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Langmuir. 2017 Sep 26;33(38):9521-9529. doi: 10.1021/acs.langmuir.6b04149. Epub 2017 Jan 12.

Thermochemical Analysis of Molybdenum Thin Films on Porous Alumina.

Author information

1
Department of Energy Resources Engineering, Stanford University , 367 Panama Street, Stanford, California 94305, United States.
2
Applied Materials, 974 E. Arques Avenue, Sunnyvale, California 94085, United States.
3
Department of Chemical Engineering, McMaster University , 1280 Main Street West, Hamilton, ON L8S 4L7, Canada.
4
Department of Chemical and Biological Engineering, Colorado School of Mines , 1613 Illinois Street, Golden, Colorado 80401, United States.

Abstract

Molybdenum (Mo) thin films (thickness <100 nm) were physically deposited by e-beam evaporation on a porous alumina substrate and were analyzed for their stability and reactivity under various thermal and gas conditions. The Mo thin-film composites were stable below 300 °C but had no reactivity toward gases. Mo thin films showed nitrogen incorporation on the surface as well as in the subsurface at 450 °C, as confirmed by X-ray photoelectron spectroscopy. The reactivity toward nitrogen was diminished in the presence of CO2, although no carbon species were detected either on the surface or in the subsurface. The Mo thin films have a very stable native oxide layer, which may further oxidize to higher oxidation states above 500 °C due to the reaction with the porous anodized alumina substrate. The oxidation of Mo thin films was accelerated in the presence of oxidizing gases. At 600 °C in N2, the Mo thin film on anodized alumina was completely oxidized and may also have been volatilized. The results imply that choosing thermally stable and inactive porous supports and operating in nonoxidizing conditions below 500 °C will likely maintain the stability of the Mo composite. This study provides key information about the chemical and structural stability of a Mo thin film on a porous substrate for future membrane applications and offers further insights into the integrity of thin-film composites when exposed to harsh conditions.

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