X-ray investigations of formation efficiency of buried azobenzene polymer density gratings

We present the results of time-dependent x-ray scattering measurements during the formation of a buried, modulated density structure below polymer film surface created at temperatures above the glass transition temperature T-G during the thermal erasure of a holographically written surface relief grating. The surface relief gratings are initially formed on polymer films containing azobenzene side groups by exposure to a polarization holographic pattern made using light at 488 nm. The material responds to the actinic light by forming a sinusoidal surface relief pattern in a one-step process. Theoretical predictions show that the surface relief grating formation is accompanied by a density grating just below the film surface. Upon annealing above polymers glass transition temperature the surface relief grating melts while some of the density modulation in the bulk remains and a nonsinusoidal density grating is rebuilt after long term annealing at a temperature approximately 30 K above the glass transition temperature. The growth of density volume structure is assisted by exposure to red laser light during annealing. The observed homopolymer pDR1M was found to be the most effective material to build the modulated buried density grating. This might be due to the formation of clusters below the former peak positions of the surface relief grating. A quantitative description and preliminary model is given for this behavior. (C) 2003 American Institute of Physics.