Field Emission Investigations Research Articles

Morphology-dependent field emission investigations from the 2-dimensional Bi2Se3-RGO nanocomposites

The two-dimensional bismuth selenide (Bi2Se3)-reduced graphene oxide (RGO) nanocomposite have been synthesized by simple hydrothermal route for carrying out field emission (FE) studies. The Bi2Se3-RGO nanocomposite field emitters exhibit enhancement in the current densityas compared to pristine Bi2Se3emitter. The turn-on field for Bi2Se3-RGO nanocomposite field emitter decreases by ∼37% of its value for pristine Bi2Se3 emitters. The maximum current density observed from the Bi2Se3-RGO nanocomposite field emitter is ∼1000 µA/cm2 at an applied field of 6.0 V/μm. The influence of Se weight percentage in the Bi2Se3-RGO nanocomposite has been studied to understand the field emission behavior via morphological changes of the emitter surface. The Bi2Se3-RGO nanocomposite structure is thus seen as a prospective candidate for the development of efficient nanoscale field emission devices.

Photochemical synthesized NiO nanoparticles based dye-sensitized solar cells: a comparative study on the counter lectrodes and dye-sensitized concentrations

In this project, we report on the prepare of nickel oxide nanoparticles (NiO NPs) via a photolysis method using UV lamb followed by calcination at 400 C for 3 h. the synthesized Nano-powder were investigated field emission scanning electron microscope (FE-SEM), photoluminescence spectroscopy (PL) and X-ray diffraction (XRD). The SEM image confirmed the crystal structure of the synthesized NiO nanoparticles with an average particle size of 23 nm, and the XRD analysis revealed the absence of impurity peaks. The optical properties were analyzed using photoluminescence spectroscopy (PL), and the bandgap was determined to be 3.4 eV. The semiconductor property, which can be exploited for solar cell applications, is responsible for the broad bandgap. To make dyesensitized solar cells (DSSC), we used photo-chemically synthesized NiO NPs as a photoanode. Two counter electrode were used in this study: Graphene oxide Nano-Sheets and Graphene oxide\silver nanocomposite. cibacron brilliant red B is one of the dyes that are used in the textile factory of Wasit Governorate, and the rest of it is often discarded as waste water Which we used in our study as a photosensitizer. The open-circuit voltage (Voc), short t current density (Jsc), fill factor (FF), and efficiency (h) were determined from the J-V curves, where efficiency was between 0.231 to 1.47 %, at 100 mW/cm2. Finally, it can be confirmed that the presence of nickel oxide nanoparticles with a cibacron brilliant red B dye can improve the performance of dye-sensitized solar cells.

Multifunctional characteristics of polypyrrole-zinc oxide (PPy-ZnO) nanocomposite: Field emission investigations and gas sensing application

Multifunctional behavior of Polypyrrole-Zinc oxide (PPy-ZnO) nanocomposite, synthesized by chemical and electrochemical routes, towards field emission (FE) and ammonia (NH3) sensing has been investigated. The preparation of the nanocomposite embraces the specific motivation of subsuming 1-dimensional (1D) form of the ZnO nanorods with PPy. The morphological, structural, chemical and optical analysis of the PPy-ZnO nanocomposite has been done employing various characterization techniques such as Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Analysis (EDAX), Fourier Transform Infrared (FTIR), Raman, UV–vis and Photoluminescence (PL) spectroscopy. The field emission (FE) investigations of PPy-ZnO nanocomposite exhibited lower values of turn-on and threshold fields (3.1 and 4.5 V/ μm, respectively) along with competency to deliver current density of ∼1.5 mA/cm2 at relatively lower applied field of ∼6.5 V/μm. The superior FE behavior of PPy-ZnO nanocomposite emitter is attributed to synergic effect of unique morphology and electrical property (enhancement in charge carrier density). Furthermore, NH3 sensing characteristics of pristine ZnO nanorods and PPy-ZnO nanocomposite thin films, were studied under static condition. Interestingly, the PPy-ZnO nanocomposite showed promising NH3 sensing characteristics, as compared to the pristine ZnO nanorods and other nanocomposites. The present attempt towards synthesis of organic-inorganic nanocomposite exhibiting promising multifunctional behavior can be extended to explore alike nanocomposites.

