Rare Mononuclear Lithium-Carbene Complex for Atomic Layer Deposition of Lithium Containing Thin Films

Lithium is the core material of modern battery technologies and fabricating the lithium-containing materials with atomic layer deposition (ALD) confers significant benefits in control of film composition and thickness. In this work, a new mononuclear N-heterocyclic carbene (NHC) stabilized lithium complex, [Li(^tBuNHC)(hmds)], is introduced as a promising precursor for ALD of lithium-containing thin films. Structural characterization is performed, comparing density functional theory (DFT) and single-crystal X-ray diffraction (SC-XRD), confirming a rare mononuclear structure. Favorable thermal properties for ALD applications are evidenced by thermogravimetric analysis (TGA). The compound exhibits a low melting point, clean evaporation, and its volatility parameters are encouraging compared to other lithium precursors. ALD trials using [Li(^tBuNHC)(hmds)] with ozone demonstrate its effectiveness in depositing LiSi_xO_y films. The ALD process exhibits a saturated growth per cycle (GPC) of 0.95 Å. Compositional analysis using Rutherford backscattering spectrometry/nuclear reaction analysis (RBS/NRA), X-ray photoelectron spectrometry (XPS), and glow discharge optical emission spectrometry (GD-OES), confirms the presence of lithium and silicon in the expected ratios. This work not only presents a new ALD precursor but also contributes to the understanding of lithium chemistry, offering insights into the intriguing coordination chemistry and thermal behavior of lithium complexes stabilized by NHC ligands.