Synthesis of Calcium(II) Amidinate Precursors for Atomic Layer Deposition through a Redox Reaction between Calcium and Amidines |
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| Authors: | Dr. Sang Bok Kim Chuanxi Yang Dr. Tamara Powers Dr. Luke M. Davis Xiabing Lou Prof. Dr. Roy G. Gordon |
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| Affiliation: | 1. Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA;2. Department of Chemistry, Texas A&M University, College Station, TX, USA |
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| Abstract: | We have prepared two new CaII amidinates, which comprise a new class of ALD precursors. The syntheses proceed by a direct reaction between Ca metal and the amidine ligands in the presence of ammonia. Bis(N,N′‐diisopropylformamidinato)calcium(II) ( 1 ) and bis(N,N′‐diisopropylacetamidinato)calcium(II) ( 2 ) adopt dimeric structures in solution and in the solid state. X‐ray crystallography revealed asymmetry in one of the bridging ligands to afford the structure [(η2‐L)Ca(μ‐η2:η2‐L)(μ‐η2:η1‐L)Ca(η2‐L)]. These amidinate complexes showed unprecedentedly high volatility as compared to the widely employed and commercially available CaII precursor, [Ca3(tmhd)6]. In CaS ALD with 1 and H2S, the ALD window was approximately two times wider and lower in temperature by about 150 °C than previously reported with [Ca3(tmhd)6] and H2S. Complexes 1 and 2 , with their excellent volatility and thermal stability (up to at least 350 °C), are the first homoleptic CaII amidinates suitable for use as ALD precursors. |
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| Keywords: | amidines atomic layer deposition calcium redox chemistry thin films |
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