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Charectization carbon nanotubes based on spectroscopic and optical properties

Nanotube Charectization carbon based on spectroscopic and optical properties.

The optical properties of carbon nanotubes refers to absorption, photoluminescence, and Raman spectroscopy of carbon nanotubes. Because spectroscopic techniques quickly and reliably the quality of the characterization of nanotubes "" In terms of carbon content of tubular structure (Chirality) of the nanotubes produced, and structural defects. These characteristics determine almost any other properties such as optical, mechanical and electrical properties.

Carbon nanotubes are unique, "a three-dimensional system," can be achieved by rolling graphene sheet.This can be done at different angles and curves resulting from the properties of different nanotubes. The diameter canvaries the range of 0.4-40 nm, but the nanotube length is about 10,000 times to achieve ~ 4 cm. Thus, the nanotubes have aspect ratio (ie the relationship between length and diameter) of up 28,000,000:1, which is unmatched by any other material.As result, all properties of carbon nanotubes with respect to the semiconductor are highly anisotropic conventional and adjustable.

The possibility of setting properties is very useful in optics and photonics.

Nanotubes carbon are of three types

1.zig-zag

2.armchair

3.chiral

Next are the optical methods of CNTs OGF charecterization:

1. Optical absorption

optical absorption in carbon nanotubes differs from conventional 3D materials absorption in the presence sharp peak (1D nanotubes) instead of an absorption threshold followed by an increase in absorption (most of the solids in 3D). Absorption origin nanotubes electronic transitions in the v2 c2 (E22 energy) or v1 in c1 (E11) levels, etc. The transitions are relatively strong and can be used to identify the types of nanotubes.

Interactions between the nanotubes, as a group, extend sightlines. While strongly affects photoluminescence group, which has a much weaker effect on optical absorption and Raman scattering.

Optical absorption is commonly used to justify the quality of carbon nanotube powders. The spectrum is analyzed in terms of intensity of the peaks related to nanotubes, training and pi-carbon peak of the latter two in their Most come from the lack of carbon nanotubes.
2.Carbon nanotubes as a black body

An ideal black body must have emissivity or absorbance of 1.0, which is difficult to achieve in practice, especially in a wide spectral range. Vertically aligned "forests" of carbon nanotubes can be single wall absorbances of 0.98-0.99 in the far ultraviolet (200 nm) to far infrared (200 micron) wavelengths. By coating Super black (a nickel-phosphorus chemically etched) absorption of 1.0 is achievable.

These SWNT forests (buckypaper) were grown by the CVD method of super-growth to about 10 microns in height. Two factors could contribute to the strong light absorption by these structures: (i) a distribution of CNT chiralities bandgaps led to various individual CNTs. Thus, a composite material formed with the absorption of broadband. (Ii) light could be trapped in the forests due to multiple reflections.

3.Luminescence

The map of the photoluminescence of carbon nanotubes single wall. It may be useful in helping identify the semiconductor nanotubes nanotubes with indices (n, m). PL measurements do not detect other nanotubes with indices m = nm and photoluminescence excitation mechanism.Hence (PL) is a powerful tool for the characterization of nanotubes.

The PL excitation mechnism

The excitation of mechnism PL occurs as follows: an electron in a nanotube absorbs excitation light through S 22 transition, the creation of a pair electron-hole (exciton). Both electron and hole relaxation quickly (through phonon-assisted processes) from C 2 to C 1 and v 2 v 1 states, respectively. Then recombine through a c 1 - v 1 resulting transition light emission.

No excitonic luminescence can be produced in the metal - electrons can be excited, resulting in optical absorption, but the hole is immediately filled by another electron from many available in metal. Consequently, there is no exciton.

properties

1.Photoluminescence, optical absorption and Raman scattering SWCNT is linearly polarized along the axis of the tube ..

2.PL is fast: relaxation typically occurs within 100 ps.

3.PL efficiency is generally low (~ 0.01%).

4. The PL spectral range is quite wide. emission wavelength varies between 0.8and 2.1 micrometers depending on the structure of nanotubes.

5. The interaction between the nanotubes or between nanotubes and other materials (eg substrate) off PL.Hence, PL is not observed in carbon nanotube multi-wall.

6. PL double wall carbon nanotubes preparation method greatly dependsthe. For example, cardiovascular diseases are grown DWCNTs emissions of both inner and outer shells. Position of (S 22, S 11) PL peaks depend slightly (2%) in the nanotube environment (air, dispersing, etc.) However, the change depends the (n, m) index, and therefore the entire map PL not only shifts, but also deforms by changing the middle of the CNT.

