Enhanced Electron Field Emission Properties Research Articles

Low-Defect Nanodiamonds and Graphene Nanoribbons Enhanced Electron Field Emission Properties in Ultrananocrystalline Diamond Films

It is known that the electron field emission (EFE) properties of ultrananocrystalline diamond (UNCD) films were usually produced by doping. Here, we performed a low-pressure annealing treatment wit...

Effect of metal nanoparticle doping concentration on surface morphology and field emission properties of nano-diamond films* *Project supported by the Science and Technology Major Project of Shanxi Province, China (Grant No. 20181102013) and the Fund from the “1331 Project” Engineering Research Center of Shanxi Province, China (Grant No. PT201801).

Nano-diamond particles are co-deposited on Ti substrates with metal (Ti/Ni) nanoparticles (NPs) by the electrophoretic deposition (EPD) method combined with a furnace annealing at 800 °C under N2 atmosphere. Modifications of structural and electron field emission (EFE) properties of the metal-doped films are investigated with different metal NPs concentrations. Our results show that the surface characteristics and EFE performances of the samples are first enhanced and then reduced with metal NPs concentration increasing. Both the Ti-doped and Ni-doped nano-diamond composite films exhibit optimal EFE and microstructural performances when the doping quantity is 5 mg. Remarkably enhanced EFE properties with a low turn-on field of 1.38 V/μm and a high current density of 1.32 mA/cm2 at an applied field of 2.94 V/μm are achieved for Ni-doped nano-diamond films, and are superior to those for Ti-doped ones. The enhancement of the EFE properties for the Ti-doped films results from the formation of the TiC-network after annealing. However, the doping of electron-rich Ni NPs and formation of high conductive graphitic phase are considered to be the factor, which results in marvelous EFE properties for these Ni-doped nano-diamond films.

Growth behavior of CVD diamond films with enhanced electron field emission properties over a wide range of experimental parameters

In this study, diamond films were synthesized on silicon substrates by microwave plasma enhanced chemical vapor deposition (CVD) over a wide range of experimental parameters. The effects of the microwave power, CH4/H2 ratio and gas pressure on the morphology, growth rate, composition, and quality of diamond films were investigated by means of scanning electron microscope (SEM), X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). A rise of microwave power can lead to an increasing pyrolysis of hydrogen and methane, so that the microcrystalline diamond film could be synthesized at low CH4/H2 levels. Gas pressure has similar effect in changing the morphology of diamond films, and high gas pressure also results in dramatically increased grain size. However, diamond film is deteriorated at high CH4/H2 ratio due to the abundant graphite content including in the films. Under an extreme condition of high microwave power of 10kW and high CH4 concentration, a hybrid film composed of diamond/graphite was successfully formed in the absence of N2 or Ar, which is different from other reports. This composite structure has an excellent measured sheet resistance of 10–100Ω/Sqr. which allows it to be utilized as field electron emitter. The diamond/graphite hybrid nanostructure displays excellent electron field emission (EFE) properties with a low turn-on field of 2.17V/μm and β=3160, therefore it could be a promising alternative in field emission applications.

The Significant Role of Hydrophilic and Hydrophobic Interfaces in Graphene‐Based 1D Heterostructures for Highly Enhanced Electron Emission

AbstractThe role of hydrophilic and hydrophobic substrate with graphene is crucial to define the interfacial properties of graphene (G)‐based heterostructures in the field of electronic device applications. Herein, the novel strategy of graphene wrapped hydrophilic/hydrophobic silicon nanowires (SiNWs) heterostructure is reported for highly enhanced electron field emission (EFE) studies with low turn‐on field. The combined effect of sharp edged graphene layers induced by different kinds of SiNWs is envisioned to enhance field enhancement factors and turn‐on voltage. The systematic results show the best EFE properties of hydrophilic SiNWs‐G based field emitters, with a lower turn‐on voltage of 0.53 V µm−1, a current density of 2.7 mA cm−2, and a higher field enhancement factor (β) of 14825. In addition, both the SiNWs‐G‐based field emitters are tested as the practical flat panel displays, where the hydrophilic‐based display exhibits at low voltage as 210 V. The superior EFE performance of hydrophilic SiNWs‐G based field emitters are ascribed to their large distortion field. Since more electrons can be trapped for easy tunneling, this increases the emission sites, and thereby contributes to a high enhancement field. This striking result from hydrophilic SiNWs‐G field emitters can be tailored for high‐performance EFE device applications.

