Characterization Techniques<br /><ul><li> Characterization and manipulation of individual nanostructures require not only extreme sensitivity and accuracy, but also atomic-level resolution. It therefore leads to various microscopy that will play a central role in characterization and measurements of nanostructured materials and nanostructures.
The various structural characterization methods that are most widely used in characterizing nanomaterials and nanostructures</li></li></ul><li>Structural Characterization<br /><ul><li>Characterization of nanomaterials and nanostructures has been largely based on the surface analysis techniques and conventional characterization methods developed for bulk materials.</li></ul>The structural characterization techniques include:<br /><ul><li>X-ray diffraction (XRD)
Gas adsorption</li></li></ul><li>Chemical Characterization<br /><ul><li>Chemical characterization is to determine the surface and interior atoms and compounds as well as their spatial distributions.
Mass Spectrometry</li></li></ul><li>X-ray diffraction (XRD)<br /><ul><li>XRD is a very important experimental technique that has long been used to address all issues related to the crystal structure of solids, including lattice constants and geometry, identification of unknown materials, orientation of single crystals, preferred orientation of polycrystals, defects, stresses, etc.
In XRD, a collimated beam of X-rays, with a wavelength typically ranging from 0.7 to 2 A, is incident on a specimen and is diffracted by the crystalline phases in the specimen according to Bragg's law:</li></ul>A = 2d sin θ<br />where d is the spacing between atomic planes in the crystalline phase and A is the X-ray wavelength. The intensity of the diffracted X-rays is measured as a function of the diffraction angle8 and the specimen's orientation.<br />
Small angle X-ray scattering (SAXS)<br /><ul><li>SAXS is another powerful tool in characterizing nanostructured materials. Strong diffraction peaks result from constructive interference of X-rays scattered from ordered arrays of atoms and molecules.
A lot of information can be obtained from the angular distribution of scattered intensity at low angles. Fluctuations in electron density over lengths on the order of l0 nm or larger can be sufficient to produce an appreciable scattered X-ray intensities at angles 28 < 5".</li></li></ul><li>Scanning electron microscopy (SEM) <br /><ul><li> SEMis one of the most widely used techniques used in characterizationof nanomaterials and nanostructures.
Resolution of the SEMapproaches a few nanometers, and the instruments can operate at magnificationsthat are easily adjusted from - 10 to over 300,000.
Not only doesthe SEM produce topographical information as optical microscopes do, italso provides the chemical composition information near the surface.
In a typical SEM,a source of electrons is focused into a beam, with avery fine spot size of 5 nm and having energy ranging from a few hundredeV to 50 Key that is rastered over the surface of the specimen bydeflection coils.
As the electrons strike and penetrate the surface, a numberof interactions occur that result in the emission of electrons and photonsfrom the sample, and SEMimages are produced by collecting theemitted electrons on a cathode ray tube.</li></li></ul><li>Transmission electron microscopy (TEM)<br /><ul><li>In TEM, electrons are accelerated to 100 KeV or higher (up to 1 MeV), projected onto a thin specimen (less than 200 nm) by means of the condenser lens system, and penetrate the sample thickness either undeflected or deflected.
The greatest advantages that TEM offers are the high magnification ranging from 50 to l06 and its ability to provide both image and diffraction information from a single sample.</li></li></ul><li>Optical spectroscopy<br /><ul><li>Optical spectroscopy has been widely used for the characterization of nanomaterials
Optical techniques can be generally categorized into two groups:
The absorption and emission spectroscopy determines the electronic structures of atoms, ions, molecules or crystals through exciting electrons from the ground to excited states(absorption) and relaxing from the excited to ground states (emission).
The vibrational techniques involves the interactions of photons with species in a sample that results in energy transfer to or from the sample via vibrational excitation or de excitation. The vibrational frequencies provide the information of chemical bonds in the detecting samples. </li></li></ul><li>Absorption and transmission spectroscopy<br /><ul><li> The characteristic lines observed in the absorption and emission spectra of nearly isolated atoms and ions due to transitions between quantum levels are extremely sharp.
As a result, their wavelengths or photon energies can be determined with great accuracy.
The lines are characteristic of a particular atom or ion and can be used for identification purposes.</li></li></ul><li>Electron spectroscopy<br /><ul><li>The electron spectroscopy relies on the unique energy levels of the emission of photons (X-ray) or electrons ejected from the atoms
When an incident electron or photon, such as X-ray or y-ray, strikes an unexcited atom, an electron from an inner shell is ejected and leaves a hole or electron vacancy in the inner shell</li></li></ul><li>Mass spectroscopy<br /><ul><li>NPs have become interesting materials for mass spectrometry because they can act as probe to recognize targeted molecules and as matrices like the organic molecules used in matrix assisted laser desorption mass spectrometry (MALDI-MS) to assist desorption/ionization of the analytes.
Most common NPs used in mass spectrometry are Au NPs, TiO2 NPs, and Fe3O4 NPs.</li>