Self-Diffusion at a melting surface observed by He scattering

FWN – Publicaties zonder aanstelling Universiteit Leide

Transition of Molecule Orientation during Adsorption of Terephthalic Acid on Rutile TiO2(110)

Rahe P, Nimmrich M, Nefedov A, Naboka M, Wöll C, Kühnle A. Transition of Molecule Orientation during Adsorption of Terephthalic Acid on Rutile TiO2(110). Journal of Physical Chemistry C. 2009;113(40):17471-17478.The coverage-dependent mode of adsorption of terephthalic acid [C6H4(COOH)(2), TPA] on rutile TiO2(110) was investigated by means of noncontact atomic force microscopy (NC-AFM) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy under ultrahigh vacuum conditions at room temperature. Individual molecules are observed to adsorb in an disordered, flat-lying geometry at low coverages up to similar to 0.3 monolayer (ML). The molecules are immobile at room temperature. implying a diffusion barrier larger than 0.8 eV. This rather high value might be explained by anchoring to surface defect sites. A transition from flat-lying to upright-oriented molecules is revealed by NEXAFS when saturation coverage is achieved. High-resolution NC-AFM images reveal two different Structures at coverages between similar to 0.8 and 1 ML: (i) a well-ordered (2 x 1) structure and (ii) a structure of single and paired rows oriented along the [001] crystallographic direction. The latter structure might originate from a pairwise interaction of two neighboring molecules through the top carboxyl groups. Further increase in the exposure results in it saturation of the corresponding signal in the NEXAFS spectra, revealing that the growth of TPA oil TiO2(110) at room temperature is self-limiting

Phonons and specific heat of linear dense phases of atoms physisorbed in the grooves of carbon nanotube bundles

The vibrational properties (phonons) of a one-dimensional periodic phase of atoms physisorbed in the external groove of the carbon nanotube bundle are studied. Analytical expressions for the phonon dispersion relations are derived. The derived expressions are applied to Xe, Kr and Ar adsorbates. The specific heat pertaining to dense phases of these adsorbates is calculated.Comment: 4 PS figure

Relaxation and reconstruction on (111) surfaces of Au, Pt, and Cu

We have theoretically studied the stability and reconstruction of (111) surfaces of Au, Pt, and Cu. We have calculated the surface energy, surface stress, interatomic force constants, and other relevant quantities by ab initio electronic structure calculations using the density functional theory (DFT), in a slab geometry with periodic boundary conditions. We have estimated the stability towards a quasi-one-dimensional reconstruction by using the calculated quantities as parameters in a one-dimensional Frenkel-Kontorova model. On all surfaces we have found an intrinsic tensile stress. This stress is large enough on Au and Pt surfaces to lead to a reconstruction in which a denser surface layer is formed, in agreement with experiment. The experimentally observed differences between the dense reconstruction pattern on Au(111) and a sparse structure of stripes on Pt(111) are attributed to the details of the interaction potential between the first layer of atoms and the substrate.Comment: 8 pages, 3 figures, submitted to Physical Review