Chemical vapor deposition systems include elements to preheat reactant gases prior to reacting the gases to form layers of a material on a substrate, which provides devices and systems with deposited layers substantially free of residual compounds from the reaction process. Heating reactant gases prior to introduction to a reaction chamber may be used to improve physical characteristics of the resulting deposited layer, to improve the physical characteristics of the underlying substrate and/or to improve the thermal budget available for subsequent processing. One example includes the formation of a titanium nitride layer substantially free of ammonium chloride using reactant gases containing a titanium tetrachloride precursor and a ammonia precursor.