Development of Nanofluidic Cells for Ultrafast X rays Studies of Water Melvin E. Irizarry-Gelpí Aaron Lindenberg

Brief Outline  Background Water and its structure Water and its structure Experiments Experiments Confined liquids Confined liquids  Nanofluidic cells  The apparatus  Sample Characterization  Results

Water Ice structure Liquid water Liquid water exhibits structural rearrangements on picosecond and femtosecond time-scales How does the structure and dynamics of liquids confined to nanoscopic length-scales differ from the bulk?

Femtosecond x-ray absorption spectroscopy  Use femtosecond laser to drive hydrogen bond network  Ultrafast soft x-ray pulses provide the necessary resolution to probe bonding dynamics  In order to perform measurements, nanofluidic cells (<500 nm thickness) are required

Previous Methods

Nanofluidic Cells  Two Si 3 N 4 1 mm x 1 mm and 0.5 mm x 0.5 mm windows  Thickness < 500 nm  Photoresist spacer and Polystyrene nanospheres with different diameters (200 nm and 500 nm) window water layer window spacer

The SIMPLEtron  Simple and reproducible way to make cells  Micrometer stages allow for accurate position of sample cells and application of nanoliter quantities of water  Sample preparation takes minutes

Sample holder

Sample characterization FTIR at SU XAS at beamline ALS - LBNL

Results (FTIR) Peaks related to vibrational modes

Results (XAS)

Thickness (FTIR) Plain water Polystyrene spheres 1000 nm 1010 nm 450 nm 520 nm 220 nm 1750 nm 145 nm 1500 nm 150 nm 500 nm 1800 nm

Thickness (XAS) Plain water Polystyrene spheres 15 nm 1 nm 5 nm 10 nm 15 nm 17 nm 25 nm

Preliminary observation of confinement effects  Observe shift in main absorption peak to lower energy as sample thickness decreases  Indication of change in structure (to a more ice-like configuration) for ultrathin samples

Confined Liquids

Conclusions  A simple and reliable means of producing nanofluidic water cells has been developed  A range of thickness may be produced, although random  Evidence for changes in the x-ray absorption spectrum for ultrathin samples is observed  Future experiments will couple a femtosecond laser into the sample to probe the structural dynamics of water on ultrafast time-scales

Acknowledgements  U. S. Department of Energy, Office of Science, SULI Program  SLAC and Stanford University  Advance Light Source at Lawrence Berkeley National Laboratory  Special thanks to Aaron Lindenberg

Thank you for your attention Questions

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