  Tip-enhanced Raman spectroscopy (TERS) combines inelastic light scattering
well below the diffraction limit down to the nanometer range and scanning probe
microscopy and, possibly, spectroscopy. In this way, topographic and
spectroscopic as well as single- and two-particle information may
simultaneously be collected. While single molecules can now be studied
successfully, bulk solids are still not meaningfully accessible. It is the
purpose of the work presented here to outline approaches toward this objective.
We describe a home-built, liquid helium cooled, ultrahigh vacuum tip-enhanced
Raman spectroscopy system (LHe-UHV-TERS). The setup is based on a scanning
tunneling microscope and, as an innovation, an off-axis parabolic mirror having
a high numerical aperture of approximately $0.85$ and a large working distance.
The system is equipped with a fast load-lock chamber, a chamber for the
\textit{in situ} preparation of tips, substrates, and samples, and a TERS
chamber. Base pressure and temperature in the TERS chamber were approximately
$3\times 10^{-11}$~mbar and 15~K, respectively. Polarization dependent
tip-enhanced Raman spectra of the vibration modes of carbon nanotubes were
successfully acquired at cryogenic temperature. Enhancement factors in the
range of $10^7$ were observed. The new features described here including very
low pressure and temperature and the external access to the light
polarizations, thus the selection rules, may pave the way towards the
investigation of bulk and surface materials.
