Showing papers on "Field electron emission published in 2010"

Single-crystalline CdS nanobelts for excellent field-emitters and ultrahigh quantum-efficiency photodetectors.

Abstract: The single crystalline CdS nanobelts were synthesized by an improved vapor-liquid-solid (VLS) process Field emission measurements show that the nanostructures have a low turn-on field of 37 V&m-1 at a current density of 10 μA cm-1, a low threshold field of 93 V μm cm-1 and a high enhancement factor of 1298 When assembled into nanoscale visible light photodetectors, the CdS nanobelts showed good sensitivity and wavelength selectivity The results imply that the present CdS nanobelts are excellent candidates for applications in high-performance field emitters and photodetectors

Hybridized nanowires and cubes: A novel architecture of a heterojunctioned TiO2/SrTiO3 thin film for efficient water splitting

Abstract: A unique morphology of SrTiO 3 nanocubes precipitated on TiO 2 nanowires is successfully synthesized in the form of a thin-film heterojunctioned TiO 2 / SrTiO 3 photocatalyst using facile hydrothermal techniques. The formation mechanisms of the synthesized photocatalysts are meticulously studied and described. Growth of SrTiO 3 single crystal nanocubes (≈50 nm in width) on anatase polycrystalline nanowires follows an in situ dissolution-precipitation pathway. This is consonant with the classic LaMer model. By analyzing the results of field emission scanning electron microscopy (FESEM), field emission transmission electron microscopy (FETEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy, X-ray photoelectron spectroscopy (XPS), and UV-vis spectrophotometry, a comprehensive structural and morphological characterization of the photocatalysts is established. FESEM images reveal that the anatase film comprises mainly of nanowires bristles while the tausonite film is primarily made up of nanocube aggregations. In comparison to the respective pristine semiconductor photocatalysts, the heterostructured photocatalyst demonstrates the highest efficiency in photocatalytic splitting of water to produce H 2 , 4.9 times that of TiO 2 and 2.1 times that of SrTiO 3 . The enhanced photocatalytic efficiency is largely attributed to the efficient separation of photogenerated charges at heterojunctions of the two dissimilar semiconductors, as well as a negative redox potential shift in the Fermi level.

Metal-like single crystalline boron nanotubes: synthesis and in situ study on electric transport and field emission properties

Abstract: Boron nanotubes (BNTs) have been theoretically proposed to have metallic properties whether they are in armchair or zigzag structure, so they have attracted much interest from researchers. However, their real properties have been not understood until now because they are hard to synthesize. In this paper, we have successfully fabricated a large quantity of boron nanotubes, which may provide a way to master their electric and field emission (FE) properties. Study on individual boron nanotubes shows that BNTs have metallic properties with an averaged conductivity of 40 Ω−1cm−1. Moreover, individual BNTs can sustain a high current of about 80 μA and their current density can reach 2.04 × 1011 A m−2, which is very close to those of CNTs. They are also incorporated into prototype luminescent tube devices for the first time and exhibit high luminescent efficiency and stability, which suggests that BNTs have a promising future in the FE area.

Field electron emission characteristics and physical mechanism of individual single-layer graphene.

Abstract: Due to its difficulty, experimental measurement of field emission from a single-layer graphene has not been reported, although field emission from a two-dimensional (2D) regime has been an attractive topic. The open surface and sharp edge of graphene are beneficial for field electron emission. A 2D geometrical effect, such as massless Dirac fermion, can lead to new mechanisms in field emission. Here, we report our findings from in situ field electron emission characterization on an individual singe-layer graphene and the understanding of the related mechanism. The measurement of field emission from the edges was done using a microanode probe equipped in a scanning electron microscope. We show that repeatable stable field emission current can be obtained after a careful conditioning process. This enables us to examine experimentally the typical features of the field emission from a 2D regime. We plot current versus applied field data, respectively, in ln(I/E(3/2)) ∼ 1/E and ln(I/E(3)) ∼ 1/E(2) coordinates, which have recently been proposed for field emission from graphene in high- and low-field regimes. It is observed that the plots all exhibit an upward bending feature, revealing that the field emission processes undergo from a low- to high-field transition. We discuss with theoretical analysis the physical mechanism responsible for the new phenomena.

Remarkably low turn-on field emission in undoped, nitrogen-doped, and boron-doped graphene

Abstract: Field emission studies have been carried out on undoped as well as N- and B-doped graphene samples prepared by arc-discharge method in a hydrogen atmosphere. These graphene samples exhibit very low turn-on fields. N-doped graphene shows the lowest turn-on field of 0.6 V/μm, corresponding to emission current density of 10 μA/cm2. These characteristics are superior to the other types of nanomaterials reported in the literature. Furthermore, emission currents are stable over the period of more than 3 h for the graphene samples. The observed emission behavior has been explained on the basis of nanometric features of graphene and resonance tunneling phenomenon.

