High Field Enhancement Factor Research Articles

Effect of Crystallinity on the Field Emission Characteristics of Carbon Nanotube Grown on W-Co Bimetallic Catalyst.

Carbon nanotube (CNT) is an excellent field emission material. However, uniformity and stability are the key issues hampering its device application. In this work, a bimetallic W-Co alloy was adopted as the catalyst of CNT in chemical vapor deposition process. The high melting point and stable crystal structure of W-Co helps to increase the grown CNT diameter uniformity and homogeneous crystal structure. High-crystallinity CNTs were grown on the W-Co bimetallic catalyst. Its field emission characteristics demonstrated a low turn-on field, high current density, stable current stability, and uniform emission distribution. The Fowler-Nordheim (FN) and Seppen-Katamuki (SK) analyses revealed that the CNT grown on the W-Co catalyst has a relatively low work function and high field enhancement factor. The high crystallinity and homogeneous crystal structure of CNT also reduce the body resistance and increase the emission current stability and maximum current. The result provides a way to synthesis a high-quality CNT field emitter, which will accelerate the development of cold cathode vacuum electronic device application.

Optical gain-tunable wideband metasurface device with high electric field enhancement

The metasurface devices with high electric field enhancement factor values have been widely discussed in recent years. However, these types of metasurface devices usually have very strict minimum spacing limitations, which seriously affect the difficulty of device fabrication and the reproducibility of experiments. In this work, we proposed a metasurface based on a metal-insulator-metal configuration that significantly enhances the electric field enhancement factor of the surface plasmon resonance structure on the upper surface by utilizing a bottom metal-SiO2 spiral lens. The results indicated that the gain bandwidth of this proposed device is more than 100 nm with a maximum electric field gain of 377 within the orange-red wavelength range. Furthermore, the electric field enhancement factor can be adjusted based on the number of rings in the spiral lens. Moreover, the minimum fabrication scale of this device is 130 nm, which facilitates easier fabrication and experimental replication. The focal pattern of the electric field generated inside the spiral lens with different polarization states of light was also examined.

Tubular Diamond as an Efficient Electron Field Emitter

Herein, we present a straightforward and cost-effective procedure for producing conductive diamond tubes on the surface of porous carbon nanotube hollow fibers using successive 10-pulsed laser annealing shots and 6 h of hot filament chemical vapor deposition techniques. Room-temperature Raman and X-ray diffraction spectra reveal the signature T2g peaks near 1332.4 cm–1 and 111 planes of diamonds near 43.9°, respectively. A low turn-on field (ETO) ∼1.85 V/μm@1 μA/cm2 and a threshold field (ETH) ∼2.54 V/μm@10 μA/cm2 were observed for the tubular diamond structures. The field enhancement factor (β) was calculated at 3594 and highly stable field emission current stability was observed over a long period of 4 h. For the first time, a good insight into the field emission results of the diamond is established with the structural, electronic properties, and the work function (φ) ∼4.84 eV analysis conducted by the density functional theory simulation. Finite electronic states at the Fermi level are observed beyond a band gap, and it demonstrates the wide-band gap (4.4 eV) semiconducting nature of the diamond. The Bader charge analysis and maximum entropy method pattern revealed the negative electron affinity of the diamond, and it is responsible for the emission of electrons from the conduction band of the diamond. Besides, the accumulation of charge carriers, which contributes to the electric field emission, takes place due to the weak π bonds of carbon atoms. The low turn-on field, the high field enhancement factor, and the good field emission current stability of tubular diamond offer great prospects for future efficient and low-cost field emission devices.

