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A circular disk resonator is used to study the gas sensing properties of carbon nanotubes. It detects the presence of gases based on the change in the dielectric constant rather than electrical conductivity of single walled carbon nanotubes (SWNTs) upon gas exposure. A conducting circular disk is coated with electric arc prepared SWNTs and degassed by heating under a high vacuum. It exhibits noticeable shifts in resonant frequency to both polar (NH3 and CO) and nonpolar gases (He, Ar, N2, and O2). Gas concentrations as low as 100 ppm can be detected using this sensor configuration.

We report atomic level high resolution transmission electron microscopy (HRTEM), electron nanodiffraction and nano-electron energy loss spectroscopy (nano-EELS) of boron-doped carbon nanostructures obtained by laser ablation of Co/Ni/B-doped carbon targets. The observations provide direct evidence for structural systematics and atomic structural defects as a function of the B content in the target. Targets with low B concentration (below 3 at%), produced ropes of single wall carbon nanotubes (SWCNTs) with no detectable boron present in the SWCNT ropes. However, unintended N-doping of the curved honeycomb lattice was observed in the 2.5 at% B sample (which is attributed to the possible presence of small amounts of N in the targets or reaction environments), with striking consequences for doping of heteroatoms within the hexagonal lattice of the graphene layer. At higher B concentration (3.5 at% and higher), there are significant changes in the nanostructure, which exhibits defective graphite layers and a small number of double wall carbon nanotubes (DWCNTs). At the higher B concentration, boron-doping is evidenced in the form of very small amorphous B clusters trapped in graphite-like defective sites.

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It is shown that 1,4-benzenediol (hydroquinone) and TiO2 nanotubes can form a hybrid structure that is stable in aqueous environment. The incorporation of hydroquinone restores the local structure of nanotubes to anatase-like as evidenced by Raman spectroscopy. Subtle overall structural changes take place upon annealing of the hybrid structure contributing to its stability. The hybrid system shows a broad optical absorption peak extending significantly beyond 700 nm with potential applications in photocatalysis and photoelectrochemistry.