Showing papers by "Stefan E. Schulz published in 2001"
TL;DR: In this article, the density/porosity and Young's modulus values of a range of nanoporous silica aerogel films via dispersion of laser-generated, wideband, surface acoustic waves were measured.
48 citations
TL;DR: In this article, the thickness and optical constants of xerogel films with low dielectric constants were derived from variable-angle spectroscopic ellipsometry measurements, and the as-prepared films were further treated by hexamethyldisilazane to achieve the hydrophobization of the pore surfaces.
Abstract: Silica xerogel films with low dielectric constants were prepared using a sol-gel spin coating method. The as-prepared films were further treated by hexamethyldisilazane to achieve the hydrophobization of the pore surfaces, by replacing hydrophilic silanol groups with hydrophobic trimethylsilyl (TMS) groups. The thickness and optical constants of the films were derived from variable-angle spectroscopic ellipsometry measurements. The determined refractive index decreases from 1.271±0.008 to 1.188±0.003 (values at 632.8 nm) while the porosity increases from 40.4 to 58.6% with the process parameters used. The Maxwell-Garnet approximation was used to relate the ellipsometric data to porosity. The IR absorption bands of CH species in TMS groups reveal that the surface area of the pores is larger in the samples with lower porosity.
25 citations
TL;DR: In this article, the authors report 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.
Abstract: Density/porosity and stiffness are the most critical parameters determining properties of porous films, however they are difficult to measure. Here we report 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. Results are compared to dielectric constant, Rutherford Backscattering Spectrometry (RBS), Ellipsometric Porosimetry (EP) and Nanoindentation (NI). RBS density correlates well to SAW. EP and NI also show a correlation, however the absolute values do not match. Low Young’s modulus values show that the film stiffness is drastically reduced with increasing porosity. The technique is rapid, nondestructive and relatively inexpensive, and yields absolute values of nanoporous aerogel elastic properties which are useful for process control and are difficult to access with other techniques.
2 citations