Time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) using an ionic‐liquid primary ion beam source

Abstract

An orthogonal acceleration time-of-flight secondary ion mass spectrometry (TOF-SIMS) system has been developed using a prototype vacuum-electrospay primary beam source that is capable of producing continuous ion beam of an ionic liquid. As a primary ion beam, an imidazolium ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl) amide (EMI-TFSA), was electrosprayed at pressures around 2 × 10 À4 Pa and a flow rate of 50 nL/min. Using the TOF-SIMS system, three samples were analyzed: (i) EMI-TFSA, (ii) an ammonium ionic liquid, N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl) amide (DEME-TFSA), and (iii) a polyethylene glycol (PEG300). Preliminary data showed that the vacuum electrospray of the ionic liquid was applicable to a primary ion beam source for SIMS. Nevertheless, irradiation of the ionic-liquid beam caused deposition as well as sputtering. The deposition would result from larger m/z components of ionic-liquid charged droplets. This is because projectile energy per nucleon of the larger m/z components seems too low to sputter materials. Because m/z values of charged droplets decrease with decreasing flow rate, it is required to reduce the flow rate of the ionic liquid so as to suppress the deposition of the ionic-liquid beam.

Effects of a proton‐conducting ionic liquid on secondary ion formation in time‐of‐flight secondary ion mass spectrometry

“…The system used in the second TOF‐SIMS experiment was another orthogonal acceleration TOF‐SIMS system equipped with a vacuum‐electrospray beam source. A detailed description of the system has been reported previously . In brief, it consists of the vacuum‐electrospray beam source, a sample plate, electrostatic lenses for transporting secondary ions, and another orthogonal acceleration time‐of‐flight (TOF) mass spectrometer.…”

“…[23][24][25][26][27] For the purpose of use in SIMS, we investigated ionic-liquid beam generation in vacuum [28][29][30] as well as at reduced pressures, [31] and subsequently developed a vacuumelectrospray beam source using room-temperature ionic liquids, performing TOF-SIMS analysis. [32] However, there are still some problems to be resolved; one of the most important problems is to increase secondary ion intensities of organic molecules.…”

Time‐of‐flight secondary ion mass spectrometry using a new primary ion beam generated by vacuum electrospray of a protic ionic liquid, propylammonium nitrate

“…For further improvement in TOF‐SIMS analysis, it seems to be necessary to develop a new ion source capable of producing a focused primary ion beam of massive clusters. Electrospraying (or electrohydrodynamic spraying) of ionic liquids in vacuum seems a promising way to address this issue . Ionic liquid ion beams can be generated using two kinds of emitters: sharp needles and capillary tubes .…”

“…Electrospraying (or electrohydrodynamic spraying) of ionic liquids in vacuum seems a promising way to address this issue. 24,25 Ionic liquid ion beams can be generated using two kinds of emitters: sharp needles and capillary tubes. [26][27][28][29][30][31] Sharp needles emit polyatomic ions similarly to liquid metal ion sources, 26 whereas capillary tubes emit charged droplets as well as polyatomic ions.…”

Development of a Primary Ion Column for Mass Spectrometry-Based Surface Analysis

“…Fujiwara, however has not reported this type of particular degradation. Notwithstanding, in this early work the acceleration energy was generally a total of +/-1 kV, only generating ~20 nA of current 121 .More recently, Fujiwara's group has been able to generate ~100 nA+ ion streams utilizing a DC power source where a 30 μm stainless steel capillary is charged to generate the Taylor cone for the electrospray 127,128 . They report no degradation at low flow rates and low ionization…”