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Register a new userOptoelectronic Sensitization of Carbon Nanotubes by CdTe Nanocrystals
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Added by
Alexander W. Holleitner
Publication date
2009
fields
Physics
and research's language is
English
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We investigate the photoconductance of single-walled carbon nanotube-nanocrystalhybrids. The nanocrystals are bound to the nanotubes via molecular recognition. We find that the photoconductance of the hybrids can be adjusted by the absorption characteristics of the nanocrystals. In addition, the photoconductance of the hybrids surprisingly exhibits a slow time constant of about 1 ms after excitation of the nanocrystals. The data are consistent with a bolometrically induced current increase in the nanotubes caused by photon absorption in the nanocrystals.
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We have calculated the effects of structural distortions of armchair carbon nanotubes on their electrical transport properties. We found that the bending of the nanotubes decreases their transmission function in certain energy ranges and leads to an increased electrical resistance. Electronic structure calculations show that these energy ranges contain localized states with significant $sigma$-$pi$ hybridization resulting from the increased curvature produced by bending. Our calculations of the contact resistance show that the large contact resistances observed for SWNTs are likely due to the weak coupling of the NT to the metal in side bonded NT-metal configurations.
Carbon nanotubes (CNT) belong to the most promising new materials which can in the near future revolutionize the conventional electronics. When sandwiched between ferromagnetic electrodes, the CNT behaves like a spacer in conventional spin-valves, leading quite often to a considerable giant magneto-resistance effect (GMR). This paper is devoted to reviewing some topics related to electron correlations in CNT. The main attention however is directed to the following effects essential for electron transport through nanotubes: (i) nanotube/electrode coupling and (ii) inter-tube interactions.It is shown that these effects may account for some recent experimental reports on GMR, including those on negative (inverse) GMR.
We have generated and detected the radial-breathing mode of coherent lattice vibrations in single-walled carbon nanotubes using ultrashort laser pulses. Because the band gap is a function of diameter, these diameter oscillations cause ultrafast band gap oscillations, modulating interband excitonic resonances at the phonon frequencies (3-9 THz). Excitation spectra show a large number of pronounced peaks, mapping out chirality distributions in great detail.
Through magnetic linear dichroism spectroscopy, the magnetic susceptibility anisotropy of metallic single-walled carbon nanotubes has been extracted and found to be 2-4 times greater than values for semiconducting single-walled carbon nanotubes. This large anisotropy is consistent with our calculations and can be understood in terms of large orbital paramagnetism of electrons in metallic nanotubes arising from the Aharonov-Bohm-phase-induced gap opening in a parallel field. We also compare our values with previous work for semiconducting nanotubes, which confirm a break from the prediction that the magnetic susceptibility anisotropy increases linearly with the diameter.
We use DFT to study the effect of molecular adsorbates on the conductance of metallic carbon nanotubes. The five molecules considered (NO2, NH2, H, COOH, OH) lead to similar scattering of the electrons. The adsorption of a single molecule suppresses one of the two available channels of the CNT at low bias conductance. If more molecules are adsorbed on the same sublattice, the remaining open channel can be blocked or not, depending on the relative position of the adsorbates. If a simple geometric condition is fulfilled this channel is still open, even after adsorbing an arbitrary number of molecules.
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