Secondary Ion Mass Spectrometry with Massive Projectiles

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Professors Emile Schweikert and Stanislav Verkhotrov of Texas A&M University are supported by the Analytical and Surface Chemistry program to investigate the use of gold clusters as projectiles for the detection of attomol amounts of analyte and for identifying molecules colocated on surfaces within submicron distances. The experimental procedure is secondary ion mass spectrometry (SIMS), with two key differences: the nature of the projectile and the mode of bombardment with individual projectiles resolved in time and space. In previous NSF-supported work, this lab worked with a liquid metal ion source which produces a wide range of gold clusters, e.g. 200 gold atoms with a +4 charge. This work will investigate the fundamental issues related to the efficiency of massive gold projectiles to generate secondary ions. The PI's will also develop negative ion mass spectrometry using the gold particles to assess spatial resolution. A sequence of individual projectiles spaced one millisecond apart is focused on a small surface area. The impacts which occur are each recorded individually via the emitted electrons and correlated with the time-of-flight data of the secondary ions detected from the same event. These data should allow compilation of a chemical map giving a 2D or 3D distribution of molecules with an anticipated spatial resolution of 25 nm. The development of mass spectrometry as a chemical microscopy is very important for achieving the goal of chemically mapping biological structures such as the single cell. These images will lead to a greater understanding of how the cell works and interacts with other cells. Chemical imaging with nanoscale resolution will also be very useful in characterizing nanoparticles.