Field Emission Properties Research Articles

Carbon ion irradiation effects on surface modifications and field emission properties of molybdenum

Carbon ion irradiation effects on surface modifications and field emission properties of molybdenum

Changes in morphology and field emission property of nano-tendril bundles after high temperature annealing

• Helium plasma with additional neon formed nano-tendril bundles. • Thermal response of nano-tendril bundles (NTB) was investigated up to 1673 K. • Sharp tips disappeared and fiber radius of NTB increased significantly around 1573 K. • Field emission from nano-tendril bundles decreased after the thermal treatment. • The thermal treatment significantly decreased the probability to ignite arcing. Nano-tendril bundles (NTBs) are known to be formed on tungsten by helium plasma exposure with additional neon impurity gas. In this study, the annealing experiments were conducted at the sample temperature of 1473 – 1673 K to investigate the changes of morphology and field emission property of NTBs. With NTBs formed on a W surface, the surface did not fully recover to a smoothed surface and the NTBs remained the fiber-form structures after the annealing at 1673 K for one hour. In addition, the onset electric field for field emission increased, while the emission current from NTBs significantly decreased after the annealing. When the samples were biased at −250 V during helium plasma exposure, arc ignition was confirmed on W surface with NTBs, whereas no arc ignition appeared on W with annealed NTBs.

Investigation and correlation between surface modifications and field emission properties of laser-induced silicon plasma ion irradiated stainless steel

Laser-induced silicon (Si) plasma has been used as a source of ion irradiation for modifications in surface, structural and field emission properties of Stainless Steel (SS). Nd:YAG (532 nm, 10 ns) laser at irradiance of 15 GW/cm2 was used to generate Si-plasma ions which were detected by solid-state nuclear track detector (CR-39) and Faraday Cup (FC). Both the energy and fluence of Si ions were measured by FCs. In response to a stepwise increase in the number of laser pulses from 3000 to 12000, the ion fluence varies from 4.6 × 1014 to 18.3 × 1014 ions/cm2 with constant energy of 30 keV. Fourier Transformation Infrared (FTIR) spectroscopy analysis revealed that irradiated silicon makes the stretch band with oxygen Si–O–Si. X-Ray Diffraction (XRD) analysis confirmed the identification of new phase of Si (111) with an anomalous trend in crystallite size, dislocation line density and induced stresses in response to the irradiation with various Si ion fluences. Optical microscopy analysis showed the formation of pits, voids and tracks. Scanning electron microscope (SEM) analysis revealed the formation of nanoscale surface features including pores, craters, embedded particulates and protruded disk-like structures with multiple ablative layers at the fluence of 4.6 × 1014 to 13.7 × 1014 ions/cm2. At the highest ion fluence of 18.3 × 1014 ions/cm2, the flake/flower-like morphology is observed. Field emission (FE) properties were studied under ultra-high vacuum condition in a parallel plate configuration using planar virgin SS as an anode and structured SS as a cathode. The Fowler–Nordheim plots were obtained from I–V characteristics to evaluate the turn-on field, field enhancement factor β and a maximum current density ranging 1.5–4.5 V/µm, 5008–12807 and 96–454 nA/cm2, respectively. The variation in the FE properties is attributed to the different morphological features at varying silicon ion fluences.

Design of new process for stabilization of LaxGd1-xB6 nanorods and their Field Emission properties

Among all the rare earth metal hexaboride, GdB6 shows the lowest work function of 1.5 eV, which makes GdB6 a promising field emitting material. In the present work, synthesis of LaxGd1-xB6 (x = 0.1, 0.2, 0.3, 0.4 and 0.5) was attempted via borothermal reaction of LaxGd1-x(OH)3 nanorods and sodium borohydride at 1000 °C. The synthesis of ultrafine nanorods of LaxGd1-x(OH)3 (x = 0.1, 0.2, 0.3, 0.4 and 0.5) has been attempted via the hydrothermal route. The LaxGd1-x(OH)3 is annealed with NaBH4 in presence of argon, which leads to the formation of LaxGd1-xB6. TEM study of LaxGd1-xB6 indicates the nanorods formation of diameter 30–40 nm and length 130 nm. Further, as-synthesised LaxGd1-xB6 sample has been spin-coated over the silicon substrate and deposited LaxGd1-xB6 film was used for the field emission study. The field emission study shows the lowest turn-on field for LaxGd1-xB6 (x = 0.5) which is 5.01 V/μm with the highest field enhancement factor (β = 1568).

