Next generation direct electron detectors for diffraction measurements in the scanning electron microscope

用于扫描电子显微镜衍射测量的下一代直接电子探测器

• 批准号: 2436029
• 金额: --
• 依托单位: University of Strathclyde
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2020
• 资助国家: 英国
• 起止时间: 2020 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2436029
• 关键词: Next; generation; direct; electron; detectors

The aim of this project is to develop next generation detectors for the scanning electron microscopy (SEM) techniques of electron backscatter diffraction (EBSD).EBSD exploits diffraction of backscattered electrons to provide information on the structural properties of materials rapidly and non-destructively, with a spatial resolution of tens of nanometres, from large areas of the surface of a sample. It is a well-established technique for texture analysis, quantifying grain boundaries and crystal phases and the use of cross-correlation-based analysis of allows the measurements of relative strain, geometrically necessary dislocations, lattice tilt and twist, antiphase domains, and crystal polarity.In EBSD, the impinging electrons are scattered inelastically through high angles forming a diverging source of backscattered electrons which can be diffracted. The resultant electron backscatter pattern (EBSP) consists of a large number of overlapping bands, known as Kikuchi bands, which are closely related to a 2D projection of the crystal structure. EBSP are generally detected by an electron-sensitive phosphor or scintillator screen and a charge-coupled device (CCD) or complementary metal-oxide-semiconductor (CMOS) camera. In this project, direct electron detectors are being developed as a replacement for the conventional phosphor screen and visible camera combination. The advantages of direct electron detectors include the ability to reduce the electron beam energy; beam current; and acquisition time compared with conventional systems. There is also no distorting optics; acquisition can be noiseless; and for the detectors to be exploited in the present project, energy discrimination of the backscattered electrons is also possible. This will lead to improved lateral and spatial resolution and will allow the acquisition of small-scale details in the EBSP which are not in practice obtainable with existing commercial EBSD systems. This may provide routes to, for example, the determination of lattice constant, crystal phase identification, and the mapping of strain with greater sensitivity. The reduced voltage and current capabilities will also allow the microstructural analysis of materials which generally damage under the beam, such as halide perovskites for next generation solar cells. The first demonstrations of energy filtered direct electron detection EBSD were carried out here at Strathclyde, which demonstrated the capabilities of Timepix, a digital CMOS hybrid pixel detector. This detector was an outcome of an international collaboration (Medipix2) hosted at CERN, established to provide a solution for a range of problems in X-ray and gamma-ray imaging. In collaboration with National Physical Laboratory (NPL), the use of Timepix for 3D EBSD where EBSD maps are acquired sequentially as a sample is sliced in a focussed ion beam SEM. EDAX has also very recently launched a commercial direct electron detector EBSD system based on the Timepix detector.This PhD project will go beyond this first commercial system. In collaboration with the University of Glasgow and NPL, the newest hybrid pixel detectors for EBSD will be exploited. New detectors will allow EBSD to be performed at even lower voltages (of order 1 kV, present systems operate down to around 5 kV) and with higher acquisition rates (of order 10,000 frames per second). The complex data analysis of the squired EBSPs will be in collaboration with Dr Aimo Winkelmann (AGH University of Science and Technology, Krakow, Poland and visiting professor at Strathclyde) using his world-leading dynamical simulations analysis software.

该项目的目的是为电子背散射衍射（EBSD）的扫描电子显微镜（SEM）技术开发下一代探测器。EBSD利用背散射电子的衍射，快速和非破坏性地提供材料结构特性的信息，空间分辨率为数十纳米，从样品表面的大面积。EBSD是一种成熟的织构分析技术，可以量化晶界和晶相，并使用基于互相关的分析方法，可以测量相对应变、几何上必要的位错、晶格倾斜和扭曲、反相畴和晶体极性。在EBSD中，撞击的电子通过大角度非弹性散射，形成可以衍射的背散射电子的发散源。所得到的电子背散射图案（EBSP）由大量的重叠带组成，称为菊池带，其与晶体结构的2D投影密切相关。EBSP通常通过电子敏感的磷光体或闪烁体屏幕和电荷耦合器件（CCD）或互补金属氧化物半导体（CMOS）相机来检测。在这个项目中，正在开发直接电子探测器，以取代传统的荧光屏和可见光摄像机组合。与传统系统相比，直接电子探测器的优点包括降低电子束能量、束电流和采集时间的能力。也没有扭曲的光学;采集可以是无噪声的;对于本项目中要利用的探测器，也可以对背散射电子进行能量鉴别。这将导致改进的横向和空间分辨率，并将允许在EBSP中获取小尺度细节，这在实践中是无法用现有的商业EBSD系统获得的。这可以提供途径，例如，晶格常数的测定，晶体相鉴定，并以更高的灵敏度应变的映射。降低的电压和电流能力还将允许对通常在光束下损坏的材料进行微观结构分析，例如用于下一代太阳能电池的卤化物钙钛矿。能量过滤直接电子探测EBSD的第一个演示是在斯特拉斯克莱德进行的，它展示了数字CMOS混合像素探测器Timepix的能力。该探测器是欧洲核子研究中心主持的国际合作（Medipix 2）的成果，旨在为X射线和伽马射线成像中的一系列问题提供解决方案。与国家物理实验室（NPL）合作，使用Timepix进行3D EBSD，当样品在聚焦离子束SEM中切片时，EBSD图按顺序获取。EDAX最近还推出了一个基于Timepix探测器的商业直接电子探测器EBSD系统。这个博士项目将超越这个第一个商业系统。与格拉斯哥大学和NPL合作，将开发用于EBSD的最新混合像素探测器。新的探测器将允许EBSD在甚至更低的电压（1 kV的量级，目前的系统工作低至约5 kV）和更高的采集速率（每秒10，000帧的量级）下执行。EBSP的复杂数据分析将与Aimo Winkelmann博士（波兰克拉科夫AGH科技大学和斯特拉斯克莱德访问教授）合作，使用他世界领先的动态模拟分析软件。