Development of an Ionic-liquid Ion Beam Source for Secondary Ion Mass Spectrometry (SIMS)

Abstract

Beam characteristics generated by vacuum electrospray of ionic liquids were investigated at gas pressures of 10^-5 Pa. An imidazolium ionic liquid, 1-ethyl-3-methyl imidazolium bis(trifluoromethanesulfonyl) amide (EMI-TFSA), and an ammonium ionic liquid, N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl) amide (DEME-TFSA), were tested. Transient response measurements showed that m/z values of EMI-TFSA charged droplets were smaller than those of DEME-TFSA charged droplets under the same experimental conditions. The m/z values of EMI-TFSA charged droplets decreased with decreasing flow rate. A target current exceeding 30 nA was produced at a capillary voltage of 1.6 kV even with a low flow rate of 3 nL/min, at which the peak value of m/z distribution was 7.9×10⁴. The average mass, charge number and diameter of the charged droplets at m/z = 7.9×10⁴ were estimated to be about 6.1×10⁶ u, 77 and 23 nm, respectively. [DOI: 10.1380/ejssnt.2014.119]