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.