A. Bartasyte

New sterically hindered Hf, Zr and Y β-diketonates as MOCVD precursors for oxide films

New Zr, Hf and Y 2,7,7-trimethyl-3,5-octanedionates (tod) as well as the corresponding Cu β-diketonate have been synthesized and characterized by FT-IR, elemental analyses, TGA, and 1H NMR or ESR. The molecular structure of Hf(tod)4 has been determined by single-crystal X-ray diffraction, the metal displays a square antiprismatic geometry. Zr, Hf and Y β-diketonates were investigated as precursors for MOCVD deposition of ZrO2, HfO2 and yttria-stabilized hafnia thin films. The films were characterized by XRD, XPS, EDS and AFM. Highly textured and in-plane oriented films were deposited on sapphire by pulsed liquid injection MOCVD. Zr(tod)4 and Hf(tod)4 precursors lead to higher growth rates of ZrO2 and HfO2 films at lower temperatures than conventional Zr(thd)4 and Hf(thd)4 precursors (thd = 2,2,6,6-tetramethyl-3,5-heptanedionate) and are attractive new precursors for oxide films.

Investigation of thickness-dependent stress in PbTiO3 thin films

X-ray diffraction (XRD) and Raman spectroscopy were used to investigate stress dependence on thickness in PbTiO3 (PTO) films grown by pulsed liquid injection metalorganic chemical vapor deposition on a LaAlO3 (001) substrate (LAO). Films on sapphire substrate (R plane) were used as the polycrystalline film reference. Epitaxial PTO films with a dominant c domain structure are grown on LAO substrate, whereas the films on sapphire are polycrystalline. A detailed investigation of the PTO/LAO film microstructure by XRD gives evidence of PTO twinning. Both techniques reveal that PTO films are under tensile in-plane stresses. The study of the film thickness dependence of microstrains, grain size, volume fraction of a domains, as well as surface morphology of PTO/LAO films indicates that these parameters are clearly correlated. A change in the relaxation mechanism between 65 and 125 nm of film thickness has been evidenced. A c parameter gradient occurs throughout the film depth; it originates in stress relaxation...

Resolved E-symmetry zone-centre phonons in LiTaO3 and LiNbO3

E-symmetry optical phonons at the Γ point of LiNbO3 and LiTaO3 were experimentally resolved in spectra measured by infrared and Raman spectroscopy. For this purpose, congruent and nearly stoichiometric crystals of LiNbO3 and LiTaO3, and mixed LiNb1−xTaxO3, crystals were studied. The results show that some of the E modes have weak intensities in Raman or infrared spectra. Thus the complete assignment of E-symmetry modes has been achieved by comparing Raman and infrared data. In addition, this assignment has been confirmed by Raman measurements at low temperatures.

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

Phase 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.

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

Domain structures of 320 nm thin epitaxial films of ferroelectric PbTiO3 grown by MOCVD technique in identical conditions on SmScO3 and TbScO3 perovskite sub- strates 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.

Packageless AlN/ZnO/Si Structure for SAW Devices Applications

The possibility to perform a packageless structure for acoustic wave sensors applications based on AlN/interdigital transducer/ZnO/Si structure was investigated. The effect of thicknesses of AlN and ZnO thin films on structure performance was simulated by 2-D finite element method. Theoretical predictions were confirmed by in-situ measurements of frequency, insertion loss, and thickness during deposition of AlN layer on ZnO/Si.

Metal-organic chemical vapour deposition of mixed-conducting perovskite oxide layers on monocrystalline and porous ceramic substrates

Perovskite oxide layers, i.e. manganites La1−x(Sr,Ca)xMnO3, ferrates La1−xSrxFe1−yCoyO3, gallates La1−xSrxGa1−y(Co,Ni,Fe)yO3 of a thickness of 0.8–2 μm, were deposited by pulsed injection MOCVD (metal-organic chemical vapour deposition) on various monocrystalline and porous ceramic substrates. The layers were characterised by X-ray diffraction, scanning electron microscopy, wavelength dispersion spectroscopy and by electrical measurements of the total conductivity vs. temperature. Such oxides are known as mixed electronic–ionic conductors and are largely studied as materials for the fabrication of oxygen permeable membranes. One of the aims of this work was to estimate the suitability of the pulsed injection MOCVD technique for the preparation of dense perovskite layers for their use as membranes for oxygen.

Ferroelectric domains in epitaxial PbTiO3 films on LaAlO3 substrate investigated by piezoresponse force microscopy and far-infrared reflectance

Domain structures of 100–300 nm thin epitaxial films of ferroelectric PbTiO3 grown by metalorganic chemical vapor deposition technique on LaAlO3 perovskite substrate have been investigated by piezoresponse force microscopy and infrared reflectance spectroscopy techniques. Normal-incidence reflectance spectra reveal both E- and A1-symmetry modes of PbTiO3. The latter ones demonstrate the presence of a minor fraction of a-domains (with in-plane orientation of the spontaneous polarization) in the film. The piezoresponse force microscopy images allow to get local insight in the complex nanodomain architecture composed by few hundred nm large areas of primarily c/a/c/a but also a1/a2/a1/a2 domain pattern types, with participation of all six tetragonal ferroelectric domain states and both 180 ° and 90 ° ferroelectric walls.

Raman spectroscopy and X-ray diffraction studies of stress effects in PbTiO/sub 3/ thin films

The evolution of domain structure and in-plane and out-of-plane lattice parameters in PbTiO3 (PTO) films on SrTiO3 (STO), LaAlO3 (LAO) and MgO substrates was studied as a function of film thickness and temperature by X-ray diffraction (XRD). Microstrains and average grain sizes were determined in several crystallographic directions for films of different thicknesses using a Williamson-Hall and Langford analysis. Stress relaxation with film thickness was observed in different domains by Raman spectroscopy and greatly influences lattice parameters. Specific contributions of a-and c-domains on Raman spectra were analyzed and correlated to domains fraction. The high temperature structural phase transition was followed by Raman spectroscopy, showing that the transition depends on the nature of stress.

Residual stresses and clamped thermal expansion in LiNbO3 and LiTaO3 thin films

Residual stresses in LiNbO3 and LiTaO3 epitaxial thin films were evaluated taking into account Li nonstoichiometry by means of Raman spectroscopy and x-ray diffraction. The epitaxial films were grown on C-cut sapphire substrates by pulsed injection metal organic chemical vapour deposition. Clamping of the epitaxial films by the substrate induced a transfer from the in plane thermal expansion to the out of plane component. The temperature of the phase transition of clamped LiTaO3 films was close to that expected for a bulk sample.