Influence of initial amorphous structure on the in-situ crystallization of metastable thin films

Full text: Many technologically relevant materials are in fact kinetically stabilized and not at their true thermodynamic free energy minimum, i.e., they are metastable. These kinetically stabilized materials can show improved functionality over their thermodynamically stable counterparts. However, it is difficult at best to predict formation pathways for such metastable materials. In this work, we aim to understand how the initial state of amorphous thin films of VO_x influences the final crystalline form or polymorph. We employ a range of synchrotron based techniques: grazing incidence pair distribution function (GIPDF), x-ray absorption spectroscopy (XAS), and x-ray diffraction (XRD) during in-situ crystallization. We focus on amorphous VO_x films deposited by pulsed laser deposition with varying laser repetition rates and oxygen partial pressures and subsequently crystallized by annealing under different conditions. These different synthesis conditions create several different amorphous structures, as identified from GIPDF and XAS analysis. In-situ 2D-XRD during film crystallization shows that the different starting amorphous structures result in the formation of different polymorph. We use these results to relate the local structure of the initial amorphous structures to the VO_x polymorph structure. This work is part of a larger effort to help better understand the pathways needed to synthesize different polymorph. (author)