Field emission from single-walled carbon nanotubes aligned on a gold plate using a self-assembly monolayer

Field emission from single-walled carbon nanotubes (SWNTs) aligned on a patterned gold surface is reported. The SWNT emitters were prepared at room temperature by a self-assembly monolayer technique. SWNTs were cut into sub-micron lengths by sonication in an acidic solution. Cut SWNTs were attached to the gold surface by the reaction between the thiol groups and the gold surface. The field-emission measurements showed that the turn-on field was 4.8 V/μm at an emission current density of 10 μA/cm². The current density was 0.5 mA/cm² at 6.6 V/μm. This approach provides a novel route for fabricating CNT-based field-emission displays. Received: 3 May 2002 / Accepted: 6 May 2002 / Published online: 4 December 2002 RID="*" ID="*"Corresponding author. Fax: +82-54/279-8298, E-mail: ce20047@postech.ac.kr     

Field emission from patterned SnO2 nanostructures

A simple and reliable method has been developed for synthesizing finely patterned tin dioxide (SnO₂) nanostructure arrays on silicon substrates. A patterned Au catalyst film was prepared on the silicon wafer by radio frequency (RF) magnetron sputtering and photolithographic patterning processes. The patterned SnO₂ nanostructures arrays, a unit area is of ∼500 μm × 200 μm, were synthesized via vapor phase transport method. The surface morphology and composition of the as-synthesized SnO₂ nanostructures were characterized by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). The mechanism of formation of SnO₂ nanostructures was also discussed. The measurement of field emission (FE) revealed that the as-synthesized SnO₂ nanorods, nanowires and nanoparticles arrays have a lower turn-on field of 2.6, 3.2 and 3.9 V/μm, respectively, at the current density of 0.1 μA/cm². This approach must have a wide variety of applications such as fabrications of micro-optical components and micropatterned oxide thin films used in FE-based flat panel displays, sensor arrays and so on.     

Enhanced field emission and patterned emitter device fabrication of metal-tetracyanoquinodimethane nanowires array

Ag(TCNQ) and Cu(TCNQ) nanowires were synthesized via vapor-transport reaction method at a low temperature of 100 °C. Field emission properties of the as-obtained nanowires on ITO glass substrates were studied. The turn-on electric fields of Ag(TCNQ) and Cu(TCNQ) nanowires were 9.7 and 7.6 V/μm (with emission current of 10 μA/cm²), respectively. The turn-on electric fields of Ag(TCNQ) and Cu(TCNQ) nanowires decreased to 6 and 2.2 V/μm, and the emission current densities increased by two orders at a field of 8 V/μm with a homogeneous-like metal (e.g. Cu for Cu(TCNQ)) buffer layer to the substrate. The improved field emission is due to the better conduct in the nanowires/substrate interface and higher internal conductance of the nanowires. The patterned field emission cathode was then fabricated by localized growing M-TCNQ nanowires onto mask-deposited metal film buffer layer. The emission luminance was measured to be 810 cd/m² at a field of 8.5 V/μm.     

Field emission from lotiform-like ZnO nanostructures synthesized via thermal evaporation method

Novel lotiform ZnO nanostructures were synthesized on silicon substrate via simple thermal evaporation. The average diameter of the ZnO nanostructures is ∼1.5 μm. The lotiform-like ZnO structures were formed by nanorods arrays with the average diameter of 70 nm. The as-grown lotiform ZnO nanostructures have excellent field-emission properties such as the low turn-on field of 3.4 V/μm, and very high emission current density of 12.4 mA/cm² at the field of 9.6 V/μm. These features make the lotiform-like ZnO nanostructures competitive candidates for field-emission-based displays. PACS 61.46.-w; 61.82.Rx; 78.67.-n; 73.63.Bd; 74.78.Na     

Enhanced field emission from PbTiO3 nanodots prepared by phase separation approach

Uniformly distributed PbTiO₃ nanodots were successfully prepared by phase separation approach. A precursor sol film was first spin-coated on Si wafer and then spontaneously separated into two distinct phases owing to the Marangoni instability. PT nanodots with tailorable size and density were obtained after further heat treatment. X-ray diffraction analysis indicated that these nanodots showed a perovskite structure. An excellent room temperature field emission property of PbTiO₃ nanodots was observed: the minimum turn-on voltage was about 5.3 V/μm; while the emission current density reached about 270 μA cm⁻² at an applied field of about 9.25 V/μm.     

