Enhanced Field Emission Properties Research Articles

Structure and enhanced field emission properties of cone-shaped Zn-doped SnO2 nanorod arrays on copper foil

Single crystal Zn-doped SnO2 (Zn–SnO2) nanorods with cone-shaped tips (~25nm) on copper foil were synthesized by an organic-free hydrothermal method. The effects of the Zn doping on the morphology, microstructure and field-emission (FE) properties of Zn–SnO2 were investigated. It is found that the Zn doping play an important role in tuning the morphology and size of the SnO2 nanorods. The turn-on fields of SnO2 and Zn–SnO2 nanorods were 3.16 and 2.37V/μm, and field enhancement factors (β) were 960 and 3352, respectively. The enhanced FE property is due to the tapered structures of nanorods with sharp tips and the weak screening effect, and the better electrical contact between conductive copper substrate and field emitters.

Enhanced field emission properties of tilted graphene nanoribbons on aggregated TiO2 nanotube arrays

Graphene nanoribbons (GNRs) slanted on aggregate TiO2 nanotube arrays (A-TNTs) with various compositions as field-emitters are reported. The morphology, crystalline structure, and composition of the as-obtained specimens were characterized by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and Raman spectrometry. The dependence of the turn-on electric field and the field enhancement factor β on substrate morphology was studied. An increase of GNRs reduces the specimens’ turn-on electric field to 2.8V/μm and the field enhancement factor increased rapidly to about 1964 with the addition of GNRs. Results show a strong dependence of the field emission on GNR composition aligned with the gradient on the top of the A-TNT substrate. Enhanced FE properties of the modified TNTs can be mainly attributed to their improved electrical properties and rougher surface morphology.

Enhanced field emission properties of CuO nanoribbons decorated with Ag nanoparticles

The structural and field emission properties of CuO nanoribbons decorated with Ag nanoparticles by a wet chemical method were investigated. The results demonstrated a remarkable enhancement of field emission performance of CuO nanoribbons decorated with Ag nanoparticles. The effect of Ag amount on the field emission performance was studied in detail, and excellent field emission properties such as a low turn-on electric field of 2.1V/μm and a high field enhancement factor of 2528 were obtained.

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.

Synthesis of Ni-doped ZnO nanostructures by low-temperature wet chemical method and their enhanced field emission properties

In this study, we report an enhancement in the field emission (FE) properties of ZnO nanostructures obtained by doping with Ni at a base pressure of ∼1 × 10−8 mbar, which were grown by a simple wet chemical process.

Surface modification of aligned CdO nanosheets and their enhanced field emission properties

Porous aligned CdO nanosheets were grown by simple and cost effective method of thermal annealing. These nanosheets were decorated with Au nanoparticles, and the field emission properties of the Au-decorated aligned CdO nanosheets were enhanced.

Highly conductive nitrogen-doped ultrananocrystalline diamond films with enhanced field emission properties: triethylamine as a new nitrogen source

In this study, triethylamine (TEA) dissolved in the methanol was used as a liquid nitrogen source to synthesize nitrogen-doped ultrananocrystalline diamond (N-UNCD) films on silicon substrates via microwave plasma enhanced chemical vapor deposition (MPCVD).

UV Enhanced Field Emission Properties of ZnO Nanosheets Grown on a Si Substrate

In this research, ZnO nanosheets were successfully grown on Si substrate by using an aqueous solution at room temperature. All the synthesized ZnO nanosheets exhibited hexagonal wurtzite structures. The thin nanosheets perpendicular to the Si substrate surface interwove into networks and formed a continuous nanosheet film. The field enhancement $\beta $ factors for the field emission (FE) devices were approximately 1014 in the dark and 1743 under UV illumination, respectively. The improvement in the FE properties under UV illumination is attributed to the generation of a large number of excited electrons and the edge effect, which demonstrates that the presented route is a simple route for realizing FE devices.

Ultralow effective work function surfaces using diamondoid monolayers.

