Synthesis, Characterization, and Thermal Properties of Homoleptic Rare-Earth Guanidinates: Promising Precursors for MOCVD and ALD of Rare-Earth Oxide Thin Films

Eight novel homoleptic tris-guanidinato complexes M[(NiPr)(2)CNR2](3) [M = Y (a), Gd (b), Dy (c) and R = Me (1), Et (2), Pr-i (3)] have been synthesized and characterized by NMR, CHN-analysis, mass spectrometry and infrared spectroscopy. Single crystal structure analysis revealed that all the compounds are monomers with the rare-earth metal center coordinated to six nitrogen atoms of the three chelating guanidinato ligands in a distorted trigonal prism geometry. With the use of TGA/DTA and isothermal TGA analysis, the thermal characteristics of all the complexes were studied in detail to evaluate their suitability as precursors for thin film deposition by MOCVD and ALD. The Pr-i-Me2N-guanidinates of Y, Gd and Dy (la-c) showed excellent thermal characteristics in terms of thermal stability and volatility. Additionally, the thermal stability of the iPr-Me2N-guanidinates of Y and Dy (1a, c) in solution was investigated by carrying out NMR decomposition experiments and both the compounds were found to be remarkably stable. All these studies indicate that iPr-Me2N-guanidinates of Y, Gd and Dy (la-c) have the prerequisites for MOCVD and ALD applications which were confirmed by the successful deposition of Gd2O3 and Dy2O3 thin films on Si(100) substrates. The MOCVD grown films of Gd2O3 and Dy2O3 were highly oriented in the cubic phase, while the ALD grown films were amorphous.