Source oxidation of easily oxidizing elements such as Ca, Sr, Ba, and Ti in an oxidizing ambient leads to their flux instability and is one of the biggest problems in the multi-elemental oxide Molecular Beam Epitaxy technique. Here we report a new scheme that can completely eliminate the source oxidation problem: a self-gettering differential pump using the source itself as the pumping medium. The pump simply comprises a long collimator mounted in front of the source in extended port geometry. With this arrangement, the oxygen partial pressure near the source was easily maintained well below the source oxidation regime, resulting in a stabilized flux, comparable to that of an ultra-high-vacuum environment. Moreover, this pump has a self-feedback mechanism that allows a stronger pumping effectiveness for more easily oxidizing elements, which is a desired property for eliminating the source oxidation problem.
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