Low Turn-on Field Research Articles

Enhanced electron field emission from NiCo2O4 nanosheet arrays

Electron emission properties of electrodeposited spinel NiCo2O4 nanosheet arrays grown on Ni foam have been studied. The work function of NiCo2O4 was calculated by density functional theory using the plane-wave basis set and used to estimate the field enhancement factor. The NiCo2O4 nanosheet arrays exhibited a low turn-on field of 1.86 V μm−1 at 1 μA cm−2 and current density of 686 μA cm−2 at 3.2 V μm−1, with field enhancement factor β = 1460 and good field emission current stability. The field emission properties of the NiCo2O4 nanosheet arrays showed enhanced performance compared to chemically prepared NiCo2O4 nanosheets. Hence, the nanosheet arrays have great potential as robust high performance vertical structure electron emitters for future flat panel displays and vacuum electronic device applications.

Synthesis of single-crystalline sodium vanadate nanowires based on chemical solution deposition method

We have demonstrated a simple and convenient chemical solution deposition method without employing catalysts, surfactants or carrier gases to synthesize sodium vanadate (β-Na0.33V2O5) nanowires (NWs) supported on conducting substrates. Both high resolution transmission electron microscopy and X-ray diffraction studies indicate the single-crystalline properties of such NWs. The morphologies of the β-Na0.33V2O5 NWs can be controlled by varying the growth temperature and duration. Moreover, the β-Na0.33V2O5 NWs show promising field emission (FE) performance with a high current density (54 mA cm−2), low turn-on field voltage (0.60 V μm−1) and a high degree of emission stability. These results suggest that β-Na0.33V2O5 NWs can serve as a candidate material for future electronic and FE devices.

Improvement on electrical conductivity and electron field emission properties of Au-ion implanted ultrananocrystalline diamond films by using Au-Si eutectic substrates

In the present work, Au-Si eutectic layer was used to enhance the electrical conductivity/electron field emission (EFE) properties of Au-ion implanted ultrananocrystalline diamond (Au-UNCD) films grown on Si substrates. The electrical conductivity was improved to a value of 230 (Ω cm)−1, and the EFE properties was enhanced reporting a low turn-on field of 2.1 V/μm with high EFE current density of 5.3 mA/cm2 (at an applied field of 4.9 V/μm) for the Au-UNCD films. The formation of SiC phase circumvents the formation of amorphous carbon prior to the nucleation of diamond on Si substrates. Consequently, the electron transport efficiency of the UNCD-to-Si interface increases, thereby improving the conductivity as well as the EFE properties. Moreover, the salient feature of these processes is that the sputtering deposition of Au-coating for preparing the Au-Si interlayer, the microwave plasma enhanced chemical vapor deposition process for growing the UNCD films, and the Au-ion implantation process for inducing the nanographitic phases are standard thin film preparation techniques, which are simple, robust, and easily scalable. The availability of these highly conducting UNCD films with superior EFE characteristics may open up a pathway for the development of high-definition flat panel displays and plasma devices.

Fabrication of graphene and ZnO nanocones hybrid structure for transparent field emission device

Fabrication of a transparent and high performance electron emission device is the key challenge for suitable display applications. Here, we demonstrate fabrication of a transparent and efficient field emission device integrating large-area chemical vapor deposited graphene and carbon doped zinc oxide (C:ZnO) nanocones. The ZnO nanocones were obtained with ion irradiation process at room temperature, over which the graphene film was transferred without destroying nanocone tips. Significant enhancement in field emission properties were observed with the transferred graphene film on C:ZnO nanocones. The threshold field for hybrid and pristine C:ZnO nanocones film at current density of 1μA/cm2 was obtained as 4.3V/μm and 6.5V/μm, respectively. The enhanced field emission properties with low turn-on field for the graphene/C:ZnO nanocones can be attributed to locally enhance electric field. Our finding shows that a graphene/C:ZnO hybridized structure is very promising to fabricate field emission devices without compromising with high transparency.