Carbon nanotube-based electron field emitters

Abstract: The current status of research and development of carbon nanotubes (CNTs) electron field emitters is reviewed. The physical aspects of electron field emission that underlie the unique emission properties of CNTs are considered. Physical effects and phenomena affecting the emission characteristics of CNT cathodes are analyzed. Effects given particular attention include the electric field enhancement near a CNT tip; electric field screening by neighboring nanotubes; statistical spread of the parameters of the individual CNTs comprising the cathode; the effects of heat leading to thermal degradation of nanotubes during emission, and adsorbate effects on the surface of the emitter. Advances in vacuum electronics due to the use of CNT field cathodes are reviewed.

Plasma treatment of multiwall carbon nanotubes for dispersion improvement in water

Abstract: Microwave excited Ar/H2O surface-wave plasma was used to treat multiwall carbon nanotubes (MWCNTs) to modify their surface characteristics and thus improve their dispersion capability in water. Changes in the atom composition and structure properties of MWCNTs were analyzed using x-ray photoelectron spectroscopy and Raman spectroscopy, and the surface morphology of MWCNTs was observed by field emission scanning electron microscopy and scanning transmission electron microscopy. The results indicated that Ar/H2O plasma treatment greatly enhanced the content of oxygen, and modified surface microstructure properties. The integrity of nanotube patterns, however, was not damaged.

ZnS Branched Architectures as Optoelectronic Devices and Field Emitters

Abstract: A unique ZnS branched architecture was fabricated by a facile thermal evaporation method. Stable UV emission at 327 nm and superior field emission with a low turn-on field, a high field-enhancement factor, a large current density, and small fluctuation were observed.

Tip-morphology-dependent field emission from ZnO nanorod arrays.

Abstract: Vertically well-aligned ZnO nanorod arrays with three kinds of tip morphology?abruptly sharpened, tapered and plane?have been controllably fabricated with wafer size uniformity by vapor phase transport and condensation. Except that the tip morphology is distinctly different, all of these nanorods are single crystalline, growing along their wurtzite 0001 axis, with similar diameters, lengths and densities. The field emission properties of these nanorod arrays are comparatively investigated and are found to be strongly affected by the tip morphology. A nanorod with the abruptly sharpened tip possesses the lowest turn-on and threshold electric fields as well as the highest field enhancement factor. Further analysis reveals that the abruptly sharpened tip morphology can reduce the screening effect more efficiently than the others. These results are very helpful for the design, fabrication and optimization of integrated field emitters using 1D nanostructures as the cathode material.

Raman spectroscopy and field emission characterization of delafossite CuFeO2

Abstract: Delafossite p-type CuFeO2 (CFO) semiconductors were synthesized by a modified solid state reaction technique and investigated by x-ray diffraction, x-ray photoemission spectroscopy (XPS), energy dispersive x-ray spectroscopy, and scanning electron microscopy, revealing the single-phase nature of CFO with 1:1 Cu/Fe atomic ratio. The valance states of CFO were examined by XPS and suggest Cu and Fe ions are in +1 and +3 valance states with high spin S=5/2. The “turn-on field” which is the macroscopic field needed to get an emission current of 9 nA, was calculated as 5.72 V/μm. Room temperature Raman spectra of CFO displayed two main Raman active modes at Eg∼351 cm−1 and Ag∼692 cm−1 in accord with other delafossite structures. Temperature dependent Raman spectra showed that both the modes shifted to lower frequency with significant decrease in intensity with increase in temperature. Frequency shift and linewidth of both phonon lines matched well with the theoretical damped harmonic oscillator model based on t...

Ultrathin single-crystal ZnO nanobelts: Ag-catalyzed growth and field emission property.

Abstract: We report the growth of ultrathin single-crystal ZnO nanobelts by using a Ag-catalyzed vapor transport method. Extensive transmission electron microscopy and atomic force microscopy measurements reveal that the thickness of the ultrathin ZnO nanobelts is ~ 2 nm. Scanning electron microscopy and post-growth annealing studies suggest a '1D branching and 2D filling' growth process. Our results demonstrate the critical role of catalyst in the deterministic synthesis of nanomaterials with the desired morphology. In addition, these ultrafine nanobelts exhibit stable field emission with unprecedented high emission current density of 40.17 mA cm − 2. These bottom-up building blocks of ultrathin ZnO nanobelts may facilitate the construction of advanced electronic and photonic nanodevices.

