S.H. Jhang

Non-ohmic current–voltage characteristics in single-wall carbon nanotube network

Abstract The non-ohmic current–voltage ( I – V ) characteristics of the single-wall carbon nanotube network were investigated at low temperatures. The temperature dependence of resistivity at low current ( I μ A) shows non-metallic negative d ρ /d T from T =1.4–300xa0K. Below T I – V curves in the non-ohmic regime can be fitted well by the fluctuation-induced tunneling model, indicating the importance of inter-tubular contacts or inherent energy barriers inside the tubes.

Orientation dependence of magneto-resistance behaviour in a carbon nanotube rope

The orientation dependence of magneto-resistance behaviour for a single-walled carbon nanotube (SWCN) rope is reported.A clear delineation of behaviours is observed between applying a magnetic field perpendicular or parallel to the rope axis.For a perpendicular field, monotonic negative magneto-resistance is observed due to two-dimensional weak localisation within the rope. By contrast, for a parallel field, complicated oscillatory behaviour is observed due to the Altshuler–Aronov–Spivak effect around closed electron trajectories on discrete cylinders within the SWCN rope.A dominant oscillatory mode can be identified which corresponds to closed paths around the outer circumference of the SWCN rope.However, due to the composite filamentary nature of the rope, the overall oscillatory behaviour is rather complicated and can be classified as universal conductance fluctuations. With a backgate voltage applied to the sample, Coulomb blockade peaks are observed in the transport current with additional peak structure superimposed due to resonant tunnelling.We find an interesting effect whereby these peaks are suppressed in the presence of a magnetic field. 2002 Elsevier Science B.V. All rights reserved.

Frequency and field dependent conductivity of carbon nanotube networks

Abstract The measured resistance of carbon nanotube networks is often dominated by defects, inter-tube and inter-rope contacts. We show that the peak reported in the frequency-dependent conductivity of single-wall carbon nanotube networks is consistent with metallic conduction interrupted by nonmetallic defects that act as barriers. Such barriers also contribute to the electric field dependence of the conductivity. Using Shengs model, we calculate the field dependence of fluctuation-assisted tunnelling conduction between metallic regions separated by an insulating barrier, obtaining nonlinearities consistent with our experimental data on carbon nanotube networks.

Properties of single-wall carbon nanotubes

Measurements are reported of the Raman spectra (including the second order spectrum), the diffuse reflectance (for photon energies 0.5 - 5 eV), and dc conductivity of purified single-wall carbon nanotube (SWCN) pellets made using the catalytic arc discharge method. The Raman data indicate a strong presence of SWCNs of diameter 1.22 nm. The diffuse reflectance shows a sharp increase above 4 eV, and a gradual increase below 3 eV down to the limit of measurements at 0.5 eV. Metallic conduction is indicated by the observation that the dc conductivity does not extrapolate to zero at zero temperature. The temperature dependence of conductivity, which remains nonmetallic in sign up to 300 K, is consistent with tunnelling through thin barriers between metallic regions.

Random Telegraph Noise in Individual Single-walled Carbon Nanotubes

The switching of resistance between two discrete values, known as random telegraph noise (RTN), was observed in individual single-walled carbon nanotubes (SWNTs). The RTN has been studied as a function of bias-voltage and gate-voltage as well as temperature. By analyzing the features of the RTN, we identify three different types of RTN existing in the SWNT related systems. While the RTN can be generated by the various charge traps in the vicinity of the SWNTs, the RTN for metallic SWNTs is mainly due to reversible defect motions between two metastable states, activated by inelastic scattering with electrons.

Negative differential resistance in single-wall carbon nanotube network

The current-voltage (I-V) characteristic of single-wall carbon nanotube (SWNT) network was investigated at low temperatures. At T∼ 1.6K, S-shaped negative differential resistance (NDR) was observed, which was systematically examined under the variation of temperature, magnetic field in transverse direction and distances between probes. S-shaped NDR was explained by the nondestructive impact ionization of carriers and the resulting rmation of inhomogeneous spatial structures such as high-current filaments. Critical electric field for impact ionization was estimated to be about IV/ cm.

Random Telegraph Noise in Carbon Nanotube Peapod Transistors

Abstract We investigated the switching of resistance between two discrete values, known as random telegraph noise (RTN), observed in carbon nanotube peapod transistors [single‐walled carbon nanotubes (SWNTs), C60‐peapods, and Cs‐encapsulated SWNTs (so‐called Cs‐peapods)]. By analyzing the features of the RTN, we suggest that this noise for SWNTs is due to the random transition of defects between two metastable states, activated by inelastic scattering with ballistic electrons. The noise for C60‐peapods (Cs‐peapods) is attributed to the motion of C60s (Cs) in the nanotubes.

Composites of conducting polymers and carbon nanotubes

The composite films of conducting polymers (MEH-PPV and m-PMEH-PPV) and single-wall carbon nanotubes (SWNTs) are fabricated. The time- and spectral-resolved photoluminescence (PL) of pure polymers and composites is investigated in the temperature range between 10 K and 300 K by means of femtosecond time-resolved PL system. The significant quenching of luminescence and the reduction of radiative exciton life time in composites are reported.