Value Of Field Enhancement Factor Research Articles

Field electron emission behavior of pristine and Au nanoparticles decorated Sb2Te3-rGO heterostructure emitters

A facile one-pot hydrothermal method was used to synthesize pristine Sb2Te3 and its heterostructure with reduced graphene oxide (rGO). A novel approach dealing with high energy (6 MeV) electron irradiation has been efficiently used for synthesis of gold nanoparticles (Au- NPs) and their in-situ decoration on Sb2Te3-rGO heterostructure. From an application point of view, we have investigated the field electron emission characteristics of pristine Sb2Te3 and Sb2Te3-rGO heterostructures, with and without Au-NPs decoration. The Au-NPs decorated Sb2Te3-rGO heterostructure emitter showed enhanced electron emission behavior in terms of reduced value of turn-on field, delivery of large emission current density (∼1171 µA/cm2) at relatively lower applied field (∼3.1 V/µm), and excellent emission stability. The improvement in emission characteristics upon decoration of Au-NPs is attributed to noticeable increase in the number of emission sites, higher value of field enhancement factor (β = 4562), and betterment in the electronic properties due to Au-NPs-Sb2Te3-rGO interface effects. The obtained results suggest that Au-NPs decorated Sb2Te3-rGO heterostructure emitter has potential towards practical applications in various vacuum microelectronic devices. Furthermore, the present approach dealing with high energy electron irradiation for synthesis and in-situ decoration of nanoparticles can extended to other inorganic heterostructures towards improving their functionality.

Influence of the electron field emission on the magnetized direct current high-pressure discharge

The influence of electron field emission on the sub-normal mode of a magnetized direct current high-pressure helium discharge is analyzed using the two-dimensional axisymmetric fluid model. It is observed that in spite of accounting for a more intense electron emission mechanism, discharge still operates in the sub-normal mode. However, the field emission driven discharge is characterized by a smaller discharge voltage and a larger discharge current. For large values of the electric field enhancement factor, the discharge voltage can be as low as ∼40 V, and the discharge current is a few amperes. It is also seen that for large values of the field enhancement factor and small values of the ballast resistor, rather dense plasma (density ∼ 1017 m−3) can be generated on the nanosecond time scale.

Enhancement of Electron Emission Properties of Carbon Nanotubes by the Decoration with Low Work Function Metal Oxide Nanoparticles.

In the present report, the properties of the field emission devices of carbon nanotubes (CNTs) were remarkably improved by decorating their surface with magnesium oxide nanoparticles (MgO NPs). The MgO NPs were attached effectively on the surface of CNTs via thermal evaporation. The Raman spectra confirm the graphitic order of as-grown pristine CNTs with RBM (radial breathing mode), D band and G band peaks at the 282 cm-1, 1347 cm-1 and 1594 cm-1 respectively. The peak at 471 cm-1 indicates successful attachment of MgO NPs to the CNTs. The enhanced field emission properties of CNTs were mainly attributed to the MgO NPs which increased the field enhancement factor and the density of emission sites. The decreased work function and increased field enhancement factor were responsible for the improved FE properties of the CNTs. Our results indicate that the MgO decorated CNTs can be used as an effective field emitter for various electron emission devices. The turn-on field decrease from 1.6 V/μm to 1.3 V/μm and the maximum current density increases from 1.581 to 3.678 mA/cm2 after the decoration of CNTs with MgO NPs. The value of field enhancement factor (β) also increases from 2.814×10³ to 9.823×10³.

First-Principles Analysis of Nanoelectromechanical Systems Using the Loewner Equation

The Loewner equation (LE) is used to obtain conformal mappings that lead to exact and analytical expressions for several electrostatic properties of realistic quasi-unidimensional nanoelectromechanical systems (NEMS). The LE approach also embraces curved geometries, impossible to be addressed by traditional methods such as the Schwarz-Christoffel transformation, often used in this scenario. Among the possible applications of the formalism, we show that it allows for an exact evaluation of the field enhancement factor (FEF) close to the apex of different emitters. Despite its key role in the demodulation process for radio-receiver nano-devices, actual FEF values have been mostly obtained via numerical and/or phenomenological approaches. This work extends the already huge universe of applications of the LE and provides an analytical method to evaluate the FEF, even for curved emitters. Furthermore, our results provide a signature of the varying emitted current's response due to the nanostructure oscillation, justifying its role in the demodulation process of radio-frequency.