Facile and single step synthesis of three dimensional reduced graphene oxide-NiCoO2 composite using microwave for enhanced electron field emission properties

We report the enhanced field emission properties of three-dimensional (3D) mixed transition metal oxide with reduced graphene oxide nanosheets (rGO-NSs) using a simple and fast synthesis route. The rGO-NSs with different/mixed transition metal oxide (rGO-MxOy) (MxOy=CoO, NiO and NiCoO2) composite has been synthesized for comparative studies for the electron field emission properties. The various rGO-MxOy composite materials were synthesized by microwave irradiation using soild precursor powder. The electron field emission properties were studied for all the samples as rGO-NSs, rGO-CoO, rGO-NiO and 3D rGO-NiCoO2 composite. It was found that specially, rGO-NiCoO2 composite shows the enhanced field emission performance due to synergic effect of mixed transition metal oxide as NiCoO2 nanoparticles with rGO-NSs and also the proper anchoring of NiCoO2 nanoparticles on rGO-NSs. The attachment of NiCoO2 mixed transition metal oxide with rGO-NSs exhibited lower turn-on field, lower threshold field, larger field enhancement factor and stable emission current stability as compared with those of the rGO-NSs, rGO-CoO and rGO-NiO composite. The surface microstructural analysis and morphology were probed by XRD, scanning and Raman. We suggest that anchoring of binary metal oxide nanoparticles on rGO-NSs could be exploited for the development of efficient field emitters.

Synthesis of reduced graphene oxide nanosheet-supported agglomerated cobalt oxide nanoparticles and their enhanced electron field emission properties

The field emission properties were demonstrated of reduced graphene oxide nanosheets (rGO-NSs) containing agglomerated Co3O4 nanoparticles (rGO–Co3O4) synthesized by a one-step microwave approach.

Enhanced electron field emission properties of diamond/microcrystalline graphite composite films synthesized by thermal catalytic etching

Diamond/microcrystalline graphite composite films were synthesized by thermal catalytic etching method with nickel as the catalyst. The surface morphology and composition of the composite films were examined by scanning electron microscopy (SEM), Raman spectroscopy and X-ray diffraction (XRD). The results show that the etching and graphitizing degree of diamond surface increased with the rising annealing temperature and the surface of as-grown diamonds were replaced by the tips of high aspect ratios and porous foam structure. The electron field emission (EFE) properties of composite films were improved compared to the as-grown diamond. The lowest turn-on field of 9.6V/μm has been detected for the composite film annealed at 900°C. The field emission current stability was influenced by graphite phase formed in the etching process. Gradual increase of emission currents along with time were observed for both samples annealed at 700°C and 800°C. However, there was a slightly decrease for the emission current of sample annealed at 900°C.

Enhanced electron field emission properties from hybrid nanostructures of graphene/Si tip array

High efficiency with excellently stable electron field emitters based on monolayer graphene coated on well-aligned Si tip (graphene/SiT) arrays fabricated by a simple transfer method is demonstrated.

Enhancement of the electron field emission properties of ultrananocrystalline diamond films via hydrogen post-treatment.

Enhanced electron field emission (EFE) properties due to hydrogen post-treatment at 600 °C have been observed for ultrananocrystalline diamond (UNCD) films. The EFE properties of H2-gas-treated UNCD films could be turned on at a low field of 5.3 V/μm, obtaining an EFE current density of 3.6 mA/cm(2) at an applied field of 11.7 V/μm that is superior to those of UNCD films treated with H2 plasma. Transmission electron microscopic investigations revealed that H2 plasma treatment induced amorphous carbon (a-C) (and graphitic) phases only on the surface region of the UNCD films but the interior region of the UNCD films still contained very small amounts of a-C (and graphitic) grain boundary phases, resulting in a resistive transport path and inferior EFE properties. On the other hand, H2 gas treatment induces a-C (and graphitic) phases along the grain boundary throughout the thickness of the UNCD films, resulting in creation of conduction channels for the electrons to transport from the bottom of the films to the top and hence the superior EFE properties.

