  We present topographic and spectroscopic scanning tunneling microscopy
measurements taken on a 21 nm thick TiN film at a temperature of 4.2 K -- above
the superconducting transition temperature (T_c = 3.8 K) of the sample. The
film was polycrystalline with crystallite diameters of d~19 nm, consistent with
other films prepared under similar conditions. The spectroscopic maps show on
average a shallow V-shape around V_b = 0 V consistent with a sample near the
Mott insulation transition. In selected regions on several samples we
additionally observed signs of Coulomb blockade. The corresponding peak
structures are typically asymmetric with respect to bias voltage indicating
coupling to two very different tunneling barriers. Furthermore, the peak
structures appear with constant peak-peak spacing which indicates quantum dot
states within the Coulomb blockade island. In this paper we discuss one such
Coulomb blockade area and its implications in detail.
