Synchrotron X-ray and neutron diffraction have been used to determine the two-dimensional crystalline structures of alkylamides adsorbed on graphite at submonolayer coverage. The calculated structures show that the plane of the carbon backbone of the amide molecules is parallel to the graphite substrate. The molecules form hydrogen-bonded dimers, and adjacent dimers form additional hydrogen bonds yielding extended chains. By presenting data from a number of members of the homologous series, we have identified that these chains pack in different arrangements depending on the number of carbons in the amide molecule. The amide monolayers are found to be very stable relative to other closely related alkyl species, a feature which is attributed to the extensive hydrogen bonding present in these systems. The characteristics of the hydrogen bonds have been determined and are found to be in close agreement with those present in the bulk materials.

In this work we present a study on the adsorption of linear alkyl aldehydes physisorbed from their bulk liquid onto a graphite substrate combining calorimetry for all homologues from C6 to C13, with more detailed diffraction, incoherent neutron scattering, and scanning tunneling microscopy techniques for one (C12) representative member. We identify solid monolayer formation for some of these species for alkyl chain lengths of 6 to 13 carbons at high surface coverages. The C12 monolayer structure is determined to be most likely Pgg and this structure is discussed in terms of the importance of dipolar interactions.

In this letter, the phase behavior of a saturated alkylamide, heptanamide (C(7)), adsorbed on the surface of graphite using synchrotron X-ray diffraction is presented. The diffraction patterns indicate that heptanamide undergoes a solid-solid phase transition in the monolayer at 330 K from pgg symmetry at lower temperatures to p2 symmetry at high temperatures. Other alkylamides with similar carbon chain lengths do not show this phase change, making the C(7) homologue unusual.

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