集成的差分相衬扫描透射电子显微镜(iDPC-STEM)技术已经得到了很好的发展,可以以亚_分辨率研究原子结构,即使在极低的电子剂量下也能够同时成像重原子和轻原子。作为一种直接相衬成像技术,原子分辨率iDPC-STEM对成像条件敏感。尽管在理论和实验方面都取得了巨大的成就,实验参数对原子分辨率iDPC-STEM图像对比度的影响尚未得到系统研究。这里,我们根据常规实验因素对SrTiO3的原型示例进行iDPC-STEM模拟,包括散焦,试样厚度,加速电压,会聚角,收集角,样品倾斜和电子剂量。通过对图像对比度和原子柱强度的评价,参数进行了讨论,以提高图像对比度和光元素的可见度。此外,剂量依赖性模拟证明了低剂量iDPC-STEM成像优于其他常规STEM模式的优势。我们的结果为实验获得可访问的原子分辨率iDPC-STEM图像提供了实用指南。
Integrated differential phase contrast scanning transmission electron microscopy (iDPC-STEM) technique has been well developed for studying atomic structures at sub-Å resolution with the capability of simultaneously imaging heavy and light atoms even at an extremely low electron dose. As a direct phase contrast imaging technique, atomic resolution iDPC-STEM is sensitive to the imaging conditions. Although great achievements have been made both in aspect of theory and experiments, the influence of experimental parameters on the contrast of atomic resolution iDPC-STEM images has not been systematically investigated. Here, we perform the iDPC-STEM simulations on the prototypical example of SrTiO3 with respect to the routine experimental factors, including the defocus, specimen thickness, accelerating voltage, convergence angle, collection angle, sample tilt and electron dose. Through the evaluation of image contrast and atom column intensity, the parameters are discussed to improve the image contrast and the visibility of light elements. Moreover, the dose-dependent simulations demonstrate the advantage of low dose iDPC-STEM imaging over other conventional STEM modes. Our results provide a practical guideline to experimentally obtain accessible atomic resolution iDPC-STEM images.