J.S.B.S. Rawat

Improving the field emission of carbon nanotubes by lanthanum-hexaboride nano-particles decoration

Field emission of carbon nanotubes (CNTs) was remarkably improved by lanthanum-hexaboride (LaB6) nano-particles (NPs) decoration. CNTs were grown on the silicon substrate by chemical vapor deposition. Field emission of bare CNTs and LaB6-NPs decorated CNTs was carried out under same conditions. Physical, morphological, elemental, and graphitic nature changes were ascertained by scanning electron microscope, transmission electron microscope, energy dispersive x-ray spectroscopy, and Raman analysis. LaB6-NPs decorated CNTs show significant reduction of turn-on electric-field from 3.0 to 2.1 V/μm. A remarkable improvement of more than six-fold from 2.05 to 13.19 mA/cm2 at a field of 4.6 V/μm was also observed in the current-density.

Functionalization Of Carbon Nanotubes With Metal Phthalocyanine For SELECTIVE Gas Sensing Application

Composites of hydroxylated single-walled carbon nanotubes and copper phthalocyanine (CuPc) has been obtained. Phthalocyanines get noncovalently adsorbed onto CNTs surface by π–π stacking. Conversion of β-form of phthalocyanine to α-form gives clear evidence of composite formation. Only carboxyl and hydroxyl CNTs react with phthalocyanine while no reaction occurs for amided CNTs. High selectivity in the thin film resistors of SWNT–OH + CuPc composites toward NOx gases is observed. The response for NOx is 10 times and 100 times more then that of ammonia and Sox, respectively. This makes the SWNT–OH + CuPc composite a candidate for detection of NOx—a common pollutant.

Effect of purity, edge length, and growth area on field emission of multi-walled carbon nanotube emitter arrays

Present report aims to study the effect of purity, edge length, and growth area on field emission of patterned carbon nanotube (CNT) emitter arrays. For development of four CNT emitter arrays (CEAs), low resistively silicon substrates were coated with thin film of iron catalyst using photolithography, sputtering, and lift off process. Four CEAs were synthesized on these substrates using thermal chemical vapor deposition with minor changes in pretreatment duration. Out of these, two CEAs have 10 μm × 10 μm and 40 μm × 40 μm solid square dots of CNTs with constant 20 μm inter-dot separation. Other two CEAs have ring square bundles of CNTs and these CEAs are envisioned as 10 μm × 10 μm square dots with 4 μm × 4 μm scooped out area and 15 μm × 15 μm square dots with 5 μm × 5 μm lift out area with constant 20 μm inter-dot spacing. Solid square dot structures have exactly constant edge length per unit area with more than four-fold difference in CNT growth area however ring square dot patterns have minor differe...

Optimization of Vertically Aligned Nature of CNTs for Improved Field Emission Behavior

For improved field emission behavior, we demonstrate the PECVD technique to grow highly ordered, selectively grown, vertically aligned carbon nanotubes (CNTs) with optimum density. We report the optimization of vertically aligned CNTs by optimizing catalyst thickness, dot size of catalyst and the spacing between them. We made an attempt to optimize the catalyst thickness to understand the effect over density, diameter and height of CNTs. SEM images reveal that the catalyst thickness as well as the dot size and the spacing is helpful in optimizing the vertical alignment of CNTs. The vertically aligned CNTs provide a large number of tips as compared to horizontally aligned CNTs over an area. Also, the high value of the enhancement factor required to achieve a better FE behavior is also plausible with vertical CNTs. The field emission results confirm that the vertically aligned CNTs bring a large current density at relatively low threshold field. We were able to achieve a current density of 100 mA/cm2 at a field of 6 V/µm. Density and therefore screening effect also becomes important factors that hinder the performance of CNT‐based emitters. However, in our typical samples we observed less discrepancy in the density, and the density so calculated was in the order of 109/cm2.

Modeling Field Emission from Single-Tip Carbon Nanotube in Triode Configuration

ABSTRACT This article presents a simulation study on the field emission characteristics of a single carbon nanotube (CNT) cathode in the triode structure. Computer Simulation Technology (CST) Particle Studio (M/s Jyoti Electronics, India) was used to simulate the triode characteristics in relation to geometrical parameters, position of the CNT, and applied gate and anode potentials. The results emphasize the significance of simulation-based optimization of structural parameters and field conditions prior to actual fabrication of CNT field emitters.

Enhanced response and improved selectivity for toxic gases with functionalized CNT thin film resistors

ABSTRACT High surface area of CNTs makes them an extremely sensitive detection element for a wide variety of analytes present in minute quantities of ppb and ppm levels. CNTs does not inherit selectivity for a particular gas/analyte, it can be introduced in CNT based gas sensor by means of functionalization, along with improvement in gas sensors response. Effects of Carboxylated group and gold nano-particles were studied on the response of CNT sensors towards toxic gases such as NO2 and NH3. Gold nanoparticles have found to enhance the response for NO2 and NH3, while oxygenated functional have brought selectivity towards NH3.

Novel ring structure for minimisation of screening effect in carbon nanotube based field emitters

Carbon Nanotubes (CNTs) are promising candidates for cold cathodes because of their high aspect ratio and robustness. However, the major hindrance in cold cathode based applications is the screening effect, which reduces the effective field at the tip and thereby the current density. The emission current can be improved by minimising the screening effect. The adverse effect of screening can be addressed by either controlling the growth density or by optimising the patterns of CNT cathodes. Here, novel patterns have been used to increase edge length per unit area in planar vertically aligned CNT bundles. Our motive was to increase the number of effective emitters, since the CNT at the edges are less screened by the proximal CNTs. By varying geometry and spacing of solid CNT dot patterns and by introducing the square ring structures; we could successfully enhance the effective emitters at the edges. It has been observed that an enhancement of edge length from 0.032 per micron to 0.2 per micron increases the current density from 0.71mA/cm2 to 16.2 mA/cm2 at a field of 4.5 V/μm. CNTs in dotted structure with high value of edge length per unit area emit very high current density as compared to other dotted structures with low value of edge length per unit area Simulation studies confirms our argument that CNTs at the corners are the least screened and have the maximum local electric field.