The mechanical robustness of atomic-layer- and molecular-layer-deposited coatings on polymer substrates

  • Miller D
  • Foster R
  • Zhang Y
 et al. 
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The mech. robustness of at. layer deposited alumina and recently developed mol. layer deposited aluminum alkoxide ("alucone") films, as well as laminated composite films composed of both materials, was characterized using mech. tensile tests along with a recently developed fluorescent tag to visualize channel cracks in the transparent films. All coatings were deposited on polyethylene naphthalate substrates and demonstrated a similar evolution of damage morphol. according to applied strain, including channel crack initiation, crack propagation at the crit. strain, crack densification up to satn., and transverse crack formation assocd. with buckling and delamination. From measurements of crack d. vs. applied tensile strain coupled with a fracture mechanics model, the mode I fracture toughness of alumina and alucone films was detd. to be KIC = 1.89 ± 0.10 and 0.17 ± 0.02 MPa m0.5, resp. From measurements of the satd. crack d., the crit. interfacial shear stress was estd. to be τc = 39.5 ± 8.3 and 66.6 ± 6.1 MPa, resp. The toughness of nanometer-scale alumina was comparable to that of alumina thin films grown using other techniques, whereas alucone was quite brittle. The use of alucone as a spacer layer between alumina films was not found to increase the crit. strain at fracture for the composite films. This performance is attributed to the low toughness of alucone. The exptl. results were supported by companion simulations using fracture mechanics formalism for multilayer films. To aid future development, the modeling method was used to study the increase in the toughness and elastic modulus of the spacer layer required to render improved crit. strain at fracture. These results may be applied to a broad variety of multilayer material systems composed of ceramic and spacer layers to yield robust coatings for use in chem. barrier and other applications. (c) 2009 American Institute of Physics. [on SciFinder(R)]

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  • David C. Miller

  • Ross R. Foster

  • Yadong Zhang

  • Shih Hui Jen

  • Jacob A. Bertrand

  • Zhixing Lu

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