Influence of substrate temperature on the stability of glasses prepared by vapor deposition

Abstract

Physical vapor deposition of indomethacin (IMC) was used to prepare glasses with unusual thermodynamic and kinetic stability. By varying the substrate temperature during the deposition from 190 K to the glass transition temperature (Tg=315 K), it was determined that depositions near 0.85Tg (265 K) resulted in the most stable IMC glasses regardless of substrate. Differential scanning calorimetry of samples deposited at 265 K indicated that the enthalpy was 8 J/g less than the ordinary glass prepared by cooling the liquid, corresponding to a 20 K reduction in the fictive temperature. Deposition at 265 K also resulted in the greatest kinetic stability, as indicated by the highest onset temperature. The most stable vapor-deposited IMC glasses had thermodynamic stabilities equivalent to ordinary glasses aged at 295 K for 7 months. We attribute the creation of stable IMC glasses via vapor deposition to enhanced surface mobility. At substrate temperatures near 0.6Tg, this mobility is diminished or absent, resulting in low stability, vapor-deposited glasses.

Physical vapor deposition as a route to hidden amorphous states

“…Fortunately, an exciting method has been developed for preparing glass films that are close to equilibrium at temperatures considerably below the conventional T g (23)(24)(25)(26)(27). Recent work has shown that, when the correct substrate temperature and deposition rate are used, physical vapor deposition can produce amorphous samples with lower enthalpies (24) and higher densities (28) than glasses formed by cooling a liquid at a few degrees Kelvin per minute.…”

“…Recent work has shown that, when the correct substrate temperature and deposition rate are used, physical vapor deposition can produce amorphous samples with lower enthalpies (24) and higher densities (28) than glasses formed by cooling a liquid at a few degrees Kelvin per minute. Extrapolation indicates that a supercooled liquid would have to be slowly cooled over at least 1,000 y to prepare a glass whose properties match those of the vapor-deposited materials (23)(24)(25). It has been proposed that the preparation of such stable glasses makes use of the strongly enhanced dynamics of molecules at the surface of a glass relative to bulk molecules.…”

High Frequency Acoustics in Colloid-Based Meso- and Nanostructures by Spontaneous Brillouin Light Scattering

“…A characteristic kink in the temperature-dependent phase velocity indicates T g and the value obtained is in reasonable agreement with the value obtained from differential scanning calorimetry. [174,175] From the phase velocities c l,t in Fig. 6.2, the moduli of the stable glass and the ordinary glass can be calculated.…”

“…These two molecules are well-known glass-formers and their glasses have been previously prepared with physical vapor deposition. [31,174,175] During deposition, the temperature of the substrate T substrate and the deposition rate are the important control parameters. For this work, T substrate was held near 0.85 T g , i.e., 265 K for IMC and room temperature (≈295 K) for TNB.…”

“…It has previously been shown that these deposition conditions produce glasses with low enthalpy, high density, and high kinetic stability. [31,[174][175][176][177] T substrate was controlled by attaching the SiO 2 substrates to a copper temperature stage (Fig. 6.1a).…”