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Improvement in the field emission properties of α-Fe2O3 nanoflakes is observed after high energy X-ray irradiation from synchrotron radiation. Field emission threshold field of α-Fe2O3 nanoflakes is found to decrease from 10.1 to 7.8 MV/m after X-ray irradiation with the dose of 9.0 × 1014 phs/cm2. Electrical measurement reveals that the potential barrier at the back contact between the α-Fe2O3 layer and the iron substrate changes after X-ray irradiation. The observed threshold field decrease is well explained by the changes in potential barrier at the back contact of α-Fe2O3 nanoflakes, which indicates the back contact plays an important role in controlling the field emission properties of α-Fe2O3 nanoflakes. Our study shows that the α-Fe2O3 nanoflakes are a promising material for the application as field emitter under X-ray environment. [ABSTRACT FROM AUTHOR]

For field emission from wide-band-gap semiconductor nanostructures, nonlinear plots on Fowler-Nordheim (FN) coordinates and unacceptably large field enhancement factors (βFN) are often obtained by fitting based on FN equation. In the present work, the field-induced hot-electron emission model is developed and is found to give theoretical findings consistent with the experimental observation. The hot electrons are produced by heating effect of penetration field into the emitting tip of the nanostructure. This energy is expressed by effective electron temperature Te, which is much higher than the temperature of bulk structure. By combining the effective electron temperature with thermal emission function and Murphy and Good integration function, the relation between emission current density and external field is derived and the field enhancement factor (βTe) can be calculated quantitatively. For evaluation of the theoretical model, ZnO nanostructure is selected as a concrete example. The results are found to agree with experiment findings. Extremely large field enhancement factor is not needed in our model and nonlinear property of saturation region emerges in nature in our calculation. [ABSTRACT FROM AUTHOR]

Pulsed-laser (neodymium doped yttrium aluminum garnet; 1.06 μm in wavelength) treatments were performed on zinc oxide (ZnO) nanowires (NWs) in nitrogen. It results in nitrogen doping of ZnO, mainly with chemical states of N2 at oxygen sites, which is demonstrated by x-ray photoelectron spectroscopy studies. The laser treated ZnO NWs show significant improvement in electrical conduction and field emission. Typically, with the critical treated conditions of peak power 400 W and pulse duration 2 ms, NWs with the highest conductivity of 1.43×10-2 S/cm was obtained. It is one order of magnitude higher than that of the as-prepared NWs (1.20×10-3 S/cm). These NWs show better field electron emission properties. The turn-on field is 2.0 MV/m and a current density of 5.3 mA/cm2 can be obtained at a field of 3.0 MV/m. The underlying mechanisms related to the enhancing effect of conduction and field emission were discussed. The pulsed-laser treatment may be developed toward a technique for application in the study of nanoelectronic devices using NWs. [ABSTRACT FROM AUTHOR]

A phenomenon of field emission instability is reported. Field emission current oscillation was observed when a single zinc oxide (ZnO) one dimensional nanostructure operated at high current density. As a result, the radius curvature of the nanoemitter apex was sharpened to less than 15 nm. This indicates the oscillation was associated with melting of the emitter material. We found that the oscillation may be ascribed to (i) the behavior of charging and (ii) the shape changing of a metallic liquid ball that exists at the tip apex under high electric field. The net force of electric force and surface tension modifies the radius of the apex periodically, which results in the oscillation of field emission current. This finding may enhance the understanding of the physical process of field emission from ZnO nanostructures. [ABSTRACT FROM AUTHOR]

The field emission characteristics of amorphous carbon (a-C) films are studied before and after H plasma treatment. It is found that H plasma treatment lowered the turn-on field and improved the field emission uniformity. Surface sp2/sp3 ratio, work function, and topography of the a-C films before and after H plasma treatment are studied using Raman spectroscopy, Kelvin probe, and atomic force microscopy, respectively. The results show that the etching effect of H plasma on a-C film is obvious, which is different from those of diamond and tetrahedral amorphous carbon (ta-C) films. We suggest that the surface component change and nanostructure of treated a-C films cause electron injection from sp2 sites to surface sp3 sites which are responsible for low macroelectrical field emission. [ABSTRACT FROM AUTHOR]

The degradation and damage of carbon nanotube (CNT) films caused by field emission were investigated by carefully studying the effect of emission current density of different levels on the CNT film. It is found that the behavior of the vacuum breakdown of a CNT film is very different from a metal cathode. A critical emission current density may be identified, 500 A/m2, for example, for our present samples, below which the evaporation of CNT tips and breaking at defect sites of a group of CNTs of long length are the major causes of damage to the CNT film. When the emission current density is higher than the critical value, microarcing gives rise to significant catastrophic damage to the CNT film. A theoretical model proposed early for CNT vacuum breakdown was adapted to explain the present findings, which assumes thermal runaway as an initiating mechanism for CNT vacuum breakdown, taking into account the important role of Joule heating. [ABSTRACT FROM AUTHOR]