Electron emission is critical for a host of modern fabrication and analysis applications including mass spectrometry, electron imaging and nanopatterning. Here, we report that monolayers of diamondoids effectively confer dramatically enhanced field emission properties to metal surfaces. We attribute the improved emission to a significant reduction of the work function rather than a geometric enhancement. This effect depends on the particular diamondoid isomer, with [121]tetramantane-2-thiol reducing gold's work function from ∼ 5.1 eV to 1.60 ± 0.3 eV, corresponding to an increase in current by a factor of over 13,000. This reduction in work function is the largest reported for any organic species and also the largest for any air-stable compound. This effect was not observed for sp(3)-hybridized alkanes, nor for smaller diamondoid molecules. The magnitude of the enhancement, molecule specificity and elimination of gold metal rearrangement precludes geometric factors as the dominant contribution. Instead, we attribute this effect to the stable radical cation of diamondoids. Our computed enhancement due to a positively charged radical cation was in agreement with the measured work functions to within ± 0.3 eV, suggesting a new paradigm for low-work-function coatings based on the design of nanoparticles with stable radical cations.

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.

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.

Enhanced Field Emission Properties of Two-Dimensional ZnO Nanosheets Under UV illumination

In this paper, ZnO nanosheets were grown on glass substrates by using an aqueous solution at room temperature. It was found that the ZnO nanosheets were structurally uniform and well oriented with the wurtzite structure. The field emission performance of ZnO nanosheets can be greatly enhanced by illuminating UV light. It was found that the turn-on electric field can be reduced from 5.9 to 5.0 V/μm and field enhancement factors (β) can be increased from 1966 to 4202. It is attributed to generate a large number of electrons by UV illumination.

UV Enhanced Field Emission Properties of ZnO Nanosheets With Different NaOH Concentration

In this paper, vertical ZnO nanosheets are synthesized on Si substrate using a simple solution-based method at room temperature to realize a field emission device. The thin nanosheets that were perpendicular to the Si substrate surface were mutually interwoven into net and formed a continuous nanosheet film, with a unique surface morphology and a high surface-to-volume ratio. The improvement in the FE properties under UV illumination is attributed to the generation of a large number of excited electrons and the edge effect, and demonstrates that the presented route is a simple route for realizing field emission devices. This method has low cost and effectively improves the FE properties of the devices.

Enhanced Field Emission Properties of Ag Nanoparticle-Decorated ZnO Nanorods Under Ultraviolet Illumination

In this paper, pure ZnO and Ag nanoparticle (NP)-decorated ZnO nanorods (NRs) were successfully synthesized via a low-temperature hydrothermal method. The as-prepared samples were characterized through high-resolution transmission electron microscopy and selected-area electron diffractometry. The enhanced field emission (FE) behavior of the Ag NP-decorated ZnO NRs along the [0002] crystal $c$ -axis and their single-crystalline hexagonal structures were characterized with surface-protruding Ag NPs. The resulting FE in the dark and under ultraviolet illumination had low turn-ON electric fields of 3.93 and 2.04 $ \rm V\,\cdot \mu m^{-2}$ , whereas the enhanced field enhancement factors were 1593 and 57 872, respectively.

Enhanced field emission properties from AlN nanowires synthesized on conductive graphite substrate

Large-scale AlN nanowires have been grown on flexible and conductive graphite substrate through the catalyst-free chemical vapor deposition (CVD). All the as-grown samples are hexagonal wurtzite structure and grow preferentially along the c-axis. The comparative study on the field emission (FE) properties of AlN nanowires grown on graphite sheet and Si substrates indicates that AlN nanowires grown directly on conductive substrates exhibit good FE properties with low turn on field of 4.9 V/μm at a current density of 10 μA/cm2 and low threshold field of 6.7 V/μm at 1 mA/cm2. The enhanced FE property is due to the tapered structures of nanowires with sharp tips and high aspect ratio, and the better electrical contact between conductive graphite substrate and field emitters. These results demonstrate the potential applications of the AlN nanowires grown on graphite sheet in optoelectronic and field-emission nanodevices.

