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Thermally induced stress hysteresis and co-efficient of thermal expansion changes in nanoporous SiO2

Martin T K Soh1, Jeremy Thurn2, J H Thomas III3 and Joseph J Talghader4

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The thermomechanical response of electron beam deposited nanoporous silicon dioxide is examined using substrate curvature measurements and nanoindentation. Analysis of the thin film bond angle strain distributions versus temperature indicates that low temperature (T < 100 °C) stress hysteresis and tensioning are primarily attributed to hydrogen bonded water desorption. However, at higher temperatures, the absence of water desorption suggests that the thermomechanical behaviour is related to thermally induced bond angle strain redistributions towards the local bonding environment of quartz and thermally grown silicon dioxide. This is supported by the co-efficient of thermal expansion data that trend lower with higher annealing temperatures. The re-absorption of water into the thin film accounts for the reproducibility of the open-loop stress hysteresis and tensioning observations.


PACS

68.60.Bs Mechanical and acoustical properties

68.60.Dv Thermal stability; thermal effects

62.20.D- Elasticity

65.40.De Thermal expansion; thermomechanical effects

81.40.Jj Elasticity and anelasticity, stress-strain relations

65.80.+n Thermal properties of small particles, nanocrystals, nanotubes

Subjects

Surfaces, interfaces and thin films

Nanoscale science and low-D systems

Condensed matter: structural, mechanical & thermal

Dates

Issue 7 (7 April 2007)

Received 30 October 2006, in final form 7 February 2007

Published 16 March 2007



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