Top PDF Fabrication and field emission properties of carbon nanotubes

Fabrication and field emission properties of carbon nanotubes

Fabrication and field emission properties of carbon nanotubes

Depending on the means of igniting and maintaining the plasma, PECVD can be subdivided into DC (Direct Current) PECVD, RF (Radio Frequency) PECVD, MPECVD, and so on. A microwave antenna is used to produce microwave at the frequency 2.45 GHz. The maximum power of the microwave is 1.2 kW. Besides the microwave power, there is a separate heating system that can heat the substrate to 900 o C independently. There is also a rotary pump that can drive the system down to 1x10 -3 Torr. The diameter of the reaction chamber is 12.5 cm. The sample stage is a molybdenum disk with a hole in the center. The thermal couple tip is set inside the hole and attached to the bottom of the sample. There are three mass flow controllers that control the flow speed of three feeding gases independently. The SEM pictures were taken by a Hitachi S-4700 Field Emission Scanning Electron Microscope. The High Resolution Transmission Electron Microscopy (HRTEM) pictures were taken by the JEOL 2010F-FasTEM. The ion-reactive etching system is a SAMCO Model RIE-1C Reactive Ion Etcher. The Raman spectra were recorded using a Dior XY triple spectrometer and collected using a charge-coupled device (CCD) cooled with LN 2 .
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Field Emission Properties and Fabrication of CdS Nanotube Arrays

Field Emission Properties and Fabrication of CdS Nanotube Arrays

Abstract A large area arrays (ca. 40 cm 2 ) of CdS nano- tube on silicon wafer are successfully fabricated by the method of layer-by-layer deposition cycle. The wall thicknesses of CdS nanotubes are tuned by controlling the times of layer-by-layer deposition cycle. The field emission (FE) properties of CdS nanotube arrays are investigated for the first time. The arrays of CdS nanotube with thin wall exhibit better FE properties, a lower turn-on field, and a higher field enhancement factor than that of the arrays of CdS nanotube with thick wall, for which the ratio of length to the wall thickness of the CdS nanotubes have played an important role. With increasing the wall thickness of CdS nanotube, the enhancement factor b decreases and the values of turn-on field and threshold field increase.
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The Influence of a TiN Buffer Layer on the PECVD Growth and Field Emission Properties of Carbon Nanotubes

The Influence of a TiN Buffer Layer on the PECVD Growth and Field Emission Properties of Carbon Nanotubes

Field emission is a quantum mechanical phenomenon defined as the emission of electrons from the surface of a condensed phase into another phase under the application of high electric fields. 1 Although field emission can take place at numerous interfaces, for simplicity we will restrict this discussion to the field emission of electrons from a metal into vacuum. When considering electron emission process such as thermionic emission and photoemission, electrons gain sufficient energy to overcome the potential barrier at a metal- vacuum interface allowing electrons to escape from the metal surface into vacuum. Field emission, on the other hand, involves the emission of electrons from the metal surface into vacuum by tunneling through a potential barrier rather than overcoming it. The likelihood that electron tunneling will occur depends on the shape of the potential barrier which is determined by the applied electric field, the work function of the metal, the image force on an electron, and any factors that influence the surface from which the electrons will be emitted.
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Excellent Field Emission Properties of Short Conical Carbon Nanotubes Prepared by Microwave Plasma Enhanced CVD Process

Excellent Field Emission Properties of Short Conical Carbon Nanotubes Prepared by Microwave Plasma Enhanced CVD Process

The potential of CNTs for field emission (FE) was first reported in 1995. FE from an isolated single multiwalled CNT (MWNT) was first observed by Rinzler et al. [4] and that from a MWNT film was reported by de Heer et al. [5]. Since then a number of experimental studies on FE aspects of both MWNTs [6–16] and single-walled CNTs [17, 18] grown by different processes such as arc discharge and various versions of chemical vapor deposition (CVD) both with and without plasma have been investigated. Many parameters such as density, length of CNTs, spacing between neighboring nanotubes, open/closed tips, presence of adsorbates, metal particles, etc., have been reported to affect the FE characteristics of CNT films. Carbon nano- structures other than CNTs, such as carbon nanofibers (CNFs) [19, 20], carbon nanocones (CNCs) [21, 22], car- bon nanosheets/nanowalls [23, 24], etc., are also promising material structure as field emitters. Recently, there have been continuous efforts on growth of one-dimensional carbon nanostructures with a very sharp tip structure S. K. Srivastava ( & ) V. Kumar
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Fabrication, purification and characterization of multiwall carbon nanotubes