Highly stable field emission from micron sized homogeneous β-Ga2O3 sheets grown using vapor phase transport route

Microstructures of gallium oxide with diverse morphologies are synthesized using vapor phase transport route. Structural and micro structural investigations using XRD, SEM and micro Raman technique confirm formation of single phase β-Ga2O3. Morphology and structural quality of the crystal growth is observed to improve with respect to growth temperature. Based on observations suitable growth mechanism is proposed to explain diverse morphologies governed by the growth temperatures. From Field Emission (FE) investigations, the structural defects associated with the crystal growth are claimed to affect the FE properties. Adequate field emission followed by steady current recorded over a long period of time for micron sized sheets of β-Ga2O3 (specimen synthesized at 1000 °C) looks favorable for various FE applications. The results are very promising looking at the possibilities to fabricate uniform, homogeneous layers of the active material, retaining excellent FE properties observed during various nano-forms of β-Ga2O3 otherwise.

ZnO/CuSCN Nano-Heterostructure as a Highly Efficient Field Emitter: a Combined Experimental and Theoretical Investigation.

We report the synthesis of two-dimensional porous ZnO nanosheets, CuSCN nanocoins, and ZnO/CuSCN nano-heterostructure thin films grown on fluorine-doped tin oxide substrates via two simple and low-cost solution chemical routes, i.e., chemical bath deposition and successive ionic layer adsorption and reaction methods. Detail characterizations regarding the structural, optoelectronic, and morphological properties have been carried out, which reveal high-quality and crystalline synthesized materials. Field emission (FE) investigations performed at room temperature with a base pressure of 1 × 10–8 mbar demonstrate superior FE performance of the ZnO/CuSCN nano-heterostructure compared to the isolated porous ZnO nanosheets and CuSCN nanocoins. For instance, the turn-on field required to draw a current density of 10 μA/cm2 is found to be 2.2, 1.1, and 0.7 V/μm for the ZnO, CuSCN, and ZnO/CuSCN nano-heterostructure, respectively. The observed significant improvement in the FE characteristics (ultralow turn-on field of 0.7 V/μm for an emission current density of 10 μA/cm2 and the achieved high current density of 2.2 mA/cm2 at a relatively low applied electric field of 1.8 V/μm) for the ZnO/CuSCN nano-heterostructure is superior to the isolated porous ZnO nanosheets, CuSCN nanocoins, and other reported semiconducting nano-heterostructures. Complementary first-principles density functional theory calculations predict a lower work function for the ZnO/CuSCN nano-heterostructure (4.58 eV), compared to the isolated ZnO (5.24 eV) and CuSCN (4.91 eV), validating the superior FE characteristics of the ZnO/CuSCN nano-heterostructure. The ZnO/CuSCN nanocomposite could provide a promising class of FE cathodes, flat panel displays, microwave tubes, and electron sources.

Uncertainty of tunnelling microscopy measurements of the field emission from multilayer nanostructures

The paper presents the results of scanning tunnelling microscopy investigation of electron field emission from multilayer nanostructures based on silica opal film Cr-SiO2-Au-C. Opal film was deposited in colloidal solvent, while other films – by vacuum deposition methods. We discuss the problem of uncertainty of measurements of the field enhancement factor and carbon nano-edge sizes using the current versus applied voltage characteristics of the emission. Field enhancement factor is defined as the ratio of the electric field at the nano-edge to the field applied to the gap. We found that at well-controlled experimental conditions the combined uncertainty of field enhancement factor measurements is ∼15% based on a 95% confidence interval and the combined uncertainty of nano-edge sizes measurements is ∼18% based on a 95% confidence interval.

