Improved Field Emission Performance Research Articles

Improved field emission performance of carbon nanotube by introducing copper metallic particles

To improve the field emission performance of carbon nanotubes (CNTs), a simple and low-cost method was adopted in this article. We introduced copper particles for decorating the CNTs so as to form copper particle-CNT composites. The composites were fabricated by electrophoretic deposition technique which produced copper metallic particles localized on the outer wall of CNTs and deposited them onto indium tin oxide (ITO) electrode. The results showed that the conductivity increased from 10-5 to 4 × 10-5 S while the turn-on field was reduced from 3.4 to 2.2 V/μm. Moreover, the field emission current tended to be undiminished after continuous emission for 24 h. The reasons were summarized that introducing copper metallic particles to decorate CNTs could increase the surface roughness of the CNTs which was beneficial to field emission, restrain field emission current from saturating when the applied electric field was above the critical field. In addition, it could also improve the electrical contact by increasing the contact area between CNT and ITO electrode that was beneficial to the electron transport and avoided instable electron emission caused by thermal injury of CNTs.

SU‐C‐301‐02: Enhanced Field Emission from Clustered TiO2 Nanotube Arrays for a High Flux X‐Ray Source

Purpose: Titanium dioxide (TiO2) nanotubes grown by electrochemical oxidation can be used as a cold cathode X‐ray source. They can potentially address some of the current limitations of carbon nanotubes. As an oxide, TiO2 is not affected by residual oxygen present in the tube, which otherwise can severely degrade the deviceˈs performance. Furthermore, TiO2 nanotubes have a good electrical contact with the conductive Ti sheet, which eliminates the heating effects. One important parameter for high performance X‐ray tubes is the electron field emission current. The current density is strongly dependent on the nanotubeˈs density due to electric field screening effects. The goal of this work was to develop a method for producing low density nanotube arrays and to investigate field emission properties. Methods: TiO2 nanotubes were grown via electrochemical oxidation of Ti sheets at 40 V using ethylene glycol, glycerol solvents and 2% NH4F acid. The field emission measurements were performed in a vacuum chamber with a base pressure of 6.6×10–5 Pa in a voltage range of 0–1000 V. A copper grid with 30 m diameter wire and 70% open area was used as an anode. Results: The samples grown in ethylene glycol + 2% NH4F revealed a clustered pattern with 1–2 μm spacing, unlike the regular pattern of dense, highly‐aligned tubular structure. Clustered nanotube samples had a significant improvement in field emission performance with reduced threshold voltage (>2 times), and increased field enhancement factor (>5 times) and current density (6 times), as compared to standard nanotube samples. This improvement is thought to be due to the reduction in electric field screening effects. Conclusions: Our results show the significant enhancement in field emission performance of clustered TiO2 nanotube arrays when compared to the standard highly‐aligned nanotubes. This implies possibility for further increase the X‐ray flux from the emission source.

Improvement in Field Electron Emission Performance of Natural-Precursor-Grown Carbon Nanofibers by Thermal Annealing in Argon Atmosphere

Carbon nanofibers (CNFs) were grown on a graphite substrate by the spray pyrolysis of a botanical hydrocarbon, turpentine oil, using ferrocene as the catalyst and sulfur as the promoter. The as-grown CNFs were annealed at 450 °C for 30 min in an air, and then at 1800 °C in an argon atmosphere for 2 h. The annealed CNFs have better degree of crystallinity and reduced number of defects compared with the as-grown CNFs confirmed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and thermogravimetric analysis. The as-grown and annealed CNFs were found to be effective electron emitters with turn-on fields of 3.2 and 2.1 V/µm, respectively. The improvement in field emission (FE) performance can be explained in terms of the higher degree of graphitization of the CNFs after thermal annealing. This improved FE performance of the natural precursor grown CNFs was comparable to the FE performance level attainable for the conventional carbon nanomaterials grown using petroleum products. Thus, it was considered that the use of petroleum products could be avoidable for CNF growth and that CNFs grown using ecofriendly materials are very promising for the application in future field emission displays (FEDs).

Improvement in Field Electron Emission Performance of Natural-Precursor-Grown Carbon Nanofibers by Thermal Annealing in Argon Atmosphere

Carbon nanofibers (CNFs) were grown on a graphite substrate by the spray pyrolysis of a botanical hydrocarbon, turpentine oil, using ferrocene as the catalyst and sulfur as the promoter. The as-grown CNFs were annealed at 450 °C for 30 min in an air, and then at 1800 °C in an argon atmosphere for 2 h. The annealed CNFs have better degree of crystallinity and reduced number of defects compared with the as-grown CNFs confirmed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and thermogravimetric analysis. The as-grown and annealed CNFs were found to be effective electron emitters with turn-on fields of 3.2 and 2.1 V/µm, respectively. The improvement in field emission (FE) performance can be explained in terms of the higher degree of graphitization of the CNFs after thermal annealing. This improved FE performance of the natural precursor grown CNFs was comparable to the FE performance level attainable for the conventional carbon nanomaterials grown using petroleum products. Thus, it was considered that the use of petroleum products could be avoidable for CNF growth and that CNFs grown using ecofriendly materials are very promising for the application in future field emission displays (FEDs).

