Enhanced Field Emission Performance Research Articles

Field emission properties of LIG/ZnO heterojunction prepared by ultrafast laser direct writing

The facile in situ synthesis of graphene-coated metal-oxide nanoparticles and their potential applications in optoelectronic devices are highly anticipated. In this study, we prepared three-dimensional graphene flakes decorated with ZnO nanoparticles (LIG/ZnO) using femtosecond laser-induced zinc salt-containing cork. The LIG/ZnO heterojunction was formed by carbonizing the cork and decomposing the zinc salt in situ to coat LIG during laser irradiation. The correlation between the zinc salt concentration and the morphology, structure, and field-emission characteristics of LIG/ZnO was systematically investigated. The optimized LIG/ZnO-5 emitters demonstrate a decreased threshold electric field (Eth) of 1.07 V/μm, an enhanced field enhancement factor (β) value of 20,559, and a maximum current density of 18.07 mA/cm2 at 1.96 V/μm, representing the most superior performance reported to date. The enhanced field-emission performance of LIG/ZnO can be attributed to the larger number of effective emission sites from ZnO nanoparticles and LIG edges, as well as to the energy band variation induced by the heterostructures. Density functional theory (DFT) calculations show the migration of electrons from the LIG to the ZnO after the formation of the heterojunction, which elevates the Fermi level of emitters. In addition, the accumulation of electrons on the surface of ZnO nanoparticles in the presence of a strong electric field results in a downward shift of the energy band, thereby enhancing the likelihood of electron-vacuum tunneling.

Enhanced field emission performance of Si nanopillars coated with LaB6 hats fabricated by microspheres lithography

LaB6 nanofilm is coated on the top surface of silicon nanopillars forming a field emission array (FEA). Such a structure will be referred to subsequently as a ‘LaB6 hat-coated Si-FEA’. The electron emission mechanism of the LaB6 hat-coated Si-FEA is analyzed by OPERA simulation software. It reveals that the electron emission mainly depends on the LaB6 film edge. Moreover, the LaB6 hat-coated Si-FEA sample is prepared by microsphere lithography, and the field emission properties are tested. The results show that when the anode voltage is 850 V, the field emission current density reaches 458 mA cm−2, which is in good agreement with the simulation results. This work demonstrates that the field emission cathodes with low cost, high integration and high current can be realized by using LaB6 as emitter material combined with microsphere lithography technology.

Enhanced field emission performance of growth-optimized CuO nanorods

Enhanced field emission performance of growth-optimized CuO nanorods

Enhanced field electron emission properties of graphite nanoplatelet paste emitters using graphite binder and graphite nanoparticle filler

Graphite nanoplatelet (GNP) paste field emitters fabricated using all-carbon-based materials, such as GNPs, graphite nanoparticles, graphite binders, and a graphite rod substrate have been demonstrated. The GNP field emitters on the graphite rod substrate showed an emission current density of 84.3 mA/cm2 and good emission stability with a degradation rate of less than 10%, indicating higher emission performance than other GNP field emitters. The enhanced field emission performance of the GNP field emitter is attributed to a low work function barrier between carbon materials, low contact resistance between GNPs and the graphite rod substrate, and good GNP paste bulk electrical conductivity. The new approach to fabricate GNP field emitters using all-carbon-based materials can be useful for various field emission devices.

Systematic growth of carbon nanotubes on aluminum substrate for enhanced field emission performance

For more than two decades, carbon nanotubes (CNTs) have shown great potential for a wide range of applications. Several methods are known to synthesize CNTs, though only a few of them are able to produce good quality and economically available CNTs. Chemical vapor deposition (CVD) is one of those methods that produce economically feasible and good quality CNTs onto specific substrates, even with nanopatterning. However, growing CNTs by CVD at temperatures below 700 °C remained a long-time challenge, as this meant keeping a host of low-melting materials out of bounds for direct CNT growth on them. In this work, CNTs have been synthesized directly onto a low-melting, conducting substrate, aluminum, by thermal CVD, at a temperature as low as 550 °C and up to as high as 650 °C (just below the melting point of aluminum). The diameters of the grown CNTs were observed to be influenced by process parameters, e.g., temperature and pressure. The effect of synthesis parameters on CNT diameters was verified by scanning electron microscopy and transmission electron microscopy. The quality of the CNTs was checked by Raman spectroscopy, selected area electron diffraction pattern of transmission electron microscopy, and XPS. It was observed that an increase in temperature and pressure had a significant effect on the diameters of the CNTs. Randomly entangled CNTs were measured to have an average diameter of 28 nm at 550 °C and one atmospheric (760 Torr) pressure, whereas it was observed to be 78 nm at a temperature of 650 °C and pressure of 0.01 Torr. The field emission response, i.e., the turn-on field (2.5 V/μm) and the maximum emission current density (2.17 mA/cm2) of the CNTs synthesized at the temperature of 550 °C and pressure of 1 atm (760 Torr) was found to be excellent.