Applications of photoluminecense

PL is widely used to derive (n, m) indices: first, the nanotubes are isolated (dispersed) using an agent suitable chemical ("dispersant") to reduce the extinction intertube. PL is then measured, scanning both the excitation and emission energies and producing and a PL map. The ovals on the map define (S 22, S 11) pairs, which identify unique (n, m) index of a tube. Weisman data and Bachelor conventionally used for identification.

Sensitization

Optical properties, including the PL efficiency, can be modified by encapsulating organic dyes (carotene, lycopene, etc.) inside the tubes. efficient energy transfer occurs between the dye encapsulated and nanotubes - light is efficiently absorbed by the dye and without significant loss is transferred to the SWCNT. So potentially, optical properties of a carbon nanotube can be controlled by certain molecule encapsulated within it.

Cathodoluminescence

Cathodoluminescence (CL) - The light emission excited by electron beam - is a process commonly seen in television screens. A beam of electrons can be well designed and scanning through the material studied. This technique is widely used to study defects in semiconductors and nanostructures with nanometer-scale spatial resolution. It would be beneficial to apply this technique to carbon nanotubes. However, CL unreliable, ie sharp peaks assigned to certain (n, m) indices, have been detected from carbon nanotubes yet.

Electroluminescence

Where the electrical contacts are attached to a nanotube, electron-hole pairs (excitons) can be generated by injection of electrons and holes of contacts. Following the results of the exciton recombination electroluminescence (EL). electroluminescent devices have been produced from nanotubes.

Raman spectra of nanotubes of single-walled carbon

Raman spectroscopy has good spatial resolution (~ 0.5 micrometers) and sensitivity to individual nanotubes, but requires a minimum sample preparation is rather informative. Raman spectroscopy is the most popular technique for characterization of carbon nanotubes. Raman scattering in SWCNTs is resonant, ie the tubes are tested only one of the bandgaps equal to the exciting laser energy. As photoluminescence mapping, the energy of the excitation light can be scanned in Raman measurements, which Raman maps produced. The maps also contain oval-shaped unique identifying characteristics (n, m) indices. In contrast to PL, the Raman mapping detects not only semiconductor, but also the metal, and is less sensitive to sales packages nanotube PL.

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Anti-Stokes scattering

All this Raman modes can be observed both in Stokes and anti-Stokes scattering. As mentioned above, CNT Raman scattering is resonant in nature, ie only tubes whose band gap energy is similar to laser energy are excited. The difference between these two energies, and thus the band gap of individual tubes can be estimated from the intensity ratio of the Stokes / anti-Stokes line. But This estimate is based on the temperature factor (Boltzmann factor), which are often miscalculated - focused laser beam is used in measurement, which can locally heat the nanotubes without changing the overall temperature of the sample.

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G as follows:

G mode (graphite gG) corresponds a flat vibration of carbon atoms and is present in most materials such as graphite. SWCNT G-band shifts to lower frequencies on graphite (1580 cm-1) and is divided into several peaks. The pattern of division and intensity depend on the structure of the tube and the excitation energy and that can be used, albeit with much lower accuracy compared to the RBM mode, to estimate the diameter of the tube and if the tube is metallic or semiconducting

Rayleigh Scattering

Carbon nanotubes are very largeaspect relationship, ie, its length is much greater than its diameter. Consequently, as expected classical electromagnetic theory, the elastic scattering of light (or Rayleigh scattering) by a straight CNT is anisotropic angular dependence, and its spectrum, differences in individual nanotubes band can be deduced.

References

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12. ^ * Openov, Leonid A.; Elesin, Vladimir F. (1998). "Prismane C8: A new form of carbon?". JETP Letters 68: 726. doi: 10.1134/1.567936. http://www.jetpletters.ac.ru/ps/969/article_14784.pdf.
13. External Links
14. http://www.dendritics.com/scales/c-allotropes.asp

http://cst-www.nrl.navy.mil/lattice/struk/carbon.html

Diamond 3D animation.

Tanveer Rabiya.

LECTURER IN PHYSICS

Chaitanya and PG COLLEGE DEGREE

HNK, Warangal, INDIA.

AFFILIATION:

1.NANO Science and Technology Consortium,

Noida, UP.INDIA.

2.PHOTONICS 21 technology platform Europe. EMAIL: munaizag@gmail.com

About the Author

lecturer in physics & electronics dept. of physics & electronics, chaitanya degree & p.g college, kishan pura ,hanamkonda, warangal.A.P.

Lec 31 | MIT 8.02 Electricity and Magnetism, Spring 2002

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