Excellent Field Emission Properties Research Articles

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

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.

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.

Morphological evolution and its correlation with optical and field emission properties in pulsed laser deposited ZnO nanostructures

The present report illustrates the effect of growth temperature on the morphological features, optical, and field emission properties (FE) of ZnO thin films deposited on Si substrate (100) through the pulsed laser deposition (PLD) technique. The as-deposited films have been characterized by employing various characterizations tools particularly X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), High- resolution TEM, etc., and confirms the successful deposition of the films. It demonstrates that as the growth temperature increases from ∼ 5000C to ∼ 8000C during 30 min, the spherical particle-like nanostructures transform into the truncated nanocones. Further, at a fixed deposition temperature of ∼ 8000C, and with enhancement in the growth time from ∼10 to 30 min, the nanoparticles get transformed into nanocones. Henceforth, the substrate temperature and growth time have been identified as determinant factors for the formation of these ZnO nanocones. XRD and TEM analysis suggest that the majority of nanocones have been aligned epitaxially with a preferred c-axis orientation on the Si substrates. Optical measurements reveal that the optical band gap of ZnO films exhibits a decreasing tendency from ∼3.26 to 3.22 eV with an increase in substrate temperature from ∼ 500 to 8000C. Subsequently, the field emission (FE) measurement of these aligned ZnO nanocones signifies a stable field emission with a low threshold field (2.40 V/μm) and a high field enhancement factor (∼2786). Their tapered morphologies and small tip diameters suggest as-deposited samples to be highly reproducible and henceforth as-deposited ZnO nanocones bearing excellent FE properties, through high-pressure PLD growth method without using any catalyst offer usage in various futuristic electronic applications.

The Parameters of the Field Emission Model and the Fabrication of Zinc Oxide Nanorod Arrays/Graphene Film

A large-scale growth of zinc oxide (ZnO) nanorod arrays on graphene sheets was fabricated by a hydrothermal technique, and the Fowler–Nordheim theory was used to build a model to describe the properties of the arrays’ field emission. The results indicated that the morphological characteristics of the ZnO nanorods grown on the graphene sheets can be easily tuned by varying the reaction time and concentrations of the reaction solution. The regular ordered ZnO nanorods arrays on the graphene sheets were obtained under the appropriate experimental conditions. Further, this composite cathode was demonstrated to possess excellent field emission properties due to the outstanding mechanical and electrical properties of graphene. The field emission current density of the composite cathode reached 1,448 μA cm–2 at the electric field of 16.5 V μm–1. The key parameter, field enhancement factor, reached 6,366, while the pure graphene cathode field is about 1,660. These specific nanorod arrays with enhancement of the field emission properties would be useful to sensor or modulator units for accessing networks.

A simple method to synthesize worm-like AlN nanowires and its field emission studies* *Project supported by the National Natural Science Foundation of China (Grant Nos. 11774017 and 51761135129).

The worm-like AlN nanowires are fabricated by the plasma-enhanced chemical vapor deposition (PECVD) on Si substrates through using Al powder and N2 as precursors, CaF2 as fluxing medium, Au as catalyst, respectively. The as-grown worm-like AlN nanowires each have a polycrystalline and hexagonal wurtzite structure. Their diameters are about 300 nm, and the lengths are over 10 μm. The growth mechanism of worm-like AlN nanowires is discussed. Hydrogen plasma plays a very important role in forming the polycrystalline structure and rough surfaces of worm-like AlN nanowires. The worm-like AlN nanowires exhibit an excellent field-emission (FE) property with a low turn-on field of 4.5 V/μm at a current density of 0.01 mA/cm2 and low threshold field of 9.9 V/μm at 1 mA/cm2. The emission current densities of worm-like AlN nanowires each have a good stability. The enhanced FE properties of worm-like AlN nanowires may be due to their polycrystalline and rough structure with nanosize and high aspect ratio. The excellent FE properties of worm-like AlN nanowires can be explained by a grain boundary conduction mechanism. The results demonstrate that the worm-like AlN nanowires prepared by the proposed simple and the PECVD method possesses the potential applications in photoelectric and field-emission devices.

