Malac Marek, Beleggia Marco, Egerton Ray, Zhu Yimei
National Institute for Nanotechnology, 11421 Saskatchewan Drive, Edmonton, Canada T6G 2M9.
Ultramicroscopy. 2008 Jan;108(2):126-40. doi: 10.1016/j.ultramic.2007.03.008. Epub 2007 Mar 31.
We have optimized a bright-field transmission electron microscope for imaging of high-resolution radiation-sensitive materials by calculating the imaging dose n(0) needed to obtain a signal-to-noise ratio (SNR)=5. Installing a Zernike phase plate (ZP) decreases the dose needed to detect single atoms by as much as a factor of two at 300 kV. For imaging larger objects, such as Gaussian objects with full-width at half-maximum larger than 0.15 nm, ZP appears more efficient in reducing the imaging dose than correcting for spherical aberration. The imaging dose n(0) does not decrease with extending of chromatic resolution limit by reducing chromatic aberration, using high accelerating potential (U(0)=300 kV), because the image contrast increases slower than the reciprocal of detection radius. However, reducing chromatic aberration would allow accelerating potential to be reduced leading to imaging doses below 10 e(-)/A(2) for a single iodine atom when a CS-corrector and a ZP are used together. Our simulations indicate that, in addition to microscope hardware, optimization is heavily dependent on the nature of the specimen under investigation.
我们通过计算获得信噪比（SNR）=5所需的成像剂量n(0)，优化了一台明场透射电子显微镜，用于对高分辨率辐射敏感材料进行成像。安装一个泽尼克相板（ZP）可使在300 kV下检测单个原子所需的剂量降低多达两倍。对于成像较大的物体，例如半高宽大于0.15 nm的高斯物体，ZP在降低成像剂量方面似乎比校正球差更有效。成像剂量n(0)不会随着通过使用高加速电压（U(0)=300 kV）降低色差来扩展色差分辨率极限而降低，因为图像对比度的增加比检测半径的倒数慢。然而，当同时使用一个球差校正器和一个ZP时，降低色差将允许降低加速电压，从而使单个碘原子的成像剂量低于10 e(-)/A(2)。我们的模拟表明，除了显微镜硬件外，优化在很大程度上还取决于所研究样品的性质。
