Field Emission Properties Research Articles

Fullerene Transformed into a 3-D Structure of Nitrogen-Doped Few-Layer Graphene Sheets: Growth and Field Emission Properties

3-D-structured nitrogen-doped few-layer graphene sheets (3-D NFLGs) have been prepared using a fullerene C60 precursor combined with a microwave excited nitrogen plasma process. A deep understanding of the growth mechanism and regulating of morphology that can adjust the field emission properties is crucial for its widespread application. In this work, the detailed growth process and microstructure and the field emission properties of the as-synthesized vertical aligned 3-D NFLGs were studied. The growth of the 3-D NFLGs can be divided into three steps: evaporation of the C60, opening of the C60, and formation of the 3-D NFLGs. The growth process and morphology of the materials can be neatly regulated by changing the evaporating temperature of the C60, electron temperature of the plasma, and substrate temperature through our self-designed reaction equipment. Interestingly, the vertical 3-D NFLGs grew at a limited microwave power and nitrogen pressure and could be divided into three different morphological features, reflected in their distribution uniformity, interparietal distance, number of layers, and crystallinity, which exhibited different field emission properties. Additionally, the 3-D NFLGs were all in situ doped with ∼4% nitrogen atoms from nitrogen gas during the growth process, while different compositions of the nitrogen atoms were reflected in the graphitic N increasing with increasing nitrogen pressure. Furthermore, the field emission measurements show that the as-obtained vertical 3-D NFLGs exhibited the lowest turn-on electric field (1.30 V/μm@10 μA/cm2) and threshold field (2.1 V/μm@1 mA/cm2) at the M1 morphology and the highest stability at the M3 morphology. Remarkable field emission performance was obtained for the 3-D NFLGs with M2 morphology, showing their great potential for field emission applications.

Investigation of Field Emission Properties of Multi-Emitter Carbon Nanotube Cathodes

Currently, scientists are actively studying the properties of cathodes based on various carbon materials, including carbon nanotubes. The purpose of this work is the possibility of using multi-emitter carbon nanotube cathodes for the development of field cathodes. A study was made of the field emission properties of multi-emitter cathodes based on filaments of multi-walled carbon nanotubes. For the experiments, a structure was assembled from a plurality of cathodes placed on a common base. As a result, the hypothesis of additivity of currents at low voltage was confirmed.

Controlled growth, characterization and field emission properties of high-quality WS2 nanowires by chemical vapor deposition

The controlled synthesis of high-quality WS2 nanowires exhibiting good physical and chemical properties is urgent and remains challenging. In this work, the WS2 nanowires are deposited on SiO2/Si substrates by chemical vapor deposition method using sulfides and halides with transition metal oxides as precursors. The effects of various experimental parameters, such as reaction temperature, Ar gas flow rate, holding time and substrate position, on the growth of WS2 nanowires are investigated. The detailed structural analyses indicate that the deposited WS2 nanowires with high crystalline quality possess the hexagonal 2H phase structure, and exhibit a smooth surface, uniform size and density distribution with a diameter of about 200 nm. Raman spectrum exhibits empirical characteristic peaks of in-plane vibration E12g(Г) and out-of-plane vibration A1g(Г) for the deposited WS2 nanowires. The formation mechanism of deposited 2H-WS2 nanowires is due to the preferential formation of WO3 nanowires during the reaction process, which is caused by further vulcanization to form the 2H-WS2 nanowires. Field emission property measurements are carried out based on the deposited WS2 nanowires, showing good turn-on field Eto of 2.4 V and threshold field Ethr of 6.8 V as well as excellent stability, which are attributed to their unique geometrical features.