Morphology-dependent low macroscopic field emission properties of titania/titanate nanorods synthesized by alkali-controlled hydrothermal treatment of a metallic Ti surface

One-dimensional (1D) and two-dimensional (2D) titania/titanate nanostructures are fabricated directly on a self-source metallic titanium (Ti) surface via in situ surface re-construction of a Ti substrate using potassium hydroxide (KOH) under a hydrothermal (HT) condition. The effect of temperature and the concentration of KOH on the variations in morphology and titania-to-titanate phase changes are studied and explained in detail. A growth model is proposed for the formation process of the platelet-to-nanorod conversion mechanism. The field emission (FE) properties of titania/titanate nanostructures are studied, and the effects of the morphologies (such as 1D nanorods, 2D nanoplatelets, and a mixture of 1D nanorods and 2D platelets) on the FE properties of the samples are investigated. The samples depict a reasonable low turn-on field and emission stability. The FE mechanism is observed to follow standard Fowler–Nordheim (FN) electron tunneling. The geometrical field enhancement factor (β) is measured to be very high, and is compared with theoretical values calculated from various existing models to explore the feasibility of these models. The surface modification of metallic Ti by a simple non-lithographic bottom-up method and the low-macroscopic FE properties can provide a potential alternative to field emission displays for low-power panel technology.

ZnO:Ga nanowires with low turn-on field for field-emission lighting

ZnO:Ga nanowires were synthesized using a ZnO seed layer as a pseudo-catalyst by a vapor-phase transport method. Nanowire growth was facilitated along the longitudinal axis, and the aspect ratio was increased from 27.3 to 54.1 by doping with Ga3+, which also slightly enhanced growths of the (100) and (101) planes. The luminescent spectrum was narrower, more red-shifted, and less intense when the Ga3+ doping concentration was increased. However, the substitution of Ga for Zn enhanced the tunneling capability of electrons at the ZnO–vacuum interface. ZnO:Ga nanowires doped with 0.5mol% of Ga3+ achieved a low turn-on electric field of 0.57V/μm. A stable emission current of 0.85mA/cm2 with fluctuations within ±12.9% was observed over 5h of operation.

Cl-Doped ZnO Nanowire Arrays on 3D Graphene Foam with Highly Efficient Field Emission and Photocatalytic Properties.

An environmentally friendly, low-cost, and large-scale method is developed for fabrication of Cl-doped ZnO nanowire arrays (NWAs) on 3D graphene foam (Cl-ZnO NWAs/GF), and investigates its applications as a highly efficient field emitter and photocatalyst. The introduction of Cl-dopant in ZnO increases free electrons in the conduction band of ZnO and also leads to the rough surface of ZnO NWAs, which greatly improves the field emission properties of the Cl-ZnO NWAs/GF. The Cl-ZnO NWAs/GF demonstrates a low turn-on field (≈1.6 V μm(-1)), a high field enhancement factor (≈12844), and excellent field emission stability. Also, the Cl-ZnO NWAs/GF shows high photocatalytic efficiency under UV irradiation, enabling photodegradation of organic dyes such as RhB within ≈75 min, with excellent recyclability. The excellent photocatalytic performance of the Cl-ZnO NWAs/GF originates from the highly efficient charge separation efficiency at the heterointerface of Cl-ZnO and GF, as well as improved electron transport efficiency due to the doping of Cl. These results open up new possibilities of using Cl-ZnO and graphene-based hybrid nanostructures for various functional devices.

High-Performance Stable Field Emission with Ultralow Turn on Voltage from rGO Conformal Coated TiO2 Nanotubes 3D Arrays.

A facile method to produce conformal coated reduced graphene oxide (rGO) on vertically aligned titanium oxide (TiO2) nanotubes three dimensional (3D) arrays (NTAs) is demonstrated for enhanced field emission display applications. These engineered nano arrays exhibit efficient electron field emission properties such as high field emission current density (80 mA/cm2), low turn-on field (1.0 V/μm) and field enhancement factor (6000) with high emission current stability. Moreover, these enhancements observed in nano arrays attribute to the contribution of low work function with non-rectifying barriers, which allow an easy injection of electrons from the conduction band of TiO2 into the Fermi level of reduced graphene oxide under external electric field. The obtained results are extremely advantageous for its potential application in field emission devices.

Highly Conductive Diamond-Graphite Nanohybrid Films with Enhanced Electron Field Emission and Microplasma Illumination Properties.

