AVS 58th Annual International Symposium and Exhibition
    Applied Surface Science Division Thursday Sessions
       Session AS-ThM

Paper AS-ThM2
Aqueous SIMS – Towards in Situ Detection of Chemical Reaction Intermediates in Aqueous Solutions

Thursday, November 3, 2011, 8:20 am, Room 102

Session: Analysis of Insulators and Challenging Samples
Presenter: Zihua Zhu, Pacific Northwest National Laboratory
Authors: Z. Zhu, Pacific Northwest National Laboratory
L. Yang, Pacific Northwest National Laboratory
X. Yu, Pacific Northwest National Laboratory
M.J. Iedema, Pacific Northwest National Laboratory
J.P. Cowin, Pacific Northwest National Laboratory
Correspondent: Click to Email
This research provides the first in-situ detection of aqueous surfaces using time-of-flight secondary ion mass spectrometry (ToF-SIMS). ToF-SIMS provides a molecular recognition capability with super-low detection limits, making it a great choice to detect short-lifetime chemical reaction intermediates in aqueous solutions. However, it is difficult to detect aqueous solutions by ToF-SIMS because ToF-SIMS is a high vacuum technique, and the vapor pressure of water is about 2-3 kPa at room temperature. We designed and fabricated a self-contained microfluidic module, allowing in-situ analysis of aqueous surfaces by ToF-SIMS. Microfluidic channels were prepared on top of a block of polydimethylsiloxane (PDMS) using a patterned silicon template with soft lithography techniques, and then a ~100nm thick silicon nitride film was placed on top of the microfluidic channels, on which a small hole with a diameter of ~2-3 microns could be drilled using a focused primary ion beam in a ToF-SIMS instrument. De-ionized water, heavy water, a 0.5% (weight ratio) formic acid aqueous solution, a 0.5% glycerol aqueous solution, and a 0.5% glutamic acid aqueous solution were successfully analyzed through the small hole using our ToF-SIMS instrument (IONTOF-V). The pressure in the analysis chamber was usually at ~5E-7 mbar during measurements, and this value was sufficient for ToF-SIMS analysis. Our device could be safely staying in vacuum for more than 8 hours, and 1 hour continuous SIMS measurements were practical. Molecular signals (M-H-) from formic acid (HCO2-), glycerol (C3H7O3-), and glutamic acid (C5H8NO4-) were clearly observed in the small hole, but not elsewhere. Based on current data, the detection limits of formic acid, glycerol, and glutamic acid were estimated to be <0.01% (weight ratio).