Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
Ultramicroscopy. 2012 Aug;119:51-6. doi: 10.1016/j.ultramic.2011.11.013. Epub 2011 Nov 23.
The spatial resolution and contrast level in electron energy-loss spectroscopy (EELS) imaging depend on the delocalization of the inelastic electron scattering cross sections. Theoretical calculations within the dipole approximation provide the lower limit for the delocalization of low loss signals, and suggest that atomic resolution EELS imaging in the low loss energy regime (<50 eV) should be possible. Here, we directly measure the localization of the inelastic electron scattering at different energy loss in the low loss regime using a clean open edge of monolayer graphene. Our results demonstrate that the delocalization depends both on the energy loss and the specific electron excitation mode contributing to the energy loss. While the plasmons are delocalized over 1.2 nm, sub-nm enhancement is observed at the edge for the low-loss signal at 11 eV, indicating the possible formation of a one-dimensional plasmon (or inter-band transition) at the edge of monolayer graphene. Our results also suggest that if the initial states or final states are atomically localized, atomic resolution EELS imaging could be obtained even in the low loss region of the spectra.
电子能量损失谱 (EELS) 成象的空间分辨率和对比度水平取决于非弹性电子散射截面的离域程度。偶极近似内的理论计算为低损耗信号的离域提供了下限，并表明在低损耗能区（<50 eV）应该可以实现原子分辨率的 EELS 成象。在这里，我们使用单层石墨烯的清洁开边缘直接测量低损耗能区不同能量损耗处的非弹性电子散射的局域化。我们的结果表明，离域化既取决于能量损耗，也取决于对能量损耗有贡献的特定电子激发模式。虽然等离子体在 1.2nm 以上离域，但在 11eV 的低损耗信号处观察到边缘的亚纳米增强，表明在单层石墨烯的边缘可能形成了一维等离子体（或带间跃迁）。我们的结果还表明，如果初始态或终态是原子局域的，即使在谱的低损耗区也可以获得原子分辨率的 EELS 成象。
