Field Emission Investigations Research Articles

Synthesis and field emission properties of carbon nanotube films modified with amorphous carbon nanoparticles by a simple electrodeposition method

Abstract Amorphous carbon nanoparticles (a-CNPs) on a multi-walled carbon nanotube (MWCNT) film, deposited on a silicon substrate, were synthesized using an electrodeposition combination from a methanol suspension of polydiallyldimethylammonium chloride-modified MWCNTs. A low-voltage electrophoretic deposition of the MWCNTs and a high-voltage electrochemical deposition of the a-CNPs were carried out to yield homogenously attached a-CNPs on the surfaces of the MWCNTs, and form a composite film with good adhesion to the substrate. This scalable technology can produce a large area of a-CNP/MWCNT film. And the field emission investigations show that the a-CNP/MWCNT film has turn-on electric field of 3.17 V μm−1 (at 10 μA cm−2) and threshold field of 4.62 V μm−1 (at 1 mA cm−2), which are lower than those of the MWCNT film. The a-CNP/MWCNT film can be deposited simply with large areas and may be a promising cathode material applied in field emission displays.

Controlled synthesis of aligned Bi2S3nanowires, sharp apex nanowires and nanobelts with its morphology dependent field emission investigations

Well-aligned ultra-long Bi2S3 nanowire arrays with three kinds of apex morphology – abruptly sharpened apex, thin belt and flat – have been systematically fabricated on tungsten (W) foil by a facile hydrothermal method. The structural and morphological studies reveal formation of distinct tip morphologies, possessing high aspect ratio, single crystalline nature and growth along the orthorhombic [001] axis. A plausible growth mechanism has been proposed on the basis of observed experimental results. The field emission properties of Bi2S3 nanowires and sharp apex Bi2S3 nanowires are investigated. From the field emission studies, the values of the turn-on field, required to draw emission current density of ∼0.1 μA cm−2, are observed to be ∼2.01 and 1.21 V μm−1 for nanowires and sharp apex nanowires, respectively. Furthermore, ultra-long Bi2S3 nanowires are also grown on the W microtip (brush-like) from which very high emission current density ∼11 mA cm−2 has been drawn. These results are helpful for the design, fabrication and optimization of integrated field emitters using 1D nanostructures as cold cathode material.

Development and Utilization of a Retarding Analyzer for Field Emission Investigation of LaB6/W Emitter

Development and Utilization of a Retarding Analyzer for Field Emission Investigation of LaB6/W Emitter

Investigation of temperature-dependent field emission from single crystal TiO2 nanorods

Temperature-dependent field emission (FE) of single crystal TiO2 nanorods has been investigated. It is found that the FE properties of TiO2 nanorods are critically affected by environmental temperature of emission tests. As the temperature increases from 290 to 500K, the turn-on field decreases from 2.16 to 1.76V/μm, whereas the current density increases. In addition, the physical mechanism of temperature dependence of FE is discussed in detail based on the variation of effective work function, which decreases from 4.3 to 3.64eV with the temperature rise from 290 to 500K. It is considered that the reduction of turn-on field and the enhancement of current density are mainly caused by the decrease of effective work function of the emitter.

Adsorption and dissociation of Cl2 molecule on ZnO nanocluster

Adsorption of chlorine molecule (Cl2) on the Zn12O12 nano-cage has been analyzed using density functional theory. It has been shown that the Cl2 molecule is strongly adsorbed on the cluster via two mechanisms including chemisorption and dissociation with Gibbs free energy changes in the range of −0.36 to −0.92eV at 298K and 1atm. These processes also significantly change the electronic properties of cluster by decreasing its HOMO/LUMO energy gap and increasing the work function. The Fermi level shifts towards lower energies upon the interactions between Cl2 and the cluster, resulting in raised potential barrier of the electron emission for the cluster and hence avoiding the field emission. The Zn12O12 cluster is transformed to a p-type semiconductor substance upon the Cl2 dissociation. We believe that the obtained results may be helpful in several fields of study such as sensors, catalysts, and field emission investigations.

