Using anisotropic vapor deposited glasses to learn about the structure and mobility of liquid surfaces

摘要

Glasses play an important role in technology as a result of their macroscopic homogeneity and the ability to tune properties through composition changes. These features are critical in organic light emitting diodes which utilize vapor-deposited glasses of organic semiconductors as active layers. While liquid-cooled glasses are usually isotropic, glasses produced by physical vapor deposition (PVD) are generally anisotropic. This anisotropy can be manipulated to increase device efficiency. In this talk, I use three examples to show how PVD glass structure can be used to deduce information about the structure and mobility of liquid surfaces. PVD glasses of Alq3 exhibit large surface potentials, and anisotropic x-ray scattering. Using computer simulations, we show that these features result from layering and polar orientation at the free surface of the equilibrium liquid. When rod-like molecules such as itraconazole and posaconazole are deposited, much more highly organized glasses can be prepared. By characterizing the structure of glasses deposited over a wide range of deposition rates, we have constructed "deposition rate/substrate temperature" master curves. These master curves encode information about surface mobility and interface structure.