118 research outputs found
CVD synthesis of boron nitride films with optimized properties for optoelectronic devices
No full textDans la famille des matériaux bidimensionnels (2D), le nitrure de bore a été identifié comme un matériau stratégique. Ce semi-conducteur à grand gap (> 6eV), atomiquement plan, résistant chimiquement et thermiquement, peut jouer plusieurs rôles dans les hétérostructures de matériaux 2D : substrat de graphène pour préserver la mobilité exceptionnelle de ses porteurs de charge ou couche encapsulante pour protéger d’autres matériaux 2D sensibles à leur environnement ou exalter leurs propriétés. Des démonstrateurs de principe ont été réalisés avec des monocristaux de BN. Les dimensions latérales et l’homogénéité en épaisseur du BN sont limitées par la dimension initiale millimétriques des cristaux et leur mise en œuvre par exfoliation mécanique. Cette technique est donc difficilement industrialisable. Il est nécessaire de développer des synthèses de films de BN de dimensions, structure et qualité contrôlées pour permettre une montée en échelle. Dans cette thèse en partenariat avec la PME Annealsys, nous avons choisi de développer la synthèse de films de BN sur nickel par dépôt chimique en phase vapeur à basse pression (LPCVD). Dans un premier temps, nous avons transposé sur le bâti de l’équipementier Annealsys le procédé de synthèse de BN sur des substrats de nickel polycristallin à partir de borazine déjà maitrisé par l'équipe. Nous avons confirmé que la morphologie et la qualité du BN dépend de l'orientation cristallographique du nickel sous-jacent et que l’orientation (111) du nickel est la plus favorable pour la synthèse de film continu de BN. Nous avons donc ensuite travaillé avec des substrats monocristallins de Ni(111) /YSZ/Si(111). Nous avons porté une attention particulière à la préparation de ces substrats spécifiques et développé un traitement de stabilisation in-situ dans le bâti de dépôt, compatible avec un procédé industriel. La structure et la qualité des films de BN synthétisés, i.e. épaisseur, rugosité, séquence d’empilement, cristallinité et taille de domaines, ont été caractérisées de l’échelle atomique à l’échelle millimétrique par un panel de techniques de microscopies et spectroscopies (AFM, MEB, Raman, MET…). Nous avons mis en place une méthodologie de caractérisation statistique à l’échelle centimétrique, indispensable à la vérification de l’homogénéité des films de BN, prérequis pour la fabrication de dispositifs performants. Nous avons fait varier des paramètres de synthèse clés tels que la quantité de gaz précurseur ou l’épaisseur du substrat de nickel et étudié leur impact sur les films de BN. Les résultats sont discutés d’un point de vue mécanisme de croissance.In the family of two-dimensional (2D) materials, boron nitride has been identified as a key material. This large GAP semiconductor (>6 eV), atomically flat, chemically and thermally inert, can play several roles in the 2D materials heterostructures: graphene substrate to preserve the exceptional mobility of its charge carriers or encapsulating layer to protect other 2D materials sensitive to their environment or to enhance their properties. Demonstrations of principle have been made with BN single crystals. The lateral dimensions and thickness homogeneity of the BN layers are limited by the initial millimetric size of the crystals, and their processing by mechanical exfoliation. This technique is therefore difficult to industrialize. The development of BN films with controlled size, structure and quality is needed to allow a scale up. In this thesis in partnership with the Annealsys society, we chose to develop the synthesis of BN films on nickel by low pressure chemical vapour deposition (LPCVD). First, we transposed the BN synthesis process on polycrystalline nickel substrates from borazine already mastered by the team to the set-up of the equipment manufacturer Annealsys. We confirmed that the morphology and quality of the BN depend on the crystallographic orientation of the underlying nickel, and that the (111) orientation of the nickel is the most favourable for the synthesis of continuous BN films. We then work with single crystalline Ni(111)/YSZ/Si(111) substrates. We paid particular attention to the preparation of these specific substrates and developed an in-situ stabilisation treatment in the deposition chamber, compatible with an industrial process. The structure and quality of the synthetized BN films, i. e. thickness, roughness, stacking sequence, crystallinity and domain size, were characterized from the atomic scale to the millimetre scale by various of microscopy and spectroscopy techniques (AFM, SEM, Raman, TEM…). We set up a methodology for statistical characterisation at the centimetre scale, which is essential for checking the homogeneity of the BN films, a prerequisite for the manufacture of high-performance devices. We varied the synthesis key parameters, such the amount of precursor or the thickness of the nickel substrate, and studied their impact on the BN films. The results are discussed from a growth mechanism perspective
