Avshish Kumar

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.

Introduction to Nanomaterials

The applications of nanomaterials have been enormous, which not only encompasses a single discipline but it stretches across the whole spectrum of science right from agricultural science to space technology. New approaches to synthesize nanomaterials in order to design new devices and processes are being developed and the techniques of fabrication of nanomaterials involve analyzing and controlling the matter at atomic scales. This fascinating research field has started a new era of integration of basic research and advanced technology at the atomic scale which has a potential to bring the technological innovations at highest level. The rudimentary capabilities of nanomaterials today are envisioned to evolve in our overlapping generations of nanotechnology products: passive nanostructures, active nanostructures, systems of nanosystems, and molecular nanosystems. This chapter presents the basic introduction to nanomaterials and their popular applications.

Effect of oxygen plasma on field emission characteristics of single-wall carbon nanotubes grown by plasma enhanced chemical vapour deposition system

Field emission properties of single wall carbon nanotubes (SWCNTs) grown on iron catalyst film by plasma enhanced chemical vapour deposition system were studied in diode configuration. The results were analysed in the framework of Fowler-Nordheim theory. The grown SWCNTs were found to be excellent field emitters, having emission current density higher than 20 mA/cm2 at a turn-on field of 1.3 V/μm. The as grown SWCNTs were further treated with Oxygen (O2) plasma for 5 min and again field emission characteristics were measured. The O2 plasma treated SWCNTs have shown dramatic improvement in their field emission properties with emission current density of 111 mA/cm2 at a much lower turn on field of 0.8 V/μm. The as grown as well as plasma treated SWCNTs were also characterized by various techniques, such as scanning electron microscopy, high resolution transmission electron microscopy, Raman spectroscopy, and Fourier transform infrared spectroscopy before and after O2 plasma treatment and the findings are be...

A multiplier generator for Xilinx FPGAs

In this paper, we present a module generator which can produce variety of multiplier designs for LUT based FPGAs. It incorporates algorithms for generating sequential, combinational and pipelined designs. The multiplier generator forms a part of the IDEAS synthesis system. Different types of multipliers which can be generated have been included in the IDEAS component library, along with functions which estimate the CLB count and delays for the given size parameters and selected FPGA device. The multiplier generator generates designs for XC3000 and XC4000 family of Xilinx FPGA devices. For Xilinx XC4000 family of devices it takes advantage of the built-in dedicated carry logic to generate fast multipliers. The output of the generator is a netlist in terms of the Xilinx XACT and XBLOX components which is finally mapped onto the FPGA using Xilinx XACT and XBLOX tools.

Study of J-E Curve with Hysteresis of Carbon Nanotubes Field Emitters

We observe hysteresis in J-E plot during field emission measurement of CNTs grown by LPCVD technique. CNTs are synthesized on Fe-coated Si substrate at 650°C. SEM and Raman study confirm that CNTs are successfully grown on Si substrate by LPCVD technique. In this study, we find that ramp-down curve has higher value of current density than ramp-up curve which indicates that CNTs show positive hysteresis. Our results show that a high current density at low turn-on voltage is obtained in ramp-down step of J-E plot which may be since not all CNTs contribute in ramp-up step process. But in ramp-down step all CNTs contribute as field emitters due to high electric field treatment. We also performed stability analysis of CNTs with current at constant applied voltage for 5 hrs and find that the sample shows long-term stability due to increase in emitting site density since a large number of CNTs participate in field emission.

Improved field emission properties of carbon nanotubes by dual layer deposition

In this paper, we tried to increase the current density of carbon nanotubes (CNTs) by depositing double layer of CNTs instead of single layer. Both the layers of CNTs are deposited by the low pressure chemical vapour deposition technique on silicon substrate with Fe catalyst. Scanning electron microscopic images show the surface morphology of single and double layer of CNTs. Dual layer deposition of CNTs is a very simple and easy method to increase the current density of CNTs based field emitters than other conventional methods. Excellent field emission properties of double layer of CNTs are exhibited with large field enhancement factor and low turn-on voltage as compared to those for single layer of CNTs. High current density of CNTs is required for field-emission-based display devices associated with field enhancement factor and number of emitting electrons. Therefore, we may say that dual layer deposition of CNTs can be utilised as an alternative approach to improve the current density for field emitters. Stability measurement of the samples was also performed for 3 h (180 min) with current at constant applied voltage, and it was found that the stability of dual layer of CNTs is remarkable than that of single layer of CNTs.

