Mechanical Properties of Structure-Tunable, Vapor-Deposited TPD Glass

Physical vapor deposition (PVD) with a slow deposition rate and substrate temperature near the glass transition temperature can produce glasses with exceptional properties that include higher density, lower enthalpy, and better kinetic stability than the corresponding properties in ordinary liquid-cooled glass. Despite intensive investigations into thermodynamic and kinetic properties of PVD glasses, little is known about their mechanical properties, such as hardness and creep. In this study, we use nanoindentation to show that the mechanical properties of N, N ′-bis(3-methylphenyl)- N, N ′-diphenylbenzidine (TPD) glass can be manipulated by varying the deposition temperature. The elastic modulus of TPD glass was found to be correlated with molecular orientation, whereas the hardness was found to be correlated with density. In addition, our studies reveal that time-dependent deformation plays a key role in the mechanical response of these glasses.