Elaboration de nanoparticules d'argent par réduction de sels métallo-organiques : contrôle de taille, stabilité, organisation et propriétés physiques
No full textThis thesis was devoted first to the synthesis of size controlled silver nanoparticles. The nanoparticles are obtained by reducing a metallo-organic silver salt RAg(PPh3)n (R=Cl, Br or NO3 and n=1 or 3) with tert-butylamineborane in presence of alcanethiols. The flexible choice of functional group and number of PPh3 in these salts as well as of the reaction temperature allows us to obtain alkanethiol coated silver nanoparticles with diameter ranging from 2.5 to 7.1 nm, with a low size distribution. We get evidence that particle growth occurs via the ligand replacement of PPh3 by alkanethiol. Whereas under dry air, silver nanoparticles are stable, under ambient air, we observe their etching. This process is thus due to the oxidation of silver by the redox couple O2/H2O. By annealing organized silver nanoparticles at a mild temperature (50° C) during 4 days, we observe the formation of well crystallized silver triangles. Due to their uniformity in size and shape, silver nanoparticles have a strong tendency to form 3D supracrystals after deposition on a solid substrate. Their morphologies and crystalline structures are shown to depend on the nature of the solvent, alkanethiol chain length and nanoparticle size. Using low-frequency Raman scattering, we demonstrate that crystallinity of silver nanoparticles modifies their vibrations. We show that the self-organized silver nanoparticles can be used as Surface Enhanced Raman Scattering (SERS) substrate and provide a high SERS signal of alkanethiol ligands. Finally, we show that it is possible to successfully generalize this metallo-organic approach to the synthesis of copper nanoparticles with different sizes and shapesCette thèse porte sur la synthèse de nanoparticules d'argent de taille contrôlée. Ces nanoparticules sont obtenues par réduction de sels d'argent métallo-organiques RAg(PPh3)n (R=Cl, Br ou NO3 et n=1 ou 3) par le tert-butylamine borane, en présence d'alcanethiols. Le choix flexible du groupement fonctionnel, du nombre de PPh3 dans ces sels ainsi que de la température de réaction, nous ont permis d'obtenir des nanoparticules d'argent habillées d'alcanethiols de diamètre contrôlé compris entre 2,5 et 7,1 nm. Nous avons mis en évidence l'échange des ligands PPh3 par les alcanethiols durant la croissance des nanoparticules. Alors que sous air sec, les nanoparticules d'argent sont stables, à l'air ambiant, nous observons leur abrasion. Ce processus est attribué à l'oxydation de l'argent par le couple redox O2/H2O. Le chauffage doux à l'air pendant 4 jours de nanoparticules d'argent organisées induit leur coalescence sous la forme de triangles d'argent cristallisés. De par leur uniformité en taille et forme, les nanoparticules d'argent forment des supracristaux, après dépôt sur un substrat solide dont les morphologies et les structures cristallines dépendent de la nature du solvant, de la longueur de chaîne alcanethiol et de la taille des nanoparticules. Par diffusion Raman basse-fréquence, nous avons montré que la cristallinité des nanoparticules affecte leurs vibrations. De plus, les nanoparticules d'argent organisées servent de substrat pour la diffusion Raman exaltée en surface (SERS) et donne un fort signal SERS des alcanethiols adsorbés à leur surface. Enfin, nous avons étendu cette approche à la synthèse de nanoparticules de cuivre de différentes tailles et forme
Elaboration de nanoparticules d'argent par réduction de sels métallo-organiques : contrôle de taille, stabilité, organisation et propriétés physiques