Fabrication, purification and characterization of multiwall carbon nanotubes

techniques involve separation process of the synthesis products, depend on their reactivity which commonly produce unavoidable defects along the tubes and at the tube ends of the pentagonal structure. Some extraordinary damages to the CNTs structure and morphology can be yielded by these techniques. The examples of chemical purification techniques are oxidation by heating, acids and oxidizing agents, alkali treatment and annealing in inert gases. Besides that, the physical techniques for example filtration, ultrasonication, centrifugation and size-exclusive chromatography are able to separate the impurities according to their sizes. These techniques are actually less effective and more complex although they are quite mild and tubes are not damaged badly. Basically, physical methods can work to remove and separate the unwanted impurities like aggregate, nanocapsules and amorphous carbon [11].
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Fabrication, structure, and electron emission of single carbon nanotubes

Fabrication, structure, and electron emission of single carbon nanotubes

− . The β factor was calculated from the slope of the three F-N plots given in Fig. 4.3.1(b) with an assumption that the work function is 5.0 ± 0.2 eV [26,27,28,29]. The three β factors are calculated and listed in Table. 4.3.1. The error bar of the field enhancement factor β consists of two parts. The first part is the error induced by the fitting of the F-N plots. The second part is induced by the uncertainty of the work function of the carbon nanotube. The true error bars have been calculated and listed in Table. 4.3.1. To eliminate the complexity of the absorbed species, the CNT No. 4 has been cleaned by heating it at 1200ºC. The F-N plots before and after cleaning are shown in Fig. 4.3.1(c). It was found that after cleaning, the slope of the F-N plot only changed 2%. Thus the measured field enhancement factors of CNT No. 1 - 3 are still valid even though no cleaning was performed. For an isolated emitter with a hemispherical tip on a cylinder, β ' = 1 /( 5 r ) is a good approximation where r is the radius of curvature of the tip [30]. Using this approximation, the field enhancement factors β ' have been predicted and compared to the experimental
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Design of a multi walled carbon nanotube field emitter with micro vacuum gauge

Design of a multi walled carbon nanotube field emitter with micro vacuum gauge

Therefore, it is very important to monitor the vacuum level in a vacuum device in order to maintain satisfying field emission properties. To measure the inner vacuum of the device, the vacuum gauge should be integrated to the vacuum device without affecting the device. MWCNTs were used to fabricate the real time- monitoring vacuum gauge that satisfies these conditions. MWCNTs facilitate the fabrication of a microstructure and this microstructure was used to build the micro vacuum gauge that could be set up in the device. Here, we demonstrate a simple screen-printed MWCNT de- vice that combines the MWCNT field emission and MWCNT-based vacuum gauge for the measurement of the vacuum level. Also, the MWCNT vacuum gauge packaged with a vacuum device is used to measure the lifetime of the vacuum device.
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Fabrication, characterization and integration of carbon nanotube cathodes for field emission x-ray source

Fabrication, characterization and integration of carbon nanotube cathodes for field emission x-ray source

Resistance to temperature fluctuation is another characteristic that has made CNTs attractive as field emission emitters. The material is very stable even at high temperatures [13] because of the strong covalent bonding. They are physically inert to sputtering and chemically inert to poisoning [14]. It has been demonstrated that MWNTs can be heated up to 2000 K in vacuum and remain stable [13]. Figure 1.11 shows a comparison of the field emission properties of nano-tips of amorphous diamond and CNTs at various temperatures. The emission from the CNTs does not change with the increasing temperature. Metal emitters, however, are different. In metals, the resistance (R) increases with temperature which indicates that more heat (Q) is produced as higher currents (I) are drawn (Q = I 2 R) [13]. The combination of the high temperature and electric field result in the field-sharpening of the tip by surface diffusion. Overall, metal- based emitters are unstable due to temperature increases, local field, and current and emitter destruction. In contrast, the resistance of a nanotube decreases with temperature which limits I 2 R heat generation, and in fact its temperature varies sub-linearly with current [13]. CNTs do not suffer electric field induced sharpening, [14] making them very stable emitters.
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Studies on Mechanical Characteristics of Carbon Nanotubes (CNT) Reinforced with 6061 Aluminium Metal Matrix Composites Coated With Nickel

