Hubert Gnaser oral presentation (FN1-Mon3-2-1)
In situ cationization of molecular ions sputtered from organic specimens under cluster bombardment
1 University of Kaiserslautern, Erwin-Schrödinger, 67663 Kaiserslautern, Germany
2 IFOS, Trippstadterstr, 67663 Kaiserslautern, Germany
3 Kyoto University, Uji, 611-0011 Kyoto, Japan
In an attempt to investigate the possibility of an in situ cationization of molecular ions in TOF-SIMS, low-energy 650 eV Cs+ ions were implanted in organic materials before their analysis by Bi3+ cluster bombardment. Specifically, three different organic samples were used: arginine, leu-enkephalin, and polyethylene glycol (as a mixture with molecular weights of ~1000, 2000, and 3000). For the pristine specimens, characteristic secondary ion species were typically observed: (M+H)+ in the case of arginine and leu-enkephalin, whereas for polyethylene glycol oligomer ions were detected with masses up to ~2500 u. Cs+ was implanted into these samples with fluences ranging from 2×1012 cm-2 to 8×1013 cm-2. Already for the lowest implantation fluence a substantial signal of Cs+ secondary ions was observed in the sputtered flux; it seems to saturate at about 4×1012 Cs+ cm-2. On the other hand, with increasing Cs incorporation molecular secondary ions containing Cs were found, notably (M+Cs)+. Concurrently, the damage induced by Cs implantation causes a decrease of the intensities of ion species such as (M+H)+ and others. This effect, however, seems to depend on the specific material: in the Cs fluence range investigated, it is rather moderate for arginine (a factor of about three), but more pronounced for leu-enkephalin and polyethylene glycol. It is envisaged that the amount of damage could be reduced considerably by employing Cs (or other) ions of much lower energy or by using thermal deposition processes. Eventually, such an in situ cationization might be beneficial in 2D and 3D TOF-SIMS analyses in order to obtain stable ion yields.