Comparison of MeV monomer ion and keV cluster ToF-SIMS

Recent results([1]) show the potential of using monomer primary ions accelerated to several MeV with a tandem accelerator to achieve the necessary secondary ion yields to image large (above 1 kDa) molecules with submicron lateral resolutions. The Surrey ion Beam Centre (Surrey IBC) has designed a time-of-flight secondary ion mass spectrometer (ToF-SIMS) combined with a 2 MV Tandem accelerator to investigate the characteristics of the desorption of secondary ions by the impact of fast, heavy, primary ions. The application of this MeV-ToF-SIMS technique is intended to eventually image biomolecules in the subcellular regime without the need for matrix application associated with other mass spectromery techniques, such as Matrix Assisted Laser Desorption ionisation (MALDI). A discussion is given to point out the merits of using a combination of Particle-Induced X-ray Emission Spectrometry (PIXE) and Rutherford Backscattering (RBS) with the MeV-ToF-SIMS measurement to improve quantification and sensitivity of this surface analysis technique. We also present data from highly focused MeV primary ions to directly compare results obtained using keV cluster-SIMS to measure various biological materials using ToF-SIMS through sputtering in both the nuclear and electronic stopping regimes. Our findings show that the mass spectra obtained with MeV ions in the electronic stopping regime show similarities to those acquired with more conventional keV ion beams (e.g. Bi+, Bi-3(+), Bi-5(+) and C-60(+)). MeV-ToF-SIMS has the potential for becoming a widely used quantitative surface analysis technique in the many ion beam analysis facilities already conducting-high energy ion beam analyses. Copyright (C) 2010 John Wiley & Sons, Ltd.