Time-of-Flight secondary ion mass spectrometry (TOF-SIMS) using the metal-cluster-complex primary ion of Ir₄(CO)₇⁺

An orthogonal acceleration Time-of-Flight Secondary Ion Mass Spectrometer (TOF-SIMS) system has been developed with a metal-cluster-complex ion source. The ion source can produce ion beams of massive molecules called metal-cluster-complexes such as Ir₄(CO)₁₂, which has a molecular weight higher than 1000 u. Using the system, TOF-SIMS of a contaminated silicon substrate and a room temperature molten salt (i.e. an ionic liquid) was performed. The ionic liquid N,N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium bis(trifluoromethanesulfonyl)imide, which has a molecular weight of 426 u, consists of a polyatomic cation, [C₈H₂₀ON] ⁺, and a polyatomic anion, [C₂F₆NO ₄S₂]^-. During SIMS analysis, an analytical sample was bombarded with a continuous primary ion beam of either Ir ₄(CO)₇⁺ or Ar⁺ in a beam energy of 10 keV at an incident angle of 45°. It was confirmed that the use of Ir ₄(CO)₇⁺ ions enhanced secondary ion intensity compared with that of Ar⁺ ions. Also, experimental results showed that the bombardment of Ir₄(CO)₇⁺ caused less fragmentation. In the case of the ionic liquid, cation-attached ionic-liquid molecules were observed in addition to the cation of the ionic liquid.