Anisotropic gold nanoparticle doped mesoporous boehmite films and their use as reusable catalysts in electron transfer reactions.

Abstract: Anisotropic Au nanoparticle (NP) doped mesoporous and oriented boehmite films of about 2 μm in thickness were prepared and used as reusable catalysts. The films were characterized by grazing incidence X-ray diffraction (GIXRD), field emission scanning electron and transmission electron microscopies, optical absorptions and surface area and pore size measurements. GIXRD of the doped films showed a preferential growth of boehmite crystallites in the (020) plane. The electron microscopy studies revealed existence of dispersed anisotropic Au NPs of ∼15−40 nm size range and irregular Au aggregates of ∼200−300 nm inside the mesoporous boehmite films. The optical absorption of the films showed Au-plasmon bands at 605 nm and broad absorption covering the near-infrared (NIR) region due to the anisotropic Au nanostructures. These films showed excellent catalytic activities in both the organic (p-nitrophenol to p-aminophenol by sodium borohydride) and inorganic (ferricyanide to ferrocyanide by thiosulphate) electron...

The Fowler-Nordheim plot behavior and mechanism of field electron emission from ZnO tetrapod structures.

Abstract: Field emission measurements of current-voltage characteristics are reported for tetrapod structures of ZnO. The nonlinear Fowler-Nordheim (FN) plot is analyzed according to a model of calculation based on saturation of conduction band current and predominance of valence band current at high-field values. The simulated FN plot exhibits similar features to those observed experimentally. The model of calculation suggests that the slope variation of the FN plot, in the high-field and low-field regions, does not depend on the magnitude of saturation. Instead, it is a characteristic of the energy band structure and voltage-to-barrier-field conversion factor of the emitting material.

Nanostructured LaB6 field emitter with lowest apical work function.

Abstract: LaB6 nanowires are ideal for applications as an electrical field-induced ion and electron point source due to their miniature dimensions, low work function, as well as excellent electrical, thermal, and mechanical properties. We present here a reliable method to fabricate and assemble single LaB6 nanowire-based field emitters of different crystal orientations. The atomic arrangement, emission brightness from each crystal plane, and field emission stability have been characterized using field ion microscopy (FIM) and field emission microscopy (FEM). It is found that the 〈001〉 oriented LaB6 nanowire emitter has the highest field emission symmetry while the 〈012〉 oriented LaB6 nanowire has the lowest apical work function. The field emission stability from the single LaB6 nanowire emitter is significantly better than either the LaB6 needle-type emitter or W cold field emitters.

Optical and Field-Emission Properties of ZnO Nanostructures Deposited Using High-Pressure Pulsed Laser Deposition

Abstract: ZnO nanostructures were deposited on GaN (0001), Al2O3 (0001), and Si (100) substrates using a high-pressure pulsed laser deposition (PLD) method. Vertically aligned hexagonal−pyramidal ZnO nanorods were obtained on the Al2O3 and Si substrates whereas interlinked ZnO nanowalls were obtained on the GaN substrates. A growth mechanism has been proposed for the formation of ZnO nanowalls based on different growth rates of ZnO polar and nonpolar planes. Both ZnO nanorods and nanowalls exhibit a strong E2H vibration mode in the micro-Raman spectra. The corresponding fluorescence spectra of ZnO nanorods and nanowalls showed near band emission at 3.28 eV. The ZnO nanorods grown on the Si substrates exhibited better crystalline and optical properties compared with the ZnO structures grown on the GaN and Al2O3 substrates. The high aspect ratio, good vertical alignment, and better crystallinity of the ZnO nanorods with tapered tips exhibited promising field emission performance with a low turn-on field of 2 V/μm, a ...

Ar plasma treatment on few layer graphene sheets for enhancing their field emission properties

Abstract: Plasma treatment in Ar gas on few layer graphene sheets (FLGSs), synthesized by plasma enhanced chemical vapour deposition, has been performed for enhancing their field emission properties. The plasma etching treatment for 3?min on the FLGSs, forming an extremely sharp edge, decreases the turn-on electric field from 3.91 to 2.23?V??m?1, and increases the maximum emission current density, drawn at a field of 4.4?V??m?1, from 33 to 1330??A?cm?2. It is expected that plasma treatment provides an efficient way to improve the field emission properties of FLGSs.