Bias-enhanced nucleation and growth of diamond-graphite nanohybrid (DGH) films on silicon substrates by microwave plasma enhanced chemical vapor deposition using CH4/N2 gas mixture is reported herein. It is observed that by controlling the growth time, the microstructure of the DGH films and, thus, the electrical conductivity and the electron field emission (EFE) properties of the films can be manipulated. The films grown for 30 min (DGHB30) possess needle-like geometry, which comprised of a diamond core encased in a sheath of sp(2)-bonded graphitic phase. These films achieved high conductivity of σ = 900 S/cm and superior EFE properties, namely, low turn-on field of 2.9 V/μm and high EFE current density of 3.8 mA/cm(2) at an applied field of 6.0 V/μm. On increasing the growth time to 60 min (the DGHB60), the acicular grain growth ceased and formed nanographite clusters or defective diamond clusters (n-diamond). Even though DGHB60 films possess higher electrical conductivity (σ = 1549 S/cm) than the DGHB30 films, the EFE properties degraded. The implication of this result is that higher conductivity by itself does not guarantee better EFE properties. The nanosized diamond grains with needle-like geometry are the most promising ones for the electron emission, exclusively when they are encased in graphene-like layers. The salient feature of such materials with unique granular structure is that their conductivity and EFE properties can be tuned in a wide range, which makes them especially useful in practical applications.

Enhanced Field Emission Performance of Hierarchical ZnO/Si Nanotrees with Spatially Branched Heteroassemblies.

Silicon nanorods (SiNRs) with a large interspace and regularly aligned structure were fabricated by combining silver-catalyzed etching with a polysterene (PS) sphere template, then a hydrothermal reaction was utilized to synthesize large-scale ZnO nanowires (NWs) on Si nanorods. Compared with the as-prepared SiNRs and ZnO NWs, the high-density ZnO NWs on SiNRs have exhibited predominant field emission (FE) characteristics with a low turn-on field of 2.18 V/μm and a high field enhancement factor of ∼8100. The FE enhancement was attributed to highly crystallized ZnO NWs densely distributed on the surface of SiNRs, which can effectively increase emission site density, diminish screening effect, favor electron transfer due to band bending, and quickly transmit heat from the nanotrees to substrate. Our results indicate that ZnO/Si hierarchical structures might be an effective candidate for field emission cathode.

Pulsed laser deposition of graphite in air and in vacuum for field emission studies

A comparative study of pulsed laser deposition (PLD) based carbon films when deposited either, in atmospheric air, or under vacuum, has been performed. Micro-structural characterization of deposited films was carried out employing X-ray diffraction and Raman spectroscopic techniques. While, nanocrystalline graphite phase was observed in carbon films deposited in air, PLD films deposited under vacuum were largely amorphous in nature. Field emission (FE) properties of films deposited in air and under vacuum were investigated. Superior FE behavior characterized by a lower turn-on field (2.72 V/μm) and high field enhancement factor (∼2580) was observed for PLD films deposited in air. This improved field emission demonstrated by carbon films deposited via PLD in air can be attributed to presence of nanocrystalline graphite aggregates in such carbon films and local field enhancement near the sp2 sites. Our results therefore, establish PLD in air as a simple technique for deposition of carbon films having good field emission capability.

Formation of urchin-like CuO structure through thermal oxidation and its field-emission lighting application

Urchin-like CuO microstructures were formed using simple, template-free, one-step thermal oxidation of Cu solid microspheres in an air atmosphere at temperatures ranging from 350 to 500°C. The urchin-like CuO microstructure consists of crystalline CuO nanowires grown radially on the surface of the sphere, a shell layer of CuO a few micrometers in thickness, and a hollow core. Study of the formation mechanism revealed that during oxidation, the nanowires grow from the surface, and the diameter, length, and population density of the nanowires increase with the oxidation time. For a sample formed at 450°C for a dwell time of 24h, the average diameter, length, and population density of the nanowires were 44.0nm, 11.5μm, and 25nanowires/μm2, respectively. The novel urchin-like structure and high aspect ratio of the nanowires elicit unique properties. Study of the magnetic properties revealed that the urchin-like CuO is a semihard magnetic material with a coercive force of 135Oe. Studies on the field-emission characteristics of the material demonstrated that an urchin-like emitter had a low turn-on field of 2.94V/μm, a high field enhancement factor of 3715, a high luminance of 11,080cd/m2, an excellent emission uniformity of over 3.5×3.5cm2, and high emission stability during a 50-h test at a current density of 100μA/cm2.