Plasmonic properties of spheroid silicon-silver nanoshells in prolate and oblate forms

Metal nanoparticles are excellent absorbers or scatterers of electromagnetic radiation, depending on their shape, size, material and refractive index of the surrounding medium. In studying the effect of shape, metallic core shell nanoparticle nanoparticles recently have attracted a great amount of interest in plasmonics due to the wide tunability of the plasmon resonances. In this paper, we have investigated the plasmonic properties of spheroid Silver-Silicon core shell nanoparticles, such as extinction, absorption and scattering cross sections and field enhancement factor as a function of parameters as: angle, wavelength and distance from the center. It has been shown that the localized surface plasmon resonance wavelength of these nanoparticles is severely dependent on shell thickness. The resonance wavelength of oblate core shell nanoparticle has a red shift relative to the prolate one. In both oblate and prolate core shell nanoparticles, field enhancement factor is extremely dependent on the shell thickness and in oblate core shell nanoparticle it’s dramatically greater than the prolate one in all distances from the center for all wavelengths and in both shapes, the maximum value of field enhancement factor take places in straight directions to applied field.

Multiwall carbon nanotubes/polyaniline: Poly‐m‐toulidine: Poly‐o‐toulidine nanocomposites—Synthesis, properties & field emission

Present paper reports synthesis of multiwall carbon nanotubes (MWCNTs)/polyaniline (PAni), MWCNTs/poly‐o‐Toluidine (PoT), and MWCNTs/poly‐m‐Toluidine (PmT) nanocomposites using in situ interfacial polymerization method. Field‐emission results show that among the PAni derivatives, the maximum value of field enhancement factor is obtained for MWCNTsTCE/PmT with corresponding lowest value of turn‐on field. The turn‐on field of the nanocomposites lies between 0.6 and 1.2 V/μm and there is a significant increase in the field enhancement factor (2.22 × 103–3.57 × 103). The average outer diameter of MWCNTs increases from 7–15 nm to 50–80 nm upon polymer coating. Raman spectrum confirms the interactions between polymer and CNTs. POLYM. COMPOS., 39:E955–E961, 2018. © 2017 Society of Plastics Engineers

Pulsed laser-deposited nanocrystalline GdB6 thin films on W and Re as field emitters

Gadolinium hexaboride (GdB6) nanocrystalline thin films were grown on tungsten (W), rhenium (Re) tips and foil substrates using optimized pulsed laser deposition (PLD) technique. The X-ray diffraction analysis reveals formation of pure, crystalline cubic phase of GdB6 on W and Re substrates, under the prevailing PLD conditions. The field emission (FE) studies of GdB6/W and GdB6/Re emitters were performed in a planar diode configuration at the base pressure ~10−8 mbar. The GdB6/W and GdB6/Re tip emitters deliver high emission current densities of ~1.4 and 0.811 mA/cm2 at an applied field of ~6.0 and 7.0 V/µm, respectively. The Fowler–Nordheim (F–N) plots were found to be nearly linear showing metallic nature of the emitters. The noticeably high values of field enhancement factor (β) estimated using the slopes of the F–N plots indicate that the PLD GdB6 coating on W and Re substrates comprises of high-aspect-ratio nanostructures. Interestingly, the GdB6/W and GdB6/Re planar emitters exhibit excellent current stability at the preset values over a long-term operation, as compared to the tip emitters. Furthermore, the values of workfunction of the GdB6/W and GdB6/Re emitters, experimentally measured using ultraviolet photoelectron spectroscopy, are found to be same, ~1.6 ± 0.1 eV. Despite possessing same workfunction value, the FE characteristics of the GdB6/W emitter are markedly different from that of GdB6/Re emitter, which can be attributed to the growth of GdB6 films on W and Re substrates.