Synthesis and field emission of patterned ZnO nanorods

A simple and self-catalytic method has been developed for synthesizing finely patterned ZnO nanorods on ITO-glass substrates under a low temperature of 500 °C. The patterned ZnO nanorod arrays, a unit area is of 400 × 100 μm², are synthesized via vapor phase transport method. The surface morphology and composition of the as-synthesized ZnO nanorods are characterized by means of scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The mechanism of formation of ZnO nanorods is also discussed. The measurement of field emission (FE) reveals that the as-synthesized ZnO nanorods arrays have a turn-on field of 3.3 V/μm at the current density of 0.1 μA/cm² and a low threshold field of 6.2 V/μm at the current density of 1 mA/cm². So this approach must have a potential application of fabricating micropatterned oxide thin films used in FE-based flat panel displays.     

Vertically aligned carbon nanotubes from natural precursors by spray pyrolysis method and their field electron emission properties

Vertically aligned carbon nanotubes have been synthesized from botanical hydrocarbons: Turpentine oil and Eucalyptus oil on Si(100) substrate using Fe catalyst by simple spray pyrolysis method at 700°C and at atmospheric pressure. The as-grown carbon nanotubes were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), thermogravimetric analysis (TGA), differential thermal analysis (DTA), and Raman spectroscopy. It was observed that nanotubes grown from turpentine oil have better degree of graphitization and field emission performance than eucalyptus oil grown carbon nanotubes. The turpentine oil and eucalyptus oil grown carbon nanotubes indicated that the turn-on field of about 1.7 and 1.93 V/μm, respectively, at 10 μA/cm². The threshold field was observed to be about 2.13 and 2.9 V/μm at 1 mA/cm² of nanotubes grown from turpentine oil and eucalyptus oil respectively. Moreover, turpentine oil grown carbon nanotubes show higher current density in relative to eucalyptus oil grown carbon nanotubes. The maximum current density of 15.3 mA/cm² was obtained for ∼3 V/μm corresponding to the nanotubes grown from turpentine oil. The improved field emission performance was attributed to the enhanced crystallinity, fewer defects, and greater length of turpentine oil grown carbon nanotubes.     

Modulation of field emission properties of vertically aligned ZnO nanorods with aspect ratio and number density

Vertically aligned ZnO nanorod arrays with different aspect ratios were synthesized by hybrid wet chemical route. Modulation of the field emission properties (FE) with aspect ratio of ZnO nanorods was examined. With the increase in the aspect ratio, the emission current density increases from 0.02 to 8 μA/cm² at 7.0 V/μm. Turn-on voltage was seen to decrease from 9.6 to 7 V/μm at a current density of 10 μA/cm² with the increase in aspect ratio in the ZnO films. The interrelation between the FE characteristics (emission thresholds, current density, surface uniformity, etc.) and microstructure of the ZnO nanostructure obtained from scanning electron microscopy (SEM) and atomic force microscopy (AFM) was discussed. Quality of the ZnO nanorods was also examined by using Raman spectroscopy and Fourier transformed infrared spectroscopy (FTIR). It was found that the observed enhancements of FE characteristics could mainly be attributed to the increase in aspect ratio and associated number density of ZnO nanorods.     

