Geometry core-shell

Anandan et al. [37] reported the sonochemical synthesis of gold-silver bimetallic nanoparticles with core-shell geometry by the sonochemical co-reduction of Au and... 

The formation of nanocomposites can be done using different arrangements, for example, the dispersion of a semiconductor in a continuous matrix, the formation of stacked layers, core-shell geometries, or simply physically contacted, with consequences for the energy transfer between the phases (Figure 4.5) [76]. 

Composite semiconductor nanoclusters can be classified into two categories, namely, capped- and coupled-type heterostructures. The capped nanoclusters essentially have a core-shell geometry while in a coupled system two semiconductor nanoclusters are in contact with each other. The principle of charge separation in capped and coupled semiconductor systems is illustrated in Fig. 12. 

Figure 12 Principle of charge separation in semiconductor heterostructures (a) capped (or Core-Shell) geometry and (b) coupled geometry. Electrons accumulate at the conduction band (CB) of Sn02 while holes accumulate at the valence band (VB) of Ti02.

An ansatz for treating the resultant optical properties is to treat the shell using MG theory to yield an approximate average dielectric function for the shell, and then to use this function in the core-shell geometry. The predictions of this model are shown in Fig. 8. A fixed latex or silica core of 50 nm is shown surrounded by a 5 nm shell of Au Si02 where the Au volume fraction is varied. The medium is taken to be water for simplicity. 

Fig. 1 Four types of semiconductor-based composite architectures (a) semiconductor/matrix (b) layered configuration of two semiconductors, A and B (c) coupled semiconductors (d) core-shell geometry SC denotes the semiconductor [12]...

Core-Shell Geometry by Post-Treatment of Nanofibers... 

The LBL method can also be used for the assembly of nanoparticles on suitable colloid templates. This procedure was recently developed by Caruso et al. ° and has found application in a great variety of materials. In this system, the optical effects observed for the macroscopic thin films are obtained for colloidal particles, which possess themselves a core-shell geometry and can be used in turn for the construction of more complex, nanoscale materials. The resulting spheres are essentially different to continuous metal shells grown on colloid templates, which have been recently reported. " Such continuous shells display optical properties associated to resonances along the whole shell, and are therefore extremely sensitive to both core size and shell thickness, while in the system presented here the optical properties only depend on the nature and dimensions of the constituting units and the number of deposited monolayers. 

Hsu, C.-Y., et ah, Supersensitive, ultrafast, and broad-band tight-harvesting scheme employing carbon nanotube/Ti02 core-shell nanowire geometry. ACS Nano, 2012. 6(8) p. 6687-6692. 

On the other hand, when low concentrations of metal are used to cap the semiconductor core we can expect the outer layer to be discontinuous. Such a configuration of core shell particles (i.e. small metal islands deposited on the Ti02 core) provides a favorable geometry for facilitating the interfacial charge transfer under UV irradiation. It should be noted that, a new band appears at 390 nm in the case of Ti02/Au nanoparticles as the transient absorption corresponding to (SCN)2 ... 

To avoid simple but more tedious computations, we restrict our further analysis to the case of a relatively thick shell of the thickness S. = R2 - R > R. Is such core-shell nanociystals, the geometry factor a = R IR2f is much less than 1, a 1. Therefore, computing zeroes of the real part of denominator in Eq. (5), we can omit the term proportional to a. Then, the resonance frequencies are determined by the equations ... 

In core-shell nanociystals we still have one free parameter - the geometry factor ct. An appropriate choice of the geometiy factor enables increasing one of the magnitudes ... 

---