No full textThis thesis was devoted first to the synthesis of size controlled silver nanoparticles. The nanoparticles are obtained by reducing a metallo-organic silver salt RAg(PPh3)n (R=Cl, Br or NO3 and n=1 or 3) with tert-butylamineborane in presence of alcanethiols. The flexible choice of functional group and number of PPh3 in these salts as well as of the reaction temperature allows us to obtain alkanethiol coated silver nanoparticles with diameter ranging from 2.5 to 7.1 nm, with a low size distribution. We get evidence that particle growth occurs via the ligand replacement of PPh3 by alkanethiol. Whereas under dry air, silver nanoparticles are stable, under ambient air, we observe their etching. This process is thus due to the oxidation of silver by the redox couple O2/H2O. By annealing organized silver nanoparticles at a mild temperature (50° C) during 4 days, we observe the formation of well crystallized silver triangles. Due to their uniformity in size and shape, silver nanoparticles have a strong tendency to form 3D supracrystals after deposition on a solid substrate. Their morphologies and crystalline structures are shown to depend on the nature of the solvent, alkanethiol chain length and nanoparticle size. Using low-frequency Raman scattering, we demonstrate that crystallinity of silver nanoparticles modifies their vibrations. We show that the self-organized silver nanoparticles can be used as Surface Enhanced Raman Scattering (SERS) substrate and provide a high SERS signal of alkanethiol ligands. Finally, we show that it is possible to successfully generalize this metallo-organic approach to the synthesis of copper nanoparticles with different sizes and shapesCette thèse porte sur la synthèse de nanoparticules d'argent de taille contrôlée. Ces nanoparticules sont obtenues par réduction de sels d'argent métallo-organiques RAg(PPh3)n (R=Cl, Br ou NO3 et n=1 ou 3) par le tert-butylamine borane, en présence d'alcanethiols. Le choix flexible du groupement fonctionnel, du nombre de PPh3 dans ces sels ainsi que de la température de réaction, nous ont permis d'obtenir des nanoparticules d'argent habillées d'alcanethiols de diamètre contrôlé compris entre 2,5 et 7,1 nm. Nous avons mis en évidence l'échange des ligands PPh3 par les alcanethiols durant la croissance des nanoparticules. Alors que sous air sec, les nanoparticules d'argent sont stables, à l'air ambiant, nous observons leur abrasion. Ce processus est attribué à l'oxydation de l'argent par le couple redox O2/H2O. Le chauffage doux à l'air pendant 4 jours de nanoparticules d'argent organisées induit leur coalescence sous la forme de triangles d'argent cristallisés. De par leur uniformité en taille et forme, les nanoparticules d'argent forment des supracristaux, après dépôt sur un substrat solide dont les morphologies et les structures cristallines dépendent de la nature du solvant, de la longueur de chaîne alcanethiol et de la taille des nanoparticules. Par diffusion Raman basse-fréquence, nous avons montré que la cristallinité des nanoparticules affecte leurs vibrations. De plus, les nanoparticules d'argent organisées servent de substrat pour la diffusion Raman exaltée en surface (SERS) et donne un fort signal SERS des alcanethiols adsorbés à leur surface. Enfin, nous avons étendu cette approche à la synthèse de nanoparticules de cuivre de différentes tailles et forme
Elaboration de nanoparticules d'argent par réduction de sels métallo-organiques (contrôle de taille, stabilité, organisation et propriétés physiques)
No full textCette thèse porte sur la synthèse de nanoparticules d argent de taille contrôlée. Ces nanoparticules sont obtenues par réduction de sels d argent métallo-organiques RAg(PPh3)n (R=Cl, Br ou NO3 et n=1 ou 3) par le tert-butylamine borane, en présence d alcanethiols. Le choix flexible du groupement fonctionnel, du nombre de PPh3 dans ces sels ainsi que de la température de réaction, nous ont permis d obtenir des nanoparticules d argent habillées d alcanethiols de diamètre contrôlé compris entre 2,5 et 7,1 nm. Nous avons mis en évidence l échange des ligands PPh3 par les alcanethiols durant la croissance des nanoparticules. Alors que sous air sec, les nanoparticules d argent sont stables, à l air ambiant, nous observons leur abrasion. Ce processus est attribué à l oxydation de l argent par le couple redox O2/H2O. Le chauffage doux à l air pendant 4 jours de nanoparticules d argent organisées induit leur coalescence sous la forme de triangles d argent cristallisés. De par leur uniformité en taille et forme, les nanoparticules d argent forment