Fabrication and analysis of new azo-based thin films are explored for holographic data storage systems by exploiting the bulk assisted molecular photomigration shown by polymeric and monomeric azo-based materials. , Holographic systems have the advantage of storing information in 3 dimensions; moreover, when applied to organic materials, the holographic process allows for thinner, cheaper and rewritable holographic systems. Azo-based materials present several advantages such as E-Z photoisomerization and photomigration leading to the formation of reversible surface relief gratings (SRG) , hence they appear as perfect candidates for rewritable data storage media. The azo-derivatives used for these purposes are depicted in Figure 1.
The well-defined bulky molecules have been designed to form amorphous films with a glass transition temperature Tg well above room temperature, making them thermally stable without crystallization. Various deposition techniques, such as spin-coating and vacuum thermal evaporation, are used to generate thin films which encounter different photophysical behaviors depending on the thickness. Photoisomerization kinetics, holography reaction and absorption UV-vis spectra allow us to characterize the photochromic behavior and migration of the azo derivatives in thin films. Rewritability, photoisomerization of the back Z-to-E thermal reaction, formation and time-stability of the gratings formed in the azo materials are explored. The photochromic monomeric materials behave differently from similar photoactive polymers with a faster photoisomerization and migration, and distinct time-stability of SRG. Atomic force microscopy (AFM) measurements are performed to image the topography created in the different materials.