Enhancement of secondary ion yield on gas cluster ion beam-secondary ion mass spectrometry with nonaromatic matrices: Dependence on matrix species and molecular weight

The Ar gas cluster ion beam (Ar-GCIB) technique is advantageous for soft sputtering of large organic molecules. However, in secondary ion mass spectrometry (SIMS) measurements using Ar-GCIB, the secondary ion yield is typically very low. Matrix-enhanced (ME)-SIMS is a technique that has the potential to enhance the yield. In a previous study on ME-SIMS, aromatic compounds that are typically employed for matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) were used for the matrix. Although aromatic rings are involved in soft ionization by absorption of energy from the laser probe in MALDI-MS, aromatic rings may not be required for ME-SIMS, which does not use a laser probe. In this study, the effect of non-aromatic matrices was investigated. The results indicated that some nonaromatic compounds are effective for enhancing sensitivity and that the degree of enhancement depends on the molecular weight of analytes. To investigate the reason for this, it was assumed that the yield in SIMS measurements is simply determined by the sputtering yield, the survival rate, and the ionization probability, each of which has molecular weight dependence. Under these assumptions, the SIMS yield is found to be dependent on the matrix species.