Apparatus and method for volatilizing a source reagent susceptible to particle generation or presence of particles in the corresponding source reagent vapor, in which such particle generation or presence is suppressed by structural or processing features of the vapor generation system. Such apparatus and method are applicable to liquid and solid source reagents, particularly solid source reagents such as metal halides, e.g., hafnium chloride. The source reagent in one specific implementation is constituted by a porous monolithic bulk form of the source reagent material. The apparatus and method of the invention are usefully employed to provide source reagent vapor for applications such as atomic layer deposition (ALD) and ion implantation.