Glass transition temperatures in pure and composite organic thin-films.

In a non-crystalline molecular material, glass-transition temperature T g is typically defined by an inflection point in the specific volume (or thickness) vs. temperature plot. In this paper, the glass-transitions in thin-film organic semiconductors are investigated by using various temperature spectroscopic ellipsometer. We observed that glass transition temperatures in organic thin films are characterized by a disruptive change in thickness vs. temperature plot. In order to modify the glass transition temperature of an organic semiconductor, we also made composite thin-films by inclusion of another organic molecule with higher T g . We found that the transition temperature can be significantly improved by inclusion of another organic molecule. The glass-transition processes of these composite semiconductors, however, also proceed in a disruptive manner, in stark contrast to typical polymeric materials. Despite this disruptive glass transition behavior, the experimental T g of the composite semiconductors are found to follow precisely a simple inverse sum equation of constituent temperatures with their respective weight factors. [ABSTRACT FROM AUTHOR]