Maryline Guilloux-Viry

Epitaxial growth of LiNbO3 thin films in a microwave oven

Abstract Oriented LiNbO 3 thin films were prepared using a polymeric precursor solution deposited on (0001) sapphire substrate by spin coating and crystallized in a microwave oven. Crystallization of the films was carried out in a domestic microwave oven. The influence of this type of heat treatment on the film orientation was analyzed by X-ray diffraction and electron channeling patterns, which revealed epitaxial growth of films crystallized at 550 and 650 °C for 10 min. A microstructural study indicated that the films treated at temperatures below 600 °C were homogeneous and dense, and the optical properties confirmed the good quality of these films.

Ion beam etching of lead–zirconate–titanate thin films: Correlation between etching parameters and electrical properties evolution

Ion beam etching of sputtered Pb(Zrx,Ti1−x)O3 (PZT) with x equal to 0.54 thin films grown on Pt/Ti/SiO2/Si substrates has been performed using pure Ar gas. The etch rate dependence on the process parameters (current density, acceleration voltage, gas pressure) has been investigated. The PZT etch rate can reach 600 A/min with acceleration voltage of 1000 V and current density of 1 mA/cm2. Selectivity ratios between PZT and masks of various natures (photoresist, Pt, Ti) have been evaluated to determine a pertinent material for etching mask. According to our etching conditions, titanium seems to be the best candidate. We evaluated the PZT surface damage by contact mode atomic force microscopy. It appears that the roughness increases after ion bombardment, and that the grain boundary zone is preferentially etched. For some etching parameters, we also observed electrical damage. Carrying out C(V) and hysteresis loops P(E) measurements before and after etching have provided evidence of degradation. We noted a l...

LiNbO3 thick films grown on sapphire by using a multistep sputtering process

We present the results of investigations of lithium niobate (LiNbO3) films grown on (0001) sapphire substrate by radio-frequency magnetron sputtering. With the aim of producing thick films we have developed a multistep process. To assess the structural quality of our films, we performed x-ray diffraction, transmission electron microscopy, and atomic force microscopy of the films. The results revealed that the epitaxial structure is verified on sapphire whatever the film thickness. Based on our studies we concluded that the proposed multistep process leads to a good controlled epitaxy of thick LiNbO3 samples on sapphire. Using the prism coupling technique we have characterized the optical properties of the deposited layers. The ordinary (no) and extraordinary (ne) refractive indices are, respectively, 2.289±0.001 and 2.206±0.001 at 632.8 nm, and waveguide losses of 1.2 dB/cm have been demonstrated. In addition, we have qualified the film properties between each growth step and between the substrate to laye...

RF sputtered amorphous chalcogenide thin films for surface enhanced infrared absorption spectroscopy

The primary objective of this study is the development of transparent thin film materials in the IR enabling strong infrared absorption of organic compounds in the vicinity of metal nanoparticles by the surface plasmon effect. For developing these optical micro-sensors, hetero-structures combining gold nanoparticles and chalcogenide planar waveguides are fabricated and adequately characterized. Single As2S3 and Ge25Sb10Se65 amorphous chalcogenide thin films are prepared by radio-frequency magnetron sputtering. For the fabrication of gold nanoparticles on a chalcogenide planar waveguide, direct current sputtering is employed. Fabricated single layers or hetero-structures are characterized using various techniques to investigate the influence of deposition parameters. The nanoparticles of gold are functionalized by a self-assembled monolayer of 4-nitrothiophenol. Finally, the surface enhanced infrared absorption spectra of 4-nitrothiophenol self-assembled on fabricated Au/Ge-Sb-Se thin films hetero-structures are measured and analyzed. This optical component presents a ~24 enhancement factor for the detection of NO2 symmetric stretching vibration band of 4-nitrothiophenol at 1336 cm−1.

Electrical properties of (110) epitaxial lead-free ferroelectric Na0.5Bi0.5TiO3 thin films grown by pulsed laser deposition: Macroscopic and nanoscale data

We report the electrical properties, measured both at the macroscopic and nanometric scales, of epitaxial (110)-Na0.5Bi0.5TiO3 (NBT) thin films grown on (110)Pt/(110)SrTiO3 by pulsed laser deposition (PLD). The influence of the A-site composition (Na and/or Bi excess) on both the structural/microstructural characteristics and the electrical properties is discussed. Whatever the composition of the NBT target, the final layers are systematically epitaxially grown, with NBT crystallites mainly (110)-oriented, and as well (100)-oriented for some minor proportion. Atomic force microscopy (AFM) images reveal the coexistence of two kinds of grains presenting different shapes: namely flat and elongated grains, corresponding to (100)- and (110)-oriented NBT crystallites, respectively. The macroscopic ferroelectric properties were measured at room temperature. A rather well-defined shape of the hysteresis loops was obtained: the incorporation of a Bi excess in the target clearly improves the saturation of the loops...

