Publications by authors named "Jacques F Aarts"

2 Publications

  • Page 1 of 1

Co-adsorption of water and hydrogen on Ni(111).

Phys Chem Chem Phys 2008 Aug 4;10(32):4994-5003. Epub 2008 Jul 4.

Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden, The Netherlands.

We have studied the surface coverage dependence of the co-adsorption of D and D(2)O on the Ni(111) surface under UHV conditions. We use detailed temperature-programmed desorption studies and high resolution electron energy loss spectroscopy to show how pre-covering the surface with various amounts of D affects adsorption and desorption of D(2)O. Our results show that the effects of co-adsorption are strongly dependent on D-coverage. In the deuterium pre-coverage range of 0-0.3 ML, adsorption of deuterium leaves a fraction of the available surface area bare for D(2)O adsorption, which shows no significant changes compared to adsorption on the bare surface. Our data indicate phase segregation of hydrogen and water into islands. At low post-coverages, D(2)O forms a two-phase system on the remaining bare surface that shows zero-order desorption kinetics. This two phase system likely consists of a 2-D solid phase of extended islands of hexamer rings and a 2-D water gas phase. Increasing the water post-dose leads at first to 'freezing' of the 2-D gas and is followed by formation of ordered, multilayered water islands in-between the deuterium islands. For deuterium pre-coverages between 0.3 and 0.5 ML, our data may be interpreted that the water hexamer ring structure, (D(2)O)(6), required for the formation of an ordered multilayer, does not form anymore. Instead, more disordered linear and branched chains of water molecules grow in-between the extended, hydrophobic deuterium islands. These deuterium islands have a D-atom density in agreement with a (2x2)-2D structure. The disordered water structures adsorbed in-between form nucleation sites for growth of 3-D water structures. Loss of regular lateral hydrogen bonding and weakened interaction with the substrate reduces the binding energy of water significantly in this regime and results in lowering of the desorption temperature. At deuterium pre-coverages greater than 0.5 ML, the saturated (2x2)-2D structure mixes with (1x1)-1D patches. The mixed structures are also hydrophobic. On such surfaces, submonolayer doses of water lead to formation of 3-D water structures well before wetting the entire hydrogen-covered surface.
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August 2008

The interaction of water with Ni(111) and H/Ni(111) studied by TPD and HREELS.

Phys Chem Chem Phys 2008 Apr 29;10(16):2227-32. Epub 2008 Feb 29.

Leiden Institute of Chemistry, Gorlaeus Laboratories, PO Box 9502, 2300 RA, Leiden, the Netherlands.

We have used temperature-programmed desorption in combination with specular and off-specular high resolution electron energy loss spectroscopy to study the interaction of H(2)O and D(2)O with the bare and hydrogen-covered Ni(111) surface. Our results for the bare metal surface agree with previous reports and we are able to relate two prominent features in vibrational spectra to nuclear motions at the surface. Pre-covering Ni(111) with hydrogen alters both adsorption and desorption of water significantly. The strong H-Ni bond does not allow for isotopic exchange with co-adsorbed D(2)O. Strong resemblance of desorption traces and vibrational spectra of submonolayer coverages on H-covered Ni(111) and multilayers on bare Ni(111) suggests that adsorption of hydrogen makes this nickel surface hydrophobic.
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April 2008