Sharp folded graphene ribbons formed by CO2 laser ablation for electron field emission studies

A facile approach is used to grow sharp folded and wrinkled graphene structures by laser ablation process. The laser-graphite target interaction mechanism and effect of substrate temperature variation (400 °C and 700 °C) on the growth structure of graphene is studied. The low solubility of carbon in Cu helps in the deposition of graphene flakes by self-limiting process. High resolution transmission electron microscopy and Raman spectroscopy are utilized to confirm the crystalline structure of graphene at higher temperatures. These exotic structures are further studied for their electron field emission characteristics after transferring over Si/SiO2 substrates. The sharp folded graphene structures (turn-on field 1.4 V/μm) displayed enhanced electron field emission properties in comparison to wrinkled graphene (turn-on field 2.0 V/μm). The obtained wrinkled graphene structure is extremely suitable for field emission applications. This work presents an efficient technique to grow different graphene structures using laser ablation process that can act as potential candidates for future field emission devices.

Structure-modified stress dynamics and wetting characteristics of carbon nanotubes and multilayer graphene for electron field emission investigations.

In the present work, feasibility of achieving enhanced electron field-emission properties of stress-induced carbon nanotubes (CNTs) and multilayer graphene (MLGs) by ion modification is studied. Micro-Raman spectroscopy is used as a potent technique for in-depth investigations of stress-induced CNTs and MLGs. It is found that iron used as a catalyst, compresses at particular fluence and induces stresses in CNTs and MLGs to modify these structures, supported by high-resolution transmission electron microscopy (HRTEM) studies. The stresses are explained by the buckling wavelength (λ ∝ e((r/t)0.5)). Furthermore, the stresses induced in exotic nanostructures are studied for investigating wetting properties, which are well-corroborated with electron emission characteristics. It is found out that less-wetted CNTs and MLGs display enhanced emission properties with turn-on voltages (Eon) of 1.5 and 2.1 V/μm, respectively, in comparison to hydrophilic CNTs and MLGs with Eon of 2.6 and 4 V/μm, respectively.

Fast growth of ultrananocrystalline diamond films by bias-enhanced nucleation and growth process in CH4/Ar plasma

This letter describes the fast growth of ultrananocrystalline diamond (UNCD) films by bias-enhanced nucleation and growth process in CH4/Ar plasma. The UNCD grains were formed at the beginning of the film's growth without the necessity of forming the amorphous carbon interlayer, reaching a thickness of ∼380 nm in 10 min. Transmission electron microscopic investigations revealed that the application of bias voltage induced the formation of graphitic phase both in the interior and at the interface regions of UNCD films that formed interconnected paths, facilitating the transport of electrons and resulting in enhanced electron field emission properties.

Enhanced Electron Field Emission Properties of Conducting Ultrananocrystalline Diamond Films after Cu and Au Ion Implantation

The effects of Cu and Au ion implantation on the structural and electron field emission (EFE) properties of ultrananocrystalline diamond (UNCD) films were investigated. High electrical conductivity of 186 (Ω•cm)(-1) and enhanced EFE properties with low turn-on field of 4.5 V/μm and high EFE current density of 6.70 mA/cm(2) have been detected for Au-ion implanted UNCD (Au-UNCD) films that are superior to those of Cu-ion implanted UNCD (Cu-UNCD) ones. Transmission electron microscopic investigations revealed that Au-ion implantation induced a larger proportion of nanographitic phases at the grain boundaries for the Au-UNCD films in addition to the formation of uniformly distributed spherically shaped Au nanoparticles. In contrast, for Cu-UNCD films, plate-like Cu nanoparticles arranged in the row-like pattern were formed, and only a smaller proportion of nanographite phases along the grain boundaries was induced. From current imaging tunneling spectroscopy and local current-voltage curves of scanning tunneling spectroscopic measurements, it is observed that the electrons are dominantly emitted from the grain boundaries. Consequently, the presence of nanosized Au particles and the induction of abundant nanographitic phases in the grain boundaries of Au-UNCD films are believed to be the authentic factors, ensuing in high electrical conductivity and outstanding EFE properties of the films.

