Development of a Vacuum Electrospray Droplet Ion Gun for Secondary Ion Mass Spectrometry.

Atmospheric pressure electrospray had been used in previous studies to generate massive water droplet ion beams, and the beams successfully achieved efficient desorption/ionization of biomolecules, low damage etching of polymers and nonselective etching of metal oxides. However, this droplet ion beam was not practical as a primary ion beam for surface analysis instruments because it required differential pumping and lacked adequate beam current and density. To improve the beam performance, we have proposed to use vacuum electrospray of aqueous solutions as a beam source, and developed a technique for producing a stable electrospray of aqueous solution in vacuum. We also designed a prototype of a vacuum electrospray droplet ion gun, and measured the beam properties. Finally, the applicability of this ion gun in secondary ion mass spectrometry is discussed.