Reduced turn-on field through solution processed MoS2 nanoflakes anchored MWCNTs

Abstract An investigation of field emission on solution processed MWCNTs, MoS2 and MoS2 anchored MWCNTs thin films on low cost stainless steel substrates have been performed. Decorative morphology of MoS2 nanoflakes over MWCNTs interconnected high surface area nanonetwork supports the active path for the application of field emission. Drastic diminishing in turn-on field value has been obtained for MWCNTs/MoS2 nanocomposite compared to bare MWCNTs and MoS2. Hence, present investigation opens path for the development of low-temperature solution processed MWCNTs/MoS2 thin film in the field of nanoelectronics and the used process can be integrated for large scale.

Field emission investigations of solvothermal synthesized and soaked rutile-TiO2 nanostructures

In present work we report synthesis of rutile-TiO2 by using a simple solvothermal method. The formation of pure single phase rutile-TiO2 has been confirmed by X-ray diffraction (XRD) and Raman spectroscopy analysis. The XRD analysis revealed that as-prepared and soaked-TiO2 has pure rutile phase with tetragonal crystal structure. The field emission scanning electron microscopy and high resolution transmission electron microscopy analysis shows that as-prepared TiO2 has nano-rods like morphology whereas soaked-TiO2 has nano-flowers like morphology with atomically sharp edges. The UV–Visible spectroscopy analysis showed that as-prepared and soaked rutile-TiO2 nano-structures have absorption edge in the visible range and having band gap of ~ 3.58 eV. The field emission (FE) properties of as-prepared and soaked rutile-TiO2 nano-structures were investigated and it was observed that as-prepared and soaked rutile-TiO2 display excellent FE properties with low turn-on field (~ 4.8 V/µm for 10 µA/cm2), maximum current density [~ 444 µA/cm2 (as-prepared) and 508 µA/cm2 (soaked)] and superior current stability (~ 3 h for ~ 1 µA). The obtained results show that the rutile-TiO2 nanostructures can be useful for practical applications in vacuum nano/microelectronic devices.

Investigation of the temperature dependent field emission from individual ZnO nanowires for evidence of field-induced hot electrons emission

ZnO nanowires as field emitters have important applications in flat panel display and x-ray source. Understanding the intrinsic field emission mechanism is crucial for further improving the performance of ZnO nanowire field emitters. In this article, the temperature dependent field emission from individual ZnO nanowires was investigated by an in situ measurement in ultra-high vacuum. The divergent temperature-dependent Fowler–Nordheim plots is found in the low field region. A field-induced hot electrons emission model, that takes into account penetration length, is proposed to explain the results. The carrier density and temperature dependence of the field-induced hot electrons emission current are derived theoretically. The obtained results are consistent with the experimental results, which could be attributed to the variation of effective electron temperature. All of these are important for a better understanding on the field emission process of semiconductor nanostructures.

Field emission investigations of single crystal LaB6 FEA fabricated by femtosecond laser direct writing

The femtosecond laser direct writing method has been used to fabricate the single crystal lanthanum hexaboride (LaB6) field-emission tip arrays (FEAs). The morphologies, structure phase, and field emission of the single crystal LaB6 FEAs are systematically studied. The nanostructures on the surface of tips with the LaB6 phase were formed, resulting in favor of improving field emission, particularly for samples with the nanohill shaped bulges having the size of about 100 nm. The produced single crystal LaB6 FEAs have a uniform structure and a controllable curvature radius of about 0.5–3.0 μm. The FEAs with a curvature radius of about 0.5 μm as field emitters have the best field emission performance, which the field emission turns on and the threshold electric fields are as low as 2.2 and 3.8 V/μm with an emission current of 1.0 A/cm2 at 8.0 V/μm, and the emission current exhibits high stability. These indicate that the processed LaB6 FEAs have a good prospect applied in vacuum microelectronic devices and the simple femtosecond laser direct writing method could lead to an approach for the development of electron sources.