Studies on Mechanical Characteristics of Carbon Nanotubes (CNT) Reinforced with 6061 Aluminium Metal Matrix Composites Coated With Nickel

Aluminium alloy 2000, 6000 and 7000 series are used for fabrication of the automotive parts. MMC’s under study consist of matrix material of aluminium alloy. An advantage of using aluminium as matrix material is casting technology is well established, and most important it is light weight material. Aluminium alloy is associated with some disadvantages such as bonding is more challenging than steel, low strength than steel and price is 200% of that of steel. But with proper reinforcement and treatment the strength can be increased to required level. 6061Al is quite a popular choice as a matrix material to prepare MMC’s owing to its better formability characteristic.
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Synthesis and Field Emission Properties of Carbon Nanotube Films

Synthesis and Field Emission Properties of Carbon Nanotube Films

One of nano-building block candidates - carbon nanotubes (CNTs) have attracted a great deal of attention due to their unique structural, chemical, electronic, and mechanical properties. 1 Especially small diameter CNTs (i.e. single- and double-walled) ranging from 1-5 nm demonstrate either semiconducting or metallic properties governed by their chirality and diameter, 2 which opens a possibility of replacing traditional silicon with CNTs in microelectronics devices. The CNTs have not only exhibited great potential in nano-electronics, but also to nano-electro-mechanical systems (NEMS), 3 and for potential biology target application when functionalized. 4 Other significant applications of CNTs include electron field emission emitters 5 where carbon nanotube emitters are able to deliver a relatively high emission current (or current density), show extremely low threshold voltage, have demonstrated emission operation of > 5000 hours 6 and excellent chemical stability. 7
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A Parametric study of gas sensing response of ZnO nanostructures and carbon nanotubes

A Parametric study of gas sensing response of ZnO nanostructures and carbon nanotubes

semiconducting metal oxides are cheap, easily available and easy to synthesize as a result, these materials have been used extensively over the years for gas sensor fabrication [1,2,3,8,9,10]. However recent discovery of CNTs and their sensitivity to different analytes, lower operating temperatures, faster response times and shorter recovery times has attracted great interest for their potential use in gas sensors [15,16,18], but synthesis of good quality CNTs by Laser Ablation or Chemical Vapor Deposition methods, involves sophisticated tools and is limited at this time. Also the quality of commercially available CNTs varies from different manufacturers and different methods of synthesis, which makes in-house characterization necessary in order to understand the sensitivity with respect to its material properties. Table 1 compares the two materials for different factors. As both ZnO and CNTs have some advantages and disadvantages, it is difficult to choose the material for fabrication of gas sensors unless the application is specified.
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Study of Electronic Properties of III-Nitrides and Carbon Nanotubes by Electron Energy Distribution Analysis

Study of Electronic Properties of III-Nitrides and Carbon Nanotubes by Electron Energy Distribution Analysis

The wurtzite polytypes of GaN, AlN, and InN form a continuous alloy system whose direct band gaps range from 1.9 eV for InN, to 3.4 eV for GaN, to 6.2 eV for AlN. These wide band gaps make III-nitrides useful for fabrication of optical devices active at wavelengths ranging from the red well into the UV. Wider band gaps translate directly into higher breakdown fields, delaying the onset of impact ionization or avalanche breakdown. 21 Thus, AlN having the widest band gap of all the III-nitrides makes it the best material for high electric field transport experiments without reaching the onset of impact ionization. In this dissertation, we focused on studying the transport properties of AlN at high electric fields. Additional results from transport experiments in GaN are described in the Appendix of this dissertation. In the following sections, brief
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Three Separated Growth Sequences of Vertically-Aligned Carbon Nanotubes on Porous Silicon: Field Emission Applications

Three Separated Growth Sequences of Vertically-Aligned Carbon Nanotubes on Porous Silicon: Field Emission Applications

complete consumption of the carbon source. After the multilayer CNTs was synthesized onto the PSi substrate, both furnaces were permitted to cool to room temperature under a continuous Ar gas flow. FE scanning electron microscopy (FESEM; ZEISS 77 Supra 40VP) was used to examine the CNTs growth morphology. In addition, crystallinity of samples was characterized by micro-Raman spectroscopy with a laser of 514 nm (Horiba Jobin Yvon 79DU420A-OE-325).