UV Enhanced Field Emission Properties of Ga-Doped ZnO Nanosheets

High-density gallium (Ga)-doped ZnO nanosheets were fabricated successfully on a glass substrate by aqueous solution method. The diameter and length of the Ga-doped ZnO nanosheets were $\sim 25$ nm and 2.16 $\mu \text{m}$ , respectively. In the dark, the turn-ON field of Ga-doped ZnO nanosheets was 4.67 V/ $\mu \text{m}$ , and the field enhancement factor ( $\beta $ ) was 4037. Under UV illumination, the turn-ON field and field enhancement factor were 2.83 V/ $\mu \text{m}$ and 6616, respectively.

Facile synthesis of cadmium sulphide-polyaniline (CdS-PANI) nanocomposite and its field emission investigations

A simple two step chemical route has been employed to synthesize cadmium sulphide - polyaniline (CdS-PANI) nanocomposite. In the first step PANI nanotubes are synthesized by oxidative polymerization followed by deposition of CdS nanoparticles on them. In order to investigate the structural, chemical and optical properties of the CdS-PANI nanocomposite, various characterization techniques have been used. The microscopic analysis reveals that the PANI nanotubes having length in several microns with cavity diameter of ~ 10 to 20 nm are decorated with CdS nanoparticles of 5 to 10 nm. The XRD spectrum indicates formation of crystalline hexagonal phase of CdS, supported by the SAED pattern obtained during TEM analysis. The FTIR and UV-visible spectra confirm formation of the conducting phase of PANI. The field emission studies of the CdS-PANI nanocomposite indicate low turn on field of 1.4 V/μm, corresponding to emission current density ~ 1 μA/cm2, and emission current density of ~ 5.5 mA/cm2 has been drawn at an applied field of 3.8 V/μm. Furthermore the emission current is observed to be fairly stable at the preset values over long term duration. The enhanced field emission properties, exhibited in terms of low turn on field, and delivery of very high emission current density at relatively lower applied field, are attributed to the nanometric dimensions of the PANI nanotubes and CdS nanoparticles, and modulation of electronic properties due to formation of heterojunction. The overall field emission results propose the CdS-PANI nanocomposite as a promising material for field emission based devices.

A simple chemical synthesis of amorphous carbon nanotubes–MnO2 flake hybrids for cold cathode application

A simple approach has been implemented to synthesize amorphous carbon nanotubes (a-CNTs) and manganese oxide (MnO2) hybrid nanostructure at temperature as low as ∼250°C in open atmosphere. Microscopic studies of the samples revealed that the walls of the a-CNTs were coated uniformly by MnO2 nanoflakes. The composition of the as prepared sample was studied with the help of energy dispersive X-ray and X-ray photoelectron spectroscopy. Electron field emission study was done in a custom built high vacuum field emission setup for the prepared a-CNT and manganese oxide (MnO2) hybrid nanostructure. It is seen that the performance of the a-CNTs as cold cathode emitter has been enhanced greatly when MnO2 nanoflakes were coated uniformly over it. The turn on field has been reduced from 7.17 to value as low as 3.82V/mm with enhancement factor increases from 2428 to 6965. Finite element based simulation study theoretically confirms the enhancement of field emission properties of as prepared MnO2 nanoflake coated a-CNTs. The results have been explained due to enhanced surface roughness leading to higher enhancement factor and overall increase of emission sites.

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.

Investigation on field emission properties of N-doped graphene-carbon nanotube composites

The aim of this paper is to improve the field emission properties of graphene-carbon nanotube composites by doping nitrogen atom. The electronic structure and field emission mechanism of the composite have been investigated by first principle methods. Compared to pristine graphene-carbon nanotube composite, work functions and ionization potentials with ten different doping positions decrease drastically as well as energy gap, which illustrates the enhancement of field emission properties. In this study, the most preferable doping position (doping position 2) can be inferred. Due to the doping of nitrogen atom, coupled electron states is generated, more electrons aggregate at the doping position. All results suggest that the field emission properties of graphene-carbon nanotube composite can be improved by doping nitrogen atom. The work we have done is significant for obtaining better electron sources with less energies, our investigation will provide a theoretical reference for the design and manufacture of new field emission devices.