Field Electron Emission Performance Research Articles

Nitrogen doped reduced graphene oxide: Investigations on electronic properties using X-ray and Ultra-violet photoelectron spectroscopy and field electron emission behaviour

The practice of heteroatom doping has been proven to significantly enhance the intrinsic properties of host materials. A facile, one-step process due to the thermal reduction of ammonium hydroxide-treated graphene oxide (GO) was employed to yield nitrogen (N) doped reduced graphene oxide (rGO). In-depth characterization has been performed to reveal the phase, structure, morphology, and electronic properties of as-synthesized products. It is observed that the processing temperature noticeably affects the concentration and type of doped N species. The N-doped rGO (N-rGO) prepared at 900 ℃ exhibited excellent field electron emission (FEE) performance with relatively lower values of turn-on and threshold fields ∼ 1.28 and 1.52 V/µm, defined at emission current densities of 10 and 100 µA/cm2, respectively. Furthermore, a high current density of 5.83 mA/cm2 was drawn at an applied field of 2.51 V/µm, and the emitter showed equitably current stability tested at 10 µA. The obtained results promote the N-rGO emitter, with tuned concentrations of doped N-species, as a promising candidate for practical applications in various vacuum microelectronic devices.

Field electron emission performance of Janus MoSSe and MoSSe-MWCNTs composite: Corroboration by Hall measurement and DFT simulation

Janus MoSSe and its composite with multiwalled carbon nanotubes (MWCNTs) have been synthesized using a facile one pot hydrothermal route. Formation of Janus MoSSe has been confirmed from the X-ray Diffraction, Raman, and X-ray Photoelectron spectroscopic analysis. Furthermore, field electron emission (FEE) behaviour of the as-synthesized Janus MoSSe and MoSSe-MWCNTs composite has been investigated at base pressure of ∼ 1 × 10−8 mbar in a planar diode configuration. Interestingly, the MoSSe-MWCNTs emitter exhibited enhanced FEE characteristics in terms of lower values of turn-on and threshold fields, competency to deliver large emission current density, in contrast to the pristine Janus MoSSe and MWCNTs emitters. An attempt has been made to reveal the underlying physics facilitating improvement in FEE behavior using computational analysis. In this regard, density functional theory (DFT) simulation was carried out to find electronic structure of the as-synthesized emitters. The DFT results indicate charge transfer from C 2p to Mo 4d orbitals, thereby enhancing electrical conductivity and reduction in work function of MoSSe-MWCNTs composite. Moreover, the experimental validation due to Hall measurements undoubtedly revealed noticeable increase in carrier concentration. The observed results clearly exemplify modulation electronic properties of Janus materials thereby highlighting their potential for various applications, including vacuum microelectronic devices.

Directly tuning the surface morphologies and electron pathway of graphite/diamond composite films for enhanced electron field emission

Cathode electron field emitters are widely used in high-power and high-frequency vacuum electron devices. The development of novel technique to fabricate the emitters with high electron field emission performance has stimulated extensive research. Here we present a unique one-step microwave plasma chemical vapor deposition process to fabricate the graphite/diamond composite films. The gaseous methane is replaced by liquid n-butylamine, which acts as the single reactive carbon source. The components and surface morphologies of the graphite/diamond composite films can be effectively tuned upon changing the deposition temperatures. The vertically oriented graphite/diamond composite film with a graphite-diamond-graphite nanostructure is obtained and shows superior electron field emission performance of low turn-on field (E0 = 4.0 V/µm) and high emission current density (J@8.8 V/µm = 13.0 mA/cm2). Our study reveal that the sharp edges, appropriate distribution density of the nanosheets, as well as good electron pathway from the bulk to the surface are the key ingredients for the electron field emission performance. This work on graphite/diamond composite films provides a new carbon source instead of methane to fabricate the emitters with high electron field emission performance, which may promote the industrial-scale application.

Fabrication of rutile TiO2 nanoarrays/free-standing diamond composite film and its field emission properties

Highly aligned TiO2 nanoarrays (TNAs) are fabricated on free-standing diamond (FSD) films and Si wafers (for comparison). Different anodizing times (e.g., 5, 15, 25, 45, and 60 min) are used to investigate the morphologies of TNAs and their effect on the electron field emission (EFE) properties. With the increase of the anodizing time, the features of TNAs grown on the FSD film undergo the transition from nanorods to nanopores and then to nanotubes. The XRD, Raman, and TEM results reveal that TNAs synthesized on the FSD film are preferentially oriented rutile phase, while those synthesized on the Si wafers show the anatase structure. Rutile TiO2 has a relatively low work function and is favorable to EFE performance. Importantly, the nanotubes on the FSD substrate with a 45 min anodizing time grow perpendicularly to each crystal face of the diamond grains and exhibit a superior EFE behavior, which can be turned on at a low field of 0.7 V/μm and attain a high current density of 0.6 mA/cm2 at an applied field of 1.6 V/μm. The enhanced EFE performance of TNAs/FSD composite film is ascribed to the synergetic effects among the electron acceleration layer played by the FSD film, more electron emission sites provided by the nanotubes with large aspect ratios, and lower work function of rutile TiO2. Moreover, the heterogeneity of the FSD substrate and TNAs also can decrease the interface barrier to make electrons transmit effectively.

