Chemistry Weekly Seminar - PhD Candidate Amara Zuhaib

Title:

Structural Characterization of Organic Glasses by NEXAFS Spectroscopy

Abstract:

Glasses are non-equilibrium material that lack long-range order. Over the last decade, organic glasses with exceptional stability and increased density have been formed by physical vapour deposition (PVD). The stability of these glasses is attributed to the increased surface mobility during deposition. There are knowledge gaps in understanding the formation and structure of these highly stable dense glasses. The first objective of this research work uses the Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy to study the internal conformation of molecules in these glasses. We hypothesize that observed changes in glass density can be related to molecular conformations which permits tighter packing. Different conformations of molecules within organic glass are probed by NEXAFS spectroscopy and interpreted with DFT spectroscopic simulations. Characteristic spectroscopic energy shifts were related to the conformation of the molecules that makeup the glass as a function of deposition conditions.

The second objective of this research work was to utilize the orientation sensitivity (linear dichroism) in the NEXAFS spectroscopy of molecular glasses to study their orientational order. Molecular glasses grown at substrate temperatures ranging from 0.79 Tg - 1.01 Tg (where Tg is the glass transition temperature) show characteristic linear dichroism differences in their NEXAFS spectra. Some unique information has been explored in detail to understand this orientation in organic glasses.