Ions at aqueous interfaces studied by in situ broadband sum-frequency generation spectroscopy
Final Report Abstract
Surface charging and ion specificity effects occurring at the metal oxide/ aqueous solution interface play a decisive role in various biological, environmental, geophysical, and industrial processes. Despite their importance, the influence of these effects on interfacial water molecules ordering at charged oxide surfaces is not fully understood. In this funding period, the surface charging and ion specificity at the tin-doped indium oxide (ITO)/ aqueous solution interface was investigated using in situ vibrational sum-frequency-generation (SFG) spectroscopy in combination with voltammetry. The n-type, wide bandgap semiconductor ITO was chosen as test material because of its good chemical stability, high optical transparency, and low electrical resistivity, which enables simultaneous spectroscopic and controlled voltammetric measurements in aqueous environments. In order to perform these measurements at this interface and other solid/ liquid interfaces, the previously existing SFG spectrometer setup was extensively modified, especially with the addition of a Fabry-Perot etalon for pulse shaping and phase-independent measurements, the redesign of the sample stage area for easy manipulation and quick exchange of measuring cells, and the addition of a reference line for absolute intensity measurements. Furthermore, a novel three-electrode spectroelectrochernical cell with ITO-coated IR-transparent prism as working electrode was designed and constructed. The sputter-deposited and annealed ITO thin film was first characterized in terms of structural, electrical, and optical properties using X-ray diffraction, scanning electron microscopy, four-point probe resistivimetry, and optical spectroscopies. An homogeneous, polycrystalline structured surface with low resistivity (~ 10^-2 Q-cm) and high transmissivity (~80-90%) in the visible range was found. The isoelectric point of 1T0 (pH,ep z 3) was determined by streaming potential measurements in water and aqueous salt solutions. The influence of applied potential on water ordering and ion affinity was investigated by SFG measurements at two positions of the bonded-OH-region (~ 3150 cm^-1 and ~ 3400 cm^-l) with deuterated water, normal water, and two series of anionic and cationic salt solutions; The experiments with water revealed the presence of a strong non-resonant contribution from the ITO film which could potentially dominate all resonant contributions, except at high positive potentials. With the anionic and cationic salt solutions, no ion specific effects could be detected but certain soft ions showed a definite propensity for the ITO surface. Surface current density was also recorded in both Spectral regions and showed-the presence of corrosion effects on ITO, especially important for halogenated salts. The results from this research funding and closely related studies are documented in 10 publications in peer-reviewed international journals and supported two PhD theses and one habilitation.
Publications
- Probing the extracellular matrix with sum-frequency-generation spectroscopy. Langmuir, 24(24): 13819-13821,2008
C. Howell, M.-O. Diesner, M. Grunze, and P. Koelsch
- Sum-frequency spectroscopy of DNA films in air and aqueous environments. Biointerphases, 3(3):FC47-FC51,2008
C. Howell, R. Schmidt, V. Kurz, and P. Koelsch
- Electrically driven director-rotation of swollen nematic elastomers as revealed by polarized Fourier transform infrared spectroscopy. Physical Review E, 79(5):051702,2009
A. Fukunaga, K. Urayama, P. Koelsch, and T. Takigawa
- Orientation and ordering in monomolecular films of sulfur-modified homo-oligonudeotides on gold. Journal of Physical Chemistry C, 113(42):18312-18320,2009
N. Ballav, P. Koelsch, and M. Zharnikov
- Ultraviolet irradiation suppresses adhesion on TiO2. Journal of Physical Chemistry C, 113(19):8273-8277,2009
R. Jribi, E. Barthel, H. Bluhm, M. Grunze, R Koelsch, D. Verreault, and E. Sondergard
- Charge separation in Ag@TiO2 core shell nanoparticle films. Surface and Interface Analysis, 42:835-841,2010
I. Tunc, M. Bruns, H. Ghemann, M. Grunze, and P. Koelsch
- In situ characterization of thermo-responsive poly(nisopropylacrylamide) films with sum-frequency generation spectroscopy. Chemphyschem, 11(7):1425-1429,2010
V. Kurz, M. Grunze, and P. Koelsch
- In vitro characterization of surface properties through living cells. Journal of Physical Chemistry Letters, 1(15):2339- 2342,2010
M.-O. Diesner, C. Hovwell, V. Kurz, D. Verreault, and P. Koelsch
- Interactions of hydrophobic and hydrophilic self-assembled monolayers with water as probed by sum-frequency-generation spectroscopy. Chemical Physics Letters, 494(4r-6): 193-197,2010
C. Howell, R. Maul, W. Wenzel, C. Barth, and P. Koelsch
- Sample cells for probing solid/liquid interfaces with broadband sum-frequency-generation spectroscopy. Rev. Sci. Instrum., 81(6):063111,2010
D. Verreault, V. Kurz, C. Howell, and P. Koelsch