Role of carbon nanotube interlayer in enhancing the electron field emission behavior of ultrananocrystalline diamond coated Si-tip arrays.

We improved the electron field emission properties of ultrananocrystalline diamond (UNCD) films grown on Si-tip arrays by using the carbon nanotubes (CNTs) as interlayer and post-treating the films in CH4/Ar/H2 plasma. The use of CNTs interlayer effectively suppresses the presence of amorphous carbon in the diamond-to-Si interface that enhances the transport of electrons from Si, across the interface, to diamond. The post-treatment process results in hybrid-granular-structured diamond (HiD) films via the induction of the coalescence of the ultrasmall grains in these films that enhanced the conductivity of the films. All these factors contribute toward the enhancement of the electron field emission (EFE) process for the HiDCNT/Si-tip emitters, with low turn-on field of E0 = 2.98 V/μm and a large current density of 1.68 mA/cm(2) at an applied field of 5.0 V/μm. The EFE lifetime stability under an operation current of 6.5 μA was improved substantially to τHiD/CNT/Si-tip = 365 min. Interestingly, these HiDCNT/Si-tip materials also show enhanced plasma illumination behavior, as well as improved robustness against plasma ion bombardment when they are used as the cathode for microplasma devices. The study concludes that the use of CNT interlayers not only increase the potential of these materials as good EFE emitters, but also prove themselves to be good microplasma devices with improved performance.

V2O5 nanoparticles grown on ZnO nanowires for enhanced field emission properties

To improve field emission (FE) properties of V2O5, ZnO nanowires were used as templates and V2O5 nanoparticles were successfully grown and coated on them via a chemical vapor deposition (CVD) route followed by a rapid anneal treatment. The particle size and shape were determined by the temperature sensitive crystallization of V2O5. Three different samples having different surface morphologies were obtained at 370, 450 and 510°C, respectively, in which V2O5 nanoparticles were grown on the surface forming sharp tips. SEM results revealed that the sample of 450°C had the sharpest tips, and its chemical states and components were examined by XRD analysis, confirming the coating of V2O5 on ZnO. FE measurements for the three samples showed enhanced FE properties compared with pure V2O5 and bare ZnO. Moreover, FE properties for the sample of 450°C are the best in the three samples, showing a low turn-on field reduced markedly from 4.38V/μm (V2O5) to 2.25V/μm and a high current density (at 5V/μm) increased markedly from 0.21mA/cm2 (V2O5) to 4.98mA/cm2. The corresponding field enhancement factor (β) also increased greatly to 3066, much higher than the value of pure V2O5 nanoparticles (βV2O5≈920) and higher than the value of bare ZnO (βZnO≈1590). The equipotential model analyses revealed that the enhanced FE properties were attributed to sharp tips formed by V2O5 nanoparticles, where the introduced V2O5 tips act as independent emitters on the surface and high local electric field around these tips increased the tunneling probability.

Bias-enhanced post-treatment process for enhancing the electron field emission properties of ultrananocrystalline diamond films

The electron field emission (EFE) properties of ultrananocrystalline diamond films were markedly improved via the bias-enhanced plasma post-treatment (bep) process. The bep-process induced the formation of hybrid-granular structure of the diamond (bep-HiD) films with abundant nano-graphitic phase along the grain boundaries that increased the conductivity of the films. Moreover, the utilization of Au-interlayer can effectively suppress the formation of resistive amorphous-carbon (a-C) layer, thereby enhancing the transport of electrons crossing the diamond-to-Si interface. Therefore, bep-HiD/Au/Si films exhibit superior EFE properties with low turn-on field of E0 = 2.6 V/μm and large EFE current density of Je = 3.2 mA/cm2 (at 5.3 V/μm).