Electric field enhancement in Au and Ag nanodisks-based photonic crystals: Relevant design insights for efficient SERS substrates

In recent years, noble metal nanoparticle-based periodic nanoarrays (photonic crystals) have received special attention due to their gross potential to achieve exceptionally high Electric-Near Field Enhancement (ENFE) factors for visible light and their prospects as candidates for the fabrication of ultra-sensitive Surface-Enhanced Raman Spectroscopy (SERS) substrates. In this work, we report a simple but exhaustive theoretical analysis of the ENFE in Au and Ag nanodisks-based photonic crystals by Finite-Difference Time-Domain (FDTD) method. Nanostructures with arrays periodicities from 200 to 1000 [nm], nanodisks diameters from 100 to 500 [nm] and thicknesses from 20 to 200 [nm] were studied. Results show that the ENFE is strongly dependent on each one of these geometrical parameters, observing |E/E0|2 factors that can reach up to 1200 for the visible light spectrum. The effects of nanodisks surface curvature-based defects on the ENFE were also analyzed. This kind of defects seem to be also relevant to maximize the ENFE effects, observing that higher surface curvatures tend to considerably attenuate the electric field amplification. Our research provides relevant insights on the design optimization of this kind of photonic crystals to maximize the ENFE effects, which is a critical issue to assess the future fabrication conditions of efficient SERS substrates.

Efficient field emission from ultrafine nanostructured lanthanum sulfide synthesized by chemical route

Lanthanum sulfide having a rocksalt structure has attracted lots of research interest because of its tremendous applications in the field of display devices, optoelectronic, field emission, and thermoelectric devices due to their low work function, and excellent chemical and physical properties. In the present work, we have synthesized LaS2 ultrafine nanostructures using anisotropic nanostructures of La(OH)3. The synthesis of anisotropic La(OH)3 has been attempted by the micellar-assisted hydrothermal route. The obtained La(OH)3 was further heated with elemental Sulfur at ambient pressure, leading to the stabilization of LaS2 of size ∼25 nm. Further, the as-obtained lanthanum disulfide was used for making LaS2 ink and spin-coated over a silicon substrate to fabricate LaS2 film. Field emission study of LaS2 film shows the lowest turn-on field (<3.9 V/μm), high field enhancement factor (β = 14,594), and high current density of 7.15 μA/cm2 has been obtained, which is around 10 times higher than earlier reports.

Photoelectron properties and enhanced field electron emission of cobalt ferrite-reduced graphene oxide nanocomposite

In the present report, field electron emission (FE) characteristics of cobalt ferrite (CF) nanoparticles (NPs) decorated on reduced graphene oxide (rGO) are studied. The rGO-CF nanocomposite was synthesized by simple glycol-based route. The formation of rGO-CF nanocomposite was confirmed using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). TEM results indicated the uniform decoration of CF NPs on the rGO sheet. The average particle size of decorated CF NPs is ∼8 nm. XPS results revealed the partial reduction of GO to rGO. The ultraviolet photoelectron spectroscopy (UPS) was utilized to calculate the work function of the nanocomposite and it was found to be ∼4.3 eV. The FE properties of rGO-CF nanocomposite were investigated in planer diode assembly. The nanocomposite showed excellent FE performance with low turn-on ∼ 1.34 V/μm and threshold field ∼ 1.72 V/μm values. The maximum current density was found to be 2.8 mA/cm2, at an applied field of 2.88 V/μm. This enhancement in FE characteristics was explained on the basis of surface morphology, increased number of emitting sites, high field enhancement factor, and reduction in the work function of the emitter. The FE results suggest that rGO-CF based emitters have the potential for the development of various micro-nano electronic devices.

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 Enhancement in Nanoparticles Due to IR Vortex Beams

In this report we present our study of interaction of light carrying OAM (Orbital Angular Momentum) with nanometric metallic discs. Plasmonic effects are known to give rise to high local field enhancement factors in gold nano-discs. These high intensities near fields have found use in a wide variety of imaging and detection applications. The local field enhancement factor near the surface of the disc was calculated numerically using finite element method using the Comsol package. We report a significant increase in the local field enhancement factor for light beams carrying OAM compared to Gaussian beams which are attributed to Localised Surface Plasmon Resonances (LSPR). Such large enhancements in the field can be immensely useful in the field on near field microscopy and electron generation.

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.