des supracristaux, après dépôt sur un substrat solide dont les morphologies et les structures cristallines dépendent de la nature du solvant, de la longueur de chaîne alcanethiol et de la taille des nanoparticules. Par diffusion Raman basse-fréquence, nous avons montré que la cristallinité des nanoparticules affecte leurs vibrations. De plus, les nanoparticules d argent organisées servent de substrat pour la diffusion Raman exaltée en surface (SERS) et donne un fort signal SERS des alcanethiols adsorbés à leur surface. Enfin, nous avons étendu cette approche à la synthèse de nanoparticules de cuivre de différentes tailles et formesThis thesis was devoted first to the synthesis of size controlled silver nanoparticles. The nanoparticles are obtained by reducing a metallo-organic silver salt RAg(PPh3)n (R=Cl, Br or NO3 and n=1 or 3) with tert-butylamineborane in presence of alcanethiols. The flexible choice of functional group and number of PPh3 in these salts as well as of the reaction temperature allows us to obtain alkanethiol coated silver nanoparticles with diameter ranging from 2.5 to 7.1 nm, with a low size distribution. We get evidence that particle growth occurs via the ligand replacement of PPh3 by alkanethiol. Whereas under dry air, silver nanoparticles are stable, under ambient air, we observe their etching. This process is thus due to the oxidation of silver by the redox couple O2/H2O. By annealing organized silver nanoparticles at a mild temperature (50 C) during 4 days, we observe the formation of well crystallized silver triangles. Due to their uniformity in size and shape, silver nanoparticles have a strong tendency to form 3D supracrystals after deposition on a solid substrate. Their morphologies and crystalline structures are shown to depend on the nature of the solvent, alkanethiol chain length and nanoparticle size. Using low-frequency Raman scattering, we demonstrate that crystallinity of silver nanoparticles modifies their vibrations. We show that the self-organized silver nanoparticles can be used as Surface Enhanced Raman Scattering (SERS) substrate and provide a high SERS signal of alkanethiol ligands. Finally, we show that it is possible to successfully generalize this metallo-organic approach to the synthesis of copper nanoparticles with different sizes and shapesPARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF
TRACES OF THE NOBLE SAVAGE MYTH IN THE TALE “AMANDINE OR THE TWO GARDENS”
No full textMichel Tournier, yapıtlarındaki mitsel gönderimlerin zenginliğiyle tanınır ve mitlerin yeniden yorumlanmasında örnek teşkil eden yazarlar arasındadır. İlk öykü kitabı olan Çalı Horozu’nda da birçok mite gönderim yapar. Çocuk izleği yazarın yazınında önemli bir yer tuttuğundan, bu yapıtında birden fazla öykünün kahramanı çocuktur. Amandine ya da İki Bahçe adlı öykünün kahramanı da bir kız çocuğudur ve yazar bu yapıtında, bir kız çocuğunun doğal yaşamla karşılaşma serüvenini anlatır. Çocuk kahramanının gözünden uygar toplum ve doğal ortamı betimler. Bu betimlemeler yapılırken yazar, modern dünyadaki, başta eğitim olmak üzere, yanlış gördüğü doğruları eleştirir. Estetik olarak daha güzel bir ortamda bulunmasına karşın, bir çocuğun doğal ortamda daha mutlu olduğunu belirtir. Bu yapıtta yazar, “iyi vahşi”mitinde anlatılan öz yeterliliğe sahip insan örneğindeki gibi, çocukların yetiştirilmesi gerektiğini ve insanların kendi cennetlerini aramasının önündeki engellerin kalkması gerektiğini salık verir. Dahası, Tournier için cennet olabilecek yerler uygar toplumun dışında kalan bir uzamda olabilir. Amandine, çocukların kuşatıldığı yapay ortamlardan uzaklaşma isteğini ve doğal bir ortamda daha mutlu olduklarını ortaya koyan bir figürdür. Bu yolculuktan bahsederken, Tournier her ne kadar bir çocuğun ergenliğe geçişini anlatsa da, iyi vahşi mitik izlekleri yardımıyla da bu yolculuğun daha iyi nasıl olabileceğine ışık tutar. Bu çalışmada, yapıttaki iyi vahşi mitini mit eleştirisi yaklaşımı ile incelemeyi amaçlıyoruz.Michel Tournier, known for the rich mythical references in his works, is an author who serves as a model for reinterpreting the myths. In his first tale book The Fetishist, he refers to several myths. As the theme of child holds a significant place in his literature, there are few children as heroes in this book. The hero of Amandine or the two gardens is a female child and the author presents the adventure of this girl, encountering with wild nature. He describes the modern