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Synthesis of One-Dimensional And Two-Dimensional Carbon Based Nanomaterials

Synthesis of One-Dimensional And Two-Dimensional Carbon Based Nanomaterials

Continuous requirements of miniaturization and complex nanoscale devices have generated an increasing interest in developing novel nanomaterials with complicated structures. CNTs have drawn considerable attention due to their outstanding electrical and mechanical properties [1-4]. Furthermore, their complex spatial architecture has contributed to their potential applications in sensors, fuel cells, field emission devices, transistors, and logic circuits [5-9]. In order to integrate nanomaterials with different properties into functional systems, much attention has been focused on branched CNTs [10-12]. Up to now, many techniques have been employed to produce branched carbon nanotubes. Initially, Y-shape CNTs were synthesized by arc discharge [13] and alumina template [14, 15]. A high-intensity electron beam was used to join crossed CNTs [16]. Another approach was to attach catalyst particles to the grown CNTs during the CVD growth process to initialize and sustain branches formation [17, 18]. Recently, more complicated branched CNTs have been reported by using a pyrolysis method, in which gas flow fluctuation has been considered the key factor that influences the branch occurrence [19, 20]. These studies have presented valuable information about the synthesis process and opened new routes in finding novel properties of nanostructured carbon. However, these methods have the disadvantages of inconsistent repeatability and introduction of external templates or additional steps that make the process complex and difficult to control.
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CARBON NANOTUBES – AN OVERVIEW

CARBON NANOTUBES – AN OVERVIEW

Drug delivery is one of the rapidly growing medical field in which nano tube technology is applied. Systems that are in current use for drug delivery are dendrimers, polymers, and liposomes. Since, carbon nanotubes consists of effective structures that possess high drug loading capacities and good cell penetration properties, as these carbon nanotubes function with larger inner volume that can be used as the drug container and their ability to be readily taken up by the cell make these tube structures as potential sources of drug delivery [57]. Due of the tube structure of carbon nanotubes, they can be made with or without end caps and this quality of being made with-out end caps make the drug that exists inside carbon nano tube more accessible. But, carbon nanotube drug delivery systems, also give rise to some problems like the lack of solubility, clumping occurrences and half-life [58]. To overcome these problems is an essential aspect for further advancements in carbon nano tube technology. Methods to overcome include drug encapsulation which has shown to enhance water dispersibility, better bioavailability, and reduced toxicity. Encapsulation also provides a material storage application, protection and controlled release of the loaded molecules [59]. All these properties result in a better drug delivery basis from which further research and understanding could make advancements in carbon nano tube technology like increased water solubility, decreased toxicity, sustained half-life, increased cell penetration and uptake, all of these properties are currently novel but undeveloped [60].
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Field emission and stability

Field emission and stability

• The fabricated field emitters showed that the extension of a metal-coated silicon tip with a carbon nanotube enhances its field emission properties. The extraction voltage of the extended emitter is only 25 Volts compared to 200 Volts of the silicon tip, both at a tip sample distance of 200 nm. As predicted by the theory the narrow and long geometry will increase the field enhancement factor. • The distance between the tip and sample influences the stability of the field emission current. When the distance between the tip and sample is increased, the emission area of the emitter gets bigger. This means that electrons have the possibility to emit from a larger area at the apex of the tip. This increase in area, also increases the probability of adatoms influencing the emission current. This behavior is observed during measurements at two different distances, here the measurement with the largest distance have the highest frequency of fluctuations caused by the presence of adatoms. The influence of surface diffusion at the surface of the sample materials decreases when the distance to the tip increases.
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Study of carbon nanotubes structures and its properties for sensor applications

