Limitation of the current from nanographite multiemitter field-emission cathodes

The limiting field-emission current of a nanographite film cathode is studied experimentally. The maximal field-emission current density reaches 1 A/cm². Experimental data agree with numerical estimates based on the general theory of field emission with regard to features inherent in nanostructured carbon materials.     

大电流碳纳米管场发射阴极研究

报道了在较大发射面积上获得较大场发射电流的碳纳米管场发射阴极。为了加强场发射电流,在丝网印刷浆料中增加一种金属纳米颗粒,金属颗粒增强了碳纳米管发射体和衬底的接触,提高碳纳米管和衬底的粘附作用。利用改进后的丝网印刷方法制备了大电流碳纳米管场发射阴极,测得最大发射电流为68.0 mA,阴极有效发射面积约1.1 mm2,发射电流密度约6.2 A/cm2;并成功将改进方法制备的大电流场发射碳纳米管阴极应用于场发射真空器件原型。实验证明这种具有较大发射电流和较大发射电流密度的场发射能够满足部分大功率电子器件的需求。收稿日期:; 修订日期:     

大电流碳纳米管场发射阴极研究

报道了在较大发射面积上获得较大场发射电流的碳纳米管场发射阴极。为了加强场发射电流,在丝网印刷浆料中增加一种金属纳米颗粒,金属颗粒增强了碳纳米管发射体和衬底的接触,提高碳纳米管和衬底的粘附作用。利用改进后的丝网印刷方法制备了大电流碳纳米管场发射阴极,测得最大发射电流为68.0 mA,阴极有效发射面积约1.1 mm2,发射电流密度约6.2 A/cm2;并成功将改进方法制备的大电流场发射碳纳米管阴极应用于场发射真空器件原型。实验证明这种具有较大发射电流和较大发射电流密度的场发射能够满足部分大功率电子器件的需求。收稿日期:; 修订日期:     

On the feasibility of observing electron antibunching in a field-emission beam

In contrast to the belief that low degeneracy and short coherence time prevent the direct observation of fermion anticorrelation in a free particle beam, it is shown that the antibunching of electrons in a field-emission electron beam should, in principle, be observable with current technology. This opens a gateway to fundamentally new tests of quantum mechanics.     

On the field-emission properties of sulfide minerals under high-power nanosecond pulses

The mechanism of absorption of the energy of high-power electromagnetic nanosecond pulses due to the field emission from the surface of natural semiconductors is considered. The limitations and possibilities of implementing this mechanism in sulfide minerals (pyrite and arsenopyrite) are demonstrated.     

Hot nanotubes: stable heating of individual multiwall carbon nanotubes to 2000 k induced by the field-emission current

Field emission (FE) electron spectroscopy from an individual multiwalled carbon nanotube (MWNT) is used to measure quantitatively stable temperatures at the apex, T(A), of up to 2000 K induced by FE currents approximately 1 microA. The high T(A) is due to Joule heating along the length of the MWNT. These measurements also give directly the resistance of the individual MWNT which is shown to decrease with temperature, and explain the phenomenon of FE-induced light emission which was observed simultaneously. The heating permits thermal desorption of the MWNT and, hence, excellent current stability.     

Effect of molecules adsorbed on the cathode surface on the prebreakdown field-emission current at the initial stage of a high-voltage gas discharge

Formulas for calculating the prebreakdown current density are derived taking into account the present of clusters of adsorbed atoms, polar and nonpolar molecules, as well as nanofilms on the cathode surface. It is shown that the expression for the current-voltage characteristic is an analog of the Fowler-Nordheim equation in all cases. The presence of a thin nonmetallic film necessitates the replacement of the Nordheim function by any tabulated function that can also be expressed in terms of elliptic integrals. If the degree of coating is smaller than unity, corrections should be introduced into the expression for the work function.     

Bi-layer steady state current cloak

We report that bi-layer copper and polystyrene cylinders can cloak steady current. We fabricated two hollow cylinders, the one made of copper, and the other made of polystyrene. Two hollow copper and polystyrene cylinders nested concentric bi-layer hollow copper and polystyrene cylinders. The background media are made of aluminum. Theory and experiment demonstrated that the electric potential gradients are parallel and equal outside the outer circle, the iso-potential lines are parallel outside the outer circle, and the electric potential is zero in the inner circle.     

Statistical simulation of the energy spectra of field-emission electrons

Random energies of electrons that escape from the source in the course of field emission are simulated using energy spectra. A relationship of the random values of total energy and the energy related to the normal (with respect to surface) component of momentum is established. A family of quadrature formulas needed for the integration of the distribution density of particles is analyzed. A hypothesis on the compliance of selected random energies with desired distribution laws is statistically tested.     

On the effect of laser irradiation and heat treatment on the structure and field-emission properties of carbon nanowalls

The composition and structure of carbon nanowalls formed on silicon substrates from the gas phase of hydrogen and methane activated by a direct-current glow discharge are studied by methods of scanning electron microscopy, X-ray diffractometry, IR spectroscopy, and Raman spectroscopy. It is shown that nanowalls are comprised of a porous material consisting of curved lamellar (flaky) crystallites with a thickness of 3–10 nm. The effect of heat treatment and laser irradiation in air on the structure of the carbon nanowalls is studied, and the current–voltage characteristics of field-emission cathodes on their basis are obtained. The heating temperatures and laser-radiation power densities at which the morphology of the surface of carbon nanowalls changes and the characteristics of field-emission cathodes on their basis are determined.     

