Enhanced Electron Field Emission Research Articles

Probing the effect of molar concentration on TiO2 nanorod/nanoflower films toward enhanced field electron emission properties

Probing the effect of molar concentration on TiO2 nanorod/nanoflower films toward enhanced field electron emission properties

Controlled growth of CuO nanowires on Cu grid via thermal oxidation process with enhanced field electron emission properties

Controlled growth of CuO nanowires on Cu grid via thermal oxidation process with enhanced field electron emission properties

Enhanced electron field emission of two-dimensional boron-doped ZnO nanoflakes on nanocrystal diamond films

Enhanced electron field emission of two-dimensional boron-doped ZnO nanoflakes on nanocrystal diamond films

Surface plasmon-mediated enhanced field electron emission based on metasurfaces with a nano-gap driven by LEDs

Vacuum electronic devices have the advantages of no scattering, anti-irradiation, and extreme operating temperatures. With their superiorities, light-assisted field emission can be utilized to drive ultrafast micro-/nano-vacuum electronic devices. However, traditional multiphoton or optical field emission is limited by the access of the lasers with high power and energy. In this Letter, an asymmetric non-semiconductor nanostructure may be applied to reduce cost with a nano-level gas or vacuum channel. We find that the basic LED may be a candidate to enhance the electron emission current by utilizing the multi-stage field enhancement consisting of tip effects and plasmon-based enhancement. By designing a field electron emission device with LEDs in standard atmospheric environment, we realize a 25% increase in field electron emission current at the resonance frequency with the light intensity under W cm−2 and the voltage less than 5 V. By comparing with lasers, simple LEDs are beneficial to increase the scope of applications with low-energy requirements. Meanwhile, the structure paves the way to the application of microelectronic and nano-electronic components in the on-chip electronic devices, such as switches and modulators.

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.

In situ synthesis of 3D metal oxides/Ni3C on the macroporous electrically conductive network for enhanced electron field emission

• The TiO 2 /Ni 3 C are prepared in situ on the 3D substrate by sputtering. • CuO/Ni 3 C, and WO 3 /Ni 3 C are also synthesized by sputtering method. • The field emission performance of the TiO 2 /Ni 3 C is better than others. • The TiO 2 nanosheets show the turn-on and threshold fields of 1.30 and 1.69 V/μm. • The field emitter also exhibits good repeatability and stability for 50 min. Three-dimensional metal oxides/Ni 3 C structures ( TiO 2 /Ni 3 C, CuO/Ni 3 C, and WO 3 /Ni 3 C ) are prepared in situ on the macroporous electrically conductive network ( MECN) and the field emission (FE) characteristics are investigated systematically. The TiO 2 /Ni 3 C nanosheets deposited on MECN show the smallest turn-on and threshold fields of 1.30 V/μm and 1.69 V/μm, respectively, compared to CuO/Ni 3 C and WO 3 /Ni 3 C. The excellent FE properties of TiO 2 /Ni 3 C/MECN arise from the low work function and change in hybridization from sp 2 to sp 3 carbon atoms at the electron emission sites. In situ synthesis of TiO 2 /Ni 3 C is environmentally friendly, efficient, and compatible with microelectronics manufacturing boding well for application to high-performance FE and vacuum nanodevices.

Photoelectron properties and enhanced field electron emission of cobalt ferrite-reduced graphene oxide nanocomposite

In the present report, field electron emission (FE) characteristics of cobalt ferrite (CF) nanoparticles (NPs) decorated on reduced graphene oxide (rGO) are studied. The rGO-CF nanocomposite was synthesized by simple glycol-based route. The formation of rGO-CF nanocomposite was confirmed using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). TEM results indicated the uniform decoration of CF NPs on the rGO sheet. The average particle size of decorated CF NPs is ∼8 nm. XPS results revealed the partial reduction of GO to rGO. The ultraviolet photoelectron spectroscopy (UPS) was utilized to calculate the work function of the nanocomposite and it was found to be ∼4.3 eV. The FE properties of rGO-CF nanocomposite were investigated in planer diode assembly. The nanocomposite showed excellent FE performance with low turn-on ∼ 1.34 V/μm and threshold field ∼ 1.72 V/μm values. The maximum current density was found to be 2.8 mA/cm2, at an applied field of 2.88 V/μm. This enhancement in FE characteristics was explained on the basis of surface morphology, increased number of emitting sites, high field enhancement factor, and reduction in the work function of the emitter. The FE results suggest that rGO-CF based emitters have the potential for the development of various micro-nano electronic devices.