Solvothermal synthesis of tin sulfide (SnS) nanorods and investigation of its field emission properties

In the present study, we report synthesis of tin sulfide (SnS) nano-rods using a simple solvothermal method at different reaction time period. The formation of single phase SnS has been confirmed by X-ray diffraction (XRD) and Raman analysis. The XRD analysis revealed that the predominant phase in all prepared samples is orthorhombic SnS. The formation of nano-rods of SnS was confirmed by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM) analysis. To investigate the optical properties of SnS nano-rods UV–visible spectroscopy analysis was carried out. We observed that the band gap of SnS nano-rods decreases with increase in reaction time and can be attributed to the quantum confinement effect. Finally, field emission investigations on the SnS nano-rods at the base pressure of 1 × 10− 8 mbar were carried out and found to be superior to the other chalcogenide nanostructures. As-synthesized SnS nano-rods emitter exhibits excellent field emission properties such as low turn-on field (~ 2.5 V/µm for 10 µA/ cm2), high emission current density (~ 647 µA/cm2 at 3.9 V/µm) and superior current stability (~ 5 h for ~ 1 µA). Thus, the facile one-step synthesis approach and robust nature of SnS nano-rods emitter can provide prospects for the future development of large-area emitter applications such as flat-panel-display devices.

Synthesis, characterization of graphene oxide wrapped silicon carbide for excellent mechanical and damping performance for aerospace application

Graphene oxide (GO) and silicon carbide (SiC) are the most promising raw materials with their unique mechanical and structural excellent performance qualities. Herein, we synthesized graphene oxide sheets via modified Hummers method. The surface morphology of silicon carbide particles was tailored with wrapping of synthesized graphene oxide sheets through a facile route. The assembled film structure of GO on SiC particles are investigated Field emission scanning electron microscopy (FE-SEM), X-Ray photo-electron spectroscopy (XPS), transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis. In addition, the formation of well-ordered micro structure was investigated through elemental mapping and X-ray energy dispersion spectroscopy (EDX) analysis. Furthermore, using GO wrapped SiC as reinforcement, we fabricate aluminium metal matrix composite via friction stir processing. Additionally, grain refinement of fabricated composites analyzed by electron backscatter diffraction (EBSD) analysis. The damping behaviour of the fabricated composite (SiC/GO/Al) were analyzed in wide range of temperature starting from −100 °C to 400 °C. In this research, storage modulus (SM) and ultimate tensile strength (UTS) measurements revealed that SM and UTS of SiC/GO/Al composite are improved approximately by a factor of ∼ 2.1 and ∼ 3.4, respectively as compare to pure aluminium and graphene oxide nanosheets can serve as excellent material for assembly of SiC particles.

PbS Nanostar‐Like Structures as Field Emitters

AbstractThe crystalline PbS nanostars were synthesized by thermal decomposition of thioacetamide (TAA) in aqueous solutions of lead acetate and acetic acid at 80 °C. The structure and morphology of the PbS nanostars have been characterized using X‐Ray Diffraction (XRD), Raman Spectroscopy, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The optical properties of the PbS nanostars have been studied using UV‐Visible absorption Spectroscopy (UV‐Vis). The field emission investigations have been carried out on the as synthesized PbS nanostars at the base pressure of ∼1×10−8 mbar. The turn on field required to draw an emission current density of 1 μA/cm2 is found to be 1.8 V/μm. The emission current‐time plots show good emission current stability of the PbS nanostar emitter over a period of 4 hrs. The results in terms of low turn‐on field and long term emission current stability of the PbS nanostars emitter reveals that it can be used in field emission based vacuum microelectronics / nanoelectronic devices.

