Atomic scale structure of amorphous aluminum oxyhydroxide, oxide and oxycarbide films probed by very high field 27Al nuclear magnetic resonance

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 27Al 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 (+H2O), and DMAI (+O2), 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 AlO4, AlO5, AlO6 and Al(O,C)4 units with minor proportions of the 6-fold aluminum coordination and significant amounts of oxycarbides in the films processed from DMAI (+O2). 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 AlO6 units. The evidence of an additional environment in films processed from DMAI (+O2) by 27Al SSNMR and first-principle NMR calculations on Al4C3 and Al4O4C crystal structures supports that carbon is located in Al(O,C)4 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

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

We propose a method to apply amorphous alumina films on the inner surface of glass containers aiming to improve their hydrothermal barrier property. We have carried out alumina deposition on Si substrates as a function of deposition temperature to determine the physicochemical properties of the thin film materials, and on glass containers to evaluate the influence of postdeposition hydrothermal ageing on the films properties. Film preparation has been achieved by metal-organic chemical vapor deposition (MOCVD), using triisopropoxide aluminum (ATI) dissolved in anhydrous cyclohexane as precursor, in a temperature range between 360 °C and 600 °C. A direct liquid injection technology is used to feed the reactor in a controlled and reproducible way. The amorphous alumina films have been characterized by several techniques such as XRD, EPMA, XPS, SEM, AFM and scratch-test method. Films are amorphous and hydroxylated at 360 and 420 °C and close to stoichiometric at 490 and 560 °C. Hydrothermal ageing simulated by a standard sterilization cycle modifies the adhesion and surface morphology of the alumina film on glass containers to a rough, porous and nonadhesive layer. Elemental compositions of alumina films on Si substrates. O/Al atomic ratios (EPMA) for films processed in the horizontal (blue dots) and vertical (red dots) reactors. Carbon concentration for films deposited in the horizontal (black dots) and vertical (white dots) reactors, determined, respectively, by XPS and EPMA. Films processed at high temperatures (490-560 °C) are stoichiometric Al2O3 with a very low amount of hydroxyl groups. Carbon concentrations are lower than 1 at%

Efficient, durable protection of the Ti6242S titanium alloy against high-temperature oxidation through MOCVD processed amorphous alumina coatings

With their exceptional strength-to-weight ratio, titanium alloys find applications in numerous key enabling technologies. However, their implementation in harsh environments comes up against their limited resistance to high-temperature oxidation. To face this problem, in this work dense, amorphous alumina, Al2O3 coatings are applied on the surface of Ti6242S alloy by metalorganic chemical vapor deposition, MOCVD, from aluminum triisopropoxide, ATI and from dimethylaluminum isopropoxide, DMAI. Isothermal oxidation tests show that the parabolic rate constants of the mass gain of the coated Ti6242S coupons are reduced up to two orders of magnitude compared with the bare material. 5000 h long oxidation of DMAI Al2O3 coated alloy at 600 °C results in 0.180 mg cm−2 weight gain to be compared with 1.143 mg cm−2 for the bare alloy. In these conditions, an interfacial layer is formed, containing the complex Ti3(Al0.5Sn0.5) (or (Ti,Sn)2N) phase. Cyclic oxidation consisting of eighty, 1 h cycles between 50 and 600 °C show null mass gain of the coated sample. Finally, the hardness profiles determined on cross sections of oxidized coupons reveal a very limited oxygen dissolution for the coated alloy. MOCVD coatings of amorphous Al2O3 have great potential for efficient, durable protection against oxidation of Ti6242S alloys

Alumina thin films prepared by direct liquid injection chemical vapor deposition of dimethylaluminum isopropoxide: a process-structure investigation

