Abstract Soil structure is defined by many physical properties and functions. If detailed information about the structure is known, a number of modelling techniques can be used to perform simulations to assess the physical properties of soil and evaluate them at different scales that cannot be measured otherwise or to predict changes due to variation in boundary conditions. With the widespread accessibility of X-ray computed tomography (XCT), it is possible to describe soil structure at µm scale. However, it is now evident that such characterization is not enough to describe all the necessary processes or properties of soils since detailed information about the soil structure at the nano-scale is still lacking. This paper presents the initial results of the nanostructure characterization of soils using focused ion beam plus scanning electron microscopy (FIB-SEM) imaging technique. We prepared two ~50 × 50 µm2 FIB milled and polished surfaces, each for Retisol and Chernozem soil aggregates. In addition to the FIB-SEM imaging with a resolution of up to 4 nm, we performed regular SEM surface imaging and high-resolution XCT scanning with a resolution of 1.01 µm. The images obtained using the three approaches showed their varying capabilities of distinguishing structural features at different scales. The FIB-SEM images were useful in the characterization of pore size distributions and we observed pore inscribed radii ranging from 2.5 nm to ~1 µm. We also observed three general types of nanoporosity: one is between the mineral grains and the organomineral assemblages, another within the organic matter and then within the minerals. We highlighted all the advantages and shortcomings of the FIB-SEM imaging and proposed practical solutions to addressing the disadvantages as well; In addition, future directions for research using FIB-SEM to improve the characterization of soil structure at the nano-scale were outlined.

中文翻译：

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土壤结构精确分析中的亚微米级：纳米级 FIB-SEM 成像研究

摘要 土壤结构由许多物理性质和功能决定。如果了解有关结构的详细信息，则可以使用多种建模技术进行模拟，以评估土壤的物理特性，并以其他方式无法测量的不同尺度对其进行评估，或者预测由于边界条件变化而导致的变化。随着 X 射线计算机断层扫描 (XCT) 的广泛普及，可以在微米级描述土壤结构。然而，现在很明显，这种表征不足以描述土壤的所有必要过程或特性，因为仍然缺乏关于纳米级土壤结构的详细信息。本文介绍了使用聚焦离子束加扫描电子显微镜 (FIB-SEM) 成像技术对土壤进行纳米结构表征的初步结果。我们准备了两个 ~50 × 50 µm2 FIB 研磨和抛光的表面，每个表面用于 Retisol 和黑钙土土壤聚集体。除了分辨率高达 4 nm 的 FIB-SEM 成像外，我们还进行了常规 SEM 表面成像和分辨率为 1.01 µm 的高分辨率 XCT 扫描。使用三种方法获得的图像显示了它们在不同尺度上区分结构特征的不同能力。FIB-SEM 图像可用于表征孔径分布，我们观察到的孔内切半径范围为 2.5 nm 到 ~1 µm。我们还观察到三种一般类型的纳米孔隙：一个是在矿物颗粒和有机矿物组合之间，另一个在有机物内，然后在矿物内。我们强调了 FIB-SEM 成像的所有优点和缺点，并提出了解决缺点的实用解决方案；此外，还概述了使用 FIB-SEM 在纳米尺度上改进土壤结构表征的未来研究方向。