In EUV TOF MS, bright laser pulses from a compact 46.9-nm-wavelength laser [1] are focused into nanometer size spots to ablate craters a few nanometers deep on selected regions of the sample. Elemental and molecular ions in the laser-created plasma are extracted and identified by their mass-to-charge ratio (m/z) using a time-of-flight (TOF) mass spectrometer. Analysis of the spatially resolved mass spectra obtained as the sample is displaced with respect to the focused laser beam enables one to construct 3-D composition images with nanoscale resolution [2]. In this talk I will describe recent advances of extreme ultraviolet MSI that show its unique capabilities to identify low concentration of high Z elements into glass matrices, and to map isotopic ratios [3].
[1] S. Heinbuch et al, "Demonstration of a desk-top size high repetition rate soft x-ray laser," Opt. Express 13, 4050-4055 (2005).
[2] I. Kuznetsov et al, "Three dimensional nanoscale molecular imaging by extreme ultraviolet laser ablation mass spectrometry, " Nature Communications, Vol. 6, Article No. 6944(2015).
[3] T. Green, et al, “Characterization of extreme ultraviolet laser ablation mass spectrometry for actinide trace analysis and nanoscale isotopic imaging,” J. Analy. At. Spectrom. Vol. 32, 1092 (2017).
We have previously shown soft x-ray laser ablation time-of-flight mass spectrometry has the ability to detect singly ionized alanine molecules arising from the single shot ablation of a ∼50 zeptoliter volume. This superior sensitivity results from the ability to focus the 46.9 nm wavelength (26.4 eV energy per photon) laser beam to the diffraction limit, the strong absorption, and the efficient photoionization of the soft x-ray photons. In this paper we describe results on the application of soft x-ray laser mass spectrometry to elemental trace analysis in inorganic materials. Two dimensional imaging with spatial resolution of 80 nm in inorganic samples is also demonstrated.
There are significant advantages for using a compact capillary discharge soft x-ray laser (SXRL) with wavelength of 46.9 nm for mass spectrometry applications. The 26.4 eV energy photons provide efficient single-photon ionization while preserving the structure of molecules and clusters. The tens of nanometers absorption depth of the radiation coupled with the focusing of the laser beam to diameter of ∼100 nm result in the ablation of atto-liter scale craters which in turn enable high resolution mass spectral imaging of solid samples. In this paper we describe results on the analysis of composition depth-profiling of multilayer oxide stack and material studies in photoresists, ionic crystals, and magnesium corrosion products using SXRL ablation mass spectrometry, a method first demonstrated by our group. These materials are used in a variety of soft x-ray applications such as detectors, multilayer optics, and many more.
Mass spectrometry plays a vital role in the direct examination of the chemical composition of solids. We have introduced the use of soft x-ray laser ablation for mass spectrometry imaging. Here we demonstrate the method potential for composition depth profiling of multilayer stacks consisting of tens of nanometers thick metal and dielectric films.
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