Excellent Field Emission Research Articles

Vertical tellurium nano-tower arrays: Topological shape engineering to excellent field emission and optical performance

Vertically aligned tellurium nano-towers (TNTs) building blocks comprising sharp edges have been attained by Au assisted controlled CVD method. The density, size and novel TNTs structures have been optimized in a comprehensive systematic way. The measured base diameter of the TNTs is nearly 150 nm which slowly decreases towards their tip (∼20 nm) in the form of steps realizing their sharp edges. The high density growth of TNTs is estimated to be approximately 2.5 × 108mm2. The two prominent binding energy peaks of TNTs positioned at 583.8 eV and 573.6 eV in XPS graphs are credited to Te-3d3/2 and Te-3d5/2 states of Te along with their XRD lattice parameters a = 4.14 Å and c = 5.25 Å. Owing to distinctive morphology of TNTs which is supportive to easy electron emission, have displayed incredible low turn-on value (3.15 Vμm−1 with excellent stability, exhibiting insignificant (<5 %) FE current fluctuation for 120 min. The intense photoluminescence (PL) peaks displayed by TNTs at 368 nm and comparatively weak shoulder peak at 428 nm (2.897 eV) evidences their potential application in light emitting devices (LEDs). Hence, the incredible PL properties and exclusive FE characteristics revealed by unique TNTs provides the potential applications in opto-electronics and FE display devices.

Formation of Diamond Films with Different Grain Sizes on TiO2 Nanotubes and Its Field Emission Properties

Diamond films with different grain sizes are deposited on TiO2 nanotube (TNT) arrays prepared by anodic oxidation using a microwave plasma chemical vapor deposition reactor. The scanning electron microscope, X‐Ray diffractometer, and Raman results indicate that the diamond film is successfully deposited and that the substrate undergoes a phase transition due to the diamond deposition temperature, resulting in the rutile phase becoming dominant with lower energy bandgap and work function. Notably, after 5 h of deposition, a relatively continuous microcrystalline film is formed on the TNTs, and the diamond grains change from spherical to pyramidal and show excellent electron field emission behavior, with a low turn‐on field of 0.5 V μm−1 and a current density of 85.9 μA cm−2. In addition, the deposition environment of the nanocrystalline diamond has a large impact on the substrate morphology, resulting in a blocked electron transport path, which reduces the overall field emission performance. The enhanced performance is attributed to the synergistic effect between the highly efficient 1D electron path of the TNTs, the negative electron affinity of the diamond surface, and the lower work function of rutile TiO2.

Effect of Crystallinity on the Field Emission Characteristics of Carbon Nanotube Grown on W-Co Bimetallic Catalyst.

Carbon nanotube (CNT) is an excellent field emission material. However, uniformity and stability are the key issues hampering its device application. In this work, a bimetallic W-Co alloy was adopted as the catalyst of CNT in chemical vapor deposition process. The high melting point and stable crystal structure of W-Co helps to increase the grown CNT diameter uniformity and homogeneous crystal structure. High-crystallinity CNTs were grown on the W-Co bimetallic catalyst. Its field emission characteristics demonstrated a low turn-on field, high current density, stable current stability, and uniform emission distribution. The Fowler-Nordheim (FN) and Seppen-Katamuki (SK) analyses revealed that the CNT grown on the W-Co catalyst has a relatively low work function and high field enhancement factor. The high crystallinity and homogeneous crystal structure of CNT also reduce the body resistance and increase the emission current stability and maximum current. The result provides a way to synthesis a high-quality CNT field emitter, which will accelerate the development of cold cathode vacuum electronic device application.