Temperature dependence of field emission characteristics of tungsten sub-oxide (W18O49) nanowires was investigated in the range from 143 K to room temperature. It is found that the field emission currents under the same applied electrical field decrease with the decreasing temperature. A two-step process involving the phonon-assisted tunneling from defect states to conduction band was introduced to explain the observed phenomenon. A good agreement between the theoretical and experimental results was achieved. [ABSTRACT FROM AUTHOR]

The changes in the microstructure of ZnO nanowire were studied after exposure to different radiation doses of energetic x-rays. Detailed structural, composition and optical analyses were carried out. It was found that the surface composition changed and defects were formed in the irradiated ZnO nanowires. The structural change of ZnO nanowires after thermal treatment was also studied and similar defects were observed. It is proposed that phonon-induced localized heating is the main reason for the observed changes in microstructure. Finally, the field emission properties of ZnO nanowires before and after x-ray radiation were studied. It was found that the increase of work function and change in morphology induced by the irradiation were the reasons for the observed change in field emission properties. [ABSTRACT FROM AUTHOR]

A simplified simulation approach aiming at reducing computational complexity has been proposed for gated field emitters. In this approach, a thin-film cold cathode consisting of quasi-one-dimensional nanoemitters is modeled as a flat metallic thin-film. The surface of the thin-film is divided into equal-size grids. Fowler-Nordheim parameters fitted with experimental current-voltage data are used to calculate emission current from these individual grids. The statistics of the total emission current and its distribution between the gates and the anode are analyzed by summing the currents from all of the grids. The validity of the proposed approach is evaluated by comparing the simulation results with experimental data from gated carbon nanotube (CNT) thin-film field emitters. CNTs at the edge of the CNT film stand out as superior emitters, and proper consideration of such emitters plays a critical role in determining the validity of the proposed approach. [ABSTRACT FROM AUTHOR]

Using nanowire field emitters can be a way to overcome the high cost of field emission display using Spindt-type tip arrays. How to integrate nanowire emitters into the field emission display device structure without influencing the device structure is an important issue. In this study, a gated CuO nanowire field emitter arrays were fabricated by a microfabrication process. By using a thermal oxidation process, the CuO nanowire field emitter arrays are prepared from copper thin film pads defined in a planar-gate structure. Effective emission current modulation by the gate voltage is achieved. Using a green phosphor screen as anode, a brightness of 92 cd/m2 was obtained at an anode voltage of 4.5 kV and a gate voltage of 120 V when operating under direct current mode. A vacuum-packaged field emission display using CuO nanowire field emitter arrays was also fabricated and display of moving images was demonstrated. The reported technique could be a promising route to achieved large area field emission display with high resolution display at low cost. [ABSTRACT FROM AUTHOR]

W18O49 nanowires exhibit stable field emission at low fields. To explore the potential application of such nanowires in backlight and display devices, it is necessary to achieve uniform emission on a large area. In the present study, the authors demonstrate that field-emission uniformity of large-area samples may be improved by following an electrical-current treatment procedure. This is due to the increase in the number of nanowires that join in the field emission during the process, in which a small number of strong emitters are gradually melted down. The process of self-melting occurring in field emission is studied using a point anode in situ with a scanning electron microscope. The self-melting is attributed to the effect of Joule heating occurring due to passing of current through field electron emitting nanowires. These results are useful for the device application of W18O49 nanowires as large-area cold cathodes. [ABSTRACT FROM AUTHOR]

Wire-type cold cathode was prepared by direct growth of carbon nanotube (CNT) on stainless-steel wire using thermal chemical vapor deposition. By varying the growth temperature, gas flow direction, and reactant gas mixture, improved field-emission uniformity and stability were achieved. The results show that the CNT cathodes grown by H2/C2H2 mixture exhibit better current stability than those grown by Ar/C2H2 mixture. Fully sealed fluorescent lamps have been fabricated using wire-type CNT cold cathode. Luminescent efficiencies of 37 and 21 lm/W were obtained for the fully sealed lamps with green and white phosphor screens. [ABSTRACT FROM AUTHOR]

