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.

中文翻译：

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低压 SEM 和冷冻 SEM 中的显微照片对比

现代高分辨率扫描电子显微镜 (SEM) 配备场发射枪 (FEG)，设计用于在低加速电压下运行，为研究没有导电涂层的导电或绝缘系统开辟了新的机会。更好的电子源、光学器件、真空和探测器使高分辨率 SEM 成为一种强大的表征和分析工具，并提供有关纳米材料结构-性能关系和相关应用的宝贵信息。可以利用轻微的样品充电来增强不同材料和相之间的对比度，同时最大限度地减少成像伪影。充电效应的优化和显微照片对比度的改进对于陶瓷、聚合物、有机材料和热固定液体的不同尺度特征的研究至关重要，包括生物学研究。可以根据电子束与类似样品相互作用的先验知识以及人们希望获得的信息类型，将操作 SEM 参数调整为特定样品。在这项工作中，我们研究了加速电压和不同探测器的使用对几种类型样品对比度形成的影响，重点关注主要由碳和氧形成的材料，在 SEM 中固有对比度较低。这包括低温扫描电镜 (cryo-SEM) 以研究天然状态的乳液。我们还通过低温扫描电镜研究了分散在水中并溶解在超强酸中的碳纳米管 (CNT)。在室温下对沉积在玻璃上的 CNT 薄膜进行 HR-SEM。我们展示了显微图像对比度如何随不同的探测器、不同的加速电压而变化。