Field Emission Behavior Research Articles

Formation of Diamond Films with Different Grain Sizes on TiO2 Nanotubes and Its Field Emission Properties

Diamond films with different grain sizes are deposited on TiO2 nanotube (TNT) arrays prepared by anodic oxidation using a microwave plasma chemical vapor deposition reactor. The scanning electron microscope, X‐Ray diffractometer, and Raman results indicate that the diamond film is successfully deposited and that the substrate undergoes a phase transition due to the diamond deposition temperature, resulting in the rutile phase becoming dominant with lower energy bandgap and work function. Notably, after 5 h of deposition, a relatively continuous microcrystalline film is formed on the TNTs, and the diamond grains change from spherical to pyramidal and show excellent electron field emission behavior, with a low turn‐on field of 0.5 V μm−1 and a current density of 85.9 μA cm−2. In addition, the deposition environment of the nanocrystalline diamond has a large impact on the substrate morphology, resulting in a blocked electron transport path, which reduces the overall field emission performance. The enhanced performance is attributed to the synergistic effect between the highly efficient 1D electron path of the TNTs, the negative electron affinity of the diamond surface, and the lower work function of rutile TiO2.

Design of a new process for the stabilization of FeS-Bi2S3 hybrid nanostructure and its application as a field emitter.

The relentless pursuit for technological advancement has fuelled intensive research into nanoarchitectures as fundamental components of various devices. One-dimensional (1-D) nanomaterials, including nanorods, nanowires, and nanotubes, have garnered significant attention due to their distinctive catalytic, optical, and electronic properties. Metal chalcogenides have emerged as promising candidates for diverse applications ranging from sensing devices to solar cells, particularly bismuth sulphide (Bi2S3). Bi2S3 exhibits unique properties owing to its low work function and anisotropic crystal structure. This work presents a novel approach to synthesize Bi2S3 nanorods and decorate them with FeS to form an FeS-Bi2S3 heterostructure via a one-step, template-free hydrothermal method. The synthesized nanomaterials are evaluated for their field emission characteristics, which are vital properties for numerous electronic applications. By comparing the field emission behaviour of the pristine Bi2S3 and FeS-Bi2S3 heterostructures, insights into the impact of hetero-structuring FeS for field emission performances are elucidated. This study presents insights into tailoring the heterostructure of different transition metals with Bi2S3 and studying their field emission behaviours.

Systematic synthesis of Bi2S3 nanoplates by template free solid-state approach and its field emission behaviour

We have demonstrated herewith controlled synthesis of Bi2S3 nanoplates by simple, template free, one step solid-state reaction at moderate temperature. The process parameters viz. precursor ratio, reaction temperature and duration were optimized. Nanostructured Bi2S3 synthesized at optimum conditions was further characterized by XRD, FESEM and FETEM, to study their phase, morphology and structure. The microscopic and XRD study reveals the formation of nanoplates like structures of orthorhombic Bi2S3. An attempt has been made to provide with a plausible growth mechanism as a function of reaction temperature and duration. In order to exploit the high 'aspect ratio' of the Bi2S3 nanoplates and explore its feasibility as potential electron source, field emission (FE) study has been performed at base pressure of ∼1 × 10−8 mbar. The results obtained herein reveal the morphology dependent FE behaviour of Bi2S3 nanoplates. The emitter comprised of Bi2S3 nanoplates synthesized at 180 °C showed better FE properties, lower turn-on field value, delivery of large emission current density (∼1670 µA/cm2 at 6.9 V/µm) and excellent emission current stability which are comparable to alike emitters due to semiconducting nanostructures. Highly crystalline nature and high aspect ratio of Bi2S3 nanoplates might be responsible for their good FE performance. These Bi2S3 nanostructures may have potential for applications in other optoelectronics devices.