Impact of edge functionalization on electron field-emission characteristics of carbon nanotubes: A theoretical approach

A theoretical approach using first-principle calculations of the density of states (DOS) of functionalized carbon nanotubes (CNTs) is carried out to understand their enhanced electron field emission (FE) properties. The theoretical functionalization of CNTs is perceived using hydrogenation (H/O–H) and oxidation methods. In order to investigate the enhancement in the FE properties of functionalized CNTs, both single-walled carbon nanotubes (SWCNT) and double-walled carbon nanotubes (DWCNT) are studied. The work function is observed to be more decreased in case of zigzag SWCNT (φ = 3.32 for oxygenated SWCNT) as compared to others SWCNT. The dependence of DOS on zigzag/armchair edge functionalization has also been investigated to reveal the impact of DOS on FE. The observed results indicate that edge functionalization of CNTs leads to significant changes in the band structure, DOS, and work functions. The shifting of DOS away from the Fermi level and decrease in work function is evidenced owing to the reduction in the curvature effect of CNT. Also, due to enhanced DOS near the Fermi level, making them a better proposition for FE applications. Our calculations provide an in-depth insight into the functionalization mechanism to understand the enhanced FE properties from them.

Low-Defect Nanodiamonds and Graphene Nanoribbons Enhanced Electron Field Emission Properties in Ultrananocrystalline Diamond Films

It is known that the electron field emission (EFE) properties of ultrananocrystalline diamond (UNCD) films were usually produced by doping. Here, we performed a low-pressure annealing treatment wit...

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.

Enhanced field electron emission of single-walled carbon nanotubes prepared by imprinting technique

In this work, single-walled carbon nanotubes (SWCNTs) field electron emitters were fabricated by imprinting SWCNTs on substrates with a silver buffer layer. It was found that the field emission properties of imprinted SWCNTs were significantly improved with turn-on field at 0.62 V/μm and threshold field at 1.04 V/μm, comparing to screen-printed SWCNTs emitters who had turn-on field at 1 V/μm and threshold field at 2 V/μm. These improvements of SWCNTs emitters were owing to the directly imprinting method which made SWCNTs have clean surface and more emitters on the substrates. The lower turn-on electric field of field emission was attributed to no impurities encapsulate on the emitters and the large aspect ratio of SWCNTs resulting in high field enhancement factor of 15800. The emission performance of the imprinted cathode was almost unchanged after many times repeated experiments. This simple and low cost technique can fabricate high performance field emission cathodes efficiently and also demonstrates potential applications in many electronic devices.

Origin of Conductive Nanocrystalline Diamond Nanoneedles for Optoelectronic Applications.

Microstructural evolution of nanocrystalline diamond (NCD) nanoneedles owing to the addition of methane and nitrogen in the reactant gases is systematically addressed. It has been determined that varying the concentration of CH4 in the CH4/H2/N2 plasma is significant to tailor the morphology and microstructure of NCD films. While NCD films grown with 1% CH4 in a CH4/H2/N2 (3%) plasma contain large diamond grains, the microstructure changed considerably for NCD films grown using 5% (or 10%) CH4, ensuing in nanosized diamond grains. For 15% CH4-grown NCD films, a well-defined nanoneedle structure evolves. These NCD nanoneedle films contain sp3 phase diamond, sheathed with sp2-bonded graphitic phases, achieving a low resistivity of 90 Ω cm and enhanced field electron emission (FEE) properties, namely, a low turn-on field of 4.3 V/μm with a high FEE current density of 3.3 mA/cm2 (at an applied field of 8.6 V/μm) and a significant field enhancement factor of 3865. Furthermore, a microplasma device utilizing NCD nanoneedle films as cathodes can trigger a gas breakdown at a low threshold field of 3600 V/cm attaining a high plasma illumination current density of 1.14 mA/cm2 at an applied voltage of 500 V, and a high plasma lifetime stability of 881 min is evidenced. The optical emission spectroscopy studies suggest that the C2, CN, and CH species in the growing plasma are the major causes for the observed microstructural evolution in the NCD films. However, the increase in substrate temperature to ∼780 °C due to the incorporation of 15% CH4 in the CH4/H2/N2 plasma is the key driver resulting in the origin of nanoneedles in NCD films. The outstanding optoelectronic characteristics of these nanoneedle films make them suitable as cathodes in high-brightness display panels.

