色散方向平行，从而在采集电子能量损失谱时在垂直于能量色散方向具有一定的空间分辩率的实验方法。对于同一元素，当处于不同化学环境时，其电子能量损失近阈精细结构（Energy Loss Near Edge Structure,ELNES）升起点处的绝对能量会有所差异，     

利用电子能量损失谱对二氧化铀电子结构的研究

锕系元素因具有复杂的5f电子结构,其显示出神秘而又独特的物理、化学特性.为了加深对锕系金属、合金和化合物的特异行为的理解,对其电子结构精确表征的重要性日益凸显.电子显微技术与电子能量损失谱技术的结合在锕系元素原子结构和电子结构研究中发挥了至关重要的作用.本文采用电子能量损失谱研究二氧化铀的5f电子结构,并讨论了铀5f电子的相互作用特性.     

3D-analysis of semiconductor structures by electron tomography

The analysis of advanced nano-devices by the classical 2D imaging with transmission or scanning transmission electron microscopy suffers from projection effects over the sample thickness that result in e.g. blurring due to interfacial roughness or superposition of different structures. Electron tomography allows to overcome these problems. The method involves the acquisition of tilted series of 2D-images, the accurate alignment of these images and the 3D volume reconstruction. Slicing in any direction through this volume yields sections through the device structure with resolution of a few nanometer. The methodology is discussed and illustrated with some case studies.     

Correlative microscopy analyses of thin-film solar cells at multiple scales

In the present work, a brief overview is given on how to apply transmission (TEM) as well as scanning electron microscopy (SEM) and their related techniques (electron diffraction, energy-dispersive X-ray spectrometry, electron energy-loss spectroscopy, electron holography; electron backscatter diffraction, electron-beam-induced current, cathodoluminescence) for the analysis of interfaces between individual layers or extended structural defects in a thin-film stack. All examples given in the present work were recorded on Cu(In, Ga)Se₂ thin film solar cells, however, the shown experimental approaches may be used on any similar thin-film semiconductor device. A particular aspect is the application of various techniques on the same identical specimen area, in order to enhance the insight into structural, compositional, and electrical properties. For (aberration-corrected) TEM, the spatial resolutions of such measurements can be as low as on the subnanometer scale. However, when dealing with semiconductor devices, it is often necessary to characterize electrical and optoelectronic properties at larger scales, of few 10 nm up to even mm, for which SEM is more appropriate. At the same time, these larger scales provide also enhanced statistics of the analysis. In the present review, it is also outlined how to apply SEM techniques in combination with scanning-probe and optical microscopy, on the same identical positions. Altogether, a multiscale toolbox is provided for the thorough analysis of structure-property relationships in thin-film solar cells using correlative microscopy approaches.     

Atomically resolved mapping of EELS fine structures

Over the past two or three decades, nanoscience and nanotechnology have clearly established themselves as prominent domains in research in physics, not only because of the innovative concepts and properties that they display but also for their capacity to generate many important applications and commercial developments. As many of these new devices exhibit a range of properties (transport, optical, magnetic, catalysis) which are governed by local structural and electronic configurations, such as coordination and bonding at the atomic level, it is no surprise that new tools of investigation are constantly being developed for imaging, analyzing, understanding and controlling at the relevant scale. Among them, electron microscopy has recently demonstrated its ability to meet many of these requirements. In particular, Å-sized probes are nowadays generated by aberration correctors in a scanning transmission electron microscope (STEM) and they can investigate the electron excitation spectrum of the specimen (through electron energy-loss spectroscopy, EELS) with a typical energy resolution of 0.1–0.3 eV over a broad spectral band from the IR to the X ray domain. In the high energy range, characteristic signals due to the excitation of atomic core levels are quite useful because they identify the atoms in the analyzed volume (which can itself be as small as a single atom) and can therefore deliver atomically-resolved elemental maps. But the pixel-by-pixel recording of the fine structures beyond the characteristic threshold is much more informative and tells us how the excited atom is surrounded by its neighbors, what is its exact structural environment and its charge population. The present review focuses on this particularly exciting field, with a special interest in the types of information accessible and their signature. After summarizing the ingredients required for successful experiments (instrumental as well as theoretical), examples encountered in different situations, in particular in single layers of 2D materials and at the interfaces in oxide heterostructures, will demonstrate the present capabilities of this STEM-EELS technique.