Nanocrystals three-dimensional superlattice

The way in which the nanocrystals organize themselves depends critically on the core diameter, the nature of the ligand, substrate and even the dispersive medium used [101]. Thiolized metal nanocrystals readily arrange into two-dimensional arrays on removal of the solvent [29]. Using suitable methods, they can also be put into one-dimensional organization in the form of strings or assembled in a stepwise fashion in a three-dimensional superlattice (see Figure 4.8). 

Fig. 4.15. Three-dimensional superlattices of 4.8 nm CdSe nanocrystals (a) along orientation (b) along <101) orientation (c) along orientation. High resolution...

Fig. 3.11. TEM images of three-dimensional superlattices of 4.8 nm CdSe nanocrystals along (a) (100), (b) (101), and (c) (111) orientation. High-resolution images as weU as selected area electron diffraction patterns are shown alongside in each case (reproduced with permission from [602])...

Redl, F. X., Cho, K. S., Murray, C. B. O Brien, S. Three-dimensional binary superlattices of magnetic nanocrystals and semiconductor quantum dots. Nature (London) 423, 968—971 (2003). 

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. 

Harfenist SA, Wang ZL, Whetten RL, Vezmar 1, Alvarez MM (1997) Three-dimensional hexagonal close-packed superlattice of passivated Ag nanocrystals. Adv Mater 9 817-822 Haruta M (1997) Size- and support-dependency in the catalysis of gold. Catal Today 36 153-166 He ST, Xie SS, Yao IN, Gao HI, Pang SJ (2002) Self-assembled two-dimensional superlattice of Au-Ag alloy nanocrystals. Appl Phys Lett 81 150-152... 

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