Characterization of ferrite nanoparticles by laser desorption/ionization mass spectrometry

Magnetic nanoparticles are important materials used in magnetic storage med ia. The specific physical properties of nanophase particles can have profou nd effects on magnetism and will determine the merits of particular particl es as components in storage devices. However, obtaining a detailed depictio n of the structural features of nanoparticles is a non-trivial process. We have employed laser desorption/ionization mass spectrometry (LDI-MS) to aid in the characterization of nanoscale magnetic particles. Our investigation reports on two types of ferrite nanoparticles, having Fe2O3 and Fe3O4 crys tal structures, that were each synthesized in reverse micelles, During posi tive and negative LDI-MS of both types of particles, iron oxide peaks were consistently produced. Compared to Fe2O3, Fe3O4 particles yielded more peak s at the high m/z end of the mass spectrum, and the relative intensities of higher m/z peaks were typically greater. A negative ion mode depth profili ng experiment revealed the capacity of the LDI-MS approach to obtain inform ation regarding changes in nanoparticle composition as a function of sampli ng depth. Over the course of prolonged irradiation of stationary Fe2O3 nano particles, distinctly different desorption/ionization behavior was observed at the particle surface as compared to the core region. The depth profilin g experiment was particularly useful for distinguishing surface impurities from core constituents.