society and wild nature from this female child’s perspective. While making these descriptions, the author firstly criticizes modern education and then truths that turn out to be wrong. Even if a child lives in aesthetically nice places, s/he feels happier in wild nature. In this work, the author advises to raise children as autonomous beings as it is explained in the noble savage myth and to remove obstacles in order to encourage them to find their heavens. Moreover, heaven can take place where there is no modern civilization. Amandine is a figure for all children who desire going away from artificial environments and who are happier in wild nature. Although Tournier explains the process of a child’s entrance into puberty, he also enlightens by showing how this process would be better by using noble savage mythemes. In this regard, this study aims to examine the noble savage in this tale in the light of myth criticism
CVD synthesis of Graphene-Boron Nitride heterostructures with optimized properties for optoelectronics devices
No full textInternational audienceSince graphene isolation in 2004, the 2D materials is a blooming research field. Due to its unique properties, sp² hybridized boron nitride (BN) has been acknowledge as a key towards integration of other 2D materials in devices. Indeed, it is structurally very close to graphene – their lattice mismatch is only 1.7%- a semiconductor, atomically flat and thermally and chemically inert. It is therefore a choice material to be used in the van der Waals heterostructures with other 2D materials (see Figure 1) either as a top layer to protect another 2D material from its environment [1][2], or as a dielectric interlayer [3] and mostly, as a flat substrate [4]. However, these applications have been demonstrated using mechanically exfoliated BN from low defective and highly crystalline single crystals. Yet this process limits the size of the devices that can be created to sub millimetre scale. In order to develop devices at a wafer scale, it is therefore critical to master the synthesis sp² hybridized BN layers at low cost, large scale and high quality. In that respect, the goal of the researches we have undertaken is to develop the synthesis of sp² hybridized multilayer BN films with structural specifications fitting these requirements. By processing chemical vapour deposition using a dedicated reactor, we aim to control both the structure and the qualities of the film (thickness, roughness, stacking sequence, crystallinity and domain size, impurities and stacking faults). We have already successfully obtained heteroepitaxial growth of a few nanometer-thick BN film of well-stacked and flat layers on single crystalline Ni surface [5]. In this work, we will show how we can better understand the mechanism of nucleation and growth of BN on nickel in order to reach films with optimized quality and structure for each application, through an in-depth study of the impact of synthesis parameters on film structural properties. For that purpose, it is essential to develop and master efficient transfer techniques from the growth substrate to dedicated substrates for devices or characterizations. To access to the structural characteristics and quality of the BN films, the synthesized samples are characterized from the macroscale to the nanoscale via a panel of techniques: optical microscopy, SEM, TEM, AFM, Raman and luminescence spectroscopies, by capitalizing the characterization procedures which have been established on reference BN crystals [6]. References [1] G.C. Constantinescu, N.D.M. Hine, Nano Letters, 16 (2016) 2586. [2] A. Favron et al., Nature Materials, 14 (2015) 826. [3] M. Parzefall et al., Nature Nanotechnology, 10 (2015) 1058. [4] L. Banszerus et al., Science Advances, 1 (2015) e1500222. [5] A. Andrieux-Lédier et al, under review (2020). [6] L. Schué et al, 2D Materials, 4 (2017) 015028
Stability of Self-Ordered Thiol-Coated Silver Nanoparticles: Oxidative Environment Effects
No full textHere,
we study the stability of the 2D organization of thiol-coated
silver nanoparticles (NPs) by transmission electron microscopy. Whatever
the alkyl chain length and the nature of the silver precursor, we
show the rapid corrosion (over a few days) of the NPs by O2 from laboratory air whereas they remain stable for several weeks
under a nitrogen atmosphere. We show that this phenomenon is amplified
by the humidity in the air and by thiols trapped in the NP monolayers.
