Synthesis of straight multi-walled carbon nanotubes by arc discharge in air and their field emission properties

The possibility of preparing straight multi-walled carbon nanotubes (MWCNTs) on a large scale is demonstrated using direct current arc discharge with a rotating graphite anode in low pressure air. The process is time-saving, economical, and non-hazardous. It is found that the optimum air pressure for the highest yield of MWCNTs is about 60 Torr. Investigation of the internal organization of the cathode deposit reveals that many columns about 40 μm in diameter are closely packed and mechanically stable. The highest content of MWCNTs is found in the intercolumnar spaces between columns. Emitters made of the cathode deposits that contain a large number of straight nanotubes exhibit outstanding field emission properties. The turn-on electric field decreases from 1.44 to 0.93 V/μm and the field enhancement factor β increases from about 3,190 to 7,830 only after simple burning at 750 °C for 30 min in air. The results indicate that MWCNTs prepared by arc discharge in air are promising for field emission application.     

Effects of residual gas exposure on the field emission properties of ZnO nanorods

We compare the effects of O2, CO2, N2, H2, and Ar residual gas exposure on the field emission (FE) properties of ZnO nanorods. In contrast to carbon nanotubes and Mo metal microtips, we find that O2 and CO2 exposures do not significantly degrade the FE properties of ZnO nanorods. However, N2 exposure significantly degrades the FE properties. We propose that this could be due to the dissociation of N2 into atomic nitrogen species and the reaction of such species with ZnO. H2 and Ar exposures are not observed to significantly degrade the FE properties.     

Spectral properties of a diffuse-constricted arc discharge

An extensive high-current electric discharge under atmospheric pressure is characterized by considerable instability, unless special measures for its stabilization are assumed (e.g., by the walls, electrodes, rotational twist, etc.). For the experimental investigation of such a discharge, both the complex diagnostics of electrical and spectral properties have been applied, supplemented with synchronous video filming of the discharge gap. The information on the spectral composition of the radiation of different discharge sections can be obtained by measuring with a system of optical fibers. Spectral measurements at the selected point of space at various moments of time make it possible to determine the alteration dynamics of plasma composition near the reference spots, as well as far from them.     

脉冲电弧源的发射特性建模

脉冲电弧源是脉冲电弧离子镀方法制备薄膜的重要部件，其发射特性是影响薄膜均匀性的重要因素，本文从理论出发，建立脉冲电弧源发射特性的数学模型，编程计算得到理论的均匀性曲线，与实际的沉积薄膜厚度的均匀性对比，结果表明：脉冲电弧源的蒸发特性可以等效于多个面源的叠加，每一个面源发射的离子密度空间分布符合余弦定律。     

Numerical simulation of interaction between arc discharge and transverse magnetic field

An unsteady-state three-dimensional numerical model of radiation magnetogasdynamics is used to calculate the structure of an arc discharge which interacts with an external transverse magnetic field and transverse gas flow. The velocity field and the distribution of gas temperature obtained as a result of calculations agree with experimental data. The difference between the calculated and measured values of temperature in the discharge column is approximately 5%.     

Enhancement of antibacterial properties of Ag nanorods by electric field

Abstract

The effect of an electric field on the antibacterial activity of columnar aligned silver nanorods was investigated. Silver nanorods with a polygonal cross section, a width of 20–60 nm and a length of 260–550 nm, were grown on a titanium interlayer by applying an electric field perpendicular to the surface of a Ag/Ti/Si(100) thin film during its heat treatment at 700 °C in an Ar+H₂ environment. The optical absorption spectrum of the silver nanorods exhibited two peaks at wavelengths of 350 and 395 nm corresponding to the main surface plasmon resonance bands of the one-dimensional silver nanostructures. It was found that the silver nanorods with an fcc structure were bounded mainly by {100} facets. The antibacterial activity of the silver nanorods against Escherichia coli bacteria was evaluated at various electric fields applied in the direction of the nanorods without any electrical connection between the nanorods and the capacitor plates producing the electric field. Increasing the electric field from 0 to 50 V cm^?1 resulted in an exponential increase in the relative rate of reduction of the bacteria from 3.9×10^?2 to 10.5×10^?2 min^?1. This indicates that the antibacterial activity of silver nanorods can be enhanced by applying an electric field, for application in medical and food-preserving fields.     

