Improved Field Emission Properties Research Articles

Influence of high-energy electron irradiation on field emission properties of multi-walled carbon nanotubes (MWCNTs) films

The effect of very high energy electron beam irradiation on the field emission characteristics of multi-walled carbon nanotubes (MWCNTs) has been investigated. The MWCNTs films deposited on silicon (Si) substrates were irradiated with 6MeV electron beam at different fluence of 1×1015, 2×1015 and 3×1015electrons/cm2. The irradiated films were characterized using scanning electron microscope (SEM) and micro-Raman spectrometer. The SEM analysis clearly revealed a change in surface morphology of the films upon irradiation. The Raman spectra of the irradiated films show structural damage caused by the interaction of high-energy electrons. The field emission studies were carried out in a planar diode configuration at the base pressure of ∼1×10−8mbar. The values of the threshold field, required to draw an emission current density of ∼1μA/cm2, are found to be ∼0.52, 1.9, 1.3 and 0.8V/μm for untreated, irradiated with fluence of 1×1015, 2×1015 and 3×1015electrons/cm2. The irradiated films exhibit better emission current stability as compared to the untreated film. The improved field emission properties of the irradiated films have been attributed to the structural damage as revealed from the Raman studies.

Preparation of graphene–polyaniline composites by simple chemical procedure and its improved field emission properties

Graphene–polyaniline composites have been synthesized using simple chemical procedure in two different ways (i) by mixing of the pre-synthesized graphene and polyaniline nanofibers and (ii) by in situ polymerization in presence of graphite oxide followed by further reduction. Detailed optical spectroscopic studies of the synthesized composites along with the pristine polyaniline nanofibers were performed by Fourier transformed infrared spectroscopy and UV–vis spectroscopy. The structural and morphological characterizations were performed by X-ray diffraction, transmission electron microscope measurements and field emission scanning electron microscope measurements, respectively while the chemical characters were studied by X-ray photoelectron spectroscopic measurement. The graphene–polyaniline composite retained the photoluminescence property of the as synthesized polyaniline nanofibers. The electron field emission property of the composite showed marked improvement compared to pristine polyaniline fibers with a turn-on field as low as 3.91 V/μm at a current density of 1 μA/cm 2. The field enhancement factor was found to be 7012 which is much higher for the case of a polymer based composite.

First-Principles Study of Field Emission Properties of Graphene-ZnO Nanocomposite

The electronic structures and field emission properties of hybrid graphene-ZnO are investigated by density functional theory. The binding energies, energy levels, and the corresponding local electron density distributions of neutral and charged graphene-ZnO in electric fields are analyzed, which show that the electronic structures of graphene-ZnO are modified significantly by the applied electric fields. The reduction of the energy gaps and the change of the electron density distributions of the states in the vicinity of the Fermi level are observed. The work functions of graphene-ZnO decrease linearly with increasing electric fields, which indicate the enhancement of field emission properties. In addition, the ionization potentials decrease drastically with increasing electric fields, which further indicate the improvement of field emission properties of graphene-ZnO. The Hirshfeld charges and the electrostatic potential derived charges are also explored, and it is found that the electron accumulation be...

Field emission arrays fabricated utilizing conjugated ZnO quantum dot/carbon nanotube hybrid nanocomposite

In situ growth of ZnO quantum dots (QDs) on the surface of multiwalled carbon nanotube (MWCNTs) was realized via a mild solution-process method, and their application in field emission device was demonstrated. High resolution transmission electron microscopy observation revealed the conjugation between ZnO QDs and MWCNTs. Field emission arrays based on ZnO QD/MWCNT hybrid nanocomposite exhibited significantly improved luminance intensity and emitting dot density when compared with the MWCNT-only arrays. It is proposed that the introduction of the ZnO QDs on the sidewall of MWCNTs can enhance the tunnelling probability, and result in the improved field emission property for the hybrid emitters.

