Mapping Surface Chemistry and Molecular Orientation with Combinatorial Near-Edge X-Ray Absorption Fine Structure Spectroscopy

The demands of preparing, processing, and characterizing novel materials and structures, and the need for full exploration of the typically broad parameter space has led to the development of a plethora of novel combinatorial approaches.Most experimental combinatorialmethods concentrate on probing only a singlematerial property, such as chemical information, topography, etc. For some applications, it is desirable that multiple properties be probed simultaneously in a single experiment. In particular, information on the chemistry andmolecular organization of chemical groups on surfaces is needed to shed light on the behavior of amphiphilic surface modifiers or characterizing new classes of catalysts. In this paper, we show that information about the chemistry (including bond concentration and rehybridization) and molecular orientation on Summary: Mapping the bond chemistry and molecular orientation of self-assembled monolayer gradients on flat surfaces and reaction intermediates in catalyst arrays is made possible using combinatorial near-edgeX-ray absorption fine structure (NEXAFS) spectroscopy. These spatially resolved NEXAFS maps have been made by utilizing synchrotronbasedNEXAFS spectroscopy in conjunctionwith a computer controlled precision sample manipulator. The NEXAFS maps reveal bond concentration, rehybridization, and orientation of the surface-bound molecules with sub-millimeter planar spatial resolution and sub-monolayer molecular sensitivity. The wide applicability of the combinatorial NEXAFS method is illustrated by mapping: (1) the concentration and molecular orientation of semifluorinatedmolecules inmolecular gradients; (2) the concentration of amino groups in molecular gradients used for nanoparticle templating, and (3) the rehybridization of propylene intermediates on zeolite catalyst arrays used for measuring solid-state acidity and catalyst activity.