Fe3O4 nanoparticles capped with a 40%/60% oleic acid/oleylamine surfactant were synthesized by solvo-thermal methods and the nature of the nanoparticle-capping agent interactions were studied by x-ray photoelectron spectroscopy (XPS).  X-ray diffraction (XRD) confirmed that the nanoparticle oxide phase was Fe3O4 and determined the particle size to be 11 nm.  XPS showed the existence of carboxylate adsorbate from the oleic acid and chemisorbed amine in approximately the same surface composition as in the solvent during synthesis, and that surface hydroxylation was below detection limits at the Fe3O4 interface even for samples with extensive air exposure.  The surface of the Fe3O4 nanoparticle was slightly reduced, by approximately 25% relative to bulk Fe3O4, and some changes in Fe 2p satellite structure were also observed.  The capping agents were stable under UHV to 250 oC, at which temperature the oleylamine capping agent decomposed with alkyl carbon surface deposition, loss of nitrogen adsorbate, and ~ 40% surface reduction to FeO.  The carboxylate adsorbate persisted to temperatures of up to 600 oC, although with loss of the alkyl tail and continued reduction of the surface, eventually to produce an FeO/metallic Fe mixture contaminated with a small amount of Fe3C.

XPS analysis of Fe<sub>3</sub>O<sub>4</sub> nanoparticle: Surfactant interactions

246th National Meeting (2013)

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XPS analysis of Fe3O4 nanoparticle: Surfactant interactions

XPS analysis of Fe₃O₄ nanoparticle: Surfactant interactions