Laser surface treatment of screen-printed carbon nanotube emitters for enhanced field emission

This paper investigates the surface treatment of screen-printed carbon nanotube (CNT) emitters using a 248 nm (KrF) excimer laser. The field emission characteristics of the CNT emitters are measured following irradiation using laser fluences ranging from 80 to 400 mJ/cm². The results show that the turn-on electric field, the current density, and the distribution of the emission sites are highly dependent on the value of the laser fluence and are optimized at a fluence of 150 mJ/cm². Two distinct laser fluence regimes are identified. In the low fluence regime, i.e. 80-150 mJ/cm², the surface treatment process is dominated by a photo ablation mechanism, which results in the gradual removal of the binding material from the cathode surface and leads to an improvement in the emission characteristics of the CNT cathodes with an increasing fluence. However, in the high fluence regime, i.e. 150-400 mJ/cm², the thermal ablation mechanism dominates; resulting in a removal of the CNTs from the cathode surface and a subsequent degradation in the emission characteristics.     

Time-dependent interaction across two conducting spheres in an applied electrostatic field

Charged particles exist widely in variety of technological areas as well as in nature. Even a weak charge on the particles can significantly influence their electric interaction. We investigated the phenomenon of time-dependent electric interaction between two conducting spheres in an electrostatic field. A mirror-image method was developed to analyze this system, and the fundamental role of the charges on the spheres was studied. We concluded that charges conducted to the lower sphere through the alumina tube used in our system play a main role in determining the time-dependent interaction, whereas the influence from air ions is negligible.     

Enhanced field emission properties of screen-printed doubled-walled carbon nanotubes by polydimethylsiloxane elastomer

Field emission (FE) properties of double-walled carbon nanotubes (DWCNTs) treated by polydimethylsiloxane (PDMS) elastomer with different heating temperature have been systematically studied. The current density of treated DWCNT films decreases with the increase of heating temperature. The screen-printed DWCNTs treated by PDMS elastomer with drying temperature 150 °C for 20 min have the best FE performance with a marvelous field enhancement factor (β = 20194). The optimized FE performance is attributed to the morphological change of DWCNT films after PDMS elastomer treatment and the change of separation energy for the CNT-substrate interface. It is proved that the PDMS treatment is a facile and effective method for field emission display (FED) application, especially for low-temperature FED preparation.     

A hybrid aerodynamic and electrostatic atomization system for enhanced uniformity of thin film

Droplet deposition processes by the mechanisms of either aerodynamics or electrostatic spray have been widely studied in various applications such as aerosol generators, thin film coatings, and nanoparticle formations. Among the current state-of-art methodologies, air spray deposition can produce small-sized droplets without fine control on their sizes and uniformity in deposited thin films. Conventional electrospray depositions, on the other hand, can fabricate thin films with good uniform with a relatively slow deposition speed. In this paper, a hybrid mechanism by means of aerodynamic and electrostatic deposition is investigated and demonstrated to allow high throughput and improved uniformity for thin film depositions. It utilizes both the electrostatic force and aerodynamic force to atomize the liquid and control the droplet spraying process with good stability/repeatability. A uniform thin TiO₂ film has been deposited as the demonstration example using this method. The velocities and trajectories of droplets during the deposition process have been characterized under different experimental parameters by using the technique of particle image velocimetry (PIV). This hybrid thin film fabrication method could be applicable in several industrial processes for better uniformity in making transparent electrodes, solar cells, displays, and automobiles.     

静电场对静止液体压强的影响

论述了由于静电场的存在,在大气压力场中,静止液体内任意两点间的压强差与重力和静电场力的关系.     

静电场描绘仪的改进

利用稳恒电流场在导体中的分布可以模拟静电场的分布．传统的静电场描绘仪存在着一系列缺陷,针对传统静电场描绘仪的不足作了部分的改进．通过实验比较,改进后的描绘仪能很好地模拟静电场．     

A mathematical model of external electrostatic field of a special collector for electrospinning of nanofibers

This article focuses on the analysis of electrostatic field generated by a special collector consisting of two parallel cylindrical conductors used for electrospinning. Computed values of critical electrical potential obtained by an analytical model are compared with measurements. Here we show that the gap distance between the special collector and a spinning electrode, i.e., a syringe needle, has not substantial effect on the critical potential if the special collector distance from the syringe needle is higher than the gap distance between cylindrical conductors. The presented model is a good analytical approximation of electric field created by the used special collector.     

