纳米单晶电子衍射仪仪器设备的研究开发与应用

Facing up to the challenges of the atomic structure solution for nano-sized crystalline materials, a new instrument which can collect complete three-dimensional single crystal diffraction data is proposed. The instrument has a similar design of X-ray single crystal diffractometer, but built inside a transmission electron microscope. Nano-beam electron diffraction using transmission electron microscope (TEM) has become a unique tool to perform electron diffraction on a nano-sized crystal. Modern TEMs could allow us to control coils, the goniometer and also the CCD camera of the instrument by programming that gives us a chance to design and make TEM devices for specific applications. Electron beam in a TEM can be rotated relative to a static crystal by electromagnetic coils with very precise rotation (> 0.001°) although the electron beam can only be rotated in a small range (3° - 5°). When rotations of both the electron beam and the goniometer are combined, electron beam could be rotated relative to the crystal with very precise steps and in a large rotation range. CCD cameras could be used to track the movements of the crystal and recode electron diffraction patterns after each beam rotation. In such a case, the crystal is kept stationary all the time and a series of electron diffraction patterns can be collected. Based on the modification of TEM and programming, the whole procedure can be done in an automatic way. When the nano-beam electron diffraction is used, a nano-beam single crystal electron diffractometer is expected.

为解决目前纳米尺寸晶体材料的单晶结构解析难题，本项目旨在发展一种可用于纳米尺寸晶体材料的单晶衍射数据采集设备。透射电子显微镜具备观察纳米尺寸晶体的先天优势，选区或纳米电子衍射功能可实现对纳米尺寸晶体的电子衍射分析。利用程序控制电子束的倾转可实现高精度的小角度倾转，利用程序控制样品台可实现对晶体的大角度倾转。通过透射电子显微镜的图像与衍射工作模式之间的切换，数字相机可以在图像模式下对晶体倾转过程中的位置变化进行跟踪，而在衍射模式下采集晶体的衍射数据，从而实现纳米尺寸晶体的三维电子衍射数据的自动采集。本项目将对透射电子显微镜加以改装，制造一种可用于纳米尺寸晶体单晶电子衍射数据采集的新型设备——纳米单晶电子衍射仪。

结构解析是研究材料性质最关键的一步。目前应用最广泛的X射线衍射方法由于受到衍射峰叠加以及晶体尺寸等的限制，使得纳米晶体材料的结构解析成为一大难题。而电子衍射方法则能克服这些困难。本项目主要研究内容及成果为：基于电子显微学最新发展的旋进电子衍射原理，在透射电子显微镜（透射电镜）中成功研发出了用于纳米尺寸单晶体材料的3维(3D)单晶电子衍射谱数据全自动采集、数据处理、纳米单晶结构解析的仪器设备：纳米单晶电子衍射仪。目前该设备成功完成对样品图像及衍射谱的自动化托管数据收集；采用相关法，保证了50纳米以内直径纳米晶体在数据收集过程中全自动跟踪，并对10纳米左右的样品仍然能够很好的进行图像的漂移校正；本套设备使用网络接口进行仪器控制与数据传输，对原透射电镜不造成任何影响；衍射仪已经成功在JEOL和FEI两家公司生产的透射电镜上安装运行，并且对不同机型设计了大角度倾转样品杆（±70°）；多次试验结果证明该设备能够准确确定样品的晶体结构，并取得了一定科研成果。该套设备的成功研发，不仅能解决纳米材料领域的结构解析难题，并且在晶体缺陷及物相分析等领域具有很大的应用前景。