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In this paper, amorphous InGaZnO 4 thin-film transistors with an asymmetric structure exhibit ultraviolet (UV) light sensing property. At the offset region near the drain electrode, the extended active layer plays the role of a resistor. However, the ON-state current is obviously reduced with increasing offset length at the offset region near the source electrode and the characteristics cannot be turned ON when offset length is over 4 μm. After exposure to UV light, photogenerated holes-induce source barrier lowering and then amplifying the photocurrent response. Therefore, the devices in this paper reach a high-ON/OFF ratio of UV sensitivity to 10 6 .

The adaptability of field emitters in oxidizing environment is an important issue for practical applications. Herein, the effect of ozone exposure on the field emission property of molybdenum (Mo) nanowalls was studied. Results indicate that Mo nanowall cold cathode shows strong resistance to high doses of atomic oxygen exposure. The immunity of Mo nanowalls to oxidizing environment was attributed to the protection of surface amorphous layer. Mo nanowall cold cathode could be a promising candidate for electron source used in oxidizing environment.

Lanthanum boride (LaB x ) thin films with various thicknesses were deposited on ZnO nanowire arrays by electron beam evaporation. Field emission characteristics of ZnO nanowires show close dependence on LaB x coating thickness. The turn-on field increases with increasing LaB x coating thickness from 10 nm to 50 nm. The observed phenomena were explained by a model that the tunneling at ZnO/LaB x interface dominates the emission process.

In this paper, we report the degradation of gasochromic coloration performance in Pt-coated WO 3 (Pt/WO 3 ) nanowire films when the samples were exposed in air, due to the poisoning of Pt nanoparticles catalyst. The poisoned Pt nanoparticles can be reactivated by annealing in air, suggesting that the degradation originated from the absorption of certain gas species. X-ray photoelectron spectroscopy (XPS) was applied to investigate the gas desorption from poisoned Pt/WO 3 nanowire films during the annealing process. Based on the XPS results, a model involving chemical reactions and physical processes on the surface of Pt/WO 3 nanowires during annealing was developed to explain the degradation phenomenon.

Self-heating effect can be applied to develop gas sensors avoiding use of external heaters. We report here a prototype self-heated hydrogen gas sensor based on Pt-coated W 18 O 49 nanowire networks. Such a sensor has been shown to have promising performance, e.g., high sensitivity (able to detect down to 50 ppm of H 2 ), good selectivity (poor response to ethanol, CH 4 , CO, and C 3 H 8 ), and low power consumption of 30–60 mW at 6 V compatible to a portable device. Coaxial cable model and percolation theory are applied to explain the gas sensing effect of the Pt-coated W 18 O 49 nanowire networks.

Being a typical Kondo topological insulator, samarium hexaboride (SmB6) attracts much interest in condensed physics and material sciences in recent years. In comparison with their bulk counterparts, SmB6 nanostructures have more abundant surface electron states due to larger specific surface area, which are believed as idea platforms for studying surface quantum properties and physic mechanism. Through chemical vapor deposition (CVD), SmB6 nanobelt and nanowire films were respectively prepared on Si substrate. Both SmB6 nanowires and nanobelts are proven as the cubic single crystals, and their growth directions are, along [100] and [110], respectively. Field emission (FE) results show that SmB6 nanobelts have a turn-on field of 3.24 V/μm and their maximum current density arrives at 466.16 µA/cm 2, which are better than SmB6 nanowires. Considering that SmB6 nanostructures have lower electron affinity, higher electron conductivity and more abundant surface states, they are regarded as excellent cold cathode nanomaterials if their FE performances can be further improved.

H2 sensors able to operate at room temperature are very important for safe detection of H2 leakage. We report the large electrical response to H2 of Pt-coated WO3 (Pt−WO3) nanowire films without the need of using an external heater. More important, hydrogen sensing processes have been investigated under various conditions, including in air, vacuum filled with pure gas, and a mixture of H2 and other gases. This is carried out with both electrical and optical methods. The evidence shows that hydrogen will inject into the nanowire and create oxygen vacancy, in addition to reducing adsorbed oxygen at the surface, as is often recognized. It is experimentally demonstrated that the increase of electrical conductivity resulting from the reaction with hydrogen is hampered by coadsorption of O2, while N2 has no such effect. A model has been developed to combine these new findings to give a clearer understanding of the mechanism responsible for H2 sensing behavior.

