Observation on CNT-FED under various vacuum levels and calculation on number of electron–gas collisions

Based on experimental observation and theoretical analysis, it explicates that light emission of a carbon nanotube-field emission display (CNT-FED) is mainly caused by electron bombardment on the phosphour if the level of vacuum ranges from 10⁻⁴ to 5 Pa. In this case, light emission of the phosphour excited by ultraviolet (UV) light derived from gas discharge cannot be observed. If vacuum level is greater than 5 Pa, no emitted light is observed, since a large amount of gas ionisation reduces the electric potential difference between the cathode and the anode. To analyze collision between electron and gas under field emission conditions, a mathematical and physical model was built. Based on this model the number of electron–gas collisions is calculated. Calculations results indicate that the product of gas pressure and distance between the electrodes (pd) is a better parameter to characterize the effect of vacuum level for FED than gas pressure only. Calculations results also show that if the distance between the cathode and the anode is increased, it should be to improve the vacuum level to obtain the same effect.     

小波神经网络在场发射开启电场预测中的应用

文章利用小波神经网络模型,结合薄膜场发射的特性建立了场发射开启电场的神经网络预测模型,并用碳纳米管薄膜的开启电场数据样本进行验证。结果表明,该模型预测的相对误差小于4.6%,具有很好的预测性能。     

Development of a parallel Poisson's equation solver with adaptive mesh refinement and its application in field emission prediction

A parallel electrostatic Poisson's equation solver coupled with parallel adaptive mesh refinement (PAMR) is developed in this paper. The three-dimensional Poisson's equation is discretized using the Galerkin finite element method using a tetrahedral mesh. The resulting matrix equation is then solved through the parallel conjugate gradient method using the non-overlapping subdomain-by-subdomain scheme. A PAMR module is coupled with this parallel Poisson's equation solver to adaptively refine the mesh where the variation of potentials is large. The parallel performance of the parallel Poisson's equation is studied by simulating the potential distribution of a CNT-based triode-type field emitter. Results with ∼100 000 nodes show that a parallel efficiency of 84.2% is achieved in 32 processors of a PC-cluster system. The field emission properties of a single CNT triode- and tetrode-type field emitter in a periodic cell are computed to demonstrate their potential application in field emission prediction.     

结合多空间特征的多尺度马尔可夫随机场彩色图像分割

提出了一种结合多空间特征的多尺度马尔可夫随机场(MRF)模型——MS-MRMRF。针对RGB单空间对彩色图像描述不足的问题,模型首先将图像转化为HSV空间并与RGB空间结合形成多空间特征;然后根据多空间特征的形式,提出了一种模糊化估参的多尺度MRF模型对其进行分割。彩色图像的分割实验表明：相比现有的单空间特征的多尺度MRF算法,结合多空间特征的多尺度MRF可以有效地提高分割精度。     

Differential pulse voltammetric determination of N-acetylcysteine by the electrocatalytic oxidation at the surface of carbon nanotube-paste electrode modified with cobalt salophen complexes

The preparation and electrochemical performance of the carbon nanotube-paste electrode modified with salophen complexes of cobalt(III) perchlorate, with various substituents on the salophen ligand, as well as their electrocatalytic activity toward the oxidation of N-acetylcysteine (NAC) is investigated. Several Schiff base complexes containing various nucleophilic and electrophilic functional groups were prepared, and their electrochemical characteristics for the electro-oxidation of NAC were evaluated using cyclic and differential pulse voltammetry (CV and DPV). The results revealed, the modified electrodes show an efficient and selective electrocatalytic activity toward the anodic oxidation of NAC among biologically important compounds in buffered solutions at pH of 7.0. The best voltammetric responses were obtained for a carbon-paste electrode (CPE) modified with a salophen complex containing para-methoxy groups on its salicylaldehyde ring. The analytical response of the modified electrode for response to other sulfhydryl compounds (e.g., cysteine, penicillamine, captopril and mercaptopropionyl glycine) in comparison to NAC was investigated by CV and DPV methods. The DPV method was applied as a sensitive method for the quantitative detection of the trace amounts of NAC. A linear dynamic range from 1 × 10⁻⁷ to 1 × 10⁻⁴ M with calibration sensitivity of 0.0646 μA/μM is resulted for NAC in DPV measurements. The detection limit was 5 × 10⁻⁸ M, which is remarkably lower than those reported previously for NAC using other modified electrodes. The results of voltammetric determinations show a very good reproducibility, and the R.S.D. for the slope of the calibration curve, based on 10 measurements in a period of two months, was <3.9%. The detection system provides very stable electrochemical responses toward NAC, makes it very suitable for using in pharmaceutical and clinical measurements.     