One‐pot synthesis, characterization, and field emission investigations of composites of polypyrrole with graphene oxide, reduced graphene oxide, and graphene nanoribbons

ABSTRACTPyrrole monomer was polymerized by a chemical oxidative route in the presence of graphene oxide (GO), reduced GO (rGO), and graphene nanoribbons (GNR) separately to prepare composites of polypyrrole (PPy) as PPy–GO, PPy–rGO, and PPy–GNR, respectively. The morphological, chemical, and structural characterization of the as‐synthesized products was carried out using scanning electron microscopy, Raman spectroscopy, and Fourier transform infrared spectroscopy. Field emission studies of the PPy–GO, PPy–rGO, and PPy–GNR emitters were performed at the base pressure of 1 × 10−8 mbar in a planar “diode” configuration. The turn‐on field values, corresponding to an emission current density of 1 µA/cm2, are observed to be 1.5, 2.2, and 0.9 V/µm for the PPy–GO, PPy–rGO, and PPy–GNR emitters, respectively. The maximum emission current density of 2.5 mA/cm2 is drawn from PPy–GO at an applied electric field of 3.2 V/µm, 1.2 mA/cm2 at 3.6 V/µm from the PPy–rGO, and 8 mA/cm2 at 2.2 V/µm from the PPy–GNR emitters. All of the composites exhibit good emission stability over more than 2 h. The results indicate the potential for a facile route for synthesizing composites of conducting polymers and graphene‐based materials, with enhanced functionality. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45170.

The effects of gas flow rate and annealing on the morphological properties of zinc oxide nanostructures thin film using chemical vapour deposition process

Zinc Oxide nanostructures thin films have been deposited on glass substrates by using chemical vapour deposition technique at 1000°C assisted by gas blocker. Glass substrates was sputtered by ~5nm of gold to form a catalyst layer on top of glass. Different gas flow rates of 0.05, 0.10, 0.20, 0.40 L/min were used in the deposition. After the deposition, the layer was annealed at temperatures of 500°C for 1 hours under atmospheric pressure. The surface morphologies of ZnO thin film were investigated field emission scanning electron microscope (FESEM). X-ray diffraction (XRD) results confirm the presence of ZnO layer with high peak of (002) crystal orientation and shows improvement after annealing. The mechanism of ZnO nanostructures formation will be discussed in this paper

Enhanced field emission performance of NiMoO4 nanosheets by tuning the phase

In this paper we report, large scale synthesis of α and β-NiMoO4 by a facile hydrothermal method and we observed that urea plays important role on the growth of β-NiMoO4 nanosheets. We have also carried out field emission (FE) investigations of α and β-NiMoO4 at a base pressure of ∼1×10−8mbar. The obtained turn-on field at emission current density of 1μA/cm2 for β-NiMoO4 nanosheets and α −NiMoO4 is 1.3V/μm and 2.2V/μm respectively were observed. The maximum field emission current density of 1.006mA/cm2at an applied electric field of 2.7V/μm was achieved for β-NiMoO4 nanosheets. Furthermore, we found that the β-NiMoO4 nanosheets possess good field emission performance compared to α-NiMoO4. The results indicate that NiMoO4can be used as a promising material in FE applications with possibility of tuning field emission performance by controlling the phase.

Morphological, structural and field emission characterization of hydrothermally synthesized MoS2-RGO nanocomposite

