Energy-loss-and thickness-dependent contrast in atomic-scale electron energy-loss spectroscopy

Tan, Haiyan; Zhu, Ye; Dwyer, Christian; Xin, Huolin

doi:10.1103/PhysRevB.90.214305

Journal Article

FZJ-2015-01058

Energy-loss-and thickness-dependent contrast in atomic-scale electron energy-loss spectroscopy

Tan, H. (Corresponding Author) ; Zhu, Y. ; Dwyer, C.FZJ* ; Xin, H.

2014
APS College Park, Md.

Physical review / B 90(21), 214305 (2014) [10.1103/PhysRevB.90.214305]

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Please use a persistent id in citations: http://hdl.handle.net/2128/8331 doi:10.1103/PhysRevB.90.214305

Abstract: Atomic-scale elemental maps of materials acquired by core-loss inelastic electron scattering often exhibit an undesirable sensitivity to the unavoidable elastic scattering, making the maps counterintuitive to interpret. Here, we present a systematic study that scrutinizes the energy-loss and sample-thickness dependence of atomic-scale elemental maps acquired using 100-keV incident electrons in a scanning transmission electron microscope. For single-crystal silicon, the balance between elastic and inelastic scattering means that maps generated from the near-threshold Si−L signal (energy loss of 99 eV) show no discernible contrast for a thickness of 0.5λ (λ is the electron mean-free path, here approximately 110 nm). At greater thicknesses we observe a counterintuitive “negative” contrast. Only at much higher energy losses is an intuitive “positive” contrast gradually restored. Our quantitative analysis shows that the energy loss at which a positive contrast is restored depends linearly on the sample thickness. This behavior is in very good agreement with our double-channeling inelastic scattering calculations. We test a recently proposed experimental method to correct the core-loss inelastic scattering and restore an intuitive “positive” chemical contrast. The method is demonstrated to be reliable over a large range of energy losses and sample thicknesses. The corrected contrast for near-threshold maps is demonstrated to be (desirably) inversely proportional to sample thickness. Implications for the interpretation of atomic-scale elemental maps are discussed.

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