Efficient Field Emission Research Articles

Improving field emission properties of CuO nanowires by coating with ZnO nanoparticles

A facile solution route of self-assembled zinc oxide (ZnO) nanoparticles (NPs) on the surface of cupric oxide (CuO) nanowires (NWs) was presented, and field emission arrays with ZnO NPs–CuO NWs hybrid emitters were fabricated. The NW based conjugation by coating ZnO NPs on CuO NWs was confirmed by transmission electron microscopy (TEM) image. The turn on electric fields of the ZnO NPs–CuO NWs hybrid emitters decreased to 2·37 V μm−1 compared with 4·95 V μm−1 of pure CuO NWs, and the field enhancement factor was significantly enhanced from ∼869 (pure CuO NWs) to ∼1678 (ZnO NPs–CuO NWs). The ZnO–CuO NWs hybrid emitters also have higher emitting uniformity, which indicated the efficient field emission properties for the hybrid emitters.

Patterned growth of carbon nanotubes over vertically aligned silicon nanowire bundles for achieving uniform field emission.

A fabrication strategy is proposed to enable precise coverage of as-grown carbon nanotube (CNT) mats atop vertically aligned silicon nanowire (VA-SiNW) bundles in order to realize a uniform bundle array of CNT-SiNW heterojunctions over a large sample area. No obvious electrical degradation of as-fabricated SiNWs is observed according to the measured current-voltage characteristic of a two-terminal single-nanowire device. Bundle arrangement of CNT-SiNW heterojunctions is optimized to relax the electrostatic screening effect and to maximize the field enhancement factor. As a result, superior field emission performance and relatively stable emission current over 12 h is obtained. A bright and uniform fluorescent radiation is observed from CNT-SiNW-based field emitters regardless of its bundle periodicity, verifying the existence of high-density and efficient field emitters on the proposed CNT-SiNW bundle arrays.

Geometrical Shape Dependence Field Emission From Patterned Carbon Nanotube Array: A Simulation Based Study

Designing an efficient field emission source requires theoretical optimization of electron emitters’ geometrical distribution over the surface for its best performance in terms of current density. Seven and nineteen bundles of CNT arrays arranged in different models are analysed in detail using a computational theory in CST studio suite software based on the particle tracking mode. A three dimensional model has been employed to calculate FE properties with high accuracy. Simulations were carried out for a particular number of CNTs of constant height and radius located at fixed distances from each other and arranged in different geometrical patterns. Among all patterns, rectangular arrangement of CNTs is found to produce the maximum current. The edge effect and screening effect are incorporated in calculating total emission current and are found to diminish the contribution of inner rings 10% or less than that of maximum contribution. These findings can be employed as guideline to fabricate pattered CNT structures experimentally for industry applications. Copyright © 2014 VBRI press.

V2O5 precursor-templated synthesis of textured nanoparticles based VN nanofibers and their exploration as efficient field emitter

Textured Vanadium Nitride (VN) nanofibers are prepared from hydrothermally derived V2O5 nanofibers by NH3 reduction and nitridation approach. The reaction temperature is seen to be a crucial parameter to prepare pure VN phase. VN produced via this route has distinctive structural characteristics. The crystal structure, morphology, and oxidation states of the elements of VN nanofibers are characterized by XRD, FESEM, TEM, HRTEM, and XPS studies. Field emission properties for these textured VN nanofibers have been explored. The field emission properties show the reproducible turn-on field of 3.4 V/μm for the emission current density of 10 μA/cm2. The observed turn-on field is found to be quite superior compare to carbide, nitride and oxide nanostructures. High emission current density of 44 μA/cm2 has been found at a field of 4 V/μm. Emission current stability for the preset current of 5 μA has been recorded for the period of 2 h. Present results indicate the considerable potential for the utilizing VN nanofibers as a cold cathode in the field emitter devices.

Fabrication and properties of planar gate field emission arrays with patterned ZnO nanowires

Field emission arrays (FEAs) based on a planar gate triode with patterned ZnO nanowires have been successfully fabricated by conventional photolithography, screen printing and thermal evaporation. ZnO nanowires were synthesised on the cathode and the gap between cathode and gate electrodes (C–G gap). The SEM images show that the diameters of ZnO nanowires are scattered in a range of 80–200 nm and the length up to 5 μm. Field emission investigations indicate that the turn-on voltage of 875 V at emission current density of 1 μA cm−2 in the triode mode is lower than that of 1575 V in the diode mode. In triode mode, the anode current and gate current come to 330 and 320 μA at the gate voltage and anode voltage of 300 and 1000 V respectively and at the anode–cathode spacing of 500 μm, which indicates that the triode mode based on planar gate FEAs with patterned ZnO nanowires has efficient field emission characteristics.

