Scanning transmission electron microscopy (STEM) at low energies (≤ 30 keV) in a scanning electron microscope is well suited to distinguish weakly scattering materials with similar materials properties and analyze their microstructure. The capabilities of the technique are illustrated in this work to resolve material domains in PTB7:PC71BM bulk-heterojunctions, which are commonly implemented for light-harvesting in organic solar cells. Bright-field (BF-) and high-angle annular dark-field (HAADF-) STEM contrast of pure PTB7 and PC71BM was first systematically analyzed using a wedge-shaped sample with well-known thickness profile. Monte-Carlo simulations are essential for the assignment of material contrast for materials with only slightly different scattering properties. Different scattering cross-sections were tested in Monte-Carlo simulations with screened Rutherford scattering cross-sections yielding best agreement with the experimental data. The STEM intensity also depends on the local specimen thickness, which can be dealt with by correlative STEM and scanning electron microscopy (SEM) imaging of the same specimen region yielding additional topography information. Correlative STEM/SEM was applied to determine the size of donor (PTB7) and acceptor (PC71BM) domains in PTB7:PC71BM absorber layers that were deposited from solution with different contents of the processing additive 1,8-diiodooctane (DIO).

中文翻译：

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扫描电镜中聚合物：富勒烯本体-异质结的成像：方法方面和相关SEM和STEM的纳米形态

在扫描电子显微镜中低能量（≤30 keV）的扫描透射电子显微镜（STEM）非常适合区分具有相似材料特性的弱散射材料并分析其微观结构。在这项工作中说明了该技术的功能，以解决PTB7：PC71BM体异质结中的材料域，通常用于实现有机太阳能电池的光收集。首先使用具有众所周知厚度轮廓的楔形样品系统地分析了纯PTB7和PC71BM的明场（BF-）和高角度环形暗场（HAADF-）STEM对比度。蒙特卡洛模拟对于分配散射特性稍有不同的材料的材料对比度至关重要。在蒙特卡洛模拟中测试了不同的散射横截面，筛选出的卢瑟福散射横截面与实验数据最吻合。STEM强度还取决于局部样本厚度，这可以通过对相同样本区域进行相关的STEM和扫描电子显微镜（SEM）成像来处理，从而产生更多的形貌信息。应用相关的STEM / SEM来确定PTB7：PC71BM吸收剂层中的施主（PTB7）和受体（PC71BM）域的大小，这些区域是从具有不同含量的加工添加剂1,8-二碘辛烷（DIO）的溶液中沉积的。可以通过相关样品的相关STEM和扫描电子显微镜（SEM）成像来处理，从而产生更多的形貌信息。应用相关的STEM / SEM来确定PTB7：PC71BM吸收剂层中的供体（PTB7）和受体（PC71BM）域的大小，这些区域是从具有不同含量的加工添加剂1,8-二碘辛烷（DIO）的溶液中沉积的。可以通过相关样品的相关STEM和扫描电子显微镜（SEM）成像来处理，从而产生更多的形貌信息。应用相关的STEM / SEM来确定PTB7：PC71BM吸收剂层中的施主（PTB7）和受体（PC71BM）域的大小，这些区域是从具有不同含量的加工添加剂1,8-二碘辛烷（DIO）的溶液中沉积的。