02-10-2012, 03:19 PM
Notes on Nanoscience and Nanotechnology
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Nature has provided us the matter, considered as bulk matter, with its diversifying properties like; different colors, light, heavy, brittle, ductile, hard and soft etc. Every material has its own unique property, which compels the human being to understand the nature of that particular material. Depending on their physical and chemical properties, all the “solid-state” materials have been classified in three basic categories; (i) insulators, (ii) semiconductors and (iii) metals in accordance with their electron densities. Further studies revealed that all materials are made of tiny particles, called atoms, which consist of nucleus at the center surrounded by moving electrons in certain selected circular orbits. Therefore, the number of electrons and their configurations are mainly responsible for different properties of atoms and so of the materials. Bulk materials have certain optical, electrical, magnetic, thermal and catalytic properties, which may be tuned by (i) engineering their size/shape, (ii) adding foreign atoms in the host and (iii) creating controlled defects in the material. It has been observed that in certain size regime, so called nanoscale regime, materials possess extra-ordinary physical and chemical properties, which are entirely different from those they have in atomic scale or bulk state [1-5].
Physical Significance of Nanostructures
The nanotechnology covers the design, construction and utilization of functional structures with at least one characteristic dimension in nanometric range. Such materials and systems can be synthesized to exhibit novel and significantly improved physical, chemical properties, and phenomenon as a result of the limited size of their constituent particles or molecules. The main reason for the interesting and useful behavior is due to their characteristic structural features, which are intermediate in extent between isolated atoms and bulk macroscopic materials. Thus the nanostructured materials display physical attributes substantially different from those displayed by either atoms or bulk and hence leading to new technological opportunities as well as challenges [3-5].
Classification of Nanostructures
Since, the reduction in spatial dimensions or confinement of particles leads to changes in different physical properties of the nanostructured systems [2-3]. The nanostructured materials have been classified into three different categories depending on their number of dimensions confined within nanometric range like; (a) systems confined in three dimensions (b) systems confined in two dimensions and © systems confined in one dimensions. Systems confined in three dimensions are called quantum dots or nanoparticles. Those confined in two dimensions are called nanorods or nanowires, however, those confined in one dimension are called as nanoplates or thin films. Fig. 1.2 illustrates the process of diminishing the size/shape for the rectilinear geometry.
Change in Mechanical Properties It is expected that atomic vacancies reduce the number of chemical bonds and hence, the strength of a porous material. However, the hardness of a specimen does not follow this simple picture of coordination counting. Vacancies not only acts as pinning centers inhibiting dislocation motion and thus enhancing the mechanical strength within a certain concentration but also provide sites initiating structure failure. An introduction of limited amount of atomic vacancies could indeed enhance the mechanical strength of the pours specimen. Atomic vacancies could not only enhance the mechanical strength of the specimen, but also cause a substantial depression of the temperature of melting.
[attachment=35036]
Nature has provided us the matter, considered as bulk matter, with its diversifying properties like; different colors, light, heavy, brittle, ductile, hard and soft etc. Every material has its own unique property, which compels the human being to understand the nature of that particular material. Depending on their physical and chemical properties, all the “solid-state” materials have been classified in three basic categories; (i) insulators, (ii) semiconductors and (iii) metals in accordance with their electron densities. Further studies revealed that all materials are made of tiny particles, called atoms, which consist of nucleus at the center surrounded by moving electrons in certain selected circular orbits. Therefore, the number of electrons and their configurations are mainly responsible for different properties of atoms and so of the materials. Bulk materials have certain optical, electrical, magnetic, thermal and catalytic properties, which may be tuned by (i) engineering their size/shape, (ii) adding foreign atoms in the host and (iii) creating controlled defects in the material. It has been observed that in certain size regime, so called nanoscale regime, materials possess extra-ordinary physical and chemical properties, which are entirely different from those they have in atomic scale or bulk state [1-5].
Physical Significance of Nanostructures
The nanotechnology covers the design, construction and utilization of functional structures with at least one characteristic dimension in nanometric range. Such materials and systems can be synthesized to exhibit novel and significantly improved physical, chemical properties, and phenomenon as a result of the limited size of their constituent particles or molecules. The main reason for the interesting and useful behavior is due to their characteristic structural features, which are intermediate in extent between isolated atoms and bulk macroscopic materials. Thus the nanostructured materials display physical attributes substantially different from those displayed by either atoms or bulk and hence leading to new technological opportunities as well as challenges [3-5].
Classification of Nanostructures
Since, the reduction in spatial dimensions or confinement of particles leads to changes in different physical properties of the nanostructured systems [2-3]. The nanostructured materials have been classified into three different categories depending on their number of dimensions confined within nanometric range like; (a) systems confined in three dimensions (b) systems confined in two dimensions and © systems confined in one dimensions. Systems confined in three dimensions are called quantum dots or nanoparticles. Those confined in two dimensions are called nanorods or nanowires, however, those confined in one dimension are called as nanoplates or thin films. Fig. 1.2 illustrates the process of diminishing the size/shape for the rectilinear geometry.
Change in Mechanical Properties It is expected that atomic vacancies reduce the number of chemical bonds and hence, the strength of a porous material. However, the hardness of a specimen does not follow this simple picture of coordination counting. Vacancies not only acts as pinning centers inhibiting dislocation motion and thus enhancing the mechanical strength within a certain concentration but also provide sites initiating structure failure. An introduction of limited amount of atomic vacancies could indeed enhance the mechanical strength of the pours specimen. Atomic vacancies could not only enhance the mechanical strength of the specimen, but also cause a substantial depression of the temperature of melting.