Vertically aligned carbon nanotubes synthesized from waste cooking palm oil

Abstract: For the first time, vertically aligned carbon nanotubes (VACNT) were produced using waste cooking palm oil as green starting materials. The synthesis was carried out in a floating-catalyst thermal chemical vapor deposition reactor. Field emission scanning electron microscopy, energy dispersive X-ray, micro-Raman and thermogravimetric analyses, showed that the carbon nanotubes are of excellent quality, comparable to those obtained using conventional carbon sources. Under a typical synthesis condition of 5.33 wt ferrocence as catalyst and a furnace temperature of 750 degrees C, a mixture of single and multi-walled carbon nanotubes of 85 purity, vertically aligned on a silicon substrate, were produced. Field emission from the VACNT indicated reasonable turn-on field at 2.25 V/mu m which corresponded to the current density of 10 mu A/cm(2). The threshold field was observed to be about 3.00 V/mu m at 1 mA/cm(2). The maximum current density of 6 mA/cm(2) measured was obtained for 4 V/mu m. It is concluded that the VACNT from the reuse of waste material are suitable for applications in flat panel displays and flat lamps. (C) 2010 The Ceramic Society of Japan. All rights reserved.

Laser-induced field emission from a tungsten tip: Optical control of emission sites and the emission process

Abstract: Field-emission patterns from a clean tungsten tip apex induced by femtosecond laser pulses have been investigated. Strongly asymmetric field-emission intensity distributions are observed depending on three parameters: (i) the polarization of the light, (ii) the azimuthal, and (iii) the polar orientation of the tip apex relative to the laser incidence direction. In effect, we have realized an ultrafast pulsed field-emission source with site selectivity of a few tens of nanometers. Simulations of local fields on the tip apex and of electron emission patterns based on photoexcited nonequilibrium electron distributions explain our observations quantitatively. Electron emission processes are found to depend on laser power and tip voltage. At relatively low laser power and high tip voltage, field-emission after two-photon photoexcitation is the dominant process. At relatively low laser power and low tip voltage, photoemission processes are dominant. As the laser power increases, photoemission from the tip shank becomes noticeable. © 2010 The American Physical Society

Three-dimensional carbon nanowall field emission arrays

Abstract: This letter reports on the fabrication of regular arrays of three dimensional graphitic structures, by growing carbon nanowalls on forests of conical Si microspikes. The high field enhancement achieved by this hierarchical growth process indicates a potential for electron emission applications. Experiments show that the field emission performance and long-term stability of the structures is by far superior to that of planar carbon nanowall mats and comparable to that reported for optimized carbon nanotube based emitters. The improved field emission properties of the fabricated arrays are attributed to the dual micro and nanomorphology of the emitters, involving a two-scale enhancement process.

Observation of Photoconductivity in Sn-Doped ZnO Nanowires and Their Photoenhanced Field Emission Behavior

Abstract: Sn-doped ZnO nanowire films have been successfully synthesized by electrodeposition on zinc foil followed by annealing in air at 400 °C for 4 h. The XRD patterns of the annealed specimens exhibit a set of well-defined diffraction peaks indexed to the wurtzite phase of ZnO. The surface morphology of the as-synthesized films showed a network of densely packed flakes/sheets on the substrate. However, upon annealing, the formation of ZnO nanowires, processing length in the range of several micrometers and diameter less than 150 nm, on the entire substrate is observed. The relative atomic percentage of Sn, estimated from the energy dispersive spectra, was found to be 0.5 and 2.0 in the ZnO films deposited for 10 and 40 min durations, respectively. From the field emission studies, the values of the turn-on field and threshold field, required to draw emission current density of 10 and 100 μA/cm2, are observed to be 0.68 and 1.1 V/μm for 0.5% Sn-doped ZnO and 1.72 and 2.25 V/μm for 2.0% Sn-doped ZnO, respectively...

Shape and Doping Enhanced Field Emission Properties of Quasialigned 3C-SiC Nanowires

Abstract: We have reported the enhanced field emission properties of quasialigned 3C-SiC nanowires synthesized via catalyst assisted pyrolysis of polysilazane. The as-synthesized Al-doped SiC nanowires possess a tapered and bamboo-like structure with clear and tiny tips sized in several to tens of nanometers. The fabricated SiC nanowires have extremely low turn-on fields of 0.55−1.54 V μm−1 with an average of ∼1 V μm−1, which is the lowest one ever reported for any type of SiC emitters. The field-enhancement factor has been calculated to be 2983. The superior FE properties can be clearly attributed to the significant enhancements of the tapered and bamboo-like unique morphology and Al doping of SiC nanowires. Density functional theory calculations suggest that Al dopants in 3C-SiC nanowires could favor a more localized state near the Fermi energy, which improves the electron field emissions. We strongly believe that the present work will open a new insight in the fabrication of field emission sources with ultralow ...