The gasochromic effect has important applications in energy savings, for example, in a smart window. This study reveals evidence of the existence of localized water molecules in colored WO3 nanowir...

High density ZnO nanowire arrays were successfully synthesized without catalyst by direct oxidation of zinc substrate in air below 400 °C, lower than the melting point of zinc metal. The as-grown ZnO nanowires are single crystalline with a Wurzite structure extending in direction. The diameters of the ZnO nanowires range from 20 to 150 nm and the lengths from several to over ten micrometers. Room temperature photoluminescence measurements reveal an intense ultraviolet emission at 397 nm. The present work highlights the promise of the low temperature, direct oxidation process in the high-yield synthesis of high quality semiconductor nanowire arrays for nano-devices.

W18O49 nanowires were synthesized by a high-temperature physical evaporation technique. The structure, morphology, and composition of the nanowires were characterized by SEM, EMPA, XRD, XPS, and HRTEM techniques. The intrinsic Raman spectrum of W18O49 nanowires was obtained, and the effect of laser power on the change of their structure was also studied. W18O49 nanowires were first oxidized to tungsten trioxide nanowires under irradiation of a certain laser power, and then the tungsten trioxide nanowires underwent a phase transition from monoclinic to orthorhombic with increasing laser power; this phase transition was reversible on turning down the laser power. Copyright © 2006 John Wiley & Sons, Ltd.

The mechanical resonance behavior of a ZnO nanowire/nanorod at ambient condition has been studied under optical microscope by cutting its length using focused ion beam microscopy. Nanobalance using a ZnO nanowire as the cantilever has been demonstrated for measuring the mass in the order of pico-grams in working atmosphere (see optical microscopy images). The measurement limit of the balance is estimated to be ∼1 pg. The technique demonstrated here has potential for commercial applications in general laboratories, especially for measuring the mass of wet biological cells or species.

The frequency characteristics of a lighting element using carbon nanotube-based composite as cold-cathode material were studied. A delay response characteristic and a cutoff frequency have been observed. Furthermore, the dependence of cutoff frequency on the structural parameters of the electron gun of the lighting element has been investigated. The results show that the cutoff frequency increases with the vacuum gap between gate electrode and cathode, and decreases with the area and the thickness of cold cathode film.

Large-scaled MoO2 nanowire arrays have been prepared on silicon substrates by thermal evaporation of Mo in a flow of argon gas without using any catalyst. The nanowires are well aligned and vertically oriented to substrate surface. The cross-section of most of the nanowires has a polygonal shape with the width of about 150 nm, and the typical lengths of the nanowires vary from 2 to 4 lm. The X-ray energy dispersive spectroscopy reveals that the nanowires contained elements of Mo and O. X-ray diffraction analyses and high-resolution transmission electron microscopy study show that the MoO2 nanowires are of monoclinic structure. 2003 Elsevier B.V. All rights reserved.

Experimental studies were devoted to the effect of structural parameters, i.e., tube diameter and density, on the field electron emission characteristics of carbon nanotubes. Thermal chemical vapor deposition system was employed to synthesize carbon nanotubes. Nanotubes with different diameters and densities were obtained by adjusting the thickness of the iron (Fe) catalyst film. The morphologies of the Fe and carbon nanotube film were characterized by scanning electron microscopy respectively. Further field emission measurement confirmed that the tube diameter and density could significantly affect the electron emission properties of the carbon nanotube. Possible physical reasons for the effect are discussed.

A model for field emission through an amorphous diamond thin film with defects is constructed. Theoretical study shows that the emission is enhanced by attractive defects which would make the resonant emission observable for films with thickness of about 10 nm. The emitted current density in typical parameters is calculated as functions of thickness, field strength and defect density. The energy distribution of emitted electrons is attained.

