Research


Projects

P1

Post-ionization in Secondary Ion Mass Spectrometry: from Pre-ionization to Adaptive Control


Secondary ion mass spectrometry is an excellent technique of analytical chemistry, where primary ions sputter a solid sample generating the secondary ions which are determined. Although the ion yield is inherently low, it can be enhanced by using a post-ionization of sputtered neutral species. An alternative, utilizing laser pre-ionization, is introduced. The native Ag sample surface is first irradiated with laser pulse (100 fs duration, 1010-1011 W/cm2 intensity, 1240 nm wavelength) and subsequently bombarded with primary ions (Bi3+, 10 ns duration, 25 keV energy). Multiple correlation patterns are observed in the mass spectra, confirming the mutual laser and secondary ion mass spectrometry interplay. Two ionization mechanisms are identified, the ion sputtering regime for intensities of less than 1.4x1011 W/cm2 and the multiphoton ionization at higher intensities. The Ag saturation intensity obtained from fitting is 2.4x1013 W/cm2, close to the one reported for post-ionization. A novel approach of post-ionization integrates the secondary ion mass spectrometry with a near infrared femtosecond laser post-ionization based on an adaptive control through a laser pulse shaper. The shaping of the laser pulse provides adaptive control to select a mass peak of interest and to enhance this peak intensity. Versatility is confirmed by optimizing the ion yield for different molecules (tryptophan, anthracene, polyethylene, and oxalic acid) with focus on parent ion enhancement, fragmentation process, sublimation effect, and excited secondary species. This proof-of-concept experiment provides not only a nonspecific increase of the overall ion yield, but also the selection of specific secondary species and the adaptive enhancement of their intensities on the order of 100, potentially simplifying data interpretation. Such tailored spectra might advance the (secondary ion) mass spectrometry to new capabilities.

  1. Lorenc, Dusan - Jane, Eduard - Stupavska, Monika - Jerigova, Monika - Velic, Dusan: Infrared Femtosecond Laser Preionization in Secondary Ion Mass Spectrometry of Silver Surface, Journal of the American Society for Mass Spectrometry. - Vol. 23, No. 7 (2012), s. 1266-1270
  2. Dusan Lorenc, Monika Jerigova, Monika Stupavska, Dusan Velic: Adaptive Control of Ion Yield in Femtosecond Laser Post-ionization for Secondary Ion Mass Spectrometry, Scientific Reports - 2017, 7, 5953