Papers by Keyword: Field Emission

Abstract: The method of manufacturing BaO thin layers on carbon nanotubes (CNT) from Ba(NO₃)₂ aqueous solutions was demonstrated. Ordered carbon nanotubes arrays were synthesized by catalytic plasma-stimulated chemical deposition from the gas phase. The influence of the BaO content on the work function and, accordingly, carbon nanotubes emission properties were investigated. Significant field emission threshold voltage of CNT arrays treated by solutions with the lowest Ba(NO₃)₂ concentrations was demonstrated.

Abstract: Based on the Sommerfeld free-electron model, the specifics of field emission from metal cathode covered by nanometer oxide layer into vacuum was theoretically studied by the example of systems «W-WO₃-vacuum» and «Al-Al₂O₃-vacuum». The significant influence of natural oxide on the current-voltage (CV) characteristics in the region of strong electric fields (more than 10⁷ V/cm) was investigated, where the transition to the faster current increase in the terms of Fowler-Nordheim (FN) coordinates occurs. At low electric fields (less than 10⁷ V/cm) the CV characteristics may be described by the FN formula for the emission current and can be used to estimate the effective barrier height, which is important in selecting a good cathode material.

Abstract: The structural and field electeron emission properties of pure and Al doped ZnO nanorods synthesized on the Al substrates using sol-gel method has been studied. Al doping at different levels was achieved by adding Al₂NO₃ at 1, 3 and 5 Al at. % with respect to Zn in the synthesis solution. X-ray analysis shows that all the obtained ZnO nanorods can be indexed to the hexagonal ZnO wurtzite structure. Field electron emission measurement using the nanorods as cathode gave a trend of decreasing turn-on field values with increasing Al-doping levels, with values of 7.2 V/μm, 6.6 V/μm, 6.0 V/μm and 5.8V/μm for pure ZnO nanorods, 1, 3 and 5 at% Al-doped ZnO nanorods, respectively. The F-N plot has a linear relationship and the field enhancement factor for all samples has been obtained.

Abstract: Electrochemical synthesis of Polypyrrole (PPy) thin films on Sn substrates has been carried out under cyclic voltammetry (CV) mode. The structural, morphological and chemical properties of the as-synthesized PPy films were investigated using various characterization techniques like SEM, UV-Visible and FTIR. Furthermore, field emission (FE) behaviour of the PPy thin film emitter were carried out at base pressure of ~ 1×10^-8 mbar and found to be interesting. The threshold field, required to draw emission current density of 1 μA/cm², is observed to be 0.90 V/μm and very high emission current density of 12.87 mA/cm² has been drawn at applied field of ~ 2.8 V/μm. The emission current stability investigated at preset values of 1, 10 and 100 μA/cm² is observed to be fairly good over duration of more than three hours. The simplicity of the synthesis route coupled with the capability to deliver very high emission current density at relatively lower applied field make the PPy thin field emitter as a potential candidate for practical applications in field emission based devices

Abstract: The structural and field emission properties of ZnO nanorod at different growth time by sol-gel method have been successfully prepared. FESEM results illustrated that dense ZnO nanorods with hexagonal wurtzite structure were vertically well-aligned and uniformly distributed on the substrate. X-ray diffraction pattern analysis shows that all the obtained ZnO nanorods can be indexed to the hexagonal ZnO wurtzite structure. Field emission measurement was conducted for ZnO nanorod growth at different time to study emission properties. The turn-on field value decreases while field enhancement value increases as longer growth time was applied which related to the increasing of aspect ratio of ZnO nanorod respectively.

Abstract: Effective field emitting angle plays an important role when investigating field emission characters. In this work, effective field emitting angle is introduced for Spindt-type emitter to relate spatial variation of current density along tip’s surface to emission current. The effects of various parameters on effective field emitting angle are analyzed. The results show that effective field emitting angle decreases exponentially as half angle increases, decreases quadratically as radius of gate aperture increases, but increases logarithmically as gate voltage increases linearly. It is also found that effective field emitting angle increases first and then decreases with emitter’s height increasing. Similar trends can be also found with insulator height. Grid thickness nearly has no effect on the effective field emitting angle.

Abstract: In this paper, we report a recent experimental observation of the effect of thermal accumulation to the field emission properties of the carbon nanotubes. The carbon nanotubes are grown on Ni by CVD. We compare the field emission characteristics of carbon nanotubes cathodes under DC and pulse mode. Our research shows that the higher current and higher current density could be acquired by suppressing the thermal accumulation. The Fowler-Nordheim plot shows a good linear fit, indicating that the emission current of carbon nanotubes follows Fowler-Nordheim behavior.

Abstract: Graphene film on silicon carbide is considered to be promising material for high-frequency vacuum nanoelectronics. However, the possibility of graphene application in this area is still poorly understood. We have carried out the simulation of the electric field distribution in interelectrode gap of the anode-cathode system pointed field emission cathode based on silicon carbide with graphene film on its surface subject to the rounding-off radius of the top, interelectrode gap, height and cathode forming half-angle of the cone opening by the finite element method. The influence of constructional parameters on the electric field strength in the test structure was analyzed. It is shown that the values of rounding-off radius of the cone point and interelectrode distance has the biggest influence on the electric field in the investigated structure. Changing of the height and cathode forming half-angle of the cone opening does not lead to a significant increase or decrease of the electric field value.

Abstract: The CNx powders were prepared by a polymerization process. The phase structure and bonding structure of the as-prepared powder were analyzed by X–ray diffraction and X–ray photoelectron spectroscopy, respectively. To prepare CNx field emission cathode, the CNx powders were coated onto Ti substrate using a suspension sedimentation method, followed by an annealing treatment to form a TiC phase. A three layer (Ti substrate–TiC joint network–CNx particles) structure model was proposed to explain the electron field emission properties for the as-prepared field emission cathode. The field emission measurement shows that for the as-prepared CNx cathode, the threshold electric field is 2.04 V/μm and the emission current density at 3.73 V/μm is 158 μA/cm.

Abstract: The sphere-like diamond microcrystalline-aggregates were fabricated by microwave plasma chemical vapor deposition (MPCVD) method. The ceramic with a Ti metal layer was used as substrates. The fabricated diamond microcrystalline aggregates were evaluated by Raman scattering spectroscopy, x-ray diffraction spectrum (XRD), scanning electron microscopy (SEM). The field emission properties were tested by using a diode structure in a vacuum. A phosphor-coated indium tin oxide (ITO) anode was used for observing and characterizing the field emission. It was found that the sphere-like diamond microcrystalline-aggregates films exhibited good electron emission properties. The turn-on field was only 0.55V/μm, and emission current density as high as 11mA/cm2 was obtained under an applied field of 2.18V/μm for the first operation. After several cycling operations, the field emission tended to stable characteristics of current versus voltage. The stability evolvement and mechanism are investigated relating to microstructure of the sphere-like diamond microcrystalline-aggregates films.