Fabrication and photoluminescence properties of hollow Gd2O3:Ln (Ln = Eu3+, Sm3+) spheres via a sacrificial template method

Abstract: Hollow Gd2O3:Ln (Ln = Eu3+, Sm3+) microspheres were successfully fabricated by using carbon spheres as a template and urea as a precipitating agent, which involved the deposition of an inorganic coating on the surface of carbon spheres and subsequent calcination in the air. Various approaches including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR), thermogravimetric and differential thermal analysis (TG-DTA), photoluminescence spectroscopy as well as kinetic decays were used to characterize the samples. The results indicate that the as-prepared products can be indexed to pure cubic Gd2O3 phase. The samples are composed of uniform hollow Gd2O3:Ln spheres with a mean particle size of about 300 nm. The possible mechanism of evolution from glucose to carbon microspheres and the chemical reaction of each step to form the final hollow spheres are proposed. In particular, the urea-assisted precipitation process was carried out in aqueous solution without any organic solvent, and the hollow spheres formation process was achieved by simple calcination without using any etching agents. The hollow Gd2O3:Ln phosphors exhibit light emission under ultraviolet excitation, which may find promising applications in the fields of field emission displays (FED) and MRI contrast agents.

Facile Fabrication and Field Emission of Metal-Particle-Decorated Vertical N-Doped Carbon Nanotube/Graphene Hybrid Films

Abstract: In this study, vertical N-doped carbon nanotube (VNCNT) arrays were decorated with Au, Ru, or Mn nanoparticles, and the effects of the particles on the field-emission properties were investigated. Uniform catalyst nanoparticles were prepared by block copolymer lithography on a graphene film, and the VNCNT arrays were grown from the nanopatterned catalyst particles by plasma-enhanced chemical vapor deposition (PECVD). The surfaces of the VNCNT arrays were subsequently decorated with metal particles, and the vertical alignment of the NCNT arrays was maintained by high-vacuum annealing. The field-emission properties of the metal-particle-decorated VNCNT arrays varied according to the changes in the work-function values, with the Mn-VNCNT field emitter showing the best performance among the emitters tested. Our results revealed that the field-emission properties of VNCNT arrays may be tuned by decoration with metal particles and that particle decoration with a low-work-function material may be used to develop...

Characterization of thin water-based silane pre-treatments on aluminium with the incorporation of nano-dispersed CeO2 particles

Abstract: Thin silane films with the incorporation of nano-dispersed CeO 2 particles have been deposited by dip-coating over aluminium substrates. The silane molecule under investigation is bis-1,2-(triethoxysilyl)ethane (BTSE), which has been used as a water-based solution in order to fulfill the industry need for reducing the impact on human health and environment. The influence of the nano-oxides on the silane was first analyzed in the solution by means of 29 Si NMR, which showed that the ageing and stability of BTSE are not affected by the presence of CeO 2 nanoparticles in the silane matrix. The chemical interactions between CeO 2 nanoparticles and the BTSE in the cured coating were investigated by XPS, and the results pointed to the possible formation of a bond between Ce and Si. Field emission scanning electron microscopy (FE-SEM), field emission Auger electron spectroscopy (FE-AES) and focused ion beam coupled with transmission electron microscope (FIB–TEM) were used to investigate the film structure and surface morphology. A major challenge in the formation of thin layers with the incorporation of nano-oxides is to avoid the formation of particles agglomeration, which affects the film uniformity and might create preferential paths for corrosion attack. This issue has been overcome and the resulting films appear uniform and homogeneous, with the nanoparticles well embedded in the silane matrix and always covered by a thin silane layer. Electrochemical impedance spectroscopy (EIS) measurements have been performed on the samples and the results show how the barrier properties of the thin silane films are improved by the addition of CeO 2 nano-dispersed particles.

Electron field emission from Fe-doped TiO2 nanotubes

Abstract: Titanium dioxide nanotubes were prepared by refluxing TiO2 in 10 M NaOH at 200 °C for 12 h. The light absorption edge was slightly shifted to a longer wavelength when 0.025 mol % of iron was incorporated to TiO2 nanotubes. A turn-on field at 12 V/μm and a maximum current density of 12 mA/cm2 at 19 V/μm was observed for the Fe-doped but not for pure TiO2. The field emission behavior can be correlated with the geometry and electronic states of the nanotubes.