  We present a first-principles study of the electronic properties of silicon
clathrate nanowires intercalated with various types of alkali or alkaline-earth
atoms. We find that the band structure of the nanowires can be tuned by varying
the impurity atom within the nanowire. The electronic character of the
resulting systems can vary from metallic to semiconducting with direct band
gaps. These properties make the nanowires specially suitable for electrical and
optoelectronic applications.
