Analysis of the Homogeneity of a Thin Ceramic Polymer Composite Film by Atomic Force Microscopy Infrared Spectroscopy (AFM-IR) and Other Complementary Techniques

Producing thin films by tape casting is well known for manufacturing multilayer electronic components. In the present work, this process was used to manufacture a scintillator made of YAG:Ce with a thickness of a few hundred micrometers, for application in the fourth-generation particle accelerator located at the National Center for Energy and Materials Research (CNPEM) in Brazil. Tape casting consists of a directed spreading of the ceramic suspension through the space between the blade and the substrate at a constant velocity, producing a tape with uniform height. Because of the oriented flow and shear forces, there is a preferential direction of both the ceramic filler and the polymer chains resulting in anisotropy of orientation in the film and consequently different behavior and properties between x- and y- axis. During film drying, the polymer and solvent tend to migrate from the surface in contact with the substrate (base) to the surface exposed to the atmosphere (top), resulting in anisotropy in the distribution of polymer in the z-axis of the film (cross-section). Therefore, it is expected that a non-isotropic film will be formed, and possible warping will occur during the next sintering stage. These phenomena described above are well-known and have been widely reported in literature. Typically, the characterization techniques used to verify these anisotropies are, for example, scanning electron microscopy, polarized light microscopy, and thermogravimetric analysis. We propose a new method of analyzing film homogeneity through topography and infrared mapping using the AFM-IR technique. To produce the YAG:Ce thin film, a stirred ball mill was used with 5 mm diameter zirconia spheres at a rotation of 360 rpm and a chemical formulation composed of ethanol and toluene (solvents); Menhaden Fish oil (dispersants); polyvinyl butyral (binder); diethylene glycol, benzyl butyl phthalate and polyethylene glycol (plasticizer). To characterize the film surfaces (top, base, and cross-section), the AFM-IR technique with thermomechanical response was used. Topography images and infrared spectra were obtained in a nanoIR2-s atomic force microscope (Bruker™) in contact mode. A ContGB-G probe (BudgetSensors™) with a nominal spring constant of 0.2 N/m and <50.0 nm. tip end radius was used for the scanning. Through topographic and infrared mapping (constant wavenumber value of 1728 cm-1) of 2 μm x 2 μm regions of the sample, differences in topography and regions with apparent polymer accumulation were noted. Scanning electron microscopy analyses were complementary to this.