Electron Field Emission Characteristics Research Articles

Effect of Metal Nanoparticles in the Field Emission of Silicon Nanowires

In this work, an efficient method is reported for creating a metal nanoparticle (silver) / Si composite structure consisting of a vertical array of silicon nanowires (SiNWs) decorated with silver metal nanoparticles. A two-stage metal-assisted etching method is employed to obtain SiNWs and Silver (Ag) metal nanoparticles are decorated on the SiNWs using the electroless deposition method. It allows the good coverage of silver metal nanoparticles over SiNWs. Scanning Electron Microscopy (SEM) analysis revealed that Ag was covered with SiNWs. High-work function metal nanoparticles such as Ag nanoparticles on SiNWs have been utilized in different applications such as photovoltaics and sensors. The size of SiNWs is determined through the Raman shift. The silicon optical phonon peak showed an increase in redshift and a decrease of full-width at half maxima with a decrease in diameter due to the quantum confinement. The Electron Field Emission (EFE) characteristics of the Agdecorated SiNW films were studied based on the current-voltage measurements and analyzed using the Fowler-Nordheim (F-N) equation. The low turn-on field is obtained through the Ag metal nanoparticles which have wider applications in lowpower operational devices.

Improved field electron emission behavior of ultrathin lanthanum hexaboride-coated copper oxide nanowires

A simple approach dealing with thermal oxidation at atmospheric pressure was used to synthesize copper oxide nanowires (CuO-NWs) on copper substrate. The vertically oriented CuO-NWs were used for further subjected to deposition of ultrathin layer (∼20[Formula: see text]nm) of lanthanum hexaboride (LaB[Formula: see text] using the electron beam evaporation technique. The observation of the characteristic vibrational mode of LaB6 in the Raman spectrum of LaB6-coated CuO-NWs (LaB6@CuO-NWs) revealed the existence of LaB6 in the deposited sample. Furthermore, confirmation of LaB6 coating on CuO-NWs was corroborated by X-ray photoelectron spectroscopy (XPS) analysis. The field electron emission (FEE) characteristics of pristine CuO-NWs and LaB6@CuO-NWs were investigated in a planer diode geometry at a base pressure of [Formula: see text][Formula: see text]mbar. The values of turn-on and threshold fields (defined at emission current density of 1 and 10[Formula: see text][Formula: see text]A/cm2, respectively) were found to be 5.4[Formula: see text]V/[Formula: see text]m and 1.6[Formula: see text]V/[Formula: see text]m (for pristine CuO-NWs emitter) and 6.75, and 2.85[Formula: see text]V/[Formula: see text]m (for LaB6@CuO-NWs emitter). Interestingly, a noticeably large emission current density of [Formula: see text][Formula: see text][Formula: see text]A/cm2 has been extracted from the LaB6@CuO-NWs emitter at a relatively lower applied field of 5.8[Formula: see text]V/[Formula: see text]m. The Fowler–Nordheim (FN) plots of both the emitters showed nonlinear behavior, indicative of their semiconductive nature. Furthermore, both the emitters showed relatively stable emission behavior tested at a pre-set value of 1[Formula: see text][Formula: see text]A more than 3[Formula: see text]h. The enhanced FEE behavior of LaB6@CuO-NWs emitter is attributed to the modulation of electronic properties due to LaB6-CuO interface-induced effects. Although the promising FEE behavior of LaB6@CuO-NWs emitter warrants its potential for practical applications, further improvement can be achieved via fabricating an array emitter due to CuO NWS and optimizing the thickness of LaB6 coating.

Size- and temperature-dependent optical, and electron field emission characteristics on SnO2 nanocrystals

Size-dependent SnO2 nanocrystals (NCs)) were synthesized using a co-precipitation technique. The particle size was varied by annealing the as-prepared SnO2 NCs with the estimated size of 2.3 nm at different temperatures. The particle size obtained was 4.7, 9.0, 15.4, 19.6, and 48.0 nm at annealing temperatures of 400, 600, 800, 1000, and 1200 °C, respectively. The XRD data revealed the tetragonal rutile structured for all SnO2 NCs. The temperature-dependent photoluminescence (PL) studies showed that the sub-bridging oxygen vacancy contributed dominantly compared to the in-plane and bridging oxygen vacancies at 5K. The function of nanocrystals’ size on field emission properties is also reported. The current density was high (1.9 μA/cm2) with modest the turn-on field (8.4 V/μm) for as-prepared SnO2 QDs with the lowest size (2.3 nm) compared to the high temperature annealed SnO2 nanocrystals.

