Residual stress measurement in thin carbon films by Raman spectroscopy and nanoindentation

• Published in: Thin solid films Vol. 429; no. 1; pp. 190 - 200
• Main Authors: Taylor, Craig A, Wayne, Mark F, Chiu, Wilson K.S
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 01.04.2003; Elsevier Science
• Subjects: Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Materials science; Materials testing; Mechanical and acoustical properties; Nanoindentation; Nondestructive testing: optical methods; Physical properties of thin films, nonelectronic; Physics; Pyrolytic carbon; Raman spectroscopy; Residual stress; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Pyrolytic carbon; Raman spectroscopy; Residual stress; Nanoindentation; Optical fibers; Measuring methods; Residual stresses; Experimental study; Carbon; Surface stresses; Thin films; Non destructive method; Stress distribution; Nonmetals; Optical method; Protective coatings; Thermal stresses
• DOI: 10.1016/S0040-6090(03)00276-1
• ISSN: 0040-6090

The reliability of hermetic carbon-coated optical fibers is affected by residual stresses in the coating created during the fiber draw process. Thermally induced residual stresses are caused by differences in the coefficient of thermal expansion (CTE) of the coating and the optical fiber. This mismatch creates shear stresses at the interface that can delaminate the film. This work presents and validates a surface residual-stress measurement technique using Raman spectroscopy. Since select Raman peaks for carbon films exhibit a wavenumber shift in proportion to the magnitude of residual stress, Raman spectra can be correlated to a theoretical model to obtain its residual stress. The model, validated with nanoindentation, shows an equi-biaxial stress field through the depth of the film. Nanoindentation also provides an accurate measure of residual stress in thin films with unknown material properties. The approach presented in this study is a non-destructive and non-intrusive method for measuring residual surface stress in thin films, and is ideal for small curved-surface specimens such as carbon-coated optical fibers.