Cobalt nanocrystals

Under deposition of cobalt nanocrystals, self-assemblies of particles are observed and the nanocrystals are organized in a hexagonal network (Fig. 2). However, it can be seen that the grid is not totally covered. We do not have a simple explanation for such behavior. In fact, the size distribution, which is one of the major parameters in controlling monolayer formation, is similar to that observed with the other nanocrystals, such as silver and silver sulfide. One of the reasons could be that the nanocrystals have magnetic properties, but there is at present no evidence for such an assumption. 

Lisiecki, I. and Pileni, M.P. (2003) Synthesis of well-defined and low size distribution cobalt nanocrystals the limited influence of reverse micelles. Langmuir, 19 (22), 9486-9489. 

Sun, S. Murray, C. B. 1999. Synthesis of monodisperse cobalt nanocrystals and their assembly into magnetic superlattices. J. Appl. Phys. 85 4325 1330. 

Figure 5.3 (a) Sulfur surrounding a cobalt nanocrystal (b) hollow nanocrystal of cobalt sulfide. 

A very recent novel hquid-phase route to hollow nanocrystals of cobalt oxide and cobalt sulfide takes advantage of the Kirkendall effect (Section 6.4.1). Injection of sulfur or oxygen into a colloidal cobalt nanocrystal dispersion created hollow nanocrystals of... 

Black C. T., Murray C. B., Sandstrom R. L. and Sun S., Spin-dependent tunneling in self-assembled cobalt-nanocrystal superlattices. Science 290 (2000) pp. 1131-1134. 

Hollow Magnetic Nanocrystals Hollow nanoscale stmctures were first obtained by Y. Yin during the sulfurization of cobalt nanocrystals at elevated temperatures [145]. This process was found to lead to the formation of hollow cobalt sulfide nanocrystals such that, depending on the size of the cobalt nanocrystals and the cobalt sulfur molar ratio, different stoichiometries of hollow cobalt sulfide could be obtained. Hollow nanostmctures are usually formed through the nanoscale Kirkendall effect, which is based on the difference in diffusion rates of two species, and results in an accumulation and condensation of vacancies [146]. This phenomenon was first observed by Kirkendall at the interface of copper and zinc in brass in 1947 [147]. As a typical example of the nano-Kirkendall effect, the controllable oxidation of iron nanoparticles by air can lead to the formation of hollow iron oxide nanostructures, as shown in Figure 3.137. During the course of metal nanoparticle oxidation, the outward diffusion of metal occurs much faster in... 

Legrand, J., Petit, C., Pileni, M.P. Domain shapes and superlattices made of 8 nm cobalt nanocrystals fabrication and magnetic properties. J. Phys. Chem. B 105, 5643-5646 (2001)... 

FIGURE 5.6 X-ray absorption spectrum of the Co L-edge of cobalt nanocrystals calculated from the single-impurity Anderson model, illustrating a charge transfer from metal nanocrystals to ligand molecules. Reprinted with permission from Ref. [19]. American Chemical Society. 

FIGURE 5.17 X-ray absorption spectra of the O K-edge and Co L-edge of 4,10, and 15 nm cobalt nanocrystals after exposure to a mixture of CO and He (1 1) at room temperature and 250°C. Reprinted with permission from Ref. [35]. American Chemical Society. 

Lim, S. 1., Ojea-Jimeenez, 1., Varon, M., Casals, E., Arbiol, J., and Puntes, V. (2010) S3mthesis of platinum cubes, polypods, cuboctahedrons, and raspberries assisted by cobalt nanocrystals. Nano Lett., 10(3), 964-973. 

In a 1999 study of cobalt nanocrystals, D. P. Dinega and M. G. Bawendi discovered that cobalt forms an interesting cubic structure unlike any of the cubic structures described in this chapter. They called this new form eunit cell has an edge length of 609.7 pm and contains 20 atoms. The density of e-cobalt is p = 8.635 g cm . Use these data to estimate the number of cobalt atoms in a spherical nanocrystal of e-cobalt if the diameter of the nanocrystal is 2 nm. 

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