A study of ta-C, a-C : H and Si-a : C : H thin films on polymer substrates as a gas barrier

GA Abbas, JAD McLaughlin, E Harkin-Jones

Research output: Contribution to journalArticle

44 Citations (Scopus)

Abstract

Two types of diamond-like carbon (DLC) films were grown on Poly (ethylene terepthalate) (PET) substrates have been investigated for density, internal stress, gas permeability and structural properties by an X-ray reflectometry, surface profilometer, Raman spectroscopy and water vapour permeation analysis system, respectively. The high density tetrahedral amorphous carbon (ta-C) films (3.27 g/cm(3)) prepared by filtered vacuum cathodic arc (FCVA) showed unexpected high water vapour transmission rate (WVTR) (1.3 g/m(2) day) and a surface covered by a network of deep micro-cracks, which is due to intrinsic stress inside the ta-C films (up to 12 GPa). The soft Si doped hydrogenated amorphous carbon (Si-a:C:H) films prepared by plasma enhanced chemical vapour deposition (PECVD) exhibited low transmission rate (0.03 g/m(2) day) with a water vapour reduction factor up to 98% and a surface almost completely free of micro-cracks. Si incorporation in the a-C:H films reduced both the film density from 2.3 g/cm(3) to 1.85 g/cm(3) and the compressive stress to < 0.5 GPa. This could be understood by two possibilities. Firstly, the increasing in the hydrogen content within the films (as indicated by increasing the Raman background slope) developed more polymer-like bonds, which weakens the microstructure. Second, replacing the stronger C-C bonds (3.7 eV) by C-Si (3.21 eV) bonds where the relaxation of residual stress would occur with large strains in the C-Si bonds. (C) 2003 Elsevier B.V. All rights reserved.
Original languageEnglish
Pages (from-to)1342-1345
JournalDiamond and Related Materials
Volume13
Issue number4-8
DOIs
Publication statusPublished - Apr 2004

Keywords

  • DLC
  • coatings
  • diffusion
  • surface characterization

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