Contact Transport and Field Emission Properties of Low-Dimensional 2D Carbon Heterostructures

Contact Transport and Field Emission Properties of Low-Dimensional 2D Carbon Heterostructures

Investigation of 500 keV Si ion induced surface structuring of Ni and Ti for enhancement of field emission properties

The present paper reports the investigation of surface morphology, elemental composition, phase changes and field emission properties of Si ion irradiated nickel (Ni) and titanium (Ti). The Ni and Ti targets have been irradiated with 500 keV Si ions generated by Pelletron accelerator at various fluences ranging from 6.9 × 1013 to 77.1 × 1013 ions/cm2. Stopping range of ions in matter analysis revealed higher values of electronic stopping and sputtering yield for Ni as compared with Ti. For both irradiated metals, electronic energy loss dominant over the nuclear stopping. The growth of induced surface structures have been analysed by using field emission scanning electron microscopy (FESEM) analysis. In case of Ni, as the ion fluence increases from 6.9 × 1013 to 65.8 × 1013 ions/cm2, the formation of spherical particulates, agglomers and sputtering is observed. Although in the case of Ti, with the increase of Si ion fluence from 11.6 × 1013 to 77.1 × 1013 ions/cm2, the formation of irregular‐shaped particulates along with crater and sputtered channels is observed. X‐ray diffraction (XRD) analysis shows that no new phase is identified. However, a significant increase in peak intensity is observed with increasing ion fluence. The variation in crystallite size and dislocation line density is also observed as a function of Si ion fluence. Fourier transform infrared spectroscopy analysis shows that no bands are formed after the Si ion irradiation. Field emission properties of ion‐structured Ni and Ti are well correlated with the growth of surface structures observed by SEM and dislocation line density evaluated by XRD analysis.

Local Characterization of Field Emission Properties of Graphene Flowers

AbstractAn experimental study about field emission properties of commercially available graphene flowers cloth is reported. Material characterization by means of X‐ray diffraction, Raman spectroscopy, and X‐ray photoemission spectroscopy confirms the formation of high quality vertical few‐layers graphene nanosheets. A tip‐anode setup is exploited in which nanomanipulated tungsten tip is used as the anode at controlled distance from the emitter in order to reduce the effective emitting area below 1 µm2, giving access to local characterization. A turn‐on field as low as 0.07 V nm−1 and field enhancement factor up to 32 for very small cathode–anode separation distances is demonstrated, in the range 400–700 nm. It is also shown that the turn‐on field increases for increasing distances, while the field enhancement factor decreases. Finally, time stability of the field emission current is reported, evidencing a reduction of the fluctuations for lower current levels.

Experimental and theoretical approaches of electron emission from hydrophobic rGO modified silicon nanowires

Grass like tapered silicon nanowires are synthesized by metal assisted chemical etching process under 60 °C temperature for 40 (SiNW40), 60 (SiNW60) and 80 min (SiNW80) to investigate the optimum time of etching for the SiNWs to act as an efficient field emitter.It is observed that 60 minof HF etching areoptimum forsilicon nanowires for its low turn-on field but SiNW80 requires higher turn-on field than SiNW60 though the current density is extremely high after reaching the turn-on electric field. This disadvantage is attributed to the tip bundling effect of SiNW80. In order to obtain low turn-on field along with high current density, SiNW80 is wrapped with rGOfor the first time and it shows the lowest turn-on field of 0.12 V/µm with the highest current density. Surface roughness properties related tofield emission are analyzed by wettability study. Additionally, ANSYS simulation conducted for the theoretical validation of field emission properties has added another novelty of work. There is reduction of work function from SiNW80 to rGO-SiNW80 as obtained from the computational analysis. Morphological variation, surface edges, surface roughness related to water contact angle, moderate work function and energy band bending cause such enhancementfield emission properties.

Understanding the role of sheet thickness on field emission from engineered hexagonal tin disulphide

The 2D metal chalcogenide has attracted lots of research interest in the field of catalysis, optoelectronics, energy storage, electron emission, light emission as well as in sensors. These properties arise due to their low bandgap, high surface area, moderate work function and high charge carrier mobility. Therefore, in the present work, we synthesise SnS2 using the micellar-assisted hydrothermal route. The role of surfactant charge on the morphology of SnS2 has been also extensively explored. Microstructure analysis shows the formation of hexagonal sheets of size 250–300 nm; whereas the sheet thickness is strongly dependent on the surfactant charge. The presence of cationic and anionic surfactants leads to the formation of the ultrathin sheet (∼3.3 nm) and ∼ 11 nm respectively; whereas the SnS2 sheet obtained in absence of any surfactant has a thickness of ∼ 76 nm. For the fabrication of SnS2 film, synthesised samples have been dispersed in ethanol and ethylene glycol mixture via ultrasonication and spin-coated over the silicon substrate. The field emission properties of CTAB assisted SnS2 to show the lowest turn-on field 4.4 V/μm and a high current density (∼9.6 μA/cm2). Earlier, the lowest reported turn-on field of SnS2 was 4.8 V/μm at 1 μA/cm2 current density.