Linking Catalyst Phase with CNT Morphology and its Subsequent Field Emission Characteristics: An Optimization Study

The effect of phase transition in catalyst nanoparticles due to increasing growth temperatures and its effect over the morphology and field emission of carbon nanotubes (CNT) films is reported here. Thin Fe film coated Si substrates are used to obtain Fe nanoparticles under hydrogen and argon plasma treatment. For this, three different microwave powers (400, 500 and 650 watts) in a microwave plasma enhanced CVD system is used. TEM images of plasma annealed films shows Fe nanoparticles of size ranging from 10 nm to 70 nm. The SAED images of these Fe nanoparticles shows additional diffraction rings for the films annealed at higher microwave power (i.e., higher growth temperatures). Acetylene and hydrogen plasma is used for 2 minutes to deposit the CNT films over three different sized Fe nanoparticles. High resolution TEM (HRTEM) images are used to further investigate any effect of growth temperature on catalyst encapsulated in the CNTs. The field emission studies and Kelvin probe measurements are carried out to examine the suitability of films for its field emission application. It is established that, only under specific optimized growth parameters CNT film must be grown for its usefulness as efficient field emitters.

Silicon nanowires prepared by metal induced etching (MIE): good field emitters

Efficient field emission from silicon nanowires prepared using metal induced etching.

Highly efficient field emission from large-scale and uniform monolayer graphene sheet supported on patterned ZnO nanorod arrays

A graphene/patterned ZnO (G/PZO) nanorod array composite was successfully fabricated by using the colloidal nanosphere monolayer templating strategy. Compared with graphene/compact ZnO (G/CZO) nanorod arrays, the G/PZO nanorod array composite exhibited a highly efficient and stable field emission with a low turn-on field. The field emission had a strong dependence on the density and the inter-distance of the emitters. By changing the diameter of polystyrene (PS) colloidal nanospheres, optimal emitter inter-distance was obtained. Graphene supported on ZnO nanorod arrays, patterned by an 886 nm PS colloidal nanosphere monolayer, displayed the best field emission with a turn-on electric field of only 6.4 V μm−1 and the field enhancement factor β was 1158. The K point in the Fowler–Nordheim plot demonstrated the electron tunneling mechanism took place in this composite material. The cyclic experiment showed that the field emission of the G/PZO nanorod array composite was of high stability.

Highly efficient field emission properties of a novel layered VS2/ZnO nanocomposite and flexible VS2 nanosheet

Multi-layered VS2 nanosheets were synthesized via a facile hydrothermal process. Due to the large quantities of sharp edges, VS2 nanosheets showed excellent field emission properties and their performance was further improved by ZnO nanoparticle coating.

Field electron emission of layered Bi₂Se₃ nanosheets with atom-thick sharp edges.

Field electron emission properties of solution processed few-layer Bi₂Se₃ nanosheets are studied for the first time, which exhibit a low turn-on field of 2.3 V μm(-1), a high field enhancement factor of up to 6860 and good field emission stability. This performance is better than that of the as reported layered MoS₂f sheets and is comparable to that of single layer graphene films. The efficient field emission behaviours are found to be not only attributed to their lower work function but also related to their numerous sharp edges or protrusion decorated structure based on our simulation results. Besides, the contribution of possible two-dimensional electron gas surface states of atom-thick layered Bi₂Se₃ nanosheets is discussed in this paper. We anticipate that these solution processed layered Bi₂Se₃ nanosheets have great potential as robust high-performance vertical structure electron emitters for future light weight and highly flexible vacuum micro/nano-electronic device applications.

Facile fabrication of aligned SnO2 nanotube arrays and their field-emission property

The aligned SnO2 nanotube arrays on Si substrate have been prepared via liquid-phase deposition with the solution system of SnF2 utilizing ZnO nanorod arrays as sacrificial template. The SnO2 nanotubes are distributed uniformly and grown perpendicularly to the substrate. The SnO2 nanotubes are rutile phase with the outside diameter of ~190–310nm and the wall thickness of ~45 nm. The template-related growth mechanism for the formation of SnO2 nanotube is investigated. Experimentally, the SnO2 nanotube array shows an efficient field-emission property, which is favorable for realizing high performance cold cathode electron emitters.