Crystalline alumina nanowires were synthesized at elevated temperatures in a catalyst-assisted process using iron as catalyst. Nanotrees that formed by alumina nanowires were also found. SEM shows that typical nanowires are around 50 nm in diameter and around 2 μ m in length. The tree trunk of the nanotrees are around 100 nm in diameter and around 10 μ m in length. HRTEM with electron diffraction study reveals that the nanostructures are crystalline. The EDX confirms that the nanostructures contain only elements of Al and O. The XRD study shows that the nanowires are α-Al2O3. The results are explained in the light of growth mechanism based on a vapor–liquid–solid (VLS) process.

Nano-Y-junctions and nano-staggered-junctions that are formed by SiC nanorods were grown at elevated temperatures in a catalyst-assisted process. Transmission electron microscopy shows that the nanorods are typically around 20 nm in diameter and around 2 μ m in length. Nanorods with diameter down to below 2 nm may be observed from nano-junctions. High-resolution transmission electron microscopy shows that the nanorods are crystalline β-SiC.

Field electron emission properties of multi-walled nitrogen-containing carbon nanofibers were studied with particular interest in the mechanism responsible for their non-linearity of a Fowler–Nordheim (FN) plot. With vacuum gap d between anode and cathode varying in the range of 0.4–1.4 mm, the FN plots show distinct non-linearity and regular changes with the gap separation. Typically, two linear sections may approximately be defined in a FN plot, and thus two field enhancement factors may be derived rather than one. The variation of the field enhancement factors of the two sections with gap d show different behavior. The physical mechanisms responsible for the strong gap-dependent of I – V characteristics and their implication on technical applications are discussed.

At elevated temperatures, silicon carbide nanowires were synthesized in a catalyst-assisted process using aluminum as a catalyst. Transmission electron microscopy shows that the nanowires are around 20 nm in diameter and around 2 μm in length. High resolution transmission electron microscopy shows that the nanowires are crystalline β-SiC. Raman spectra show the typical features of nano-SiC. A model based on vapor–liquid–solid process is proposed to explain our finding.

Details of the recent experimental and theoretical studies of the frequency characteristic of the field emission electron source of a lighting element are given. The response times at different frequencies (0.02–200 kHz) and applied gap fields, acting on cathode surface, have been studied. A correlation has been found to exist between the response time and the frequency of applied voltage pulse. The response time remains almost constant within a range of frequencies between 1 and 30 kHz, and it remains nearly constant with increasing applied gap field higher than the threshold field. Finally, the cutoff frequency of the electron source is found, and with the current design of the electron source, it can be as high as 40 kHz. An equivalent circuit model is proposed, and theoretical results based on this model agree well with experimental findings.

Details are given of an experimental investigation carried out to study the field electron emission characteristics of a field emission flat panel display unit using a carbon nanotube-epoxy composite as electron emission material. These include: (i) dependence of direct emission current-voltage characteristic on vacuum gap spacing, (ii) the variation of the proportion of emission current passing through an aperture hole of a gate electrode with changing structural parameters of the device, and (iii) the uniformity and display characteristics of a typical display unit. Our findings indicate that it is very likely for one to produce a near-market prototype high voltage field emission flat panel display, if more sophisticated fabrication and assembly technique is adapted.

Field electron emission properties of aligned multi-walled carbon nanotube films were studied with variation of the vacuum gap d between anode and cathode. With d varying in the range of 0.4-2 mm, the emission current-gap voltage characteristics and the corresponding Fowler-Nordheim (FN) plots show distinct nonlinearity and regular changes with electrode separation. Three field enhancement factors may be derived from the three linear sections of a FN plot. Their variation with gap d results in different behaviours; significantly a drop of five times in the field enhancement factor is observed. The physical process responsible for our findings is suggested to be the space charge effect and both theoretical and experimental evidence is provided to support our arguments. The implication of our findings in technical applications is also discussed.