Synthesis and field emission properties of Cu-filled vertically aligned carbon nanotubes

A highly conductive metal core modifies the electronic properties of a carbon shell, offering the possibility of enhancing its field emission (FE) behavior. Herein, a method has been devised to synthesize copper-filled vertically aligned carbon nanotubes (Cu@VACNTs) directly on Cu disks without extra metal catalysts via plasma-enhanced chemical vapor deposition. An ensemble of Cu particles formed on the surface of Cu disks due to surface reconstruction in a reducing environment plays a crucial role in the nucleation and growth of Cu@VACNTs. The filling of Cu inside the VACNTs can be controlled by tuning the growth temperature. The study of FE properties revealed that a conductive Cu-core extending throughout the entire length of the VACNTs could significantly enhance the FE properties of the VACNTs. Excellent FE properties including low turn-on field (ETo = 1.57 V/µm), low threshold field (ETh = 2.43 V/µm), high field enhancement factor (β = 3061), and high FE stability were observed for the Cu@VACNTs. The enhanced FE properties of the Cu@VACNTs can be accredited to low field screening due to bundled morphology and improved electrical and thermal conductivities offered by the encapsulation of highly conductive Cu nanowires inside the cores of VACNTs.

Direct synthesis of micropillars of vertically aligned carbon nanotubes on stainless-steel and their excellent field emission properties

Vacuum micro/nano-electronics can greatly benefit from the improved emission current density and temporal stability of the electron beam due to the morphological control and direct contact of cold field-emitters on a conducting substrate. In this work, high-performance vertically aligned carbon nanotube (VACNT) pillar-based field-emitter arrays (VACNT-P-FEAs) were synthesized directly on stainless-steel (SS) via plasma-enhanced chemical vapor deposition. Nanosphere lithography was employed to limit the growth sites of VACNTs and form VACNT-P-FEAs of different sizes on the SS substrate. The field emission (FE) properties of the VACNT-P-FEAs were dependent on the size of the pillar emitters. Remarkable FE properties, such as low turn-on electric field (ETo = 1.57 V/μm), low threshold electric field (ETh = 2.94 V/μm), high field enhancement factor (β = 4977), and high emission current density (∼33 mA/cm2 at a field of 4 V/μm) were observed from the VACNT-P-FEAs grown using polystyrene microspheres (450 nm diameter) for lithography. The excellent FE performance can be ascribed to the inherent properties of the sample, such as the high conductivity of the SS substrate, low contact resistance between the SS substrate and VACNTs, the suitable number of active VACNT pillar field-emitters, and the reduced screening effect between the VACNT pillars.

Template-free one-step synthesis of the multi-layer carbon or stacked graphene sheets coessentially coating N-doped graphene tubes and their field emission and photoluminescence properties

Graphene nanotubes (GNTs), as a rising member among the carbon nanomaterials family, has drawn significant research interest. The fabrication of the GNTs-based coessential composites could be a more facile and effective strategy to promote GNTs performances. Herein, based on the self-prepared N-doped graphene tubes (N-GNTs), multi-layer carbon wrapped N-doped GNTs (MLC@N-GNTs) and numerous stacked wrinkled graphene sheets encapsulated N-doped GNTs (GS@N-GNTs) are constructed via a facile free-template, one-step CVD method. The growth mechanism of the two types of coessential carbon composites was investigated in detail. The products, especially GS@N-GNTs display the most excellent field emission properties with a very low Eto of 0.33 V/mm, Ethr of 0.96 V/mm and a high field enhancement factor of 50237. The excellent field emission properties is attributed to the synergistic effect of the improved electronic conductivity, the high density of structure defects, the abundance of effective electron emission sites along with the high field enhancement factor and the electronic properties changes induced by the winkled graphene. In addition, MLC@N-GNTs and GS@N-GNTs show the more intense photoluminescence emission than that of pristine N-GNTs, because the coessential coatings induces the interfaces and large amounts of structure defects, which can act as trapping sites for the excitation energy.

