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

Abstract

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 Alq 3 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.

Elastic Properties of Poly(ethylene glycol) Nanomembranes and Respective Implications

“…Note that the derived Young’s modulus values of the PEG membranes in the entire studied thickness range are very small, which renders these membranes extremely elastic. For comparison, the Young’s modulus of a 55 nm polyethylene membrane was estimated at 10 GPa [ 27 ], that of carbon nanomembranes of 1 nm thickness was reported to be 45 GPa [ 28 ], that of a vapor-deposited, 30 nm tris(8-hydroxyquinoline) aluminum film was 2.81–3.88 GPa [ 29 ], and that of 320 nm Si membrane was 220 GPa [ 30 ]. One of the lowest Young’s modulus values (32 MPa) was reported for ~100 nm plasma-polymerized allylamine films [ 31 ], but even this value is more than an order of magnitude higher than that for the PEG membranes.…”

“…The bioinert and ultraflexible character of the PEG nanomembranes makes them suitable for different applications ranging from extremely sensitive sensing elements in microelectromechanical systems [ 26 , 29 , 44 , 45 ] to biomolecule-friendly supports for biological samples in high-resolution transmission electron microscopy [ 19 , 46 , 47 ].…”