The authors report the fabrication and characterization of a 4.5 in. field emission display (FED) prototype. The FED prototype consists of 14×14 matrix addressable pixels. The pixel is 5 mm in diameter. The characteristics including current-voltage properties, current stability, brightness, and image quality of the display prototype were characterized. The average static brightness of the display prototype is 2500 cd/m2. Characters were displayed in a scanning pulsed driving mode. The adjacent pixels are tangent to each other, making continuous display feature. The results show that the FED prototype has promising potential for high-resolution giant display application. [ABSTRACT FROM AUTHOR]

Screen-printed carbon nanotube (CNT) emitter arrays were prepared by using slurry of mixture of multiwall CNTs, organic vehicles, and inorganic binder, i.e., silicon dioxide sol. The composition of the slurry was optimized by varying the CNT content in the mixture. It was found that only the cathode with appropriate CNT contents had low turn-on field and high emission current density. A post-treatment process was introduced to further improve the field emission properties which selectively etches away the silicon dioxide binder by inductively coupled plasma etching. The results show that the selective etching process could effectively remove the inorganic binder layer from screen-printing CNT emitters and improve field emission performances. [ABSTRACT FROM AUTHOR]

Polymethyl methacrylate (PMMA) thin films were prepared by spin coating using chloroform solvent. The field emission current versus applied field characteristics were tested. Stable field emission was observed after a switch-on process. The field emission properties of PMMA film exhibit vacuum gap dependence characteristics. The scanning electron microscope inspection reveals that after emission process microwhiskers were formed at the surface. The gap dependence of the field emission properties was explained. It is proposed that the high field during the switch-on process leads to the formation of the microwhiskers. [ABSTRACT FROM AUTHOR]

Cathodoluminescent properties of a SrGa2S4:Eu2+ phosphor, which was synthesized by a high-temperature solid-phase reaction, have been studied. Cathodoluminescent spectra, the Commission International de l’Eclairage color coordinates, and photoluminescence spectra were obtained. The cathodoluminescent intensity was measured at an operating voltage of 0–10 kV and current density of 0–160 μA/cm2. The degradation of cathodoluminescence after high-current-density bombardment was observed. X-ray photoelectron-spectroscopy analysis showed the electron-bombardment-induced chemical reaction in the SrGa2S4:Eu2+ phosphor in which SrSO4 was formed. The cathodoluminescent properties were compared with commercial green phosphor ZnS:Cu,Au,Al and it was found that the properties of SrGa2S4:Eu2+ phosphor under high current bombardment were more stable. [ABSTRACT FROM AUTHOR]

A theoretical formalism is developed to study the intrinsic properties of field emission from the single-walled carbon nanotubes (SWCNTs), including the current-voltage characteristic, the energy spectrum, and their responses to the magnetic field. The SWCNTs can be classified to two kinds, metallic and semiconducting tubes, according to field-emission properties. They have different slopes of the Fowler-Nordheim [Proc. R. Soc. London, Ser. A 119, 173 (1928)] plot, energy spectra, and different responses to the magnetic field, which originate from the energy band structure of SWCNTs. [ABSTRACT FROM AUTHOR]

The influence of temperature and electric field on field emission energy distribution (FEED) is studied. It is found that higher temperature energizes more higher-energy electrons. FEED peaks shift toward low energy linearly with the increase in applied voltage because of the electric field penetration. The theoretic current-voltage characteristic is fitted to the experimental data by the density of states, field enhancement factor, and temperature, from which the average energy of emitted electrons and then Fermi level of the carbon nanotube (CNT) is ascertained. This research confirms that the electric field competes with temperature and provides a method to ascertain the Fermi level of CNT. [ABSTRACT FROM AUTHOR]

In order to apply various cold cathode nanoemitters in a field emission display (FED) and to achieve high brightness, a FED device structure with double gates and corresponding driving method have been proposed. Individual pixel addressing can be achieved by applying proper sequence of positive or negative voltage to the lower gate and upper gate, respectively. The feasibility of the device has been demonstrated by using carbon nanotube and tungsten oxide nanowire cold emitters. Display of moving images has been demonstrated and high luminance up to 2500 cd/m2 was obtained. The reported device structure is versatile for nanoemitters regardless of substrate or preparation temperature. The results are of significance to the development of FED using nanoemitters. [ABSTRACT FROM AUTHOR]

Single crystalline silicon carbide (SiC) nanowires were grown directly on the surface of bulk SiC ceramic substrate in a catalyst-assisted thermal heating process. The morphology of the nanowire film and the diameter of nanowires were found to be sensitive to the thickness of catalyst film and both of them had a strong effect on field emission performance. Very low turn-on and threshold fields for electron emission were observed with SiC nanowires of small diameter. A model is proposed to qualitatively explain the field emission findings, which assumes the occurrence of an insulator-to-metal-like transition in a field emitting nanowire. [ABSTRACT FROM AUTHOR]