Raman Characteristics of Vertically Aligned Single Wall Carbon Nanotubes Grown by Plasma Enhanced Chemical Vapor Deposition System

Vertically aligned single wall carbon nanotubes (VA-SWCNTs) of diameter 0.8–1.5 nm suitable for semiconducting applications have been successfully grown on Iron catalyst film using Plasma Enhanced Chemical Vapor Deposition (PECVD) System. The Raman signal positions of the spectra in RBM, D and G bands confirm the existence of SWCNTs. The grown sample is excited with laser excitation wavelengths, 633 nm from He–Ne laser. The field emission study has been carried out in a vacuum chamber under a pressure of 10−6 torr. Highly sensitive, capital intensive equipment such as Field Emission Scanning Electron Microscope (FESEM), has been used to identify the state and morphology of nanotube samples.

Diversity and Biopotential of Endophytic Fungal Flora Isolated from Eight Medicinal Plants of Uttar Pradesh, India

Endophytic fungi are hidden diversity mines of microbes that reside in the healthy and symptomless interior of plant tissues without causing any harmful effects. This chapter focuses on fungal endophytic diversity of eight medicinal plants of Uttar Pradesh, India with their biopotential ability. Total of 4,002 (38.38 % CF) endophytic isolates were recovered from 10,425 segments representing 131 endophytic fungal species belonging to different fungal classes. Out of 4,002 isolates, hyphomycetes were more pronounced with 71.43 % recovery followed by coelomycetes 16.61 %, ascomycetes 6.59 %, mycelia sterilia or unidentified 5.32 % and least from zygomycetes 0.020 %. Among total endophytic fungal species isolated, Cladosporium cladosporioides (3.39 % CF) was found to be the most dominated taxa followed by Alternaria alternata (2.35 % CF), Curvularia lunata (2.13 % CF), Aspergillus niger (1.95 % CF), Chaetomium globosum (1.85 % CF), Nigrospora oryzae (1.57 % CF) and Phoma glomerata (1.09 % CF). From a total of 131 endophytic species, 101 were tested for their antimicrobial and antioxidant activity. Out of 47 active species, 29.78 % displayed antibacterial activity, 27.65 % showed antifungal activity, 38.29 % exhibited antibacterial and antifungal activity both while only 4.25 % displayed antimalarial as well as antioxidant activity. Twenty-one endophytic fungal species were tested for extracellular production of amylase, xylanase and phosphate solubilization where 76.19 % found to produce amylase, 23.80 % for xylanase and 14.28 % exhibited phosphate-solubilization activity.

Enhancement of Field Emission Properties of Carbon Nanotubes by ECR-Plasma Treatment

We report a significant improvement in electron field emission property of carbon nanotubes film by using an electron cyclotron resonance plasma treatment. Our research results reveal that plasma treatment can modify the surface morphology and enhance the field emission characteristics of carbon nanotubes. Raman spectra indicate that plasma treated CNTs sample has lesser defects. Before plasma treatment, low current density of 6.5 mA/cm2 at 3.0 V/μm and at a high turn-on field of 2.4 V/μm was observed. ECR plasma treated CNTs showed a high current density of 20.0 mA/cm2 at 3.0 V/μm and at a low of 1.6 V/μm. The calculated enhancement factors are 694 and 8721 for ECR-plasma untreated and treated carbon nanotubes, respectively. We found an increase in the enhancement factor and emission current after the ECR-plasma treatment. This may be attributed to creation of geometrical features through the removal of amorphous carbon and catalyst particles.

Field-Emission Study of Carbon Nanotubes Grown by Low Pressure Chemical Vapour Deposition on Single and Dual Layer of Catalyst

In the present research work, CNTs are synthesized by Low Pressure Chemical Vapor Deposition (LPCVD) method at 600 °C. The Si substrate is coated with Ni (single layer) in one sample and Ni over Cr layer (dual layer) as a catalyst on the other sample by using RF- sputtering method. Three precursor gases Acetylene (C2H2), Ammonia (NH3) and Hydrogen (H2) with flow rates 10, 50 and 50 sccm respectively are allowed to flow through the tube reactor for 20 min. Acetylene is used as source gas and Ammonia to etch the amorphous carbon and for the further reduction of catalyst size. The as grown CNTs sample was characterized by Scanning Electron Microscope (SEM) and Raman. Raman Spectra show the graphitic nature of CNTs grown on dual layer of catalyst. Field enhancement factor is increased in the dual layer coated samples.