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30] Note the reversal of the hydrophilic±hydrophobic character of the two surface regions on going from operation 2 to operation 4 (Fig. 2).[31] a) [32] The role of atmospheric humidity in this tip-induced surface oxidation (by analogy with previously reported processes of scanning-probe anodization [26,33]) remains to be elucidated.[35] As suggested by the spectroscopic data and additional chemical derivatization experiments, NTS eo generated in this manner appears to be the enolate of a hydroxy carbonyl (ketone/aldehyde) species. Examples of some related enolic carbonyls may be found in a) S. ForsØn, M.

Very small nanometric oxide particles (CoO and Co 3 O 4 , around 2 nm in diameter) well dispersed inside a polymer matrix were prepared by solid-state oxidation of a metallic colloid precursor (1.6 nm Co particles). WAXS (wide-angle X-ray scattering) and HREM (highresolution electronic microscopy) were used to observe very precisely the structural changes occurring during the oxidation process. With cobalt particles a few nanometers large, air oxidation at room temperature results in a surface passivation. Consequently the particles show a composite structure with a metallic core surrounded by an oxide surface layer. Preliminary magnetic measurements reveal that unidirectional exchange anisotropy between the metallic ferromagnetic core and the antiferromagnetic oxide layer occurs below 130 K.

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Cross-shaped and octahedral nanoparticles (hexapods) of MnO in size, and fragments thereof, are created in an amine/carboxylic acid mixture from manganese formate at elevated temperatures in the presence of water. The nanocrosses have dimensions on the order of 100 nm, but with exposure to trace amounts of water during the synthesis process they can be prepared up to about 300 nm in size. Electron microscopy and X-ray diffraction results show that these complex shaped nanoparticles are single crystal face-centered cubic MnO. In the absence of water, the ratio of amine to carboxylic acid determines the nanocrystal size and morphology. Conventionally shaped rhomboehdral/square nanocrystals or hexagonal particles can be prepared by simply varying the ratio of tri-n-octylamine/oleic acid with sizes on the order of 35-40 nm in the absence of added water. If the metal salt is rigorously dried before the synthesis, then "flower-shaped" morphologies on the order of 50-60 nm across are observed. Conventional squareshaped nanocrystals with clearly discernible thickness fringes that also arise under conditions producing the nanocrosses mimic the morphology of the cross-shaped and octahedral nanocrystals and provide clues to the crystal growth mechanism(s), which agree with predictions of crystal growth theory from rough, negatively curved surfaces. The synthetic methodology appears to be general and promises to provide an entryway into other nanoparticle compositions.

Single-source molecular precursors were found to produce iron phosphide materials. In a surfactant system of trioctylamine and oleic acid, H2Fe3(CO)9PtBu reacted to form Fe4(CO)12(PtBu)2, which decomposed to give Fe2P nanorods and "bundles." Control of the morphology obtained was possible by varying the surfactant system; addition of increasing amounts of oleic acid resulted in crystal splitting, while the addition of microliter amounts of an alkane enhanced the crystal splitting to give sheaflike structures. The different morphologies seen were attributed to imperfect crystal growth mechanisms.

The reaction of Co(η3-C8H13)(η4-C8H12) and Pt2(dba)3 (dba = bis-dibenzylidene acetone) under dihydrogen leads in the presence of poly(vinylpyrrolidone) to nanometric bimetallic particles Co x Pt1 - x . The composition of the material is determined by the initial ratio of the two organometallic precursors. The bimetallic character of the particles is evidenced by magnetic, structural, and spectroscopic studies. Structural changes are evidenced both by HREM and WAXS:  platinum rich particles adopt a fcc crystalline structure while cobalt rich particles adopt a non periodic polytetraedral arrangement. The magnetic properties of the materials have been investigated. ZFC/FC measurements show that the particles are superparamagnetic and that their size dispersity is very low. From isothermal magnetization measurements, the extrapolated value of the coercive field H C (T = 0) is shown to increase continuously with Pt concentration, which is characteristic of bimetallic particles.