The Effect of Gap Width on Field Emission Properties of Lateral Silicon Diodes

A simple method for fabricating lateral Si diodes with various gap widths were designed using the special properties of anisotropic TMAH wet etching and local anodic oxidation. The electrical performance of lateral diode was characterized using an HP4156c semiconductor parameter analyzer (SPA300HV, Agilent) at room temperature in a vacuum environment lower than 10-8Torr. The emission current from the silicon emitter cathode was measured as a function of the applied anode voltage. The effect of changing the anode-cathode gap was observed in the I-V characteristics, with a distinct reduction in the device turn-on with a decrease in the gap. For narrowed nanogaps from 55 nm to 35 nm, the turn-on voltage was decreased from 21 V to 16 V. Values of field enhancement factor β and emitting area A for different gap width were measured using Fowler-Nordheim plot. Our results indicate that β reduces and emitting area increases with increasing of gap width.

Arc plasma synthesized LaB6 nanocrystallite film on various substrates as a field emitter

Lanthanum hexaboride (LaB6) nanocrystallites/nanowires have been successfully synthesized using gas phase condensation in arc plasma. Our results show that the LaB6 nanowires have ~20 nm diameter and length of several micrometers. The as-synthesized LaB6 nanocrystallites and nanowires are crystalline in nature. Field emission studies were carried out on as synthesized LaB6 nano-powder deposited on W and Re tips and foils, and also on Si foil substrates under ultra high vacuum. The Fowler–Nordheim plots obtained from the current–voltage characteristics are found to be linear in accordance with the quantum mechanical tunneling phenomenon. High value of field enhancement factor (8177) is observed for LaB6 on Re substrate, indicating that the electron emission is from the nanometric features of the LaB6. Our results show that the arc plasma synthesized LaB6 nanocrystalline film exhibits good emission stability as emitter without severe deviations from the initial set value and also a strong ability to withstand the ion bombardment, which is useful for low operation voltage vacuum micro/nano electronic devices.

Electron field emission characteristics of carbon nanotube on tungsten tip

Electron field emission characteristic of carbon nanotubes on tungsten tip was investigated in 2×10-6 Torr vacuum. The measurement results showed that the CNTs/W tip could emit electron at 0.7 V/μm (nearly 10 times lower than that of the W tip itself) and reach up to 26 μA at the electric field of 1 V/μm. The emission characteristic follows the Fowler-Nordheim mechanism. Analysis of the emission characteristic showed that the CNTs/W tip has a very high value of field enhancement factor (β = 4.1 × 104 cm-1) that is much higher than that of the tungsten tip itself. The results confirmed the excellent field emission behavior of the CNTs materials and the CNTs/W tip is a prospective candidate for advanced electron field emitter.

Field emission studies of Te nanorods grown on Si (111) substrate

Tellurium nanorods were grown on silicon (111) substrates by thermal evaporation. The synthesized Te nanorods were characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM), prior to the field emission investigations. The TEM image revealed that the nanorods are needle-like having diameter less than 20 nm and length in the range of 200–400 nm. The selected area electron diffraction (SAED) pattern and high resolution TEM micrographs clearly reveal the crystalline nature of the Te nanorods. The field emission studies were carried out in a planar diode (close proximity) configuration at background pressure of ∼1 × 10 −9 mbar. An emission current density of ∼8.5 μA/cm 2 has been drawn at an applied field of ∼3.2 V/μm. The Folwer–Nodhiem plot, showed a non-linear behaviour. The high value of field enhancement factor ( β ∼ 1 × 10 4), estimated from the slope of the F–N plot, suggests that the emission is indeed from the nanometric tips of the Te nanorods. The emission current stability studied at the preset value ∼3.5 μA over duration of more than 3 h is found to be very good, suggesting the use of Te nanorods as promising electron source for field emission based micro/nano-electronic devices.

Electrical and structural characterizations of one-dimensional carbon nanostructures synthesized at ambient pressure

One-dimensional carbon nanostructures were synthesized at ambient pressure on molybdenum substrates using the pulsed laser deposition techniques. Scanning electron microscopy images revealed the evolutions of the nanostructures for different substrate temperatures, but otherwise identical growth conditions. Transmission electron microscopy images showed that the obtained carbon nanorods were about 20 nm in diameter and 1 µm in length. The crystallographic structures, chemical compositions and bond structures of the carbon materials were investigated using x-ray diffraction, energy dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy and Raman scattering spectroscopy, respectively.The electron field emission behaviours of the carbon nanostructures were considerably improved with the increase in substrate temperature. The rod-shaped nanostructures synthesized at 600 °C geometrically increase the effective emission sites, which consequently leads to a high value of field enhancement factor.

