Effect of Purity and Substrate on Field Emission Properties of Multi-walled Carbon Nanotubes

Multi-walled carbon nanotubes (MWNT) have been synthesized by chemical vapour decomposition (CVD) of acetylene over Rare Earth (RE) based AB2(DyNi2) alloy hydride catalyst. The as-grown carbon nanotubes were purified by acid and heat treatments and characterized using powder X-ray diffraction, Scanning Electron Microscopy, Transmission Electron Microscopy, Thermo Gravimetric Analysis and Raman Spectroscopy. Fully carbon based field emitters have been fabricated by spin coating a solutions of both as-grown and purified MWNT and dichloro ethane (DCE) over carbon paper with and without graphitized layer. The use of graphitized carbon paper as substrate opens several new possibilities for carbon nanotube (CNT) field emitters, as the presence of the graphitic layer provides strong adhesion between the nanotubes and carbon paper and reduces contact resistance. The field emission characteristics have been studied using an indigenously fabricated set up and the results are discussed. CNT field emitter prepared by spin coating of the purified MWNT–DCE solution over graphitized carbon paper shows excellent emission properties with a fairly stable emission current over a period of 4 h. Analysis of the field emission characteristics based on the Fowler–Nordheim (FN) theory reveals current saturation effects at high applied fields for all the samples

Influence of spherical anisotropy on the optical properties of plasmon resonant metallic nanoparticles

10.1007/s00339-010-6090-5Applied Physics A: Materials Science and Processing1023673-679APAM

Strain hardening behavior of a two-phase Cu–Ag alloy processed by high-pressure torsion

Disks of a coarse-grained Cu–28 wt.% Ag alloy and pure Cu were processed by high-pressure torsion and the microhardness wasinvestigated as a function of the imposed strain. It is shown that the Cu–Ag alloy displays a much stronger strain hardening capability than Cu due to a continuous refinement of the microstructure. A two-stage Hall–Petch relationship was obtained for the Cu–Ag alloy which is attributed to the development of multi-strengthening mechanisms.<br/

Microstructural evolution and mechanical properties of a two-phase Cu–Ag alloy processed by high-pressure torsion to ultrahigh strains

Disks of a coarse-grained Cu–28 wt.% Ag alloy were processed by high-pressure torsion up to 20 revolutions to reveal the microstructural evolution and mechanical properties. The eutectic shows a faster evolution process than the Cu matrix. A banded structure forms in the Cu matrix, and both the eutectic spacing and the band width decrease with increasing shear strain. After 20 revolutions, the substructure may even diminish in the Cu matrix. The microhardness increases with increasing revolutions, and a saturation microhardness is ultimately achieved. After 20 revolutions, the tensile strength was improved to 1420 MPa, and the failure mode of the sample was transferred from necking to full shearing without plasticity.<br/

Comparison of microstructures and mechanical properties of a Cu–Ag alloy processed using different severe plastic deformation modes

A Cu–8 wt.% Ag alloy was processed by equal-channel angular pressing (ECAP), dynamic plastic deformation (DPD) and high-pressure torsion (HPT) at room temperature, and the microstructures and mechanical properties were investigated. It is shown that the microstructures of the Cu–Ag alloy can be refined to different levels by these severe plastic deformation (SPD) modes with the smallest grains produced by HPT. The results provide a clear demonstration that the yield strength and microhardness are inter-related over a wide range of value

Formation of fivefold deformation twins in an ultrafine-grained copper alloy processed by high-pressure torsion

Fivefold deformation twins (DTs) are formed in an ultrafine grain, with a size of 100 nm, of a Cu–16 at.% Al alloy processed by high-pressure torsion. Formation occurs through the sequential emission of partial dislocations from grain boundaries and other multiple twin boundaries. These observations confirm the emission of partial dislocations from multiple-fold nodes which can be attributed to increased twinnability via the introduction of Al atoms which lower the driving force for partial emission.<br/

Significance of stacking fault energy on microstructural evolution in Cu and Cu-Al alloys processed by high-pressure torsion

Disks of pure Cu and several Cu–Al alloys were processed by high-pressure torsion (HPT) at room temperature through different numbers of turns to systematically investigate the influence of the stacking fault energy (SFE) on the evolution of microstructural homogeneity. The results show there is initially an inhomogeneous microhardness distribution but this inhomogneity decreases with increasing numbers of turns and the saturationmicrohardness increases with increasing Al concentration. Uniform microstructures are more readily achieved in materials with high or low SFE than in materials with medium SFE, because there are different mechanisms governing the microstructural evolution. Specifically, recovery processes are dominant in high or medium SFE materials, whereas twin fragmentation is dominant in materials having low SFE. The limiting minimum grain size (dmin) of metals processed by HPT decreases withdecreasing SFE and there is additional evidence suggesting that the dependence of dmin on the SFE decreases when the severity of the external loading conditions is increased