Electron Field Emission Properties Research Articles

Synthesis and field electron emission properties of multi-walled carbon nanotube films directly grown on catalytic stainless steel substrate

The multi-walled CNT films were directly grown on stainless steel substrates using an oxidation-reduction treatment with chemical vapor deposition. Microstructure and field emission properties of the as-received CNT films were detailedly investigated. The results indicate that the CNTs have originally random orientation with relative high density, good crystalline perfection and large diameter. Besides, the CNT films exhibit superior field electron emission performances with low threshold electric field (∼4.2 V/μm) and very high emission current density (∼24 mA/cm2). Importantly, the CNTs directly grown on stainless steel substrates have remarkable long-term stability with ∼3.4% fluctuation over 50 h continuous measurement under high current density, ∼10 mA/cm2. The perfect graphitization, large field enhancement factor, low contact resistance, good adhesion and high thermal conductivity are believed to be principally responsible for their superior field emission properties, which make them very promising application as an electron source in microthrust space electric propulsion neutralizer.

Nanoscale investigation of enhanced electron field emission for silver ion implanted/post-annealed ultrananocrystalline diamond films

Silver (Ag) ions are implanted in ultrananocrystalline diamond (UNCD) films to enhance the electron field emission (EFE) properties, resulting in low turn-on field of 8.5 V/μm with high EFE current density of 6.2 mA/cm2 (at an applied field of 20.5 V/μm). Detailed nanoscale investigation by atomic force microscopy based peak force-controlled tunneling atomic force microscopy (PF-TUNA) and ultra-high vacuum scanning tunneling microscopy (STM) based current imaging tunneling spectroscopy (CITS) reveal that the UNCD grain boundaries are the preferred electron emission sites. The two scanning probe microscopic results supplement each other well. However, the PF-TUNA measurement is found to be better for explaining the local electron emission behavior than the STM-based CITS technique. The formation of Ag nanoparticles induced abundant sp2 nanographitic phases along the grain boundaries facilitate the easy transport of electrons and is believed to be a prime factor in enhancing the conductivity/EFE properties of UNCD films. The nanoscale understanding on the origin of electron emission sites in Ag-ion implanted/annealed UNCD films using the scanning probe microscopic techniques will certainly help in developing high-brightness electron sources for flat-panel displays applications.

Cu incorporated amorphous diamond like carbon (DLC) composites: An efficient electron field emitter over a wide range of temperature

The effect of temperature on the electron field emission properties of copper incorporated amorphous diamond like carbon (a-Cu:DLC) thin films have been reported. The a-Cu:DLC thin films have been deposited on indium tin oxide (ITO) coated glass and silicon substrate by the radio frequency sputtering process. The chemical composition of the films was investigated using X-ray photoelectron spectroscopy and the micro structure was established using high resolution transmission electron microscopy. The sp2 and sp3 bonding ratio in the a-Cu:DLC have been analyzed by the Fourier transformed infrared spectroscopy studies. The material showed excellent electron field emission properties; which was optimized by varying the copper atomic percentage and temperature of the films. It was found that the threshold field and effective emission barrier were reduced significantly by copper incorporation as well as temperature and a detailed explanation towards emission mechanism has been provided.

Field Electron Emission From CVD Nanocarbon Films Containing Scrolled Graphene Structures

Electron field emission properties of nanocarbon films produced by plasma‐enhanced chemical vapor deposition (PECVD) were investigated. The films contained nanostructured diamond and graphitic components in different ratios depending on the parameters of the deposition process. Low threshold fields in the range of 1–2 V μm−1 (at 0.1 mA cm−2) are detected for all types of the studied films. It is found that the scrolled graphene structures, contained in the film material, are responsible for the field emission. The individual graphene scrolls show standard Fowler–Nordheim behavior and sustained maximum field emission currents of several microamperes. Long‐time field emission at moderate currents causes partial destruction of the scrolls that significantly changed the threshold field and emission site density of the films. Obtained results show that PECVD growth and post‐treatments allow monitoring of the amount and heights of emission centers providing tailored field emission properties of nanocarbon films for particular applications in vacuum electronic devices.

