Organized silica microspheres carrying ferromagnetic cobalt nanoparticles as a basis for tip arrays in magnetic force microscopy

Two-dimensional arrays of hard spherical particles carrying a nanoprobe hold potential as scanning tip arrays (STA) in force microscopy. Though rigid single molecules of proteins were originally envisioned as suitable probes, we foresee the possibility that magnetic nanoparticles, as well, could qualify the criteria. Ferromagnetic cobalt nanoparticles of size ∼10 nm well adhered to hard silica microspheres (225-250 nm) were synthesized by the sonochemical decomposition of a volatile organic precursor cobalt nitrosyl carbonyl [Co(CO)₃NO] in a suspension of silica in Decalin, followed by crystallization of the resultant amorphous produt. The morphological, thermal, and magnetic properties of the amorphous and nanocrystalline cobalt particles adhered to the microspherical silica were investigated by XRD, TEM, SEM/EDAX, TGA, DSC, EPR and magnetic susceptibility methods. Silica spheres carrying ferromagnetic cobalt nanocrystals were deposited on a single crystalline silicon <100> substrate by spin coating. The two-dimensional organization of the magnetic microspheres on silicon and the adhesion of cobalt nanoparticles on the surface of microspherical silica have been examined by scanning electron microscopy and atomic force microscopy (AFM), respectively. While the system described here forms only a basis for a functioning device, a chemical approach toward the synthesis, evaluation, and assembly of the components is emphasized.