Physical vapor deposition as a route to hidden amorphous states

Stable glasses of indomethacin (IMC) were prepared by using physical vapor deposition. Wide-angle X-ray scattering measurements were performed to characterize the average local structure. IMC glasses prepared at a substrate temperature of 0.84 T-g (where T-g is the glass transition temperature) and a deposition rate of 0.2 nm/s show a broad, high-intensity peak at low q values that is not present in the supercooled liquid or melt-quenched glasses. When annealed slightly above T-g, the new WAXS pattern transforms into the melt-quenched glass pattern, but only after very long annealing times. For a series of samples prepared at the lowest deposition rate, the new local packing arrangement is present only for deposition temperatures below T-g - 20 K, suggesting an underlying first-order liquid-to-liquid phase transition.