Nanostructured tungsten trioxide developed from environmentally friendly green process as a promising cathode for excellent field emission

Extensively explored as cathodes for field emission, nanostructured metal oxides play a crucial role in diverse applications such as microwave amplifiers, renewable energy systems, flat panel displays, and micro-electronics. The quest for high current density, low threshold field, and stable field emission persists. In present study, we introduce a green synthesis approach using vegetable oil as a reaction medium to produce hexagonal tungsten trioxide (h-WO3). The structural analysis confirmed the formation of h-WO3 with a nanorod-like morphology. The spin-coated h-WO3 film on a silicon substrate exhibited promising field emission properties, including a field enhancement factor (β) of 1596 and a turn-on field of 4.60 V/μm, comparable to reported values. This research opens avenues for the cost-effective and scalable utilization of h-WO3 as an electron emitter in advanced optical and electrical devices.

Highly Ordered Bamboo-Like 4H-SiC Nanowire Array Enabling Low Turn-On Field and Excellent Field Emission Stability

Highly Ordered Bamboo-Like 4H-SiC Nanowire Array Enabling Low Turn-On Field and Excellent Field Emission Stability

High performance field emission cathode based on the diamond nanowires prepared by nanocrystalline diamond films annealed in air

This paper reports the field emission (FE) characteristics of a diamond nanowires (DNWs) array. The nanocrystalline diamond (NCD) film was deposited on silicon by microwave plasma chemical vapor deposition (MPCVD) and then annealed in air forming DNWs and hydrogenated at last. A high-field flat-plate emission test structure with a 1.03 μm gap between anode and cathode was prepared and the electrical properties proved it feasible. The FE performance of DNWs array was measured in a vacuum test system and that of NCDs film as a comparison. Finally, their FE parameters were analyzed and extracted based on the Fowler–Nordheim (F-N) theory. The results show that transforming NCDs film into DNWs array can improve the FE characteristics greatly. The turn-on field is as low as 1.36 V μm−1 dropping by one order of magnitude, while the field enhancement factor and FE current density are up to 156.68 and 484.75 mA cm−2 respectively rising both by two orders of magnitude. This excellent FE performance stems from the characteristics of large aspect ratio, very small tip radius and high density of DNWs.

Excellent field emission with enhanced photodetection behavior of multiwalled carbon nanotubes: experimental and theoretical study

In this study, we synthesized multiwalled carbon nanotubes (MWCNTs) using the direct liquid injection chemical vapor deposition (DLICVD) method, the growth temperatures were varied to investigate their unique properties.

Needle-Shaped Single-Crystalline Molybdenum Micro-Nano Structure with High Conductivity and Excellent Field Emission Properties: Implications for Large-Current Cold-Cathodes

Needle-Shaped Single-Crystalline Molybdenum Micro-Nano Structure with High Conductivity and Excellent Field Emission Properties: Implications for Large-Current Cold-Cathodes

Effect of N2 flux on the field emission properties of synthesized ZnO/ZrN core-shell nanostructures

In this paper, the highly oriented ZnO/ZrN nanoneedle emitters with excellent field emission performance were fabricated by sputtering ZrN particles with different N2 flux to modify ZnO nanoneedle arrays. The effects of different N2 flow on the microscopic morphology, structure and field emission properties of ZnO nanoneedles were investigated. The results shows that the ZnO/ZrN nanoneedles (ZnO/ZrN-1.6) emitter prepared when the flow of N2 gas is 1.6 SCCM exhibits the best field emission performance, with the lowest turn-on electric field Eto at 0.81 V/μm, and a field emission current density of 25 mA/cm2 which was 25 times of pure ZnO. In addition to the improvement of band structure, the improvement of field emission performance can also be attributed to the tunneling effect of electrons through heterostructure. This well-aligned ZnO/ZrN core-shell cathode with excellent emission characteristics grown on carbon cloth substrate has the potential applications in future flexible light source devices.