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.

Comparative study on atomically heterogeneous surface with conical arrays of field emitters generated using plasma based low-energy ion beams

A comparative study of the field emission properties of conical arrays of atomically heterogeneous, self-organized, micro–submicro–nanodimensional structures, irradiated at normal incidence by high flux of 2 keV argon (flux=6.47×1015cm−2s−1) and krypton ions (flux=4.81×1015cm−2s−1) on copper substrates, without employing any external seeding, is presented. The variation in surface structural growths with ion beam fluence is investigated using scanning electron, atomic force, and transmission electron microscopy. The exposed surfaces are atomically heterogeneous due to the presence of embedded argon and krypton ions in the interstitial layers (≈nm) as observed from the x-ray photoelectron spectroscopy analysis. Kelvin probe force microscopy is employed to analyze the variation in local work function caused by surface deformities and implantation of inert gaseous ions. The conical arrays are naturally selected field emitter sources, and their field enhancement factor is calculated from the Fowler–Nordheim equations. The argon ion treated substrate at a fluence of 4.85×1018cm−2 gives rise to uniformly distributed structures and has a low turn-on voltage of 2.76 kV with an electron emission current of 0.58 nA. Among the krypton ion irradiated substrates, the sample irradiated at the highest fluence of 5.12×1018cm−2 produces self-organized conical arrays having uniform dimension, orientation, distribution, and even a higher electron emission current of 0.81 nA with a lower turn-on voltage of 2.12 kV. Thus, it may be concluded that krypton ion irradiation provides better generation of naturally selected arrays of field emitters.

Synthesis of α-MoO3 nanofibres for enhanced field-emission properties

Synthesis of α-MoO₃ nanofibres for enhanced field-emission properties

Field emission properties of tetrapod-shaped ZnO/TiN point light source with semicircle reflecting anode

A novel point light source composed of tetrapod-shaped ZnO/TiN (T-ZnO/TiN) cathode and semi-circular groove reflective anode is demonstrated. The T-ZnO/TiN cathode is fabricated on nickel wire by spraying T-ZnO NRs powder and subsequent sputtering of TiN film. Semicircular reflective anodes with different opening sizes were prepared by wire electro-discharge machine. The field-emission properties of point light sources could be dramatically enhanced under semicircle reflecting anode by decreasing the threshold field from 2.61 to 2.10 V/μm. The point light source of D1500 has an extremely high emission current density of 132.73 mA/cm2 at 3.53 V/μm. The value of Jmax is about 2.7 times to that of D3000 (∼47.89 mA/m2 at 4.18 V/μm). Experiments and ANSYS electric field simulation show that the combination of low work function hybrid cathode and semicircular reflective anode structure leads to the increase of local field concentration and the enhancement of field emission characteristics. As far as we know, this point light source with semicircular reflective anode is prepared and applied for the first time. The results show that the point light source structure proposed here can not only effectively reduce the threshold field, but also improve the emission current density and luminescence uniformity.

Synthesis and Characterization of MWCNTs/ZnO Nanocomposites for Device Applications

The nanocomposite was created in order to investigate field emission (FE) applications. A MWCNTs/ZnO nanocomposite, by combining ZnO thin films with multi-wall carbon nanotubes (MWCNTs), was synthesized by the use of chemical vapor deposition (CVD) techniques for FE applications. The thin films were then prepared by dip-coating and drop-casting onto a silicon substrate. The field emission scanning electron microscopy (FESEM), Raman spectroscopy and the X-ray diffraction (XRD) techniques were used to characterize the MWCNTs and MWCNTs/ZnO nanocomposite separately and compare the results. From Raman spectra, the calculated values of ID/IG are, respectively, 0.521 and 0.950, which confirm the certain defects and disorders produced after coating of ZnO nanoparticles on the MWCNTs’ surface. From the current density–electric field plot, it is found that the FE properties increased by three times which indicates that MWCNTs/ZnO nanocomposite can be useful for ideal cathode emitters.

