Magnetite Nanoparticles Anchored to Crystalline Silicon Surfaces

Magnetite nanoparticles of 5 nm mean diameter, coated with 10-undecynoic acid, have been anchored to crystalline Si(100) surfaces via the hydrosilylation reaction at 180 °C. The iron content in the sample (0.54 ± 0.05 ¼g/cm²) has been determined by atomic absorption analysis. The sample has been further characterized by X-ray photoelectron spectroscopy, field emission scanning, scanning-tunneling, and atomic force (AFM) microscopies. The thermal anchoring does not alter the morphology of the nanoparticles, causing only a slight oxidation of their surfaces. However, a second layer of nanoparticles was also formed, covering about 50% of the surface. The magnetic properties were studied using a SQUID magnetometer. ZFC (zero-field cooled) and FC (field cooled) curves were obtained in the 5-300 K temperature range. The ZFC curve shows a rounded maximum at T_max ~20 K. A hysteretic magnetization cycle was also observed at 5 K with associated magnetization saturation and coercitivity values of 40 emu/g and 160 Oe, respectively. The magnetic behavior of the sample was found to be typical of an assembly of noninteracting (or very weakly interacting) super-paramagnetic particles.