Low-Pressure CVD Synthesis of Tetragonal Borophene Single-Crystalline Sheets with High Ambient Stability

Being a typical graphene-like two-dimensional (2D) material, borophene has received a lot of attention due to its low density, high electron mobility, large Young’s modulus, and good chemical stability. Compared with the corresponding bulk counterparts, 2D borophene has larger specific surface area, higher conductivity, and smaller work function, finding potential applications in high-speed transistors, optoelectronic detection, field emission (FE), and mechanical enforcement areas. In this paper, 2D tetragonal borophene sheets with high ambient stability have been successfully fabricated on the surface of 1 cm2 copper foil using a developed low-pressure chemical vapor deposition (LPCVD) method. The vapor–solid mechanism was used to comprehend the formation of the tetragonal borophene sheets. The electrical conductivity of individual borophene sheets ranged from 4 to 5 × 10–4 S/cm, and the band gap was about 2.1 eV, suggesting their narrow semiconductive nature. Also, the maximum FE current of individual borophene sheets was close to 1 μA, and their emission properties enhanced with the decreasing sheet thickness, comparable to many other nanomaterials with excellent FE performances. More interestingly, individual borophene sheets were found to retain good enough electrical transport and FE behaviors even if they experienced several days’ atmospheric conservations. Our research results suggest that the LPCVD-grown borophene may be a promising building block for constructing high-performance nanodevices with good ambient stability.

Self-nucleated tellurium nanorods patterned growth: Their applications for excellent field emitters and optical devices

Self-nucleated tellurium nanorods patterned growth: Their applications for excellent field emitters and optical devices

Controllable synthesis of indium oxide nanorod‐flowers for high field emission performance

AbstractIn this paper, indium oxide (In2O3) nanomaterials are successfully synthesized on the silicon substrates by hydrothermal method and calcination. By changing the ratio of raw materials, In2O3 exhibits three morphologies of nanorods, nanomaces, and nanorod‐flowers. Among the three morphologies of In2O3 nanomaterials, the nanorod‐flowers shaped In2O3 shows a strong field emission property, the turn‐on electric field as low as 0.97 V/µm and the field enhancement factor β up to 1053. The excellent performance is attributed to the higher length to diameter (L/D) ratio of the emitting tips and the better crystal quality for nanorod‐flowers shaped In2O3. The authors also show that for the nanorod‐flowers shaped In2O3, increasing separation distance, the turn‐on electric field increases up to about 3.67 V/µm and β decreases to 573 at d = 900 µm. This work provides new insights to design and synthesize nanomaterials with excellent field emission properties.

Synthesis and Physical Characteristics of Undoped and Potassium-Doped Cubic Tungsten Trioxide Nanowires through Thermal Evaporation.

We report an efficient method to synthesize undoped and K-doped rare cubic tungsten trioxide nanowires through the thermal evaporation of WO3 powder without a catalyst. The WO3 nanowires are reproducible and stable with a low-cost growth process. The thermal evaporation processing was conducted in a three-zone horizontal tube furnace over a temperature range of 550-850 °C, where multiple substrates were placed at different temperature zones. The processing parameters, including pressure, temperature, type of gas, and flow rate, were varied and studied in terms of their influence on the morphology, aspect ratio and density of the nanowires. The morphologies of the products were observed with scanning electron microscopy. High resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction studies were conducted to further identify the chemical composition, crystal structure and growth direction of the nanostructures. Additionally, the growth mechanism has been proposed. Furthermore, we investigated the potassium doping effect on the physical properties of the nanostructures. Photoluminescence measurements show that there were shorter emission bands at 360 nm and 410 nm. Field emission measurements show that the doping effect significantly reduced the turn-on electric field and increased the enhancement factor. Furthermore, as compared with related previous research, the K-doped WO3 nanowires synthesized in this study exhibited excellent field emission properties, including a superior field enhancement factor and turn-on electric field. The study reveals the potential of WO3 nanowires in promising applications for sensors, field emitters and light-emitting diodes.

Electric-Field Emission Mechanism in Q-Carbon Field Emitters.

