Ionic liquid ion sources (ILISs) are externally wetted and electrochemically etched and sharpened tungsten tips used as electrospraying sources for ionic liquids in a vacuum. They have recently shown an ability to operate as emitters of pure ion beams (no drops), even with ionic liquids of moderate surface tension (γ<40 dyncm) and electrical conductivity (K<1 Sm) that had in all prior reports (all based on conventional internally fed capillary tips) always operated in the mixed ion-drop regime. The present study uses time of flight mass spectrometry to analyze full ion beams emitted from ILISs for a diversity of ionic liquids with properties in the wide range 0.26<K (Sm) <2.8, 39.3<γ (dyncm) <48.6. Remarkably, all liquids tested achieve the purely ionic regime. The main effect of reducing electrical conductivity is a reduction of the emission current from 180 to 10 nA.
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We are thankful to Professor Martínez-Sánchez (MIT) for many contributions to the electrospraying aspects of the problem. This work has been supported by the US AFOSR through Grant Nos. F-49620-01-1-0416 and FA9550-06-1-0104 to Yale, as well as Yale subcontracts from STTR grants to the companies Busek and Connecticut Analytical Corporation.
Copyright 2008 Elsevier B.V., All rights reserved.