X-ray absorption spectroscopy as a direct probe of nanoparticle morphology

When properties of nanoparticles are found to vary from expected bulk values it is uncertain whether this is the result of a mixed-phase or amorphous product, or an observation of a true intrinsic size or surface effect. We present x-ray absorption spectroscopy (XAS) as an ideal tool for answering this technologically important and academically interesting question. The strength of XAS lies in the fact that it is a direct element specific probe of electronic structure. We present XAS data on nanoparticles (4-20 nm diameter spheres) of gamma-Fe$_{2}$O$_{3}$, Co$_{3}$O$_{4}$, and TiO$_{2}$. The data reveals that gamma-Fe$_{2}$O$_{3}$ may be grown in the pure phase down to at least 4 nm, while TiO$_{2}$ shows intrinsic size effects at around 10 nm. Our Co$_{3}$O$_{4}$ data presents an example of a mixed phase system.