Field emission properties of carbon cloth-supported SnO2 with different morphological structures

• SnO 2 nanorods were successfully fabricated on carbon cloth through a facile hydrothermal method. • The nanocone-like SnO 2 /CC sample showed more excellent field emission properties. In this paper, SnO 2 nanorods and SnO 2 nanocone-like structure were synthesized on carbon cloth by facile hydrothermal route. When the carbon cloth (CC) is naturally placed at the bottom of the reaction solution during the process, the SnO 2 nanorods/CC composites were successfully obtained. The turn-on field and field enhancement factor of which were found to be approximately 0.95 V/μm and 21782. However, when the CC was inverted and fixed horizontally in the reaction solution, the top part of the SnO 2 nanorods became a tip structure. The prepared sample has an excellent field emission performance with the lower turn-on field of 0.78 V/μm and higher field enhancement factor of 32268.

Synergistic Effect of Field Emission Properties on Growth of CNTs by One-Pot Preparation of Various Concentrations Composite Catalyst

Multi-walled carbon nanotubes (MWCNTs) were grown on Silicon (Si) substrate by using low-pressure chemical vapor deposition (LPCVD) technique where iron (Fe) and silver (Ag) colloidal solution act as a catalyst were prepared by chemical route. The as-prepared solutions in varied concentrations were deposited on a Si substrate using a spin coating process at 700[Formula: see text]rpm. The purpose of Fe in composite catalysts is to have high carbon solubility and diffusion rate, and Ag utilization can change catalyst activity temperature and enhance carbon yields. In this work, we demonstrate the growth of carbon nanotubes (CNTs) on different catalyst concentrations ([Formula: see text]Fe/[Formula: see text]Ag), ([Formula: see text]Fe/[Formula: see text]Ag), ([Formula: see text]Fe/[Formula: see text]Ag) and ([Formula: see text]Fe/[Formula: see text]Ag) catalytic films. Field Emission Scanning Electron Microscopy (FESEM) was used to image the morphologies of various catalyst concentrations MWCNTs. The natures of the synthesized CNTs were determined using Raman spectroscopy and it was revealed that as-prepared CNTs are MWCNTs due to the absence of radial breathing mode (RBM). Raman spectroscopy demonstrated the lower ID/IG ratio (Ratio of the intensity of D-Raman peak and G-Raman peak) of ([Formula: see text]Fe/[Formula: see text]Ag) MWCNTs. The ID/IG ratio for ([Formula: see text]Fe/[Formula: see text]Ag) catalyzed MWCNTs was 0.76, while the ID/IG ratio for ([Formula: see text]Fe/[Formula: see text]Ag) catalyzed MWCNTs was 0.89. The ([Formula: see text]Fe/[Formula: see text]Ag) catalyzed MWCNTs were found to be more defective as compared to other. Electron Emission from ([Formula: see text]Fe/[Formula: see text]Ag) catalyzed MWCNTs were much stronger than from other samples, as demonstrated by Field Emission measurement using diode configuration. The turn-on field for ([Formula: see text]Fe/[Formula: see text]Ag) catalyzed MWCNTs was (0.92 V/[Formula: see text]m) which is slightly lower than that of ([Formula: see text]Fe/[Formula: see text]Ag) catalyzed MWCNTs (1.83 V/[Formula: see text]m), indicating superior enhancement.

Fabrication of rutile TiO2 nanoarrays/free-standing diamond composite film and its field emission properties

