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Register a new userInfrared spectroscopic studies on unoriented single-walled carbon nanotube films under hydrostatic pressure
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Added by
Christine Kuntscher
Publication date
2009
fields
Physics
and research's language is
English
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The electronic properties of as-prepared and purified unoriented single-walled carbon nanotube films were studied by transmission measurements over a broad frequency range (far-infrared up to visible) as a function of temperature (15 K - 295 K) and external pressure (up to 8 GPa). Both the as-prepared and the purified SWCNT films exhibit nearly temperature-independent properties. With increasing pressure the low-energy absorbance decreases suggesting an increasing carrier localization due to pressure-induced deformations. The energy of the optical transitions in the SWCNTs decreases with increasing pressure, which can be attributed to pressure-induced hybridization and symmetry-breaking effects. We find an anomaly in the pressure-induced shift of the optical transitions at $sim$2 GPa due to a structural phase transition.
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Using the first principles calculations we have studied the vibrational modes and Raman spectra of a (10, 10) single-walled carbon nanotube (SWNT) bundle under hydrostatic pressure. Detailed analysis shows that the original radial breathing mode (RBM) of the SWNT bundle disappears after the structural phase transition (SPT). And significantly a RBM-like mode appears at about 509 cm^{-1}, which could be considered as a fingerprint of the SPT happened in the SWNT bundle, and further used to determine the microscopic structure of the bundle after the SPT.
The structural, electronic, optical and vibrational properties of the collapsed (10,10) single-walled carbon nanotube bundle under hydrostatic pressure have been studied by the first-principles calculations. Some features are observed in the present study: First, a collapsed structure is found, which is distinct from both of the herringbone and parallel structures obtained previously. Secondly, a pseudo-gap induced by the collapse appears along the symmetry axis textit{$Gamma $X}. Thirdly, the relative orientation between the collapsed tubes has an important effect on their electronic, optical and vibrational properties, which provides an efficient experimental method to distinguish unambiguously three different collapsed structures.
We study the behaviour of the non-retarded van der Waals force between a planar substrate and a single-walled carbon nanotube, assuming that the system is immersed in a liquid medium which exerts hydrostatic pressure on the tubes surface, thereby altering its cross-section profile. The shape of the latter is described as a continual structure characterized by its symmetry index $n$. Two principle mutual positions of the tube with respect to the substrate are studied: when one keeps constant the minimal separation between the surfaces of the interacting objects; when the distance from the tubes axis to the substrates bounding surface is fixed. Within these conditions, using the technique of the surface integration approach, we derive an integral form of the expressions which give the dependence of the commented force on the applied pressure.
We show that a multi-walled carbon nanotube film can be used as the sensing element of a low-cost sensor for the alcoholic concentration in liquid solutions. To this purpose, we investigate the electrical resistance of the film as a function of the isopropanol concentration in a water solution. The analysis reveals a growing resistance with increasing isopropanol concentration and a fast response. The sensing element is re-usable as the initial resistance value is restored once the solution has evaporated. The electrical resistance increases linearly when the multi-walled carbon nanotube film is exposed to common beverages with increasing alcoholic content. This work paves the way for the development of low-cost, miniaturized MWCNT-based sensors for quality monitoring and control of alcoholic beverages and general liquid solutions.
Chirality-selected single-walled carbon nanotubes (SWCNTs) ensure a great potential of building ~1 nm sized electronics. However, the reliable method for chirality-selected SWCNT is still pending. Here we present a theoretical study on the SWCNTs chirality assignment and control during the catalytic growth. This study reveals that the chirality of a SWCNT is determined by the kinetic incorporation of the pentagon formation during SWCNT nucleation. Therefore, chirality is randomly assigned on a liquid catalyst surface. Furthermore, based on the understanding, two potential methods of synthesizing chirality-selected SWCNTs are proposed: i) by using Ta, W, Re, Os, or their alloys as solid catalysts, and ii) by changing the SWCNTs chirality frequently during the growth.
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