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CHAPTER-4

SPECIAL NANO MATERIALS, CHARACTERIZATION AND TOOLS

 

Characterization and tools:

Introduction:

Materials in the nanometer scale, such as colloidal dispersions and thin films, have been studied over many years and many physical properties related to the nanometer size, such as coloration of gold nanoparticles, have been known for centuries. One of the critical challenges faced currently by researchers in the nanotechnology and nanoscience fields is the inability and the lack of instruments to observe measure and manipulate the materials at the nanometer level by manifesting at the macroscopic level. In the past, the studies have been focused mainly on the collective behaviors and properties of a large number of nanostructured materials. The properties and behaviors observed and measured are typically group characteristics. A better fundamental understanding and various potential applications increasingly demand the ability and instrumentation to observe measure and manipulate the individual nanomaterials and nanostructures. Characterization and manipulation of individual nanostructures require not only extreme sensitivity and accuracy, but also atomic level resolution. It therefore leads to various microscopies that will play a central role in characterization and measurements of nanostructured materials and nanostructures. Miniaturization of instruments is obviously not the only challenge; the new phenomena, physical properties and short-range forces, which do not play a noticeable role in macroscopic level characterization, may have significant impacts in the nanometer scale. The development of novel tools and instruments is one of the greatest challenges in nanotechnology.

Characterization, when used in materials science, refers to the use of external techniques to probe into the internal structure and properties of a material. Characterization can take the form of actual materials testing, or analysis, for example in some form of microscope.

Analysis techniques are used simply to magnify the specimen, to visualize its internal structure, and to gain knowledge as to the distribution of elements within the specimen and their interactions.

Magnification and internal visualization are normally done in a type of microscope, such as:

In this chapter, various structural characterization methods those are most widely used in characterizing nanomaterials and nanostructures are discussed. These include X-ray diffraction, various electron microscopy (EM) including scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and scanning probe microscopy(SPM). Scanning tunneling microscopy and atomic force microscopy comes under the family of scanning probe microscopy.

Electron Microscopy:

With the new found knowledge the metallurgist obtained about phases of the materials through the optical microscope, the desire came for more knowledge. The optical microscope was only able to resolve up to 1/125,000 of an inch, and scientists wanted to do better than that. This desire was satisfied with the invention of the electron microscope. Instead of using a light beam, the electron microscope focuses a beam of electrons which were accelerated from a thermionic triode electron gun. The electron beam travels directly down the microscope column and collides with the surface of the specimen. The best optical microscopes can resolve image up to 2000 angstroms while the electron microscope can resolve an image to 2 angstroms.