Process‐structure‐properties relationship in direct liquid injection chemical vapor deposition of amorphous alumina from aluminum tri‐isopropoxide

Phys. Chem. Chem. Phys.

Sarou‐Kanian

Florian

et al. 2017

The atomic scale structure of aluminum in amorphous alumina films processed by direct liquid injection chemical vapor deposition from aluminum tri-isopropoxide (ATI) and dimethyl isopropoxide (DMAI) is investigated by solid-state Al nuclear magnetic resonance (SSNMR) using a very high magnetic field of 20.0 T. This study is performed as a function of the deposition temperature in the range 300-560 °C, 150-450 °C, and 500-700 °C, for the films processed from ATI, DMAI (+HO), and DMAI (+O), respectively. While the majority of the films are composed of stoichiometric aluminum oxide, other samples are partially or fully hydroxylated at low temperature, or contain carbidic carbon when processed from DMAI above 500 °C. The quantitative analysis of the SSNMR experiments reveals that the local structure of these films is built from AlO, AlO, AlO and Al(O,C) units with minor proportions of the 6-fold aluminum coordination and significant amounts of oxycarbides in the films processed from DMAI (+O). The aluminum coordination distribution as well as the chemical shift distribution indicate that the films processed from DMAI present a higher degree of structural disorder compared to the films processed from ATI. Hydroxylation leads to an increase of the 6-fold coordination resulting from the trend of OH groups to integrate into AlO units. The evidence of an additional environment in films processed from DMAI (+O) by Al SSNMR and first-principle NMR calculations on AlC and AlOC crystal structures supports that carbon is located in Al(O,C) units. The concentration of this coordination environment strongly increases with increasing process temperature from 600 to 700 °C favoring a highly disordered structure and preventing from crystallizing into γ-alumina. The obtained results are a valuable guide to the selection of process conditions for the CVD of amorphous alumina films with regard to targeted applications.

Section: Sample Preparationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Atomic scale structure of amorphous aluminum oxyhydroxide, oxide and oxycarbide films probed by very high field²⁷Al nuclear magnetic resonance

Phys. Chem. Chem. Phys.

Sarou‐Kanian

Florian

et al. 2017

“…S2b). Moreover, this difference in morphology is correlated to a significant difference in composition with the formation of a stoichiometric oxide using DLI DMAI at 500 8C [29], in contrast to the formation of partly hydroxylated aluminum oxide (O/Al ¼ 1.80) when using DLI ATI at 420 8C [30]. The crystal structure of the Ti films before and after deposition of alumina was monitored using XRD.…”

Section: Materials Characterizationmentioning

confidence: 99%

“…2 and SI Fig. S2) and the presence of hydroxyl groups as revealed by the off-stoichiometric composition (O/Al ¼ 1.80) of the DLI ATI films [30]. For the alumina films prepared from the DLI DMAI and ALD processes, TiO 0.48 and Ti phases from the starting bilayer stack evolve after post-annealing at 500 8C for 65 h to a mixture of cubic Fm-3m TiO and hexagonal P63/mcm Ti 5 Si 3 (Fig.…”

Section: Materials Characterizationmentioning

confidence: 99%

Amorphous alumina thin films deposited on titanium: Interfacial chemistry and thermal oxidation barrier properties

Physica Status Solidi (a)

Charvillat

Thébault

et al. 2015

Self Cite

bilayer stacks are used as model systems to investigate the role of atomic layer deposition (ALD) and chemical vapor deposition (CVD) to prepare 30-180 nm thick amorphous alumina films as protective barriers for the medium temperature oxidation (500-600 8C) of titanium, which is employed in aeronautic applications. X-ray diffraction (XRD), transmission electron microscopy (TEM) with selected area electron diffraction (SAED), and X-ray photoelectron spectroscopy (XPS) results show that the films produced from the direct liquid injection (DLI) CVD of aluminum tri-isopropoxide (ATI) are poor oxygen barriers. The films processed using the ALD of trimethylaluminum (TMA) show good barrier properties but an extensive intermixing with Ti which subsequently oxidizes. In contrast, the films prepared from dimethyl aluminum isopropoxide (DMAI) by CVD are excellent oxygen barriers and show little intermixing with Ti. Overall, these measurements correlate the effect of the alumina coating thickness, morphology, and stoichiometry resulting from the preparation method to the oxidation barrier properties, and show that compact and stoichiometric amorphous alumina films offer superior barrier properties.

