Constant force topographic AFM images showing the evolution of tetradecyl , hexadecyl , and octadecyalmine islands on mica during exposure to ambient laboratory air (ripening). The numbers at the top of each image indicate days elapsed after preparation.
Fractional surface area covered by islands of , , and alkylamines vs ripening time. The horizontal lines have been drawn to mark the coverage expected from a tilted configuration . The value of indicates the number of methylene groups unmatched in neighboring molecules (see text for details).
Left axis: Friction contrast between alkylamine islands and the surrounding mica substrate. Right axis: pull-off force measured on top of the islands and on the mica substrate for , , and alkylamines during the accretion stage, where scattered molecules diffuse on the mica before attaching to the islands. Friction values are obtained from the difference between left to right and the right to left traces in friction force images, using the same tip and experimental conditions for , , and .
Island height vs ripening time for , , and alkylamines on mica. The horizontal gray lines indicate theoretical heights for states characterized by discrete tilt angles in the nearest neighbor and next-nearest neighbor directions , as explained in the text.
Topographic AFM images of hexadecylamine SAM islands showing coexistence of two heights (images at 1, 15, and ripening). Tilting state is indicated in line profiles.
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