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Proceedings Paper

Structural changes induced by thermal annealing in W/C multilayers
Author(s): Benjamin S. Chao; Jesus Gonzalez-Hernandez; D. A. Pawlik; Stanford R. Ovshinsky; James Scholhamer; James L. Wood; Kevin Parker
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Paper Abstract

Tungsten/carbon (W/C) multilayer thin films with a nominal d spacing varying from 2.5 to 14 nm were prepared by magnetron sputtering technique. The thicknesses of the W and C layers were varied from 0.5 to 12 nm. The multilayers were subjected to isochronal anneals in a quartz tube furnace in the range of 300 to 1000 C under high purity Ar flow conditions. X-ray diffraction, Raman scattering and Auger depth profiling were used to characterize the structure of the as-prepared and annealed films. It is found that an overcoat layer of silicon nitride (30-50 nm) prevents the multilayers from oxidation during the 1 hr heat treatment at temperatures as high as 1000 C in Ar flow. In all studied W/C multilayers, the carbon layers are amorphous (up to 12 nm). The tungsten layers are also amorphous when their thicknesses are less than 5 nm. Tungsten layers thicker than 5 nm show crystalline W peaks in addition to the amorphous W feature. Annealing of samples with a silicon nitride protective layer results in several structural changes which depend on annealing temperature, d spacing, the as-deposited W layer structure and the layer thickness ratio of W to C. For W layer thicker than C layer and W layer thickness > 4 nm and/or C layer thickness < 1 nm, the multilayers show the initial crystal formation of microcrystalline W2C occurring at C-W interfaces (that interface in which C was deposited on W) after 600 C anneal, followed by a second crystallization of a-W or a-W and WC at W-C interfaces (W was deposited on C) at the annealing temperature of 900 C. They reveal a relatively small (< 5 %) or essentially no layer expansion. For those multilayers having thin W layers (2 nm) and the same or thicker C layer thicknesses, the initial crystallization takes place at both W-C and C-W interfaces at 900 C or higher. The crystal formed is a-W or a-W and WC. The layer pair period of the multilayers in this group increases monotonically with increasing annealing temperature. Expansion is up to 16 % of the original d spacing and occurs in both W and C layers at approximately equal rates. The expansion in all multilayers is interpreted to be associated mainly with the structural ordering processes in the amorphous W and C layers.

Paper Details

Date Published: 1 January 1992
PDF: 16 pages
Proc. SPIE 1547, Multilayer Optics for Advanced X-Ray Applications, (1 January 1992); doi: 10.1117/12.51280
Show Author Affiliations
Benjamin S. Chao, Energy Conversion Devices, Inc. (United States)
Jesus Gonzalez-Hernandez, Energy Conversion Devices, Inc. (United States)
D. A. Pawlik, Energy Conversion Devices, Inc. (United States)
Stanford R. Ovshinsky, Energy Conversion Devices, Inc. (United States)
James Scholhamer, Ovonic Synthetic Materials Co. (United States)
James L. Wood, Ovonic Synthetic Materials Co. (United States)
Kevin Parker, Ovonic Synthetic Materials Co. (United States)

Published in SPIE Proceedings Vol. 1547:
Multilayer Optics for Advanced X-Ray Applications
Natale M. Ceglio, Editor(s)

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