AVS 65th International Symposium & Exhibition
    Processing and Characterization of Air-Liquid, Solid-Liquid and Air-Solid Interfaces Focus Topic Wednesday Sessions
       Session PC+AS+BI+EM+PB+SS-WeM

Paper PC+AS+BI+EM+PB+SS-WeM4
Electrowetting of Liquid Drops Revisited by XPS

Wednesday, October 24, 2018, 9:00 am, Room 202A

Session: Novel Approaches and Challenges of Interfaces
Presenter: Sefik Suzer, Bilkent University, Turkey
Authors: S. Suzer, Bilkent University, Turkey
P. Gokturk, Bilkent University, Turkey
B. Ulgut, Bilkent University, Turkey
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Electrowetting behavior of liquid drops has been followed in-situ and in-vacuum using XPS in a chemically resolved fashion, under both dc and ac excitations. Various Liquid drops, compatible with the UHV conditions, consisted of an Ionic Liquid (DEME-TFSI), Poly-ethylene-glycol (M.W. ~600 amu) and their mixtures. For the dielectric substrate, a ~300 nm thick silicon oxide (SiO2/Si) without and with a thin hydrophobic coating (CYTOP) has been employed. XPS data have been recorded both in the conventional scan- and also in the fast (<1s) snap-shot modes. Intensity and position of the peaks, representing the liquid drops (F1s in the case of the IL, or C1s/O1s of the PEG) as well as those of the substrates (Si2p for the oxide only and F1s for the hydrophobic coated one) have been recorded under various electrical excitations. Under ac excitation at a fixed frequency, intensity modulations in the XPS peaks reveal geometrical changes of the drops, while the peak position modulations reveal electrical potentials developed. Monitoring position modulations as a function of the changes in the ac frequency (10-2 – 105 Hz) allows us to tap into ionic, dipolar and electrical contributions of the dielectric susceptibility of both the liquid drops and the substrates. Experimental details and various application will be presented and discussed.

*This work is partially supported by TUBITAK through Grant No. 215Z534