High-throughput study of mechanical properties of organic stable glasses by nanoindentation

Glasses with enhanced stability over ordinary glasses have been formed by the process of Physical Vapor Deposition using a sufficiently slow deposition rate and appropriate temperatures. These stable glasses have been shown to exhibit higher density, lower enthalpy, and better kinetic stability over ordinary glasses, and are typically optically birefringent. These properties depend on the temperature at which the substrate is held during deposition, with temperatures near .85T_g (glass transition temperature) producing the most stable glasses. Given such exceptional properties, it is of interest to further investigate how the properties of stable glasses vary with deposition temperature and compare to those of ordinary glasses. In particular, the mechanical properties of these glasses remain relatively under-investigated. Nanoindentation is a useful technique for determination of mechanical properties, though it can present a problem of surface detection in cases of soft surfaces. Correcting for this, and using a temperature gradient sample for high-throughput acquisition of data, mechanical properties are obtained for several organic glass-formers in order to explore the relationship between chemical structure, deposition temperature, and mechanical properties of stable glasses.