Enhanced Field Emission Properties Research Articles

Field emission from two-dimensional (2D) CdSSe flake flowers structure grown on gold coated silicon substrate: An efficient cold cathode.

Field emission finds a vital space in numerous scientific and technological applications, including high-resolution imaging at micro- and nano-scales, conducting high-energy physics experiments, molecule ionization in spectroscopy, and electronic uses. A continuous effort exists to develop new materials for enhanced field emission applications. In the present work, two-dimensional (2D) well-aligned CdSSe flake flowers (CdSSe-FFs) were successfully grown on gold-coated silicon substrate utilizing a simple and affordable chemical bath deposition approach at ambient temperature. The time-dependent growth mechanism from nanoparticles to FFs was observed at optimized parameters such as concentration of precursors, pH (~11), deposition time, and solution temperature. The crystalline nature of CdSSe-FFs is confirmed by high-resolution transmission electron microscopy (HRTEM) results, and selected area electron diffraction (SAED) observations reveal a hexagonal crystal structure. Additionally, the CdSSe-FFs thickness was confirmed by TEM analysis and found to be ~20-30 nm. The optical, photoelectric, and field emission (FE) characteristics are thoroughly explored which shows significant enhancement due to the formation of heterojunction between the gold-coated silicon substrate and CdSSe-FFs. The UV-visible absorption spectra of CdSSe-FFs show enhanced absorption at 700 nm, corresponding to the energy band gap (Eg) of 1.77 eV. The CdSSe-FFs exhibited field emission and photosensitive field emission (PSFE) characteristics. In FE study CdSSe-FFs shows an increase in current density of 387.2 μ A cm-2 in an applied field of 4.1 V m-1 which is 4.08 fold as compared to without light illumination (95.1 μ A cm-2). Furthermore, it shows excellent emission current stability at the preset value of 1.5 μA over 3 h with a deviation of the current density of less than 5% respectively. RESEARCH HIGHLIGHTS: Novel CdSSe flake flowers were grown on Au-coated Si substrate by a cost-effective chemical bath deposition route. The growth mechanism of CdSSe flake flowers is studied in detail. Field emission and Photoluminescence study of CdSSe flake flowers is characterized. CdSSe flake flowers with nanoflakes sharp edges exhibited enhanced field emission properties.

Enhanced Field Emission Properties of CNT Film Emitters through Densification using Nitric Acid

Enhanced Field Emission Properties of CNT Film Emitters through Densification using Nitric Acid

Thermal plasma treatment of tin for the enhancement of field emission properties

Thermal plasma treatment of tin for the enhancement of field emission properties

Tuneable effects of pyrrolic N and pyridinic N on the enhanced field emission properties of nitrogen-doped graphene.

Graphene is one of the most potential field emission cathode materials and a lot of work has been carried out to demonstrate the effectiveness of nitrogen doping (N doping) for the enhancement of field emission properties of graphene. However, the effect of N doping on graphene field emission is lacking systematic and thorough understanding. In this study, undoped graphene and N-doped graphene were prepared and characterized for measurements, and the field emission property dependence of the doping content was investigated and the tuneable effect was discussed. For the undoped graphene, the turn-on field was 7.95 V μm-1 and the current density was 7.3 μA cm-2, and for the 10 mg, 20 mg, and 30 mg N-doped graphene samples, the turn-on fields declined to 7.50 V μm-1, 6.38 V μm-1, and 7.28 V μm-1, and current densities increased to 21.0 μA cm-2, 42.6 μA cm-2, and 13.2 μA cm-2, respectively. Density functional theory (DFT) calculations revealed that N doping could bring about additional charge and then cause charge aggregation around the N atom. At the same time, it also lowered the work function, which further enhanced the field emission. The doping effect was determined by the content of the pyrrolic-type N and pyridinic-type N. Pyridinic-type N is more favourable for field emission because of its smaller work function, which is in good agreement with the experimental results. This study would be of great benefit to the understanding of N doping modulation for superior field emission properties.

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.

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

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

Enhanced field emission properties of rGO wrapped Ga2O3 micro/nanobricks: Experimental investigation with theoretical validation

Aiming for efficient cold cathode applications in low dimension, pure and rGO wrapped gallium oxide micro/nanobricks were synthesized via cost-effective solid-state and hydrothermal routes. The synthesized samples were characterized using X-ray diffractometry, field emission scanning electron microscopy, high-resolution transmission electron microscopy, and Raman spectroscopy for phase, morphology, composition, and structure-related investigations. In addition, all samples were thoroughly investigated, and as a result, experimental modifications were adapted accordingly for improving the field emission properties. Remarkable enhancement of field-emission performances with a high emission current-density of 1.08 mA/cm2 and enhancement factor of 7400 has been observed as an effect of rGO wrapping. The results have been correlated with the increase in the availability of emission sites and proper charge carrier transport between the components in the hybrid structure. Furthermore, the probability of charge carrier transport across Ga2O3 /rGO junction was validated using theoretical analysis via DFT calculations. Moreover, the improvement of field emission properties due to rGO wrapping was also predicted from ANSYS simulations. Hence, 3.5 times increment of current density and 2.5 times lowering of turn-on field, the Ga2O3/rGO hybrid system emerged as one of the most functional future cold cathodes. This work opens up new applications for Ga2O3-based composites beyond the sensing and catalysis sectors.