Improvement of field emission performance on nitrogen ion implanted ultrananocrystalline diamond films through visualization of structure modifications

The relationship between the electron field emission properties and structure of ultra-nanocrystalline diamond (UNCD) films implanted by nitrogen ions or carbon ions was investigated. The electron field emission properties of nitrogen-implanted UNCD films and carbon-implanted UNCD films were pronouncedly improved with respect to those of as-grown UNCD films, that is, the turn-on field decreased from 23.2 V/μm to 12.5 V/μm and the electron field emission current density increased from 10E−5 mA/cm 2 to 1 × 10E−2 mA/cm 2. The formation of a graphitic phase in the nitrogen-implanted UNCD films was demonstrated by Raman microscopy and cross-sectional high-resolution transmission electron microscopy. The possible mechanism is presumed to be that the nitrogen ion irradiation induces the structure modification (converting sp 3 -bonded carbons into sp 2 -bonded ones) in UNCD films.

Fabrication and field emission performance of arrays of vacuum microdiodes containing CuO nanowire emitters grown directly on glass without a catalyst

Arrays of vacuum microelectronic sources are fabricated on a glass substrate using cupric oxide (CuO) nanowire emitters. The arrays of electron sources possess a microdiode structure, which can effectively induce field emission and control the delivery of emitted electrons to the anode in a triode-type device operation. A technique for precisely growing CuO nanowires at the centre of microcavities in an array without using a catalyst and at temperatures as low as 400°C is presented. Such a simplified fabrication procedure results in improved field emission performance from the array compared with previous vacuum microelectronic devices. Typical prototype devices have turn-on gate voltages as low as 169 V to give emission current densities of 10 μA/cm2 at the anode. The ratio of anode current to cathode current reaches ∼0.85, and the maximum change in emission current density per volt is 1 μA/cm2. Electron emission from the arrays is stable and reproducible under either pulsed or direct current fields. These characteristics indicate that microgate-controlled CuO nanowire emitters may find application in practical devices.

Zinc sulfide nanowire arrays on silicon wafers for field emitters

Wurtzite structured zinc sulfide (ZnS) nanowire arrays are synthesized on silicon(111) wafers by a facile evaporation–condensation approach. These ZnS nanowirearrays possess predominant field emission properties with a low turn-on field of 2.9 V µm−1, a low thresholdfield of 4.25 V µm−1, a high field-enhancement factor (over 2700), and a high stability with a low fluctuation (∼0.8%). The improved field emission performance of these ZnS nanowire arrays is attributed totheir specific crystallographic feature—array structures with nanotips and high singlecrystallinity. These results suggest that such ZnS nanowire arrays can be used as buildingblocks for field emitters.

Polymer-nanotube composite mats with improved field emission performance and stability

The results of electron field emission from single walled carbon nanotubes (SWCNTs) mats deposited on different composite films of SWCNTs and poly(3-octylthiophene) (P3OT) semiconducting polymer are presented. Three different structures were tested: (a) dense and sparse SWCNT mats on n+ -Si; (b) SWCNT mats on composite films with different SWCNT-P3OT ratios; (c) composite films with different SWCNT-P3OT ratios on n+ -Si. The experiments show that there is a critical SWCNT-P3OT concentration in which the field emission stability of SWCNT mats is remarkably improved with a small reduction in the emission threshold compared to the optimum pristine SWCNT film. The contribution of the composite film morphology as well as the role of polymer-nanotube interaction on the emission performance are evaluated. The physical mechanism behind the stability of composite field emitters is also discussed.

Effects of welding head on the carbon nanotube field emission in ultrasonic nanowelding

Ultrasonic nanowelding technique was used to improve the field emission properties of carbon nanotube (CNT) cathodes. Two kinds of welding heads were used and the effects of the head on the emission properties were studied. The results show that cathodes welded by Al 2O 3 flat head demonstrate excellent field emission properties with high emission current density and good current stability. The improved field emission performance is attributed to the reliable and low resistance contact between CNTs and metal substrates. Cathodes welded by steel matrix head show a lower turn-on electric field due to the protruding CNTs at the edge of the welded pits.