Electron spectrometer in adjustable triode configuration for photo-induced field emission measurements

We have constructed a new ultrahigh vacuum apparatus with a triode configuration for the systematic investigation of photo-induced field emission (PFE) from metallic or semiconducting cathodes. These are exposed to electric fields up to 400 MV∕m and laser irradiation by means of hole or mesh gates. Cathodes and gates are in situ exchangeable and adjustable with high precision to ensure a homogeneous extraction of electrons which are partially transmitted to the fixed electron spectrometer. Its hemispherical sector analyzer provides an energy resolution limit of 8 meV. The commissioning of the measurement system has been performed with a tungsten needle. Its temperature showed up in the high-energy tail of the electron spectrum, while its work function was derived from the spectral low-energy part combined with the integral current-voltage curve. First PFE measurements on B-doped Si-tip arrays yielded a small field emission current increase under green laser illumination. A shift and splitting of the energy spectra was observed which revealed different emission regimes as well as the photosensitivity of the cathode due to carrier excitation into the conduction band. For the full exploitation of the PFE system, a tunable laser over a wide eV-range is required.

Vertical arrays of SiNWs–ZnO nanostructures as high performance electron field emitters

Multicomponent hybrid materials of nanostructured building blocks are essential for the development of complex devices and advanced applications due to their role as either functional or interconnecting elements. This study introduces a simple and cost effective strategy for the synthesis of vertical arrays of silicon nanowires and ZnO nanostructures (nanorod and multipod structures). Formation of vertical nanostructured arrays is confirmed by SEM and HRTEM imaging as well as XRD and Raman measurements. We have investigated field emission properties of the as-synthesized vertical nanostructured arrays. Our results show that these SiNWs–ZnO nanostructures are highly efficient and stable field emitters.

Synthesis of CeB6 thin films by physical vapor deposition and their field emission investigations

Abstract High quality CeB 6 thin films have been obtained through direct evaporation of raw micron-sized CeB 6 powders at a pressure of 70 Pa. The X-ray diffraction (XRD), Raman spectrum, scanning electron microscope (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED) and the field-emission equipment were used to characterize the morphology, structure, composition and FE properties of the samples. The XRD and Raman spectrum analysis results show the as-prepared product is cubic phase CeB 6 . The TEM, SAED and HRTEM analysis reveal that the samples are mixtures of thin films (polycrystalline) and small crystals (single crystallines aligned preferentially in the [1 1 0] direction). Compared to oxide nanostructures, field-emission measurements show that the CeB 6 films have better FE performance with turn-on field and threshold field of 12.93 V/μm and 14.86 V/μm, respectively.

ZnO Nanostructures and Field Emission Properties on Cu Substrate Achieved by Electrodeposition Method

In the present work, ZnO nanostructures with tunable size were successfully synthesized on non-seeded Cu substrates by a simple electrodeposition method. The effects of growth conditions on the morphology of the products were studied in detail by scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The as-prepared products exhibited flake-like morphology when the concentration of ZnCl2 was higher enough, while the products showed flower-like morphology when the concentration was lower enough. Field emission investigation indicated that the nanoflowers exhibited good emission properties. The ZnO nanoflowers show potential application as field emitters.

Determination of satellite valley position in GaN emitter from photoexcited field emission investigations

Argon plasma etched GaN field-emitter rods with nanometer-scale diameter were fabricated on GaN grown on an n+-GaN substrate. Their electron field emission properties were investigated both without and under illumination by using light sources with various wavelengths. The Fowler–Nordheim current-voltage characteristics of the cathodes show a change in slope for illuminated cathodes. The electron affinity difference ΔE between the different valleys in the conduction band has been ascertained and is in the range from 1.18 up to 1.21 eV.

Fabrication of In-doped SnO2 nanowire arrays and its field emission investigations

The field emission of In-doped SnO2 wire array has been performed in parallel plate diode configuration. A maximum current density of 60 µA/cm2 is drawn from the emitter at an applied field of 4 V/µm. The nonlinearity in the Fowler–Nordheim plot, characteristics of semiconductor emitter has been observed and explained on the basis of electron emission from both the conduction and the valence bands. The current stability recorded at a preset value of 1 µA is observed to be good. The high emission current density, good current stability and mechanically robust nature of the wires offer unprecedented advantages as promising cold cathodes for many potential applications based on field emission.

