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Relationship between the microstructure and nanoindentation hardness of thermally evaporated and magnetron-sputtered electrochromic tungsten oxide films

Published online by Cambridge University Press:  31 January 2011

C. W. Ong ,
H. Y. Wong ,
G. K. H. Pang ,
K. Z. Baba-Kishi  and
C. L. Choy
C. W. Ong*
Affiliation:
Department of Applied Physics and Materials Research Center, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, People's Republic of China
H. Y. Wong
Affiliation:
Department of Applied Physics and Materials Research Center, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, People's Republic of China
G. K. H. Pang
Affiliation:
Department of Applied Physics and Materials Research Center, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, People's Republic of China
K. Z. Baba-Kishi
Affiliation:
Department of Applied Physics and Materials Research Center, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, People's Republic of China
C. L. Choy
Affiliation:
Department of Applied Physics and Materials Research Center, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, People's Republic of China
*
a)Address all correspondence to this author. e-mial: apacwong@hkpucc.polyu.edu
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Abstract

Tungsten oxide (WOx) films were fabricated by (i) reactive thermal evaporation (RTE) at room temperature with oxygen ambient pressure PO2 as a parameter, and (ii) reactive magnetron sputtering (RMS) with substrate temperature Ts as a parameter. The film structure revealed by x-ray photoelectron spectroscopy, x-ray diffraction, density measurements, infrared absorption, and atomic force microscopy was correlated with the nanoindentation hardness H. The RTE WOx films deposited at high Po2 were amorphous and porous, while H depended appreciably on normalized penetration depth hD (indentation depth/film thickness) due to the closing of the pores at the point of indentation. Decrease in Po2 from 10 to 2 × 10−3 mtorr led to smaller porosity, weaker hD dependence of H, and higher average H (measured at hD ≈ 0.2 to 0.3, for example). The RMS WOx film deposited at room temperature was amorphous and denser than all RTE films. The rise in substrate temperature Ts first densified the film structure (up to 110 °C) and then induced crystallization with larger grain size for Ts ≥ 300 °C. Correspondingly, the hD dependence of H became weaker. In particular, H of the RMS sample deposited at 110 °C showed a peak at hD slightly above 1 owing to pileup at the contact point of indentation. For higher Ts, pileup occurred at shallower hD and the average H (measured at hD ≈ 0.2 to 0.3, for example) rose, accompanied by the increase of grain size.

Type
Articles
Information
Journal of Materials Research , Volume 16 , Issue 6 , June 2001 , pp. 1541 - 1548
Copyright
Copyright © Materials Research Society 2001

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