Samina Husain

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...

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.

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.

Highly Efficient Field Emission Characteristics of Ultra-long Vertical Aligned Single Wall Carbon Nanotubes

In this work, ultra long vertically aligned single wall carbon nanotubes are synthesised by Plasma enhanced chemical vapour deposition (PECVD) technique at 600 °C temperature. The presence of built-in electric field in a plasma sheath aligns the growing CNTs along the field lines. Also, PECVD method favours low temperature synthesis of VA-SWCNTs. SEM and Raman are used to characterized as grown sample. Enhanced Field emission properties of as-grown VA-SWCNTs are also studied.