Molecular Colocalization Using Massive Gold Cluster Secondary Ion Mass Spectrometry.

We report on the ion emission from impacts of hypervelocity massive gold clusters for use in secondary ion mass spectrometry. Two massive gold clusters are considered, 520 keV Au and 1040 keV Au. The emission of fragment ions and molecular ions is evaluated for a series of neat samples, glycine, phenylalanine, arginine, and gramicidin S. A 2 to 4-fold increase of molecular ion emission is observed from impacts of 1040 keV Au versus 520 keV Au. Compared to impacts of 20 keV Ar and 20 keV (HO) in static conditions, impacts of 1040 keV Au display a 6 to 9-fold increase in the number of detected molecular ions per projectile impact. To explain the increased emission of molecular species, we examine the size of the impact craters and calculate the ratio of molecular ions to fragment ions. The characterization of Au and the operating conditions of the gold liquid metal ion source are presented.