Increase In Field Enhancement Factor Research Articles

Non-crystallization and enhancement of field emission of cupric oxide nanowires induced by low-energy Ar ion bombardment

The effect of low energy Ar ion bombardment on the structure and field emission properties of CuO nanowires was studied. The morphology and structure were characterized by scanning electron microscopy and high resolution transmission electron microscopy. Non-crystallization of the nanowire was found after bombardment, which was due to the diffusion of the defects induced by knock-on ions. The work function of nanowires decreased after bombardment which was attributed to the preferential sputtering of oxygen. Field emission measurements showed that after bombardment with different energy the turn-on field decreased first and then increased with increasing ion energy. The lowest turn-on field was obtained with the optimal ion energy of 215eV. The typical turn-on fields of the as-grown samples and samples after Ar ion bombardment with energy of 215eV were about 6.5V/μm and 5.25V/μm, respectively. The lowered field emission turn-on field was attributed to the increase of field enhancement factor and decrease of work function.

Enhanced field emission from lanthanum hexaboride coated multiwalled carbon nanotubes: Correlation with physical properties

Detailed results from field emission studies of lanthanum hexaboride (LaB6) coated multiwalled carbon nanotube (MWCNT) films, pristine LaB6 films, and pristine MWCNT films are reported. The films have been synthesized by a combination of chemical and physical deposition processes. An impressive increase in field enhancement factor and temporal stability as well as a reduction in turn-on field and threshold field are observed in LaB6-coated MWCNTs compared to pristine MWCNT and pristine LaB6 films. Surface morphology of the films has been examined by scanning electron microscopy. Introduction of LaB6 nanoparticles on the outer walls of CNTs LaB6-coated MWCNTs films is confirmed by transmission electron microscopy. The presence of LaB6 was confirmed by X-ray photoelectron spectroscopy results and further validated by the Raman spectra. Raman spectroscopy also shows 67% increase in defect concentration in MWCNTs upon coating with LaB6 and an upshift in the 2D band that could be attributed to p-type doping. Ultraviolet photoelectron spectroscopy studies reveal a reduction in the work function of LaB6-coated MWCNT with respect to its pristine counterpart. The enhanced field emission properties in LaB6-coated MWCNT films are correlated with a change in microstructure and work function.

Field emission enhancement of polypyrrole due to band bending induced tunnelling in polypyrrole-carbon nanotubes nanocomposite

Polypyrrole–multiwalled carbon nanotubes (PPy–MWCNT) nanocomposites with high field emission characteristics have been fabricated by a very simple and effective in situ chemical polymerization technique that bypasses the need of de-agglomerating the MWCNT. Based on structural characterization, we have proposed formation of a three tier structure of PPy–MWCNTs composite with granular PPy on the top. Field emission studies, explained on the basis of band bending at the PPy–MWCNT interface, show drastic increase of field enhancement factor (∼4664) and low turn on field (1.7V/μm), opening new possibilities of improvement of PPy/PPy–MWCNT composites.

Local electron field emission study of two-dimensional carbon

A systematic field-emission study has been carried out on different types of two-dimensional carbons in ultrahigh vacuum with the cathode-anode distance ranging from near-contact to about 124 nm. An analytical model has been developed to explain the increase of field enhancement factor with the cathode-anode distance. Good agreement has been achieved between the calculation results and experimental data, including those reported in literature. The work provides useful insights into the characteristics of field emission from two-dimensional carbon.

Field Emission from Nanocrystalline Diamond/Carbon Nanowall Composite Films Deposited on Scratched Substrates

ABSTRACTWe report the deposition and field emission properties of nanostructured composites consisting of carbon nanowalls (CNWs) and nanocrystalline diamond films by introducing two kinds of substrate scratching pretreatment, i.e., undulation and ultrasonic vibration. With increasing duration of scratching pretreatment, the morphology of the deposits changes from simple CNWs to a film/CNW composite and lastly to CNWs on a film, and then the space between the walls is increased. The emission turn-on field is reduced from 2.1 V/μm for simple CNWs to around 1.2 V/μm for the composite films, accompanied by an increase in field enhancement factor. The results indicate that electric field screening between the walls is successfully suppressed by widening of the wall spacing.

