Improved Mechanical Properties of Organic Stable Glasses by Nanoindentation*

Glasses with stability over ordinary, liquid-quenched glasses can be formed by the process of physical vapor deposition using sufficiently slow deposition rates at appropriate temperatures. These stable glasses have been shown to exhibit several interesting features including higher density, lower enthalpy, and better kinetic stability over ordinary glasses. Properties are dependent on the substrate temperature during deposition, with temperatures near .85T_g (glass transition temperature) producing the most stable glasses. Given these exceptional properties, it is of interest to further investigate the properties of stable glasses, including consideration of mechanical properties such as hardness and modulus. Using a temperature gradient for high-throughput acquisition of data, and nanoindentation for investigation of mechanics, we find that accurate determination of these properties requires a careful approach due to surface detection error. We are able to correct for this while achieving consistent, reliable results. We show enhancement of mechanics in stable glasses, consistent with trends in density increase. This increase in mechanics holds across several small molecule organic glasses of varying chemical structure.