“…Interplay between simulation and deposition experiments allowed identifying the process conditions which led to the deposition of transparent coatings with uniform thickness profi le. [ 20,21 ] In a continuation of this theoretical work and of recently published preliminary experimental results, [ 22 ] we report hereafter on the experimental investigation of the process-structure-property relationship of coatings obtained by the DLI-CVD of ATI. First, we focus on the dissolution of ATI, with the aim to establish criteria for the selection of the different solvents and defi ne a priori the most appropriate one.…”

Section: Introductionmentioning

confidence: 99%

Amorphous Alumina Barrier Coatings on Glass: MOCVD Process and Hydrothermal Aging

Etchepare

Vergnes

et al. 2016

Adv Materials Inter

Self Cite

OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author-deposited version published in : http://oatao.univ-toulouse.fr/ Eprints ID : 15772 [ 9 ] radio frequency magnetron sputtering, [ 2 ] atomic layer deposition, [ 10 ] sol-gel, [ 5 ] and metalorganic chemical vapor deposition (MOCVD). [ 7,[11][12][13] CVD is one of the most attractive techniques for the time effi cient deposition of such coatings on complexin-shape geometries with conformal coverage, i.e., uniform thickness along the surface. Composition, stoichiometry, crystallinity, and microstructure of the material can be adjusted by fi ne tuning of the MOCVD experimental parameters such as reactor design, precursor selection, reactive atmosphere, deposition temperature, and pressure. The MOCVD of alumina from vaporized aluminum tri-isopropoxide (ATI) is very well documented. [ 7,8,[11][12][13][14][15][16] ATI yields amorphous and stoichiometric alumina coatings with a smooth and dense microstructure at 5 Torr in the temperature range 420 to 650 °C. [ 7,8,14,15 ] Higher process temperatures lead to the deposition of nanocrystallized γ -Al 2 O 3 [ 15 ] or to the homogeneous decomposition of ATI, which generates a different microstructure. [ 11 ] The ATI molecule is well described in the literature.[ 17 ] It is sensitive to water vapor and thus it is subjected to ageing upon exposure to ambient atmosphere, which results in its partial or total hydrolysis in nonvolatile compounds, Al(O i Pr) 3− n (OH) n ( n = 1, 2) and Al(OH) 3 , respectively. [ 12,17 ] The precursor is usually melted, maintained in supercooled state, and vaporized with a bubbler.Despite the simplicity and the cost effectiveness of this solution, the use of ATI in the supercooled state has two drawbacks. First, maintaining ATI at the vaporization temperature for a long-period impacts the stability of the molecule and subsequently the coating quality. [ 12 ] Second, it is diffi cult to know exactly the mass fl ow rate of the generated reactive gas. Such poorly controlled transport conditions lead to nonreproducible processes, especially for the present case when low activation energy prevails in the entire temperature range of interest, de facto resulting in mass transport limited process. The direct liquid injection (DLI) technology overcomes these drawbacks with the controlled vaporization of the solution made of ATI dissolved in a carrier solvent. [ 18 ] The DLI of ATI is insuffi ciently documented in the literature. Song et al. [ 19 ] and Krumdieck et al. [ 13 ] implemented the technique in a pulsedpressure MOCVD process. The authors used a solution of ATI in n -octane and in dry toluene, respectively. Coatings obtained