Conductive molecular silicon

Bulk silicon, the bedrock of information technology, consists of the deceptively simple electronic structure of just Si–Si σ bonds. Diamond has the same lattice structure as silicon, yet the two materials have dramatically different electronic properties. Here we report the specific synthesis and electrical characterization of a class of molecules, oligosilanes, that contain strongly interacting Si–Si σ bonds, the essential components of the bulk semiconductor. We used the scanning tunneling microscope-based break-junction technique to compare the single-molecule conductance of these oligosilanes to those of alkanes. We found that the molecular conductance decreases exponentially with increasing chain length with a decay constant β = 0.27 ± 0.01 Å–1, comparable to that of a conjugated chain of C═C π bonds. This result demonstrates the profound implications of σ conjugation for the conductivity of silicon.