Development of diamond cathode materials for enhancing the electron field emission and plasma characteristics using two-step microwave plasma enhanced chemical vapor deposition process

The enhancement on the plasma illumination characteristics of a cylindrical microplasma device due to the utilization of hybrid-diamond (HiD) films as cathode was systematically investigated. The improved plasma illumination behavior was closely related to the enhanced electron field emission (EFE) properties of the diamond films. The HiD films, which possessed better EFE properties, including lower turn-on field for inducing the EFE process [(E0)efe = 2.7 V/μm] and higher EFE current density [(Je)efe = 2.8 mA/cm2, at 10.6 V/μm], resulted in superior illumination performance for the microplasma devices. The plasma can be triggered at a low threshold field of (Eth)pl. = 0.166 V/μm, attaining a large plasma current density of (Je)pl. = 9.6 mA/cm2 at an applied field of 0.266 V/μm (plasma density of ne = 1.70 × 1015 cm−3). The better EFE for the HiD films is ascribed to the unique granular structure of the films. Transmission electron microscopic studies revealed that the HiD films contained large diamond aggregates evenly distributed among the ultrasmall grain matrix. There presents a-few-layer graphite, surrounding the large aggregates that formed electron transport networks and improved the EFE properties for the HiD films. The superior EFE properties for the HiD cathode materials are the prime factor for improving plasma illumination characteristics for the cylindrical microplasma devices.

Electron Field Emission Enhancement of Vertically Aligned Ultrananocrystalline Diamond‐Coated ZnO Core–Shell Heterostructured Nanorods

Enhanced electron field emission (EFE) behavior of a core-shell heterostructure, where ZnO nanorods (ZNRs) form the core and ultrananocrystalline diamond needles (UNCDNs) form the shell, is reported. EFE properties of ZNR-UNCDN core-shell heterostructures show a high emission current density of 5.5 mA cm(-2) at an applied field of 4.25 V μm(-1) , and a low turn-on field of 2.08 V μm(-1) compared to the 1.67 mA cm(-2) emission current density (at an applied field of 28.7 V μm(-1) ) and 16.6 V μm(-1) turn-on field for bare ZNRs. Such an enhancement in the field emission originates from the unique materials combination, resulting in good electron transport from ZNRs to UNCDNs and efficient field emission of electrons from the UNCDNs. The potential application of these materials is demonstrated by the plasma illumination measurements that lowering the threshold voltage by 160 V confirms the role of ZNR-UNCDN core-shell heterostructures in the enhancement of electron emission.

The induction of nanographitic phase on Fe coated diamond films for the enhancement in electron field emission properties

A thin layer of iron coating and subsequent post-annealing (Fe-coating/post-annealing) is seen to significantly enhance the electron field emission (EFE) properties of ultrananocrystalline diamond (UNCD) films. The best EFE properties, with a turn on field (E0) of 1.98 V/μm and current density (Je) of 705 μA/cm2 at 7.5 V/μm, are obtained for the films, which were Fe-coated/post-annealed at 900 °C in H2 atmosphere. The mechanism behind the enhanced EFE properties of Fe coated/post-annealed UNCD films are explained by the microstructural analysis which shows formation of nanographitic phase surrounding the Fe (or Fe3C) nanoparticles. The role of the nanographitic phase in improving the emission sites of Fe coated/post-annealed UNCD films is clearly revealed by the current imaging tunneling spectroscopy (CITS) images. The CITS images clearly show significant increase in emission sites in Fe-coated/post-annealed UNCD films than the as-deposited one. Enhanced emission sites are mostly seen around the boundaries of the Fe (or Fe3C) nanoparticles which were formed due to the Fe-coating/post-annealing processes. Moreover, the Fe-coating/post-annealing processes enhance the EFE properties of UNCD films more than that on the microcrystalline diamond films. The authentic factor, resulting in such a phenomenon, is attributed to the unique granular structure of the UNCD films. The nano-sized and uniformly distributed grains of UNCD films, resulted in markedly smaller and densely populated Fe-clusters, which, in turn, induced more finer and higher populated nano-graphite clusters.