Thermal plasma synthesized nano-powders of (LaCe)B6 starting from oxide-based precursors and its field electron emission performance

High temperature synthesis process of microcrystalline and nanocrystalline (LaCe)B6 using Self-propagating High temperature Synthesis (SHS) and arc plasma gas phase condensation methods, respectively have been investigated. These methods are rapid and economically viable processes used for the synthesis of technologically important refractory hexaborides. Microcrystalline powders of (LaCe)B6 were synthesized using the SHS process, starting from oxide precursors of lanthanum, cerium, and boron. The powders obtained using SHS process were used as a precursor to getting nanocrystalline (LaCe)B6 using the thermal plasma route. The thermal plasma synthesis was carried out using nitrogen and argon plasmas, respectively. In-situ plasma diagnostics were used to identify evaporated species and determine plasma temperature during the formation of nanocrystalline (LaCe)B6 using optical emission spectroscopy. Further, an effect of plasma input parameters on the structural and optical properties of as synthesized nanocrystalline (LaCe)6 were investigated using XRD analysis, Raman spectroscopy, and X-ray photoelectron spectroscopy. A thorough investigation of morphological and structural properties of synthesized nanocrystalline (LaCe)6 was carried out using transmission electron microscopy. Finally, field effect electron emission properties of the microcrystalline and nanocrystalline product were investigated and current density, turn on field, stability of emission performance were determined.

The effect of diamond film grain size on electron field emission performance

The effect of diamond film grain size on electron field emission performance

WITHDRAWN: Thermal plasma synthesized nano-powders of (LaCe)B6 starting from oxide-based precursors and its field electron emission performance

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UV light exposure can enhance the field emission performance of nano vacuum devices

The field electron emission performance of a silicon gated field emission array improved by a factor of 10 after a 70-minute exposure to UV light.

A Carbon Nanotube-Based Hundred Watt-Level Ka-Band Backward Wave Oscillator

Carbon nanotube (CNT) cold-cathodes hold much promise in a variety of millimeter-wave and terahertz vacuum electronic radiation devices due to their inherent near instantaneous temporal turn-on and near-ideal ideal field electron emission performance. Here we report on the development of a CNT cold-cathode Ka -band backward-wave oscillator (BWO). Using a novel beam compression stage, theoretical studies, simulation results, and empirical findings collectively demonstrate that this device affords an unprecedentedly high output power of 230 W at a technologically important operating frequency of 33.65 GHz. The developed magnetic injection electron gun achieves a high emission current of 265.5 mA (emission current density of 188.3 mA/cm2) and a high focused beam current density of 18.5 A/cm2, which our studies suggest, is essential to the BWOs high output power.

Germanium-assisted growth of titanium dioxide nanowires for enhanced photocatalytic and electron emission performance

In this study, free-standing and well-aligned titanium dioxide (TiO2) nanowires were grown on a Ti foil by precisely controlling the growth temperature and the thickness of the Ge catalyst layer. The catalyst layer played an important role in activating the surface of the Ti foil, facilitating the growth of TiO2 nanowires on it in a chemical vapor deposition furnace system. The structure of the TiO2 nanowires was investigated using scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. The photocatalytic experiment results showed that the optimum Ge catalyst layer thickness significantly improved the rhodamine B (RhB) degradationefficiencyofthe nanowires. The TiO2 nanowires grown using a 40-nm-thick Ge layer could degrade 74% of RhB after 5 h of ultraviolet irradiation. In addition, the TiO2 nanowires exhibited excellent electron field emission performance as compared to the TiO2 nanocrystals grown without the Ge catalyst layer. The results suggested that TiO2 nanowires grown using a Ge catalyst layer are promising materials for next-generation electronic emitters and photocatalytic systems.