Well-aligned periodic germanium nanoisland arrays with large areas and improved field emission performance induced by femtosecond laser

Si-based field emitters with high and stable current densities have gained increasing attention owing to their relevant compatibility with other silicon-based microelectronic and photonic devices. Currently, well-aligned Ge nanostructure arrays can be used in fabrication of Si-based field emitters with excellent performance. In this study, large-area well-aligned Ge nanoisland arrays are induced by femtosecond laser (120 fs, 800 nm, 1 kHz). Scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), Raman analyses, and X-ray photoelectron spectroscopy (XPS) reveal that well-aligned Ge nanoisland arrays with good quality. Field emission (FE) measurements indicate Ge nanoisland arrays with high emission current densities and good stability. Overall, the excellent FE properties of the proposed Ge nanoisland arrays will make them potential for applications in high-performance field emitters integrated with Si nanodevices.

A new process for the stabilization of vertically aligned GdB6 nanorods and their field emission properties

Excellent field emission properties of borothermally synthesised vertically aligned GdB6 nanorods.

Density control of vertically aligned carbon nanotubes and its effect on field emission properties

Vertically aligned carbon nanotubes (VACNTs) were synthesized directly on stainless steel substrate and their surface densities were tuned by an order of magnitude via growing them at different temperatures. The surface density of the VACNTs was correlated with the surface evolution of the substrate, a process in which catalyst nano hills were generated at different growth temperatures in the presence of reducing gas environment. Enhanced field emission (FE) properties including low turn-on electric field (ETurn-on = 0.66 V μm-1), low threshold electric field (ETh = 1.07 V μm-1), high field enhancement factor (β = 4084), and high FE stability for 600 min were obtained from VACNT arrays synthesized at 650 °C. It is speculated that the inherent features of our sample such as the conductive substrate, the low contact resistance between the substrate and the VACNTs, the uniform length and the appropriate spacing between the VACNTs have contributed to the excellent field emission properties. Simulation on the electrostatic field of various VACNT arrays was performed and the result is in good agreement with the experimental data.

Graphene nanosheets assisted carbon hollow cylinder for high-performance field emission applications

Electron sources are critical constituents for myriad many electronic applications including electron imaging, mass spectroscopy etc. Here, we report the realization of high-performance field emission from graphene assisted carbon hollow cylinders (Gr-CHCs) composed of multi-stacked radially aligned CNTs. These CHCs have built-in synthesis related Fe nanoparticles (NPs). This engineered nano-structure exhibits excellent field emission properties such as one of the ultra-low turn-on field (0.64 V μm−1 at 10 μA cm−2), low threshold field (0.74 V μm−1 at 100 μA cm−2), very high current density (15.49 mA cm−2 at 1.32 V μm−1) which is nearly double the current density obtained in our previous study. High field enhancement factor (0.72 × 104) with highly stable emission current at 100 μA was observed for more than 3 hrs at the base pressure of ∼1 × 10−8 mbar. This study suggests an approach to enhance the current density using the proposed innovative nanostructure and forms the basic theme of this communication. Highly efficient and stable field emissions observed are attributed to the geometry of cylinder and the production of the high density of sharp protrusions within the graphene sheets which enhance the local electric field and dramatically enhance field emission. This innovative cylindrical geometry associated with graphene assisted on Fe bearing aligned CNTs along with the periphery of the bulk cylinder provides an easy injection of electrons from the conduction band of CHCs into the vacuum in the presence of an external electric field. The tunability of field emission properties of these CHCs can be easily achieved by tailoring their diameter (10 and 20 mm) and different concentrations of the precursor. This new approach of the graphene assisted cylindrical geometry-based field emitter source provides enormous prospects and demand for next-generation high resolutions display devices.

Using Si textured structure to build vertical graphene sharp edges for electron field emission

The Vertically-orientated graphene (GP) sharp edges can provide a high density of individual field emission sites and a high field emission enhancement factor. In this report, we used a Si textured structure to build the vertical GP field emission edges. Relying on the periodical textured arrays of the Si surface, a large number of vertical sharp edges of GP are formed on the Si substrate during the electrophoretic deposition process. The vertical GP edges on the textured structure of Si shows a low turn-on electric field of 0.43 V −1 μm−1, a high enhancement factor of 9450, excellent stability behavior and a uniform luminance intensity image. The excellent field emission properties for the vertical edges are explored and discussed in detail. This investigation of the vertical GP edges on a textured Si surface suggests a potential prospect in application in future field electron emission devices.