Using Ultrafast Differential Scanning Calorimetry to Correlate Fragility to Ultrastability in Amorphous Chalcogenide Films

Amorphous materials, even of the same composition, can have highly variable material properties due to the local structure. This local structure also leads to the so-called "energy landscape" of a glass. An ultrastable glass is any that lies lower in this energy landscape than a traditional quenched glass. It has been hypothesized that fragility is a measure of surface to bulk diffusivity, and is therefore a controlling factor in allowing for vapor-deposited glasses to be grown as ultrastable films. By using ultrafast differential scanning calorimetry, we measure the glass transition temperature and thermodynamic properties of chalcogenide as-deposited films (including Ge-Te and Si-Te) to explore the dependence of ultrastability on fragility.