Epitaxial growth and properties of lead-free ferroelectric Na0.5Bi0.5TiO3 thin films grown by pulsed laser deposition on various single crystal substrates

International audienceThe epitaxial growth of lead-free ferroelectric Na0.5Bi0.5TiO3 (NBT) thin films on various single crystal substrates was successfully achieved, using the pulsed laser deposition technique (PLD). The present work is divided in two parts, focused on: (i) the growth of NBT layers on c- and r-sapphire (Al2O3) substrates, with and without introducing a CeO2 buffer layer, and (ii) the growth of NBT layers on bare (001)SrTiO3 substrates, with and without introducing a LaNiO3 layer, that could be used as a bottom electrode. In the first part, it was shown that the introduction of a CeO2 buffer layer completely modifies the out-of-plane growth orientation of the NBT films, as well as their microstructure. Indeed, (001)NBT films epitaxially grow only on r-Al2O3 substrates buffered with epitaxial (001)CeO2 layers, while, growing simply NBT on top of bare c or r-Al2O3 substrates, or on top of CeO2/c-Al2O3 heterostructures leads to polycrystalline or textured films. In the second part, we demonstrate that (001)-oriented NBT layers deposited on either bare (001)SrTiO3 or (001)SrTiO3 substrates (STO) covered with (001)LaNiO3 (LNO) are systematically epitaxially grown. Furthermore, the microstructure of the samples is strongly affected by the introduction of the LaNiO3 layer

Targeted Sub-Attomole Cancer Biomarker Detection Based on Phase Singularity 2D Nanomaterial-Enhanced Plasmonic Biosensor

Detection of small cancer biomarkers with low molecular weight and a low concentration range has always been challenging yet urgent in many clinical applications such as diagnosing early-stage cancer, monitoring treatment and detecting relapse. Here, a highly enhanced plasmonic biosensor that can overcome this challenge is developed using atomically thin two-dimensional phase change nanomaterial. By precisely engineering the configuration with atomically thin materials, the phase singularity has been successfully achieved with a significantly enhanced lateral position shift effect. Based on our knowledge, it is the first experimental demonstration of a lateral position signal change > 340 μm at a sensing interface from all optical techniques. With this enhanced plasmonic effect, the detection limit has been experimentally demonstrated to be 10–15 mol L−1 for TNF-α cancer marker, which has been found in various human diseases including inflammatory diseases and different kinds of cancer. The as-reported novel integration of atomically thin Ge2Sb2Te5 with plasmonic substrate, which results in a phase singularity and thus a giant lateral position shift, enables the detection of cancer markers with low molecular weight at femtomolar level. These results will definitely hold promising potential in biomedical application and clinical diagnostics

A study on controllable aluminium doped zinc oxide patterning by chemical etching for MEMS application

This present work reports on the study of controllable aluminium doped zinc oxide (AZO) patterning by chemical etching for MEMS application. The AZO thin film was prepared by RF magnetron sputtering as it is capable of producing uniform thin film at high deposition rates. X-Ray diffraction (XRD) and atomic force microscopy (AFM) characterization were done to characterize AZO thin film. The sputtered AZO thin film shows c-axis (002) orientation, low surface roughness and high crystalline quality. To pattern AZO thin film for MEMS application, wet etching was chosen due to its ease of processing with few controlling parameters. Four etching solutions were used namely: 10 % Nitric acid, 10 % Phosphoric acid, 10 % Acetic acid and Molybdenum etch solutions. For the first time, chemical etching using Molybdenum etch that consist of a mixture of CH3COOH, HNO3 and H3PO4 was characterized and reported. The effect of these acidic solutions on the undercut etching, vertical and lateral etch rate were studied. The etched AZO were characterized by scanning electron microscopy (SEM) and stylus profilometer. The investigations showed that the Molybdenum etch has the lowest undercut etching of 7.11 µm, and is highly effective in terms of lateral and vertical etching with an etch ratio of 1.30. Successful fine patterning of AZO thin films was demonstrated at device level on a surface acoustic wave resonator fabricated in 0.35 μm CMOS technology. The AZO thin film acts as the piezoelectric thin film for acoustic wave generation. Patterning of the AZO thin film is necessary for access to measurement probe pads. The working acoustic resonator showed resonance peak at 1.044 GHz at 45.28 dB insertion loss indicating that the proposed Molybdenum etch method does not adversely affect the device’s operating characteristic

Optimisation du dépôt par ablation laser de films minces d'alumine et de carbone tétraédrique amorphe pure et dopé; propriétés des couches et intégration dans le fabrication de composants MEMS RF

