Gamma-alumina (γ-Al2O3), like other low-Z oxides, is readily damaged when exposed to an electron beam. This typically results in the formation of a characteristic pre-edge peak in the oxygen-K edge of electron energy-loss spectra (EELS) acquired during or after the damage process. This artifact can mask the presence of intrinsic O-K edge fine structure that would reveal chemical properties of the material; therefore, its suppression is key. In this work, we systematically investigate the conditions that give rise to the damage-induced O-K pre-edge peak and show that it can be effectively suppressed by performing EELS experiments at cryogenic (cryo) temperatures. Prolonged exposure of γ-Al2O3 to a focused electron beam results in a hole bored through the sample; this was used as a reproducible beam damage condition. O-K edge EELS spectra were collected from a single-crystal γ-Al2O3 sample both during and after focused electron beam hole drilling, and at room and cryo temperatures, using a monochromated scanning transmission electron microscope (STEM). The characteristic 531 eV pre-edge peak visible in the room temperature EELS spectra was completely suppressed in the cryo-EELS spectra, even in the presence of a visible drilled hole. We then correlated these experimental observations with multiple-scattering EELS simulations to determine the likely atomistic origin of the damage-induced O-K pre-edge peak. The findings indicate that the pre-edge peak is caused primarily by the presence of surface O-O bonds formed during beam damage, and that operating at cryo temperature suppresses the formation of surface O-O bonds, thus preventing formation of the O-K pre-edge peak. Additionally, Al-L2,3 edge EELS spectra revealed Al loss primarily from tetrahedral sites during hole drilling.

中文翻译：

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使用 Cryo-EELS 从 γ-Al2O3 产生光束损伤诱导的氧-K 边缘伪影的起源和抑制

γ-氧化铝 (γ-Al2O3) 与其他低 Z 氧化物一样，在暴露于电子束时很容易损坏。这通常会导致在损伤过程期间或之后获得的电子能量损失光谱 (EELS) 的氧-K 边缘中形成特征前边缘峰。这种伪影可以掩盖可以揭示材料化学性质的固有 OK 边缘精细结构的存在；因此，它的抑制是关键。在这项工作中，我们系统地研究了导致损伤引起的 OK 前边缘峰的条件，并表明它可以通过在低温（低温）温度下进行 EELS 实验来有效抑制。γ-Al2O3 长时间暴露在聚焦电子束下会导致在样品上钻出一个孔；这被用作可重现的光束损坏条件。OK edge EELS 光谱是在聚焦电子束钻孔期间和之后，以及在室温和低温下，使用单色扫描透射电子显微镜 (STEM) 从单晶 γ-Al2O3 样品中收集的。在室温 EELS 光谱中可见的特征 531 eV 前边缘峰在低温 EELS 光谱中被完全抑制，即使存在可见的钻孔。然后，我们将这些实验观察与多次散射 EELS 模拟相关联，以确定损伤引起的 OK 前边缘峰的可能原子起源。研究结果表明，前边缘峰主要是由光束损坏期间形成的表面 OO 键的存在引起的，并且在低温下操作会抑制表面 OO 键的形成，从而防止形成 OK 前缘峰值。此外，Al-L2,3 边缘 EELS 光谱揭示了钻孔过程中主要来自四面体位置的 Al 损失。