Self-consistent numerical solution of quantum regime with exchange-correlation effects of space charges for electron field emission in a nano-gap

The quantum effects of space charge on electron field emission have been widely investigated since the last century. When electrons energy and their mean spacing approach the Hartree level and the de Broglie wavelength respectively, the influence of the quantum effects on the field emission current becomes significant. In this work, by developing an in-house software, we self-consistently solve the one-dimensional Poisson-Schrödinger equation together with the Wentzel-Kramers-Brillouin-Jeffreys (WKBJ) model for metal-vacuum-metal nanogaps, after considering the anode screening effect, space charge Coulomb potential and exchange-correlation effects simultaneously. Employing the method, the electron field emission characteristics were studied by varying the nanogap spacing (D) and the electric field strength (F), and four different emission regimes including quantum regime (QR), space charge limited regime (SCLR), direct tunnelling regime (DTR) and field emission regime (FER) are defined. The influences of space charge field components on the field emission characteristics and space charge distribution are analyzed for different emission regimes in nanogap. In addition, the impact of using different exchange-correlation functionals (LDA, GGA and meta-GGA) on Jacob’s ladder for describing the quantum effects of space charge on the electron emission current density was analyzed. Finally, electron field emission properties of one-dimensional (1-D) nanogaps consisting of refractory metals (W and Mo) as well as the three-dimensional (3-D) nano-tip are discussed to elucidate the impact of the exchange-correlation effects on the enhanced field emission process at nanoscale.

Thickness dependent field emission study of LaB6 coated Si nanowire arrays

A simple physical metal mask is efficiently employed to obtain an array of silicon (Si) nanowires (Si-NWs) on a Si substrate grown using the hot filament chemical vapor deposition route. Well adhered and uniform coating of different thicknesses (20 and 50 nm) of lanthanum hexaboride (LaB6) on Si-NWs was obtained using electron beam evaporation technique. The thickness of LaB6 coating was estimated from ellipsometry measurement. Structural, morphological, and chemical properties of the LaB6 coated Si-NWs (LaB6@Si-NWs) arrays were revealed using x-ray diffraction, field emission scanning electron microscope, transmission electron microscope, Raman spectroscopy, and x-ray photoelectron spectroscopy. Field electron emission characteristics of pristine Si-NW array and LaB6 coated Si-NWs array emitters were studied in planar diode configuration at a base pressure of 1 × 10−8 mbar. The values of turn-on field (current density ∼1 μA/cm2) were observed as ∼2.2, 1.2, and 1.6 V/μm for pristine Si-NWs, LaB6@Si-NWs_20, and LaB6@Si-NWs_50 array emitters, respectively. Furthermore, maximum emission current densities of ∼1276.81, 2763.64, and 2231.81 μA/cm2 have been extracted from the pristine Si-NWs, LaB6@Si-NWS_20, and LaB6@Si-NWS_50 array emitters at an applied field of 3.1, 2.7, and 2.7 V/μm, respectively. The LaB6@Si-NWS_20 array emitter demonstrated superior FEE properties as compared to the pristine Si-NWs and LaB6@Si-NWS_50 emitters. Furthermore, LaB6@Si-NWS_20 emitter depicted very good emission current stability tested at a preset value of 1 μA over a duration of 3 h. The enhanced FEE performance exhibited by the LaB6@Si-NWs_20 array emitter is attributed to reduction in effective work function and enhanced electron tunneling probability across the LaB6–Si interface.

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.