Explanation of the quasi-harmonic field emission behaviour observed on epoxy-coated polymer graphite cathodes

Explanation of the quasi-harmonic field emission behaviour observed on epoxy-coated polymer graphite cathodes

Fabrication of In2Te3 nanowalls garnished with ZnO nanoparticles and their field emission behavior

Two-dimensional (2D) vertical oriented indium sesquitelluride (In2Te3) nanowalls, and ZnO/In2Te3 nanoheterostructures were grown on Si substrate via simple chemical vapor deposition (CVD) technique. The monitored In2Te3 nanowalls are single crystalline, 120–150 nm in size and approximately 50 nm thin. Indium sesquitelluride (In2Te3) has a suitable band gap for optoelectronic and energy field applications but its field emission properties have not been investigated yet. For the first time, In2Te3 structures have been subjected for field emission analysis which pointed out reasonable properties of field emission. Owing to field emission improvement, ZnO nanoparticles were garnished on In2Te3 nanowalls. This causes an impressive reduction in turn on field which approaches to 2.1 Vμm−1 as compared to pure In2Te3 nanowalls 3.2 Vμm−1. In addition, excellent emission stability without significant current degradation is noted. These findings indicated that 2D nanowalls of In2Te3 and ZnO/In2Te3 nanoheterostructures have great potentials for future applications in the energy field.

Enhanced field emission behaviour from ethylene glycol mediated synthesis of 2D hexagonal SnS2 disc with nanoparticle decoration

Herein, octahedron and stacked 2D hexagonal disc - like nanostructures of SnS2 were obtained by hydrothermal and ethylene glycol mediated hydrothermal methods, respectively. Attempt has been made to shade light on the plausible growth mechanism. Liquid phase exfoliation followed by centrifugation process leads to presence of tiny single crystalline SnS2 nanoparticles (∼5 nm) on the hexagonal discs over C substrate, characterized by preferred growth along {001} direction. The observed Raman shift and enhanced intensities of A1g and Eg modes infer charge interactions between the SnS2 disc and C substrate. Interestingly, the SnS2-C emitter exhibited superior field emission (FE) behaviour due to the unique morphology, excellent charge transfer, and reduced work function (∼4.1 eV). Here the extraction of large current density of ∼1137 μA/cm2 at an applied field of 3.72 V/μm, with good emission current stability. The present strategy is beneficial to design architectured morphology for multi-functionality.

First principle studies revealing the effect of O2, CO2, and H2 adsorption on field emission behaviour of graphene

The effects of the absorption of the gas molecule on the work function and the field emission current of graphene have been theoretically investigated. The results demonstrate that the absorbed O2, CO, and H2 on graphene with different absorption and absorption types have a large effect on its field emission properties. All absorbed O2, CO, and H2 on graphene with different absorption sites and absorption types except H2 on the bridge site lead to a reduction in its field emission current. It agrees with the experimental conclusion that the adsorption of O2 on the graphene will reduce its field emission current in the literature. Numerical results suggest that the density of adsorbed molecules, the types of adsorbed molecules, the type of adsorption and the location of adsorption could be detected by measuring the variation rule of the field emission current under different applied electric fields. This implies that the characteristics of field emission properties of graphene can be implemented as a working principle of a feasible gas sensor.

Numerical determination of field emission performance of GaN nanowire arrays

Determining the field emission turn-on field of the GaN nanowire array can better adapt to the application of field-assisted photocathode. A numerical simulation of the field emission behavior based on the finite difference method is proposed. Considering the influence of nanowire radius, height, cathode-anode spacing and interwire spacing on the field emission of GaN nanowires. The simulation proves that field enhancement factor of a single GaN nanowire is the most excellent, while emission electrons is relatively small. When GaN nanowires have a larger aspect ratio, it will have a larger enhancement factor and a small required turn-on electric field. Due to an enhanced field shielding, the enhancement factor of the GaN nanowire array reduces as interwire spacing reduces. Cathode-anode spacing hardly influences enhancement factor of GaN nanowire array, while potential distributions are affected by cathode-anode spacing to a certain extent.

Explanation of the Quasi-Harmonic Field Emission Behaviour Observed on Epoxy-Coated Polymer Graphite Cathodes

Explanation of the Quasi-Harmonic Field Emission Behaviour Observed on Epoxy-Coated Polymer Graphite Cathodes

Strain engineering of electronic structure and mechanical switch device for edge modified Net-Y nanoribbons