Improved field emission property of graphene paper by plasma treatment

Lateral orientation and aggregation of the graphene sheets limited field enhancement of graphene paper (GP). To improve the field enhancement of GP, argon plasma treatment was induced to destroy the aggregation and cause formation of surface protrusions. After Ar plasma treatment, turn-on field and threshold field of GP were reduced from 2.3 V/μm to 1.6 V/μm and 4.4 V/μm to 3.0 V/μm, respectively. The enhancement was attributed to the protrusions. Scanning electron microscopy and hydrophobicity had been used to prove the morphology change after plasma treatment.

Thermal desorption and its effects on field emission properties of carbon nanowalls

The thermal desorption behaviors of highly graphitized carbon nanowalls (CNWs) and their effects on CNW field emission properties have been investigated. The hydrocarbon materials are identified to be the main contents adsorbed on CNWs, and the absorption of H 2O and O 2, to a large degree, associates with the surface hydrocarbon. These major species desorb from CNW surface at 350–400 °C, and after desorption the CNWs present distinctly improved field emission properties.

Improved field emission properties of CdS deposited single walled carbon nanotube emitter

A film of shaped CdS nanoparticle deposited single walled carbon nanotubes (CdS-SCWNTs) on silicon wafer is successfully fabricated by the method of layer-by-layer deposition cycle. The field emission (FE) properties of CdS-SWCNTs film are investigated for the first time. The film of CdS-SWCNTs exhibits better FE properties, a lower turn-on field, and a higher field enhancement factor than that of the film of pristine SWCNTs, for which the physical and chemical properties of the CdS nanoparticle have played an important role. As a II-VI semiconductor compound, CdS has attracted considerable interest in optoelectronic application because of its relatively low electron affinity, high chemical inertness, and sputter resistance.

CVD growth of secondary carbon nanotubes and its effect on field electron emission

Secondary carbon nanotubes (CNTs) were grown on primary ones by simply changing the methane concentration. No additional catalyst was used throughout the whole deposition process. The CNT growth was carried out using hot filament chemical vapor deposition in a gas mixture of methane and hydrogen. The structure and surface morphology of the deposited CNTs were studied and the field emission properties of the CNTs were tested. It was found that synthesizing primary CNTs at extremely low methane concentration is the key for the secondary growth without additional catalyst. The CNT samples grown with secondary nanotubes exhibited improved field emission properties.

Field emission properties of composite nano-Au/DLC films prepared by CVD technique

Nanocrystalline gold incorporated diamond-like carbon (nano-Au/DLC) films were deposited by capacitively coupled plasma (CCP) r.f. chemical vapour deposition (CVD) technique. Gold content in the DLC matrix was controlled by the amount of argon in the argon + methane mixture in the plasma. Field emission properties of these films were studied critically. Bonding environment (sp 2/sp 3 ratio) in these films was obtained from Raman measurements. Modification of the surface with the incorporation of gold nanocrystallites and associated modulation of sp 2/sp 3 ratio in the films culminated in improved field emission properties. Fowler–Nordheim model was used to ascertain the work function ( ϕ) which varied between 19 and 64 meV. The field factor ( β) varied between 172 and 1050.

Three-dimensional carbon nanowall field emission arrays

This letter reports on the fabrication of regular arrays of three dimensional graphitic structures, by growing carbon nanowalls on forests of conical Si microspikes. The high field enhancement achieved by this hierarchical growth process indicates a potential for electron emission applications. Experiments show that the field emission performance and long-term stability of the structures is by far superior to that of planar carbon nanowall mats and comparable to that reported for optimized carbon nanotube based emitters. The improved field emission properties of the fabricated arrays are attributed to the dual micro and nanomorphology of the emitters, involving a two-scale enhancement process.

Optimization of a Tip with Carbon Nanofibers for Improved Field Emission Properties

To obtain a good field emission (FE) performance, the shape of a Pd/W tip substrate with carbon nanofibers is optimized. We succeeded in maximizing FE current by adjusting the apex angle of the tip. When the apex angle of the tip substrate is nearly 50°, a high FE efficiency and a narrow divergence emission angle for the convergence of the electron beam are obtained, which can be potentially used for the cathode of electrical devices with a low power consumption and a high FE efficiency.