Field Electron Emission Characteristics of Tungsten–Polyethylene Composite Material As a Source of Electron Emission

Abstract: This work provides an experimental study on the effects of polyethylene coating on the field electron emission characteristics of clean (uncoated) tungsten tips. Several tungsten tips, with different apex radii, have been prepared, coated with different thicknesses of polyethylene layers and then examined using a standard field electron emission microscope. Various field electron emission characteristics have been measured under high-vacuum conditions. These include current-voltage characteristics, Fowler-Nordheim plots, scanning electron micrographs and spatial current distributions (electron-emission images). Based on this work, it is proved that coating tungsten tips with polyethylene layers has caused dramatic improvements on the tip emission properties. In particular, coating the tips improves the current-voltage characteristics, which is reflected in lowering the extraction voltage, getting more stable emission currents, expressing the current-voltage characteristics using Fowler-Nordheim plots and finally, the spatial distributions of the emitted electrons for the coated tips are more stable and uniform. Keywords: Field electron emitter, Polyethylene dielectric layer, Composite emitter, Field electron microscope, Scanning electron microscope.

Field electron emission from tungsten micro-tips coated with various thicknesses of polystyrene nanolayers: Characteristics & analysis

This paper studies and analyses the characteristics of cold field electron emission from uncoated polycrystalline tungsten tips before and after being coated with an insulating polystyrene layer of different thicknesses. The process of testing the samples has been carried out under high vacuum conditions (10−8 mbar). Uncoated tungsten tips were prepared using the electrochemical etching process. The current-voltage characteristics of the samples before and after being coated were presented and analysed using Murphy-Good plots. Scanning electron micrographs for the samples under investigation have been included. Additionally, the electron emission patterns, before and after the coating process have been included. This is to compare the obtained results and study the effect of the coating layer on the performance of the electron source. The results show significant improvements on the performance of the coated tungsten emitters in comparison with the uncoated emitters.

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.

Nanoscale Vacuum Field Emission Triode With a Double Gate Structure

A planar lateral Vacuum Field Emission Triode (VFET) with a double gate structure is proposed to improve the gate modulation characteristics in this letter. The preparation of this double gate structure is obtained by using the mature bottom gate VFET manufacturing process without any additional dedicated masks. The emission characteristics of the fabricated VFET under vacuum and atmosphere condition are measured. The experimental results demonstrate that both the bottom gate and the top gate can effectively control the emission electrons in the vacuum channel with width of about 110–200 nm which is successfully prepared by the electro-forming process. The operating mechanism of the device is basically the same as that of the plane-bottom gate VFET, and the device has achieved good field electron emission characteristics and double-gate modulation characteristics. Meanwhile, the vacuum channel is covered by the top gate insulator layer, which relaxing the vacuum requirement and improving the collection efficiency of emitted electrons by drain electrode about 50% in air.

Investigation of changes in field electron emission characteristics of industrial fine-grained graphite when operated in an argon atmosphere up to 10–2 Pa

Studying of field electron emission properties of carbon cathodes operating under technical vacuum conditions is a promising scientific field. Massive cathode made of commercial fine-grained graphite of MG (Russian abbreviation) grade is being investigated. Experiments on obtaining current-voltage characteristics and long-term testing are being carried out. The emitter made of fine-grained graphite demonstrates good emission properties under technical vacuum conditions. Carbon cathode is capable of operating at pressures up to 2×10–2 Pa. Increased pressure in the vacuum chamber leads to deterioration of cathode emission properties. Electric field enhancement factors were calculated for all stages of studies. Analysis of experimental data demonstrates decrease in enhancement factor due to ion bombardment of cathode surface during exploitation. This results in higher electric field for operation of investigated graphite cold cathodes.