Field Emitters: Epitaxial ZnO Nanowire‐on‐Nanoplate Structures as Efficient and Transferable Field Emitters (Adv. Mater. 40/2013)

Field Emitters: Epitaxial ZnO Nanowire‐on‐Nanoplate Structures as Efficient and Transferable Field Emitters (Adv. Mater. 40/2013)

Flexible Three-Dimensional SnO2 Nanowire Arrays: Atomic Layer Deposition-Assisted Synthesis, Excellent Photodetectors, and Field Emitters

Flexible three-dimensional SnO2 nanowire arrays were synthesized on a carbon cloth template in combination with atomic layer deposition and vapor transport. The as-grown nanostructures were assembled by high density quasi-aligned nanowires with a large aspect ratio. Nanoscale photodetectors based on the flexible nanostructure demonstrate excellent ultraviolet light selectivity, a high speed response time less than 0.3 s, and dark current as low as 2.3 pA. Besides, field emission measurements of the hierarchical structure show a rather low turn-on field (3.3 Vμm(-1)) and threshold field (4.5 Vμm(-1)), as well as an excellent field enhancment factor (2375) with a long-term stability up to 20 h. These results indicate that the flexible three-dimensional SnO2 nanowire arrays can be used as functional building blocks for efficient photodetectors and field emitters.

Epitaxial ZnO Nanowire‐on‐Nanoplate Structures as Efficient and Transferable Field Emitters

Highly epitaxial ZnO nanowire-on-nanoplate structures as efficient and transferable electron field emitters are reported here. Well-faceted ZnO nanoplates can be used as efficient substrates for the epitaxial growth of nanowires with a sharp and high-quality interface, which significantly improves its field emitter performance. Because of its scalable preparation, high performance and facile transfer, the novel material is of high potential for applications in various optoelectronic devices.

Electron Field Emission Enhancement of Vertically Aligned Ultrananocrystalline Diamond‐Coated ZnO Core–Shell Heterostructured Nanorods

Enhanced electron field emission (EFE) behavior of a core-shell heterostructure, where ZnO nanorods (ZNRs) form the core and ultrananocrystalline diamond needles (UNCDNs) form the shell, is reported. EFE properties of ZNR-UNCDN core-shell heterostructures show a high emission current density of 5.5 mA cm(-2) at an applied field of 4.25 V μm(-1) , and a low turn-on field of 2.08 V μm(-1) compared to the 1.67 mA cm(-2) emission current density (at an applied field of 28.7 V μm(-1) ) and 16.6 V μm(-1) turn-on field for bare ZNRs. Such an enhancement in the field emission originates from the unique materials combination, resulting in good electron transport from ZNRs to UNCDNs and efficient field emission of electrons from the UNCDNs. The potential application of these materials is demonstrated by the plasma illumination measurements that lowering the threshold voltage by 160 V confirms the role of ZNR-UNCDN core-shell heterostructures in the enhancement of electron emission.

Improved electron field emission from metal grafted graphene composites

Metal nanoparticle grafted graphene films (GFs) form a new composite for electron field emission devices. The GFs were deposited on Ni coated Si wafers by microwave plasma enhanced chemical vapour deposition. Graphene-based composites using Ti, Pd, Ag and Au were formed by thermal evaporation. The surface morphology and microstructure were probed by scanning and high resolution transmission electron microscopy. Improvement in the electron field emission and reduction in the turn on and threshold fields were observed in metal grafted GFs as compared to those from pristine films. It was found that among the grafted metals, Ti adsorption contributed more efficiently in enhancing the electron field emission properties by lowering its work function. The enhanced electron field emission characteristics were analyzed using the density functional theory calculations for metal grafted graphene ribbon. Our results indicate increased density of states near the Fermi level for metal grafted graphene ribbon which is responsible for the improvement in electron field emission. We suggest that grafting of metal nanoparticles on GFs could be exploited for the development of efficient field emitters.

