A quantitative time-of-flight secondary ion mass spectrometry study of ion formation mechanisms using acid-base alternating Langmuir-Blodgett films

The effect of pre-existing acid-base proton transfer on ion formation in secondary ion mass spectrometry (SIMS) is studied with model systems constructed by Langmuir-Blodgett techniques. Reflection-Absorption FTIR was used to verify proton transfer in tri-layer LB assemblies of docosanoic acid (A) and 1-docosylamine (B). A recently developed quantitative method for quasi-molecular ions in Static SIMS was extended to Time-of-Flight SIMS. The formation of protonated base ions ((B + H)⁺) is highly dependent on film structure and pre-existing chemistry. The formation of the conjugate (A-H)^-) carboxylate anion is more dependent on concentration of species rather than local chemistry. The implications for molecular quantitative analysis in SIMS are discussed.