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 characterization of density/porosity and Young's modulus values of a range of nanoporous silica aerogel films via dispersion of laser-generated, wideband, surface acoustic waves. The technique shows a clear relationship between dielectric constant, porosity and Young's modulus. Low Young's modulus values show that film stiffness is drastically reduced with increasing porosity. The technique is rapid, non-destructive and relatively inexpensive, and yields absolute values of aerogel elastic properties, which are useful for process control; such properties are difficult to access using other techniques. (C) 2001 Elsevier Science B.V. All rights reserved.