The development of a new process to obtain amorphous alumina thin films is presented. We show for the first time the direct liquid injection chemical vapor deposition (DLI CVD) of alumina thin films using dimethylaluminum isopropoxide (DMAI) precursor in two oxidizing atmospheres. At high process temperature (500-700 °C), the film growth takes place in the presence of O2 whereas at low temperature (150-300 °C) H2O vapor is used. The materials characteristics, such as the surface morphology and roughness (SEM and AFM), crystal structure (XRD), composition (EPMA) and chemistry (XPS) are discussed in detail. Very smooth films, with typical roughness values lower than 2.0 nm are obtained. The thin films are all composed of an amorphous material with varying composition. Supported by both EPMA and XPS results, film composition evolves from a partial oxyhydroxide to a stoichiometric oxide at low deposition temperature (150-300 °C) in the presence of H2O. At higher growth temperature (500-700 °C) in the presence of O2, the composition changes from that of a stoichiometric oxide to a mixture of an oxide with aluminum carbide. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

A Process-Structure Investigation of Aluminum Oxide and Oxycarbide Thin Films prepared by Direct Liquid Injection CVD of Dimethylaluminum Isopropoxide (DMAI)

We present the direct liquid injectionCVDof aluminum oxide and oxycarbide thin films using dimethylaluminum isopropoxide at high process temperature (500–700 8C) with the addition ofO2 gas, and at low temperature (150–300 8C) with the addition of H2O vapor. Very smooth films with typical roughness values lower than 2 nm are obtained. The thin films are composed of an amorphous material. The composition evolves as a function of temperature from that of a partial hydroxide to a stoichiometric oxide at low deposition temperature(150–300 8C), and from that of a stoichiometric oxide to a mixture of an oxide with an(oxy)carbide at higher temperature (500–700 8C)

In situ X-Ray absorption spectroscopy of germanium evaporated thin film electrodes

The understanding of germanium Li-ion insertion/extraction reaction mechanism is drawing more and more attention in the field of Li-ion batteries. When a germanium thin film electrode is inserted with Li ions, the material remains amorphous until it crystallizes into Li15Ge4 as evidenced by X-ray diffraction. The local coordination environment of the Ge atoms of the intermediate amorphous phases was investigated by in situ X-ray absorption spectroscopy. Li-ion insertion and extraction were electrochemically controlled by continuous and intermittent galvanostatic methods. The evolution of the coordination number and interatomic distance of Ge–Ge and Ge–Li shells was determined as a function of Li composition. From a short range ordering perspective, it was observed that the first Ge–Ge interatomic distance increases and the Ge–Ge coordination number decreases with increasing Li content. The opposite is observed for the first Li–Ge interaction. Moreover, it was found that electrochemical lithiation is reversible at the atomic scale

Reaction mechanism of tin nitride (de)lithiation reaction studied by means of 119Sn Mössbauer spectroscopy

Tin nitride thin films have been reported as promising negative electrode materials for lithium-ion solid-state microbatteries. However, the reaction mechanism of this material is not yet fully understood. Results on thin film electrodes pointed out that the conversion mechanism of tin nitride most likely differs from the conversion mechanism usually observed for other oxide and nitride conversion electrode materials. The electrochemical data showed that more than six Li per Sn atom can be reversibly exchanged by this material while about four are expected. In order to investigate in more detail the reaction mechanism of tin nitride, thick film electrodes of two compositions (1:1 and 3:4) have been studied. The as-prepared materials were characterized by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy and 119Sn Mössbauer spectroscopy. Moreover, films (de)lithiated to various extents were analyzed ex situ with Mössbauer spectroscopy. The corresponding results indicate that a more complex reaction mechanism than that generally accepted takes place. During Li-ion insertion, the disappearance of Sn4+ environments is correlated with the formation of Li–Sn phases, and most likely also of Li3N. In the case of the SnNx 1:1 composition films, the formation of various Li–Sn phases is evidenced while only the signature of ‘Li22Sn5’ is clearly measured for the 3:4 composition. Upon Li-ion extraction, the Li–Sn phases and Li3N recombine to form octahedrally and tetrahedrally coordinated Sn4+. The extraction is not fully reversible and the end product consists of a mixture of a tin nitride structure plus a LiySn product having the same isomer shift as LiSn but a much higher quadrupole splitting, and most likely some Li3N