In this paper, we report the excellent field emission properties of Q-carbon and analyze its field emission characteristics through structural, morphological, and electronic property correlations, supported by density functional theory (DFT) simulation studies. The Q-carbon field emitters show impressive and stable field emission properties, such as a low turn-on electric field of ∼2.38 V/μm, a high emission current density of ∼33 μA/cm2, and a critical field of ∼2.44 V/μm for the transition from a linear region to the saturation region in the F-N plot. The outstanding field emission properties of Q-carbon are attributed to (i) a unique sp2/sp3 mixture in Q-carbon, (ii) sp2-bonded highly conductive amorphous carbon-rich channels inside the Q-carbon cluster, (iii) a large local field enhancement due to the local geometry and microstructure of Q-carbon, and (iv) the presence of sp2-bonded amorphous carbon regions in the composite film. The temperature-dependent field emission properties, such as extreme sensitivity and an enhancement in the emission current density with temperature, can be explained by the local density of states near the Fermi level and the excellent thermal stability of the Q-carbon field emitters. From DFT simulation studies, the computed work function and the field-enhancement factor were determined to be 3.62 eV and ∼2300, respectively, which explains the excellent field emission characteristics of Q-carbon. The obtained field emission properties, in most cases, were superior to those from other carbon/diamond-based field emitters, which will open new frontiers in field emission-based electronic applications.

Simulation and Optimization of CNTs Cold Cathode Emission Grid Structure

Carbon nanotubes (CNTs) show significant advantages in the development of cold cathode X-ray tubes due to their excellent field emission performance; however, there are still some problems, such as short lifetime and the low emission current of large-area CNTs. In this paper, a front-grid carbon nanotube array model was established, and the electric field intensity near the tip of the CNTs' electric field enhancement factor was analytically calculated. A simulation model of a CNT three-dimensional field emission electron gun was established by using computer simulation technology (CST). The effects of grid wire diameter, grid aperture shape, and the distribution of grid projection on the cathode surface on the cathode current, anode current, and electron transmission efficiency were analyzed. The aperture ratio was used to evaluate the grid performance, and the simulation results show that the ideal aperture ratio should be between 65% and 85%. A grid structure combining a coarse grid and a fine grid was designed, which can make the electric field intensity around the grid evenly distributed, and effectively increased the cathode emission current by 24.2% compared with the structure without the fine grid. The effect of grid aperture ratio on the electron transmission efficiency was tested. The simulation results and optimized structure can provide a reference for the grid design of cold cathode emission X-ray tubes.

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.

Field emission properties of carbon cloth-supported SnO2 with different morphological structures

• SnO 2 nanorods were successfully fabricated on carbon cloth through a facile hydrothermal method. • The nanocone-like SnO 2 /CC sample showed more excellent field emission properties. In this paper, SnO 2 nanorods and SnO 2 nanocone-like structure were synthesized on carbon cloth by facile hydrothermal route. When the carbon cloth (CC) is naturally placed at the bottom of the reaction solution during the process, the SnO 2 nanorods/CC composites were successfully obtained. The turn-on field and field enhancement factor of which were found to be approximately 0.95 V/μm and 21782. However, when the CC was inverted and fixed horizontally in the reaction solution, the top part of the SnO 2 nanorods became a tip structure. The prepared sample has an excellent field emission performance with the lower turn-on field of 0.78 V/μm and higher field enhancement factor of 32268.

A dual-functional micro-focus X-ray source based on carbon nanotube field emission

A micro-focus X-ray source with miniature pressure sensor was developed based on the multi-walled carbon nanotube (MWNT) field emission. The field emitters for both X-ray cathode and the pressure sensor were synthesized by direct chemical vapor deposition growth of MWNTs on catalytic substrates. MWNTs exhibited excellent field emission properties with the threshold field at 10 mA/cm2 of 2.30 V/μm, and the high current density of 10 A/cm2 could be reached at the field of 4.36 V/μm. The field emission electron gun was constructed with the aid of electrostatic simulations on the electron beam trajectories and the focal spot size (FSS) on the target with the demagnification factor of 5. The practical objects, including the semiconductor chip and the ceramic heating element, were tested by the X-ray source with the spatial resolution of less than 35 μm, and the fracture of the ceramic element inside metal case could be clearly detected. The pressure sensor monitored the in-situ pressures inside the source during the processing and after the sealing-off. The pressures in the sealed sources were generally in 10−4 Pa level and could rise to 10−2 Pa level during the operation.

