Études des fuites excitoniques dans des familles de boîtes quantiques d'InAs/InP par PLRT par addition de fréquences

Ce mémoire porte sur les mécanismes de relaxation et de fuite des excitons dans des systèmes de boîtes quantiques(BQs) d’InAs/InP. Les systèmes sont composés d’un sub- strat volumique d’InP, appelé matrice (M), d’un puits quantique d’InAs, nommé couche de mouillage (CM), et des familles de BQs d’InAs. La distinction entre les familles est faite par le nombre de monocouche d’épaisseur des boîtes qui sont beaucoup plus larges que hautes. Une revue de littérature retrace les principaux mécanismes de relaxation et de fuite des excitons dans les systèmes. Ensuite, différents modèles portant sur la fuite thermique des excitons des BQs sont comparés. Les types de caractérisations déjà produites et les spécifications des croissances des échantillons sont présentés. L’approche adoptée pour ce mémoire a été de caractériser temporellement la dynamique des BQs avec des mesures d’absorbtion transitoire et de photoluminescence résolue en temps (PLRT) par addition de fréquences. L’expérience d’absorption transitoire n’a pas fait ressortir de résultats très probants, mais elle est expliquée en détails. Les mesures de PLRT ont permis de suivre en température le temps de vie effectif des excitons dans des familles de BQs. Ensuite, avec un modèle de bilan détaillé, qui a été bien explicité, il a été possible d’identifier le rôle de la M et de la CM dans la relaxation et la fuite des excitons dans les BQs. Les ajustements montrent plus précisément que la fuite de porteurs dans les BQs se fait sous la forme de paires d’électrons-trous corrélées.This thesis focuses on the mechanisms of relaxation and leakage of excitons in systems of quantum dots (QDs) InAs / InP. The systems are composed of a substrate of InP volume, called matrix (M), of a quantum well of InAs, named wetting layer (CM), and of QD families of InAs. The distinction between the families can be explained by the number of monolayer-thick boxes that are wider than high. A literature review highlights the main relaxation mechanisms and leakage of excitons in systems. Then, different models on the thermal leakage of the QD excitons are compared.Then, a presentation of the different types of characterizations already and of the specifications on the samples growths. The approach used for this thesis is to temporarily characterize the dynamic of the QDs with transient absorption and upconversion. The transient absorption experiment’s results are not very convincing, but are minutely explained. PLRT measures were used to follow in temperature the excitons effective lifetime in the QDs families. Then, with a detailed balance model, which has been well explained, it was possible to identify the role of theMand CM in relaxation and leakage of excitons in QDs. As shown by the adjustement, the escape of carriers in the QDs is made in a correlated electron-hole pairs form