Enhanced field emission performance of MXene-TiO2 composite films.

A facile method to produce an MXene-TiO2 composite is demonstrated for enhanced field emission display applications. The field emission performance of two-dimensional free-standing and linear-shaped field emitters has been systematically investigated and enhanced electron emission behaviors (e.g. emission current, stability and emission patterns) are achieved by compositing MXene and TiO2 nanowires. The relationship between the emission current density, electric field and anode-cathode gap distance is studied and the emitters, especially the cross-section of the composite film, show good performance. The emission current from the cross-section of the composite film can reach 289 mA cm-2, which is the best result of the state of the art compared to single MXene and TiO2 nanowires. We have also reported a triboelectric nanogenerator powered by free-standing MXene-TiO2 composite emitters, implying the feasibility of the self-powering field emission devices and possibly enlarging the applications of cold emitters in various fields.

Synthesis of a finger-like MoS2@VS2 micro–nanocomposite with enhanced field emission performance

A MoS2@VS2 micro–nanocomposite showed enhanced field emission properties benefiting from the synergy of the two materials.

Enhanced field emission performance of lanthanum hexaboride coated on graphene film

Lanthanum hexaboride (LaB6) is coated on electrophoretically deposited-graphite film by electron beam evaporation method. Surface morphology, Raman spectra and field emission properties are discussed by varying LaB6 coating thickness. It is demonstrated that this film cathode always shows much better field emission performance than pristine graphite cathode. Especially when LaB6 film thickness is 90 nm, the emission current increases from 153 μA to 850 μA with the applied electric field of 6.7 V μm−1, and the turn-on field decreases from 2.3 V μm−1 to 1.0 V μm−1. The results suggest that the graphene-based composite is an excellent field emission cathode, especially suitable for vacuum devices such as field emission display.

Morphology-dependent field emission characteristics of CVD-grown AlN nanostructures@carbon fabric heterostructures

Large-scale AlN nanostructures with different morphologies are successfully fabricated on flexible carbon cloth by a feasible chemical vapor deposition without catalyst. The as-produced nanostructures are single crystalline and exhibit [0001]-preferential growth. The influence of growth time and growth temperature on the morphology and field emission characteristics of AlN nanostructures has been systematically analyzed. Morphology-dependent field emission characterizations exhibit that the turn-on and threshold field can be tuned in the range of 1.10–3.53 V μm−1 and 1.55–4.21 V μm−1, respectively. The enhanced field emission performance of AlN nanostructures@carbon fabric heterostructures is aroused from the combination of high aspect ratio, appropriate density of nanostructures and the woven geometry of carbon cloth with high conductivity.

Enhanced Field Emission Performance of MoO3 Nanorods and MoO3‐rGO Nanocomposite

AbstractThe graphene and semiconducting hybrid based nanostructures have emerged as a new class of multifunctional materials with improved performance in comparison to the pristine semiconductors. Here, as‐synthesized MoO3‐reduced graphene oxide (rGO) nanocomposite emitter exhibits enhanced field emission (FE) behavior as compared to the pristine 1D MoO3 nanorods. The hydrothermally synthesized 1D MoO3 nanorods (1D) are grafted on the rGO sheet (2D) using a simple room temperature sonochemical method. The morphological and structural analysis confirms the attachment of MoO3 nanorods with rGO and the improved conductivity of the sample indicates a strong electronic interaction between them. Furthermore, the FE studies of as‐synthesized MoO3 nanorods and MoO3‐rGO nanocomposite emitters, carried out at a base pressure ∼1×10−8 mbar, reveals the values of turn on field (required to draw an emission current density of 1 μA/cm2) as 1.6 and 1.4 V/μm, respectively. Interestingly, the maximum emission current density of 2810 μA/cm2 is achieved at a lower applied field of 2.7 V/μm from the MoO3‐rGO nanocomposite emitter. The enhancement in FE performance of MoO3‐rGO nanocomposite is attributed to the improved electrical conductivity, mechanical properties and higher concentration of protruding edges (emission sites). This observation can be extended to other graphene‐based 1D inorganic hybrid semiconductor nanocomposites, which can provide a valuable opportunity to explore novel hybrid materials for vacuum nano‐electronic devices.