Resonant Tunneling Induced Enhancement of Electron Field Emission by Ultra-Thin Coatings

The emission of electrons from the surface of a material into vacuum depends strongly on the material’s work function, temperature, and the intensity of electric field. The combined effects of these give rise to a multitude of related phenomena, including Fowler-Nordheim tunneling and Schottky emission, which, in turn, enable several families of devices, ranging from vacuum tubes, to Schottky diodes, and thermionic energy converters. More recently, nanomembrane-based detectors have found applications in high-resolution mass spectrometry measurements in proteomics. Progress in all the aforementioned applications critically depends on discovering materials with effective low surface work functions. We show that a few atomic layer deposition (ALD) cycles of zinc oxide onto suspended diamond nanomembranes, strongly reduces the threshold voltage for the onset of electron field emission which is captured by resonant tunneling from the ZnO layer. Solving the Schroedinger equation, we obtain an electrical field- and thickness-dependent population of the lowest few subbands in the thin ZnO layer, which results in a minimum in the threshold voltage at a thickness of 1.08 nm being in agreement with the experimentally determined value. We conclude that resonant tunneling enables cost-effective ALD coatings that lower the effective work function and enhance field emission from the device.

Manganese ion implanted ultrananocrystalline diamond films: Optical and electrical characterization

We report the optical and electrical properties of high-dose (1015–1017 ions/cm2) Mn-ion implanted ultrananocrystalline diamond (Mn-UNCD) films. Mn-ion implantation and post-annealing of UNCD films lead to the formation of Mn-related color centers, characterized in Mn-UNCD films by their zero phonon line emissions at 621.2 nm and phonon sidebands at 611.2 nm and 630.3 nm. Raman spectra of Mn-UNCD films indicated amorphization via high-dose Mn-ion implantation and that the annealing process results in graphitization of the films. The Mn-UNCD film implanted with the Mn-ion dose of 1017 ions/cm2 exhibits a conductivity of 122.25 (Ω cm)−1, as well as enhanced field electron emission (FEE) properties such as a turn-on field of 10.67 V/μm and a FEE current density of 0.85 mA/cm2.

Electron Field Emission Enhancement Based on Pt-Adsorbed ZnO Nanorods With UV Irradiation

Zinc oxide, a low-cost and practical II–VI chemical material, is utilized to absorb platinum nanoparticle on ZnO nanorods (Pt/ZnO NRs). This material can improve the electrical characteristics of ZnO. Samples were prepared for different prerequisites of Pt precursors and named as ZnO and Pt/ZnO NRs with 0 and 30 s sputter deposition times, respectively. Results indicated that ZnO and Pt/ZnO NRs presented an average diameter and length of ∼50 nm and ∼1.9 μm, respectively. Moreover, the topography surfaces of ZnO and Pt/ZnO NRs showed no evident changes. ZnO NRs were structurally uniform and vertically grown on glass substrates and well oriented with pure wurtzite structure by hydrothermal method. The turn-on field values of ZnO and Pt/ZnO NR samples in the dark were 2.85 and 2.52 V/ μ m, and the field enhancement factor β values were 702.19 and 1924.98, respectively.

Low Temperature Synthesis of Lithium-Doped Nanocrystalline Diamond Films with Enhanced Field Electron Emission Properties.

Low temperature (350 °C) grown conductive nanocrystalline diamond (NCD) films were realized by lithium diffusion from Cr-coated lithium niobate substrates (Cr/LNO). The NCD/Cr/LNO films showed a low resistivity of 0.01 Ω·cm and excellent field electron emission characteristics, viz. a low turn-on field of 2.3 V/µm, a high-current density of 11.0 mA/cm2 (at 4.9 V/m), a large field enhancement factor of 1670, and a life-time stability of 445 min (at 3.0 mA/cm2). The low temperature deposition process combined with the excellent electrical characteristics offers a new prospective for applications based on temperature sensitive materials.

Nanosized graphene sheets enhanced electron field emission behavior in pure carbon film

We reported the field emission behavior of pure carbon films deposited by low-energy electron irradiation in electron cyclotron resonance plasma. First, the field emission behaviors of amorphous, graphene sheets embedded and graphite-like structures were investigated, and the graphene sheets embedded carbon film exhibited an enhanced performance. Then by controlling the electron irradiation energies and densities, the effects of the graphene sheets on the field emission properties were examined. The best electron emission property (turn-on field of 8.4 V/μm and maximum current density of 2.10 mA/cm2 at electric field of 16 V/μm) was obtained with the carbon film under the electron irradiation energy of 50 eV and density of 65 mA/cm2. The mechanism of enhanced field emission was attributed to the nanosized graphene sheets which acted as electron emitters and transport channels. The method of controlling nanosized graphene sheets is important for developing the nanostructured carbon coatings in field emission applications.