Enhancement of antibacterial properties of Ag nanorods by electric field

The effect of an electric field on the antibacterial activity of columnar aligned silver nanorods was investigated. Silver nanorods with a polygonal cross section, a width of 20–60 nm and a length of 260–550 nm, were grown on a titanium interlayer by applying an electric field perpendicular to the surface of a Ag/Ti/Si(100) thin film during its heat treatment at 700 °C in an Ar+H₂ environment. The optical absorption spectrum of the silver nanorods exhibited two peaks at wavelengths of 350 and 395 nm corresponding to the main surface plasmon resonance bands of the one-dimensional silver nanostructures. It was found that the silver nanorods with an fcc structure were bounded mainly by {100} facets. The antibacterial activity of the silver nanorods against Escherichia coli bacteria was evaluated at various electric fields applied in the direction of the nanorods without any electrical connection between the nanorods and the capacitor plates producing the electric field. Increasing the electric field from 0 to 50 V cm⁻¹ resulted in an exponential increase in the relative rate of reduction of the bacteria from 3.9×10⁻² to 10.5×10⁻² min⁻¹. This indicates that the antibacterial activity of silver nanorods can be enhanced by applying an electric field, for application in medical and food-preserving fields.     

C基薄膜电子场发射的一般特性及发射模型

介绍了几种碳基材料的场发射特性及其发射模型.金刚石表面具有较低的或负的电子亲和势,因无法实现N型掺杂,难以用作电子发射材料.类金刚石膜及非晶碳膜材料经过"激活"后在表面形成具有较大场增强因子的熔坑,在几～几十V/μm的低阈值电场下得到非本征的电子发射,纳米结构的碳和碳纳米管本身具有较大的场增强因子,是较有前途的平面阴极场发射材料.碳基材料的导电性不同,遵循的发射模型不同.     

Features of the growth of carbon microplates during arc discharge in argon

Arc discharge in argon is accompanied by the growth of colorless needlelike plates (whiskers) on substrates in the discharge chamber. The first results of investigation of such deposits are presented. It is suggested that the deposited material can be used instead of graphite for obtaining synthetic diamonds.     

Single crystal TiO2 nanorods: Large-scale synthesis and field emission

A facile growth procedure of low-pressure chemical vapor deposition has been developed to synthesize single crystal TiO₂ nanorods on Ni-coated Ti substrate. The results indicate that the as-prepared nanorods are high purity single crystal with a [110] preferential orientation. Using directly the nanorods as emitters, their field emission (FE) properties have been investigated. The turn-on field of the nanorods decreases from 3.96 V/μm to 2.98, and 2.16 V/μm as the growth temperature increases from 700 °C to 750, and 800 °C, respectively. In addition, the nanorods show good FE stability during 480 min. Such behavior is mainly related to the morphology of nanorods, which depends on the growth temperature. Also, the growth mechanisms of the nanorods are analyzed in detail based on the experimental results.     

氧化锌纳米阵列场发射性能研究

采用物理气相沉积的方法通过控制生长参数，在硅衬底上获得不同形貌的氧化锌纳米阵列。在金属场发射系统中测量了它们的场致电子发射性能，发现阴极发射电流不稳定主要是由于氧化锌纳米阵列的不均匀性造成的．采用高压励炼技术可以增强氧化锌场发射的稳定性，使电流波动明显降低．此外，形貌对氧化锌纳米阵列的场发射电流密度和阈值电压有明显影响，而且不同形貌的氧化锌纳米阵列的抗溅射能力也不相同．     

Structure and field emission properties of SnO2 nanowires

SnO₂ nanowires were fabricated using a simple and economical method of rapid heating SnO₂ and graphite powders at 850 °C in a flow of high-purity N₂ as carrier gas. Research by using X-ray diffraction (XRD) indicates that SnO₂ nanowires are primitive tetragonal in structure with the lattice constant a = b = 0.443 nm and c = 0.372 nm. Observations by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that SnO₂ is of nanowire structure. The selected area electron diffraction (SAED) shows that the nanowires are perfect single crystal structure. The Fourier transform infrared (FT-IR) exhibits the difference of nanostructure materials and general materials. The field emission (FE) properties had also been studied.     

金刚石微米聚晶结构的生长及其场发射特性研究

在覆盖金属钛层的陶瓷上,利用微波等离子体化学气相沉积(MPCVD)法制备出类球状微米金刚石聚晶薄膜.利用扫描电子显微镜、拉曼光谱、X射线衍射,分析了薄膜的结构和表面形貌.测试了类球状微米金刚石聚晶膜的场致电子发射特性.开启电场仅为0.55V/μm,在2.18V/μm的电场下,其场发射电、流密度高达11mA/cm2.对类球状微米金刚石聚晶阵列形成机理和场发射机理进行了研究.     

