Characterizing a New Composite Material: Effect of NaOH Coating of Variable Thickness on the Properties of a Tungsten Microemitter

Abstract

Tungsten based microemitter tips have been prepared with various tip radii ranging from 30 to 100 nm. These tips were manufactured by electrochemical etching of a 0.1 mm diameter high purity (99.95%) tungsten wire at the meniscus of two molar NaOH solutions. Contrary to the standard procedure, the tips' surfaces have not been cleaned off NaOH solution by ultrasonic cleaning in distilled water. Only a coarse cleaning by dipping the electro-polished samples a few times in distilled water has been performed. Thus, a layer of NaOH remained on the surface, which acts like a coating. The thickness of this coating layer left on the core material depends on the number of dips of the sample in water after etching. This procedure produced composite microemitters which consisted of a tungsten core with three different thicknesses of coating – thick, medium or thin – consecutively produced by dipping the etched samples in water for one, six or twelve time(s). A conventional field emission microscope with a tip (cathode) – screen (anode) separation standardized at ~ 10 mm was used to characterize the electron emitters. The system was evacuated down to a base pressure of ~10-⁸mbar when baked at up to ~180 °C overnight. This allowed measurements of typical Field Electron Emission (FE) characteristics; namely the current – voltage (IV) characteristics and the emission images on a conductive phosphorus screen (the anode).

Keywords: Nickel ferrite; Lattice parameters; Magnetic hysteresis; Cationic distribution.