Switching of carbon‐nanotube emitters by an integrated MOSFET

Abstract— The integration of carbon‐nanotube (CNT) emitters with a metal‐oxide‐semiconductor field‐effect transistor (MOSFET) can stabilize and control the emission current of CNTs. CNTs were grown by using the resist‐assisted patterning (RAP) process and plasma‐enhanced chemical vapor deposition (PECVD) and were connected to the drain part of an external MOSFET. The electron‐emission current of CNTs was switched by applying a low gate voltage to the MOSFET, and the switching current was very stable because the MOSFET was operated in the saturation region. Based on these results, the emission current of CNTs was stabilized and switched by using a low‐voltage‐driven MOSFET.     

Effect of MgZnO-bilayer/BA-CH3 combination interlayer on emission characteristics of MoO3/F8BT/ZnO hybrid light emitting diodes fabricated on ZnO/Ag/ZnO transparent cathode

The characteristics of MoO₃/F8BT/ZnO inorganic/organic hybrid light emitting diodes (IO-HyLEDs) fabricated on ZnO/Ag/ZnO dielectric/metal/dielectric (DMD) and conventional ZnO/ITO were investigated. The DMD had a low sheet resistance of 9 Ω/sq and a high transmittance of 90.7%. The device fabricated on DMD showed similar current density–voltage (J–V) and luminance–current density (L–J) characteristics to that on ZnO/ITO, indicating the possibility of DMD as a promising transparent conductive layer for IO-HyLEDs. The maximum luminous intensity of 237,000 cd/m² was demonstrated under pulsed condition for the DMD device. We also investigated the effect of the combination interlayer (CIL) at the F8BT/ZnO interface on the IO-HyLEDs. The CIL was composed of a Mg_0.52Zn_0.48O/Mg_0.25Zn_0.75O bilayer and a self-assembled dipole molecule (SADM) of BA-CH₃. The devices with CIL exhibited an approximately threefold enhancement of the luminous intensity and efficiency in comparison with the devices without CIL. This improvement was considered to be brought about by the enhancement of the electron injection efficiency by CIL.     

基于PSO的SVM的煤岩声发射源定位研究

为了准确的预测采空区煤矿煤岩破裂与失稳前岩石所释放出来的声发射信息的位置,并且根据山西焦煤的官地矿16403工作面获得的声发射事件的数据,因为该数据是一个非线性、高维的问题,提出了用PSO和SVM算法相结合的方法在煤矿煤岩声发射定位中的应用进行了研究。以往的方法只是单纯的收集煤岩或岩石声发射信息,以至于定位会出现失准、精度低和误差大的缺点。文章提出了“1+1=1”的定位方法,既收集同一位置的岩石和煤岩体的声发射信号,分析处理后,得到其位置。在煤岩失稳前两者都会发出强烈的信号。仿真结果表明：应用PSO和SVM理论结合的方法进行煤矿煤岩声发射定位的预测,在提高准确性和精确度的同时,也大大的提高了泛化的能力,该方法也大大减小定位失准的误差。     

Direct excitation of xenon by ballistic electrons emitted from nanocrystalline‐silicon planar cathode and vacuum‐ultraviolet light emission

Abstract— To verify the possible use of energetic electrons for direct excitation of inert gas molecules, a nanocrystalline‐silicon (nc‐Si) planar ballistic emitter is operated in a high‐pressure xenon gas ambience. Under the pulse drive, vacuum‐ultraviolet (VUV) light emission is detected without any signs of discharge. The transient behavior of the VUV light emission properly corresponds to that of the nc‐Si emitter. In accordance with quantitative analyses of electron‐emission characteristics and the VUV output, the electron‐to‐photon conversion efficiency reaches 81% in the relatively efficient emitter case. The VUV output power is mainly determined from the number of electrons with energies compatible the with internal excitation of xenon. The emission spectrum observed at a pressure of 10 kPa shows peaks at 152 and 172 nm, which are thought to be originated from metastable Xe²* states. In contrast to the case of conventional impact ionization, no near‐infrared (NIR) peaks are seen in the spectrum. These results strongly suggest that the incidence of energetic electrons causes direct excitation of xenon molecules followed by radiative relaxation through intermediate states. The generated VUV light can be easily converted to visible light using a phosphor screen. As a discharge‐free VUV light emission, this phenomenon is potentially applicable to mercury‐free, high‐efficacy, and high‐stability flat‐panel light‐emitting device.     