Enhanced field emission properties of CsPbBr3 films by thermal annealing and surface functionalization with boron nitride

The relatively low work function, high defect tolerance, high electron mobility, and ease of fabrication nanostructures with high aspect ratio make all inorganic cesium lead halide perovskites promising emitter materials, but little research efforts have been devoted to them for potential applications in field emission devices. Herein, we report the enhanced field emission properties of CsPbBr3 films after thermal annealing and boron nitride modification. For as-grown CsPbBr3 films, the turn-on field at a current density of 10 μA cm−2 is 4.0 V μm−1, it decreases to 3.375 V μm−1 after thermal annealing at 150 °C, which is attributed to better crystallinity and formation of nanoscale emitter tips with sharp edges and optimized tips density. The field emission performance is further enhanced by surface functionalization with boron nitride deriving from the surface transfer induced n-type doping of CsPbBr3, and hence reduced work function. As a result, a lowest turn-on field of 2.875 V μm−1 and highest enhancement factor of 2518 are achieved. Finally, a good emission current stability of CsPbBr3 films after boron nitride modification have been demonstrated. The emission current fluctuations are 2.36% and 0.56% at initial current density of 20 and 100 μA/cm2, respectively.

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

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

Highly enhanced field emission properties of a carbon nanotube cathode on a titanium alloy substrate modified by alkali

Field emission electron sources with low turn-on electric fields, high emission current density, and good stability are of paramount importance in widespread applications, and in particular vacuum nanoelectronic equipment. Herein, an alkali modification approach was rationally designed to tailor the morphology of the commonly used compact and planar titanium alloy substrate. As expected, the modified substrate exhibited an interconnected porous network morphology, which offers remarkably strengthened adhesion with the screen-printed carbon nanotube cathode atop. As a result, the devices delivered comprehensively improved performance. Specifically, in the continuous driving mode, the turn-on electric field was as low as 0.79 V/μm, while the emission current of 85.13 mA/cm2 was relatively high. In parallel, in the pulse driving mode, the emission current density reached 1.266 A/cm2 under an electric field of 6.1 V/μm. Encouragingly, the cathode exhibited rather decent emission stability even under continuous operation for hours. This work provides a practical strategy for further enhancement of the field emission performance of carbon nanotube cathodes and highlights the significance of engineering titanium alloy substrates in future development.

Controlled decoration of palladium (Pd) nanoparticles on graphene nanosheets and its superior field emission behavior

Development in nanoscience and nanotechnology has inspired scientists to continuously explore new cathode material for field emission applications. In the present article, different weight (wt) % of Pd nanoparticles (Pd NPs) ensemble on graphene (Gr) nanosheets (Pd-Gr) were prepared via one step simple chemical route. The field emission (FE) properties of Pd decorated Gr nanosheets were studied. Structural and morphological analysis of as synthesized Pd-Gr composites were carried out by using X-ray diffraction (XRD), Raman spectroscopy and transmission electron microscope (TEM). The FE properties of the Pd-Gr changed according to the variation in the wt% of Pd NPs. The Pd3-Gr field emitter showed better performance among all the emitters with lower turn on field, threshold field and maximum emission current density (J). The enhanced FE properties of Pd-Gr are due to the decoration of low work function Pd NPs. The FE results demonstrated herein suggest that, Pd-Gr based field emitters can open up many opportunities for their potential utilization in large area field emitters in various vacuum micro-nanoelectronic devices such as flexible field emission displays, portable X-ray and microwave tubes.

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.

Enhanced field emission properties of single-walled carbon nanotube from dip-coating catalyst

Here we use a simple method of dip-coating catalyst to prepare single walled carbon nanotube (SWCNT), and study its cathode field emission property. The field emission performances of SWCNT films are not significantly different when the hydrogen flow quantities are in the range of 10–50 sccm. SWCNT prepared by different catalyst are also used as cathode to test field emission performance. SWCNT fabricated by Mo and Co (SWCNT-MoCo) cathode has a better field emission property than SWCNT prepared by Mo, Co and Fe, with lower Eon and Eth (electric field at the emission current density of 10 μA/cm2 and 0.1 mA/cm2) of 1.95 V/μm and 2.47 V/μm, which is because that SWCNT-MoCo cathode has a higher density of field emitter, so that under the same electric field SWCNT-MoCo cathode has more tips and sites to emit electrons. This method is simple and easy to operate, and the purity of the cathode film is high, with few impurities, which can be further applied in the future.

