Charge contrast imaging of fine-scale microstructure and compositional variation in garnet using the environmental scanning electron microscope
Charge contrast imaging of fine-scale microstructure and compositional variation in garnet using the environmental scanning electron microscope
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使用环境扫描电子显微镜对石榴石精细尺度微观结构和成分变化进行电荷对比成像
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发表时间：
2005
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通讯作者：
J. Buckman
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作者：
S. Cuthbert;J. Buckman
摘要榴辉岩石榴石的气体二次电子（GSE）成像环境扫描电子显微镜（ESEM）在低室气压下揭示了详细的图像对比度模式（电荷对比度图像，CCI），不存在于背散射或二次电子图像。图像强度是表面电荷累积量的函数。CCI的成功获取取决于在给定的腔室气体压力和束流下的帧大小和束扫描速率。图像在几秒钟内获得，并且是稳定和可重复的。CCI模式不相关的裂纹或晶界，但密切对应的主要元素组成的变化，无论是在同心（生长）分区的形式，和分支，线性功能解释为裂纹已愈合的新石榴石生长。CCI的原因还没有很好地理解，但可能与晶格缺陷密度的变化及其对电荷捕获和耗散的影响有关。这些反过来又影响样本表面或非常接近样本表面的电荷积聚速率。一个有趣的可能性是，CCI图像检测到与涉及例如REE和羟基的非同价偶联取代相关的空位，因此该方法提供了一种对石榴石中这些痕量物质的分布进行成像的方法。CCI图像具有丰富的微观结构细节，并提供了快速，高分辨率，低噪声侦察映射的天然和合成石榴石的晶内微观结构和成分变化的潜力。
Abstract Gaseous secondary electron (GSE) imaging of eclogite garnets under the environmental scanning electron microscope (ESEM) at low chamber gas pressures reveals detailed image contrast patterns (charge-contrast images, CCI) that are not present in back-scattered or secondary electron images. Image intensity is a function of the amount of surface charge accumulation. Successful acquisition of CCI depends on frame size and beam scan rate at a given chamber gas pressure and beam current. Images are obtained in a few seconds, and are stable and reproducible. CCI patterns do not correlate with cracks or grain boundaries, but do correspond closely to variations in major-element composition, both in the form of concentric (growth) zoning, and branching, linear features interpreted as cracks that have been healed by new garnet growth. Causes of CCI are not yet well understood, but may be related to variations in lattice defect density and their influence on charge-trapping and dissipation. These in turn influence the rate of charge build-up at or very close to the specimen surface. One interesting possibility is that CCI images detect vacancies related to non-homovalent coupled substitutions involving, for example, REE and hydroxyl, so the method offers a way of imaging the distribution of these trace species in garnets. The CCI images are rich in microstructural detail and offer the potential for rapid, high-resolution, low-noise reconnaissance mapping of intragranular microstructure and compositional variation in both natural and synthetic garnets.