Water-assisted secondary ion mass spectrometry using gas cluster ion beams

A novel methodology is presented for increasing the sensitivity of secondary ion mass spectrometry (SIMS) using soft-landed massive water cluster ions to enhance the yield of protonated molecular ions generated by subsequent C60 bombardment. The effect is sensitive to sample temperature, water cluster velocity, and dose. Colder samples dosed with larger, slower, (H2O)n clusters reach optimum [M + H]+ signals at lower cluster dose. For adenosine triphosphate and glucose at temperatures −120 to −160 °C, we demonstrate protonated ion yield enhancements up to 2 orders of magnitude using 0.05–0.13 eV/u (H2O)n at doses 1011–1012 ion/cm2. The level of enhancement exceeds that reported previously for gas-phase water dosing in vacuo. The methodology may be particularly useful for samples that cannot be prepared in a frozen-hydrated state or where the desired lateral resolution of the SIMS analysis exceeds that of a reactive gas cluster ion beam such as (H2O)n.