Synthesis of SnO2 functionalized amorphous carbon nanotube for efficient electron field emission application

Amorphous carbon nanotubes (aCNTs) were synthesized by a very simple low-temperature solid state reaction. The walls of the as prepared aCNTs were decorated with chemically synthesized SnO2 nanoparticle both by in situ and ex situ process. All the samples were characterized by X-ray diffraction, field emission scanning electron microscope, high resolution transmission electron microscope, X-ray photoelectron spectroscopy. It is observed that when functionalization of SnO2 particles onto aCNTs wall was performed by in situ process it results a uniform coating, whereas ex situ treatment gives discrete attachment of SnO2 onto aCNTs wall. The field emission properties of as synthesized and modified sample were carried out in the laboratory made high vacuum field emission set up. Result of field emission has been compared with pure aCNTs and pure SnO2. It has been found that attachment of SnO2 nanostructure can effectively enhance the field electron emission of the aCNTs with lowering the turn on field from 6.57 to 2.15V/μm. The enhancement of field emission characteristic is believed to be due to the enhanced roughness of the coated aCNTs wall as well as lower work function of outer SnO2 material.

Growing Uniform Copolymer Nanowire Arrays for High Stability and Efficient Field Emission

not Available.

An atmospheric pressure-based electrospraying route to fabricate the multi-applications bilayer (AZO/ITO) TCO films

A bilayer film composed of an upper-layer of aluminum-doped ZnO (AZO) film and a lower-layer of tin-doped indium oxide (ITO) film (designated as AZO/ITO) has been successfully fabricated using an atmospheric pressure-based electrospraying method and studied as an excellent transparent electrode, efficient field-emitter and the dye-sensitized solar-cell (DSSC) electrodes in order to develop a cost-effective alternative fabrication method. The morphological, optical and electrical properties were examined for the single layer of an ITO, an AZO and the bilayer AZO/ITO film. The composition of the films was confirmed with the help of energy-dispersive spectroscopy (EDS) and X-ray photospectroscopy (XPS). The bilayer AZO/ITO film presented an enhanced optical transparency of 95% with improved electrical performance, exhibited a resistivity of 9.3 × 10−5 Ω cm and a mobility of 49.5 cm2 V−1 s−1 compared to single layer TCO films that might be useful for optoelectronic devices. Moreover, the lowest turn-on field of ∼3.8 V μm−1, and highest emission current density of 3.9 mA cm−2 was obtained for bilayer AZO/ITO film under the field of 7.6 V μm−1, and the highest field enhancement factor (β) was estimated to be 3315 ± 2, compared with AZO and ITO single layer films. Furthermore, films exhibit good long period emission current stability with a variation of less than 4% during 30 h under a field of 7.6 V μm−1. For DSSCs, the photoanode composed of AZO film only showed a power conversion efficiency (PCE) as low as 0.57% with a short-circuit photocurrent density (JSC) of 2.5 mA cm−2 and an open-circuit voltage (VOC) of 425 mV. The photoanode with ITO film only exhibited higher PCE (0.84%) because of higher JSC (4.0 mA cm−2), whereas VOC (375 mV) was lower than that of AZO film. Compared to AZO and ITO single layer films, the bilayer structured AZO/ITO film demonstrated much higher PCE (2.4%) because of both higher JSC (7.4 mA cm−2) and VOC (600 mV). Addition of an AZO layer over the ITO layer significantly improved the electron transport and lifetime compared to the ITO only film. One order of magnitude slower charge recombination rate for the bilayer film than for the ITO film was found to be a major factor for the improved efficiency. The fabricated cells show highly durable cell performances, even after 40 days under atmospheric conditions. The proposed atmospheric pressure-based electrospraying film fabrication method was well suitable for the deposition of bilayer AZO/ITO films which found multi-applications as an excellent transparent electrode, efficient field-emitter and improved DSSC when compared with other vacuum-based methods.

High efficiency electron field emission from protruded graphene oxide nanosheets supported on sharp silicon nanowires

Graphene oxide (GO) potentially has applications in vacuum microelectronic devices for realization of field emission displays. Graphene and its derivatives are expected to be efficient field emitters due to their unique electrical properties. However, the flat sheet structure of graphene or GO allows electron field emission only from the edges of graphene and GO nanosheets. In order to extract maximum field emission current density at lower applied voltage from the GO nanosheets, we supported and stretched them on sharp tips of silicon nanowires (SiNWs). Highly efficient and stable field emission with low turn-on field was observed for these SiNW–GO heterostructures. The sharp protrusions created by stretching of the GO nanosheets on SiNWs locally enhance the electric field and thus enhance the field emission characteristics. The dominant use of silicon in electronic devices makes this approach robust for the development of field emission devices using graphene based field emitters.