Impact of edge functionalization on electron field-emission characteristics of carbon nanotubes: A theoretical approach

A theoretical approach using first-principle calculations of the density of states (DOS) of functionalized carbon nanotubes (CNTs) is carried out to understand their enhanced electron field emission (FE) properties. The theoretical functionalization of CNTs is perceived using hydrogenation (H/O–H) and oxidation methods. In order to investigate the enhancement in the FE properties of functionalized CNTs, both single-walled carbon nanotubes (SWCNT) and double-walled carbon nanotubes (DWCNT) are studied. The work function is observed to be more decreased in case of zigzag SWCNT (φ = 3.32 for oxygenated SWCNT) as compared to others SWCNT. The dependence of DOS on zigzag/armchair edge functionalization has also been investigated to reveal the impact of DOS on FE. The observed results indicate that edge functionalization of CNTs leads to significant changes in the band structure, DOS, and work functions. The shifting of DOS away from the Fermi level and decrease in work function is evidenced owing to the reduction in the curvature effect of CNT. Also, due to enhanced DOS near the Fermi level, making them a better proposition for FE applications. Our calculations provide an in-depth insight into the functionalization mechanism to understand the enhanced FE properties from them.

Stable Field Electron Emission and Plasma Illumination from Boron and Nitrogen Co‐Doped Edge‐Rich Diamond‐Enhanced Carbon Nanowalls

AbstractSuperior field electron emission (FEE) characteristics are achieved in edge‐rich diamond‐enhanced carbon nanowalls (D‐ECNWs) grown in a single‐step chemical vapor deposition process co‐doped with boron and nitrogen. The structure consists of sharp, highly conductive graphene edges supplied by a solid, diamond‐rich bottom. The Raman and transmission electron microscopy studies reveal a hybrid nature of sp3‐diamond and sp2‐graphene in these nanowalls. The ab‐initio calculations were carried out to support the experimental observations of diamond‐graphene hybrid structure. Finally, this hybrid D‐ECNWs is employed as a cathode in an FEE device resulting in a low turn‐on field of 3.1 V µm−1, a large field enhancement factor, a high FEE Je of 2.6 mA cm−2, and long lifetime stability of 438 min. Such an enhancement in the FEE originates from the unique materials combination, resulting in good electron transport from the graphene phases and efficient FEE of electrons from the sharp edges on the nanowalls. The prospective application of these materials is displayed by employing these hybrids as cathodes in a microplasma device ensuing a low threshold voltage of 160 V and high plasma stability of 140 min, which confirms the role of these hybrid structured nanowalls in the enhancement of electron emission.

Highly efficient field emission properties of vertically aligned 2D CuSe nanosheets: An experimental and theoretical investigation

We report the synthesis of klockmannite (CuSe) via a three-probe electrochemical set-up (chronoampereometry). The structural properties are examined by X-ray diffraction and Raman spectroscopy. Field emission scanning electron microscopy (FESEM) analysis revealed the formation of vertically aligned CuSe nanosheets with an average thickness of 34 nm and an average lateral size of 700 nm. The CuSe nanosheets exhibit impressive field electron emission characteristics with a turn-on field of 1.4 V/µm for 10 µA/cm2 emission current density. Also, a high current density of 5.8 mA/cm2 is observed at a relatively low applied field of 3.1 V/µm. Complementary first-principles DFT calculations show that CuSe displays metallic conductivity, and the (001) surface has a low work function of 5.12 eV, which is believed to be responsible for the impressive field emission characteristics.

Laser-Patternable Graphene Field Emitters for Plasma Displays.

This paper presents a plasma display device (PDD) based on laser-induced graphene nanoribbons (LIGNs), which were directly fabricated on polyimide sheets. Superior field electron emission (FEE) characteristics, viz. a low turn-on field of 0.44 V/μm and a large field enhancement factor of 4578, were achieved for the LIGNs. Utilizing LIGNs as a cathode in a PDD showed excellent plasma illumination characteristics with a prolonged plasma lifetime stability. Moreover, the LIGN cathodes were directly laser-patternable. Such superior plasma illumination performance of LIGN-based PDDs has the potential to make a significant impact on display technology.