Facile and single step synthesis of three dimensional reduced graphene oxide-NiCoO2 composite using microwave for enhanced electron field emission properties

We report the enhanced field emission properties of three-dimensional (3D) mixed transition metal oxide with reduced graphene oxide nanosheets (rGO-NSs) using a simple and fast synthesis route. The rGO-NSs with different/mixed transition metal oxide (rGO-MxOy) (MxOy=CoO, NiO and NiCoO2) composite has been synthesized for comparative studies for the electron field emission properties. The various rGO-MxOy composite materials were synthesized by microwave irradiation using soild precursor powder. The electron field emission properties were studied for all the samples as rGO-NSs, rGO-CoO, rGO-NiO and 3D rGO-NiCoO2 composite. It was found that specially, rGO-NiCoO2 composite shows the enhanced field emission performance due to synergic effect of mixed transition metal oxide as NiCoO2 nanoparticles with rGO-NSs and also the proper anchoring of NiCoO2 nanoparticles on rGO-NSs. The attachment of NiCoO2 mixed transition metal oxide with rGO-NSs exhibited lower turn-on field, lower threshold field, larger field enhancement factor and stable emission current stability as compared with those of the rGO-NSs, rGO-CoO and rGO-NiO composite. The surface microstructural analysis and morphology were probed by XRD, scanning and Raman. We suggest that anchoring of binary metal oxide nanoparticles on rGO-NSs could be exploited for the development of efficient field emitters.

Synthesis of self-assembled and hierarchical palladium-CNTs-reduced graphene oxide composites for enhanced field emission properties

We report the synthesis of palladium-graphene oxide based (Pd-rGO) composite and its enhanced electron field emission studies. The palladium nanoparticles decorated reduced graphene oxide (Pd-NPs-rGO) and Pd catalyst assisted grown CNTs on reduced graphene oxide (Pd-CNTs-rGO) composite have been synthesized employing microwave. The hierarchical Pd-CNTs-rGO composite shows enhanced field emission performance due to the synergestic effect of Pd catalyst assisted grown CNTs on rGO nanosheets (rGO-NSs) and its proper contact on rGO surfaces. The enhanced field emission behavior of Pd-CNTs-rGO composite is attributed to the easy electron tunneling from the one-dimensional CNTs, which increases the emission sites and hence the field emission current density. The Pd-CNTs-rGO composite exhibits lower turn-on field, lower threshold field, larger field enhancement factor and high emission current stability as compared to Pd-NPs-rGO composite.

Enhanced field emission performance of NiMoO4 nanosheets by tuning the phase

In this paper we report, large scale synthesis of α and β-NiMoO4 by a facile hydrothermal method and we observed that urea plays important role on the growth of β-NiMoO4 nanosheets. We have also carried out field emission (FE) investigations of α and β-NiMoO4 at a base pressure of ∼1×10−8mbar. The obtained turn-on field at emission current density of 1μA/cm2 for β-NiMoO4 nanosheets and α −NiMoO4 is 1.3V/μm and 2.2V/μm respectively were observed. The maximum field emission current density of 1.006mA/cm2at an applied electric field of 2.7V/μm was achieved for β-NiMoO4 nanosheets. Furthermore, we found that the β-NiMoO4 nanosheets possess good field emission performance compared to α-NiMoO4. The results indicate that NiMoO4can be used as a promising material in FE applications with possibility of tuning field emission performance by controlling the phase.

Controllable Ag nanoparticle coated ZnO nanorod arrays on an alloy substrate with enhanced field emission performance

Ag–ZnO nanocomposites are conveniently prepared on alloy substrates, leading to much improved field emission performances.

Morphology-controlled synthesis and electron field emission properties of ZnSe nanowalls

Novel ZnSe nanowalls on a Zn substrate with optimum morphology exhibit enhanced field emission performance.

Tuning the work function of randomly oriented ZnO nanostructures by capping with faceted Au nanostructure and oxygen defects: enhanced field emission experiments and DFT studies

