We examine the properties of ultrathin TiN films grown by reactive dc magnetron sputtering on single-crystalline MgO(100) substrates at growth temperatures ranging from 30 to 650 degrees C. The resistance of the films is measured in-situ, during growth, to study the thickness at which the films coalesce and become structurally continuous. Both the in-situ resistance measurements and X-ray diffraction measurements show a clear transition from polycrystalline growth to epitaxial (100) growth well below typical TiN growth temperatures, or between 100 and 200 degrees C. The coalescence and continuity thicknesses are 1.09 +/- 0.06 nm and 5.5 +/- 0.5 nm, respectively, at room temperature but reach a minimum of 0.08 +/- 0.02 nm and 0.7 +/- 0.1 nm, respectively, at 600 degrees C. A large drop in resistivity is seen with increasing growth temperature and the resistivity reaches 16.6 mu Omega cm at 600 degrees C. Achieving epitaxy at such a low temperature and a low continuity thickness is important in a variety of applications such as device interconnects and metal-oxide-semiconductor devices. (C) 2011 Elsevier B.V. All rights reserved.