Vertically aligned carbon nanotubes from natural precursors by spray pyrolysis method and their field electron emission properties

Vertically aligned carbon nanotubes have been synthesized from botanical hydrocarbons: Turpentine oil and Eucalyptus oil on Si(100) substrate using Fe catalyst by simple spray pyrolysis method at 700°C and at atmospheric pressure. The as-grown carbon nanotubes were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), thermogravimetric analysis (TGA), differential thermal analysis (DTA), and Raman spectroscopy. It was observed that nanotubes grown from turpentine oil have better degree of graphitization and field emission performance than eucalyptus oil grown carbon nanotubes. The turpentine oil and eucalyptus oil grown carbon nanotubes indicated that the turn-on field of about 1.7 and 1.93 V/μm, respectively, at 10 μA/cm2. The threshold field was observed to be about 2.13 and 2.9 V/μm at 1 mA/cm2 of nanotubes grown from turpentine oil and eucalyptus oil respectively. Moreover, turpentine oil grown carbon nanotubes show higher current density in relative to eucalyptus oil grown carbon nanotubes. The maximum current density of 15.3 mA/cm2 was obtained for ∼3 V/μm corresponding to the nanotubes grown from turpentine oil. The improved field emission performance was attributed to the enhanced crystallinity, fewer defects, and greater length of turpentine oil grown carbon nanotubes.

Versatile transfer of aligned carbon nanotubes with polydimethylsiloxane as theintermediate

A simple technique to transfer aligned multi-walled carbon nanotubes (MWCNTs) isdemonstrated in this work. With polydimethylsiloxane (PDMS) as the transfer medium,as-grown or patterned MWCNT arrays are directly transferred onto a wide variety ofPt-coated substrates such as glossy paper, cloth, polymers, glass slides, and metal foils atlow temperatures. The surface of the transferred CNTs is cleaner with better alignment,compared with the as-grown one. Furthermore, the transferred CNTs show strong adhesionand good electric contact with the target substrates. A maximal current density of∼104 A cm−2 has been achieved from the CNT interconnects prepared with this technique.Because of the lower density and open-ended structures, improved field emissionperformance has been obtained from CNTs transferred on polymers, based onwhich flexible emitter devices can be fabricated. In addition, the surface oftransferred CNTs becomes more hydrophilic, with an averaged contact angle of93.4 ± 5.8°, in contrast to the super-hydrophobic as-grown CNT surface (contact angle151.6 ± 5.5°). With versatile properties and flexible applications, the technique provides a simple andcost-effective way towards future nanodevices based on CNTs.

XPS Investigation and Field Emission Property of the Ar Plasma Processed Carbon Nanotube Films

Carbon nanotube films were fabricated by the catalytic CVD method. Plasma processed time effects on the field emission property were studied. The atomic structure was observed by using X-ray photoelectron spectroscopy (XPS). The surface composition changes were observed on the plasma processed CNT films. The O1s/C1s signal ratio and the Fls/Cls signal ratio changed from 1.1 % to 24.65 % and from 0 % to 3.1 % with plasma process time, respectively. We could guess it from these results that the Ar plasma process could change the surface composition effectively. In the case of the original-CNT film, no carbon shift was observed. In the case of the Ar plasma processed CNT films, however the oxygen related carbon shifts were observed. This oxygen related carbon shift at higher binding energy implies the increment of amount of the oxygen. It's possible that the increment of these bonds between carbon and oxygen results in the improvement of field emission performance.

Improved Crystallinity of Double-Walled Carbon Nanotubes after a High-Temperature Thermal Annealing and Their Enhanced Field Emission Properties

High-purity double-walled carbon nanotubes (DWCNTs) were synthesized by catalytic decomposition of CH4 over Fe−Mo/MgO catalyst at 900 °C. After purification, the DWCNTs were annealed at 1300 °C in vacuum condition of 10-5 Torr. The DWCNTs before and after the high-temperature thermal annealing were characterized using scanning electron microscopy, high-resolution transmission electron microscopy, Raman spectroscopy, and thermogravimetric analysis. It was observed that the annealed DWCNTs had enhanced crystallinity and reduced defects. In addition, the DWCNTs showed better field emission performance after high-temperature thermal annealing. The annealed DWCNTs indicated the turn-on field of about 1.16 V/μm at 0.1 μA/cm2 and the threshold field of about 2.12 V/μm at 1.0 mA/cm2. Moreover, the annealed DWCNTs exhibited better emission stability compared with the nonannealed DWCNTs. Such a remarkable improvement of field emission performance was attributed to the enhanced crystallinity and reduced defects of t...

Electronic structure and field emission properties of in situ potassium-doped single-walled carbon nanotubes

In situ potassium (K)-doped single-walled carbon nanotube (SWCNT) was synthesized using a hydrogen arc-discharge method. X-ray photoelectron spectroscopy analysis showed that the K-doped SWCNTs consisted of 0.12% K mass composition. The K-doped SWCNTs showed the lower turn-on electric field of 2.0V∕μm at a current density of 10−9A∕cm2 and the higher emission current density of 3.0mA∕cm2 at an applied field of 4.6V∕μm compared with the undoped SWCNTs. The improved field emission performance of K-doped SWCNTs was mainly attributed to the decreased work function and the increased density of state near the Fermi energy.