ABSTRACT
The significance of the Fowler-Nordheim-type plots lies in the possibility of extracting useful and reliable physical parameters of the field electron emitters. This is achieved by the parameter's extraction methods. We report on the application of two parameters extraction methods on field emission data from bundles of carbon fibers (CFs) grouped in nickel tubes and operated inside a typical field emission microscope setup. These methods are the Murphy-Good plot and the conventional Fowler-Nordheim plot iterative method. The physical parameters include the area extraction parameter, the notional (actual) emission area, the formal area efficiency factor and the voltage conversion length. The results obtained from the two methods are discussed and compared to shed light on the controversial nature of these methods. The mechanism of field electron emission is analyzed based on the parameters extracted.
ABSTRACT
The behavior of the Folwer-Nordheim (FN) plot is investigated for large-area emitters arrays composed of perfectly aligned single-walled carbon nanotubes (CNTs). The field emission currents are calculated based on the standard FN model using the Murphy-Good equation. The aspect ratio of the CNTs is varied such that the height of the CNT has predefined uniform or Gaussian distributions. Continuous degradation of the high-aspect-ratio CNTs is assumed to take place at predefined values of the scaled barrier field. The effects, on the FN plot behavior, of the size distribution and the scenario of the degradation of the emitter are determined and discussed. These factors are found to produce the two behaviors of the experimental FN plots, i.e. the upward and the downward bending behaviors. This work shows the possibility to expand the application of the standard FN model for the investigation of the field emission characteristics from nanoscaled emitters such as CNTs.
ABSTRACT
The Fowler - Nordheim (FN) plot behavior is investigated for field emitted electrons from virtual carbon nanotubes (CNTs)-based large area field emitters (LAFEs) arrays. The field emission currents are calculated using the Murphy-Good field emission equation assuming emission from two sets of geometrically-different CNTs. No screening effects are considered in the calculations. The FN plots nonlinear behavior, in the form of an upward bend, is observed, analyzed and attributed to the emitters' geometrical features and their numbers in the arrays. The calculations emphasize that the nonlinear characteristic depends, not only on the two-class geometries of the emitters but also on the statistical distribution of these emitters in the arrays. The calculations adopted in the present work allow fitting the experimental data of the LAFEs for any desirable range of applied voltages with minimal adjustable parameters. The present investigation is believed to help further development of the LAFEs for future applications.
ABSTRACT
Hybrid heterojunction thin films, based on poly-(3-octylthiophene) (P3OT) polymer and oleic acid (OA)-capped cadmium selenide (CdSe) nanoparticles (NPs) are prepared by a spin-coating method. The structural and morphological properties of the CdSe NPs and of the hybrid thin films are investigated. The results of the dielectric characterization show that conductivity of the hybrid thin films is dependent on frequency and CdSe NP concentration. The Nyquist plots of the impedance characteristics of the layers exhibit circular features irrespective of the NP concentration. The dependence of the dielectric permittivity on frequency and CdSe NP concentration are studied.
ABSTRACT
Field emission measurements of current-voltage characteristics are reported for tetrapod structures of ZnO. The nonlinear Fowler-Nordheim (FN) plot is analyzed according to a model of calculation based on saturation of conduction band current and predominance of valence band current at high-field values. The simulated FN plot exhibits similar features to those observed experimentally. The model of calculation suggests that the slope variation of the FN plot, in the high-field and low-field regions, does not depend on the magnitude of saturation. Instead, it is a characteristic of the energy band structure and voltage-to-barrier-field conversion factor of the emitting material.
