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The etching of ZnO thin films using acetylacetone (Hacac) doses with long exposure times, followed by purging and subsequent exposure to O2 plasma, is studied in a hot-wall reactor using simultaneous in situ spectroscopic ellipsometry and quadrupole mass spectrometry. The static exposure step results in the efficient consumption of Hacac. For each etch cycle, the O2 plasma plays a crucial role in removing unreacted Hacac from the ZnO surface, priming the surface for subsequent Hacac etching. This is confirmed by the production of CO2 during the O2 plasma pulse. The temperature window for etching is established as 220–280 °C with a maximum etch per cycle (EPC) of 0.15 nm/cy. Under these conditions, the Hacac pulse is 2 s long with a 30 s static hold step followed by 5 s O2 plasma step at 300 W power. Statistical analyses of etch data at the granularity level of each cycle reveal the importance of the static hold step in determining EPC. Arrhenius behavior of etching during the hold step reveals a piecewise linear trend with a low temperature (120–200 °C) activation energy (Ea) of 202 meV and a high temperature (200–320 °C) Ea of 32 meV. It is shown that saturation behavior in EPC is pulse time and static hold time dependent. Shorter Hacac pulses (≤1 s) demonstrate saturation behavior for static hold times ∼30 s, longer pulses of Hacac (≥2 s) show no saturation in EPC with static hold times up to 75 s. 

The purpose of this article is to give new constructions of linear orders which are minimal with respect to being non-σ-scattered. Specifically, we will show that Jensen's diamond principle implies that there is a minimal Countryman line, answering a question of Baumgartner. We also produce the first consistent examples of minimal non-sigma-scattered linear orders of cardinality greater than aleph1, as given a successor cardinal kappa+, we obtain such linear orderings of cardinality kappa+ with the additional property that their square is the union of kappa-many chains. We give two constructions: directly building such examples using forcing, and also deriving their existence from combinatorial principles. The latter approach shows that such minimal non-sigma-scattered linear orders of cardinality kappa+ exist for every infinite cardinal kappa in Gödel's constructible universe, and also (using work of Rinot [28]) that examples must exist at successors of singular strong limit cardinals in the absence of inner models satisfying the existence of a measurable cardinal mu of Mitchell order mu++.