  Metal nanoparticles are the most frequently used nanostructures in
plasmonics. However, besides nanoparticles, metal nanowires feature several
advantages for applications. Their elongation offers a larger interaction
volume, their resonances can reach higher quality factors, and their mode
structure provides better coupling into integrated hybrid dielectric-plasmonic
circuits. It is crucial though, to control the distance of the wire to a
supporting substrate, to another metal layer or to active materials with
sub-nanometer precision. A dielectric coating can be utilized for distance
control, but it must not degrade the plasmonic properties. In this paper, we
introduce a controlled synthesis and coating approach for silver nanowires to
fulfill these demands. We synthesize and characterize silver nanowires of
around 70 nm in diameter. These nanowires are coated with nm-sized silica
shells using a modified St\"ober method to achieve a homogeneous and smooth
surface quality. We use transmission electron microscopy, dark-field microscopy
and electron-energy loss spectroscopy to study morphology and plasmonic
resonances of individual nanowires and quantify the influence of the silica
coating. Thorough numerical simulations support the experimental findings
showing that the coating does not deteriorate the plasmonic properties and thus
introduce silver nanowires as usable building blocks for integrated hybrid
plasmonic systems.
