Stéphanie Députier

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...

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

Highly tunable microwave stub resonator on ferroelectric KTa0.5Nb0.5O3 thin film

A coplanar waveguide (CPW) stub resonator has been fabricated on a pulsed-laser deposited KTa(0.5)Nb(0.5)O(3) (KTN) thin film (600 nm-thick) onto a r-plane sapphire substrate. It was designed to operate at 10 GHz when the applied bias voltage is zero. We show experimentally that the resonance frequency is shifted by 44% under a 70 kV/cm DC applied electric field. In addition, the dielectric characteristics of the KTN film have been assessed through post-processed measurements of CPW 50-Omega transmission lines using the conformal mapping method.

Intercomparison of Permittivity Measurement Techniques for Ferroelectric Thin Layers

The dielectric properties of a KTa0.65Nb0.35O3 (KTN) ferroelectric composition for a submicronic thin layer were measured in the microwave domain using different electromagnetic characterization methods. Complementary experimental techniques (broadband methods versus resonant techniques, waveguide versus transmission line) and complementary data processing procedures (quasi-static theoretical approaches versus full-wave analysis) were selected to investigate the best way to characterize ferroelectric thin films. The measured data obtained from the cylindrical resonant cavity method, the experimental method that showed the least sources of uncertainty, were taken as reference values for comparisons with results obtained using broadband techniques. The error analysis on the methods used is discussed with regard to the respective domains of validity for each method; this enabled us to identify the best experimental approach for obtaining an accurate determination of the microwave dielectric properties of ferroelectric thin layers.

Metallurgical study of Ni/GaSb (111) and (001) contacts: Comparison with the Ni/GaAs and Ni/AlAs systems

Solid‐state interdiffusions at the Ni/GaSb(111) and (001) interfaces were investigated in the temperature range 200–600 °C using 1.8 MeV He+ ion backscattering and channeling and also using x‐ray diffraction. The starting point was the experimental determination of the Ni‐Ga‐Sb phase diagram. The steps of the interaction were the same for GaSb(111) and GaSb(001). Three various phases were observed: the ternary A phase with the Ni2.5GaSb atomic composition, Ni2Ga3, and Ni2Ga0.25Sb1.75, the Ga‐rich limit of the substituted NiSb binary compound. All these phases had a hexagonal pseudocubic structure. First, an epitaxial Ni2.5GaSb A phase reacted layer was obtained. This phase was not in thermodynamical equilibrium with GaSb and the final product was a mixture of Ni2Ga3 and Ni2Ga0.25Sb1.75 grains with an average atomic composition equal to Ni1.6GaSb. The metallurgical behavior of the Ni/GaSb contacts was compared to that of the Ni/GaAs and Ni/AlAs contacts. It was concluded that the experimental ternary diagr...

Direct and Reverse Limiting Series of Transition Metal Phosphides with Ordered Defects and Metal/Non Metal Ratio Close to 2

Two new limiting series of ternary compounds with ordered defects have been evidenced, which crystallize with hexagonal symmetry, space group P6m2. The first one (direct series) shows one metal vacancy and corresponds to the chemical formula □RTX. The compounds α-UCr6P4 (n = 0) and Zr4Co13Si9 (n = 1) are the first members of the series. X-ray single crystal determination and/or electron microprobe analysis confirm the ternary phosphides Ce9Ni25P13 and Ce16Ni36P22 to be the following members. The second family (reverse series) with chemical formula R□TX comprises the ternaries α-UCr6P4 (in fact member n = 0 in both series) and UMo13P9 (n = 1), the structure of which has been determined on a single crystal. The limiting structures to which the two series converge have been found to be YbPtP (direct) and WC (reverse). The structural relationships between the direct and reverse series have been discussed in terms of metal vacancies and coordination polyhedra. Moreover, a general crystal chemical rule has been established that permits prediction of the different members for the two series and their structural definition in terms of lattice parameters, atomic coordinates and theoretical X-ray diffraction patterns. Finally, this rule permits to give for each member the number of metal vacancies as well as the distribution of the metalloid polyhedra occupied by the metal atoms (trigonal prisms, pyramids, tetrahedra, triangles).

