Secondary ion and neutral mass spectrometry with swift heavy ions: Organic molecules

The authors report on experiments regarding the electronic and nuclear sputtering of organic films. The newly built swift heavy ion induced particle emission and surface modifications setup [Meinerzhagen et al., Rev. Sci. Instrum. 87, 013903 (2016)] at the M1 Branch at the universal linear accelerator (UNILAC) beam line at GSI in Darmstadt, Germany, has been used for research on organic molecules in the electronic sputtering regime. This setup has the unique capability not only to investigate electronically sputtered ions by projectiles with kinetic energies up to several giga-electron-volt but also to detect their neutral counterparts as well by laser postionization. For this purpose, the experiment is equipped with a laser system delivering 157 nm pulses with photon energies of 7.9 eV to be utilized in single photon ionization. In addition to the investigation of sputtered ions and neutrals in the electronic sputtering regime, a comparison of typical fragments between fundamentally different sputtering mechanisms has been performed by using two different common time of flight secondary ion mass spectrometry (SIMS) instruments. The use of the different instruments offers the possibility to investigate the influence of the differing sputter processes from the linear cascade regime over collisional spikes to the thermal spike regime under high energy ion bombardment. The experiments in the collision-dominated nuclear stopping regime have been performed using 20 keV Bi⁺ and Bi₃⁺ as atomic and small cluster projectiles and using 20 keV C₆₀⁺ representing a medium-sized cluster. In the electronic sputtering regime, 4.8 MeV/u ¹⁹⁷Au²⁶⁺ swift heavy ions created by the UNILAC have been used as projectiles. As targets thin films of coronene on silicon substrates, a polycyclic hydrocarbon and Irganox 1010, an antioxidant well known from different studies in the SIMS community, have been utilized.