The morphology dependent plasmonic optics of urchin-like gold nanoparticles in different silver-coating modes

In this work, the spectral properties of urchin-like gold nanoparticles (ULGNs) have been studied theoretically and experimentally. Firstly, a model with six branches evenly distributed on the spherical core was built. Its spectrum and electric field distributions are simulated and calculated using discrete dipole approximation (DDA) method. Two extinction peaks generated by plasmon resonance on spherical core and symmetrical branches were determined. What’s more, intensities between two resonance modes can be switched by regulating the number of branches since charges are more likely to accumulate at the tips of branches. Then, branch thickness has been regulated. The highest field enhancement factor |E/E0|= 36.95 can be obtained when r = 6 nm. Models with r = 2 nm branches fail to concentrate charges at the tips while two resonance modes fuse in models with r = 8 nm branches. Secondly, ULGNs@Ag were synthesized experimentally. To study the optics and the cause of three peaks appeared in spectrum, two ULGNs@Ag models (core surrounded and full coverage) were built and simulated based on the morphology from TEM pictures. Except for plasmon resonance on silver shell and ULGNs, coupling effects between exposed gold branches and silver shell were found in core surrounded ULGNs@Ag model, which is more consistent with the experimental results. While in full coverage ULGNs@Ag model, main two peaks are formed due to the silver layer and the gold-silver core-shell branches. There are another two inconspicuous peaks emerge which may ascribed to concentration of hot spots due to negative curvature surfaces and hybridization effect on gold-silver and silver-medium interface, providing a theoretical basis for spectral analysis of both ULGNs and ULGNs@Ag.

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.

Stable Field Emission from Vertically Oriented SiC Nanoarrays.

Silicon carbide (SiC) nanostructure is a type of promising field emitter due to high breakdown field strength, high thermal conductivity, low electron affinity, and high electron mobility. However, the fabrication of the SiC nanotips array is difficult due to its chemical inertness. Here we report a simple, industry-familiar reactive ion etching to fabricate well-aligned, vertically orientated SiC nanoarrays on 4H-SiC wafers. The as-synthesized nanoarrays had tapered base angles >60°, and were vertically oriented with a high packing density >107 mm−2 and high-aspect ratios of approximately 35. As a result of its high geometry uniformity—5% length variation and 10% diameter variation, the field emitter array showed typical turn-on fields of 4.3 V μm−1 and a high field-enhancement factor of ~1260. The 8 h current emission stability displayed a mean current fluctuation of 1.9 ± 1%, revealing excellent current emission stability. The as-synthesized emitters demonstrate competitive emission performance that highlights their potential in a variety of vacuum electronics applications. This study provides a new route to realizing scalable field electron emitter production.

Morphological evolution and its correlation with optical and field emission properties in pulsed laser deposited ZnO nanostructures

The present report illustrates the effect of growth temperature on the morphological features, optical, and field emission properties (FE) of ZnO thin films deposited on Si substrate (100) through the pulsed laser deposition (PLD) technique. The as-deposited films have been characterized by employing various characterizations tools particularly X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), High- resolution TEM, etc., and confirms the successful deposition of the films. It demonstrates that as the growth temperature increases from ∼ 5000C to ∼ 8000C during 30 min, the spherical particle-like nanostructures transform into the truncated nanocones. Further, at a fixed deposition temperature of ∼ 8000C, and with enhancement in the growth time from ∼10 to 30 min, the nanoparticles get transformed into nanocones. Henceforth, the substrate temperature and growth time have been identified as determinant factors for the formation of these ZnO nanocones. XRD and TEM analysis suggest that the majority of nanocones have been aligned epitaxially with a preferred c-axis orientation on the Si substrates. Optical measurements reveal that the optical band gap of ZnO films exhibits a decreasing tendency from ∼3.26 to 3.22 eV with an increase in substrate temperature from ∼ 500 to 8000C. Subsequently, the field emission (FE) measurement of these aligned ZnO nanocones signifies a stable field emission with a low threshold field (2.40 V/μm) and a high field enhancement factor (∼2786). Their tapered morphologies and small tip diameters suggest as-deposited samples to be highly reproducible and henceforth as-deposited ZnO nanocones bearing excellent FE properties, through high-pressure PLD growth method without using any catalyst offer usage in various futuristic electronic applications.