Solid state phase equilibria in the NiGaSb system: experimental and calculated determinations

Abstract Solid state phase equilibria in the ternary NiGaSb diagram were established at 600 °C. The experimental techniques used to elaborate the phase equilibria were X-ray diffraction, electron probe microanalysis and scanning electron microscopy. A ternary phase with the nominal formula Ni3GaSb (designated as A-phase in the present study) was evidenced. This phase exists over a broad range of homogeneity and exhibits hexagonal symmetry with a disordered structure derivative from NiAs and Ni2In types. Very limited solid solubilities were measured in the constituent binary NiGa and NiSb compounds, with the exception of NiSb which showed a homogeneity range with a Ga-rich limit corresponding to the formula Ni2Ga0.25Sb1.75. The phases GaSb, Ni2Ga3 and substituted-NiSb coexist with each other to form a three-phase equilibrium that dominates the GaSb side of the phase diagram. This part of the experimental diagram is in agreement with the calculated one from available experimental thermodynamic data on the GaSb, NiGa and NiSb binaries and with interfacial reaction studies which concluded that Ni2Ga3 and substituted-NiSb are the stable phases when Ni thin films are reacted to completion on GaSb. A comparative study with the NiGaAs and NiAlAs phase diagrams is also given which points out that, contrary to NiGa (NiAl) with GaAs (AlAs), the monogallide NiGa is not in thermodynamic equilibrium with GaSb.

EFFECT OF THIN KNbO3 SEED LAYERS ON PULSED LASER DEPOSITED FERROELECTRIC KTa0.65Nb0.35O3 FILMS FOR MICROWAVE TUNABLE APPLICATION

ABSTRACT Ferroelectric KTa0.65Nb0.35O3 thin films were grown by pulsed laser deposition on R-plane sapphire substrates. The potassium enriched ceramic targets were used for compensating potassium losses. In order to improve the KTa0.65Nb0.35O3 film growth on sapphire, a thin KNbO3 layer was introduced as seed layer. The experimental results show that the crystalline quality is lowered when increasing the K-excess. Simultaneously, phase purity, orientation and crystalline quality of perovskite (h00)-oriented KTa0.65Nb0.35O3 are greatly improved by the use of the KNbO3 seed layer. In particular, the presence of the latter effectively suppresses any pyrochlore secondary phase formation.

Solid state phase equilibria in the NiAlAs system

Abstract Solid state phase equilibria in the ternary NiAlAs diagram were established at 800 °C. The experimental techniques used to elaborate the phase equilibria were X-ray diffraction (XRD), electron probe microanalysis (EPMA) and scanning electron microscopy (SEM). Three ternary phases, which crystallize in hexagonal symmetry and are all structurally derived from the NiAs type, were evidenced in the Ni-rich part of the diagram. Among them, two ternaries labelled as A and D phases, by comparison with the isostructural ternary phases in the NiGaAs diagram, reveal fully disordered structures; in contrast, the ternary B phase shows a hexagonal superlattice (a√3, 3c), which denotes an ordered structure. Very limited solid solubilities were measured in the binary constituent NiAl and NiAs compounds, with the exception of NiAs which showed a homogeneity range with an Al-rich limit corresponding to the formula NiAs0.7Al0.3. Neither nickel nor ternary phases are in thermodynamic equilibrium with AlAs, in contrast with the binaries NiAl, Ni2Al3 and NiAs which are. The bottom part of the experimental diagram differs from the theoretical one deduced from estimated thermodynamic data on NiAl and NiAs binaries using Miedemas model, but is in agreement with interfacial reaction studies which concluded that NiAl and substituted NiAs are the stable phases when Ni thin films are reacted to completion on AlAs. Finally, the influence of the IIIa element (Ga or Al) in the NiIIIaAs system was considered through a comparative study between NiGaAs and NiAlAs diagrams. The pseudoternary Ni(Ga,Al)As system was experimentally estimated for the atomic composition (Ga0.7Al0.3), which is the value usually chosen for the elaboration of GaAs (Ga,Al)As heterostructures with Ga1−xAlxAs exhibiting a direct gap of highest energy.