Center for Functional Nanomaterials Seminar

The structure and chemistry of water and other hydrogen-bonding molecules at surfaces and interfaces is an unresolved and fundamental topic in many areas of science and technology such as catalysis, electrochemistry and environmental sciences. We use low temperature scanning tunneling microscopy in combination with DFT calculations to study the adsorption and reaction of ultra thin water films and single ammonia molecules on Ru(0001). We discovered that for intact water the bonding structure between the first two water layers significantly deviates from the conventional, hydrogen-bonded, ice-like water model on hexagonal metals. Beyond the second water layer, a transition to the growth of compact ice clusters was found. In the second part, I will talk about the dissociation mechanisms of single ammonia molecules adsorbed on a flat ruthenium surface. We can induce the dehydrogenation of ammonia after applying voltage pulses of a few volts between the STM tip and adsorbed ammonia molecules. Our experiments suggest that the applied electric field between tip and surface causes the dissociation of NH3. DFT calculations confirm that an applied electric field greatly enhances the dissociation reaction rate through a reduction of the reaction energy barrier