Origin of Decomposition in a Family of Molybdenum Precursor Compounds

Synthesis, Characterization, and Single-Crystal X-ray Structures of Refractory Metal Compounds as Precursors for the Single-Source Chemical Vapor Deposition of Metal Nitrides

The chemical vapor deposition of refractory metal nitrides requires volatile precursors and has previously been achieved by using metal complexes containing a variety of imide ligands. Recently, the 1,4-di-tert-butyl-1,3-diazabutadiene (DAD) adduct of bis(tert-butylimide)dichloridemolybdenum(VI) was shown to be an excellent precursor for the single-source CVD of Mo2N thin films. Leveraging the success of this work, we prepared chromium and tungsten compounds with the same framework. Additionally, the framework has been modified slightly to allow the isolation of mono(tert-butylimide)trichloride complexes of vanadium, niobium, tantalum, and molybdenum(V) to extend the search for new vapor-phase precursors. These compounds were all fully characterized using the standard methods of multinuclear magnetic resonance spectroscopy, combustion analysis, and single-crystal X-ray diffraction. Their thermal properties were determined by using thermogravimetric analysis and differential scanning colorimetry to assess their utility as vapor-phase precursors. Finally, preliminary deposition studies were carried out to investigate their potential as single-source CVD precursors.

Diverse Post-Metathesis Reactivities of Mixed Amido-Isothiocyanato Molybdenum Complexes

Attempts to prepare mixed isothiocyanato-bis(imido) MoVI complexes led to the discovery of post-metathesis rearrangements toward three distinct products (1-3), which feature the NCS-derived chelators [N(NMe2)CS]2- (L1 in dinuclear 1 and 2) and [N(SiMe3)(NMe2)CS]- (L2 in mononuclear 3). Notably, the preparation of bidentate ligand L1 and its coordination chemistry are unprecedented. Together with computational studies, it is proposed that the putative "mono-substituted" intermediate [Mo(NtBu)2(NMe2)(NCS)] serves as the common starting point for the observed molecular transformations. Construction of the [Mo(NtBu)2(NCS)2] core was ultimately possible in the presence of additional stabilizing donors (THF or PMe3), which yielded the complexes [Mo(NtBu)2(NCS)2(THF)2] (4) and [Mo(NtBu)2(NCS)2(PMe3)2] (5).

Molybdenum(III) Amidinate: Synthesis, Characterization, and Vapor Phase Growth of Mo-Based Materials

The synthesis, characterization, and thermogravimetric analysis of tris(N,N'-di-isopropylacetamidinate)molybdenum(III), Mo(iPr-AMD)₃, are reported. Mo(iPr-AMD)₃ is a rare example of a homoleptic mononuclear complex of molybdenum(III) and fills a longstanding gap in the literature of transition metal(III) trisamidinate complexes. Thermogravimetric analysis (TGA) reveals excellent volatilization at elevated temperatures, pointing to potential applications as a vapor phase precursor for higher temperature atomic layer deposition (ALD), or chemical vapor deposition (CVD) growth of Mo-based materials. The measured TGA temperature window was 200-314 °C for samples in the 3-20 mg range. To validate the utility of Mo(iPr-AMD)₃, we demonstrate aerosol-assisted CVD growth of MoO₃ from benzonitrile solutions of Mo(iPr-AMD)₃ at 500 °C using compressed air as the carrier gas. The resulting films are characterized by X-ray photoelectron spectroscopy, X-ray diffraction, and Raman spectroscopy. We further demonstrate the potential for ALD growth at 200 °C with a Mo(iPr-AMD)₃/Ar purge/300 W O₂ plasma/Ar purge sequence, yielding ultrathin films which retain a nitride/oxynitride component. Our results highlight the broad scope utility and potential of Mo(iPr-AMD)₃ as a stable, high-temperature precursor for both CVD and ALD processes.

Disturbance of intermolecular forces: eutectics as a new tool for the preparation of vapor-phase deposition precursors

The volatile bis(tert-butylimido)dichloromolybdenum(VI) compounds, (tBuN)₂MoCl₂·dad (dad = 1,4-di-tert-butyl-1,3-diazabutadiene) (1) and [(tBuN)₂MoCl(μ-Cl)·(tBuNH₂)]₂ (2), form a eutectic, with a two to one composition (χ₂ = 0.33). A decrease of 40 °C in the melting temperature has been observed between the eutectic mixture and the pure compounds. We have isolated a co-crystal of (tBuN)₂MoCl₂·dme (dme = 1,2-dimethoxyethane) (3) and 2, also in a two to one ratio, which serves as a structural model for such mixtures. The lower melting point of carefully chosen eutectic mixtures can offer more consistent precursor delivery in deposition processes.