Whitehead group


Prof. M.A. Whitehead
Department of Chemistry
McGill University
Otto Maass Chemistry Building,
801 Sherbrooke St. West,
Room 352,
Montreal, Quebec,
H3A 2K6, Canada.

office: (514) 398-6239
lab: (514) 398-6905
fax: (514) 398-3797


Chemistry of surface anchored[Sn]-NEt2 moieties with alkyne-terminated chromophores has been used to construct close packed thin films on Si(100)SiO2. Films exhibit enhanced optical and electical properties on the surface because of extensive conjugation within the adsorbed molecules.

Discrete surface organization of 1,9-decadiyne and p-diethynylbenzene monolayers on Si(100)/SiO2/SnO2 surfaces was determined with a unique and powerful molecular modelling approach, using rigid geometry scans and periodic geometry optimizations.  Geometric arguments produced the monolayers packing space, and rapid optimizations gave small, repeating symmetric unit cells that correctly represented an infinite monolayer surface.  Semi-empirical analysis classified the infinite thin films as semiconducting materials, because of organized Pi orbital overlap and the presence of acceptor bands from the Sn headgroups. Headgroup bonding was identified as a force for controlled monolayer order. 

At natural surface packing densities, Sn-O-Sn cross-linking prevents optimal organization of the monolayer because the cross-link distance is smaller than the preferred packing separation of organic chromophores.  Optimizations at unnatural surface densities found thin films of lower energy and higher symmetry existed at increased chain-chain separations. Thin films with adjustable characteristics were created by using binary surface activation units to selectively abdorb different organic molecules.  Linking headgroups, (NMe2)3-Si-O-X-C=C-Sn(NEt2)3, greatly improved thin film order by preventing phase separation, and increasing average chain-chain distances. Self-generating arrays of highly coloured dendritic crystals, with potential optoelectronic activity, form directly on solid-state interfaces.