The uniformity in field emission from a carbon nanotube film is very important to many applications. A study has been carried out to obtain uniform emission from multiwall carbon nanotube (CNT) films by electrical treatment. The electrical treatment is based on local vacuum breakdown of CNTs under direct-current conditions. The optimal current density was found, under which the best effect of the treatment may be observed. The physical mechanism responsible for the effect of local vacuum breakdown of CNTs on emission uniformity was investigated. [ABSTRACT FROM AUTHOR]

A technique involving a combination of using self-assembled nanomask and anisotropic plasma etching is developed for fabricating vertically aligned single-crystalline Si nanowires (SiNWs). The SiNWs are shown to have excellent field emission performance with the turn-on field as low as 0.8 MV/m and the threshold field being 5.0 MV/m. In addition, an emission current density of 442 mA/cm2 can be obtained at an applied field of ∼14 MV/m. The technique is easily employed to fabricate arrays of SiNW-based field emission microtriodes. Mechanisms are proposed to explain the formation of the SiNWs and the observed field emission properties. [ABSTRACT FROM AUTHOR]

We report procedure with use of self-assembled silicon carbide (SiC) nanomasks for preparation of ultrahigh-density Si nanotips. Si nanotips with SiC apex may be firstly prepared in a CH4/H2 plasma treatment and in a subsequent H2 plasma etching a SiC apex may be converted into an amorphous silicon (a-Si) one with an additional function of sharpening the nanotips. A comparative study of the field electron emission from the Si nanotips with apexes of SiC, a-Si and pure Si is carried out, and shows that nanotips with a-Si apexes have not only the highest field enhancement factor but also the best emission uniformity. The physical origins for the above two improvements in field emission are discussed. [ABSTRACT FROM AUTHOR]

Effects of pulsed and continuous light illumination on field emission from CuO nanobelt arrays have been studied by using a transparent anode technique. It is found that, at low-field emission current level, the field emission current generally increases under a pulsed irradiation; at an emission current level of 1.1 μA, a 19% increase in emission current was recorded. The photoinduced current increase is reduced with increasing emission current and is undetectable when the emission current is higher than 15 μA. On the other hand, a long time illumination of the sample decreases the field emission current. Possible physical mechanisms behind the observed phenomena are discussed. [ABSTRACT FROM AUTHOR]

The emission current of a single-wall carbon nanotube (SWNT) in field emission is studied by the tunneling theory with the tight-binding approach. The emission current is almost independent of the chiral angle of SWNT in low fields, but increases with increase of chiral angles in very high fields. We found a room-temperature quantum size effect of SWNT on field emission. As the diameters of SWNTs increase, the current densities decrease for metallic tubes, but increase for semiconducting tubes. When the diameters of SWNTs are larger than 2 nm the current densities of metallic and semiconducting tubes are very close. These chiral and quantum size effects are originated from the energy band structure of nanotubes. [ABSTRACT FROM AUTHOR]

Films of aligned cupric oxide nanobelts have been prepared in an aqueous solution at room temperature. Field-emission characteristics, including emission-current–applied-field plot and emission site distribution, have been studied using the transparent anode technique. In addition, the temperature dependence of the field-emission characteristics has been studied from room temperature to 750 K. The threshold field for obtaining a current density of 10 µA/cm⊃2 is ∼ 11 MV/m. This decreases with increasing temperature, and at 700 K it is ∼6 MV/m. At a fixed field of 10 MV/m, about a three-orders-of-magnitude increase of the emission current level has been observed. The results show that the cupric oxide nanobelt is a promising candidate for cathode material in a thermoelectric conversion device based on field emission. [ABSTRACT FROM AUTHOR]

Silicon (Si) tip emitter arrays with uniform, smooth, and ultrathin (~2 nm) amorphous diamond (a-D) apexes were fabricated. Aqueous buffer hydrofluoric acid and H[SUB2]/Ar plasma have been employed to remove the native oxide layer of Si tips, prior to the a-D film deposition. Scanning electron microscopy study showed that uniform a-D coatings were highly localized on the apex of individual Si tips. Study using high-resolution transmission electron microscopy and x-ray energy dispersive spectroscopy confirmed that the Si/a-D junction is free from the oxide interlayer. Field-emission measurements demonstrated that the removal of the native oxide layer and the a-D apex coating are important to stabilize and enhance the electron emission from Si field emitters. [ABSTRACT FROM AUTHOR]

