Department of Chemical Engineering and the Russell Berrie Nanotechnology Institute (RBNI), Technion-Israel Institute of Technology, Haifa 3200003, Israel.
Department of Materials Science & Engineering, Technion-Israel Institute of Technology, Haifa 3200003, Israel.
Ultramicroscopy. 2020 Nov;218:113085. doi: 10.1016/j.ultramic.2020.113085. Epub 2020 Jul 30.
Modern high-resolution scanning electron microscopes (SEM), equipped with field emission guns (FEGs), designed to operate at low acceleration voltage, have opened new opportunities to study conductive or insulating systems, without conductive coating. Better electron sources, optics, vacuum, and detectors allow high-resolution SEM to serve as a powerful characterization and analytical tool, and provide invaluable information about structure-property relations of nanomaterials and related applications. Slight specimen charging can be exploited to enhance contrast between different materials and phases, with minimum imaging artifacts. Optimization of charging effects and improved micrograph contrast are essential for the study of different-scale features in ceramics, polymers, organic materials, and thermally fixed liquids, including in biological research. The operating SEM parameters can be adjusted to a specific specimen based on prior knowledge of interaction of the electron beam with similar specimens, and the type of information one wishes to acquire. In this work we examined the effect of the acceleration voltage and the use of different detectors on the contrast formation in several types of specimens, focusing on materials formed mainly of carbon and oxygen, with low inherent contrast in the SEM. That includes cryogenic SEM (cryo-SEM) to study emulsions in their native state. We also studied by cryo-SEM carbon nanotubes (CNTs) dispersed in water and dissolved in superacid. HR-SEM at room temperature was performed on CNT films, deposited on glass. We show how micrograph contrast changes with different detectors, at different acceleration voltages. Judicious selection of the SEM operation parameters leads to optimal picture contrast between domains of different composition.
现代高分辨率扫描电子显微镜（SEM）配备场发射枪（FEG），旨在低加速电压下运行，为研究导电或绝缘系统开辟了新的机会，无需进行导电涂层处理。更好的电子源、光学器件、真空和探测器使得高分辨率 SEM 成为一种强大的表征和分析工具，并提供了有关纳米材料及其相关应用的结构-性能关系的宝贵信息。轻微的样品充电可以用来增强不同材料和相之间的对比度，同时最小化成像伪影。优化充电效果和提高微观对比度对于研究陶瓷、聚合物、有机材料和热固定液体（包括生物研究）中的不同尺度特征至关重要。可以根据电子束与类似样品相互作用的先验知识以及希望获取的信息类型，调整 SEM 的操作参数以适应特定的样品。在这项工作中，我们研究了加速电压和使用不同探测器对几种类型样品对比度形成的影响，重点研究了主要由碳和氧组成且在 SEM 中固有对比度低的材料。这包括用于研究其原始状态乳液的低温 SEM（cryo-SEM）。我们还研究了分散在水中和溶解在超强酸中的碳纳米管（CNT）的 cryo-SEM。在室温下对沉积在玻璃上的 CNT 薄膜进行了高分辨率 SEM。我们展示了不同探测器和不同加速电压下微观对比度的变化。明智地选择 SEM 操作参数可以在不同组成域之间实现最佳的图像对比度。
