Abstract
We present an analysis method of normal incidence x-ray standing wave (NIXSW) data that allows detailed adsorption geometries of complex molecules to be retrieved. This method (Fourier vector analysis) is based on the comparison of both the coherence and phase of NIXSW data to NIXSW simulations of different molecular geometries as the relevant internal degrees of freedom are tuned. We introduce this analysis method using the prototypical molecular switch azobenzene (AB) adsorbed on the Ag(111) surface as a model system. The application of the Fourier vector analysis to AB/Ag(111) provides, on the one hand, detailed adsorption geometries including dihedral angles, and on the other hand, insights into the dynamics of molecules and their bonding to the metal substrate. This analysis scheme is generally applicable to any adsorbate, it is necessary for molecules with potentially large distortions, and will be particularly valuable for molecules whose distortion on adsorption can be mapped on a limited number of internal degrees of freedom.
Highlights
The normal incidence x-ray standing wave (NIXSW) technique is one of the methods of choice for determining accurate molecular adsorbate geometries [1,2,3,4,5]
We present an analysis method of normal incidence x-ray standing wave (NIXSW) data that allows detailed adsorption geometries of large and complex molecules to be retrieved
For much smaller molecules (4–5 atoms) the NIXSW coherence was used to gain information on the adsorption geometry [16, 17]. For such small systems and in presence of NIXSW data from multiple Bragg reflections a program that calculates the most likely adsorption geometry was developed [18]. It would be desirable if structural information on the arrangement of carbon atoms was available from NIXSW for larger molecules, in cases where chemical differentiation is not possible and when NIXSW data from only one single Bragg reflection are available
Summary
We present an analysis method of normal incidence x-ray standing wave (NIXSW) data that allows detailed adsorption geometries of large and complex molecules to be retrieved This method (Fourier vector analysis) is based on the comparison of both the coherence and phase of NIXSW data to NIXSW simulations of different molecular geometries as the relevant internal degrees of freedom are tuned. The application of the Fourier vector analysis to AB/Ag(111) provides, on the one hand, detailed adsorption geometries including dihedral angles, and on the other hand, insights into the dynamics of molecules and their bonding to the metal substrate This analysis scheme is generally applicable to any adsorbate, it is necessary for molecules with potentially large distortions, and will be valuable for molecules whose distortion on adsorption can be mapped on a limited number of internal degrees of freedom
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