The roles of apex dipoles and field penetration in the physics of charged, field emitting, single-walled carbon nanotubes

A 1 μm long, field emitting, (5, 5) single-walled carbon nanotube (SWCNT) closed with a fullerene cap, and a similar open nanotube with hydrogen-atom termination, have been simulated using the modified neglect of diatomic overlap quantum-mechanical method. Both contain about 80 000 atoms. It is found that field penetration and band bending, and various forms of chemically and electrically induced apex dipole play roles. Field penetration may help explain electroluminescence associated with field emitting CNTs. Charge-density oscillations, induced by the hydrogen adsorption, are also found. Many of the effects can be related to known effects that occur with metallic or semiconductor field emitters; this helps both to explain the effects and to unify our knowledge about FE emitters. However, it is currently unclear how best to treat correlation-and-exchange effects when defining the CNT emission barrier. A new form of definition for the field enhancement factor (FEF) is used. Predicted FEF values for these SWCNTs are significantly less than values predicted by simple classical formulae. The FEF for the closed SWCNT decreases with applied field; the FEF for the H-terminated open SWCNT is less than the FEF for the closed SWCNT but increases with applied field. Physical explanations for this behavior are proposed but the concept of FEF is clearly problematical for CNTs. Curved Fowler–Nordheim plots are predicted. Overall, the predicted field emission performance of the H-terminated open SWCNT is slightly better than that of the closed SWCNT, essentially because a C–H dipole is formed that reduces the height of the tunneling barrier. In general, the physics of a charged SWCNT seems much more complex than hitherto realized.

Field emission properties of Fe70Pt30 catalysed multiwalled carbon nanotubes

Multi-walled carbon nanotubes were grown on nanocrystalline Fe70Pt30 film using low-pressure chemical vapour deposition (LPCVD) method. The growth time was varied between 5 min to 30 min. SEM micrograph of this film revealed that the size of nanoparticles varied from 5 nm to 10 nm. The diameter of the carbon nanotubes varied from 20 nm to 50 nm as verified by TEM. HRTEM image confirmed that the carbon nanotubes are bamboo-shaped multiwalled carbon nanotubes (MWNTs). Field emission characteristics of MWNTs at various growth times (5 min, 15 min and 30 min) with working distances (50 µm, 100 µm and 150 µm) were also studied. The carbon nanotubes grown for 30 min with working distance 150 µm exhibited the lowest turn-on field of 2.45 V/µm. The turn-on field increases from 2.45 V/µm to 6.21 V/µm as the growth time decreases from 30 min to 5 min whereas for lower working distances (100 µm and 50 µm), the turn-on field increases from 4.74 V/µm to 6.74 V/µm and from 8.79 V/µm to 14.49 V/µm respectively. The turn-on field (E to) and field enhancement factor (β) were studied as a function working distance (d) and growth time respectively to see the effect of these parameters on field emission properties. The field enhancement factor (β) was also studied as a function of radius of apex curvature (r) . It was found the field enhancement factor (β) decreases with the increase in radius of apex curvature (r) and growth time whereas the value of field enhancement factor (β) increases as working distance (d) increases. On the basis of the dependence of β on radius of apex curvature (r) a relationship of β ∝ r −1/2 is fitted.

Enhanced field emission in modified volcano-shaped field emitter

Modified volcano-shaped field emission arrays (MVSFEAs) have been fabricated by using one photolithography mask process and selfaligned technology. Owing to the enhanced electric field at the tips causing a larger value of field enhancement factor β, consequently, the onset voltage is lower and the emission current is higher for MVSFEAs. The emission current density at gate voltage of 380 V is 8.64 × 10 6 A cm −2 and emits about 58 nA per tip for volcano aperture radius of emitter, a, equal to 0.75 μm. The emission current density of MVSFEAs for a = 0.75 μm is 37.9 times larger than that of a = 0 μm (cone-shaped emitter) owing to the larger value of β for MVSFEAs.