Optimization of field emission properties from multi-walled carbon nanotubes using ceramic fillers

The field emission properties of multi-walled carbon nanotubes were examined using a screen-printed thick film with a diode-type configuration in a vacuum. The effects of various concentrations of two different ceramic fillers, indium tin oxide (ITO) powder and a glass frit, on the emission current density and turn-on field were evaluated. The emission properties of both pastes were dependent on the amount of filler. Considerably enhanced emission properties were obtained with the paste containing 5–10 wt.% of either ITO or the glass frit compared with those without a filler. The paste containing the ceramic filler showed enhanced emission properties compared with that containing the 5 wt.% Ag conventionally used, which confirmed the importance of the filler. The paste containing 10 wt.% ITO represented an emission current density of 176.4 μA/cm² at 5 V/μA, a turn-on field of 1.87 V/μA for an emission current density of 1 μA/cm² and a field enhancement factor of 7580. The paste formulation was also found to be suitable for fine patterning using UV-lithography techniques. A long-term stability test for 110 h of a paste containing 10 wt.% ITO revealed a half-life of approximately 30000 h, which is appropriate for commercial applications.     

Field-electron emission from polyimide-ablated films

Polyimide-ablated film was deposited by using pulsed laser ablation of a polyimide target, and field-electron emission from the film was observed for the first time. The turn-on field of the polyimide-ablated film is 12 V/μm. The current density is 0.725 mA/cm², and the emission sites density is on the order of 10⁶/cm² at the applied field of 24 V/μm. The field-electron emission measurements indicate that this kind of film could be a new cold cathode material. It is suggested that the graphite-like clusters contained in the film play an important role in the field-electron emission. Received: 2 February 2000 / Accepted: 13 March 2000 / Published online: 9 August 2000     

InN纳米线的低压化学气相沉积及其场发射特性研究

利用低压化学气相沉积方法在以Au作催化剂的Si衬底上生长了InN纳米线. 扫描电子显微镜分析表明，这些纳米线的直径在60—100 nm的范围内, 而其长度大于1 μm.高分辨透射电子显微镜图像表明，合成的纳米线中含有六方相和立方相的InN晶体.这些InN纳米线具有良好的场发射特性和稳定的场发射电流，其开启场为10.02 V/μm(电流密度为10 μA/cm²)，在24 V/μm 的电场下，其电流密度达到5.5 mA/cm².此外，对InN纳米线的场发射机理也进行了讨论. 关键词： InN纳米线 场电子发射 非线性Fower-Nordheim曲线     

A simple method to synthesize worm-like AlN nanowires and its field emission studies

The worm-like AlN nanowires are fabricated by the plasma-enhanced chemical vapor deposition (PECVD) on Si substrates through using Al powder and N₂ as precursors, CaF₂ as fluxing medium, Au as catalyst, respectively. The as-grown worm-like AlN nanowires each have a polycrystalline and hexagonal wurtzite structure. Their diameters are about 300 nm, and the lengths are over 10 μm. The growth mechanism of worm-like AlN nanowires is discussed. Hydrogen plasma plays a very important role in forming the polycrystalline structure and rough surfaces of worm-like AlN nanowires. The worm-like AlN nanowires exhibit an excellent field-emission (FE) property with a low turn-on field of 4.5 V/μm at a current density of 0.01 mA/cm² and low threshold field of 9.9 V/μm at 1 mA/cm². The emission current densities of worm-like AlN nanowires each have a good stability. The enhanced FE properties of worm-like AlN nanowires may be due to their polycrystalline and rough structure with nanosize and high aspect ratio. The excellent FE properties of worm-like AlN nanowires can be explained by a grain boundary conduction mechanism. The results demonstrate that the worm-like AlN nanowires prepared by the proposed simple and the PECVD method possesses the potential applications in photoelectric and field-emission devices.     