Controlled fabrication of Si nanostructures by high vacuum electron beam annealing

Silicon nanostructures, called Si nanowhiskers, have been successfully synthesized on Si(1 0 0) substrate by high vacuum electron beam annealing (EBA). Detailed analysis of the Si nanowhisker morphology depending on annealing temperature, duration and the temperature gradients applied in the annealing cycle is presented. A correlation was found between the variation in annealing temperature and the nanowhisker height and density. Annealing at 935 °C for 0 s, the density of nanowhiskers is about 0.2 μm −2 with average height of 2.4 nm grow on a surface area of 5×5 μm, whereas more than 500 nanowhiskers (density up to 28 μm −2) with an important average height of 4.6 nm for field emission applications grow on the same surface area for a sample annealed at 970 °C for 0 s. At a cooling rate of −50 °C s −1 during the annealing cycle, 10–12 nanowhiskers grew on a surface area of 5×5 μm, whereas close to 500 nanowhiskers grew on the same surface area for samples annealed at the cooling rate of −5 °C s −1. An exponential dependence between the density of Si nanowhiskers and the cooling rate has been found. At 950 °C, the average height of Si nanowhiskers increased from 4.0 to 6.3 nm with an increase of annealing duration from 10 to 180 s. A linear dependence exists between the average height of Si nanowhiskers and annealing duration. Selected results are presented showing the possibility of controlling the density and the height of Si nanowhiskers for improved field emission properties by applying different annealing temperatures, durations and cooling rates.

Improving field emission properties of GaN nanowires by oxide coating

We compared the field emission properties of the following four types of nanowires: GaN nanowire, Ga2O3 nanowire, GaN nanowire with Ga2O3 coating, and Ga2O3 nanowire with GaN coating. The turn-on field values for the GaN, Ga2O3, GaN/Ga2O3, and Ga2O3/GaN nanowires are 4.3, 6.2, 4.7, and 2.6 V/μm, respectively. It has been found that the oxide coatings effectively improve the field emission capability of GaN nanowires, while the nitride coatings depress electron emission of Ga2O3 nanowires. The corresponding Fowler–Nordheim analysis revealed that the field emission improvement is attributed to the electron accumulation on the coated oxide particles and the interfacial electron redistribution in the nanoscale hetero-structure which results in the shift of Fermi level and the changes of work functions.

Enhanced Field Emission from Argon Plasma-Treated Ultra-sharp α-Fe2O3Nanoflakes

Hematite nanoflakes have been synthesized by a simple heat oxide method and further treated by Argon plasmas. The effects of Argon plasma on the morphology and crystal structures of nanoflakes were investigated. Significant enhancement of field-induced electron emission from the plasma-treated nanoflakes was observed. The transmission electron microscopy investigation shows that the plasma treatment effectively removes amorphous coating and creates plenty of sub-tips at the surface of the nanoflakes, which are believed to contribute the enhancement of emission. This work suggests that plasma treatment technique could be a direct means to improve field-emission properties of nanostructures.

Chemical modification of carbon nanotube for improvement of field emission property

In the present work, chemical modification of carbon nanotube was proposed for improvement of field emission property. Multi-wall carbon nanotubes (MWCNTs) were grown vertically on silicon substrate using catalytic chemical vapor deposition. Tips of grown MWCNTs were chemically modified using oxygen plasma, nitric acid, and hydrofluoric acid. Surface state and morphology of the chemically modified CNTs were investigated. CNT tips were opened and defects working as trap sites were generated on the CNT surface by the chemical modification process leading to improvement of field emission property. We suggest that two main factors determining the field enhancement factor are geometric factor and surface state of the CNT tips.