A Comparative Study of Field Emission From Pristine, Ion‐Treated and Tungsten Nanoparticle‐Decorated p‐Type Silicon Tips

The field electron emission characteristics of individual tips of a silicon field emitter array are analyzed. The array of conical‐shaped tips is fabricated on a p‐type silicon wafer by using reactive ion etching and sharpening oxidation. The tips are decorated with single tungsten nanoparticles at their apexes. Furthermore, the focused ion beam is also used to increase surface conductivity of some of the tips. Comparative measurements of field emission are performed by using the scanning anode probe field emission microscopy technique. All types of tips demonstrated emission activation consisting of a sudden current increase at a certain value of the applied voltage. Compared to the pristine tips, a noticeable reduction of the saturation effect in the current–voltage characteristics and a smaller light sensitivity for the decorated tips is found. For ion‐treated tips, saturation effects and light sensitivity are completely suppressed. Scanning electron microscopy observations reveal the formation of single nanoscale protrusions extending from the metal particles and from the apexes of bare ion‐treated tips after exposure under strong electric fields during the field emission measurements. The influence of protrusions growth on characteristics of silicon field emitter arrays is discussed.

Simple planar field-electron emitter using highly crystalline single-walled carbon nanotubes in a triode structure with in-plane under-gate electrode

The authors investigated the field-electron emission characteristics of a planar field-emission (FE) electron source with a planar conductive layer as a gate electrode embedded under a cathode composed of highly crystalline single-walled carbon nanotubes (hc-SWCNTs) as an emitter. They designed a flat-panel electron emission device that could control electron emission switching arbitrarily, and the device stably emitted electrons on the flat panel. After they assembled the FE electronic device using a wet chemical process, they attained low power consumption and high luminance efficiency. These results show that the application of hc-SWCNTs effectively conserves energy in FE electron sources. The fabrication of FE electron sources and other devices with ultralow power consumption, along with applications that utilize such devices, is expected in the future.

Electron field emission from graphene nanosheets grown on Si nanoporous pillar array

Graphene nanosheet (GNS) thin film was grown flat lying on Si nanoporous pillar array (Si-NPA) substrate using Ni nanocrystallites as catalyst by a chemical vapor deposition method, and its field electron emission characteristics were studied. The thin film was proved to be composed of high-quality few-layer GNSs with a typical size of ~6 nm. With a turn-on field of ~2.85 V/μm, an emission current density of ~53.9 μA/cm2 was obtained at an electric field of 4.2 V/μm. Based on the experimental data, the enhancement factor of few-layer GNS/Si-NPA was calculated to be ~2700 according to the Fowler–Nordheim theory. The cold cathode also showed higher emission stability than vertically standing graphene at low operating voltages. For comparison, GNS/Si-NPA with multi-layer GNSs was prepared and its turn-on field was obtained as high as 8.5 V/μm. The origin of the high emission performance was attributed to numerous emission sites formed at the edges of GNSs, unique structure and morphology of GNS/Si-NPA, and low electric resistance of GNSs. Our results might have provided an alternative approach for fabricating Si-based low-voltage cold cathodes with high device performances.

Stability of electron field emission in Q-carbon

In this study, we have investigated electron field emission (EFE) characteristics of Q-carbon at room temperature and above. At room temperature the Q-carbon requires only ~2.4 V/μm electric field to turn-on the EFE. The EFE properties of the Q-carbon composite structure improve with temperature by lowering the turn-on field and increasing the current density. At 500 K we observed a turn-on field of ~2.34 V/μm, and a maximum current density was found to be ~53 µA/cm2 at 2.66 V/μm. The Q-carbon field emitters also show very stable EFE characteristics (within 7% fluctuations) over time for current intensities between 7.5 and 47 µA/cm2.

Microstructural Effect on the Enhancement of Field Electron Emission Properties of Nanocrystalline Diamond Films by Li-Ion Implantation and Annealing Processes

The impact of lithium-ion implantation and postannealing processes on improving the electrical conductivity and field electron emission (FEE) characteristics of nitrogen-doped nanocrystalline diamond (nNCD) films was observed to be distinctly different from those of undoped NCD (uNCD) films. A high-dose Li-ion implantation induced the formation of electron trap centers inside the diamond grains and amorphous carbon (a-C) phases in grain boundaries for both types of NCD films. Postannealing at 1000 °C healed the defects, eliminated the electron trap centers, and converted the a-C into nanographitic phases. The abundant nanographitic phases in the grain boundaries of the nNCD films as compared to the uNCD films made an interconnected path for effectual electron transport and consequently enhanced the FEE characteristics of nNCD films.