Field Emission Characteristics of an Oxidized Porous Polysilicon Field Emitter Using Al2O3 Layer as a Passivation

The field emission characteristics of an oxidized porous polysilicon were investigated with different Al2O3/Ti/Pt thickness. The Al2O3/Ti/Pt emitter showed stable electron emission characteristic compared with the conventional Ti/Pt electrode. The Al2O3 layer efficiently blocked the diffusion of emitter metal, which resulted in more reliable emission characteristics. Al2O3/Ti/Pt electrode thickness at 2 nm/2 nm/7 nm showed the highest emission efficiency of 0.37% at Vps = 17 V. The investigated field emission life time of samples also demonstrated their stability over 40 minutes.

Synthesis of LaB6 micro/nano structures using picosecond (Nd:YAG) laser and its field emission investigations

Micro/nano structures have been obtained by laser surface treatment on sintered LaB6 pellets employing a picosecond pulsed Nd:YAG laser at a pressure of ∼1×10−3 mbar. The X-ray diffraction pattern of the laser treated pellet shows a set of well defined diffraction peaks, indexed to the cubic phase of LaB6 only. The scanning electron microscope studies reveal formation of micro and nano structures upon laser treatment and the resultant surface morphology is found to be strongly influenced by the laser fluence. Field electron emission studies made on the LaB6 pellet, treated with optimized laser fluence, have been performed in a planar diode configuration under ultra high vacuum conditions. The threshold field required to draw an emission current density of ∼10 μA/cm2 has been found to be ∼2.3 V/μm and a current density of ∼530 μA/cm2 has been drawn at an applied field of 5.2 V/μm. The Fowler-Nordheim plot is found to be linear in accordance with the quantum mechanical tunneling phenomenon, confirming the metallic nature of the emitter. The emission current at the pre-set value ∼10 μA shows very good stability over a period of more than 3 hours. The present results emphasize the effectiveness of a picosecond laser treatment towards fabrication of a nano metric LaB6 emitter for high current density applications.

Field emission studies of Te nanorods grown on Si (111) substrate

Tellurium nanorods were grown on silicon (111) substrates by thermal evaporation. The synthesized Te nanorods were characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM), prior to the field emission investigations. The TEM image revealed that the nanorods are needle-like having diameter less than 20 nm and length in the range of 200–400 nm. The selected area electron diffraction (SAED) pattern and high resolution TEM micrographs clearly reveal the crystalline nature of the Te nanorods. The field emission studies were carried out in a planar diode (close proximity) configuration at background pressure of ∼1 × 10 −9 mbar. An emission current density of ∼8.5 μA/cm 2 has been drawn at an applied field of ∼3.2 V/μm. The Folwer–Nodhiem plot, showed a non-linear behaviour. The high value of field enhancement factor ( β ∼ 1 × 10 4), estimated from the slope of the F–N plot, suggests that the emission is indeed from the nanometric tips of the Te nanorods. The emission current stability studied at the preset value ∼3.5 μA over duration of more than 3 h is found to be very good, suggesting the use of Te nanorods as promising electron source for field emission based micro/nano-electronic devices.

Self-catalytic Synthesis, Structures, and Properties of High-Quality Tetrapod-Shaped ZnO Nanostructures

High-quality tetrapod-shaped ZnO (T-ZnO) nanostructures were synthesized through the direct reaction of Zn and zinc acetate (ZAc) via a thermal evaporation method in Ar at 650 °C without any catalyst. Controlling the experimental parameters showed that ZAc precusor plays an important self-catalytic role in the vapor transport process. The individual legs of as-synthesized ZnO nanotetrapods were characterized using field emission scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray diffraction. The photoluminescence (PL) measurements showed the different PL features of T-ZnO nanostructures. Two typical emission peaks at ∼387 nm and ∼495 nm were observed. Especially, the emission peak at 455−495 nm includes four subordinate peaks. Field emission investigation revealed that the T-ZnO nanostructures with different morphologies possess good field emission property with the largest turn-on field of 1.85 V/μm, and the field emission density reaches 1.92 × 10−4 A/cm2 when the field is 5.5 V/μm. The growth mechanism was discussed in detail. A self-catalysis vapor−liquid−solid growth mechanism was proposed for the formation of the ZnO nanotetrapods.

