Nanoprotrusion model for field emission from integrated microtips

Abstract

A study of the field emission from Spindt-type metallic integrated single microtips and arrays of microtips has been carried out. Measurements of field emission patterns, I/V curves, current stability, energy distributions against both applied voltage and angle of emission, and high frequency noise were made throughout the seasoning process. These measurements show that the emitters are not conventional metal emitters but undergo an evolution that depends on their past history such as operating time and exposure to ambient gases. In particular, the energy distributions showed three distinct behaviors; (1) a large and even dominating part of the total emission current could come from low-energy secondary electrons generated by collisions of the emitted electrons with the grid, particularly in the beginning of the seasoning process. After seasoning, the electrons were predominantly emitted from either, (2) multiple discrete bands nearer to the Fermi level that displace with applied voltage, or, (3) from the standard conduction band at the Fermi level. This invalidates the strict use of simple Fowler–Nordheim theory for analyzing the field emission from these emitters. A model based essentially on the field emission from nanoprotrusions all along the surface of the conical shank of the deposited tip is proposed which is consistent with all the experimental results. The spatial distribution of the noncontrolled nanoprotrusions evolves from the shanks to the microtip apex regions during the seasoning process.