Phase evolution and Sn-substitution in LiMn2O4 thin films prepared by pulsed laser deposition

LiMn2O4 thin films prepared on a Pt/Ti/SiO2/Si(100) substrate by pulsed laser deposition were studied with focusing on the effects of different processing conditions and Sn substitution on phase evolvement and surface microstructure. Major experimental parameters include substrate temperature up to 770 A degrees C and working oxygen pressure of 50-250 mTorr. LiMn2O4 thin films became highly crystallized with increased grain sizes as the substrate temperature increased. Second phases such as LiMnO2 and Li2Mn2O4 were found at the temperature of 300 and 770 A degrees C, respectively. As an optimum condition, films grown at 450 A degrees C showed a homogeneous spinel phase with well-defined crystallinity and smooth surface. A high pressure of oxygen tended to promote crystallization and grain growth. Working pressure did not affect significantly the phase formation of the thin films except that unexpected LiMn3O4 phase formed at the lowest oxygen pressure of 50 mTorr. Tin-substituted thin films showed lower Mn-O stretching vibrations, which suggests that more Li-ions can be inserted into vacant octahedral sites of the spinel structure.