Optical and field emission properties of Zinc Oxide nanostructures

Zinc Oxide (ZnO) nano-pikes were produced by oxidative evaporation and condensation of Zn powders. The crystalline structure and optical properties of the ZnO nanostructures (ZnONs) greatly depend on the deposition position of the ZnONs. TEM and XRD indicated that the ZnONs close to the reactor center, ZnON-A, has better crystalline structure than the ZnONs away from the center, ZnON-B. ZnON-A showed the PL and Raman spectra characteristic of perfect ZnO crystals, whereas ZnON-B produced very strong green emission band at 500 nm in the photoluminescence (PL) spectrum and very strong Raman scattering peak at 560 cm(-1), both related to the oxygen deficiency due to insufficient oxidation of zinc vapor. ZnON-B exhibited better field emission properties with higher emission current density and lower turn-on field than ZnON-A.     

Electron field emission properties of electro-deposited diamond-like carbon coatings

Field emission studies were carried out on diamond-like carbon films deposited by an electro-deposition technique onto SnO₂-coated glass substrates. A mixture of acetic acid and water was the electrolyte. The films are compact with surface roughness 10 nm. Work function (φ) values obtained from the Fowler–Nordheim model varied between 15 and 214 meV, while the field factor (β) varied between 4 and 700. The critical field was found to vary between 2 and 28 V/μm.     

Correlated electron tunneling during the field electron emission

Elementary events of correlated electron tunneling from very small regions of a hollow metal emitter were detected. The most significant microscopic and macroscopic parameters favoring the appearance of multiparticle tunneling effects are considered.     

Hierarchical nanostructured ZnO with nanorods engendered to nanopencils and pin-cushion cactus with its field emission study

In the present investigation, we report the synthesis of highly crystalline ZnO nanorods engendered to pin-cushion cactus and 1D nanopencil like nanoforms on zinc (Zn) foil via a simple sonochemical assisted hydrothermal route. The work reported herewith is attractive for two reasons: (i) the facile one step solution approach assisted by prior ultrasonication converts nanorods/nanobelts into nanopencils, and (ii) the sharp and quasi-aligned ZnO nanopencils are potential field electron emitters. In addition, the controlled growth of pinhole like ZnO nanopencils and aligned hexagonal ZnO nanodisc was obtained. The changes in the growth rate, diameter, density, and surface area of highly oriented ZnO nanorods are examined. Considering the significances of such novel morphologies, technically detailed formation mechanism has been proposed. The field emission study of pin-cushion cactus like ZnO nanopencils was performed. Field emission measurements demonstrate remarkably low turn-on field which is explained on the basis of a sequential enhancement mechanism involving the consecutive stem and tip contribution. The Folwer-Nordheim (F-N) plot showed nonlinear behavior indicating the semiconducting nature of the emitter. Significantly, emission current is stable at the preset value of 3 μA over the period of 3 h. The simplicity of the synthesis route coupled with the promising emission properties is envisaged to be an important candidate for potential nanoelectronic devices. These unique imperative ZnO nanostructures may have potential for sensors, solar cell, photocatalysis, varisters, etc.     

Crabwise ZnO nanowires: growth and field emission properties

Crabwise ZnO nanowires with an average length of 5 microm and an average diameter of 30 nm were selectively grown on ZnO:Ga/glass templates. Cathodoluminescence measurement indicated that the crystal quality of the crabwise ZnO nanowires was good. With an applied voltage of 120 V, the crabwise ZnO nanowire field emitters gave an emission current of 0.1 mA/cm2. Moreover, the field enhancement factor, beta, of the crabwise ZnO nanowires was approximately 980.     

One-dimensional germanium nanostructures--formation and their electron field emission properties

Ge nanostructures were synthesized by reduction of GeO(2) in H(2) atmosphere at various temperatures. Entangled and straight Ge nanowires with oxide shells were grown at high temperatures. Ge nanowires with various numbers of nodules were obtained at low temperatures. Ge nanowires without nodules exhibited remarkable field emission properties with a turn-on field of 4.6 V μm(-1) and field enhancement factor of 1242.     

ZnO纳米材料制备及其场发射性能的研究

采用水热法制备形貌和尺寸各异的纳米ZnO材料。用X射线衍射分析仪(XRD)和扫描电子显微镜(SEM)测试产物结构和表面形貌,分析影响纳米ZnO材料生长的因素,探讨纳米ZnO的生长机理。研究了各种形貌ZnO阵列的场致发射特性。实验结果表明,在各种ZnO纳米结构中,纳米管的场致发射性能最好,其最大电流密度可达到0.2mA/cm2,开启场强2.5V/μm,为寻求良好场发射性能的ZnO纳米材料提供了一个可行的途径。