The lowering of the work function (Φ) can lead to a better field emission (FE) behavior at lower threshold fields. We report on enhanced FE from randomly oriented and faceted Au-capped ZnO hetero-nanostructures (HNs) having more oxygen defects. Large-area arrays of non-aligned, faceted Au-capped ZnO HNs, such as nanowires (NWs) and triangular nanoflakes (TNFs) are grown using the chemical vapor deposition (CVD) method. Enhanced FE properties from the TNF sample resulted in a turn-on field as low as 0.52 V μm−1 at a current density of 0.1 mA cm−2 and a field enhancement factor (β) as high as ≈5.16 × 105. Under similar experimental conditions, drawing the same current density from an NW specimen needs a higher turn-on field (0.86 V μm−1) and to exhibit nearly four times less field enhancement factor compared to the TNFs samples. X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) measurements confirm the presence of more oxygen defects in the TNF samples compared to the NW samples. Kelvin probe force microscopy (KPFM) measurements show the average local work function to be 4.70 ± 0.1 eV for the TNF sample, which is ≈ 0.34 eV lower than the NW sample. Using density functional theory (DFT) calculations, the estimated Φ values are found to be 4.98 eV for ZnO(0001), 4.17 eV for Au(001)/ZnO(0001) and 3.91 eV for Au(001)/Ovac-ZnO(0001) surfaces. The DFT results are qualitatively in agreement with our experimental results. The presence of Au nanostructures on top of O-deficient and sharp-tipped TNFs results in enhanced FE performance following their reduced tunneling barrier via pinning of effective Φ.

Enhanced Field-Emission Performance from Carbon Nanotube Emitters on Nickel Foam Cathodes

We present a three-dimensionally configured cathode with enhanced field-emission performance formed by combining carbon nanotube (CNT) emitters with a nickel foam (NiF) substrate via a conventional screen-printing technique. The CNT/NiF cathode has low turn-on electric field of 0.53 V μm−1 (with current density of 10 μA cm−2) and threshold electric field of 0.87 V μm−1 (with current density of 0.1 mA cm−2), and a very high field enhancement factor of 1.4 × 104. The porous structure of the NiF substrate can greatly improve the field-emission properties due to its large specific surface area that can accommodate more CNTs and increase the emitter density, as well as its high electrical and thermal conductivities that facilitate current transition and heat dissipation in the cathode. Most importantly, the local electric field was also enhanced by the multistage effect resulting from the rough metal surface, which furthermore leads to a high field enhancement factor. We believe that this improved field-emission performance makes such cathodes promising candidates for use in various field-emission applications.

Spatially branched CdS–Bi2S3 heteroarchitecture: single step hydrothermal synthesis approach with enhanced field emission performance and highly responsive broadband photodetection

This report explores the controlled hierarchical synthesis of CdS nanostructure branches on Bi2S3 nanorod cores via a facile single step hydrothermal route for field emission and photo detector applications.

Water-processed carbon nanotube/graphene hybrids with enhanced field emission properties

Integrating carbon nanotubes (CNTs) and graphene into hybrid structures provides a novel approach to three dimensional (3D) materials with advantageous properties. Here we present a water-processing method to create integrated CNT/graphene hybrids and test their field emission properties. With an optimized mass ratio of CNTs to graphene, the hybrid shows a significantly enhanced field emission performance, such as turn-on electric field of 0.79 V/μm, threshold electric field of 1.05 V/μm, maximum current density of 0.1 mA/cm2, and field enhancement factor of ∼1.3 × 104. The optimized mass ratio for field emission emphasizes the importance of both CNTs and graphene in the hybrid. We also hypothesize a possible mechanism for this enhanced field emission performance from the CNT/graphene hybrid. During the solution treatment, graphene oxide behaves as surfactant sheets for CNTs to form a well dispersed solution, which leads to a better organized 3D structure with more conducting channels for electron transport.

Hybrid nanostructured thin-films by PLD for enhanced field emission performance for radiation micro-nano dosimetry applications

We report the observation of hybrid nanostructured thin-films such as diamond-like carbon (DLC) signature on the ZnO epitaxial thin-films grown onto the device silicon/quartz substrate by reactive pulsed laser deposition (r-PLD) under the argon–oxygen (Ar|O2) ambient at 573 K. Undoped and Carbon (C) doped epitaxial ZnO thin-film layer formation is revealed by the accelerator based ion-beam analysis (IBA) technique of resonant Rutherford backscattering spectrometry (RRBS), glancing-incidence X-ray diffraction (GIXRD) pattern, micro-Raman spectroscopy (μ-RS) and field-emission (F-E) studies. The RRBS and GIXRD results show the deposition of epitaxial thin-films containing C into ZnO. The μ-RS technique is a standard nondestructive tool (NDT) for the characterization of crystalline, nano-crystalline, and amorphous carbons (a-C). As grown ZnO and C-doped ZnO thin-films μ-RS result reveal the doping effect of C-impurities that appear in the form of DLC evident from Raman peaks at 1357 and 1575 cm−1 along with a wurtzite structure peak at 438 cm−1 with E2(h) phonon of ZnO. The electron transport F-E result shows the hybrid thin-films has high conductivity than the un-doped film. Fabricated hybrid nanostructured thin-films materials could be very useful for the emerging applications of micro-nano dosimetry.