# Nanostructure in One, Two and Three Dimension and Application

The properties of nanostructures are not only dependent upon dimensionality but also determined by their physical size. When the size of a structure larger than a certain characteristic length scale, the properties approach the corresponding bulk values; on the other hand, when the size of the structure is smaller or comparable to the characteristic length scale of some property, then that property is confined and size dependent. The characteristic length scales depend on materials and specific properties.

Nanotechnology has been an exciting and rapidly expanding area of research for more than a decade . The fundamental interests come from the fact that nanometer is the length scale that bridges the microscopic world where the behavior of matter needs to be treated in quantum mechanics and the macroscopic world where quantum mechanics reduces to classical physics. Studies on the preparation, structure, and properties of nanostructures have been carried out with collective efforts that cross borders between many areas of physical sciences, engineering and biological sciences [1].

Nanostructures can be defined as systems in which the physical size in at least one- dimension (1D) is less than 100nm. As shown in Fig. 1, reducing 1, 2 and 3 dimensions of bulk materials to the nanometer scale produce nanometer thick two-dimensional (2D) structures such as graphene and quantum wells (QWs) , one-dimensional (1D) carbon nanotubes (CNTs) , nanowires , zero-dimensional (0D) Fullerenes and Quantum Dots (QDs) [2], respectively. Dimensionality plays a critical role in determining the properties of nanostructures. True low-dimensional materials should have infinitesimal sizes in one or more dimensions as suggested by their ideal geometry. In reality, nanostructures always have finite size and it is impossible to completely insolate a system from interaction with environment, therefore, the prefix

“quasi” is often added to describe the low-dimensional structures prepared in the real world. Studies on low-dimensional nanostructures have revealed fascinating properties.

For examples, studies of 2D electron gas in semiconductor hetero-structures have led to remarkably rich and often unexpected results such as the quantum-Hall effect [3].

Fig. 1 Nanostructures (a) 2-D graphene and quantum wells; (b) 1-D carbon nanotubes and nanowires; (c) fullerene and 0-D quantum dots

The properties of nanostructures are not only dependent upon dimensionality but also determined by their physical size. When the size of a structure larger than a certain characteristic length scale, the properties approach the corresponding bulk values; on the other hand, when the size of the structure is smaller or comparable to the characteristic length scale of some property, then that property is confined and size dependent. The characteristic length scales depend on materials and specific properties. Many fundamental properties of bulk materials are characterized by length scales on the order of 1 to 100 nm. As an example of size-dependent properties of nanostructures, the photoluminescence emission of semiconductor 2D quantum wells [4], nanowires , and 0D nanocrystals exhibit systematic blue-shift when their physical sizes are smaller than 5-20 nm, the exciton diameters of corresponding bulk semiconductor materials.

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On April 3, 2012 at 4:46 am

thanks lot