We report the electrical responses of water vapour and O2 adsorption onto macroscopic multi-walled carbon nanotube (MWCNT) ropes, and compare the results with mats of acid-treated MWCNTs on SiO2 substrates in order to investigate the importance of oxygen-containing defects on CNTs. In the outgassed state both carbon nanotube (CNT) materials exhibit rapid changes in electrical resistance when exposed to dry air, humid air or water vapour at standard temperature and pressure (STP). The measured electrical responses are highly reversible at STP when cycled between humid air, vacuum and dry air. We report a decrease in resistance for the CNT materials in dry air, attributed to O2 p-type doping of the CNTs, whereas there is an increase in resistance when exposed to a humid environment. This latter effect is attributed to the formation of hydrogen bonding from the polar water molecules with the oxygen-containing defects on the CNTs. Our observations indicate that the increase in electrical resistance upon water absorption affects a reduction of the electron-withdrawing power of the oxygen-containing defect groups, thus leading to a reduced hole carrier concentration in the p-type nanotubes.

Commercial purity aluminium sheets were severely plastic deformed by accumulative roll bonding (ARB). Changes in electrical resistivity at 77 K and microstructure during the ARB process were traced up to 12 cycles, which corresponded to an equivalent strain of 10. The resistivity at 77 K increased with increasing number of ARB cycles, then saturated after about the sixth ARB cycle with a maximum increment of resistivity from starting material of about 1.1 n m. Since lattice defects affect the resistivity of metals, the internal dislocation density and the density of grain boundaries were evaluated from scanning transmission electron microscopy images using Ham's method and grain boundary maps obtained from electron back-scattering diffraction, respectively. The relationship between the change in resistivity and the lattice defects is discussed.

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Amorphous carbon films containing no hydrogen were irradiated with a pulsed UV laser in vacuum. Raman spectroscopy indicates an increase in the quantity of sp 2 clustering with the highest laser energy density and a commensurate reduction in resistivity. The reduction of resistivity is explained to be associated with thermally induced graphitization of amorphous carbon films. The high field transport is consistent with a Poole-Frenkel type transport mechanism via neutral trapping centers related to sp 2 sites which are activated under high fields. Decreasing the resistivity is an important feature for use of carbon as an electronic material.

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