Influence of total beam current on HRTEM image resolution in differentially pumped ETEM with nitrogen gas
Influence of total beam current on HRTEM image resolution in differentially pumped ETEM with nitrogen gas
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DOI：
10.1016/j.ultramic.2012.08.007
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发表时间：
2013-01-01
期刊：
影响因子：
2.2
通讯作者：
Tanaka, N.
中科院分区：
文献类型：
--
作者：
Bright, A. N.;Yoshida, K.;Tanaka, N.
环境透射电子显微镜（ETEM）能够以埃级分辨率研究催化和其他反应过程。使用的显微镜是专用的ETEM（Titan ETEM，FEI Company），其具有差压泵抽真空系统和孔径，允许在样品区域中的气体压力高达20 mbar的情况下进行像差校正的高分辨率透射电子显微镜（HRTEM）成像，并且具有优于膜型E细胞支架的显著优势。改变氮气压力，电子束电流密度和总束电流的图像分辨率上的效果进行了测量，使用信息限制（杨氏条纹）上的标准交叉光栅样品和从硅晶格成像。正如预期的那样，增加气体压力会导致HRTEM图像分辨率降低。然而，总的电子束电流也会导致图像分辨率的大变化（较低的电子束电流提供更好的分辨率），而改变电子束电流密度对分辨率几乎没有影响，这是以前没有报道过的结果。即使在零损耗滤波成像中也可以看到这种行为，我们认为这表明分辨率的下降是由入射电子束产生的气体离子的弹性散射引起的。讨论了在气体环境中获取高分辨率图像的合适条件。晶格图像在氮气压力高达16毫巴显示，与0.12纳米的信息转移在4毫巴。(C)2012爱思唯尔有限公司版权所有。
Environmental transmission electron microscopy (ETEM) enables the study of catalytic and other reaction processes as they occur with Angstrom-level resolution. The microscope used is a dedicated ETEM (Titan ETEM, FEI Company) with a differential pumping vacuum system and apertures, allowing aberration corrected high-resolution transmission electron microscopy (HRTEM) imaging to be performed with gas pressures up to 20 mbar in the sample area and with significant advantages over membrane-type E-cell holders. The effect on image resolution of varying the nitrogen gas pressure, electron beam current density and total beam current were measured using information limit (Young's fringes) on a standard cross grating sample and from silicon crystal lattice imaging. As expected, increasing gas pressure causes a decrease in HRTEM image resolution. However, the total electron beam current also causes big changes in the image resolution (lower beam current giving better resolution), whereas varying the beam current density has almost no effect on resolution, a result that has not been reported previously. This behavior is seen even with zero-loss filtered imaging, which we believe shows that the drop in resolution is caused by elastic scattering at gas ions created by the incident electron beam. Suitable conditions for acquiring high resolution images in a gas environment are discussed. Lattice images at nitrogen pressures up to 16 mbar are shown, with 0.12 nm information transfer at 4 mbar. (C) 2012 Elsevier B.V. All rights reserved.