Hollow nanocrystals

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... 

Gao JH, Zhang B, Zhang XX et al (2006) Magnetic-dipolar-interaction-induced self-assembly affords wires of hollow nanocrystals of cobalt selenide. Angew Chem Int Ed. 45(8) 1220-1223... 

Yin Y, Rioux RM, Erdonmez CK, Hughes S, Somorjai GA, Alivisatos AP (2004) Formation of hollow nanocrystals through the nanoscale Kirkendall effect. Science 304(5671) 711-714... 

Alivisatos and coworkers have synthesized hollow nanocrystals by a process analogous to the Kirkendal effect observed in the bulk [712]. In bulk matter, pores are formed in alloying or oxidation reactions due to large differences in the solid-state diffusion rates of the constituents. By reacting Co nanocrystals... 

Formation of Hollow Nanocrystals through the Nanoscale Kirkendall Effect. Science, Vol. 304, No. 5671, (April 2004), pp. 711-714, SSN 0036-8075 Yun, S.H. Wu, J.Z. Dibos, A. Gao, X. Karlsson, U.O. (2005). Growth of Indined Boron nanowire Bundle Arrays in an Oxide-Assisted Vapor-Liquid-Sohd Process. Applied Physics Letters, Vo. 87, No. 11, (September 2005), pp. 113109 (1-3), ISSN 0003-6951 Zhang, P.H. Crespi, V.H. (2002). Theory of B2O and BeB2 Nanotubes New Semiconductors and Metals in One Dimension. Physical Review Letters, Vol. 89, No. 

The star-polymer template approach allows preparation of spherical nanocrystals. In the initial step, a star-like block copolymer nanoreactor was prepared, with a polyacrylic acid (PAA) inner block and an outer block of polystyrene. Then, the inner PAA block was infiltrated with the precursor for preparation of the desired nanoparticles. Finally, the precursor is transformed into the nanoparticle inside the star-polymer template, resulting in formation of uniform well-defined nanocrystals. By using a star-like triblock copolymer template, core-shell and hollow nanocrystals can be prepared following similar strategies (Scheme 9). 

In this work, Pradhan et al. demonstrated the encapsulation of crystalline Fe404 nanoparticles into the uniform carbon nanotubes by the MOCVD technique using ferrocene and that the size and number of such nanoparticles can be easily controlled by changing the MOCVD temperature or its period. At a proper MOCVD condition, Fe404 nanocrystals could be introduced into all of the nanotubes to different degrees, and more than 20% of the total volume of the tube hollow was filled with the nanoparticles. 

Fig. 9.9. Gallery of nanocrystal molecules prepared by inorganic routes, rattier than by biological assembly. These nanocrystal molecules can be branched or chained, as well as be hollow and nested. They can be coupled together electronically, as opposed to through space by plasmon coupling...

Zeolite shells on polystyrene beads were prepared by a combination of layer-by-layer (LbL) and hydrothermal synthesis techniques. The negatively charged polystyrene beads were surface modified in order to adsorb zeolite Beta nanocrystals. Such particles were then adsorbed on the surface of the beads and induced to grow into a continuous film of intergrown crystals of zeolite Beta. The effect of the preliminary treatment on the formation of the zeolite film was studied. Finally the polystyrene beads used as macro-templates were removed by calcination in air, yielding hollow spheres of zeolite Beta. The zeolite Beta/polystyrene composites and the corresponding hollow zeolite spheres were characterized by XRD, SEM, TG/DTA and BET surface area measurements. 

One very special type of shape control results in hollow nanoparticles of different geometries. In principle, the process is rather simple, in that a particle of any structure may serve as template that is coated by a layer of the desired metal. Subsequent removal of the inner template, either by calcination or by selective dissolution, will result in the formation of hollow nanostructures. Whilst this general technique can be applied to many types of material, one special application that involves only metals is as follows. In this case, silver nanocrystals of different shapes are coated by gold layers, via a simple chemical process based on the reductive power of elementary silver towards Au. ... 

The morphologies of magnetic multicomponent nanocrystals can be subdivided into several groups, namely core hdl nanoparticles, dumbbell nanopartkles, and the more recently discovered hollow nanostructures. The general approach towards the... 

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... 

Figure 3.138 TEM image of gold core-iron oxide hollow-shell nanocrystals.

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