Synthesis of La2S3 Thin Films by Sulfurization of LaCl3 and CS(NH2)2

La2S3 thin films were prepared by dipping the substrates in methanol solutions of LaCl3·7H2O and CS(NH2)2, followed by sulfurization with CS2 gas in the temperature range of 773–1073 K. The effects of the substrate and the mole ratio of LaCl3·7H2O to CS(NH2)2 on the phase formation after sulfurization were investigated. When the mole ratio of LaCl3.7H2O to CS(NH2)2 was 2:3, the tetragonal (beta)-La2S3 coatings were obtained on silica glass and Mo substrates for sulfurization at 1073 K. On the other hand, the cubic (gamma)-La2S3 coating was obtained on a soda-lime glass substrate for sulfurization at 973 K. The thin films on Ta and Ti substrates were comprised of (beta)-La2S3 and (gamma)-La2S3 phases for sulfurization at 1073 K. The LaS2 phase was identified as an intermediate product of sulfurization at about 873 K. When the mole ratio of LaCl3·7H2O to CS(NH2)2 was 1:1, the (gamma)-La2S3 coating was also obtained on silica glass substrate for sulfurization at 1073 K. Since the gaseous phases formed during sulfurization pass through the La2S3 layer, the thin films obtained were porous.