Compact ion-source based on superionic rubidium silver iodide (RbAg4I5) solid electrolyte

• Author(s): Martins, Dália Teresa Al-Alavi
• Date: 2013
• Persistent ID: http://hdl.handle.net/10362/11037
• Origin: Repositório Institucional da UNL
• Subject(s): Ionic conductivity; Solid electrolyte; Emitter; Ionic current; Ion beam
• Document Type: Master thesis
• Language: English
• Advisor(s): Tolstoguzov, Alexander
• Contributor(s): RUN

Description

Dissertação para obtenção do Grau de Mestre em Engenharia Física

A compact ion-beam source based on rubidium silver iodide (RbAg4I5) solid electrolyte, deposited on a sharpened silver tip, has been developed and studied. Through an accelerating potential above 10 kV, established between emitter and collector, silver positive ions move through the electrolyte towards the emitting surface, where they are emitted from and accelerated. Via partial redox reaction occurring at the silver/RbAg4I5 interface, silver atoms are oxidised into Ag+ ions and migrate into the electrolyte, compensating the loss of emitted ions in the apex region. The emitted ions are collected by a Faraday cup, producing an electric current in the level of tens picoamperes. It was found that silver ions (atomic or clustered) make a major contribution to the measured ion current, although rubidium ions were also detected with concentration in six times lower than silver. The apex diameters of the final emitters were estimated in the range of 4-9 μm. The highest stable current was produced by an emitter whose apex diameter corresponds to 8.2 ± 0.5 μm. This current remained in the level of 20-25 pA for nearly 90 minutes and it was obtained at 92ºC, using an extraction voltage of 20 kV. Furthermore, it was observed that the current increased exponentially with temperature and linearly with applied voltage, at least for temperatures below 150 ºC and voltages in the range of 10-22 kV. Dependence on the apex diameter was not studied, since the RbAg4I5 film deposited on silver tips was not totally uniform. Several improvements should be performed to optimize the deposition methods, the design of heating system and methodology of the measurements (m/z characterization of the emitted particles). However, the developed ion-beam source can produce a stable current over a long period of time with minimal expenditure of energy and source material. Such sources have potential applications in materials science and spacecraft engineering as principal elements of miniaturized electric propulsion systems (ionic thrusters).