Improving the field emission characteristics of tetrapod-like zinc oxide nanostructures by coating with silver nanowires

The field emission properties of tetrapod-like zinc oxide (T-ZnO) nanostructures coated with Ag nanowires were investigated. Field emission device based on T-ZnO/Ag nanowires hybrid cathode exhibited lower turn-on electric field, larger field enhancement factor and better stability as compared with the as-grown T-ZnO cathode. The results showed that the mechanical and electrical conduction between the T-ZnO and electrode have been greatly improved mainly owing to the introduction of Ag nanowires into T-ZnO nanostructures, and further the field emission properties of T-ZnO/Ag nanowires hybrid cathode have been greatly enhanced. As compared with the pure T-ZnO cathode, the T-ZnO/Ag nanowires hybrid is proved as a promising cathode candidate for field emission display.

Directed Self Assembly Of Copper-Based Hierarchical Nanostructures on Nitrogen-Doped Graphene and Their Field Emission Studies

We report a large scale root to assemble hierarchical copper-based nanostructures on nitrogen-doped graphene sheets by a pH followed by a temperature-directed self-assembly process and their electron field emission studies. Starting with a controlled pH directed self-assembly root, we assembled Cu(OH)2 NRs on NGS and further reassembled it to 1D Cu NPAs and CuO NRs by thermal annealing in H2 and Ar atmosphere, respectively. The field emission characteristics are precisely studied, which depicts a significantly lower threshold and turn-on field for 1D Cu NPAs-NGS-based emitter compared to CuO NRs-NGS and Cu(OH)2 NRs-NGS. Also it exhibited about 3 and 27 times higher emission current density than its oxide and hydroxide counterpart under a moderate field of 1 V/μm. The enhanced field emission behavior of 1D Cu NPAs-NGS is attributed to the low work function, the easy electron tunneling from the one-dimensional arrangement of Cu NPs, which increases the emission sites and hence the FE current density. On the basis of easy large-scale synthesis techniques and better FE performances, these hierarchical nanostructures offer prospects for understanding the effect of linear arrangement of nanoparticles on FE, which can be envisioned for design, fabrication, and optimization of cold cathode devices.

Enhanced field emission of graphene–ZnO quantum dots hybrid structure

The cathode of graphene was prepared by the electrophoretic deposition (EPD) and ZnO quantum dots (QDs) were grown on the surface of graphene sheets by solution method to improve the field emission (FE) properties. The graphene/ZnO QDs hybrid emitters exhibited efficient field emission with lower turn-on field of 0.9V/μm, lower threshold field of 2.6V/μm, higher field enhancement factor of 3923 and more stable emission current stability than pristine graphene. The improved field emission performance was attributed to ZnO QDs, which introduce more defects, increase the number of emitting sites and decrease the work function. This investigation proposed that graphene/ZnO QDs composites are promising field cathodes in FE applications.

Growth and field emission properties of GaN nanopencils

Novel gallium nitride (GaN) nanopencils have been synthesized on a silicon substrate by Ga2O3 with ammonia via the chemical vapor deposition (CVD) method. The observed morphology of GaN nanopencils is divided into two parts: the bottom is a nanowire with large diameter; the top is a nanowire with small diameter; the diameter of nanopencils decreases gradually from ~600nm to ~200nm along the wire axis. The formation mechanism of GaN nanopencils is a vapor–liquid–solid (VLS) mechanism. Field emission measurements show that GaN nanopencils film has high stability with a lower turn-on field of 3.5V/µm, which is sufficient for application in field emission flat panel displays and cold electron sources in display devices. Moreover, the synthesized GaN nanopencils will facilitate flexible design of device architectures for nanoelectronics.

A facile method used for controlled growth of SnO2 nanoparticles embedded in TiO2 films on FTO substrate as field emitters

Uniformly dispersed and protuberant SnO2 nanoparticles are prepared on FTO covered glass by pyrolysis and reconstruction technologies in a hydrogen environment using TiO2 sol as catalyst. By adjusting the amount of catalyst over the range of 6.5–45.5μL, the SnO2 nanoparticles are uniformly embedded in TiO2 films and display the controllable density, size and conductivity. Also, the growth mechanism of SnO2 nanoparticles is analyzed in detail based on the experimental results. The optimized SnO2 nanoparticles prepared with 32.5μL TiO2 sol show excellent field emission performances, with both a low turn-on field of 3.86V/μm and remarkable field emission stability over a 480-min period. Therefore, the reported uniformly dispersed and protuberant SnO2 nanoparticles with excellent field emission properties, may serve as one of promising candidates for application in flat panel displays and nanoelectronics building blocks.