Materials Measurement Science Division, National Institute of Standards and Technology (NIST) , Gaithersburg, Maryland 20899-8372, United States.
Environ Sci Technol. 2013 Aug 6;47(15):8575-81. doi: 10.1021/es400727x. Epub 2013 Jul 9.
Use of focused ion-beam scanning electron microscopy (FIB-SEM) to investigate the internal composition of atmospheric particles is demonstrated for assessing particle optical properties. In the FIB-SEM instrument equipped with an X-ray detector, a gallium-ion beam mills the particle, while the electron beam images the slice faces and energy-dispersive X-ray spectroscopy provides element maps of the particle. Differences in assessments of optical behavior based on FIB-SEM and conventional SEM were shown for five selected urban dust particles. The benefit of FIB-SEM for accurately determining the depth and size of optically important phases within particles was shown. FIB-SEM revealed that iron oxide grains left undetected by conventional SEM could potentially shift the single-scattering albedo of the particle from negative to positive radiative forcing. Analysis of a coke-like particle showed that 73% of the light-scattering inclusion went undetected with conventional SEM, causing the bulk absorption coefficient to vary by as much as 25%. Optical property calculations for particles as volume-equivalent spheres and as spheroids that approximated actual particle shapes revealed that the largest effect between conventional SEM and FIB-SEM analyses was on backscattering efficiency, in some cases varying several-fold.
使用聚焦离子束扫描电子显微镜（FIB-SEM）来研究大气粒子的内部成分，以评估粒子的光学性质。在配备 X 射线探测器的 FIB-SEM 仪器中，镓离子束对粒子进行铣削，同时电子束对切片表面进行成像，能量色散 X 射线光谱法提供粒子的元素图谱。对五个选定的城市尘埃粒子进行了基于 FIB-SEM 和传统 SEM 的光学行为评估差异的研究。结果表明，FIB-SEM 有助于准确确定粒子中对光学重要的相的深度和大小。FIB-SEM 揭示了传统 SEM 未检测到的氧化铁颗粒可能会使粒子的单次散射反照率从负辐射强迫变为正辐射强迫。对类似焦炭的粒子的分析表明，73%的光散射包含物未被传统 SEM 检测到，导致体吸收系数变化高达 25%。将粒子作为体积等效球体和近似实际粒子形状的椭球体进行光学性质计算表明，在传统 SEM 和 FIB-SEM 分析之间，最大的影响是在后向散射效率上，在某些情况下变化了几倍。
