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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.

In 1928, Zachariasen discovered the LiNbO 3 phase. [1] The first single crystals were grown using the flux method by Matthias Over the past five decades, LiNbO 3 and LiTaO 3 single crystals and thin films have been studied intensively for their exceptional acoustic, electro-optical, and pyroelectric and ferroelectric properties. Today, LiNbO 3 single crystals in electro-optics are equivalent to silicon in electronics, and about 70% of radio-frequency (RF) filters, based on surface acoustic waves, are fabricated on these single crystals. These materials in the form of thin films are needed urgently for the development of the next-generation of high-frequency and/or wide-band RF filters or tuneable frequency filters adapted to the fifth generation of infrastructures/networks/communications. The integration of LiNbO 3 films in guided nanophotonic devices will allow higher operational frequencies, wider bandwidth, and miniaturized optical devices in line with improved electronic conversion. Here, the challenges and the achievements in the epitaxial growth of LiTaO 3 and LiNbO 3 thin films and their integration with silicon technology and to acoustic and guided nanophotonic devices are discussed in detail. The systematic representation and classification of all epitaxial relationships reported in the literature have been carried out in order to help the prediction of the epitaxial orientations in the new heterostructures. Future prospects of potential applications and the expected performances of thin film devices are overviewed, as well.Figure 2. Schematic representation of the layer transfer process by the ion slicing technique consisting of a) ion implantation, b) wafer bonding, c) laser irradiation or heating in order to obtain d) a single crystalline layer on the host (Si) substrate. Reproduced with permission. [53]Figure 3. a,b) Electron microscopy images and c) schematic diagram of a microresonator based on LiNbO 3 film on Si and fabricated by the layer transfer technique. Reproduced with permission. [53]The first reports on the growth of c-axis-oriented LN films by liquid phase epitaxy on an LT substrate and by RF sputtering Adv. Mater. Interfaces 2017, 4, 1600998 www.advmatinterfaces.de www.advancedsciencenews.com Figure 6. Frequency response of a) HBAR and b) FBAR based on thinned X-cut LiNbO 3 layer on Si. Schematic representations of a) HBAR and b) FBAR structures are given in the insets. Reproduced with permission. [78]

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.

International audienceX-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 polycrystalline film reference. Epitaxial PTO films with a dominant c-domain structure are grown on LAO substrate whereas 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 due to a thickness increase. Raman spectra of PTO films allowed in-plane residual stress values to be estimated from the Raman shifts and are in good agreement with those determined by XRD. Both techniques also indicate that thinner films are more stressed and residual stresses are partially relaxed with increasing thickness. Moreover, a-domains are more stressed than c-domains. The two components of the large A1(2TO) and A1(3TO) Raman modes have been associated with a- and c-domains and their intensity ratio clearly correlated with the volume fraction of a-domains

Lanthanum ferrite nanofibers were electrospun from a chemical sol and calcined at 600 ºC to obtain single-phase LaFeO 3 (LFO) perovskite. High-resolution transmission electron microscopy in conjunction with 3D tomographic analysis confirmed an interwoven network of hollow and porous (surface) LFO nanofibers. Owing to their high surface area and p-type behavior, the nanofiber meshes showed high chemoselectivity towards reducing, toxic gases (SO 2 , H 2 S) that could be reproducibly detected at very low concentrations (<1 ppm) well below the threshold values for occupational safety and health. An increased sensitivity was observed in the temperature range 150-300 ºC with maximum sensor response at 250 ºC. The surface reaction at the heterogeneous solid (LFO) / gas (SO 2 ) interface was investigated

Strain dependent stabilization of metallic paramagnetic state in epitaxial NdNiO3 thin films Appl. Phys. Lett. 101, 132101 (2012) Tribological properties of nanocrystalline diamond films deposited by hot filament chemical vapor deposition AIP Advances 2, 032164 (2012) The combined effect of surface roughness and internal stresses on nanoindentation tests of polysilicon thin films J. Appl. Phys. 112, 044512 (2012) Mechanism for atmosphere dependence of laser damage morphology in HfO2/SiO2 high reflective films

domain structures of the PbTiO 3 film grown on SmScO 3 have dominantly a-domain orientation while strongly preferential c-domain orientation was found in the PbTiO 3 film grown on the TbScO 3 substrate. Differences between the two cases are traced back to the film-substrate lattice mismatch at the deposition temperature.