A few layered MoS2-RGO nanocomposite has been synthesized employing a facile hydrothermal synthesis route. The morphological and structural analysis performed using SEM, TEM, HRTEM and Raman spectroscopy clearly reveal formation of vertically aligned a few layer thick MoS2 sheets on RGO surface. Attempts have been made to reveal the influence of graphite oxide (GO) percentage on morphology of the nanocomposite. Furthermore, field emission (FE) investigations of as-synthesied MoS2-RGO nanocomposite are observed to be superior to the pristine MoS2 emitter. The values of turn-on field, defined at emission current density of 10 μA cm−2, are found to be 2.6 and 4.7 V μm−1 for the MoS2-RGO (5%) nanocomposite and pristine MoS2 emitters, respectively. The value of threshold field, defined at emission current density of 100 μA cm−2, is found to be 3.1 V μm−1 for MoS2-RGO nanocomposite. The emission current stability at the pre-set value of 1 μA over 3 h duration is found to be fairly good, characterized by current fluctuation within ±18% of the average value. The enhanced FE behavior for MoS2-RGO nanocomposite is attributed to a high enhancement factor (β) of 4128 and modulation of the electronic properties. The facile approach adopted herein can be extended to enhance various functionalities of other nanocomposites.

Facile single pot synthesis of MnO2 nanorods-reduced graphene oxide (rGO) nanocomposite: Structural, chemical and field emission investigations

MnO2 nanorods-reduced graphene oxide (MnO2-rGO) nanocomposite has been synthesized by facile single pot hydrothermal method. The decoration of crystalline α-MnO2 with tetragonal phase on rGO nanosheets has been confirmed by X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The field emission (FE) properties of MnO2-rGO emitter have been investigated and it exhibited enhanced FE properties demonstrated by lower values of turn-on and threshold field in contrast to the pristine MnO2 and rGO emitter. The superior FE characteristics of the MnO2-rGO emitter are attributed to the modulation of morphological properties offering high aspect ratio as well as electronic properties enhancing the density of states. The observed FE characteristics of MnO2-rGO emitter indicates the potential of using in vacuum microelectronics/nanoelectronics.

Numerical and experimental investigation of a beveled trailing-edge flow field and noise emission

Efficient tools and methodology for the prediction of trailing-edge noise experience substantial interest within the wind turbine industry. In recent years, the Lattice Boltzmann Method has received increased attention for providing such an efficient alternative for the numerical solution of complex flow problems. Based on the fully explicit, transient, compressible solution of the Lattice Boltzmann Equation in combination with a Ffowcs-Williams and Hawking aeroacoustic analogy, an estimation of the acoustic radiation in the far field is obtained. To validate this methodology for the prediction of trailing-edge noise, the flow around a flat plate with an asymmetric 25° beveled trailing edge and obtuse corner in a low Mach number flow is analyzed. Flow field dynamics are compared to data obtained experimentally from Particle Image Velocimetry and Hot Wire Anemometry, and compare favorably in terms of mean velocity field and turbulent fluctuations. Moreover, the characteristics of the unsteady surface pressure, which are closely related to the acoustic emission, show good agreement between simulation and experiment. Finally, the prediction of the radiated sound is compared to the results obtained from acoustic phased array measurements in combination with a beamforming methodology. Vortex shedding results in a strong narrowband component centered at a constant Strouhal number in the acoustic spectrum. At higher frequency, a good agreement between simulation and experiment for the broadband noise component is obtained and a typical cardioid-like directivity is recovered.

Surface-conducted field emission electron sources with ZnO emitters of different morphologies

Surface-conducted field emission electron sources using ZnO nanostructures as surface-conducted emitters have been successfully fabricated, where the linear cathode and gate electrodes were interdigitated and paralleled on the same plane and ZnO emitters with different morphologies were deposited in the gap between the cathode and gate electrode. Field emission investigations indicate that the turn-on voltage of the fabricated SCFE electron sources with ZnO nanorods, ZnO nanotubes, and ZnO nanocones modifies from 260 V to 220 V at the anode voltage of 2 kV. The emission efficiency of SCFE electron source with ZnO nanocones is as large as 43.6%, which is much higher than that of SCFE electron sources with ZnO nanorods and nanotubes at the gate voltage of ∼300 V. The whole surface emission of the fabricated electron source with ZnO nanocones on the fluorescent screen is more homogeneous than that of the electron sources with ZnO nanorods and nanotubes.