Fabrication of In2Te3 nanowalls garnished with ZnO nanoparticles and their field emission behavior

Two-dimensional (2D) vertical oriented indium sesquitelluride (In2Te3) nanowalls, and ZnO/In2Te3 nanoheterostructures were grown on Si substrate via simple chemical vapor deposition (CVD) technique. The monitored In2Te3 nanowalls are single crystalline, 120–150 nm in size and approximately 50 nm thin. Indium sesquitelluride (In2Te3) has a suitable band gap for optoelectronic and energy field applications but its field emission properties have not been investigated yet. For the first time, In2Te3 structures have been subjected for field emission analysis which pointed out reasonable properties of field emission. Owing to field emission improvement, ZnO nanoparticles were garnished on In2Te3 nanowalls. This causes an impressive reduction in turn on field which approaches to 2.1 Vμm−1 as compared to pure In2Te3 nanowalls 3.2 Vμm−1. In addition, excellent emission stability without significant current degradation is noted. These findings indicated that 2D nanowalls of In2Te3 and ZnO/In2Te3 nanoheterostructures have great potentials for future applications in the energy field.

Microplasma emission performances dependent on silicon nanowires morphologies

Silicon nanowires (SiNWs) are introduced into microdischarge to improve microplasma properties due to its field emission electrons and field enhancement effect. The geometrical arrangement and dimensional features of SiNWs have desicive influence on field emission properties, thus the dependence of microplasma emission performances on the SiNWs morphologies is investigated in this paper. The different morphologies of SiNWs can be prepared by electrocatalytic metal-assisted chemical etching with varied etching currents. With the increase of etching current from 3 mA to 30 mA (AgNO3:HF:H2O2 = 0.02:4.6:0.1 mol l−1, deposition time 1 min and etching time 10 min), the field emission current density J of the SiNWs prepared at 20 mA etching current is the largest ∼0.28 mA cm−2 at a field 4.5 V μm−1, and turn-on field is the lowest of 3.52 V μm−1. Accordingly, the microplasma in the device fabricated on the SiNWs-decorated substrate (etching current at 20 mA) has the strongest average emission intensity of ∼11 565 a.u., the minimal relative standard deviation of emission intensity 4.9% and the fastest propagation velocity of 471 km s−1. The field emission electrons of SiNWs could inject more seed electrons into microcavity which causes higher electron collision probability, and the field enhancement effect at tips of SiNWs can provide more energy for the charged particles, which are helpful to the microdischarge. The most difficulty is to balance the distance of emitters and the percentage of SiNWs in entire emission region because the shielding effect will reduce while the surface emitter numbers will decrease when the distance of emitters increases. Here, a ‘proper percentage of SiNWs’ of 19.3% is obtained what indicates that if SiNWs percentage is greater than the threshold, field enhancement factor β eff is weakened by the decrease of aspect ratio and the increase of percentage. When SiNWs percentage is less than 19.3%, β eff will increase and be dominated by the percentage of SiNWs. The results are significant for the application of SiNWs in microdischarge devices.

Systematic Field Electron Emission Investigations of Vapor‐Phase‐Grown Sb2Te3 Nanosheets

Micron‐sized Sb2Te3 nanosheets are grown on p‐type Si substrate by facile vapor‐phase route. Physicochemical properties of the Sb2Te3 nanosheets are revealed using X‐ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscopy (AFM), transmission electron microscope (TEM), Raman spectroscopy, and X‐ray photoelectron spectroscopy (XPS). Owing to their high aspect ratio, field emission (FE) characteristics of the Sb2Te3 nanosheets grown on Si substrate (termed as a “planar emitter”) are investigated. Furthermore, the FE behavior of a single Sb2Te3 nanosheet attached to a blunt tungsten needle is studied. The single nanosheet emitter exhibited superior emission behavior in contrast to the planar emitter. The Fowler–Nordheim (F–N) plot for the single nanosheet emitter exhibits linear nature, whereas for the planar emitter it shows deviation from linearity. An attempt has been made to reveal the FE properties of a single Sb2Te3 nanosheet in an “in‐plane” configuration, similar to the vacuum field emission transistor (VFET). In this case, a maximum emission current of 1 μA is observed at 290 V, which is comparable to other VFETs. The observed results clearly imply the potential of the single nanosheet emitters due to topological insulators, like Sb2Te3, for the development of new generation nanoscale vacuum electronic devices.

