Boštjan Jenčič oral presentation (PB1-Tue4-1-4)
MeV–SIMS imaging of organic tissue with a continuous primary beam
1 Jožef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
2 FOM - INstitute AMOLF, Science Park 104, 1098 Amsterdam, Netherlands
3 University of Ljubljana, Biotechnical faculty, Večna Pot 11, 1000 Ljubljana, Slovenia
MeV–SIMS is executed at the Jožef Stefan Institute (JSI) microprobe routinely by a pulsed 7 MeV 35Cl6+ ion beam, with a frequency of 10kHz and pulse length of approx 20ns. In this way, we are able to provide spectra and molecular images of samples with good chemical sensitivity for masses of up to 1500 Da. In this mode, the performance of the method is constrained mainly due to the pulsing of the primary ion beam. The mass resolution is limited because of the finite duration of the primary ion pulse, and had its upper limit at approx. m/dm = 500. The required high primary ion currents, which are imposed by a low duty factor of 2 x 10-4, result in large diameter of the primary ion beam and limit the lateral resolution to a value of 10 micrometers.
In order to bypass the shortcomings of the operation with the pulsed primary beam, we applied a continuous beam with random arrival of primary ions, and triggered the measurement of TOF by detection of the arrival of each individual primary ion. We positioned a continuous electron multiplier behind the thin sample and trigger the TOF measurement upon the arrival of each individual primary ion. We are applying a time-delayed extraction mechanism in order to overcome the initial energy distribution of secondary ions, and primary beam blanking during the TOF cycle. The resulting mass resolution exceeds a value of 1800, and the lateral resolution in the mapping mode equals 600 nm x 800 nm. MeV-SIMS in this configuration enables molecular imaging at subcellular level at the intact surface of freeze-dried tissue slice. In parallel, we invested significant efforts in developing ultra-thin conductive tissue substrates and tissue slicing technology to prepare tissue samples with thickness of 3 micrometers, appropriate for investigation with 7 MeV 35Cl6+ ions.