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Surface-driven, one-step chemical vapor deposition of gamma-Al4Cu9 complex metallic alloy film

A paradigm for the one-step formation of complex intermetallic coatings by chemical vapor deposition has recently been published by CNRS in Toulouse. The work genuinely addresses the challenge of depositing an intermetallic coating with comparable contents of Cu and Al. Depending on processing conditions, a pure  gamma-Al4Cu9 and multi-phaseAl-Cu films are grown with wetting properties of the former being similar to its bulk counterpart. The deposition process and its parametric investigation are detailed. Two metalorganic precursors are used taking into account their transport and chemical properties, and deposition temperature ranges. On line and ex situ characterizations enlighten the competition which occurs at the growing surface between molecular fragments, and which limits growth rates. Notably, introducing a partial pressure of hydrogen gas during deposition reduces Al growth rate from dimethylethylamine alane (DMEAA), by displacing the hydrogen desorption equilibrium. This Al partial growth rate decrease is not sufficient to achieve a Cu/Al atomic ratio that is high enough for the formation of intermetallics with close Al and Cu compositions. A fivefold increase of the flux of the gaseous copper(I) cyclopentadienyl triethylphosphine CpCuPEt3, whereas the DMEAA flux remains constant, results in the targeted Al/Cu atomic ratio equal to 44/56. Nevertheless, the global growth rate is rendered extremely low by the deposition inhibition caused by a massive phosphine adsorption (-PEt3). Despite these limitations, the results pave the way towards the conformal coating of complex surface geometries by such intermetallic compounds.

Surface view of an as-processed Al-Cu film from dimethylethylamine alane and copper cyclopentadienyl-triethylphosphine at 200°C. The X-ray diffractogramme shows that Al4Cu9 approximant is the only crystalline phase present.
This is the first report on the processing by MOCVD of a complex metallic alloy coating. Foreseen applications are antiwetting or low friction surfaces. This result was obtained by the CVD group of Dr. C. Vahlas at the Interuniversity Research and Engineering Center of CNRS in Toulouse. 
Applied Surface Science, 283 (2013) 788– 793
Surface view of an as-processed Al-Cu film from dimethylethylamine alane and copper cyclopentadienyl-triethylphosphine at 200°C. The X-ray diffractogramme shows that Al4Cu9 approximant is the only crystalline phase present. This is the first report on the processing by MOCVD of a complex metallic alloy coating. Foreseen applications are antiwetting or low friction surfaces. This result was obtained by the CVD group of Dr. C. Vahlas at the Interuniversity Research and Engineering Center of CNRS in Toulouse. Applied Surface Science, 283 (2013) 788– 793