Significant enhancement in field emission and photoluminescence properties of vertically aligned tellurium nanorods by plasma treatment

Significant improvement in electron field emission (FE) properties of high density vertically aligned tellurium nanorods (TNRs) arrays has been observed by plasma treatment. At first the TNRs are grown by catalyst free chemical vapor deposition (CVD) method and are systematically characterized by FESEM, EDS, TEM, HRTEM, XRD and XPS. Later on TNRs were treated with plasma (Ar and N) and their effects on morphology, optical and FE properties are investigated comprehensively. The FE of TNRs containing 40–50 nm size have been enhanced from 6.22 Vμm−1 to 3.25 Vμm−1 which is more than 52%. This research reveals that plasma treatment has effectively modified the surface morphology (confirmed by TEM) and created sharp tips on TNRs which act as extra source of field emitters believed to contribute the enhancement of field emission. Plasma treated TNRs not only exhibited excellent FE properties (3.25 Vμm−1), these aligned TNRs also portrayed the tremendous stability with insignificant FE current fluctuation (<4%) for 60 min. Crucially, the reported FE turn-on value is low enough for their potential applications in device fabrications. So these findings offer the improvement in the field emission of TNRs by plasma treatment proposing their potential utilization in devices.

Electronic structures and emission properties of typical binary single crystal REB&lt;sub&gt;6&lt;/sub&gt;

Binary rare earth hexaborides (REB&lt;sub&gt;6&lt;/sub&gt;) have different rare earth elements with different valence electron distributions, which lead to different strange physical properties and different emission properties. However, in the electron emission properties, whether PrB&lt;sub&gt;6&lt;/sub&gt;, NdB&lt;sub&gt;6&lt;/sub&gt;, SmB&lt;sub&gt;6&lt;/sub&gt; and GdB&lt;sub&gt;6&lt;/sub&gt; all have excellent emission properties remains to be further studied, and the physical mechanism affecting their emission properties needs investigating. In this paper, the electronic structures, work functions of typical binary single crystal REB&lt;sub&gt;6&lt;/sub&gt; (LaB&lt;sub&gt;6&lt;/sub&gt;, CeB&lt;sub&gt;6&lt;/sub&gt;, PrB&lt;sub&gt;6&lt;/sub&gt;, NdB&lt;sub&gt;6&lt;/sub&gt;, SmB&lt;sub&gt;6&lt;/sub&gt;, GdB&lt;sub&gt;6&lt;/sub&gt;) are studied by first principles calculations. The single crystal REB&lt;sub&gt;6&lt;/sub&gt; are prepared by optical zone melting method, and their thermionic electron emission properties are tested experimentally. The theoretical calculation results show that the typical binary REB&lt;sub&gt;6&lt;/sub&gt; have large densities of states near the Fermi level. The d-orbitals with broad distributions in conduction bands are beneficial to electron emission. The localized f-orbital electrons in valence bands are not conducive to their electron emission. The theoretical calculations of work functions of typical binary single crystal REB&lt;sub&gt;6&lt;/sub&gt; (100) surface are consistent with the analyses of their electronic structures. The theoretical calculation values of work functions are ordered as GdB&lt;sub&gt;6&lt;/sub&gt; (2.27 eV) &lt; CeB&lt;sub&gt;6&lt;/sub&gt; (2.36 eV) &lt; LaB&lt;sub&gt;6&lt;/sub&gt; (2.40 eV) &lt; PrB&lt;sub&gt;6&lt;/sub&gt; (2.58 eV) &lt; SmB&lt;sub&gt;6&lt;/sub&gt; (2.63 eV) &lt; NdB&lt;sub&gt;6&lt;/sub&gt; (2.91 eV). The experimental test results of thermionic electron emission of single crystal show that the experimental thermionic electron properties are consistent with the theoretical ones. The LaB&lt;sub&gt;6&lt;/sub&gt; and CeB&lt;sub&gt;6&lt;/sub&gt; both have good thermionic and field emission properties, and the GdB&lt;sub&gt;6&lt;/sub&gt; has excellent field emission properties.