The Structure of Dodecanamide Monolayers Adsorbed on Graphite
A combination of synchrotron X-ray and neutron diffraction have been used to characterise the sub-monolayer (low-coverage) crystalline structure of dodecanamide [CH3-(CH2)10-CONH2] adsorbed on graphite. The calculated structure reveals that the molecules lie flat on the graphite surface. The amide head-groups hydrogen-bond into dimers, and, significantly, adjacent dimers form further hydrogen bonds yielding extended chains in good agreement with previous STM results. This monolayer has a very high stability, as observed in its melting point which is significantly higher than the bulk melting point even at these low coverages. The characteristics of the hydrogen bonds are found to be in close agreement with those reported in the bulk crystals. The coverage dependence of the structure is discussed.
KeywordsAmide Monolayer structure Graphite X-ray neutron diffraction Hydrogen bond
The authors thank the Nehru Trust for Cambridge University (TB) and Diamond Light Source for financial assistance. We thank Tamsin Philips and Julia Parker for help with the experiments and also the staff and scientists at ILL, Thomas Hansen and Jacques Torregrossa and at SLS, Antonio Cervellino and Fabia Gozzo, for beam time and technical assistance. This work is based on experiments performed at the Swiss Light Source, Paul Scherrer Institute, Villigen, Switzerland. The research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2007- 2013) under grant agreement no. 226716.
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