Paper TF-WeA7
Benzene Adsorption on Self-Assembled Monolayers

Wednesday, October 20, 2010, 4:00 pm, Room Pecos

Non-dissociative deposition of gas-phase species onto surfaces of alkanethiol self-assembled monolayers (SAMs) allows creation of new types of multi-component nanoscale materials. Systems such as these have garnered much attention due to their central role as model systems for studies of orientation-controlled adsorption and non-dissociative attachment of functional molecules on organic surfaces of technological importance, including molecular electronics.

Benzene (C₆H­₆), perdeuterobenzene (C₆D₆) or a 50:50 mixture of these two isotopologues were deposited on SAM surfaces using a supersonic molecular beam. Supersonic molecular beam techniques permitted precise control over the dynamics of the deposition process by changes in the incident reagent’s translational energy (E_trans) and incident angle. The results presented here highlight the role these dynamical variables play in the adsorption, desorption and conformation of the resultant multilayer molecular film. A combination of in-situ infrared reflection absorption spectroscopy (FT-IRAS) and mass spectrometry was used to determine the surface coverage, molecular orientation and the sticking coefficient as a function of the surface coverage of the benzene molecules deposited on SAM surfaces. The interaction between adsorbates and the SAM substrate was also investigated by varying the SAM chain length and whether the SAM contains an odd or even number of carbon atoms. These results were compared to analogous results from adsorption on clean Au surfaces.

The results of these experiments uncovered the details of the adsorption process. The effects of E_trans and substrate temperature on sticking show the central role dynamics plays in the physisorption of molecules on surfaces. Most significantly, the sticking of gas-phase benzene was found to have a novel dependence on surface coverage, and non-Langmuirian uptake was observed.