Highly aligned TiO2 nanoarrays (TNAs) are fabricated on free-standing diamond (FSD) films and Si wafers (for comparison). Different anodizing times (e.g., 5, 15, 25, 45, and 60 min) are used to investigate the morphologies of TNAs and their effect on the electron field emission (EFE) properties. With the increase of the anodizing time, the features of TNAs grown on the FSD film undergo the transition from nanorods to nanopores and then to nanotubes. The XRD, Raman, and TEM results reveal that TNAs synthesized on the FSD film are preferentially oriented rutile phase, while those synthesized on the Si wafers show the anatase structure. Rutile TiO2 has a relatively low work function and is favorable to EFE performance. Importantly, the nanotubes on the FSD substrate with a 45 min anodizing time grow perpendicularly to each crystal face of the diamond grains and exhibit a superior EFE behavior, which can be turned on at a low field of 0.7 V/μm and attain a high current density of 0.6 mA/cm2 at an applied field of 1.6 V/μm. The enhanced EFE performance of TNAs/FSD composite film is ascribed to the synergetic effects among the electron acceleration layer played by the FSD film, more electron emission sites provided by the nanotubes with large aspect ratios, and lower work function of rutile TiO2. Moreover, the heterogeneity of the FSD substrate and TNAs also can decrease the interface barrier to make electrons transmit effectively.

Improving field emission performance of patterned ZnO electron emission source by optimizing array spacing

The field emission (FE) electron source has a wide range of application in the field of vacuum electronics, and the patterning of cathode emitters is one of the key technology. In this paper, a new idea of cathode structure to achieve good luminescence uniformity with the smallest emitter areas is proposed. First, the inkjet printing is applied to precisely position the patterned layer, and the branched ZnO arrays are grown by electrochemical deposition. Then the effect of array spacings on field emission performance is studied. The results show that with the increase of the array spacing, the FE performance first increases and then decreases, among which the arrays with the moderate spacing have the best FE properties, including the lowest turn-on field (Eon) of ∼0.46 V μm−1 and the most uniform luminescence. Finite element calculations using the ANSYS software were performed. Simulations are carried out to analyze the surface electric field distribution and electron movement trajectory, indicating the moderate array spacing is beneficial for FE due to the balance of the field superposition effect and shielding effect. The efficiency of pattern design helps to realize the high-performance field emission electron source, which is of great significance for flexible manufacturing and large-scale integration.

MoS2 nanosheet arrays grown on Mo foils for high-performance field emission

Free-standing molybdenum disulfide (MoS2) nanosheets with different morphologies on molybdenum (Mo) foil were synthesized through hydrothermal method using thiourea as the sulphur source and Mo foil as the Mo source. The effect of the concentration of thiourea in the reaction solution on the morphology and field emission (FE) properties of MoS2 nanosheets were investigated. The vertically aligned MoS2 nanosheets exhibit a low turn-on (∼1.90 V/μm) and threshold electric field (∼2.51 V/μm), along with good emission stability. The results are attributed to the high geometrical field enhancement factor (∼1979) and the sturdy structure of the MoS2 grown on highly conductive Mo substrate.

Field emission characteristics of ZnO nanowires grown by catalyst-assisted MOCVD on free-standing inorganic nanomembranes

ZnO field emitters on freely suspended inorganic nanomembranes (NMs) were synthesized by catalyst-assisted metal organic chemical vapor deposition (MOCVD) using the precursors zinc acetylacetonate hydrate and oxygen. The morphology and the possibly involved growth mechanisms of the randomly distributed ZnO nanostructures were investigated by scanning electron microscopy and by energy-dispersive x-ray spectroscopy. The findings indicate a growth process that involves the vapor–liquid–solid as well as the vapor–solid–solid mechanism. The field emission (FE) properties of such ZnO nanowire (NW) samples showed to be highly reproducible and independent of the investigated Si-based substrate types. Herein, a new type of flexible substrate for the MOCVD process has been introduced that allows for the direct growth of ZnO NWs on free-standing membranes for potential FE-based sensor applications. A turn-on field of 4.1 V µm−1 was detected for a macroscopic emission current density of 10 µA cm−2 and the stability test revealed fluctuations of only 9% around the mean emission current over a duration of 3 h proving a reliable and stable operation of such devices. Moreover, approaches were identified to further enhance the FE characteristics of the ZnO NWs by variation of the synthesis parameters and by enlargement of the NM area.

