We use x-ray scattering to attain structural information about our glasses. X-ray scattering is a technique involving the diffraction of x-rays caused by periodic molecular-scale structures in the material being investigated. The diffraction patterns can be used to determine structural information in the film. This is done at our on-campus facility as well as the Stanford Synchrotron Radiation Lightsource in Menlo Park, CA.
By varying the substrate temperature during the vapor deposition process, a number of molecular packing motifs can be trapped in the film. As an example, the diffraction patterns of various vapor-deposited glasses of TPD, a small organic molecule used in organic electronics, are shown below. The glasses were prepared at different substrate temperatures and show different scattering patterns, indicating unique microstructure in each glass. Integrating and structural and optical information from and x-ray scattering and ellipsometry, respectively, a structural model with average molecular tilt angles and spacings within the glass can be built, as sketched out in the schematic below.