Iron nanocrystals

Magnetic properties of iron nanocrystals nested in carbon cages, which grew on the cathode deposit, have been studied by Fliura el al.[29]. Magnetization (M-H) curves showed that the coercive force. He, of... 

Fig. 7. TEM picture of iron nanocrystals collected from the chamber soot nanocrystals are embedded in amorphous carbon globules. On the surface of some core crystals, a few fringes with 0.34-0.35 nm spacing suggesting the presence of graphitic layers are observed, as indicated by arrows.

Wrapped nanocrystals. Metal crystallites covered with well-developed graphitic layers are found in soot-like material deposited on the outer surface of a cathode slag. Figure 6 shows a TEM picture of an a(bcc)-Fe particle grown in the cathode soot. Generally, iron crystallites in the tv-Fe phase are faceted. The outer shell is uniform in thickness, and it usually con-... 

The protective nature of graphitic carbon against oxidation of core nanocrystals was demonstrated by an environmental test (80°C, 85% relative humidity, 7 days)[44]. Even after this test, XRD profiles revealed that the capsulated iron particles were not oxidized at... 

Tan, Y.W., Zhuang, Z.B., Peng, Q. and Li, Y.D. (2008) Room-temperature soft magnetic iron oxide nanocrystals ... 

Yu, W.W., Falkner, J.C., Yavuz, C.T. and Colvin, V.L. (2004) Synthesis of monodisperse iron oxide nanocrystals by thermal decomposition of iron carboxylate salts. Chemical Communications, (20), 2306-2307. 

Decker, S.P. Characterization and reactivity of calcium oxide and iron oxide coated — calcium oxide nanocrystals. Ph.D. thesis. Kansas State University, Manhattan, KS, 1998. 

Solution phase chemical synthesis is a convenient way for making surfactant coated magnetic nanoparticles, as described in various reviews [12-18]. Monodisperse Co nanoparticles with standard deviation less than 10% are synthesized by decomposition of Co2(CO)8 [19-22] or Co(rj3-C8Hi3X n4-C8Hi2) [23] and reduction of cobalt salt [24,25] in the presence of oleic acid and trialkylphosphine, or trialkylphosphine oxide, or alkylamine. Monodisperse iron nanoparticles are normally prepared from decomposition of Fe(CO)5 [26-28]. However, metallic iron-based particles from this decomposition procedure are difficult to characterize due to the chemical instability. A recent synthesis using decomposition of Fe[NSiMe3)2]2 offers a promising approach to monodisperse Fe nanocrystals [29]. 

A dielectric oxide layer (eg. silica) is useful as a shell material because of the stability it lends to the core and its optical transparency. The classic method of Stober for solution deposition of silica are adaptable for coating of nanocrystals with silica shells.111 This method relies on the pH and the concentration of the solution to control the rate of deposition. The natural affinity of silica to oxidic layers has been exploited to obtain silica coating on a family of iron oxide nanoparticlcs including hematite and magnetite111 Such a deposition process is not readily extendable to grow shell layers on metals. The most successful method for silica encapsulation of metal nanoparlides is that due to Mulvaney and co-workers.114 In this method, the surface of the nanoparticles is functionalized with aminopropyltrimethylsilane. a bifunctional molecule with a pendant silane group which is available for condensation of silica. The next step involves the slow deposition of silica in water followed by the fast deposition of silica in ethanol. Fig. 13 shows the TEM images... 

Hou Y. L. and Gao G., Solvothermal Synthesis and Magnetic Properties of Polymer Protected Iron and Nickel Nanocrystals, submitted to J. Mater. Chem. 

Virion templates of TMV were also used in combination with different synthetic routes for CdS, PbS, and Fe oxide nanoparticles. Nanoparticle-virion tubules were prepared by reacting a buffered solution of TMV in CdCl2 (pH 7) or TMV in Pb(N03)2 (pH 5) with H2S gas. The formation of metal sulfide nanoparticles occurred over 6 hours as observed by a uniform coating of CdS and PbS nanocrystals on the TMV surface from TEM analysis. Selected area electron diffraction of the mineralized products indicated a zinc blende crystal stracture for CdS particles and a rock salt structure for single domain PbS nanocrystals. The iron oxide nanoparticles were mineralized by the TMV templates by the oxidative hydrolysis of an Fe VFe acidic solution with NaOH. Consequently, a mineral coating of irregular ferrihydrite particles grew on the surface to a thickness of 2 nm. 

State lifetimes and modes of energy transfer within the structure. Examples of this are photoluminescence of ZnS nanoparticles studied by Wu et al. (1994), and Mn doped ZnS nanoparticles by Bhargava et al. (1994). In the latter study, the doped nanocrystals were found to have higher quantum efficiency for fluorescence emission than bulk material, and a substantially smaller excited state lifetime. In the case of environmental nanoparticles of iron and manganese oxides, photoluminescence due to any activator dopant would be quenched by magnetic coupling and lattice vibrations. This reduces the utility of photoluminescence studies to excited state lifetimes due to particle-dopant coupling of various types. The fluorescence of uranyl ion sorbed onto iron oxides has been studied in this way, but not as a function of particle size. 

The very first report of two-dimensional arrays was of Fe304 nanocrystals [128]. Bentzon et al. observed that the ferrofluid obtained by thermolysis of iron penta-carbonyl upon drying (over a period of several weeks) yielded well ordered two-dimensional arrays of Fe304 nanocrystals. Since then, easier methods have been devised to obtain arrays of Fc304 nanocrystals [129]. Two-dimensional arrays of amine-capped metal oxide nanocrystals such as C03O4 have been obtained by start-... 

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