Optical Study of Structural/Electronic Property Change in Thin Polyethylene Terephthalate Film by Stretching

Optical spectroscopy provides several useful information about polymeric ultrathin films by combining interferometric and optical absorption data contained in the UV-Vis-NIR spectra. In particular, the UV-Vis-NIR spectrum of an ultrathin polymeric film contains information about the film thickness, structural disorder, bandgap energy, type of electron transition model (direct/indirect, allowed/forbidden), cut-on wavelength (i.e., the opaque/transparent switching wavelength), etc. Here, these properties have been determined for a model semi-crystalline polymer (polyethylene terephthalate, PET) in form of ultrathin film before and after a mild mechanical deformation treatment (manual stretching). It has been found that EU and Eg parameters are not strictly depending on mechanical deformation due to their main dependence on chemical composition/constitution of the polymer.