| AVS 55th International Symposium & Exhibition | |
| Applied Surface Science | Tuesday Sessions |
| Session AS-TuP |
| Session: | Aspects of Surface Analysis Poster Session |
| Presenter: | L.K. Takahashi, Lawrence Berkeley National Laboratory |
| Authors: | L.K. Takahashi, Lawrence Berkeley National Laboratory J. Zhou, Lawrence Berkeley National Laboratory M. Ahmed, Lawrence Berkeley National Laboratory S.R. Leone, University of California, Berkeley K.R. Wilson, Lawrence Berkeley National Laboratory |
| Correspondent: | Click to Email |
Elemental chemical imaging of surfaces on the sub-micron scale with Secondary Ion Mass Spectrometry (SIMS) has yielded much new and tantalizing information. However, the method is limited in its application to more fragile organic molecules due to extensive fragmentation, which results in complicated mass spectra that are difficult to analyze. Furthermore, the sensitivities of different chemical species in SIMS are highly dependent on the local chemical environment, meaning that relative intensities in the mass spectra do not reflect the actual chemical abundances at the surface. In Secondary Neutral Mass Spectrometry (SNMS), ejected neutrals are post-ionized, effectively decoupling the desorption and ionization steps. The resulting mass spectra are less dependent on the local chemical environment. Fragmentation of organic molecules, however, has remained a problem. The ionization potentials of most organic molecules are around 9-11 eV, and commercial tabletop lasers usually have lower photon energies than this, necessitating multiphoton ionization. This ionization method imparts excessive energy to the neutral molecules which can fragment organic chemical species. Here we present a new method utilizing continuously tunable VUV synchrotron light for single photon post-ionization of secondary organic neutrals. By ionizing just above the threshold, it has been shown that fragment free mass spectra of organic molecules can be obtained. The tunability of the light also allows for isomer identification by their characteristic ionization energies and associated fragments. While the experiment is still in its early stages, preliminary results have yielded unique photoionization efficiency curves for different organic molecules. With further improvements, single photon VUV-SNMS can become a powerful tool capable of providing localized chemical information on real-world heterogeneous organic systems such as microbial cells and aerosols.