Enhanced field emission from pulsed laser deposited nanocrystalline ZnO thin films on Re and W

Nanocrystalline ZnO thin films have been deposited on rhenium and tungsten pointed and flat substrates by pulsed laser deposition method. An emission current of 1 nA with an onset voltage of 120 V was observed repeatedly and maximum current density ∼1.3 A/cm² and 9.3 mA/cm² has been drawn from ZnO/Re and ZnO/W pointed emitters at an applied voltage of 12.8 and 14 kV, respectively. In case of planar emitters (ZnO deposited on flat substrates), the onset field required to draw 1 nA emission current is observed to be 0.87 and 1.2 V/μm for ZnO/Re and ZnO/W planar emitters, respectively. The Fowler–Nordheim plots of both the emitters show nonlinear behaviour, typical for a semiconducting field emitter. The field enhancement factor β is estimated to be ∼2.15×10⁵ cm⁻¹ and 2.16×10⁵ cm⁻¹ for pointed and 3.2×10⁴ and 1.74×10⁴ for planar ZnO/Re and ZnO/W emitters, respectively. The high value of β factor suggests that the emission is from the nanometric features of the emitter surface. The emission current–time plots exhibit good stability of emission current over a period of more than three hours. The post field emission surface morphology studies show no significant deterioration of the emitter surface indicating that the ZnO thin film has a very strong adherence to both the substrates and exhibits a remarkable structural stability against high-field-induced mechanical stresses and ion bombardment. The results reveal that PLD offers unprecedented advantages in fabricating the ZnO field emitters for practical applications in field-emission-based electron sources.     

Morphological effects on the field emission characteristics of zinc oxide nanotetrapods films

The direct growth of a tetrapod-like ZnO nanostructure has been accomplished by using a thermal oxidation method without any catalysts. Studies on the field emission properties of the ordered ZnO nanotetrapods films found that the shape of the ZnO nanotetrapods has considerable effect on their field emission properties, especially the turn-on field and the emission current density. Compared with the rod-like legs ZnO nanotetrapods, the nanotetrapods with acicular legs have a lower turn-on field of 2.7 V/μm at a current density of 10 μA/cm², a high field enhancement factor of 1830, and an available stability. More importantly, the emission current density reached 1 mA/cm² at a field of 4.8 V/μm without showing saturation. The results could be valuable for using the ZnO nanostructure as a cold-cathode field-emission material.      

Low threshold field electron emission from solvothermally synthesized WO2.72 nanowires

Field emission studies of WO_2.72 nanowires synthesized by a solvothermal method have been performed in the planar diode configuration under ultra high vacuum conditions. Fowler–Nordheim plots obtained from the current-voltage characteristics follow the quantum mechanical tunneling process and a current density of ∼8.3×10⁶ μA/cm² can be drawn at an applied electric field of 2 V/μm. The field enhancement factor is 33025, while the turn-on field is only 1.4 V/μm. The emission current-time plot recorded at the pre-set value of emission current of 1 μA over a period of more than 3 h exhibits an initial increase and a subsequent stabilization of the emission current. The results reveal that the WO_2.72 nanowire emitters synthesized by the solvothermal method are promising cathode materials for practical applications.     

Field emission from a-GaN films deposited on Si (100)

Amorphous gallium nitride (a-GaN) films have been deposited on Si (100) substrates using ion-assisted deposition. The deposited films were characterised by X-ray diffraction (XRD) and atomic force microscopy (AFM). XRD confirms the amorphous nature of the films and AFM showed nanostructures in the films. The field electron emission from the film was obtained in a probe-hole field emission microscope, and the current-voltage (I-V) characteristics were studied. The corresponding Fowler-Nordheim (F-N) plots showed a linear behaviour. A current density of 0.1 A/cm² has been obtained for 1.2 V/μm electric field. The field emission current-time (I-t), curves were recorded at a current level of 500 nA for 3 h. The field emission behaviour is compared with that of crystalline GaN as reported in literature.     

ZnO nanorods with different morphologies and their field emission properties

ZnO nanorods with different morphologies were grown by changing the temperature of the process using the thermal vapor deposition method without a catalyst. The X-ray diffraction pattern of these nanorods showed a single-crystalline wurtzite structure and a c-axis orientation. The turn-on fields of the pencil-like and normal ZnO nanorods were 1.7 V/μm and 2.2 V/μm at a current density of 0.1 μA/cm², and the emission current density from the ZnO nanorods reached 1 mA/cm² at bias fields of 5.1 V/μm and 7.5 V/μm, respectively. The results indicated that ZnO nanorods could give sufficient brightness as a field emitter in a flat panel display.     

