Niobium films with constant thickness have been deposited on sapphire
(11 $($) over bar$$ 20) by electron-beam evaporation at different subs
trate; temperatures (150 degrees C less than or equal to T-S less than
or equal to 750 degrees C). The samples were characterized by X-ray d
iffraction and resistivity measurements. X-ray reflectivity shows that
all films are covered with an oxide layer of about 20 Angstrom in amb
ient atmosphere. The (110) texture at high T-S decreases towards lower
T-S, accompanied by an increasing surface roughness. Below T-S = 350
degrees C the grain size in the growth direction becomes smaller than
the film thickness and a relaxation of intrinsic stress is observed. A
transition from a columnar growth structure to a fine grained microst
ructure is inferred. The change of the microstructure with T-S is prob
ably due to the temperature dependent grain boundary mobility during t
he deposition process.