A dual-functional micro-focus X-ray source based on carbon nanotube field emission

A micro-focus X-ray source with miniature pressure sensor was developed based on the multi-walled carbon nanotube (MWNT) field emission. The field emitters for both X-ray cathode and the pressure sensor were synthesized by direct chemical vapor deposition growth of MWNTs on catalytic substrates. MWNTs exhibited excellent field emission properties with the threshold field at 10 mA/cm2 of 2.30 V/μm, and the high current density of 10 A/cm2 could be reached at the field of 4.36 V/μm. The field emission electron gun was constructed with the aid of electrostatic simulations on the electron beam trajectories and the focal spot size (FSS) on the target with the demagnification factor of 5. The practical objects, including the semiconductor chip and the ceramic heating element, were tested by the X-ray source with the spatial resolution of less than 35 μm, and the fracture of the ceramic element inside metal case could be clearly detected. The pressure sensor monitored the in-situ pressures inside the source during the processing and after the sealing-off. The pressures in the sealed sources were generally in 10−4 Pa level and could rise to 10−2 Pa level during the operation.

Induced quantum-Fano effect by Raman scattering and its correlation with field emission properties of silicon nanowires

Induced quantum-Fano effect by Raman scattering and its correlation with field emission properties of silicon nanowires

Significant enhancement in field emission and photoluminescence properties of vertically aligned tellurium nanorods by plasma treatment

Significant improvement in electron field emission (FE) properties of high density vertically aligned tellurium nanorods (TNRs) arrays has been observed by plasma treatment. At first the TNRs are grown by catalyst free chemical vapor deposition (CVD) method and are systematically characterized by FESEM, EDS, TEM, HRTEM, XRD and XPS. Later on TNRs were treated with plasma (Ar and N) and their effects on morphology, optical and FE properties are investigated comprehensively. The FE of TNRs containing 40–50 nm size have been enhanced from 6.22 Vμm−1 to 3.25 Vμm−1 which is more than 52%. This research reveals that plasma treatment has effectively modified the surface morphology (confirmed by TEM) and created sharp tips on TNRs which act as extra source of field emitters believed to contribute the enhancement of field emission. Plasma treated TNRs not only exhibited excellent FE properties (3.25 Vμm−1), these aligned TNRs also portrayed the tremendous stability with insignificant FE current fluctuation (<4%) for 60 min. Crucially, the reported FE turn-on value is low enough for their potential applications in device fabrications. So these findings offer the improvement in the field emission of TNRs by plasma treatment proposing their potential utilization in devices.

Study the electron field emission properties of silver nanoparticles decorated carbon nanotubes-based cold-cathode field emitters via post-plasma treatment

Study the electron field emission properties of silver nanoparticles decorated carbon nanotubes-based cold-cathode field emitters via post-plasma treatment

Field Emission of Multi-Walled Carbon Nanotubes from Pt-Assisted Chemical Vapor Deposition.

Multi-walled carbon nanotubes (MWNTs) were grown directly on a metal substrate with the assistance of Pt using a chemical vapor deposition method. In addition, the growth mechanism of Pt-assisted catalytic CNT was discussed. MWNTs were characterized by SEM, TEM, AFM, Raman, and EDS, and the field emission (FE) properties were investigated, comparing with the direct grown MWNTs. The results showed that CNTs could not been synthesized by Pt particles alone under the experimental condition, but Pt may accelerate the decomposition of the carbon source gas, i.e., assisting MWNT growth with other catalysts. The Pt-assisted MWNTs were longer with larger diameters of around 80 nm and possessed better structural qualities with very few catalyst particles inside. Improved field emission properties were demonstrated for the Pt-assisted MWNTs with lower turn-on fields (for 0.01 mA·cm−2 current density) of 2.0 V·μm−1 and threshold field (for 10 mA·cm−2 current density) of 3.5 V·μm−1, as well as better stability under a long-term test of 80 h (started at 3.0 mA for the Pt-assisted emitter and 3.25 mA for the direct grown emitter). This work demonstrated a promising approach to develop high performance CNT field emitters for device applications.

The role of quantum crystal radius on electron field emission properties of fractal silicon nanowire arrays

Here we report, the role of quantum crystal radius (QCR) on field emission (FE) properties of fractal silicon nanowire arrays (F-Si-NWAs) fabricated onto n-type Si(100) by metal electroless wet chemical etching (MEWCE). The energy band estimation from absorption spectra reveals the increment in optical band gap of F-Si-NWAs varies from 1.72 eV to 1.75 eV. Here, the band-gap dependent effective mass approximation (EMA) method are used to estimate the QCR present in F-Si-NWAs, which shows quantum confinement (QC) effect. The effect on FE properties have been studied using current–voltage (I-V) measurements followed by a theoretical analysis through the Fowler–Nordheim (F-N) equation as a function of the QCR. The FE studies show that the smaller QCR have low turn on voltage and high field enhancement factor due to QC effects.

