Self-alignment of molecular chains on pre-structured Sm/Si(111) interface .
Résumé
Creation of organic-inorganic heterostructures is interesting for their potential applications, in particular for molecular electronic. To realize a self-assembly molecular chain on silicon we have to use a compromise between the migration barrier height and the intermolecular interaction. The choice of the surface is thus crucial and obviously no silicon surface can satisfy these conditions. To attempt this goal we have decided to use pre-structured silicon reconstructions of the Sm/Si(111) system [1,2]. This interface presents several 1D surface reconstructions, in the sub-monolayer Sm coverage, compatible with a 1D network growth. Palmino et al. have already succeeded the growth of self-assembled lead nanowires on this interface [3]. We show in this study, the possibility to generate on a semi-conductor substrate, a 1D molecular alignment of (1,4-di-(9-ethynyltriptycene)-benzene) molecules on pre-structured on the Sm/Si(111) (8 × 2) reconstruction at room temperature. This structure is based on a combination of HCC ((3×1) structural unit) and Seitwatz chains ((3×2) structural unit). The molecule used is the (1,4-di-(9-ethynyltriptycene)-benzene) (C50H30), a part of a molecular wheelbarrow which is a nanoscale machine imagined to move on the surface. We used for our experiments the ”wheels+axle” of the weelbarrow where the triptycene end groups form the wheels and they are able to rotate around the axle via a σ-bond [4]. The adsorption has been investigated by scanning tunneling microscopy (STM) and by DFT calculation. STM images have shown the preferential adsorption sites along the Si Seiwatz chains. An experimental STM image has been simulated thanks to DFT calculation in order to determine the surface electrostatic potential distribution and to explain the possibility to generate the 1D molecules alignment on a pre-structured semi-conductor substrate at room temperature