Nickel-induced transformation of diamond into graphite and carbon nanotubes and the electron field emission properties of resulting composite films

Abstract The metal-induced transformation of diamond into graphite and carbon nanotubes (CNTs) was achieved by catalytic deposition with nickel as the catalyst. The quality of catalytic products was assessed by scanning electron microscopy, Raman spectroscopy and transmission electron microscopy. Results showed that the catalytic process could be controlled by adjusting the carbonaceous concentration in the deposition atmosphere, and new information concerning the diamond/Ni/graphite multi-phase mixed interface between diamond and carbon nanotube has been analyzed. A model was put forward to elucidate the mechanism of catalytic etching and growth on the diamond surface. In addition, the resulting diamond/CNTs composite film (10% CH4) was found to exhibit the lowest turn-on field of 6.9 V/μm as well as good current emission stability compared to the other composite films.

Field electron emission enhancement in lithium implanted and annealed nitrogen-incorporated nanocrystalline diamond films

The field electron emission (FEE) properties of nitrogen-incorporated nanocrystalline diamond films were enhanced due to Li-ion implantation/annealing processes. Li-ion implantation mainly induced the formation of electron trap centers inside diamond grains, whereas post-annealing healed the defects and converted the a-C phase into nanographite, forming conduction channels for effective transport of electrons. This resulted in a high electrical conductivity of 11.0 S/cm and enhanced FEE performance with a low turn-on field of 10.6 V/μm, a high current density of 25.5 mA/cm2 (at 23.2 V/μm), and a high lifetime stability of 1,090 min for nitrogen incorporated nanocrystalline diamond films.

Plasma-enhanced synthesis of carbon nanocone arrays by magnetic and electric fields coupling HFCVD

In this paper, magnetic and electric fields coupling hot filament chemical vapor deposition (HFCVD) was used to fabricate a series of carbon films varying from nanocrystalline diamonds (NCD) to carbon nanocone arrays. The surface morphology and composition of the film were examined by scanning electron microscopy and Raman spectroscopy. After adding magnetic field, the morphology of the as-grown NCD film was a serried form instead of a rugged topography obtained under the absence of magnetic field. As electric field intensity increased, the etching degree of NCD films enhanced and the structural transformation of NCD to microcrystalline graphite occurred. We proposed that magnetic and electric fields can effectively introduce plasma into HFCVD system to optimize the film deposition process and studied the impact of magnetic and electric fields. The presence of electric field promoted ionization of reactive gas, and magnetic field made these ionic gases bound to a certain area around the sample, increasing the regional density of plasma. Specially, unique carbon nanocone arrays were obtained by synergistic effect of magnetic and electric fields, which exhibited optimal electron field emission properties, showing the lowest turn-on field of 5.65V/μm.

Vertically aligned diamond-graphite hybrid nanorod arrays with superior field electron emission properties

A “patterned-seeding technique” in combination with a “nanodiamond masked reactive ion etching process” is demonstrated for fabricating vertically aligned diamond-graphite hybrid (DGH) nanorod arrays. The DGH nanorod arrays possess superior field electron emission (FEE) behavior with a low turn-on field, long lifetime stability, and large field enhancement factor. Such an enhanced FEE is attributed to the nanocomposite nature of the DGH nanorods, which contain sp2-graphitic phases in the boundaries of nano-sized diamond grains. The simplicity in the nanorod fabrication process renders the DGH nanorods of greater potential for the applications as cathodes in field emission displays and microplasma display devices.

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.

Structure and electron field emission properties of ion beam reduced graphene oxide sheets

We report the structure and electron field emission properties of ion beam reduced graphene oxide (GO). 500 keV Ar+ ion beam was used to reduce the GO, synthesized by modified Hummer’s method. X-ray photoelectron spectroscopy and Resonant Rutherford backscattering spectrometric analyses evidenced that the oxygen functional groups drastically reduced upon irradiation. Further, the ion beam reduced GO exhibits enhanced electron field emission property. The exponential reduction of oxygen concentration is correlated with the field enhancement factor. Raman studies shows that ion irradiation process does not introduced any additional defects in GO. Scanning electron microscopic analysis reveals layered structure of GO sheets upon ion irradiation. Our investigation demonstrated that ion beam irradiation of GO yields a highly enhanced field emission with low turn-on voltage without deteriorating its structure.