Improved field emission properties of double-walled carbon nanotubes decorated with Ru nanoparticles

The field emission properties of double-walled carbon nanotubes (DWCNTs) were remarkably improved by decorating their surface with ruthenium (Ru) metal nanoparticles. The Ru nanoparticles were attached effectively on the surface of DWCNTs via a chemical procedure. The Ru-decorated DWCNTs showed lower turn-on voltage, higher emission current density, and improved emission uniformity compared with pristine DWCNTs. The effect of Ru nanoparticles on the work function and density of states was evaluated by the first-principles calculation. The enhanced field emission properties of Ru-DWCNTs were mainly attributed to the Ru nanoparticles which increased the field enhancement factor and the density of emission sites. Our results indicate that the Ru-decorated DWCNTs can be used as an effective field emitter for various field emission devices.

一种新颖改善印刷碳纳米管薄膜的场发射特性

A novel post-treatment method, including hard hairbrush and electrical treatment, is performed intentionally to improve the field emission capability and stability of screen-printed carbon nanotubes (CNTs). Compared with untreated films, the field emission properties of the treated ones are greatly enhanced. Scanning electron microscopy (SEM) and Raman spectrum studies reveal that field emission properties are enhanced by two factors. Firstly, the improved field emission properties of CNT films can be attributed to the more active CNT surface by removing the organic material cover on the CNTs. Secondly, the generation of a high density of structural defects and the lower resistance contact to the topside CNT emitters after treatment are all helpful to improving the field emission properties of the treated CNTs.

Improved field emission properties from polycrystalline indium oxide-coated single-walled carbon nanotubes

The field emission (FE) characteristics of indium oxide (In2O3)-coated single-walled carbon nanotubes (SWCNTs) were studied. Scanning electron microscopy, x-ray diffractometer, and UV/visible spectroscopy confirmed that In2O3 exists as a polycrystalline cubic bixbyite structure on the surface of SWCNTs. The turn-on field of pristine SWCNTs decreased from 3.82to3.27V∕μm for In2O3-coated SWCNTs with optimal coating thickness. The maximum emission current density reached 3.5mA∕cm2, five times higher than that of pristine SWCNTs (0.68mA∕cm2) at an electric field of 7V∕μm. To explain the higher FE current density of In2O3-coated SWCNTs, Fowler–Nordheim plots were used with some assumptions.

Field emitter density control effect on emission current density by Ag–Cu alloy coating on carbon nanotubes

We have investigated the morphological evolution and improvement in field emission properties of carbon nanotube (CNT) emitters coated with an Ag–Cu alloy (ACa). Vertically aligned multiwalled CNTs (MWCNTs) were synthesized by direct current-plasma enhanced chemical vapor deposition. The MWCNTs were then coated with ACa by dc-magnetron sputtering and then annealed. Scanning electron microscopy revealed an increase in the size of the ACa droplets on the CNTs after thermal annealing, and a decrease in the emitter density with increasing deposition time. The emitter density was controlled by the amount of ACa with high surface tension and annealing. A lower turn-on voltage (1.18 V/μm) and higher emission current density of 588.9 μA/cm2 at 5.0 V/μm were achieved from the sample containing ACa droplets with an average radius of 500 nm.

Field Emission Properties of Single-Walled Carbon Nanotubes with a Variety of Emitter Morphologies

Field emission properties of single-walled carbon nanotubes (SWCNTs), which were prepared through alcohol catalytic chemical vapor deposition for 10–60 s, were characterized in a diode configuration. Protrusive bundles at the top surface of samples act selectively as emission sites. The number of emission sites was controlled by emitter morphologies combined with texturing of Si substrates. SWCNTs grown on a textured Si substrate exhibited a turn-on field as low as 2.4 V/µm at a field emission current density of 1 µA/cm2. Uniform spatial luminescence (0.5 cm2) from the rear surface of the anode was revealed for SWCNTs prepared on the textured Si substrate. Deterioration of field emission properties through repetitive measurements was reduced for the textured samples in comparison with vertically aligned SWCNTs and a random network of SWCNTs prepared on flat Si substrates. Emitter morphology resulting in improved field emission properties is a crucial factor for the fabrication of SWCNT-electron sources. Morphologically controlled SWCNTs with promising emitter performance are expected to be practical electron sources.