title: Vacuum electrospray of volatile liquids assisted by infrared laser irradiation.
abstract: BACKGROUND
  Current large cluster sources such as C(60) or argon utilize gas-phase sources which are of low-brightness and cannot be focused efficiently to better than 1 micron diameter spot size. The development of a high-brightness large cluster ion source is of critical importance to achieve high resolution in secondary ion mass spectrometry (SIMS) imaging of organics.
  
  
  METHODS
  We propose a new high-brightness large cluster ion source, and a technique for producing a stable electrospray of volatile liquids under vacuum. It is known that vacuum electrospray of volatile liquids such as water is extremely difficult because of freezing of the liquids introduced in vacuum by evaporative cooling. To avoid freezing, the tip of the electrospray emitter was irradiated by a continuous wave infrared laser.
  
  
  RESULTS
  Without continuous laser irradiation the vacuum electrospray of a water/methanol solution was unstable with respect to the shapes of the Taylor cone and current, whereas continuous laser irradiation produced a stable electrospray of water. The typical modes of electrospray were clearly observed with an optical microscope even under vacuum conditions. A stable vacuum electrospray could be achieved by improving the vacuum pressure to suppress electric discharge and by using the laser to maintain the liquid state.
  
  
  CONCLUSIONS
  This is the first description of the production of a stable vacuum electrospray of volatile liquids such as water. This vacuum electrospray technique can be expected to produce a novel high-brightness large cluster ion beam source.
authors.affiliation: Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, 4-3-11 Takeda, Kofu, Yamanashi, 400-8511, Japan. sninomiya@yamanashi.ac.jp
authors.forename: Satoshi
authors.initials: S
authors.lastname: Ninomiya
authors.forename: Lee Chuin
authors.initials: LC
authors.lastname: Chen
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Suzuki
authors.forename: Yuji
authors.initials: Y
authors.lastname: Sakai
authors.forename: Kenzo
authors.initials: K
authors.lastname: Hiraoka
mesh_terms: D007259:Infrared Rays; D007834:Lasers; D000432:Methanol / Q000737:chemistry; D011312:Pressure; D021241:Spectrometry, Mass, Electrospray Ionization / Q000295:instrumentation* / Q000379:methods*; D014618:Vacuum; D055549:Volatile Organic Compounds / Q000737:chemistry*; D014867:Water
chemical_list: D055549:Volatile Organic Compounds; D014867:Water; D000432:Methanol