The effect of Cu ion implantation and post-annealing on surface morphology and electron field emission in ultrananocrystalline diamond

Abstract The effects of 100 keV Cu ion implantation and subsequent annealing (i.e. common annealing or rapid annealing) at 500 °C on modifying the surface morphology and the electron field emission (EFE) properties of ultrananocrystalline diamond (UNCD) films were investigated. A Common annealing provides moderate enhancement in both electrical and EFE properties. Besides, the rapid annealing results in a low surface resistivity of 10.3 Ω/sq with a high mobility of 346.5 cm2 V−1 S−1for the UNCD film. The corresponding EFE behavior can be turned on at E0 = 5.3 V/μm, attaining a current density of 426.7 μA/cm2 at an applied field of 8.1 V/μm. The Mesh-like surface structures with the plate-like particulates, approximately 20–30 nm in size, distributed on the sample surface, which implies that the melting and recrystallization process have occurred due to the rapid annealing. Raman and X-ray photoelectron microscopy results demonstrated that the formation of Cu nanoparticles in UNCD films could catalytically provoke the formation of abundant nanographitic phase during rapid annealing process, forming the conduction channels for electron transport. Finally, the conducting and EFE properties of the UNCD films were remarkably improved.

Microplasma device architectures with various diamond nanostructures

Diamond nanostructures (DNSs) were fabricated from three different morphological diamonds, microcrystalline diamond (MCD), nanocrystalline diamond (NCD), and ultrananocrystalline diamond (UNCD) films, using a reactive ion etching method. The plasma illumination (PI) behavior of microplasma devices using the DNSs and the diamond films as cathode were investigated. The Paschen curve approach revealed that the secondary electron emission coefficient (γ value) of diamond materials is similar irrespective of the microstructure (MCD, NCD, and UNCD) and geometry of the materials (DNSs and diamond films). The diamond materials show markedly larger γ-coefficient than conventional metallic cathode materials such as Mo that resulted in markedly better PI behavior for the corresponding microplasma devices. Moreover, the PI behavior, i.e. the voltage dependence of plasma current density (Jpl−V), plasma density (ne−V), and the robustness of the devices, varied markedly with the microstructure and geometry of the cathode materials that was closely correlated to the electron field emission (EFE) properties of the cathode materials. The UNCD nanopillars, possessing good EFE properties, resulted in superior PI behavior, whereas the MCD diamond films with insufficient EFE properties led to inferior PI behavior. Consequently, enhancement of plasma characteristics is the collective effects of EFE behavior and secondary electron emission characteristics of diamond-based cathode materials.

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.

Morphology-controlled synthesis and electron field emission properties of ZnSe nanowalls

Novel ZnSe nanowalls on a Zn substrate with optimum morphology exhibit enhanced field emission performance.

Enhanced electron field emission of Cu implanted microcrystalline diamond films after annealing

Effects of Cu ions implantation on the structure and electron field emission (EFE) properties of microcrystalline diamond (MCD) films were investigated. The MCD films implanted with Cu ions at a fluence of 1.0 × 1017 ions/cm2 and subsequent annealing in N2 atmosphere at 600 °C for 2 h achieved good electrical conductivity with lower surface resistance of 0.1301 Ω/sq, high carrier concentration of 7.621 × 1018 cm−3 and hall mobility of 62 cm2 V−1s−1. Our results show that Cu nanoparticles can be formed in surface of MCD films after Cu ion implantation and annealing, which induced the formation of graphitic phases during annealing process. Consequently, the presence of Cu nanoparticles and graphitic phase formed conduction channels for efficient electron transport, ensuing better electron field emission (EFE) properties for Cu ion implanted/annealed MCD film with low turn-on field of 2.234 V/μm and high EFE current density of 28.560 μA/cm2 at an applied field of 4.172 V/μm.

Engineering the interface characteristics on the enhancement of field electron emission properties of vertically aligned hexagonal boron nitride nanowalls

Utilization of Au and nanocrystalline diamond (NCD) as interlayers noticeably modifies the microstructure and field electron emission (FEE) properties of hexagonal boron nitride nanowalls (hBNNWs) grown on Si substrates. The FEE properties of hBNNWs on Au could be turned on at a low turn‐on field of 14.3 V μm−1, attaining FEE current density of 2.58 mA cm−2 and life‐time stability of 105 min. Transmission electron microscopy reveals that the Au‐interlayer nucleates the hBN directly, preventing the formation of amorphous boron nitride (aBN) in the interface, resulting in enhanced FEE properties. But Au forms as droplets on the Si substrate forming again aBN at the interface. Conversely, hBNNWs on NCD shows superior in life‐time stability of 287 min although it possesses inferior FEE properties in terms of larger turn‐on field and lower FEE current density as compared to that of hBNNWs‐Au. The uniform and continuous NCD film on Si also circumvents the formation of aBN phases and allows hBN to grow directly on NCD. Incorporation of carbon in hBNNWs from the NCD‐interlayer improves the conductivity of hBNNWs, which assists in transporting the electrons efficiently from NCD to hBNNWs that results in better field emission of electrons with high life‐time stability.