Study of carbon nanotubes structures and its properties for sensor applications

Carbon nanotubes (CNT) have attracted by many scientists worldwide. The small dimensions, strength and the extraordinary physical properties of these structures make them a very distinctive material with a whole range of potential applications. The nanotubes can be metallic or semiconducting depending on their structural parameters[1]. CNTs are expected to have a wide variety of interesting physical and chemical properties[2]. The uniqueness of nanotubes that makes them better than their competitors for specific applications[3]. The important applications are high-strength composites; energy storage and energy conversion devices; sensors; field emission displays and radiation sources; hydrogen storage media; and nanometer-sized semiconductor devices, probes, and interconnects. Some of these applications are now realized in products[4]. The mechanical properties of CNT, starting from the linear elastic parameters, nonlinear elastic instabilities and buckling, and the inelastic relaxation, yield strength and fracture mechanisms has been overviewed [5] The synthesis of massive arrays of monodispersed carbon nanotubes that are self-oriented on patterned porous silicon and plain silicon substrates is reported[6]. The interest in carbon nanotubes has been greatly stimulated by theoretical predictions that their electronic properties are strongly modulated by small structural variations[7] Analysis of the stress-strain curves for individual MWCNTs indicated that the Young's modulus E of the outermost layer varied from 270 to 950 gigapascals.
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Effect of Substrate Morphology on Growth and Field Emission Properties of Carbon Nanotube Films

Effect of Substrate Morphology on Growth and Field Emission Properties of Carbon Nanotube Films

Abstract Carbon nanotube (CNT) films were grown by microwave plasma-enhanced chemical vapor deposition process on four types of Si substrates: (i) mirror polished, (ii) catalyst patterned, (iii) mechanically polished having pits of varying size and shape, and (iv) electrochemically etched. Iron thin film was used as catalytic material and acetylene and ammonia as the precursors. Morphological and structural characteristics of the films were investigated by scanning and transmission electron microscopes, respectively. CNT films of different morphology such as vertically aligned, randomly oriented flowers, or honey- comb like, depending on the morphology of the Si sub- strates, were obtained. CNTs had sharp tip and bamboo-like internal structure irrespective of growth morphology of the films. Comparative field emission measurements showed that patterned CNT films and that with randomly oriented morphology had superior emission characteristics with threshold field as low as *2.0 V/lm. The defective (bam- boo-structure) structures of CNTs have been suggested for the enhanced emission performance of randomly oriented nanotube samples.
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A Review of Structures and Properties of Carbon Nanotubes

A Review of Structures and Properties of Carbon Nanotubes

Both theory and experiment show extraordinary structures and properties of carbon nanotubes. Thesmall dimensions, strength and the remarkable chemical and physical properties of these structures enablea broad range of promising applications. A SWNT can be metallic and semiconducting, dependent on its chirality. Semiconducting SWNTs have been used to fabricate transistors, memory and logic devices, and optoelectronic devices. SWNT nanoelectronics can be further used for chemical and biological sensors, optical and optoelectronic devices, energy storage, and filed emissions. However, it is currently not possible to selectively control the tube chirality or obtain either metallic or semiconducting SNWTs. These constraints in addition to problems of nanoscale contacts and interconnects stand in the way of large-scale fabrications and integration and applications of CNT electronics. A MWNT basically behaves like a metal or semimetal because of the dominating larger outermost tube. Therefore, MWNTs are suitable for nanoelectrodes, field emission, and energy storage applications. In these applications, the tube chirality control is not critical. But MWNTs allow incorporation of diverse defects, which significantly affect electrical and mechanic properties.
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Carbon nanotubes and other highly curved surfaces for field emission and field promoted ionisation

Carbon nanotubes and other highly curved surfaces for field emission and field promoted ionisation

In electrospray ionization a liquid sample is pushed through a small metal needle/capillary held at a high potential by atmospheric pressure. The liquid sample will normally contain the analyte of interest, as well as solvent, and for biological samples possibly aqueous buffer. The sample delivered to the tip of the electrospray capillary will experience a strong electric field. Ionisation of the sample occurs when charged species such as H + (created through the oxidation of water) or Na + , K + or Cl - (that originate from salts) stabilise by adding onto the sample. The field causes the charged sample to accumulate at the liquid suface at the end of the capillary tip. If the potential applied to the needle is positive, it is the positive ions that will accumulate towards the liquid surface due to charge repulsion. Any negative ions present in the sample will be attracted towards the walls of the capillary. At low potentials this charge accumulation causes the liquid meniscus to bulge outwards. Slightly larger potentials can cause the meniscus to adopt a conical shape that reflects a perfect balance between the electrostatic force created by the accumlation of charged particles and the surface tension of the liquid. This meniscus is normally
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