Chemical and Strain Engineering of Functional Oxides

International audienc

Structure Modification, Evolution, and Compositional Changes of Highly Conductive La:BaSnO3 Thin Films Annealed in Vacuum and Air Atmosphere

Perovskite-type La:BaSnO3 (LBSO) has been drawing considerable attention due to its high electron mobility and optical transparency. Its thin film electrical properties, however, remain inferior to those of single crystals. This work investigates the thermal post-treatment process of films deposited using the metalorganic chemical vapor deposition method to improve the electrical properties of different stoichiometry films, and demonstrates the modification of thin film’s structural properties using short and excessive annealing durations in vacuum conditions. Using vacuum post-treatment, we demonstrate the improvement of electrical properties in Ba-rich, near-stoichiometric, and Sn-rich samples with a maximum electron mobility of 116 cm2V−1s−1 at r.t. However, the improvement of electrical properties causes surface morphology and internal structural changes, which depend on thin film composition. At temperatures of 900 °C–1400 °C the volatile nature of LBSO constituting elements is described, which reveals possible deterioration mechanisms of thin LBSO air. At higher than 1200 °C, LBSO film’s decomposition rate increases exponentially. Thin film structure evolution and previously unreported decomposition is demonstrated by Ba and La diffusion to the substrate, and by evaporation of SnO-SnOx species

Effect of deposition conditions on the stoichiometry and structural properties of LiNbO3 thin films deposited by MOCVD

Conference on Oxide-Based Materials and Devices IV, San Francisco, CA, FEB 03-06, 2013International audienceEpitaxial LiNbO3 thin films were deposited on C-sapphire substrates by pulsed injection metal organic chemical vapor deposition and atmospheric pressure metal organic chemical vapor deposition. The effect of deposition conditions, such as the ratio of Li/Nb precursors in solution and the deposition pressure, on the phase composition, Li nonstoichiometry, texture, epitaxial quality, residual stresses and formation of twins in LiNbO3 films was studied by means of X-ray diffraction and Raman spectroscopy. It was found that the deposition pressure played an important role in the incorporation of Li2O in the film and the formation of in-plane and out-of-plane twins

Ferroelectric nanodomains in epitaxial PbTiO3 films grown on SmScO3 and TbScO3 substrates

21st IEEE ISAF, held Jointly with 11th ECAPD and 4th Conference on PFM and Nanoscale Phenomena in Polar Materials, Univ Aveiro, Aveiro, PORTUGAL, JUL 09-13, 2012International audienceDomain structures of 320 nm thin epitaxial films of ferroelectric PbTiO3 grown by metal-organic chemical vapor deposition technique in identical conditions on SmScO3 and TbScO3 perovskite substrates have been investigated by Raman spectroscopy and piezoresponse force microscopy techniques. Phonon frequency shifts and typical domain structure motifs are discussed. The results reveal strikingly different domain structure architecture: domain structures of the PbTiO3 film grown on SmScO3 have dominantly a-domain orientation while strongly preferential c-domain orientation was found in the PbTiO3 film grown on the TbScO3 substrate. Differences between the two cases are traced back to the film-substrate lattice mismatch at the deposition temperature

Identification of LiNbO3, LiNb3O8 and Li3NbO4 phases in thin films synthesized with different deposition techniques by means of XRD and Raman spectroscopy

Équipe 401 : Nanomatériaux pour la vie et développement durableInternational audiencePhase composition of epitaxial/textured LiNbO3 films on sapphire substrates, grown by pulsed laser deposition, atmospheric pressure metal organic chemical vapor deposition and pulsed injection metal organic chemical vapor deposition was studied by conventional x-ray diffraction techniques. Raman spectroscopy, being highly sensitive to the symmetry of materials, was used as a countercheck in the compositional analysis. The wavenumbers of Raman modes of LiNb3O8 and Li3NbO4 phases were identified from Raman spectra of synthesized powders. Asymmetry of profiles of x-ray diffraction reflections of LiNbO3 films was studied. This asymmetry may have different origins which consequently may result in misleading conclusions about phase composition of textured LiNbO3 films

Preparation of Heteroleptic Tin(IV) N,O-beta-Heteroarylalkenolate Complexes and Their Properties as PI-MOCVD Precursors for SnO2 Deposition

We have successfully prepared and structurally characterized five novel tin(IV) heteroleptic N,O-beta-heteroarylalkenolates containing -CF3 groups. The synthetic route used reactions of Sn(OtBu)(4) with 3,3,3-trifluoro(pyridin-2-yl)propen-2-ol (PyTFPH), 3,3,3-trifluoro(dimethyl-1,3-oxazol-2-yl)propen-2-ol (DMOTFPH), and 3,3,3-trifluoro(1,3-benzthiazol-2-yl)propen-2-ol (BTTFPH) in dry aprotic solvents leading to elimination of tert-butanol and formation of Sn(OtBu)(2)(PyTFP)(2) (1), Sn(OtBu)(2)(DMOTFP)(2) (2), and Sn(OtBu)(2)(BTTFP)(2) (3). The chelating ligands employed a bidentate N boolean AND O donor set. The reactivity of OtBu groups in the obtained Sn(OtBu)(2)(N boolean AND O)(2) complexes was further investigated in reactions with fluorinated alcohols, 2,2,2-trifluoroethanol (TFEH) and 1,1,1,3,3,3-hexafluoro-2-propanol (HFPH). Two complexes Sn(TFE)(2)(DMOTFP)(2) (4) and Sn(HFP)(2)(PyTFP)(2) (5) were obtained and structurally characterized. Thermal behavior of complexes 1-5 was studied by thermogravimetry and differential scanning calorimetry (TG/DSC). The most volatile compounds Sn(OtBu)(2)(PyTFP)(2) (1) and Sn(OtBu)(2)(DMOTFP)(2) (2) were chosen and tested in a PI-MOCVD process for the SnO2 growth on sapphire-C substrates. Film growth rates at different temperatures (500-900 degrees C), crystalline quality, surface roughness, transparency in UV/Vis-mid-IR spectral ranges have been investigated. The results showed that these two compounds are suitable precursors for MOCVD deposition of high quality SnO2 films. Fabricated films displayed good response to CO and NO2 in chemo-resistive gas sensing measurements

Relationship Processing–Composition–Structure–Resistivity of LaNiO3 Thin Films Grown by Chemical Vapor Deposition Methods

Precision control of resistivity/conductivity of LaNiO3 (LNO) films is essential for their integration as electrodes in the functional heterostructures. This becomes possible if the relationship between processing parameters–composition–structure–resistivity is determined. LaNiO3 films were deposited by three different chemical vapor deposition methods using different precursor supply systems: direct liquid delivery, pulsed liquid injection, and aerosol generation. The possibilities to ameliorate the efficiency of precursor evaporation and of film growth were studied. The relationship between deposition conditions and composition was determined. Detailed analysis of the epitaxial growth of LNO films on cubic and trigonal substrates and the influence of the rhombohedral distortion on the microstructural quality was done. The resistivity of LaNiO3 films, grown by chemical vapor deposition, was mainly defined by microstructural defects and La/Ni composition. The high epitaxial quality LaNiO3/LaAlO3 films with nearly stoichiometric La/Ni ratio presented low resistivity, which was very close to that of bulk LaNiO3. Their annealing in oxygen atmosphere had little effect on the resistivity, which suggests a minor presence of oxygen vacancies in the as-grown films