Characterization of thin-film aerogel porosity and stiffness with laser-generated surface acoustic waves

Density/porosity is the most important parameter determining properties of porous films; however, it is difficult to measure. This letter reports char acterization of density/porosity and Young's modulus values of a range of n anoporous silica aerogel films via dispersion of laser-generated, wideband, surface acoustic waves. The technique shows a clear relationship between d ielectric constant, porosity and Young's modulus. Low Young's modulus value s show that film stiffness is drastically reduced with increasing porosity. The technique is rapid, non-destructive and relatively inexpensive, and yi elds absolute values of aerogel elastic properties, which are useful for pr ocess control; such properties are difficult to access using other techniqu es. (C) 2001 Elsevier Science B.V. All rights reserved.