Creation of Stable Glasses

We have prepared stables glasses of a number of organic molecules by physical vapor deposition onto substrates held somewhat below the glass transition temperature. In this temperature range, the top few nanometers of a glass can be substantially more mobile than the interior of the glass. If deposition is sufficiently slow, molecules near the surface have the opportunity to sample many configurations before they get buried and immobilized. This configuration sampling allows the top layer to attain or nearly attain equilibrium at the substrate temperature. Subsequent layers are similarly equilibrated. In this way, the usual kinetic constraints to the production of stable glasses can be avoided. Given the deep connections between glasses and other energy landscape problems (e.g., protein folding), we expect that this work will have a multidisciplinary impact. Below we show a schematic of the vapor deposition process.  We also show differential scanning calorimetry experiments on glasses deposited a different rates.  As expected from the explanation above, lower deposition rates produce glasses with greater kinetic stability.