(20−23) ZnO thin films grown by pulsed laser deposition on CeO2-buffered r-sapphire substrate

Composite ZnO∕CeO2 thin films were grown epitaxially on r-sapphire substrates using the pulsed laser deposition technique. Their crystalline properties were established using x-ray diffraction and showed the ZnO (wurtzite structure) and CeO2 (fluorite structure) layers to be highly textured with the (20−23) and (100) orientations, respectively. ϕ-scan measurements were also carried out and the (20−23)ZnO‖(100CeO2), [1−210]ZnO‖⟨011⟩ CeO2 epitaxial relations established. The rocking curve profiles indicated that the ZnO films grew as four crystallographically equivalent domains. Series of rocking curve and χ−scan measurements at varying ϕ angles, respectively, were used to investigate the domain structure. These showed that the normal to the (20−23) plane in each domain is tilted away from the substrate normal towards one of the four equivalent CeO2 ⟨111⟩ directions by ∼1.60. Atomic force microscopy measurements showed that the ZnO∕CeO2 composite film has a granular microstructure with a rough surface (typi...

KTa/sub 0.6/Nb/sub 0.4/O/sub 3/ ferroelectric thin film behavior at microwave frequencies for tunable applications

In this study about the relationships between structural and microwave electrical properties of KTa1-xNbxO3 (KTN) ferroelectric materials, a KTN thin film was deposited on different substrates to investigate how KTN growth affects the microwave behavior. Interdigital capacitors and stubs were made on these films through a simple engraving process. Microwave measurements under a static electric field showed the importance of the substrate on the circuit behavior and, notably, on the tuning factor

Surface and in-plane characterization of YBa2Cu3O7 thin films grown by laser ablation

Abstract We have used reflection high energy electron diffraction (RHEED) and oscillating crystal X-ray diffraction to analyze the surface and in-plane structural characteristics of YBa 2 Cu 3 O 7 (YBCO) thin films that were grown in-situ by laser ablation onto substrates of (100) MgO and (100) SrTiO 3 . We obtain RHEED streaks, characteristic of atomically smooth surfaces and indicative of epitaxial order, for these thin films. Oscillating crystal diffraction also indicates that the YBCO film axes are collinear with the substrate axes. The films grown on (100) substrates are solely c -axis oriented (perpendicular to the plane of the film) as determined by θ-2θ diffractometry and the FWHM of rocking curves about the (005) reflection are 0.3° to 0.5° for the best films on SrTiO 3 substrates and 0.4° to 0.6° for films grown on MgO. Weissenberg photography allows us to determine the in-plane structure of some films grown on MgO that display anomalous surface features seen by RHEED and by scanning electron microscopy.

Ferroelectric (116) SrBi2Nb2O9 thin films epitaxially grown by pulsed laser deposition on epitaxial (110) Pt/(110) SrTiO3 electrode

Epitaxial SrBi2Nb2O9 thin films have been grown by pulsed-laser deposition on (110)Pt bottom electrode epitaxially grown on (110) SrTiO3 by dc sputtering. X-ray φ-scans and electron channeling patterns reveal the epitaxial growth of the (116) SrBi2Nb2O9/(110)Pt bilayers. The hysteresis loop, dielectric response, and capacitance–voltage characteristics of this bilayer are presented. The remnant polarization was measured to be close to 5 μC/cm2, and the coercive field was calculated to be ∼120 kV/cm. The zero field permittivity was about 150 and the dielectric loss was ∼2%.

Microstructure of (001), (110) and (103) oriented thin films of YBa2Cu3O7−x investigated with STM, SEM and HRTEM

Abstract Epitaxial films of (110) or (103) YBa 2 Cu 3 O 7− x grown on (110) SrTiO 3 substrates by laser ablation are compared to (001) films. Their microstructure is investigated with scanning tunneling microscopy, scanning electron microscopy and high-resolution transmission electron microscopy. The growth of steps, terraces and spirals originating from screw dislocations commonly seen in c -axis films is inhibited in films grown on (110) SrTiO 3 . In the case of (103) oriented films, the growth of 90° twisted domains produces a tooth-like structure with preferred orientation. The influence of vicinal substrates (a few degrees of misorientation) on the film growth, on the nature of defects and on the resistive behavior is also investigated.