The measurement of atmospheric electric fields using pole mounted electrostatic fieldmeters

A pole mounted ‘field mill’ type electrostatic fieldmeter provides a simple and practical way for measurement, and for long term continuous monitoring, of ground level atmospheric electric fields. The paper describes a number of studies of this measurement method. These show how atmospheric electric field values are derived from the response of the fieldmeter when earth bonded and its height above ground level. The response of the fieldmeter is calibrated via the linear variation of its response to voltage applied during the set up procedure. The studies confirm a linearity of fieldmeter response with height above ground.     

Water vapor-induced structure modification of vertically-aligned carbon nanotube arrays and successive thin film coating for enhanced field emission properties

Vertically-aligned carbon nanotubes (VCNTs) are used as electron source in various field emission applications owing to its high aspect ratio, chemical inertness, mechanical strength and electrical conductivity. Here, we demonstrate that surface structure modification along with thin film coating enhances the field emission performance, such as turn-on voltage, emission site density, and stability. In the present study, VCNTs with different heights were grown on silicon wafers by thermal chemical vapor deposition followed by the structure modification of VCNTs using capillarity-driven water vapor condensation. We obtained various surface morphologies by varying the water vapor exposure time and heating temperature. In addition, the structure-modified VCNTs surfaces were coated with W and SiO₂ thin films using electron-beam evaporation. It was observed that W-coated VCNTs with modified surface morphology results in the best field emission performance.     

恒定流速场与静电场、静磁场的类比

本文将“物理类比法”引入大学物理电磁学部分的教学,将恒定流速场与静电场和静磁场在特征量、场的分布及其描述等方面进行了类比,使学生对电磁场有一个较清晰和全面的认识,对电磁学的理论有一个较深刻的理解和掌握,收到了较理想的教学效果.     

Focusing properties of a bounded cylindrical field

Numerical solution of motion equations has been used in the non-relativistic limit in order to determine the focussing properties of the cylindrical field between concentric cylinders of radii R₁, R₂ with two boundaries along the Z-axis, for charged particles entering the field parallel to the symmetry axis. The field is a solution of the Laplace equation ²U(R, Z)=0, with the boundary conditions as follows: U(R₁, Z)=U(R, 0)=U(R, L)=0, U(R₂, Z)=V. It was shown that this field can be used for the energy analysis with second order focussing.     

两平行相交带电圆柱导体的空间电场

用镜象法求解由两平行相交带电圆柱导体所组成的柱形导体边界静电场边值问题,通过简单的数学分析,获得两类平行相交带电圆柱导体问题的空间电场分布．     

N离子注入对金刚石膜场发射特性的影响

不同剂量的N离子被注入到化学气相沉积金刚石膜内，研究了表面结构及场发射特性的变化.Raman谱和x射线光电子能谱分析表明，N离子的注入破坏了金刚石膜表面原有的sp3结构，并在膜内形成大量的sp2 C—C 和sp2 C—N 键.样品的场发射测试显示N离子的注入显著提高了金刚石膜场发射特性，膜的场发射阈值电场从注入前的18 V/μm下降到注入后的4 V/μm.金刚石膜场发射特性的提高归因于N离子注入后膜内sp2 C键含量的增加和体内缺陷带的形成，这些变化能改变膜的表面功函数，提高Feimi能级，降低电子隧穿表面的能量势垒. 关键词： 场致电子发射 N离子注入 金刚石膜 热丝化学气相沉积     

Synthesis and field emission properties of GaN nanowires

Gallium nitride (GaN) nanowires grown on nickel-coated n-type Si (1 0 0) substrates have been synthesized using chemical vapor deposition (CVD), and the field emission properties of GaN nanowires have been studied. The results show that (1) the grown GaN nanowires, which have diameters in the range of 50-100 nm and lengths of several micrometers, are uniformly distributed on Si substrates. The characteristics of the grown GaN nanowires have been investigated using X-ray diffraction (XRD) and transmission electron microscopy (TEM), and through these investigations it was found that the GaN nanowires are of a good crystalline quality (2) When the emission current density is 100 μA/cm², the necessary electric field is an open electric field of around 9.1 V/μm (at room temperature). The field enhancement factor is ∼730. The field emission properties of GaN nanowires films are related both to the surface roughness and the density of the nanowires in the film.     