Ti3C2 (MXene) based field electron emitters

As a novel class of two-dimensional materials, MXene has provoked tremendous progress for various applications in functional devices. Here, we pioneer a preliminary understanding on the field emission behavior of MXene for the first time. Ti3C2 paper is fabricated by using facile filtration method, and multiple vertical sheets appear on the surface of MXene paper with high electrical conductivity (2.93 × 105 S m−1) and low work function (3.77 eV). The field electron emission performance and electric field distribution on MXene emitters are measured and simulated under planar and standing conditions. Both emitter conditions exhibit stable, uniform electron emission pattern, and the standing emitter achieves high emission current density of 59 mA cm−2 under 7.5 V μm−1. This work demonstrates the feasibility of MXene as cold electron source, establishing a preliminary foundation for its applications in field emission-based devices.

In Situ Construction of Hierarchical Diamond Supported on Carbon Nanowalls/Diamond for Enhanced Electron Field Emission.

The integration of sp2-/sp3-bonded carbon has aroused increasing attention on attaining a great electron field emission (EFE) performance. Herein, a novel hierarchical diamond@carbon nanowalls/diamond (D@C/D) architecture is facilely prepared through the growth of the hybrid carbon nanowalls/diamond (C/D) film followed by the in situ hydrogen plasma treatment using microwave plasma chemical vapor deposition. The hierarchical D@C/D architecture is composed of thin diamond nanoplatelets sandwiched into carbon nanowalls (CNWs) as the bottom layer and the thickened nanoplatelets constituted by diamond nanograins as the upper layer. The hydrogen plasma plays an effective role in the transformation of sacrificial sp2-bonded CNWs to sp3-bonded diamond, eventually leading to the template thickening of diamond nanoplatelets in the upper layer. Impressively, the D@C/D-90 film demonstrates much better EFE behaviors of low turn-on potential (Eo = 4.3 V μm-1), high current density (Je@8 V μm-1 = 20.81 mA cm-1), and superior long-term stability, in comparison with the pristine C/D film (Eo = 6 V μm-1, Je@8 V μm-1 = 0.33 mA cm-1). The enhanced EFE performance of the hierarchical D@C/D film is ascribed to the well-established graphite pathway for electrons transported from the bottom to the top and the increased diamond emitting sites with negative electron-affinity and robust nature at the top. This work will promote the development of the high-performance cathode EFE material based on hybrid sp2/sp3-bonded carbon, and the method proposed here also provides an effective strategy to construct a diamond nanostructure for various applications.

Controllable fabrication and field emission properties of cactus-like Cu2-xSe@Cu2-xSe nanowalls via the vertical secondary growth

The cactus-like Cu2-xSe@Cu2-xSe nanowalls was prepared by secondary growth method using Cu2-xSe nanowalls as substrate. This special nanostructure comprises Cu2-xSe nano spines neatly growing on the sharp edges of Cu2-xSe nanowalls. Reaction time has a powerful effect on the formation and morphologies of Cu2-xSe nanowalls. XRD analysis indicated the cubic berzelianite phase of Cu2-xSe. The cactus-like Cu2-xSe@Cu2-xSe nanowalls presents a better field electron emission performance than the first synthesized Cu2-xSe nanowalls, possessing the turn-on field 2.04 V/μm and the enhancement factor of 5181. The formation mechanism of cactus-like Cu2-xSe@Cu2-xSe nanowalls was discussed and proposed. The results indicated that the cactus-like Cu2-xSe@Cu2-xSe nanowalls can be used as a promising material in field emission applications.

Fabrication and Field-Emission Properties of Vertically-Aligned Tapered [110]Si Nanowire Arrays Prepared by Nanosphere Lithography and Electroless Ag-Catalyzed Etching

In this study, the controllable fabrication of a variety of vertically aligned, single-crystalline [110]-oriented Si nanowire arrays with sharp tips on (110)Si substrates is achieved using a combined self-assembled nanosphere lithography and multiple electroless Ag-catalyzed Si etching processes. All of the experiments were performed at room temperature. The morphological evolution and formation mechanism of long tapered [110]Si nanowire arrays during the multiple tip-sharpening cycle processes have been investigated by scanning electron microscopy, transmission electron microscopy and water contact angle measurements. Field emission measurements demonstrate that the field-emission behaviors of all nanowire samples produced in this study agree well with the Fowler–Nordheim theory, and the produced long tapered [110]Si nanowire array possesses superior electron emission characteristics, with a very low turn-on field of 1.4[Formula: see text]V/[Formula: see text]m and a high field enhancement factor of 3816. The simple and room temperature fabrication of the well-ordered long tapered [110]Si nanowire array and its excellent electron field emission performance suggest that it can serve as a good candidate for applications in high-performance Si-based vacuum electronic nanodevices.