Electron field emission from magnetic nanomaterial encapsulated multi-walled carbon nanotubes

The present work describes the field emission characteristics of nanoscale magnetic nanomaterial encapsulated multi-walled carbon nanotubes (MWNTs) fabricated over flexible graphitized carbon cloth. Ni/MWNTs, NiFe/MWNTs and NiFeCo/MWNTs have been synthesized by catalytic chemical vapor decomposition of methane over Mischmetal (Mm)-based AB₃ (MmNi₃, MmFe_1.5Ni_1.5 and MmFeCoNi) alloy hydride catalysts. Metal-encapsulated MWNTs exhibited superior field emission performance than pure MWNT-based field emitters over the same substrate. The results indicate that a Ni-filled MWNT field emitter is a promising material for practical field emission application with a lowest turn-on field of 0.6 V/μm and a high emission current density of 0.3 mA/cm² at 0.9 V/μm.     

Carbon nanodot arrays grown as replicas of specially widened anodic aluminum oxide pore arrays

Via a specially widened anodic aluminum oxide (AAO) pore arrays, carbon nanodot arrays with uniform size and high density were obtained through filtered cathodic arc plasma (FCAP) technique. The AAO template was prepared in oxalic acid by multi-steps to get a specially enlarged opening which plays an important role in the deposition of nanodots. The morphology of the nanodots was studied by a field emission scanning electron microscopy (FESEM). The diameter of the as-prepared nanodot demonstrated here is about 100 nm at the bottom and less than 40 nm at the top, and the density was estimated to 10¹⁰ cm⁻². Field emission properties of the nanodot arrays were investigated and a low threshold field of 5.1 V/μm at 10 mA/cm² was obtained. In this paper, the carbon nanodot arrays grown as replicas of the specially widened AAO template may support a strategy to realize the fabrication of nanodot arrays with various materials.     

Structure,transport and field-emission properties of compound nanotubes: CN<Subscript>x</Subscript> vs. BNC<Subscript>x</Subscript> (<Emphasis Type="Italic">x</Emphasis><0.1)

Transport and field-emission properties of as-synthesized CN_x and BNC_x (x<0.1) multi-walled nanotubes were compared in detail. Individual ropes made of these nanotubes and macrofilms of those were tested. Before measurements, the nanotubes were thoroughly characterized using high-resolution and energy-filtered electron microscopy, electron diffraction and electron-energy-loss spectroscopy. Individual ropes composed of dozens of CN_x nanotubes displayed well-defined metallic behavior and low resistivities of ∼10–100 kΩ or less at room temperature, whereas those made of BNC_x nanotubes exhibited semiconducting properties and high resistivities of ∼50–300 MΩ. Both types of ropes revealed good field-emission properties with emitting currents per rope reaching ∼4 μA(CN_x) and ∼2 μA (BNC_x), albeit the latter ropes se- verely deteriorated during the field emission. Macrofilms made of randomly oriented CN_x or BNC_x nanotubes displayed low and similar turn-on fields of ∼2–3 V/μm. 3 mA/cm² (BNC_x) and 5.5 mA/cm² (CN_x) current densities were reached at 5.5 V/μm macroscopic fields. At a current density of 0.2–0.4 mA/cm² both types of compound nanotubes exhibited equally good emission stability over tens of minutes; by contrast, on increasing the current density to 0.2–0.4 A/cm², only CN_x films continued to emit steadily, while the field emission from BNC_x nanotube films was prone to fast degradation within several tens of seconds, likely due to arcing and/or resistive heating. Received: 29 October 2002 / Accepted: 1 November 2002 / Published online: 10 March 2003 RID="*" ID="*"Corresponding author. Fax: +81-298/51-6280, E-mail: golberg.dmitri@nims.go.jp