Volatile Hexavalent Oxo-amidinate Complexes: Molybdenum and Tungsten Precursors for Atomic Layer Deposition

New complexes MoO 2 ( t BuAMD) 2 ( 1 ) and WO 2 ( t BuAMD) 2 ( 2 ) (AMD = acetamidinato) are synthesized and fully characterized as precursors for atomic layer deposition (ALD). They contain metal-oxo functionalities not previously utilized in ALD-type growth processes and are fully characterized by 1 H and 13 C NMR, X-ray diffraction (XRD), Fourier transform infrared, thermogravimetric analysis, single-crystal XRD, and elemental analysis. Guided by quartz-crystal microbalance studies, ALD growth methodologies for both complexes have been developed. Remarkably, these isostructural compounds exhibit dramatic differences in ALD properties. Using 1 and O 3, amorphous, ultrathin molybdenum oxynitride (MoON) films are grown on Si(100) wafers. Using 2 and H 2 O yields amorphous WO 3 films on Si(100) wafers that crystallize as WO 3 nanowires upon annealing. Although 1 /H 2 O and 2 /O 3 growth was attempted, effective ALD growth could only be obtained with 1 /O 3 and 2 /H 2 O, underscoring reactivity differences in these precursors. Film thicknesses, compositions, and optical and electrical parameters are characterized by variable angle spectroscopic ellipsometry, X-ray reflectivity, grazing incidence X-ray diffraction, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and atomic force microscopy techniques. The hitherto unknown ALD chemistry of group VI metal-oxo compounds lays a foundation for their use in the ALD synthesis of heterogeneous catalysts.