Net-Y is a new two-dimensional carbon structure, which has attracted research interest recently. Here, we study the relevant AB-type ribbons with edge modification, focusing on their strain controlling effects on their electronic structure and device characteristics. Intrinsic ribbons are metallic, but hydrogen or oxygen termination can transform them into semiconductors. Applying strain can effectively control the band gap size, resulting in a transition from an indirect band gap to a smaller direct band gap under appropriate strain, favorably to light absorbing. Strain can also change the work function of ribbons, especially for compressive strains, the work function is lowered significantly, which is beneficial to the improving of the field emission behaviors of ribbons. The analysis demonstrates that the change in band gap size is closely related to the variation of bonding and non-bonding composition between atoms with strain, while the change of work function is due to the variation of the attraction force and repulsion force between atoms upon strain. More interestingly, the strain can significantly regulates the <i>I</i>-<i>V</i> characteristic of device based on related ribbons. Therefore, a strain-gated mechanical switch with a very high current switching ratio <i>I</i><sub>on</sub>/<i>I</i><sub>off</sub> can be obtained by making it reversibly work between the “on” and “off” states with stretching and compressing ribbons, which is of great significance in developing the logic circuits for flexible wearable electronic devices.

Morphology-dependent field emission investigations from the 2-dimensional Bi2Se3-RGO nanocomposites

The two-dimensional bismuth selenide (Bi2Se3)-reduced graphene oxide (RGO) nanocomposite have been synthesized by simple hydrothermal route for carrying out field emission (FE) studies. The Bi2Se3-RGO nanocomposite field emitters exhibit enhancement in the current densityas compared to pristine Bi2Se3emitter. The turn-on field for Bi2Se3-RGO nanocomposite field emitter decreases by ∼37% of its value for pristine Bi2Se3 emitters. The maximum current density observed from the Bi2Se3-RGO nanocomposite field emitter is ∼1000 µA/cm2 at an applied field of 6.0 V/μm. The influence of Se weight percentage in the Bi2Se3-RGO nanocomposite has been studied to understand the field emission behavior via morphological changes of the emitter surface. The Bi2Se3-RGO nanocomposite structure is thus seen as a prospective candidate for the development of efficient nanoscale field emission devices.

Field emission behavior of titanium alloy nanosheets

In this study, the field emission behavior of titanium alloy nanosheets is observed for the first time. The titanium alloy nanosheets on titanium alloy substrate display low turn-on and threshold field, whose values are 3.02 V/μm and 4.51 V/μm, respectively. In addition, the titanium alloy nanosheets exhibit excellent emission stability over a period time of 1200 min. Such good field emission properties can be attributed to the relatively low work function and abundant tip structures for electrons emitting. These results show the potential of titanium alloy nanosheets as a cathode material in field-emission devices.

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.

Photo-enhanced field-emission behavior of CdSSe microflowers

In this work, we synthesized well-grown cadmium sulfoselenide (CdSSe) microflowers on gold-coated silicon substrate using a simple and low-cost chemical bath deposition technique. The deposited CdSSe film was annealed in a furnace for 30 min at [Formula: see text]C. Subsequently, the annealed CdSSe film was further characterized using structural, morphological and field-emission analyses. The CdSSe microflowers show photosensitive field-emission behavior. In the photosensitive field emission, the emission current rises by nearly 2–3 times of its primary preset current value of [Formula: see text]A.

Controlled decoration of palladium (Pd) nanoparticles on graphene nanosheets and its superior field emission behavior

Development in nanoscience and nanotechnology has inspired scientists to continuously explore new cathode material for field emission applications. In the present article, different weight (wt) % of Pd nanoparticles (Pd NPs) ensemble on graphene (Gr) nanosheets (Pd-Gr) were prepared via one step simple chemical route. The field emission (FE) properties of Pd decorated Gr nanosheets were studied. Structural and morphological analysis of as synthesized Pd-Gr composites were carried out by using X-ray diffraction (XRD), Raman spectroscopy and transmission electron microscope (TEM). The FE properties of the Pd-Gr changed according to the variation in the wt% of Pd NPs. The Pd3-Gr field emitter showed better performance among all the emitters with lower turn on field, threshold field and maximum emission current density (J). The enhanced FE properties of Pd-Gr are due to the decoration of low work function Pd NPs. The FE results demonstrated herein suggest that, Pd-Gr based field emitters can open up many opportunities for their potential utilization in large area field emitters in various vacuum micro-nanoelectronic devices such as flexible field emission displays, portable X-ray and microwave tubes.

