A photopatternable superparamagnetic nanocomposite: Material characterization and fabrication of microstructures

A superparamagnetic nanocomposite obtained by dispersing superparamagnetic magnetite nanoparticles in the epoxy SU-8 is used to fabricate microstructures by photolithography. The dispersion of the nanoparticles and the level of agglomerations are analyzed by optical microscopy, TEM (transmission electron microscope), SAXS (small-angle X-ray scattering), XDC (X-ray disc centrifuge) and XRD (X-ray diffraction). Two different phosphate-based dispersing agents are compared. In order to obtain a high-quality nanocomposite, the influence of particle concentration 1–10 vol.% (4–32 wt.%) on composite fabrication steps such as spin coating and UV exposure are systematically analyzed. Features with narrow widths (down to 1.3 μm) are obtained for composites with 5 vol.% particle concentration. Mechanical, magnetic and wetting properties of the nanocomposites are characterized. These nanocomposites exhibit superparamagnetic properties with a saturation magnetization up to 27.9 kA m−1 for10 vol.%. All nanocomposites show no differences in surface polarity with respect to pure SU-8, and exhibit a moderate hydrophobic behavior (advancing dynamic contact angles approximately 81°). Microcantilevers with particle concentrations of 0–5 vol.% were successfully fabricated and were used to determine the dynamic Young's modulus of the composite. A slight increase of the Young's modulus with increased particle concentration from 4.1 GPa (pure SU-8) up to 5.1 GPa (for 5 vol.%) was observed.