Crozier Peter A
Materials Program, School for the Engineering of Matter, Transport and Energy, Arizona State University, 501 E. Tyler Mall, Tempe, AZ 85287-6106, USA..
Ultramicroscopy. 2017 Sep;180:104-114. doi: 10.1016/j.ultramic.2017.03.011. Epub 2017 Mar 14.
In many materials systems, electron beam effects may substantially alter and destroy the structure of interest during observation. This is often true for the surface structures of catalytic nanoparticles where the functionality is associated with thin surface layers which are easily destroyed. The potential application of using aloof beam electron energy-loss spectroscopy as a non-destructive nanoscale surface characterization tool is discussed. Recent developments in monochromators make vibration and valence loss EELS possible in the electron microscope. The delocalization associated with these signals allows spectra to be acquired when the electron beam is position 2nm or more away from the particle surface. This eliminates knock-on damage and significantly reduces ionization damage. Theoretical and experimental results are employed to explore the potential strengths and weaknesses of monochromated aloof beam EELS for surface analysis. The approach is most favored for surface layers on insulators because the bandgap lowers the background for detection of the vibrational signal and bandgap states. Guided light modes and relativistic effects can complicate the interpretation of the spectra. The effects are suppressed at lower accelerating voltages and particle size especially for low refractive index materials.
在许多材料体系中，电子束效应可能会在观察过程中显著改变并破坏感兴趣的结构。对于催化纳米颗粒的表面结构来说尤其如此，其功能与易于被破坏的薄表面层相关。本文讨论了将远离束电子能量损失谱用作无损纳米级表面表征工具的潜在应用。单色仪的最新进展使电子显微镜中的振动和价态损失电子能量损失谱成为可能。与这些信号相关的离域化使得当电子束位于距颗粒表面2纳米或更远的位置时能够采集光谱。这消除了碰撞损伤并显著降低了电离损伤。利用理论和实验结果来探索单色远离束电子能量损失谱用于表面分析的潜在优势和劣势。这种方法最适用于绝缘体上的表面层，因为带隙降低了检测振动信号和带隙态的背景。导光模式和相对论效应会使光谱的解释变得复杂。在较低的加速电压和颗粒尺寸下，尤其是对于低折射率材料，这些效应会受到抑制。