Semi-analytic model of a carbon fiber thermal-field emitter

Carbon fibers passing current are subject to resistive heating. When failure occurs, this is related to their local temperature. The failure temperature and its location are estimated. The temperature variation is calculated using analytical models for electrical and thermal conductivities based on the temperature dependent electron–phonon relaxation time. In the absence of radiative heat loss, an analytic expression of temperature along the fiber is given from which a maximum possible emission current is derived and is governed by a single introduced parameter ωo. A method of treating the radiative heat loss is developed and is governed by a second parameter γ, which allows a rapid numerical means to calculate the correction to the analytic form. Heat variation along a thick carbon fiber is contrasted to that along a multi-walled carbon nanotube (MWNT): it is shown that the relative magnitude of ωo compared to γ determines that the analytical formula is a good approximation for MWNTs but requires numerical correction for fibers. Furthermore, it is shown that the analytical form of ωo specified a maximum current beyond which the carbon emitter fails due to thermal runaway. The theoretical models are used to interpret observed behavior of field emission from carbon fibers and the resulting damage they endure when the extracted field-emission current is high. Results from implementing the developed temperature variation model into the MICHELLE beam optics simulation code are presented, with an example application predicting the conditions for stable equilibrium operation as well as for the onset of fiber failure.

Hierarchical nickel sulphide microstructures for controlled water disinfection and cold cathode emission

Hierarchical nickel sulphide microtubes were prepared by cost effective sol-gel technique with tuning of morphology and applied for photo-induced hazardous dye segregation and cold electron emission. The synthesized samples were characterized for crystalline phase, morphology and composition via X-ray diffractometry, electron microscopy and energy dispersive X-ray studies respectively. The band gaps were estimated from UV–vis data. The samples were found to be effective as a dye degrading agent under UV irradiation. The pollutant removal efficiency of the nickel sulphide (NS) microstructures was found to be governed by dimension and compositional parameters jointly. The sample showing highest degradation efficiency was found to degrade phenol effectively. Scavenger test was carried out to identify the active radicals involved in the catalysis process. To ensure long term action of the catalyst sample, recyclability of the same was investigated thoroughly. The NS microstructures also showed field emission behaviour which is reported for the first time. The growth of different shapes and hierarchical units of NS structures was correlated with stoichiometric alteration which may also be extended for synthesis of other nickel chalcogenides.

Synthesis, characterization and field emission studies of NiO-rGO nanocomposite

In this work, NiO-rGO nanocomposite was synthesized by hydrothermal/solvothermal method on nickel foil. The as-synthesized product was subjected to various characterizations such as X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Raman spectroscopy, in order to reveal its phase, morphology and structure. The SEM analysis reveals formation of nearly vertically oriented and randomly distributed nanoflakes of NiO-rGO nanocomposite on entire substrate surface. The Raman spectrum of the NiO-rGO composite showed characteristic D and G bands of rGO, confirming its presence in the composite. The NiO-rGO composite emitter showed promising field emission behaviour. The values of turn-on and threshold fields, defined at emission current density of 1 and 10 µA/cm2, were observed to be 1.8 and 2.25 V/µm, respectively, which are comparable to alike composite emitters. Furthermore, from the NiO-rGO composite emitter, maximum current density of 719 µA/cm2 has been extracted at an applied field of 4.5 V/µm. The observed results imply potential of NiO-rGO composite emitter for application in vacuum microelectronic devices.

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.

Effect of electrical conduction on the electron emission properties of diamond needles

Single crystal diamond needles are promising structures as point electron sources. However, the low electrical conductivity of diamond limits their application as high brightness electron sources. Here we study experimentally and numerically the field emission behavior of single crystal diamond needles, in order to better explain the link between the low electrical conduction, the non-homogeneous field distribution in the needle, the evolution of the field enhancement factor and the saturation of the Fowler–Nordheim plot. Field emission current and voltage loss were measured as a function of the applied voltage. Numerical modelling was used to solve conduction, emission and Laplace equations taking into account the real geometry of the field emitter and its environment. The combination of experimental and numerical results shows that the conduction behavior and the field enhancement factor depend on the diamond geometry. Moreover, the Fowler–Nordheim plot saturation is shown to be affected by the electrostatic environment which can limit the range of voltage losses that can appear along the diamond needle and hence limit the field emission current. At the same time, the increase of the emission current at high field, which is sometimes argued to be caused by the breakdown of the field emitter, is here presented as a simple consequence of the conduction properties of the field emitter as it was already shown for silicon field emitters.