Gold ion implantation induced high conductivity and enhanced electron field emission properties in ultrananocrystalline diamond films

We report high conductivity of 185 (Ω cm)−1 and superior electron field emission (EFE) properties, viz. low turn-on field of 4.88 V/μm with high EFE current density of 6.52 mA/cm2 at an applied field of 8.0 V/μm in ultrananocrystalline diamond (UNCD) films due to gold ion implantation. Transmission electron microscopy examinations reveal the presence of Au nanoparticles in films, which result in the induction of nanographitic phases in grain boundaries, forming conduction channels for electron transport. Highly conducting Au ion implanted UNCD films overwhelms that of nitrogen doped ones and will create a remarkable impact to diamond-based electronics.

Fabrication of free-standing highly conducting ultrananocrystalline diamond films with enhanced electron field emission properties

Fabrication of free-standing/highly conducting ultrananocrystalline diamond (fc-UNCD) films at low growth temperature (<475 °C) is demonstrated. The fc-UNCD films show high conductivity of σ = 146 (Ω cm)−1 with superior electron field emission (EFE) properties, viz. low turn-on field of 4.35 V/μm and high EFE current density of 3.76 mA/cm2 at an applied field of 12.5 V/μm. Transmission electron microscopy examinations reveal the presence of Au/Cu clusters in film-to-substrate interface, which consequences in the induction of nanographite phases, surrounding the diamond grains that form conduction channels for electrons transport, ensuing in marvelous EFE properties of fc-UNCD films.

Synthesis of diamond nanotips for enhancing the plasma illumination characteristics of capacitive-type plasma devices

The enhancement of the plasma illumination characteristics of capacitive-type plasma devices (CP-devices) utilizing diamond-coated Si-nanotips as cathodes was systematically investigated. The enhanced electron field emission (EFE) properties of the diamond films resulted in improved plasma illumination characteristics of the devices. Microcrystalline diamond films grown using ultrananocrystalline diamond as a nucleation layer (MCD/UNCD) possessed a lower turn-on field for inducing the EFE process with a higher EFE current density and resulted in a better plasma illumination performance for the CP-devices compared with those made from MCD films grown directly on Si-substrates without the nucleation layer. Transmission electron microscopy revealed that, in a two-step microwave plasma enhanced chemical vapor deposition process, the second step altered the granular structure of the UNCD nuclear layer instead of growing a layer of large-grain diamond film on top of the UNCD nucleation layer, resulting in a duplex microstructure. The MCD/UNCD films contained large diamond aggregates evenly distributed among the ultrasmall-grain matrix, with the induction of a few layers of graphite, surrounding the large aggregates. The presence of the graphene-like phase is presumed to be the prime factor resulting in the superior EFE properties of the MCD/UNCD films and the better plasma illumination characteristics of the CP-devices.

Growth of Microcrystalline Diamond Films on Textured Si Substrates to Enhance the Electron Field Emission Properties

In this study, we grew a microcrystalline diamond film on a textured Si substrate (MCD/textured Si) and demonstrated the improved electron field emission (EFE) properties of the film. We used a simple wet chemical etching method to fabricate the textured Si substrate and then grew the MCD film by microwave plasma enhanced chemical vapor deposition. Although the Raman spectroscopy profile of the MCD film was essentially unchanged, the surface morphology of the MCD film was altered markedly owing to the utilization of the textured substrate as a template. Hillocks of nanodiamond aggregates, rather than large grain granular structures, were formed for the MCD/textured Si films. The turn-on field for the EFE of the MCD/textured Si film was as small as 3.2 V/µm, with a current density as large as 751 µA/cm2 (at an applied field of 8.8 V/µm). The enhanced EFE properties of the thus-obtained MCD/textured Si film, along with the simplicity and cost-effectivity of the substrate texturing process, renders the MCD/textured Si film a good candidate for application as an electron field emitter.