Localization model description of the interfacial dynamics of crystalline Cu and CuZr metallic glass films.

Recent studies of structural relaxation in Cu-Zr metallic glass materials having a range of compositions and over a wide range of temperatures and in crystalline UO under superionic conditions have indicated that the localization model (LM) can predict the structural relaxation time τ of these materials from the intermediate scattering function without any free parameters from the particle mean square displacement ⟨r⟩ at a caging time on the order of ps, i.e., the "Debye-Waller factor" (DWF). In the present work, we test whether this remarkable relation between the "fast" picosecond dynamics and the rate of structural relaxation τ in these model amorphous and crystalline materials can be extended to the prediction of the local interfacial dynamics of model amorphous and crystalline films. Specifically, we simulate the free-standing amorphous CuZr and crystalline Cu films and find that the LM provides an excellent parameter-free prediction for τ of the interfacial region. We also show that the Tammann temperature, defining the initial formation of a mobile interfacial layer, can be estimated precisely for both crystalline and glass-forming solid materials from the condition that the DWFs of the interfacial region and the material interior coincide.