Absorption nanotubes

A brief review is given on electronic properties of carbon nanotubes, in particular those in magnetic fields, mainly from a theoretical point of view. The topics include a giant Aharonov-Bohm effect on the band gap and optical absorption spectra, a magnetic-field induced lattice distortion and a magnetisation and susceptibility of ensembles, calculated based on a k p scheme. 

Amide bond is an effective anchor to connect CNTs to substrate surfaces. Lan et al. [52] covalently assembled shortened multi-walled carbon nanotubes (s-MWNT) on polyelectrolyte films. The shortened MWNT is functionalized with acyl chloride in thionyl chloride (SOCl2) before self-assembling. The FTIR spectrum of self-assem-bled MWNT (SA-MWNT) adsorbed on a CaF2 plate modified with PEI/(PSS/PEI)2 shows two characteristic absorption peaks at 1646cm-1 (amide I bond) and 1524cm-1 (amide II bond) resulting from the amide bond formed between the polyelectrolyte films and s-MWNTs. 

Measurements of the optical properties in this range of wavelengths can probe the fundamental electronic transitions in these nanostructures. Some of the aforementioned effects have in fact been experimentally revealed in this series of experiments (90). As mentioned above, the IF nanoparticles in this study were prepared by a careful sulfidization of oxide nanoparticles. Briefly, the reaction starts on the surface of the oxide nanoparticle and proceeds inward, and hence the number of closed (fullerene-like) sulfide layers can be controlled quite accurately during the reaction. Also, the deeper the sulfide layer in the nanoparticle, the smaller is its radius and the larger is the strain in the nanostructure. Once available in sufficient quantities, the absorption spectra of thin films of the fullerene-like particles and nanotubes were measured at various temperatures (4-300 K). The excitonic nature of the absorption of the nanoparticles was established, which is a manifestation of the semiconducting nature of the material. Furthermore, a clear red shift in the ex-citon energy, which increased with the number of sulfide layers of the nanoparticles, was also observed (see Fig. 21). The temperature dependence of the exciton... 

Fig. 10.11 Carbon nanotubes have an absorption peak between 1,000 and 1,500 nm as defined by line (a) in this figure. A decrease in absorption is seen in lines (b) and (c) due to wrapping of polysaccharides around the tubes for water solubilization (Reprinted from Casey et al., 2005. With permission from Elsevier)...

Fig. 10.12 The most efficient regions for nanotube absorption lie where water and hemoglobin have absorption minima between 700 and 900nm and around 1,100nm (Braun and Smirnov 1993 Reprinted from Weissleder, 2001. With permission from Elsevier) (See Color Plates)... 

Kouklin N, Tzolov M, Straus D, Yin A, Xu JM (2004) Infrared absorption properties of carbon nanotubes synthesized by chemical vapor deposition. Applied Physics Letters 85 4463 1465. 

Saito R, Gruneis A, Samsonidze GG, Dresselhaus G, Dresselhaus MS, Jorio A, Cancado LG, Pimenta MA, Souza AG (2004) Optical absorption of graphite and single-wall carbon nanotubes. Applied Physics A-Materials Science and Processing 78 1099-1105. 

Anand A et al. (2005) Select gas absorption in carbon nanotubes, loading a resonant cavity to sense airborne toxin gases. Nucl. Instrum. Meth. Phys. Res. B 241 511-516. 

V. Skakalova, A. B. Kaiser, U. Dettlaff-Weglikowska, K. Hrncarikova, S. Roth, Effect of chemical treatment on electrical conductivity, infrared absorption, and Raman spectra of single-walled carbon nanotubes, J. Phys. Chem. B, vol. 109, pp. 7174-7181, 2005. 

From this, the velocities of particles flowing near the wall can be characterized. However, the absorption parameter a must be determined empirically. Sokhan et al. [48, 63] used this model in nonequilibrium molecular dynamics simulations to describe boundary conditions for fluid flow in carbon nanopores and nanotubes under Poiseuille flow. The authors found slip length of 3nm for the nanopores [48] and 4-8 nm for the nanotubes [63]. However, in the first case, a single factor [4] was used to model fluid-solid interactions, whereas in the second, a many-body potential was used, which, while it may be more accurate, is significantly more computationally intensive. 

The differently produced conductive polymer structures described above all have enhanced conductivity, which can be employed in microelectronics [44] and as sensors using immobilized enzymes [46, 47[. Martin and coworkers used polarized infrared absorption spectroscopy to access the alignment of the polymer fibers on the outer surface of the nanotubes [48[. The study showed that the enhancement of the conductivity is due to the alignment of the polymer fibers on the outer surface of the tubes. 

Storing hydrogen in a carbon structure is another form of chemical bonding. New forms of carbon structures are currently being researched and promise the best and safest approach as a reversible gas absorption technology. This research is the design and use of carbon nanostractures, either nanotubes or nanofibers. 

Methods of electron spectroscopy are widely used to follow the electron-transfer process. Thus, the progress of electron transfer from naphthalene anion-radical to cup-stacked carbon nanotubes is easily detected by monitoring the UV absorption spectrum. Namely, the absorption band around 500-900 nm due to naphthalene anion-radical completely disappears after reduction of the nanotubes. At the same time, the reduced nanotubes exhibit ESR spectrum characterized with g-factor of 2.0025 (Saito et al. 2006). This g-value is close to the free spin g-factor of 2.0023 that is diagnostic of the delocalized electron on carbon nanomaterials (Stinchcombe et al. 1993). It should be parallelly... 

Ong KG, Varghese OK, Mor GK, Grimes CA (2007) Application of finite-difference time domain to dye-sensitized solar cells The effect of nanotube-array negative electrode dimensions on light absorption. Solar Energy Materials Solar Cells 91 250-257... 

A. F. Barbosa, M. G. Segatelli, A. C. Pereira, A. De Santana Santos, L. T. Kubota, P. O. Luccas and C. R. T. Tarley, Solid-phase extraction system for Pb(n) ions enrichment based on multiwall carbon nanotubes coupled on-line to flame atomic absorption spectrometry, Talanta, 71(4), 2007, 1512-1519. 

Interaction-induced absorption by the vibrational or rotational motion of an atom, ion, or molecule trapped within a Ceo cage, so-called endohedral buckmin-sterfullerene, has excited considerable interest, especially in astrophysics. The induced bands of such species are unusual in the sense that they are discrete, not continuous they may also be quite intense [127]. Other carbon structures, such as endohedral carbon nanotubes, giant fullerenes, etc., should have similar induced band spectra [128], but current theoretical and computational research is very much in flux while little seems to be presently known from actual spectroscopic measurements of such induced bands. 

Photochromism has also been observed when two porphyrinic groups are linked to a dithienylethene scaffold. The closed form showed an absorption band at 560 nm (01JA1784). The same behavior was observed in the system 318-319 (02AM918). Dithienylethene photochromic systems have also been described to be linked to single-walled nanotubes (07JA12590). 

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