| AVS 55th International Symposium & Exhibition | |
| Applied Surface Science | Wednesday Sessions |
| Session AS-WeA |
| Session: | Frontiers of Analysis and Combined Materials |
| Presenter: | K. Hiraoka, University of Yamanashi, Japan |
| Authors: | K. Hiraoka, University of Yamanashi, Japan Y. Sakai, University of Yamanashi, Japan D. Asakawa, University of Yamanashi, Japan Y. Iijima, JEOL Ltd. |
| Correspondent: | Click to Email |
A new ionization method, electrospray droplet impact (EDI) ionization, has been developed for matrix-free secondary ion mass spectrometry (SIMS).1,2 The charged water droplets formed by electrospraying 1M acetic acid aqueous solution at atmospheric pressure are sampled through an orifice with a diameter of 400 μm into the first vacuum chamber, transported into a quadrupole ion guide, and accelerated by 10kV after exiting the ion guide. The water droplets impact on a dry solid sample ( no matrix used) deposited on a stainless steel substrate. The secondary ions formed by the impact are transported to a second quadrupole ion guide and mass-analyzed by an orthogonal time-of-flight mass spectrometer (TOF-MS). EDI was applied to peptides, synthetic polymers, and inorganic materials. It was found that EDI/SIMS has a high sensitivity without damaging the sample underneath and the film thickness desorbed by a single collisional event is to be less than a few monolayers. An instant conversion (in subpicoseconds) of kinetic energy of the impinging water droplet to the internal energies of molecules in the colliding selvedge takes place, i.e., sample molecules in the shock-wave excited selvedge suffer from the electronic excitation leading to the desorption/ionization. In the EDI mass spectra for PET, several fragment ions were observed but the XPS spectra did not change with prolonged cluster irradiation. This indicates that the surface of PET was etched with little surface damage. In the EDI mass spectra for tin and silicon, the major secondary ions observed were protonated oxide ions such as H+(SnO)n and H+(SiO2)n. This suggests that the oxidative chemical etching takes place in the selvedge of the colliding interface resulting in the atomic-level surface etching. Acknowledgement: This work was supported by the Japan Science and Technology Agency
1K. Hiraoka, D. Asakawa, S. Fujimaki, A. Takamizawa, K. Mori, Eur. Phys. J. D 38 (2006) 225.
2K. Hiraoka, K. Mori, D. Asakawa, J. Mass Spectrom., 41 (2006) 894.