Président : J. Desmaison : SPCTS / CNRS, Université de Limoges Rapporteurs : E. Million : LSMCL, Université de Metz C. Godet : LPICM Ecole Polytechnique Palaiseau Examinateurs : A. Catherinot : SPCTS / CNRS, Université de Limoges C. Champeaux : SPCTS / CNRS, Université de Limoges J.F. Coudert : SPCTS / CNRS, Université de Limoges Invité : P. Blondy : IRCOM / CNRS, Université de LimogesThe fist part of this work is devoted to the pulsed laser deposition process. We propose solutions for the two main problems of PLD : the ejection of micron-sized particles and the non uniformity of film thickness profile. In the second part, we study the properties of alumina and pure and doped tetrahedral amorphous carbon deposited by laser ablation under high vacuum and at room temperature. In the last part, we present the insertion of these two materials in radio frequency micro electro mechanical system.Ce travail consiste en l'optimisation des conditions de dépôt par ablation laser à température ambiante du carbone et de l'alumine. Il se divise en huit parties principales. Le premier chapitre est une présentation du contexte de l'émergence des couches de carbone et d'alumine par ablation laser. le deuxième chapitre décrit les dispositifs expérimentaux et modes opératoires mis en œuvre, qu'ils concernent l'élaboration des films aussi bien que la détermination de leurs propriétés. Les deux chapitres suivants s'intéressent à résoudre les principaux défauts de l'ablation laser à savoir : La projection de particules solides lors du dépôt (chapitre 3) L'inhomogénéité en épaisseur des couches réalisées sur sustrat fixe (chapitre 4) le cinquième chapitre est consacré à l'étude des propriétés structurelles, électriques et mécaniques des couches de ta-C en fonction des conditiond de dépôt. Ce travail s'appuie sur une étude de l'énergie des ions dans le panache plasma (spectroscopie, imagerie résolue temporellement et spectralement) et leur rôle dans la croissance des films de ta-C (analyses Raman, XPS, MET...). le sixième chapitre reprend une étude similaire à ce qui a été présenté dans le chapitre précédent en l'applicant aux couches minces d'alumine par ablation laser. Enfin le dernier chapitre est consacré à l'intégration, dans les composants MEMS RF, des films d'alumine et de ta-C déposés par ablation laser. Ce chapitre rapporte les résultats de la collaboration menée avec l'IRCOM pour réaliser des composants fonctionnels (microcommutateurs RF, filtres accordables ...) à base de couches minces déposées par ablation laser

Optimisation du dépôt par ablation laser de films minces d'alumine et de carbone tétraedrique amorphe pur et dopé (propriété des couches et intégration dans la fabrication de composants MEMS RF)

La première partie de ce travail est consacrée au procédé. il y est question des principaux problèmes rencontrés lors du dépôt par ablasion laser, à savoir la projection de particules solides lors du dépôt et l'homogénéïté en épaisseur des couches réalisées sur substrat fixe. La seconde partie est consacrée à l'étude des propriétés des films minces d'alumine et de carbone tétraédrique amorphe déposés à température ambiante ainsi qu'à la réalisation de multicouches et de dopages. Enfin nous présenterons les résultats de l'intégration, dans les composants MEMS RF, des films d'alumine et de TA-C déposés par ablation laserLIMOGES-BU Sciences (870852109) / SudocLIMOGES-ENSIL (870852226) / SudocSudocFranceF

Fast optical activation of insulator-to-metal transition in vanadium dioxide (VO2) phase changed materials

International audienceVanadium dioxide (VO2) is undergoing a reversible insulator-to-metal transition (MIT), subject to thermal, electrical or optical stimuli. The transition is accompanied by drastic changes in the material's electrical and optical properties which, along the MIT broadband frequency response (from DC to microwaves, THz/ optical domains), triggered a plethora of interesting applications (DC to millimeter-waves switching, THz modulators, reconfigurable filters and antennas etc.). Here we report on optical switching of the VO2 material between its two dissimilar states when integrated in planar two-terminal electrical devices and submitted to laser pulses with different temporal lengths from a high-power laser diode operating at 980 nm. During optical irradiation of VO2 films with pulses having mean powers between 15mW and 140mW at repetition rates up to 500 kHz, we monitored its resistance change, witnessing on the MIT onset. We demonstrate that the MIT in VO2 is optically triggered for pulses as short as 25 ns and energies higher than 130 nJ/pulse, with insulator-to-metal response times in the range 10-15 ns. The process is highly stable and reliable; the devices are able to perform more than one billion switching cycles at frequencies up to 400 kHz without damaging the material nor the device integrity. This optical activation scheme of VO2 emerges as a promising solution for reconfiguration applications at THz and millimeter-waves frequencies

Etude de materiaux chalcogenures a changement de phase et leur integration pour la reconfiguration des dispositifs terahertz

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Optical and Telecom thin films deposited by laser ablation

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