A terbium(III) complex, Na 3 Tb(DPA) 3 ·9H 2 O, where H 2 DPA is 2,6-dicarboxy pyridine acid, has been synthesized and incorporated into silica gel by sol-gel method to obtain a composite material, SiO 2 :Na 3 Tb(DPA) 3 . Photoluminescent properties of SiO 2 :Na 3 Tb(DPA) 3 composite were studied after heat treatments between room temperature and 600°C. The strong green emission of the composite material was intensified by heat-treatment under appropriate conditions. The effects of the dopant concentration and heat-treatment on the luminescence for the composite material have been examined. The results indicate that SiO 2 :Na 3 Tb(DPA) 3 composite material possesses high thermal stability with intense green fluorescence, and may be applied as a potential luminescent material.

Stable electron emission from amorphous diamond film at a low threshold field of 6-7 mV m-1 has been observed using a transparent anode technique. The electron emission characteristics are discussed in terms of the structural properties of films. Using scanning electron microscopy and Raman spectra, the emitting and the non-emitting regions of the amorphous diamond film are analysed. The emitting regions exhibit rougher microstructure in morphology and a stronger Raman peak at 1360 cm-1 than the non-emitting regions, a signature of having more micro-sp2 components. It is suggested that field emission is prone to take place at the regions containing more sp2 nanoclusters or nanocrystalline graphite.

Cold cathode field electron emission from thin films of a new organic compound Ca–Cu–B (B=betain) is observed. The microstructure of the film grown on an Al substrate by thermal evaporating technique is examined by scanning electron microscope and electron probe microanalysis, and it is found that a large number of carbon microparticles are embedded in the film. A transparent anode is used to image the spatial distribution of the emission sites and to measure the I – V characteristics, stability and turn-on field of the films. It is proposed that the presence of embedded carbon inclusions are responsible for the emission.

The ultrafast optical emission of nanosized (∼5nm) crystallites has been detected under the picosecond (ps) laser excitation of 300nm through ultrafast fluorescence spectroscopy. This optical emission, photoluminescence (PL), induced at a laser wavelength of 300nm confines blue light. The ultrafast PL spectrum deconvoluted by a Monte Carlo method shows that two fast emission processes with decaytimes of 60 and 350ps. This type of ultrafast emission has not been observed under the same experimental conditions from the samples of a natural single crystal and an impure natural single crystal diamond. The mechanism responsible for this visible ultrafast emission is proposed by taking into account the effect of surface states and large surface-to-volume ratio of nanoparticles. All of these findings demonstrate the feasibility of using large band-gap nanomaterials to generate ultrafast optical emission at various wavelengths.

Needle-shaped 3C–SiC nanowires were grown from commercially available SiC powders in a thermal evaporation process with iron as catalyst. A strong broad photoluminescence peak located around 450 nm was observed at room temperature, which may be ascribed to quantum size effects of nanomaterials. Needle-shaped 3C–SiC nanowires may have great potential applications such as blue-green light-emitting diodes and display devices.

Findings are given from the experimental observation of the vacuum breakdown of carbon-nanotube (CNT) field emitters on a Si tip. The CNTs were grown on the apex of a Si microtip by microwave plasma-enhanced chemical vapor deposition. The electrical contact of the CNT-Si junction was shown to be of ohmic type. A fine tungsten microprobe in combination with a scanning electron microscopy (SEM) system was employed for both the field emission and the contact conductivity measurements. This arrangement allows to precisely measure the characteristics of individual CNT and to in situ inspect the morphology of the CNT emitters on Si tips before and after vacuum breakdown events. An upper limit in emission current density of ∼103 A/m2 from the CNT emitters was recorded before a vacuum breakdown event is initiated. Clear evidence was found to show that the vacuum breakdown of the CNTs results in melting of the Si tip. These findings enhance the understanding of the failure mechanism of CNT emitters. It also has im...

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/cm2 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.

Silicon (Si) tip emitter arrays with uniform, smooth, and ultrathin (∼2 nm) amorphous diamond (a-D) apexes were fabricated. Aqueous buffer hydrofluoric acid and H2/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.

