The detailed growth behavior of lanthanum oxide (La2O3) on a silicon substrate during atomic layer deposition (ALD) is investigated by in-situ, x-ray photoelectron spectroscopy (XPS) following individual ALD pulses of tris(N,N'-diisopropyl-formamidinato) lanthanum [La(iPrfAMD)3] and highly concentrated ozone (~390 g/m3). At the initial growth stage, ozone oxidized the La-ligand as well as the silicon substrate. During oxidation of silicon substrate, a noticeable amount of silicon atoms diffused into growing La2O3 film, resulting in Si-rich and La-rich La-silicates showing composition gradient of La/Si at the deposition temperature of 250 oC. The amount of La-silicate after third ALD cycle reached more than 50 % of that generated by 30 cycles. As the thickness of the film increased with sequential ALD cycles, the substrate oxidation as well as the out-diffusion of Si atoms becomes a negligible quantity, and the pure La2O3 film starts growing leaving La-silicate layers at the interface.
We present a facile route to deposit a uniform Al2O3 layer on a highly oriented pyrolytic graphite (HOPG) surface using atomic layer deposition (ALD). Al2O3 layers deposited from TMA (trimethylaluminum)/ H2O chemistry showed selective deposition only on step edges. However, TMA/O3 chemistry resulted in the deposition of Al2O3 layers on basal planes of HOPG, which has a chemically inert surface. An O3-pretreatement followed by Al2O3 deposition using TMA/O3 chemistry produced conformal and uniform Al2O3 dielectric layers with a small RMS roughness of ~ 0.2 nm. This suggests that O3-pretreatement prior to ALD deposition makes the chemically inert HOPG surface reactive toward ALD precursors, which leads to the desired two-dimensional growth mode. High-resolution transmission electron microscopy (HR-TEM) and Raman spectroscopy revealed that this O3 process used for Al2O3 deposition does not introduce a significant defect concentration to the top graphene layer. The dielectric constant of the deposited Al2O3 film on top of the HOPG surface was found to be ~ 9 from C-V measurements.
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