Dual Effort to Correlate the Electron Field Emission Performance of Carbon Nanotubes with Synthesis As Well As Annealing Temperature: Theoretical Support of the Experimental Finding.

Here a dual approach has been adopted to study the effect of both synthesis as well as annealing temperature on the electron field emission property of differently synthesized carbon nanotubes (CNTs) that include solid state chemical reaction as well as chemical vapour deposition (CVD). Experimental findings were supported by theoretical simulation. All the samples were characterized by X-ray diffraction (XRD), Fourier transformed infrared spectroscopy, Raman spectroscopy, field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). XRD as well as TEM study confirms the amorphous nature (aCNTs) of the samples for both the synthesis techniques which is attributed to lower synthesis temperature. Prominent morphological differences of these two types of aCNTs are clearly observed from both FESEM and TEM images. It is found that electron field emission characteristics of aCNTs synthesized by CVD shows better field emission properties as compared to aCNTs synthesized by solid state reaction. Finite element based simulation shows that temperature has prominent effect on morphology, screening effect or degree of graphitization that leads to improved field emission characteristics for the CVD synthesized aCNTs.

High Performance Field Emitters.

The field electron emission performance of bulk, 1D, and 2D nanomaterials is here empirically compared in the largest metal-analysis of its type. No clear trends are noted between the turn-on electric field and maximum current density as a function of emitter work function, while a more pronounced correlation with the emitters dimensionality is noted. The turn-on field is found to be twice as large for bulk materials compared to 1D and 2D materials, empirically confirming the wider communities view that high aspect ratios, and highly perturbed surface morphologies allow for enhanced field electron emitters.

Conjugated polyelectrolyte nano field emission adlayers.

Here we report on a straightforward and rapid means of enhancing the field electron emission performance of nascent vertically aligned multi-walled carbon nanotubes by introducing a polar zwitterionic conjugated polyelectrolyte adlayer at the vacuum-emitter interface. We attribute the observed 66% decrease in turn-on electric field to the augmented emitter micro-morphology and shifted surface band structure. The composite emitters can be optically modulated by exploiting the absorption cross-section of the solution cast adlayer, which increases the local carrier concentration which broadens the effective electrostatic shape of the emitter during optical excitation. Assessment via scanning anode field emission microscopy reveals a 25% improvement in DC time stability, a significant reduction in long-term hysteresis shift, and a threefold increase in bandwidth during pulsed mode operation.

Template synthesis of metal tungsten nanowire bundles with high field electron emission performance

A H2 reduction-assisted hard-templating approach is demonstrated to synthesize metallic W nanowire bundles. The W nanowire bundles show a low turn-on field of 4.1 V μm−1, a high field enhancement factor up to 3563 and good field emission stability.

Fabrication of vertically aligned carbon nanotubes–zinc oxide nanocomposites and their field electron emission enhancement

Systematic investigation on the fabrications of vertically aligned carbon nanotubes (VACNTs) and zinc oxide (ZnO) nanocomposites for two different configurations were performed to enhance the field electron emission (FEE) performance of the VACNTs synthesised from waste chicken fat. FEE tests demonstrated improvement with the addition of ZnO nanostructures under the VACNT array, where the emission current increased from 212.85 to 259.80μAcm−2, while the turn-on field reduced from 2.66 to 1.60Vμm−1. Meanwhile, the growth of ZnO nanostructures on top of the VACNTs array resulted in a tremendous increase in emission current of up to 2090.00μAcm−2 and a decrease in the turn-on field to 0.49Vμm−1. The difference in the FEE improvement by different composite configuration reflects the significant role of the composite order. The improvement of FEE is influenced by the geometrical shape of the emitters as well as tunnelling effect of electrons through the structure of nanocomposite.

Investigating of the Field Emission Performance on Nano-Apex Carbon Fiber and Tungsten Tips

Field electron emission measurements have been performed on carbon-based and tungsten microemitters. Several samples of both types of emitters with different apex radii have been obtained employing electrolytic etching techniques using sodium hydroxide (NaOH) solution with different molarities depending on the material used. A suitable, home-built, field electron microscope (FEM) with 10 mm tip to screen separation distance was used to electrically characterize the electron emitters. Measurements were carried out under ultra high vacuum (UHV) conditions with base pressure of 10-9 mbar. The current-voltage characteristics (I-V) presented as Fowler-Nordheim (FN) type plots, and field electron emission images have been recorded. In this work, initial comparison of the field electron emission performance of these micro and nanoemitters has been carried out, with the aim of obtaining a reliable, stable and long life powerful electron source. We compare the apex radii measured from the micrographs obtained from the SEM images to those extracted from the FN-type _I-V_plots for carbon fibers and tungsten tips.