Central Facility of Electron Microscopy, Group of Electron Microscopy of Materials Science, Ulm University, Albert-Einstein-Allee 11, 89081 Ulm, Germany.
Ultramicroscopy. 2011 Jul;111(8):1239-46. doi: 10.1016/j.ultramic.2011.03.012. Epub 2011 Apr 1.
The electron optical performance of a transmission electron microscope (TEM) is characterized for direct spatial imaging and spectroscopy using electrons with energies as low as 20 keV. The highly stable instrument is equipped with an electrostatic monochromator and a C(S)-corrector. At 20 kV it shows high image contrast even for single-layer graphene with a lattice transfer of 213 pm (tilted illumination). For 4 nm thick Si, the 200 reflections (271.5 pm) were directly transferred (axial illumination). We show at 20 kV that radiation-sensitive fullerenes (C(60)) within a carbon nanotube container withstand an about two orders of magnitude higher electron dose than at 80 kV. In spectroscopy mode, the monochromated low-energy electron beam enables the acquisition of EELS spectra up to very high energy losses with exceptionally low background noise. Using Si and Ge, we show that 20 kV TEM allows the determination of dielectric properties and narrow band gaps, which were not accessible by TEM so far. These very first results demonstrate that low kV TEM is an exciting new tool for determination of structural and electronic properties of different types of nano-materials.
透射电子显微镜（TEM）的电子光学性能采用低至 20keV 的电子进行直接空间成像和光谱分析进行了表征。该高度稳定的仪器配备了静电单色仪和 C(S)-校正器。在 20kV 时，即使对于晶格转移为 213pm（倾斜照明）的单层石墨烯，它也具有高的图像对比度。对于 4nm 厚的 Si，直接转移了 200 个反射（271.5pm）（轴向照明）。我们在 20kV 下表明，在碳纳米管容器内的辐射敏感富勒烯（C(60)）能够承受比在 80kV 下高约两个数量级的电子剂量。在光谱模式下，单色低能电子束能够以非常低的背景噪声获取高达非常高能量损失的 EELS 光谱。使用 Si 和 Ge，我们表明 20kV TEM 允许确定介电性能和窄带隙，这是迄今为止 TEM 无法实现的。这些初步结果表明，低 kV TEM 是一种用于确定不同类型纳米材料的结构和电子性能的令人兴奋的新工具。
