Nanostructured inorganic semiconductors

Unfortunately, the author has not come so far across any publication on concerning inorganic semiconductor surfaces (2D) or linear ID systems. The problem of correct measurement of local densities or distances between PCs in nanostructured low-dimensional systems is even more complicated. Indeed, using modem EPR technique, one can measure 1/T2 values up to 5-6 nm [124]. But it is the very size of colloidal and aggregated nanoparticles Is it possible to use the pure 2D model in this case, or is it necessary to take into consideration an input of 3D interaction Our group is working on this problem now, trying to understand where is a border between 3D and 2D cases in terms of quantitative analysis of dipole-dipole interaction. 

So far, the enormous potential of the diblock copolymer approach has been demonstrated which is based on three particular contributions (i) self-organization of block copolymers with periodicities down to a few ten nanometers, (ii) easy application of structurally well controlled thin films over large areas of various substrates, and (iii) the highly selective etching contrast which can be achieved by the incorporation of suitable inorganic components. Most importantly, the latter will allow to prepare nanostructures in semiconductors with an aspect ratio not yet conceivable by other parallel processing methods. 

Recently, many scientists and engineers have looked for methods to control the sizes of QDs and make possible the formation of ordered lateral two-dimensional superlattices or vertical superlattices for heterojunction thin films. One approach is the top-down method, molecular beam epitaxy nanolithographic technology, which has been developed with the development of microelectronics and processing techniques for traditional inorganic semiconductors. This technique of nanoscale manipulation can reach only the upper limits of sizes defined by nanostructure physics, and has successfully manipulated artificial atoms and molecules [10-12). Bottom-up method is based on molecular and supramolecular assembly techniques that have been proposed by chemists in recent years. With this method, it is possible to prepare monodispersed defect-free nanocrystal QDs 1-10 nm in size and to control easily QDs coupling to form nanocrystal molecules, even quantum dot superlattices in two or three dimensions. 

Another growing interest research field is that of ordered nanostructured materials, called photonic crystals [234]. Photonic crystals are ordered nanostructured materials with periodic variations of the dielectric constant in one, two, or three dimensions (Figure 22). This research field is very broad and complex. Here, we provide only a brief description and few examples of supramolecular architectures that may be competitive with inorganic semiconductors patterned with top-down methods. 

Hybrid organic polymer-inorganic structures can be prepared in four different ways as shown in Fig. 6.5. The first structure is a planar bilayer structure where an organic layer is deposited on top of an inorganic semiconductor layer. The next structure is a blend of nanocrystals with a polymer where semiconductor nanoparticles and a polymer are deposited from the same solution. The third one is a nanostructured porously inorganic structure where a connected semiconductor... 

This is a powerful and controllable method to synthesize the nanostructure materials of inorganic semiconductors, metals, and polymers. In the hard template method, the growth of the nanostructures takes place within the pores or channel of template membrane by polymerization and then the template is removed after the polymerization. The porous membrane is the basic and most important part of the hard template method. Porous membrane such as polycarbonate and alumina can be used as the hard template to produce conducting polymer nanotubes and nanowires as shown in Fig. 9. 

Carrasco-Orozco, M.A., et al. Superlattices of oiganic/inorganic semiconductor nanostructures from liquid-crystal templates. Phys. Rev. B 75(3), 5 (2007)... 

Figure 14.4. Semiconductor quantum dot nanocrystal synthesized by condensation of cadmium and selenium ions. This is an example of a bottom-up synthetic approach to construct nanostructures. In a bottom-up approach, the precursor atoms or molecules are combined to create a larger, hierarchical structure. In this case, cadmium ions react with selenium ions to form a cluster of the inorganic semiconductor cadmium selenide. Containing just a few hundred atoms, quantum dots are typically less than 7nm In diameter.

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