Field emission characteristics of CuO nanowires by hydrogen plasma treatment

CuO nanowires were formed on copper-coated silicon substrates by a wet chemical process, immersing them in a hot alkaline solution. The effect of hydrogen plasma treatment on the field emission characteristics of the CuO nanowires was investigated. The results showed that hydrogen plasma treatment enhanced the field emission characteristics of the CuO nanowires showing a decrease in turn-on voltage as well as an increase of field enhancement factor. It is believed that hydrogen plasma treatment plays an important role in the improvement of field emission characteristics of CuO emitters.

Thin Multiwall Carbon Nanotube Field Emitters with Microchannel Plate for High Current Emission

ABSTRACTWe report a method to amplify the electron current of carbon nanotube field emitter cathode using an electron multiplier and synthesis of thin multiwall carbon nanotubes by thermal chemical vapor deposition. A commercial microchannel plate which is an array of microscopic electron multipliers was used for this purpose. A microchannel plate placed between the cathode and anode amplified the current and also acted as protection shield for nanotubes during vacuum arcing. The turn-on field was approximately 1 V/µm for both cases, but current obtained was 3 times higher and the field was also lower. The increase in current is attributed to the electron multiplication, and to the increase in field enhancement factor from 9296 to 12815 (37%) with microchannel plate. The thin multiwall carbon nanotubes were synthesized using Mo/Fe catalyst solution. The inner and outer wall diameters of the nanotubes were in the range of 2.5-5 nm and 7-15 nm respectively, determined by Raman spectroscopy and transmission electron microscopy. The nanotubes had excellent field emission property which is attributed to their thin wall diameters ∼10 nm, high aspect ratio of 1500 and the high field enhancement factor of 9296. The emission current was stable with an average fluctuation of 2%.

Growth and field emission properties of carbon nanotubes on rapid thermal annealed Ni catalyst using PECVD

The effect of rapid thermal annealing (RTA) treatment on the growth characteristics of carbon nanotubes (CNTs) was investigated. We observed that Ni catalyst film was agglomerated by RTA treatment, resulting in the formation of Ni nanoparticles. The well-aligned CNTs were grown from the Ni nanoparticles by plasma-enhanced chemical vapor deposition (PECVD). It is shown that the size and distribution of the nanoparticles depend mainly on the annealing temperature and initial thickness of the catalytic metal layer. Also, it was found that the CNTs grown through RTA treatment had the more improved field emission characteristics than those of as-grown CNTs. This might be due to the increase of field enhancement factor, which resulted from the reduction of field screening effect.

Vertical alignment of printed carbon nanotubes by multiple field emission cycles

The effect of field emission cycles on printed carbon nanotubes was investigated using scanning electron microscopy and current–voltage measurement. After multiple emission cycles, the printed nanotubes irreversibly deformed to orient themselves parallel to the field direction and, from them, remarkably enhanced emission image with good uniformity was demonstrated. Corresponding gradual decrease in the field emission threshold and increase of field enhancement factor (β) were also observed during field emission cycles.

Effects of Materials Composition in CNT Paste on Field Emission Properties in Carbon Nanotube Cathodes

The effects of paste materials on field emission properties in a carbon nanotube(CNT) cathode were investigated for high-efficient field emission displays. The major components in CNT paste for screen printing were a metallic Ag-paste, a dielectric glass-frit and CNT ink. The emission current from the cathode by an electron tunneling effect increased with an increase in the dielectric material fraction in the CNT paste, which is related to an increase of field enhancement factor in Fowler-Nordheim equation. The surface treatment used, after soft baking of the screen-printed CNT films, greatly affected the decrease in the turn-on field in CNT cathode and the uniformity of emission sites over the entire CNT film area.

Effect of sp2 content and tip treatment on the field emission of micropatterned pyramidal diamond tips

Electron field emission characteristics of uniformly constructed micro-pyramids of polycrystalline diamond with varying sp2 content have been systemically investigated. Concurrently, tip surface treatment was performed and emission characteristics of the post-treated tips were evaluated. The experimental results show that the field emission characteristics of the diamond can be enhanced by increasing the sp2 content and performing surface treatment. The emission current is significantly improved and the turn-on electric field is drastically reduced. Hypotheses are proposed for the effect of sp2 content and surface treatment on the field emission enhancement of diamond tips: (i) lowering of the work function due to sp2 defect induced band and impurity desorption, and (ii) increase in field enhancement factor due to sp2-diamond-sp2 microstructures and a field forming process. Analysis of the experimental results indicates that (ii) is the more probable explanation.