  Electronic structure across the metal-insulator (MI) transition of
electron-doped V1-xWxO2 epitaxial films (x = 0-0.06) grown on alfa-Al2O3
substrates was studied by means of thermopower (S) measurements. Significant
increase of |S|-values accompanied by MI transition was observed, and the
transition temperatures of S (TS) decreased with x in good linear relation with
MI transition temperatures. |S| values of V1-xWxO2 films at T > TS were
constant at low values of 23 microV K-1 independently of x, which reflects a
metallic electronic structure, whereas, those at T < TS almost linearly
decreased with logarithmic W-concentrations. The gradient of -213 microV K-1
agrees well with -kB/e*ln10 (-198 microV K-1), suggesting that V1-xWxO2 films
have insulating electronic structures with a parabolic density of state around
the conduction band bottom.