We obtain evidence of these thiols in excess by infrared and energy-dispersive
spectroscopies. This study of stability has been extended to gold
nanoparticles (AuNPs) coated with dodecanethiols. The AuNPs remain
stable under laboratory air because of the higher redox potential
of Au compared to that of Ag and O2
Building a cm² scale CVD graphene-based gas sensor: modelling the kinetic with a three-site adsorption/desorption Langmuir model.
No full textInternational audienceAbstract In this article, we aim to develop and study a highly sensitive and selective cm² scale graphene-based gas sensor. We present the technology used to fabricate sensors which integrate monolayer CVD graphene: photolithography and transfer of layers. Characterization techniques (optical microscopy, AFM, micro-Raman spectroscopy, transport electrical measurements) ensure a diagnosis of graphene ribbons and allow good reproducibility of technological processes. We present the results of gas characterizations after a 200 ppm NO2 exposure. We propose a novel approach for the modelling of the sensor response with a three-site adsorption/desorption Langmuir model. This innovative way of modelling the sensor response should provide a better understanding of the sensor’s kinetic and help to overcome the long response time observed with graphene gas sensors.
Infrared photodetector with coupled Fabry-Perot nanoresonnator and graphene (Conference Presentation)
No full textInternational audienceInfrared photodetection at ambient temperature is a challenge that classical photodetectors have not been able to fulfill yet. New materials, like the 2D materials family, and plasmonic nanostructures, are currently explored to address this challenge. We will show how the combination of carefully design coupled Fabry-Perot nanoresonnators and graphene can be used has an ambient infrared photodetector
Synthesis of Silver Nanoparticles Using Different Silver Phosphine Precursors: Formation Mechanism and Size Control
No full textSilver nanoparticles (AgNPs) ranging
from 2.5 to 7.1 nm in diameter
with a narrow size distribution are prepared by reducing different
silver phosphine precursors RAg(PPh3)n (R = Cl, Br, or NO3 and n = 1
or 3) with tert-butylamine borane (TBAB) in the presence
of dodecanethiols (C12) at a temperature between 100 and
160 °C. The study of the formation process of AgNPs by UV–vis
and IR spectroscopy reveals that the phosphine (PPh3) derived
from the metal precursor and thiols coat the NPs surface. In addition,
the PPh3/C12 ligand ratio is shown to decrease
during the NPs growth. PPh3 is indeed progressively replaced
by thiols. The rate of the PPh3–thiols exchange
is shown to depend on the nature of the silver precursor and to influence
the final NPs size. By using NO3Ag(PPh3), the
surface poisoning by PPh3 is shown to be the most efficient,
leading to the smallest NPs size (2.5 nm in diameter). Furthermore,
we get evidence that the nanoparticle size is controlled by the nature
of R in the precursor. Finally, it is found that the influence of
the reaction temperature and the thiol chains length on the final
NPs size depends on the silver precursor used
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