Film surface morphology and field‐emission characteristics of a carbon‐nanotube array pattern fabricated under a magnetic field

Abstract— This study focuses on the influence of sodium metasilicate binder on CNT paste and the arrangment of Mg‐Ni alloy multi‐walled carbon nanotubes on the surface of CNT film under the influence of a magnetic field. The CNT paste was prepared by mixing CNTs with silver epoxy resin and sodium metasilicate solution and coating them onto the surface of indium tin oxide (ITO) glass. The impact of sodium metasilicate solution and magnetic strength on the morphology of the paste film's surface and on the field‐emission (FE) characterics of the cathode was examined. The experimental results showed that the CNT paste provided good adhesion between the CNT array and silver epoxy resin when sodium metasilicate solution was presented. CNT paste containing sodium metasilicate showed a better dispersion with silver epoxy resin and a better CNT‐array pattern, and better vertical alignment of the CNT was obtained when the magnetic field and grid were both appied. An optimal condition for a better CNT‐array pattern for both the morphology and FE characteristics had a magnetic strength of 1 89 mT, magnetization time of 30 min, and a grid above the cathode.     

改进的分布估计算法求解软硬件划分问题

软硬件划分是软硬件协同设计中的关键步骤,为NP难问题。分布估计算法可以解难优化问题,具有很好的全局搜索能力,但存在局部搜索能力差、种群多样性易失问题。针对此问题,对分布估计算法进行改进,对精英解进行克隆选择以加强局部搜索能力,对概率模型进行修正以改善种群多样性损失问题。同时,针对划分问题提出一种不可行解的修复方法。将改进后的分布估计算法应用于软硬件划分问题,并与现有算法做比较,结果表明所提算法在不同的约束条件下均可获得更好的优化结果。     

An ab initio study of the magnetic and electronic properties of Fe, Co, and Ni nanowires on Cu(001) surface

Magnetism at the nanoscale has been a very active research area in the past decades, because of its novel fundamental physics and exciting potential applications. We have recently performed an ab initio study of the structural, electronic and magnetic properties of all 3d transition metal (TM) free-standing atomic chains and found that Fe and Ni nanowires have a giant magnetic anisotropy energy (MAE), indicating that these nanowires would have applications in high density magnetic data storages. In this paper, we perform density functional calculations for the Fe, Co and Ni linear atomic chains on Cu(001) surface within the generalized gradient approximation, in order to investigate how the substrates would affect the magnetic properties of the nanowires. We find that Fe, Co and Ni linear chains on Cu(001) surface still have a stable or metastable ferromagnetic state. When spin–orbit coupling (SOC) is included, the spin magnetic moments remain almost unchanged, due to the weakness of SOC in 3d TM chains, whilst significant orbital magnetic moments appear and also are direction-dependent. Finally, we find that the MAE for Fe, and Co remains large, i.e., being not much affected by the presence of Cu substrate.     

Simultaneous determination of N-acetylcysteine and acetaminophen by voltammetric method using N-(3,4-dihydroxyphenethyl)-3,5-dinitrobenzamide modified multiwall carbon nanotubes paste electrode

A new dopamine-derivative, i.e. N-(3,4-dihydroxyphenethyl)-3,5-dinitrobenzamide (N-DHPB), was synthesized and its application was investigated for the simultaneous determination of N-acetylcysteine (NAC) and acetaminophen (AC) using modified multiwall carbon nanotubes paste electrode. This modified electrode exhibited a potent and persistent electron mediating behavior followed by well separated oxidation peaks of NAC and AC. The peaks current of differential pulse voltammograms of NAC and AC increased linearly with their concentration in the ranges of 0.5-200 μmol L⁻¹ NAC and 15.0-270 μmol L⁻¹ AC. The detection limits for NAC and AC were 0.2 μmol L⁻¹ and 10.0 μmol L⁻¹, respectively. The relative standard deviation for seven successive assays of 1.0 and 30.0 μmol L⁻¹ NAC and AC were 1.7% and 2.2%, respectively. The proposed sensor was successfully applied for the determination of NAC in human urine, tablet, and serum samples.     

Fabrication at wafer level of miniaturized gas sensors based on SnO2 nanorods deposited by PECVD and gas sensing characteristics

SnO₂ nanorods were successfully deposited on 3″ Si/SiO₂ wafers by inductively coupled plasma-enhanced chemical vapour deposition (PECVD) and a wafer-level patterning of nanorods layer for miniaturized solid state gas sensor fabrication were performed. Uniform needle-shaped SnO₂ nanorods in situ grown were obtained under catalyst- and high temperature treatment-free growth condition. These nanorods have an average diameter between 5 and 15 nm and a length of 160-300 nm. The SnO₂-nanorods based gas sensors were tested towards NH₃ and CH₃OH and gas sensing tests show remarkable response, showing promising and repeatable results compared with the SnO₂ thin films gas sensors.