Maintaining stable fluxes for multiple source elements is a challenging task when the source materials have significantly different oxygen affinities in a complex-oxide molecular-beam-epitaxy (MBE) environment. Considering that Sr is one of the most easily oxidized and widely used element in various complex oxides, we took Sr as a probe to investigate the flux stability problem in a number of different conditions. Source oxidation was less for higher flux, extended port geometry, and un-melted source shape. The extended port geometry also eliminated the flux transient after opening a source shutter as observed in the standard port. We also found that the source oxidation occurred more easily on the crucible wall than on the surface of the source material. Atomic oxygen, in spite of its stronger oxidation effectiveness, did not make any difference in source oxidation as compared to molecular oxygen in this geometry. Our results may provide a guide for solutions to the source oxidation problem in oxide-MBE system.

Abstract. The paper provides an overview of theoretical basis, efficiency, economics, laboratory and pilot plant testing, design and modelling of different advanced oxidation processes (combinations of ozone and hydrogen peroxide with UV radiation and catalysts ...

Depending on the offered oxygen supply as handy control variable, accumulation or depletion of these special impurity atoms at metal-oxide heterophase boundaries lead to modifications of the atomic structure and chemical composition of the interfaces. The established Kirchheim model, which also explains changes of the macroscopic material behavior, is based on structurally necessary vacancies at terminating close-packed oxide lattice planes that serve as oxygen traps. These point defects are revers-ibly refillable with excess atoms. Experimental findings on oxygen-controlled alter-ations of metal-oxide phase boundaries obtained by electron energy loss spectroscopy, quantitative gas volume measurement and the electrochemical hydrogen probe are summarized and valued with regard to the basic modeling assumptions. Thermody-namics data derived from measured isotherms show that this segregation reaction is energetically comparable with the formation of a two-dimensional oxide layer of the...