Fabrication of vertically well-aligned NiSi2 nanoneedle arrays with enhanced field emission properties

In this study, we demonstrated the controllable fabrication of periodic arrays of vertically well-aligned, fully-silicided NiSi2 nanoneedles with sharp nanotips on (100)Si substrates. The new approach proposed here eliminates the need for complicated and costly photolithographic processes and the use of toxic chemicals. All the produced vertical Si and NiSi2 nanoneedles were identified to be single crystalline and with the same geometric morphology and the same axial orientation of [100]. Additionally, the produced tapered NiSi2 nanoneedle array possessed excellent electron emission properties with a very low turn-on field of 0.85 V/μm, which is superior to many reported one-dimensional metal silicide nanostructures. Such an enhancement in the field emission can be attributed to the lower effective work function, sharp nanotips, single-crystalline structure, and good vertical alignment. The combination of the facile approach proposed here and superior electron emission performances make the well-ordered vertical NiSi2 nanoneedles promising candidates for vacuum nanoelectronics and field emission display applications.

Enhanced field emission properties From plasma treated Ti3C2Tx (MXene) emitters

MXenes are an emerging family of 2D transition metal carbides and nitrides and have already shown potential in various applications. However, up to now, studies on the field emission application of MXenes are scarce. In this study, the field emitters based on the Ti3C2Tx (MXene) flakes were prepared by facile solution process and the effect of different plasmas (H2, Ar, O2) on the field emission properties of Ti3C2Tx films was investigated. The plasma treated Ti3C2Tx films showed significantly better field emission properties than that of as-deposited Ti3C2Tx films. Compared to the Ar and O2 plasma treated Ti3C2Tx films, the H2 plasma treated Ti3C2Tx films displayed lower turn-on field (8.5 V/μm) and larger maximum current density (1222 μA cm−2). The H2 plasma treated Ti3C2Tx films also showed good emission stability. These results suggested the potential of the H2 plasma treated Ti3C2Tx films as electron source of vacuum electronic 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.

Enhancement of Electron Emission Properties of Carbon Nanotubes by the Decoration with Low Work Function Metal Oxide Nanoparticles.

In the present report, the properties of the field emission devices of carbon nanotubes (CNTs) were remarkably improved by decorating their surface with magnesium oxide nanoparticles (MgO NPs). The MgO NPs were attached effectively on the surface of CNTs via thermal evaporation. The Raman spectra confirm the graphitic order of as-grown pristine CNTs with RBM (radial breathing mode), D band and G band peaks at the 282 cm-1, 1347 cm-1 and 1594 cm-1 respectively. The peak at 471 cm-1 indicates successful attachment of MgO NPs to the CNTs. The enhanced field emission properties of CNTs were mainly attributed to the MgO NPs which increased the field enhancement factor and the density of emission sites. The decreased work function and increased field enhancement factor were responsible for the improved FE properties of the CNTs. Our results indicate that the MgO decorated CNTs can be used as an effective field emitter for various electron emission devices. The turn-on field decrease from 1.6 V/μm to 1.3 V/μm and the maximum current density increases from 1.581 to 3.678 mA/cm2 after the decoration of CNTs with MgO NPs. The value of field enhancement factor (β) also increases from 2.814×10³ to 9.823×10³.

Enhanced Field Emission Properties of Au/SnSe Nano-heterostructure: A Combined Experimental and Theoretical Investigation

We report the field emission properties of two-dimensional SnSe nanosheets (NSs) and Au/SnSe nano-heterostructure (NHS) prepared by a simple and economical route of one-pot colloidal and sputtering technique. Field Emission Scanning Electron Microscope (FESEM) analysis reveal surface protrusions and morphology modification of the SnSe NSs by Au deposition. By decorating the SnSe NSs with Au nanoparticles, significant improvement in field emission characteristics were observed. A significant reduction in the turn-on field from 2.25 V/µm for the SnSe NSs to 1.25 V/µm for the Au/SnSe NHS was observed. Emission current density of 300 µA/cm2 has been achieved at an applied field of 4.00 and 1.91 V/µm for SnSe NSs and Au/SnSe NHS, respectively. Analysis of the emission current as a function of time also demonstrated the robustness of the present Au/SnSe NHS. Consistent with the experimental data, our complementary first-principles DFT calculations predict lower work function for the Au/SnSe NHS compared to the SnSe NSs as the primary origin for improved field emission. The present study has evidently provided a rational heterostructure strategy for improving various field emission related applications via surface and electronic modifications of the nanostructures.

Water vapor-induced structure modification of vertically-aligned carbon nanotube arrays and successive thin film coating for enhanced field emission properties

Vertically-aligned carbon nanotubes (VCNTs) are used as electron source in various field emission applications owing to its high aspect ratio, chemical inertness, mechanical strength and electrical conductivity. Here, we demonstrate that surface structure modification along with thin film coating enhances the field emission performance, such as turn-on voltage, emission site density, and stability. In the present study, VCNTs with different heights were grown on silicon wafers by thermal chemical vapor deposition followed by the structure modification of VCNTs using capillarity-driven water vapor condensation. We obtained various surface morphologies by varying the water vapor exposure time and heating temperature. In addition, the structure-modified VCNTs surfaces were coated with W and SiO2 thin films using electron-beam evaporation. It was observed that W-coated VCNTs with modified surface morphology results in the best field emission performance.

Synthesis of a finger-like MoS2@VS2 micro–nanocomposite with enhanced field emission performance

A MoS2@VS2 micro–nanocomposite showed enhanced field emission properties benefiting from the synergy of the two materials.