Optical nanoscopy characterization of nanofilms

Glass formation and glassy behavior remains an important field of study in condensed matter physics, with many aspects still little understood. The approach used in this work is to observe the changes in behavior of glass-forming materials at the nanometer scale by exploring the viscoelastic properties of ultrathin free-standing glassy polymer films. An experimental measurement cell based on the nanobubble inflation method is used, consisting of inflating a polymer film suspended over an array of 5 µm diameter holes in a Si wafer. Measuring the deformation as a function of time as the material relaxes is used to determine the creep compliance. Both polystyrene (PS) and poly(vinyl acetate) (PVAc) films of a few tens of nm thickness prepared by spin-coating from solution have been studied. Interference microscopy is used to measure the deformation over several hours, which is challenging at the nanoscale due to mechanical deformations and drift. In this paper we present some of the first solutions developed to allow consistent measurements of film deformation using this novel interference nanoscopy technique. Future work will involve the measurements of creep compliance as a function of different film properties so as to be able to compare the results with theoretical predictions.