Promoted field emission and cell attachment of TiO2 nanorods/carbon fiber with hydrogen doping induced by cold atmospheric‐pressure Ar/H2 plasma jet

AbstractCold atmospheric‐pressure plasma jet not only modifies surface morphology but also introduces functional groups on sample surfaces. In this work, TiO2 nanorods/carbon fiber (TNCF) is hydrothermally prepared, and hydrogen‐doped TNCF (H:TNCF) is obtained by the surface treatment of TNCF using cold atmospheric‐pressure Ar/H2 Plasma jet. H and OH spectral lines are observed from the emitting spectrum of atmospheric‐pressure Ar/H2 plasma jet. Nanoscaled protrusions appear at top of TiO2 nanorods after the surface treatment of cold atmospheric‐pressure Ar/H2 plasma jet. OH functional groups form on the surface of H:TNCF, based on the results of FTIR, Raman and XPS analysis. Furthermore, hydrogen doping can lower the band gap from 3.2 eV of TNCF to 2.9 eV of H:TNCF, and reduce the work function from 4.97 eV of TNCF to 4.71 eV of H:TNCF. Field emission property and cell compatibility of TNCF and H:TNCF are investigated. Field emission property of TNCF is considerably improved by hydrogen doping, due to a reduced work function and a higher field enhancement factor. In the cell attachment experiments, H:TNCF exhibits more attached cells with a larger cell attachment area, compared with the TNCF sample. The obtained results show H:TNCF prepared by hydrothermal method combined with cold atmospheric‐pressure Ar/H2 Plasma jet will be a promising candidate for field emission and biocompatibility applications.

Numerical simulations of field emission characteristics of open CNT

Numerical simulations on field emission properties of an open single-walled carbon nanotube with radius r = 1 nm have been carried out. Using finite element method, we have calculated the local electric field Floc and field enhancement factor γ distribution over the surface of the open CNT. From these calculations, we plot theoretical current-voltage characteristics and assess effective field characteristics for CNT with wall thickness w = 0.2 nm and height h = {3, 11, 101, 1001} nm. It was revealed that the maximum emission current did not change when applied field at the top of the CNT corresponds to the scaled barrier field f = 0.45. Obtained values of effective emission area are in good agreement with surface area, which has the highest field enhancement factor. In addition, we have plotted a “map” of maximum field enhancement factor γa for open CNTs with various wall thickness - w ϵ [0.1; 0.9] nm and heights h ϵ [11; 1001] nm. It was shown that maximum field enhancement factor is a nonlinear function of h/r and h/w ratios.

Optically Induced Field-Emission Source Based on Aligned Vertical Carbon Nanotube Arrays.

Due to the high field enhancement factor and photon-absorption efficiency, carbon nanotubes (CNTs) have been widely used in optically induced field-emission as a cathode. Here, we report vertical carbon nanotube arrays (VCNTAs) that performed as high-density electron sources. A combination of high applied electric field and laser illumination made it possible to modulate the emission with laser pulses. When the bias electric field and laser power density increased, the emission process is sensitive to a power law of the laser intensity, which supports the emission mechanism of optically induced field emission followed by over-the-barrier emission. Furthermore, we determine a polarization dependence that exhibits a cosine behavior, which verifies the high possibility of optically induced field emission.

Synthesis, physico-chemical characterization and field emission behaviour of 3D chrysanthemum like pristine ReS2, and ReS2-rGO nanocomposite

3D chrysanthemum like pristine ReS2 and nanocomposite of ReS2 with reduced graphene oxide (rGO) have been synthesized using facile one step hydrothermal method, followed by physico-chemical characterizations to reveal their phase, structural and electronic properties. Efforts have been made to reveal the influence of process parameters on morphology and growth of the as-synthesized products. From application point of view, field emission (FE) behavior of pristine ReS2 and ReS2-rGO nanocomposite emitters has been investigated at base pressure of 1 × 10–8 torr. The ReS2 and ReS2-rGO nanocomposite emitters showed values of turn-on field (corresponding to emission current density of 1μA cm−2) as 2.10 and 1.66 V μm−1, and field enhancement factor (β) as ∼965 and 1176, Furthermore, the ReS2-rGO nanocomposite emitter delivered maximum emission current density of ∼1472 μA cm−2 at applied field of 3.1 V μm−1. Both the emitters exhibited good emission current stability at pre-set value ∼5 μA over more than 3 h duration. The superior FE properties of the ReS2-rGO nanocomposite emitter are attributed to optimized morphology offering high field enhancement factor coupled with modulation of electronic properties reflected as lowering of the work function. The value of work function of ReS2-rGO nanocomposite, measured using a retarding field analyzer, is found to be 4.29, lower than that of the pristine sample (4.49 eV). The results signify that functionality of pristine nanostructures is greatly improved via formation of nanocomposites and desirable nanocomposites possessing unique morphology can be synthesized under optimized experimental conditions using a facile and inexpensive hydrothermal route.

