Mariana Fraga - 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

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      G E Testoni, W Chiappim, R S Pessoa, M A Fraga, W Miyakawa, K K   Sakane, N K A M Galvão,L Vieira and H S Maciel.Journal of Physics   D: Applied Physics, Volume 49, Number 37.




        TiO2/Al2O3 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/Al2O3 nanolaminate   structures constructed on silicon (1 0 0) and glass substrates   using atomic layer deposition (ALD) by alternatively depositing a   TiO2 sublayer   and Al2O3 partial-monolayer   using TTIP–H2O   and TMA–H2O   precursors, respectively. The Al2O3 is   formed by a single TMA–H2O   cycle, so it is a partial-monolayer because of steric hindrance   of the precursors, while the TiO2 sublayer   is formed by several TTIP–H2O   cycles. Overall, each nanolaminate incorporates a certain number   of Al2O3 partial-monolayers   with this number varying from 10–90 in the TiO2/Al2O3 nanolaminate   grown during 2700 total reaction cycles of TiO2 at   a temperature of 250 °C. The fundamental properties of the   TiO2/Al2O3 nanolaminates,   namely film thickness, chemical composition, microstructure and   morphology were examined in order to better understand the   influence of the number of Al2O3partial-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 Al2O3 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/Al2O3 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.

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