Bunches of needle-shaped silicon carbide (SIC) nanowires were grown from commercially available SiC powders in thermal evaporation process and using iron as catalyst. Their structure and chemical composition were studied by Raman spectroscopy and high-resolution transmission electron microscopy. The powder of these nanowires may be easily dispersed, and was used to form samples of field electron emitters. The needle shape of individual nanowires is well-suited to field electron emission. Stable emission with current density of 30.8 mA/cm[sub 2] was observed at fields as low as 9.6 V/µm, and current density of up to 83 mA/cm[sub 2] was recorded. [ABSTRACT FROM AUTHOR]

Straight crystalline copper sulphide (Cu[sub 2]S) nanowire arrays have been grown by using a simple gas–solid reaction at room temperature. These were demonstrated to exhibit semiconductor properties. Field emission was observed at a field of ∼6 MV/m, and its current-field characteristics deviate from Fowler–Nordheim theory, i.e., showing a nonlinear Fowler–Nordheim plot. The uniform emission from the whole arrays was observed using transparent anode technique, and their variation with applied field was recorded. The emission from individual nanowires was also studied using a field emission microscope, and was found to consist of a number of spatially resolved diffuse spots. Finally, stable emission current at different levels and over time was recorded. These findings indicate that semiconductor nanowires as cold cathode have a potential future, worthy of further comprehensive investigation. The technical importance of using semiconductor nanowires as cold cathode emitter is given. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

To utilize high-performance nanoemitter cold cathode prepared by high-temperature direct-growth process, 4.5 in. field emission display based on double-gate driving principle has been fabricated. A stacked-metalized-aperture structure has been introduced to improve stability. This structure composes of two gate-plates and is different in terms of addressing behavior from previously reported single gate-plate structure. Device characteristics have been investigated in details and are found to comply in trend with simulated results. The upper gate is found having native focusing feature. The result is encouraging as the current structure is possible to achieve high-performance large-area display. [ABSTRACT FROM AUTHOR]

Hematite (α-Fe2O3) nanotips have been successfully synthesized on a large area by thermal oxidation of iron film on indium tin oxide coated glass. The population density and aspect ratio of the α-Fe2O3 nanotips were controlled by varying preparation temperature in the range of 325–400 °C. The field emission properties of α-Fe2O3 nanotips prepared under different temperatures were studied. Uniform and stable emission was obtained. Considering the simple preparation method and scalability for large area preparation, the α-Fe2O3 nanotips could be a promising field emitter for field emission display application. [ABSTRACT FROM AUTHOR]

In this study, the fabrication technologies for a gated CuO nanowire field emitter arrays were investigated. Fabrication process was optimized to achieve uniform emission. More uniform emission is achieved from the CuO nanowire field emitter arrays prepared with an additional lift-off process. The improved uniformity is attributed to the removal of etch residues as well as higher resistance between the CuO nanoemitter and cathode electrode. The study shows that the gated CuO nanowire field emitter arrays have potential for application in high resolution field emission display. [ABSTRACT FROM AUTHOR]

Nonlinearity is observed in Fowler-Nordheim (FN) plots of field emission from nondoped and nitrogen-doped amorphous diamond films. Based on a unified electron emission equation a detailed analysis is carried out. The results from numerical calculation of the unified equation are consistent with the experimental data. It is shown that the nonlinearity in the FN plot originates from a transition from thermionic emission to field emission as the applied field increases. The electrical field ranges are derived in which the field emission and thermionic emission approximation applies. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Understanding the origin crystalnucleation and driving force iscritical for the synthesis of one-dimensional nanomaterials with controllablesize, morphology, and crystal structure. The growth behavior of ZnOnanowires prepared by thermal oxidation of zinc film is studied. Itis found that the grown nanowires have a bicrystalline structure andgrowth direction significantly different from the commonly observed[0001] direction. On the basis of detailed high resolution morphologyand structural analysis, we propose the origin of the initial growthsite, as well as the driving force for formation of the bicrystallinestructure of aligned ZnO nanowires. The initial zinc film plays animportant role in the growth of nanowire. The edge-enhanced oxidationeffect of zinc grain initiates the ZnO nanowire nucleation. The strainwithin the ZnO layer drives and stimulates the nanowire growth. Thepresent study provides insight into the growth mechanism of ZnO nanowiresgrown from thermal oxidation of zinc film. Field emission measurementresults show that the prepared ZnO nanowires have excellent fieldemission properties. Uniform emission can be obtained and the turn-onfield is 7.8 V/μm. The results indicate that the method is advantageousfor large-scale synthesis of ZnO nanowires for field emission applications. [ABSTRACT FROM AUTHOR]