Atomic Layer Deposition of Chlorine Containing Titanium–Zinc Oxide Nanofilms Using the Supercycle Approach

Abstract

Atomic layer deposition (ALD) is a useful tool for producing ultrathin films and coatings of complex composition with high thickness control for a wide range of applications. In this study, the growth of zinc–titanium oxide nanofilms was investigated. Diethyl zinc, titanium tetrachloride, and water were used as precursors. The supercycle approach was used, and wide ZnO/TiO2 (ZTO) ALD cycles were prepared: 5/1, 3/1, 2/1, 1/1, 1/2, 1/3, 1/5, 1/10, 1/20. Spectral ellipsometry, X-ray reflectometry, X-ray diffraction, scanning electron microscopy, SEM-EDX, and contact angle measurements were used to characterize the thickness, morphology, and composition of the films. The results show that the thicknesses of the coatings differ considerably from those calculated using the rule of mixtures. At high ZnO/TiO2 ratios, the thickness is much lower than expected and with increasing titanium oxide content the thickness increases significantly. The surface of the ZTO samples contains a significant amount of chlorine in the form of zinc chloride and an excessive amount of titanium. The evaluation of the antibacterial properties showed significant activity of the ZTO–1/1 sample against antibiotic-resistant strains and no negative effect on the morphology and adhesion of human mesenchymal stem cells. These results suggest that by tuning the surface composition of ALD-derived ZTO samples, it may be possible to obtain a multi-functional material for use in medical applications.

Atomic Layer Deposition of Antibacterial Nanocoatings: A Review

“…Cytotoxicity of 26 and 52 nm films on HS-27 fibroblasts was also observed [85]. Our recent work also showed the negative effect of 40 nm ZnO on the viability of MG-63 pre-osteoblasts and mesenchymal stem cells FetMSCs [61]. Li et al found that 76 nm coatings did not significantly affect the adhesion and viability of MC3T3-E1, but they had a negative effect on spreading [86].…”

“…As demonstrated earlier in the text, most researchers have found that ALD ZnO does not pose a threat to eukaryotic cells. Nevertheless, our analysis revealed detrimental results of 40 nm thick zinc oxide on FetMSCs [61]. Basiaga et al found a negative effect of thicker coatings on MG-63 proliferation [26], and Zhu et al found a decrease in the viability of MC3T3-E1 with increasing coating thickness.…”

“…At the same time, the use of TiCl 4 /H 2 O has a significant disadvantage-chlorine contamination during synthesis at low temperatures (around 80 • C) [29]. In the synthesis of complex oxide systems, there is also the possibility of chlorine contamination [61]. Titanium oxide synthesis temperatures can vary considerably.…”

“…The Zn ion elution of AZO was significantly lower than that of pure zinc oxide, which is very important for the development of antibacterial moisture barrier films for next generation flexible touch display functional optical films. Recently, we have investigated complex oxide systems based on ZnO and TiO 2 (ZTO) with a thickness of about 40 nm [61]. ZnO and ZTO samples were very effective against S. aureus, A. baumannii, and P. aeruginosa.…”

“…Of particular note is the study [133] where osteopromotive MgO coatings were applied to the surface of collagen, which is an integral part of bone, cartilage, skin, and tendon tissue. ZnO [26,43,44,80,86,87], TiO 2 [53,57,61], MgO [133], hydroxyapatite [98], ZrO 2 [96], TaN [28], Ag [27,57,122], and TiO 2 -ZrO 2 complex oxides [39,40] have been most commonly used as coatings [63,64].…”