Properties of Single Walled Carbon Nanotube Films

<p>The preparation and physical properties of transparent, single-walled carbon nanotube (SWNT) networks fabricated from a novel, organic dispersion are described here for the first time. Characterisation of SWNT dispersions uncovered shifts in the radial breathing modes as a function of aggregation. These modes were redshifted in centrifuged butylamine dispersions by ~3cm -1. SWNT films cast using a simple, drop-deposition technique were annealed at 300'C after fabrication to remove solvent and surfactant residue. Annealed films with a sheet resistance of magnitude ~10 4 kOhms/square and transparency of ~85 % were fabricated in this study. The optoelectronic properties showed some inconsistency due to varying levels of oxygen doping and film thickness. Thin films annealed at 500'C were found to be preferentially depleted of nanotubes with high chiral angle and small diameter. Oxidative effects were also observed upon annealing at temperatures as low as 300'C. However, the reasons for this premature combustion are as yet uncertain. Temperature-dependent conduction studies revealed that the removal of adsorbed surfactant considerably reduced tunnelling barriers in annealed films. The dominant conduction mechanism in both unannealed and annealed films was found to be 3D variable range hopping. In the annealed films, a high temperature activation regime (with activation energy of 220 meV) was observed above 225 K. This regime is due to thermal activation over Schottky barriers within the nanotube network or electron activation over the pseudogap in armchair tubes.</p>

Properties of Single Walled Carbon Nanotube Films

<p>The preparation and physical properties of transparent, single-walled carbon nanotube (SWNT) networks fabricated from a novel, organic dispersion are described here for the first time. Characterisation of SWNT dispersions uncovered shifts in the radial breathing modes as a function of aggregation. These modes were redshifted in centrifuged butylamine dispersions by ~3cm -1. SWNT films cast using a simple, drop-deposition technique were annealed at 300'C after fabrication to remove solvent and surfactant residue. Annealed films with a sheet resistance of magnitude ~10 4 kOhms/square and transparency of ~85 % were fabricated in this study. The optoelectronic properties showed some inconsistency due to varying levels of oxygen doping and film thickness. Thin films annealed at 500'C were found to be preferentially depleted of nanotubes with high chiral angle and small diameter. Oxidative effects were also observed upon annealing at temperatures as low as 300'C. However, the reasons for this premature combustion are as yet uncertain. Temperature-dependent conduction studies revealed that the removal of adsorbed surfactant considerably reduced tunnelling barriers in annealed films. The dominant conduction mechanism in both unannealed and annealed films was found to be 3D variable range hopping. In the annealed films, a high temperature activation regime (with activation energy of 220 meV) was observed above 225 K. This regime is due to thermal activation over Schottky barriers within the nanotube network or electron activation over the pseudogap in armchair tubes.</p>

Relationship between Temperature Dependencies of Resistivity and Hall Coefficient in Heavily Al-Doped 4H-SiC Epilayers

The temperature dependencies of the resistivity and Hall coefficient for heavily Al-doped 4H-SiC epilayers with Al concentration (CAl) higher than 2×1019 cm-3 were investigated. The signs of measured Hall coefficients (RH) change from positive to negative at low temperatures. For the epilayers with CAl < 3×1019 cm-3 the sign inversion occurred in the hopping conduction region, which was reported to be explicable using the model for amorphous semiconductors. For the epilayers with CAl > 3×1019 cm-3, on the other hand, the sign inversion occurred in the band conduction region, which is a striking feature, because the movement of free holes in the valence band should make RH positive. The sign-inversion temperature increased with increasing CAl, while the dominant-conduction-mechanism-change temperature was almost independent of CAl.

Структура и электрические свойства тонких пленок (ZnO/SiO-=SUB=-2-=/SUB=-)-=SUB=-25-=/SUB=-

Multilayer (ZnO/SiO2)25 thin films with a bilayer thickness of 6 to 10 nm has been synthesized in a single deposition process. The structure of the films consist of nanocrystalline ZnO layers and layers of amorphous SiO2. An analysis of the temperature dependences of the electrical resistivity, showed that a consistent change of the dominant conduction mechanism are realized in (ZnO/SiO2)25 thin films at temperatures 77 – 300 K: variable length hopping mechanism in a narrow energy band near the Fermi level at temperatures 77 – 250 K changed by the thermal activated impurity conductivity at close to room temperatures. The density of localized states and the activation energy of impurity conductivity has been estimated. The effect of heat treatment on the structure and electrical properties of the synthesized films has been investigated. It was found that the chemical interaction between the ZnO and SiO2 layers occurs at 580–600°C. It accompanied by the destruction of the multilayer structure and the appearance of the chemical compound Zn2SiO4 with the tetragonal structure (I-42d space group).

Analysis of AC-Conductivity in Chalcogenide Ge10Se20 Bi80Thin Film

The alloy Ge10Se20 Bi80 has been prepared. Thin films of Ge10Se20 Bi80 has been prepared via a thermal evaporation method (melt quenching technique) with 3000A thickness, and rate of deposition (4.1) A/sec at pressure 2x10-5 Torr. The A.C electrical conductivity of a- thin films Ge10Se20 Bi80 has been studied as a function of frequency for annealing temperature within the range (423-623) K, the deduced exponent s values, was found to decrease with increasing of annealing temperature through the frequency of the range (102-106) Hz. It was found that, the correlated barrier hopping (CBH) is the dominant conduction mechanism. Values of dielectric constant ε1 and dielectric loss ε2 were found to decrease with frequency and increase with temperature. The activation energies have been calculated for the annealed thin films.

Electrical Conduction in Some Nickelates

This paper reports electrical conductivity (s) and Seebeck coefficient (s) study on rare-earth nickelates RNiO3 where R = Nd, Sm and Eu in the temperature range 400-1200 K. They have orthorhombic unit cell. The majority charge carriers are holes throughout the measurement. Both s and S variations show three regions. In higher temperature region (Above 1000K) dominant conduction mechanism is intrisic band type whereas below this temperature, hopping of holes from Ni3+ to Ni2+ centres takes place. In lower temperature region, the electrical conductions is taken over by acceptor type impurities. The conduction mechanism is explained on the basis of every band model. Break temperatures as well as mobility have also been evaluated.

Charge Transport Mechanism and the Effects of Device Temperature on Electrical Parameters of Au/ZnPc/N-Si Structures

Gold/Zinc Phthalocyanine/n-Si metal semiconductor contact with organic interfacial layer have been developed and characterized by Current–Voltage-Temperature (I-V-T) measurements, to study its junction and charge transport properties. The junction parameters, of diode ideality factor (n), barrier height (b) and series resistance (R¬S), of the device are found to shift with device temperature. The barrier height and the diode ideality factor are found to increase and the series resistance is found to decrease with increasing device temperature. The activation energy of the charge carriers is found to be 44 meV and the peak of interface state energy distribution curves is found to shift in terms of Ess-Ev value from 0.582 eV to 0.776 eV with increasing device temperature. The data analysis implies that the Fermi level of the organic interfacial layer shifts as function of device temperature by 100 meV in the device temperature range of 283K to 343K. In terms of dominant conduction mechanism, the I-V-T data analysis confirms the fit of data to the relationship log (IV4)  V1/2 for higher device temperatures and the Poole-Frenkel type is found to be the dominant conduction mechanism for the hybrid device.