Geometrical field-enhancement structures at the surface of a substrate have been expected to effectively lower fields required to inject electrons from the substrate into amorphous-diamond (a-D) films. Two techniques have been developed to create a high density of nanoprotrusions on substrate surfaces: (a) on silicon (Si) substrates using our patented chemical-etching technique, and (b) on aluminum (Al) film by following a special deposition procedure. The density of nanoprotrusions can be as high as 108/cm2, and the mean roughness of the substrates is 2–30 nm. From a-D emitters, substrate surfaces with such nanoprotrusions can lower the field for emission. The results are discussed in light of several existing theoretical models.

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/cm2 was observed at fields as low as 9.6 V/μm, and current density of up to 83 mA/cm2 was recorded.

Straight crystalline copper sulphide (Cu2S) 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.

Details are given of an experimental study of microfabrication and characterization of a diode electron source using amorphous diamond (a-D) thin films. 〈100〉 n-type etched Si wafers with microscale-rough surface were used as cathode substrates. Filtered cathodic vacuum arc deposition technique was employed to coat a thin layer of a-D film on the Si substrate. Using the conventional photolithography, an array of well-defined diode structures with 20 μm gate diameter were formed. In addition, x-ray energy dispersive spectroscopy and atomic force microscopy were used to characterize the diode structure. Furthermore, the total emission current versus applied gate voltage of the diode electron source was measured. The physics of the emission process from the a-D diode was discussed.

An analysis is carried out of the physical origin of thermal instability that can trigger a catastrophic vacuum breakdown event in vacuum microelectronic devices based on flat diamond emitters. The temperature rise in a diamond film will enhance internal field emission across metal–diamond interface. This effect can lead to a regenerative process that can initiate a breakdown event at temperature lower than the melting point of an emitter. A set of equations has been developed. These theoretical findings are successfully applied to explain the instability of field emission from the nondoped diamond films.

A field-induced electron emission phenomenon has been observed from nitrogen-doped diamond films deposited on molybdenum substrates by microwave plasma enhanced chemical vapor deposition using N-2/CH4 as feedstock. Their field-induced electron emission characteristics, i.e., current-voltage characteristics and distribution of emission sites, were studied using the transparent anode imaging technique. A repeatable abrupt change of "on" and "off" states of emission was observed at two corresponding specific fields during circling of both increasing and decreasing applied gap fields. A plausible explanation is given to this type of field-induced electron emission phenomenon, in which a two-layer structure consisting of amorphous carbon and diamond is proposed. (C) 1999 American Institute of Physics. [S0003-6951(99)02535-8].

Nanodiamond powder was annealed at each of the following temperatures: 300, 600, 800, 1000, and 1150 °C, for an hour in flowing argon ambient. The variations of x-ray diffraction patterns and Raman spectra of the powder with different annealing temperatures were studied. While being annealed at temperatures higher than 800 °C, the powder can undergo a phase-transition process from cubic diamond to graphite. In addition, the size of nanodiamond crystallites decreased from ∼50 to ∼25 A. The physical mechanism responsible for the variation in Raman spectra is discussed using a phonon-confinement model.

The field emission properties of the screen-printed carbon nanotube (CNT) composite cathode have close relationship with its microstructure. In this study, carbon nanotube composite cold cathode with ZnO nano-particles as binding material was prepared using screen-printing method. Electric field cycles were used to post-treat the carbon nanotube composite cold cathode. During the process of electric field cycle treatment, obvious heat-induced damages were observed from the cathode. Scanning electron microscope and transmission electron microscope were employed to analyze the morphology and microstructure of the cathode. The possible mechanisms responsible for damages were discussed.