Controlled Hetero‐Architectures of Au‐Nanoparticles‐Decorated ZnO Nanowires for Enhanced Field Electron Emission Displays

AbstractThe spitzer shaped pointed ZnO nanowires of diameter 120 nm and length ∼5‐6 μm synthesized via hydrothermal techniques were decorated with Au nanoparticles of diameter < 20 nm along their textural boundaries. The turn‐on field (Eon) of 1.56 V/μm required to draw current density of 10 μA/cm2 from ZnO nanowires was reduced further to 0.96 V/μm after controlled decoration of Au nanoparticle, is significantly lower than pristine/doped ZnO nanostructures, Ag@ZnO, Au@ZnO, Au@CuO, and MoS2@TiO2 heterostructure based field emission (FE) devices. The orthodoxy test confirmed the feasibility of field‐enhancement factor (βFE) of 4477 for Au/ZnO/ITO emitters. The enhanced FE behavior are attributed to pointed nanotips, individual dispersion of Au nanoparticles along the textural boundaries of ZnO nanowires, and enhanced energy well formation at their interface. Moreover, the density of state increases enormously due to the hetero‐structured interface of Au@ZnO and a significant amount of electrons from both Au and ZnO contribute for enhanced emission current density (2.1 mA/cm2 @ 1.92 V/μm), and greatly stable electron emission. Our experiments suggest that the tunable hetero‐architectures of Au nanoparticles@ZnO nanowires hold the promises for applications in display screens and intense electron source.

Microstructural modification of diamond-graphite nanohybrid films via adjusting deposition temperatures for enhanced electron field emission

To achieve enhanced electron field emission, diamond-graphite nanohybrid films are deposited on Si substrates by means of a microwave plasma chemical vapor deposition (MPCVD) reactor. Liquid diethylamine is used as a sole reactive source. An increase of deposition temperature from 730 °C to 830 °C leads to remarkable changes of morphology and microstructure of diamond-graphite nanohybrid films, namely from a typical planar ultrananocrystalline diamond (UNCD) film at 730 °C to a novel nanocrystalline diamond/graphene nanowall (ND/GNW) film at 830 °C. The electrical conductivity of a ND/GNW film is measured to be 762.4 Ω−1·cm−1, while for a UNCD film it is 18.0 Ω−1·cm−1. Moreover, the electron field emission is significantly enhanced on a ND/GNW film. With an applied electrical field of 9.9 V μm−1 its emission current density is 1.6 mA cm−2, 8-time larger than that for a UNCD film. The possible electron emission mechanism is then discussed based on the Fowler-Nordheim theory. This work offers a simple way to alter effectively the microstructures of sp2/sp3 nanohybrid films that benefit greatly to develop carbon-based field emission cold cathodes featuring high performance.

Growth behavior of CVD diamond films with enhanced electron field emission properties over a wide range of experimental parameters

In this study, diamond films were synthesized on silicon substrates by microwave plasma enhanced chemical vapor deposition (CVD) over a wide range of experimental parameters. The effects of the microwave power, CH4/H2 ratio and gas pressure on the morphology, growth rate, composition, and quality of diamond films were investigated by means of scanning electron microscope (SEM), X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). A rise of microwave power can lead to an increasing pyrolysis of hydrogen and methane, so that the microcrystalline diamond film could be synthesized at low CH4/H2 levels. Gas pressure has similar effect in changing the morphology of diamond films, and high gas pressure also results in dramatically increased grain size. However, diamond film is deteriorated at high CH4/H2 ratio due to the abundant graphite content including in the films. Under an extreme condition of high microwave power of 10kW and high CH4 concentration, a hybrid film composed of diamond/graphite was successfully formed in the absence of N2 or Ar, which is different from other reports. This composite structure has an excellent measured sheet resistance of 10–100Ω/Sqr. which allows it to be utilized as field electron emitter. The diamond/graphite hybrid nanostructure displays excellent electron field emission (EFE) properties with a low turn-on field of 2.17V/μm and β=3160, therefore it could be a promising alternative in field emission applications.