Development of a high‐performance electrospray droplet beam source

Abstract

The electrospray droplet impact (EDI) method was developed as a new massive cluster source, but the current EDI method lacks adequate beam focusing and density to achieve imaging and depth profiling with sufficient spatial resolution and within a reasonable time. To improve EDI beam performance, we have developed a technique for stable electrospraying of volatile liquids under vacuum. However, as is well known, vacuum electrospray of volatile liquids is extremely difficult because the evaporative cooling causes freezing of the volatile liquids in vacuum, and to prevent the freezing of these liquids, we irradiated the tip of the electrospray emitter with an infrared (10.6 µm) laser. The tip of the emitter was directly observed with optical microscopy, and the droplet ion beam current was measured with a Faraday cup. A stable vacuum electrospray of pure water was achieved with continuous laser irradiation. Also, typical modes of electrospray were clearly observed with the microscope even under vacuum conditions. The addition of 0.01 M trifluoroacetic acid to water caused an increase in current by at least one order of magnitude compared with water only. From these results, the vacuum electrospray technique can be expected to be a high‐performance massive cluster ion beam source. Copyright © 2012 John Wiley & Sons, Ltd.