Optical Determination of Young's Modulus of Nanoscale Organic Semiconductor Thin Films for Flexible Devices

We present a nondestructive, noncontact optical approach to estimate the elastic modulus of an organic semiconductor thin film based on solid-state solvation effect. Self-strained silicon oxide microbeams were used to apply varying amounts of tensile strain on an overlying organic semiconductor thin film to trigger nanoscale change in dielectric polarizability, and the corresponding shift in the photoluminescence spectrum was used to determine the elastic modulus of the thin film. The results were further verified by performing similar experiments on an electrostatically actuated microelectromechanical system device capable of applying dynamically controllable local tensile strain on the organic thin film. By comparing the observed modulation in the emission energy to the corresponding local strain under static and dynamic conditions, we estimated the elastic modulus of the Alq3 thin film to be within 2.81-3.88 GPa. The reported method will significantly aid in the investigation of the mechanical properties of organic semiconductor thin films, the results of which will enable the design of nanoscale flexible and wearable optoelectronic devices.