A carbon nanotube (CNT) composite cold cathode was studied for field emission display application. The CNT composite cold cathode was composed of CNTs and silicon dioxide binder. Field emission from CNT composite cold cathode with different CNT contents was studied. It was found that with increase in CNT contents, the threshold field decreased. The conductance of the composite cathode was measured and with increasing CNT content, there was a critical CNT content where the conductance increased several orders of magnitude. Plasma etching using SF(6) as the etchant was adopted to treat the cathode. Improvement in emission uniformity was achieved. It was also found that after post-treatment the threshold field of the cathode decreased. The morphology of the etched cathode was analyzed and the improvement of uniformity and lowering of the threshold field was attributed to the exposure of CNTs after etching.

Amorphous carbon film was treated by hydrogen plasma. The change of surface structure, conductivity, and work function distribution is characterized by scanning probe microscope technique and local electron emission is also analyzed. We find that chemical effect of hydrogen plasma on the a-C film is small, but the etching effect is strong and the surface morphology and conductance are obviously changed after hydrogen treatment. Electron emission enhancement is not due to the decrease of work function or existence of sp 2 conductive channels, but from the mutual effect between sp 2 and sp 3 phase. We suggest that the enhancement is due to the internal electron injection from the sp 2 -rich interface layer into the surface sp 3 -rich grains.

The effects of 300 keV O-2(+) ion irradiation on the temperature and magnetic field dependence of the critical current density (J(C)) in high quality epitaxial MgB2 thin films have been studied. Upon irradiation, the critical temperature T-C drops gradually and ultimately to less than 2 K and the residual resistivity increases from about 1 to 125 mu Omega cm with increasing doses. At a moderate radiation level of 1 x 1013 cm(-2), JC is enhanced and its performance in magnetic fields is significantly improved over a certain range of fields applied along the c-axis. The scaling behavior of reduced pinning force with reduced field reveals that the flux pinning mechanism evolves from grain-boundary-like pinning in the pristine and lightly irradiated films, to point-like pinning in moderately irradiated films, and again to grain-boundary-like pinning in heavily irradiated films. It is then concluded that point-like pinning centers, which can be modified by the damage level, have been introduced after oxygen ion irradiation.

CuO nanobelt arrays were prepared by an aqueous reaction method at room temperature. Effects of pulsed and continuous light illumination on field emission from CuO nanobelt arrays were studied. Possible physical mechanisms behind the observed phenomena are discussed.

In this study, CuO nanowire films are prepared by thermal oxidation method and their field emission properties have been studied and compared.

Large scale crystalline Fe3O4 nanopyramid arrays are fabricated by CH4 and N2 plasma sputtering of hematite [0001] wafer. The nanopyramid arrays are characterized using SEM, TEM and EELS and the possible growth mechanism is discussed

The performance of a solid-state gas sensor is characterized by its sensitivity, stability, and selectivity. The working principle relies on modulation of electrical conductivity due to surface oxidation reduction caused by gas exposure. Because only the surface layer is affected by such reactions, the sensitivity is strongly dependent on the surface-to-volume ratio of the material used. This purpose has been pursued by synthesizing layers with a porous morphology to enhance the material surface area. Porosity is enhanced by means of the thick film synthesis approach typically adopted in the gas sensing field. Such high porosity is not easy to achieve by thin film approach. Another approach largely used in the field is the rheotaxial growth and its thermal oxidation RGTO method, which allows synthesizing a porous thin film mono

We report a physical mechanism responsible for initiating a vacuum breakdown process of a single carbon nanotube (CNT) during field emission. A quasidynamic method has been developed to simulate the breakdown process and calculate the critical field, critical emission current density and critical temperature beyond which thermal runaway occurs before the CNT temperature reaches its melting point. This model is in good agreement with experiments carried out with a single CNT on a silicon microtip.

Tungsten nanoclusters films were grown on silicon carbide substrate in a thermal evaporation process without using catalyst. The temperature dependence of the field emission properties from the tungsten nanoclusters films has been studied in a range from 323 K to 543 K by using the transparent anode technique. The results show that the field emission current increases significantly with increasing temperature. As a consequence, the turn-on voltage for obtaining emission current density of 10 /spl mu/A/cm/sup 2/ decreases from 11.5 MV/m at 323 K to 2.375 MV/m at 543 K.