Influence of the Al2O3 partial-monolayer number on the crystallization mechanism of TiO2 in ALD TiO2/Al2O3 nanolaminates and its impact on the material properties. (18th August 2016)

• Record Type: Journal Article
• Authors: Testoni, G E; Chiappim, W; Pessoa, R S; Fraga, M A; Miyakawa, W; Sakane, K K; Galvão, N K A M; Vieira, L; Maciel, H S
• Is Part Of: Journal of physics. Volume 49:Number 37(2016)
• Publication Date: 2016-08-18
• Subjects: nanolaminate -- titanium dioxide -- aluminum oxide -- atomic layer deposition; Physics -- Periodicals; 530
• DOI: 10.1088/0022-3727/49/37/375301
• Languages: English
• ISSNs: 0022-3727

Abstract

Abstract: TiO2 /Al2 O3 nanolaminates are being investigated to obtain unique materials with chemical, physical, optical, electrical and mechanical properties for a broad range of applications that include electronic and energy storage devices. Here, we discuss the properties of TiO2 /Al2 O3 nanolaminate structures constructed on silicon (1 0 0) and glass substrates using atomic layer deposition (ALD) by alternatively depositing a TiO2 sublayer and Al2 O3 partial-monolayer using TTIP–H2 O and TMA–H2 O precursors, respectively. The Al2 O3 is formed by a single TMA–H2 O cycle, so it is a partial-monolayer because of steric hindrance of the precursors, while the TiO2 sublayer is formed by several TTIP–H2 O cycles. Overall, each nanolaminate incorporates a certain number of Al2 O3 partial-monolayers with this number varying from 10–90 in the TiO2 /Al2 O3 nanolaminate grown during 2700 total reaction cycles of TiO2 at a temperature of 250 °C. The fundamental properties of the TiO2 /Al2 O3 nanolaminates, namely film thickness, chemical composition, microstructure and morphology were examined in order to better understand the influence of the number of Al2 O3 partial-monolayers on the crystallization mechanism of TiO2 . In addition, some optical, electrical and mechanical properties were determined and correlated with fundamental characteristics. The results show clearly the effect of Al2 O3 partial-monolayers as an internal barrier, which promotes structural inhomogeneity in the film and influences the fundamental properties of the nanolaminate. These properties are correlated with gas phase analysis that evidenced the poisoning effect of trimethylaluminum (TMA) pulse during the TiO2 layer growth, perturbing the growth per cycle and consequently the overall film thickness. It was shown that the changes in the fundamental properties of TiO2 /Al2 O3 nanolaminates had little influence on optical properties such as band gap and transmittance. However, in contrast, electrical properties as resistivity and mechanical properties as hardness and elastic modulus were shown to be very dependent. From these analyses, several applications could be suggested for different kinds of nanolaminates obtained in this work.