Fabrication and properties of film-under-gate field emission arrays with SnO2 emitters for flat lamp

The film-under-gate field emission arrays (FEAs) have been fabricated on the glass substrates by conventional photolithography, anodic oxidation and lift-off method. SnO₂ emitters were deposited on the cathode electrodes of under-gate triode by screen printing. The image of film-under-gate field emission arrays with SnO₂ emitters was measured by the optical microscopy and field emission scanning electron microscopy (FESEM). The electric field distributions and electron trajectories of film-under-gate triode were simulated in the same anode voltage and different gate voltage by ANSYS. I-V characteristics of film-under-gate triode with SnO₂ emitters were investigated. It indicated that the SnO₂ emitters by screen printing uniformly distributed on the surface of cathode electrodes. The maximum anode current in this triode structure could come to 385 μA and the highest lightness was approximately 270 cd/m² as the gate and anode voltage was 140 V and 2000 V, respectively, at the anode-cathode spacing of 1100 μm. Moreover, the emission current fluctuation was less than 5% for 8 h. It showed that the fabricated device has a good stability of field emission performance and long lifetime, which may lead to practical applications for field emission electron source based on flat lamp for back light units (BLUs) in liquid crystal display (LCD).     

Comparison of atmospheric electric field measurements by a pole mounted fieldmeter and by a horizontal wire antenna

The studies reported show that measurements of atmospheric electric fields by pole mounted electrostatic fieldmeters can match measurements by a horizontal antenna wire. Some differences were experienced early in the tests that cannot yet be explained. The differences are tentatively attributed to tribocharging actions during initial set up of the antenna system and by wind blown airborne particulates at the antenna wire. Pole mounted fieldmeters provide opportunity for long term unattended measurements in quite adverse weather conditions with continuous checking of operational health against debris, spider's webs, etc.     

静电场环路定理的非抵消法证明

在普通物理学中,"静电场环路定理"是一个重要的基本定理.与一般教科书中的证明方法--"抵消法"不同,提出了另外两种巧妙而更为简单的非抵消法的证法.     

Electrochemical properties of nanostructured lanthanum strontium manganite cathode fabricated by electrostatic spray deposition

Electrostatic spray deposition was applied to prepare nanoporous lanthanum strontium manganite (LSM) films with high specific surface area (37.34 m²/g) for the cathode application in solid oxide fuel cell (SOFC). The electrochemical characteristics were investigated at a temperature range from 546 to 777 °C and oxygen partial pressure from 0.01 to 1.0 atm. The diffusion of atomic oxygen and oxygen ion transfer from three-phase boundary to the YSZ electrolyte were found to be the rate-determining steps for oxygen reduction reaction on LSM cathode. The polarization resistance of the LSM prepared using electrostatic spray deposition decreased from 15 to 1.2 Ωcm² with increasing temperature from 546 to 777 °C and the activation energy was 0.81 eV. It was demonstrated that the ESD method offers a promising approach for the preparation of electrochemically active nanoporous layers, particularly applicable for solid oxide fuel cells.     

Deposition conditions in tailoring the morphology of highly porous reticular films prepared by electrostatic spray deposition (ESD) technique

Spongy-like reticular structure is a unique morphology fabricated by electrostatic spray deposition (ESD) technique. The effects of solvent, substrate temperature, precursor feeding rate, static electric field strength, and deposition time on tailoring the reticular structure were investigated. Scanning electron microscopy was used to observe the film morphology. MnO_x or LiMn₂O₄ were selected as the model materials. It is found that in addition to the conventional solvent butyl carbitol, other kinds of solvents such as ethylene glycol and propylene glycol can also be used to obtain reticular films at a suitable substrate temperature. Porous films with a low cross-linking degree pore structure can be prepared by increasing precursor feeding rate or decreasing substrate temperature. Increasing the deposition time or the electric field strength helps to obtain reticular films with more homogeneous pore size distribution. In addition, the addition of a high boiling-point solvent in mixed alcohol solvent results in the increase of proper substrate temperature. It is concluded that the fluidity of the spray droplets on the surface of a hot substrate is an important factor to form a reticular film.