Electro-optical analysis in determining the field emission characteristics of carbon nanofibers on an acute tip substrate

The shape of an acute tungsten (W) tip substrate coated with palladium (Pd) and carbon nanofibers (CNFs) was optimized in order to generate efficient field emission (FE) currents. By adjusting the apex angle of the tip, we succeeded in controlling the FE properties and electron beam convergence. When the apex angle was close to 50°, a narrow convergence of electron beams was observed. By employing an original computation tool based on the surface charge method, we conducted a numerical analysis of the convergence mechanism of the FE device; this was dependent on FE properties, and displayed its maximum around the same apex angle. By simulating the electrical field distribution above the CNF, we concluded that the optimum values of the electro-optical properties of CNFs on the tip substrate were found at an angle of approximately 50° with a narrow divergence angle. After determining the relationship between the divergence angle and the tip apex angle, the electron emission property was optimized. Analysis of the characteristics of the maximum electron emission state using our computation method indicated that an acute tip covered with CNFs has potential for use as a cathode in electrical devices which require a large FE current with low power consumption.