Organic-Inorganic Thin Films from TiCl4 and 4-Aminophenol Precursors: A Model Case of ALD/MLD Hybrid-Material Growth?

Atomic layer deposition (ALD) is a sophisticated thin‐film production technology for relatively simple inorganic materials based on sequential self‐saturated surface reactions. Combining ALD with molecular layer deposition (MLD) – a variant of ALD based on purely organic precursors – offers in principle an elegant way to fabricate 2D organic–inorganic hybrid materials in an atomic/molecular layer‐by‐layer manner. In practice, however, the ALD/MLD process has disadvantages such as being prone to unwanted double surface reactions of the organic precursor molecule, which may seriously hinder the ideal film growth. Here we report the deposition of (Ti–O–C6H4–N=)n thin films from precursors TiCl4 and 4‐aminophenol (AP) with the essentially ideal growth rate of 10–11 Å per ALD/MLD cycle. We attribute the steady growth of the Ti–AP hybrid to the following facts: (1) the AP molecule is heterobifunctional and consists of a stiff aromatic backbone; moreover, (2) the –Cl ligands in TiCl4 are small enough not to cause steric hindrance. The Ti–AP films deposited at 120–160 °C were stable in ambient air and of high quality, with a root‐mean‐square (rms) roughness of 0.2–0.3 nm, a refractive index of 1.86–1.91 and a density of 1.9–2.2 g/cm3. Atomic/molecular layer deposition (ALD/MLD) was used to grow stable (Ti–O–C6H4–N=)n‐type thin films from TiCl4 and 4‐aminophenol (AP). The Ti and AP backbone in the structure was confirmed by FTIR and XPS results. The obtained growth rate, 10–11 Å per ALD/MLD cycle, is very close to that calculated from the bond lengths (9.1 Å/cycle), which indicates full monolayer coverage during the deposition.