Prof. Dr. Martina Havenith-Newen, Department of Chemistry, Ruhr-Universitaet Bochum

New tools of IR and THz laser spectroscopy: Characterization of surfaces and hydration shells

Technological developments of IR-and THz technology have given us new tools to investigate interfacial regions in condensed phase: We have developed a high power THz laser-based spectrometer which allows to directly study hydration layers of carbohydrates and proteins in solution. By a precise measurement of absorption coefficients at 3 THz we were able to determine the size and the characteristic absorption of the water in the hydration shell, which differs from bulk water: The hydration layer around a carbohydrate (lactose) is determined to extend to (5.24±0.25) Å from the surface which corresponds to ca. 110 water molecules per lactose molecule. This is to our knowledge the first experimental proof of an extension beyond the first solvation shell. Furthermore, we have developed a scanning near field infrared microscope (SNIM) which allows a 2-dim mapping of chemical fingerprints (IR spectra) with a lateral resolution of 30 nm. Using our IR-Optical Parametric Oscillator (IR-OPO) in the spectral region of the chemically important C-H and O-H stretch we were able to detect subsurface nanostructures: Implanted gallium ions in a topographically flat silicon wafer can be clearly imaged. We could demonstrate the high sensitivity of this method by distinguishing between different self assembled monolayers by their absorption in the C=O stretching region.

For more information contact Dr. Rob Dickson (404-894-4007).