Femtosecond laser processing and field emission properties of the FEAs on single crystal GdB6 (100) surface

The single crystal GdB6 were prepared by optical zone melting method. Moreover, using the femtosecond laser micromachining technology processed the field-emission tip arrays (FEAs) on the (100) surface of single crystal GdB6. The single crystal quality, field emission of the FEAs, as well as the electronic structure of single crystal GdB6 are systematically characterized. The quality of single crystal is good. The curvature radius of the produced FEAs with uniform morphology and undamaged crystal surface structure are about 0.5 μm. The FEAs showed good field emission performance, which the turn-on electric field of the FEAs is 2.6 V/μm with a field emission current of 0.46 A/cm2 at 7.3 V/μm and the emission current has high stability. The calculation electronic structure of GdB6 show that the 5d electron of Gd determines the electronic state of excellent emission performance. The high electric field will greatly decrease the surface barrier and work function of GdB6, according with the field emission theory.

Enhanced field emission performance of Si nanopillars coated with LaB6 hats fabricated by microspheres lithography

LaB6 nanofilm is coated on the top surface of silicon nanopillars forming a field emission array (FEA). Such a structure will be referred to subsequently as a ‘LaB6 hat-coated Si-FEA’. The electron emission mechanism of the LaB6 hat-coated Si-FEA is analyzed by OPERA simulation software. It reveals that the electron emission mainly depends on the LaB6 film edge. Moreover, the LaB6 hat-coated Si-FEA sample is prepared by microsphere lithography, and the field emission properties are tested. The results show that when the anode voltage is 850 V, the field emission current density reaches 458 mA cm−2, which is in good agreement with the simulation results. This work demonstrates that the field emission cathodes with low cost, high integration and high current can be realized by using LaB6 as emitter material combined with microsphere lithography technology.

Field emission enhancement from directly grown N-doped carbon nanotubes on stainless steel substrates

N-doped carbon nanotubes (NCNT) are grown directly on the stainless steel (SS) substrates by chemical vapor deposition at atmospheric pressure, and the field emission (FE) enhancement mechanism is investigated. The turn on and threshold fields of the NCNT emitters are 1.61 and 2.05 V μm−1, respectively, lower than those from the CNT emitters. The improved FE properties are mainly attributed to the reductions of the work function and the surface resistance. First-principles calculations suggest that the work function of NCNT depends highly on the N doping concentration. In addition, the N-doping in CNT leads to the charge aggregation around N, benefiting the field emission enhancement. More importantly, for the CNTs, the emission current dropped by 28.6% after ∼7h continuous emission at the pressure of 5.38 × 10−4 Pa, while the current reduced only 5.8％after 7 h test at the pressure of 8.35 × 10−4 Pa for the NCNTs, suggesting that the NCNTs exhibit better resistance to the ion bombardment in high pressure. The investigation demonstrates that the facilely grown NCNTs are promising to develop practical FE cathodes.

Multistage carbon nanotubes grown on foamed nickel with organic solutions as multifunctional high performance electrodes

In this study, carbon nanotubes (CNTs) are grown by easy method with organic solutions upon foamed nickel substrates. It is found that ethanol is most likely to grow higher quality CNTs than other organic solutions without deoxidation gas. The foamed nickel not only acted as substrates but also uesed as catalyst to grow CNTs and then formed good electrical and thermal contact with CNTs. Moerover, the foamed nickel has intrinsic low contact resistance with CNTs and their multistage structure also makes it as multifunctional electrode for electrical devices. With multistage and high enhancement factor, these CNTs grown on foamed nickel have better field emission properties with turn-on field at 1.4 V/μm and the threshold-field at 2.9 V/μm. With high specific surface area, it is also has high sensitive property to detect heavy metal ion such as Pb2+. The results show it has a good linear relationship exists in the range of 100–400 ppb, and the limit of detection is about 0.955 μg/L Pb2+.This easy CNTs growth method offers a potential application in making field emission electron source and other electrical electrodes.