Imaging isotopic content at the nanoscale using extreme ultraviolet laser ablation and ionization mass spectrometry

Extreme ultraviolet (EUV) lasers possess unique properties for ablation and ionization at the nanoscale (≤100 nm) due to their short wavelength, high absorptivity in most materials (i.e., 10's of nanometers), and efficient photoionization in the laser-created plasmas. When coupled with a mass spectrometer, an EUV laser can be used to analyze and map chemical information in three dimensions with nanoscale spatial resolution. We have previously built an EUV time-of-flight mass spectrometer (EUV TOF) that achieved ∼80 nm lateral and ∼20 nm depth resolution when mapping the chemical content in organic and inorganic solids. Here, we present results from a recent study that extends EUV TOF's high resolution capabilities to the analysis of an isotopically heterogenous uranium fuel pellet that was made by blending two isotopically distinct starting materials. We show that EUV TOF can map 235U/238U heterogeneity at the 100 nm scale, revealing micron to submicron heterogeneity. For comparison, nanoscale secondary ionization mass spectrometry (NanoSIMS) maps a similar distribution of U heterogeneity on a similar subsample at the same spatial scale. We also show that EUV TOF can measure the isotope ratio in a silver sample using single shot spectra. These results position EUV TOF as a promising technique for performing isotopic analyses at the nanoscale, finding applications in nuclear forensics, geology, and biology as well as in the semiconductor industry.