Enhanced electron emission from ternary solid solution-MWCNT hybrid with theoretical validation

Coalescence of unique properties of semiconductor and carbon nanotubes (CNTs) produces new advanced materials with exciting properties, which unwraps several new fields. Here, finite element modeling is employed to optimize the diameter of semiconducting zinc cadmium sulfide (Zn0.8Cd0.2S) microspheres on the wall of metallic CNTs to get the improved field emission property. Then, Zn0.8Cd0.2S microspheres are attached on COOH functionalized multiwalled CNTs (MWCNTs) by a simple one step solvothermal method for experimental corroboration. Field emission experiment shows a considerable enhancement of current density with respect to bare microspheres and functionalized CNTs. The turn-on field is found to be as low as 3V/μm at a current density of 10 μΑ/cm2 for the hybrid system. Density functional theory (DFT) calculation is carried out for the model structures of Zn0.8Cd0.2S and CNT-Zn0.8Cd0.2S to calculate the work functions. This improvement in field emission property of the hybrid system is demonstrated in terms of band bending, geometry, high field enhancement factor, low work function and electron affinity. Thus, non-field emitting microspheres with less toxicity have been transformed into a decent field emitter by the contribution of few carbon nanotubes.

Correlation of optical sensing with extinction coefficient and local field enhancement in gold nanosphere dimer

In this paper we systematically study the optical extinction, local field enhancement, and resonance peak shift of basic single/double gold nanosphere system. We find that in the double gold nanosphere system, the incident light can excite the coupled resonance modes when the two gold nanospheres are approaching to each other, leading the local field to be enhanced greatly. Interestingly, limited by the scant volume of local field, the extinction coefficient of the double gold nanosphere system of 2 nm gap with a high local field enhancement factor is greatly reduced, so that its optical sensing sensitivity and extinction coefficient are smaller than the 5 nm gap system’s. Studies show that the optical sensing sensitivity of the double gold nanosphere system is not directly determined by the local field enhancement amplitude, but has a similar change behavior to the extinction coefficient of the system. These results can offer us a useful route and hint for designing the gold nanoparticle systems used in the surface Raman scattering enhancement and high performance optical sensing.

Synthesis and field emission properties of Cu-filled vertically aligned carbon nanotubes

A highly conductive metal core modifies the electronic properties of a carbon shell, offering the possibility of enhancing its field emission (FE) behavior. Herein, a method has been devised to synthesize copper-filled vertically aligned carbon nanotubes (Cu@VACNTs) directly on Cu disks without extra metal catalysts via plasma-enhanced chemical vapor deposition. An ensemble of Cu particles formed on the surface of Cu disks due to surface reconstruction in a reducing environment plays a crucial role in the nucleation and growth of Cu@VACNTs. The filling of Cu inside the VACNTs can be controlled by tuning the growth temperature. The study of FE properties revealed that a conductive Cu-core extending throughout the entire length of the VACNTs could significantly enhance the FE properties of the VACNTs. Excellent FE properties including low turn-on field (ETo = 1.57 V/µm), low threshold field (ETh = 2.43 V/µm), high field enhancement factor (β = 3061), and high FE stability were observed for the Cu@VACNTs. The enhanced FE properties of the Cu@VACNTs can be accredited to low field screening due to bundled morphology and improved electrical and thermal conductivities offered by the encapsulation of highly conductive Cu nanowires inside the cores of VACNTs.