Critical properties of nanoporous aerogel films from surface-wave laser ultrasound

Nanoporous aerogel films are of great scientific and commercial interest because of their outstanding potential for application to microelectronic interconnect, associated with low dielectric constant. Of the parameters which describe such aerogel films, density/porosity and stiffness are two of the most critical but are difficult to measure. This paper shows how measurement of the dispersion of laser-generated surface acoustic wavepackets travelling on submicron-thick aerogel films on silicon substrates allows the density and Young´s modulus to be extracted reliably. A method for extracting measurements on very thin films (< 300 nm) is also presented