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.

体相硅（bulk silicon）是信息技术的基石，其仅由Si-Si σ键构成看似简单的电子结构。金刚石与硅具有相同的晶格结构，但二者的电子特性却有着天壤之别。本文报道了一类包含强相互作用Si-Si σ键的分子——低聚硅烷（oligosilanes）——的精准合成与电学表征，这类σ键正是体相半导体的核心组成部分。我们采用基于扫描隧道显微镜的断裂结技术（scanning tunneling microscope-based break-junction technique），对比了低聚硅烷与烷烃的单分子电导特性。研究发现，分子电导随链长增加呈指数衰减，衰减常数β=0.27±0.01 Å⁻¹，该数值与C=C π键构成的共轭链的衰减常数相当。本结果揭示了σ共轭效应对硅基材料导电性的深远影响。