Characterization of N-alkyl-D-gluconamide adsorbate structures by atomic force microscopy. 1. Microcrystals and layered structures

Abstract

The morphology and molecular order of the microcrystals and self-assembled layers of N-(n-alkyl)-D-gluconamide (alkyl = heptyl, octyl, nonyl, decyl) adsorbates on graphite and mica were characterized by optical and atomic force microscopy (AFM). The rectangular microcrystals have steps whose heights correspond to the 6-constants of the bulk crystal structures, and the molecular arrangements of the microscrystal surfaces found in the molecular-scale AFM images are consistent with those of the ac-planes of the bulk crystal structures. The frequently observed self-assembled layers are double-layers, the thickness of which is twice the length of the molecules in their extended conformation. These layers have a hexagonal packing of the molecules with the period of 0.52 nm. The same molecular order is found for the less-frequently observed single-layers. In the thin overlayers of the alkylgluconamides, the molecules lie parallel to the substrate and form lamellar structures in which the molecules have head-to-head packing. The width of the lamellar structures is similar to the thickness of the double-layers. Thus, the molecular conformation and packing in the self-assembled layers differ from those in their single crystals. © CNRS-Gauthier-Villars.