Kousuke Moritani oral presentation (FN1-Mon3-2-3)
Desorption and ionization of organic molecules induced by liquid cluster ion collision
University of Hyogo, Shosha 2167, 6712201 Himeji, Japan
In this decade, massive cluster ion beams have been applied to projectiles for time-of-flight secondary ion mass spectrometry (TOF-SIMS).[1-3] Recently, water and some other molecules are applied to the massive cluster projectiles for SIMS in order to improve the secondary ion yields by chemical effects.[4-6] The ionization probability should be influenced by the properties of the bombarding primary ion beams as well as the chemical nature of the sample surface during the collision with the primary ion. However, the ionization mechanism by liquid cluster is still unclear. In this study, we have investigated the secondary ion emission from hydrophobic and hydrophilic molecules by Ar and water cluster ion projectiles.
We have developed the stable liquid cluster source and equipped it with the SIMS apparatus. The liquid cluster beams were generated by bubbling argon at constant flow rate through a reservoir filled with liquids (water, methanol and benzene) at room temperature. The cluster sizes were selected by time of flight (TOF) method and the typical size-resolution M/ΔM was 5 at Ar1500+ at the acceleration voltage of 5 kV. The sample was a thin film of amino acids, a polystyrene (PS) and a 1,4-didodecylbenzene (DDB). For the amino acid samples, the intact ions are detected as the [M+H]+ for both Ar cluster and hydrogen-bond cluster, such as water and methanol cluster bombardment. The water cluster projectile enhanced the yields of [M+H]+ species at the low energy region of 2 eV/molecule. On the other hand, for DDB molecule, intact ion was detected as the M+ form and the water cluster did not enhance the yield. These results indicated that water cluster enhanced the ion formation via the proton attachment. In this presentation, the desorption and ionization mechanisms for the liquid and gas cluster ion projectiles will be discussed.
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