Carbon nanofibres from diamond film using Ar-ion bombardment and their field emission property

Carbon nanofibres (CNFs) have been fabricated by oblique ion sputtering diamond films at room temperature. Scanning electron microscopy shows that the ordered carbon protrusions with a size of ∼1 µm are formed after 1 h ion irradiation and CNFs on the protrusions with a density of 1−2×108/cm2, diameter of ∼40 nm and length of 1−4 µm are achieved after 2 h ion sputtering. Raman spectra indicates that the amorphous or defect content increases with the duration of irradiation. The investigation of field emission shows that the turn-on field is 1.8 V/µm and the threshold field is 4.6 V/µm.

Field emission investigation of single Fe-doped SnO 2 wire

Tin oxide submicronwires doped with Fe element were prepared by the thermal evaporation method. Morphological and structural characterizations revealed wires with sub micron size and crystalline in nature. The field electron emission from the single Fe:SnO 2 wire was carried out in conventional field emission microscope. The Fowler–Nordheim plot obtained from I– V characteristics of the wire showed a linear behavior typical that of metal. The field enhancement factor estimated from the slope of the F–N plot is 7455 cm −1, indicating that the field emission is from nanometric features of the emitter. A current density of 10 A/cm 2 has been obtained at an applied field of 4.845 × 10 3 V/μm. The field emission current–time record at a current level of 1 μA for more than 3 h duration is promising for various field emissions based applications.

Electron field emission from amorphous carbon with N-doped nanostructures pyrolyzed from polyaniline

Carbon-based materials have been of great interest due to their potential application in cold cathodes for field emission displays and other vacuum microelectronic devices. Pyrolyzed polyaniline (PPANI) with N-doped nanostructures was prepared by pyrolysis of polyaniline at high temperature of 900 °C. The morphologies and microstructures were investigated by scanning electron microscopy, transmission electron microscopy, AFM, Raman spectroscopy, and X-ray photoelectron spectroscopy. It was found that there were sp 2C–N and sp 3C–N bonds between the nitrogen and the carbon atoms in the nanostructures of the PPANI obtained. The electron field emission investigations showed that the turn-on field and effective work function ϕ e of PPANI were 1.7 V/μm and 0.010 eV which were lower than N-doped amorphous carbon films obtained by other methods.

Some aspects of pulsed laser deposited nanocrystallineLaB6 film: atomic force microscopy, constant force current imaging and field emissioninvestigations

Nanocrystalline lanthanum hexaboride(LaB6) films have been deposited on molybdenum foil by the pulsed laser deposition(PLD) technique. The as-deposited films were characterized by x-raydiffraction (XRD), scanning electron microscopy (SEM) and atomic forcemicroscopy (AFM). The XRD pattern shows the cubic crystallinity of theLaB6 film. The AFM studies reveal that the conical shapedLaB6 nanostructures have height 60 nm, base 800 nm, and a typical radius of curvature∼20 nm. A comparison of force and in situ current imaging AFM studies revealsthat current contrast does not originate from the surface topography of theLaB6 film. Field emission studies have been performed in the planar diode configuration. A current densityof 4.4 × 10−2 A cm−2 is drawn from the actual emitting area. The Fowler–Nordheim plot is found to be linear,in accordance with the quantum mechanical tunneling phenomenon. The fieldenhancement factor is estimated to be 3585, indicating that the field emission is fromLaB6 nanocrystallites present on the emitter surface, as confirmed by the AFM. The emissioncurrent–time plots show current stability to the extent of 5% fluctuation about the averagecurrent over a period of 3 h.

Electron field emission from semiconducting nanowires

In this paper we report on investigations of field emission (FE) properties of semiconducting (SiC, ZnO) one-dimensional (1D) nanostructures – nanowire/nanorod arrays, and fabrication of low-voltage field emission display (FED) devices based on these 1D nanomaterials. SiC nanowires were grown on Ni-coated Si substrates using a thermal metal-organic chemical vapor deposition (MOCVD) technique, and ZnO nanostructures were grown on gold-coated Si substrates by a thermal CVD method. Electron field emission properties of SiC and ZnO nanostructures were examined in plane geometry using a flat phosphor screen. The interrelation between the FE characteristics (emission thresholds, current density, surface uniformity, etc.) and microstructure and surface morphology of the produced 1D nanostructures was established. Diode-type FED devices (flat vacuum lamps) with SiC-nanowire-based cathodes were developed and fabricated. The FEDs are characterized by low threshold and operating electric fields – lower 2 V/μm and 5 V/μm, respectively, high current density and brightness, and stable performance of the nanowire-based cathodes.