Straight imaging and mechanism behind grain boundary electron emission in Pt-doped ultrananocrystalline diamond films

A detailed scanning tunneling microscopic (STM) investigation is carried out to directly image and understand the mechanism behind enhanced conductivity and electron field emission (EFE) properties for platinum (Pt) ion doped/post-annealed ultrananocrystalline diamond (UNCD) films. Straight imaging of conducting/non-conducting sites is mapped by dynamic scanning tunneling microscopy (D–STM). Energy dissipation mapping and the local current–voltage measurements illustrate that grain boundaries are the conducting/emitting sites. Further, this fact is supported by the high resolution current imaging tunneling spectroscopy (CITS). The formation of abundant conducting sp2 nanographitic phases along the diamond grain boundaries, confirmed from transmission electron microscopic examinations, is believed to be the genuine factor that helps for the easy transport of electrons and hence enhanced the conductivity/emission properties. The fabrication of these films with high conductivity and superior EFE properties is a direct and simple approach which opens up new prospects in flat panel displays and high brightness electron sources. Moreover, we expect the energy dissipation associated with assisted tunneling process of electrons from the tip of STM to sample surface, can be a very useful technique for imaging heterostructured semiconducting surfaces due to their electrical conductivity differences in nanometer scale, which can explain many physical and chemical properties.

Phase Transformation and Enhancing Electron Field Emission Properties in Microcrystalline Diamond Films Induced by Cu Ion Implantation and Rapid Annealing**Supported by the National Natural Science Foundation of China under Grant No 11405114, and the Natural Science Foundation of Shanxi Province under Grant No 2015021065.

Cu ion implantation and subsequent rapid annealing at 500°C in N2 result in low surface resistivity of 1.611 ohm/sq with high mobility of 290 cm2 V−1 S−1 for microcrystalline diamond (MCD) films. Its electrical field emission behavior can be turned on at E0 = 2.6 V/μm, attaining a current density of 19.5μA/cm2 at an applied field of 3.5 V/μm. Field emission scanning electron microscopy combined with Raman and x-ray photoelectron microscopy reveal that the formation of Cu nanoparticles in MCD films can catalytically convert the less conducting disorder/a-C phases into graphitic phases and can provoke the formation of nanographite in the films, forming conduction channels for electron transportation.

The synthesis of TiO2 nanoflowers and their application in electron field emission and self-powered ultraviolet photodetector

TiO2 nanoflowers composed of nano-needles had been synthesized by hydrothermal method and their field electron emission properties were studied for the first time, which exhibit a low turn-on field of 4.76V/μm, a high field enhancement factor of up to 5216. This performance was better than that of the as reported TiO2 nanostructure arrays. The efficient field emission behaviours were found to be not only attributed to their 3 dimensional structures of the nanoflowers but also related to their nano-needle morphology. Besides, self-powered ultraviolet photodetector based on TiO2 nanoflowers had been fabricated and it showed an obvious response trend in both UV and visible regions with good repeatability and stability, also the photoresponse mechanism at zero bias had been depicted through the energy band theory.

Dual Effort to Correlate the Electron Field Emission Performance of Carbon Nanotubes with Synthesis As Well As Annealing Temperature: Theoretical Support of the Experimental Finding.

Here a dual approach has been adopted to study the effect of both synthesis as well as annealing temperature on the electron field emission property of differently synthesized carbon nanotubes (CNTs) that include solid state chemical reaction as well as chemical vapour deposition (CVD). Experimental findings were supported by theoretical simulation. All the samples were characterized by X-ray diffraction (XRD), Fourier transformed infrared spectroscopy, Raman spectroscopy, field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). XRD as well as TEM study confirms the amorphous nature (aCNTs) of the samples for both the synthesis techniques which is attributed to lower synthesis temperature. Prominent morphological differences of these two types of aCNTs are clearly observed from both FESEM and TEM images. It is found that electron field emission characteristics of aCNTs synthesized by CVD shows better field emission properties as compared to aCNTs synthesized by solid state reaction. Finite element based simulation shows that temperature has prominent effect on morphology, screening effect or degree of graphitization that leads to improved field emission characteristics for the CVD synthesized aCNTs.