Ultrahigh-spatial-resolution field-emission projection microscopy of insulating samples

The method of ultrahigh-spatial-resolution field-emission projection imaging of nonconducting tips is implemented experimentally. An image of a glass microcapillary tip was obtained for the first time by the nonscanning method with spatial resolution no worse than 20 nm.     

Preliminary study of KCl by field-emission microscopy

Small projections of KCl grown on the tungsten substrate from the saturated solution were observed by field-emission microscopy in an ultrahigh vacuum. The observed fieldemission patterns consisted of many bright spots with different sizes and brightness, and some of the bright spots repeated periodically disappearance and reappearance under the application of a constant voltage at lower temperatures. The spots increased in number and in brightness as the applied voltage and the substrate temperature were increased. A phenomenon which seems to be a kind of vacuum arc was frequently observed with a periodicity and its period was found to decrease with increasing the applied voltage.     

Dielectric response enhancement in the current carrying CDW state

The dc electric field dependence of the low frequency dielectric constant was investigated in the linear chain compound orthorhombic TaS₃. While the dielectric constant is barely effected by an applied dc field below the threshold field of the nonlinear conduction, in the current carrying state a large enhancement is observed. Inductive response at the narrow band noise frequency was also detected.     

Spin polarized current in the ground state of superconductor-ferromagnet-insulator trilayers

We study the ground state properties of a superconductor-ferromagnet-insulator trilayer on the basis of a Hubbard Model featuring exchange splitting in the ferromagnet and electron-electron attraction in the superconductor. We solve the spin-polarized Hartree-Fock-Gorkov equations together with the Maxwell's equation (Ampere's law) fully self-consistently with respect to the order parameter and the current. For certain values of the exchange splitting we find that a spontaneous spin polarized current is generated in the ground state and is intimately related to Andreev bound states at the Fermi level. Moreover, the polarization of the current strongly depends on the band filling. Received 23 September 2002 / Received in final form 13 December 2002 Published online 1st April 2003 RID="a" ID="a"e-mail: m.a.krawiec@bristol.ac.uk     

Synthesis and field-emission properties of the tungsten oxide nanowire arrays

High-density, uniformly distributed and quasi-aligned tungsten oxide nanowire arrays have been synthesized by a conventional thermal evaporation approach on indium tin oxide (ITO) coated glass substrates without any catalysts. The temperature of the substrate was . The tungsten oxide nanowires are single crystalline with growth direction of [0 1 0]. For commercial applications, field emission properties of tungsten oxide nanowires were studied under a poor vacuum at room temperature. The electron field-emission turn-on field (E_to), defined as the macroscopic field required to produce a current density of , is about . The performance reveals that the tungsten oxide nanowire arrays can be served as a good candidate for commercial application in field-emission displays.     

Optimization of the parameters of a carbon nanotube-based field-emission cathode

A procedure for optimizing a field-emission cathode based on carbon nanotubes (CNTs) is developed. An array of identical equidistant vertical CNTs is considered. The optimization procedure takes into account the effect of screening of an electric field by neighboring nanotubes by solving a Laplace equation and the thermal instability of nanotubes, which limits the emission current density of a nanotube, by solving a heat conduction equation. The relation between the emission current and the applied voltage is described by the Fowler-Nordheim relationship containing the CNT tip temperature as a parameter. Upon optimization, the optimum distance between CNTs that ensures the maximum emission current density is calculated. The calculation results demonstrate that this parameter depends substantially on both the applied voltage and the nanotube geometry. These dependences are weakly sensitive to the choice of the transport coefficients (thermal conductivity, electrical conductivity) of nanotubes.     

The current state of public understanding of nanotechnology

The growing importance of nanotechnology in industry and society has not been accompanied by a widespread understanding of the subject among the general public. Simple questions to initially probe the smallest thing that people can see and can think of reveals a divide in the understanding of the general public. A survey of 1500 individuals ranging in age from 6 to 74 has revealed a lack of knowledge of nanotechnology and especially a lack of understanding of the context of nanotechnology in the world that is too small to see. Survey findings are corroborated by in-depth interviews with 400 adults in studies of nanoscience literacy commisioned by University of California, Berkeley and Cornell in 2002 and 2004, respectively. In general, with the exception of 14–28 year olds, over 60% of respondents say they have never heard of nano or nanotechnology. The results suggest that the general public, especially middle-school children, has no firm foundation to understand nanotechnology and likely will continue to be equally impressed by credible scientific information as well as pure fictional accounts of nanotechnology.     

The use of carbonaceous materials as field-emission cathodes

The advantages and disadvantages of carbon fibers and graphite plates with a developed surface as field-emission cathode materials are discussed. Experimental data for the chemical composition of the materials and the effect of thermal annealing on their structure and emission properties are presented. A correlation between the work function and the amount of cesium implant is studied. The feasibility of preparing planar cold cathodes with a developed surface by means of radiation technologies is considered, and the evolution of the emitting surface during bombardment by low-energy residual gas ions is traced. Cold cathode designs for various applications are recommended.