Influence of thermal contact resistance on the field emission characteristics of a carbon nanotube

A recent algorithm developed by Tripathi et al. [J. Appl. Phys. 128, 025017 (2020); Erratum, J. Appl. Phys. 131, 169901 (2022)] is modified to study the effects of thermal contact resistance on the field emission (FE) properties of a carbon nanotube (CNT). The model takes into account the temperature dependence of the CNT electrical and thermal conductivities. The boundary condition proposed by Huang et al. [Phys. Rev. Lett. 93, 7 (2004)] is used to include the effects of thermal contact resistance at a CNT/chuck interface located at x=0, i.e., Tc=T(x=0)=λπr2κ(Tc)(∂T/∂x)x=0+T0, where r is the CNT radius, κ(Tc) is the heat conduction coefficient at x=0, and λ is the thermal resistivity of the CNT/chuck interface. The chuck is assumed to be a perfect heat sink at temperature T0. For a given set of CNT parameters and values of the applied external electric field, it is shown that current constriction at the CNT/chuck contact point leads to self-heating effects which increase with the value of the thermal contact resistance, leading to an increase in the temperature profile along the CNT (including the temperature at its tip) and the FE current above their values obtained assuming the CNT/chuck interface is at the heat sink temperature T0. The fractional change of the emission current versus applied external electric field is calculated for increasing values of the parameter λ.

SnO2 Nanofibers Network for Cold Cathode Applications in Vacuum Nanoelectronics

AbstractField‐emission cold cathodes are the key components of vacuum nanoelectronics that offer great advantages over other electron sources based on the thermionic or photoelectric effects. In the effort to realize new electron sources, a systematic investigation of the field emission (FE) properties of SnO2 nanofiber networks is performed. High‐purity SnO2 nanofibers, confirmed by X‐ray photoelectron spectroscopy, are prepared by electrospinning technique and then uniformly distributed over Si wafer. Field emission properties are investigated using a nanomanipulated tip‐shaped anode, inside a scanning electron microscope, for fine tuning the anode‐cathode separation distance. A field‐emission current is observed with an applied electric field as low as 25 V μm−1. Performance parameters such as turn‐on field and field enhancement factor are evaluated within the theoretical Fowler–Nordheim framework as a function of the anode–cathode separation distance, demonstrating that a maximum enhancement factor of about 150 is obtained at a separation of 200 nm. The emission from a single nanofiber is characterized by a current saturation at high voltages that can be explained in terms of electron supply limitation within conduction band. No evidence of field emission current contribution by electron tunneling from the valence band is observed in the experimental data.

First principle studies revealing the effect of O2, CO2, and H2 adsorption on field emission behaviour of graphene

The effects of the absorption of the gas molecule on the work function and the field emission current of graphene have been theoretically investigated. The results demonstrate that the absorbed O2, CO, and H2 on graphene with different absorption and absorption types have a large effect on its field emission properties. All absorbed O2, CO, and H2 on graphene with different absorption sites and absorption types except H2 on the bridge site lead to a reduction in its field emission current. It agrees with the experimental conclusion that the adsorption of O2 on the graphene will reduce its field emission current in the literature. Numerical results suggest that the density of adsorbed molecules, the types of adsorbed molecules, the type of adsorption and the location of adsorption could be detected by measuring the variation rule of the field emission current under different applied electric fields. This implies that the characteristics of field emission properties of graphene can be implemented as a working principle of a feasible gas sensor.

Field Electron Emission from Crumpled CVD Graphene Patterns Printed via Laser-Induced Forward Transfer.

A new approach to the fabrication of graphene field emitters on a variety of substrates at room temperature and in an ambient environment is demonstrated. The required shape and orientation of the graphene flakes along the field are created by the blister-based laser-induced forward transfer of CVD high-quality single-layer graphene. The proposed technique allows the formation of emitting crumpled graphene patterns without losing the quality of the initially synthesized graphene, as shown by Raman spectroscopy. The electron field emission properties of crumpled graphene imprints 1 × 1 mm2 in size were studied. The transferred graphene flakes demonstrated good adhesion and emission characteristics.