Photo-oxydation et spectroscopie Raman de couches minces de phosphore noir

Les couches minces (CMs) de phosphore noir sont reconnues comme matériaux lamellaires, anisotropes dans le plan, prometteurs pour leurs propriétés optiques et électroniques. D’un point de vue chimique, le phosphore noir mince représente un défi puisqu’il se dégrade à l’air. Dans la mesure où le phosphore noir a le potentiel de pouvoir être produit à grande échelle, une panoplie de caractérisations optiques de base se doit d’être développée afin d’en assurer la qualité et de minimiser les défauts structuraux. À cet effet, la spectroscopie Raman représente un outil de prédilection permettant de sonder les modes de vibrations du cristal, lesquelles dépendent explicitement des interactions interatomiques. L’épaisseur des CMs, la présence de défauts ou de stress devraient avoir une influence sur les spectres Raman du phosphore noir, ce qu’une étude complète permet d’en isoler l’origine. La présente thèse porte sur l’étude des mécanismes à l’origine de l’instabilité du phosphore noir et une caractérisation de la spectroscopie Raman des CMs de celui-ci. Le but de cette thèse est de développer une théorie utile permettant de comprendre l’oxydation du phosphore noir et d’apporter une caractérisation complète de toutes les signatures Raman observées, ce qui inclut celles permettant de quantifier l’intégrité du phosphore noir mince. Dans une première partie, nous explorons la dégradation du phosphore noir. Assisté de la spectroscopie Raman et la microscopie électronique à transmission (TEM), nous isolons les ingrédients nécessaires à la dégradation et identifions le processus de la photo-oxydation assistée par un environement humide oxigéné. La modélisation du phénomène par la théorie de Marcus-Gerischer permet d’inclure l’effet de trois éléments de la dégradation, l’oxygène, l’eau et la lumière, en plus de prédire une dépendence forte sur l’épaisseur du matériau. Cette dernière est associée à un effet du confinement quantique démontré expérimentalement avec le TEM. Dans un environnement très réactif, une dégradation du phosphore noir s’accompagne d’une décroissance de l’intensité des spectres Raman et suit la dépendance en fonction de la fluence de lumière sous laquelle le matériau est exposé. Dans des conditions moins intrusives, nous identifions une signature Raman de la dégradation avec le ratio en intensité intégrée entre les modes A1g et A2g. Parallèlement, nous présentons une des premières études des spectres Raman sur des échantillons exempts d’oxydation pour des épaisseurs atomiques (n) allant de 1 à 5. Une dépendance de l’énergie des phonons est observée et permet l’identification de l’épaisseur des CMs à l’aide de la spectroscopie Raman. Plusieurs nouveaux modes sont présentés sans pouvoir être assignés à un processus en particulier. Un de ces modes est assigné à une séparation de Davydov menant à une conversion d’un mode infra-rouge en un mode Raman. Dans la seconde partie, l’origine des autres nouveaux modes est retracée. Au total, quatre modes sont identifiés dans une étude alliant une caractérisation plus complète en spectroscopie Raman avce l’épaisseur (entre n = 1 à 18) lors d’expériences en dégradation. Les modes sont associés à des modes de phonons-défauts, c’est-à-dire un processus Raman de deuxième ordre impliquant la diffusion d’un phonon avec un quasi-momentum non-nul et la présence d’un défaut dans la structure cristalline. L’analyse montre que les modes A1g et A2g peuvent participer au processus et l’anisotropie du phosphore noir sépare chacune des deux réponses en deux contributions. À l’aide de simulation de la structure de bande électronique et phononique, une modélisation de la réponse spectrale des phonons-défauts pour la monocouche est construite et corrobore l’identification des modes. Une conséquence directe de ces modes est de permettre de pouvoir quantifier les défauts dans le phosphore noir avec la spectroscopie Raman.Thin films of black phosphorus are recognized as anisotropic lamellar materials promising for their optical and electronic properties. From a chemical point of view, thin films of black phosphorus represent a challenge due to a fast degradation in air. Since black phosphorus has the potential to be produced on a large scale, optical characterization must be developed in order to ensure its integrity. To this end, Raman spectroscopy is a versatile tool for probing crystal vibration, which depend explicitly on inter-atomic interactions. The thickness of the CMs, the presence of defects or stresses should have an influence on the Raman spectra of black phosphorus, which behaviors can be isolate through a complete study. This thesis deals with the study of the mechanisms behind the instability of black phosphorus in air and with the characterization by Raman spectroscopy. The aim of this thesis is to develop a useful theory to understand the oxidation of black phosphorus and to provide a complete characterization of all Raman signatures observed, which in turn shows that Raman spectroscopy allows to quantify the integrity of thin films of black phosphorus. In a first part, we explore the degradation of black phosphorus. Assisted by Raman spectroscopy and transmission electron microscopy (TEM), we isolate the ingredients responsable for the degradation observed and identify the process of photooxidation in a wet and oxygenated environment. The modeling of the phenomenon with the help of Marcus-Gerischer theory allows to include the effect of the three key elements of degradation: oxygen, water and light and more importantly, it predicts the strong dependence on the thickness of black phosphorus observed in the experiments. The latter is associated with an effect of the quantum confinement and is shown experimentally using TEM imaging. In a highly corrosive environment, a strong degradation of the black phosphorus is accompanied by a decrease in the intensity of the Raman signal which follows the expected dependence as a function of the fluence of light under which the material is exposed. In oxidative conditions, we identify the Raman signature of the degradation using the integrated intensity ratio between the modes A1g and A2g . We also present one vii of the first studies of oxidation-free Raman spectra for atomic thicknesses (n) ranging from 1 to 5. A dependence of the phonon energy is observed and allows the thickness to be identified using Raman spectroscopy. Several new modes are presented without being able to be assigned to a particular process. One of these modes is assigned to a separation of Davydov leading to a conversion of an infrared mode into a Raman mode. In the second part, the origin of the other new modes is traced. Four modes are identified in a Raman study samples for n = 1 to 18 doing degradation experiments. They are associated to phonon-defects modes, which are second-order Raman processes involving the emission of a phonon with a non-zero quasi-momentum and a defect in the crystal. The analysis shows that the modes A1g and A2g can participate in the process and each of them are separated in two responses due to the anisotropic response of black phosphorus in the lamellar plane. Using simulations of the electronic and phononic bands structure, a modeling of the phonon-defect spectral response for the monolayer are constructed and used to the identification of the modes. A direct consequence of these modes is that it is possible to quantify the defects density in black phosphorus with Raman spectroscop

Spectroscopy on Black Phosphorus exfoliated down to the monolayer

International audienc

Liquid phase exfoliation of antimonene: systematic optimization, characterization and electrocatalytic properties

Antimonene, a novel group 15 two-dimensional material, is attracting great attention due to its outstanding physical and chemical properties. Despite its thermodynamic stability, the pronounced covalent character of the interlayer interactions imposes severe limitations on its exfoliation into mono- and few-layer. Here, we develop a systematic study of liquid phase exfoliation (LPE) with the aim to optimize antimonene production in terms of concentration and dimensional anisotropy, investigating the most relevant experimental factors affecting the exfoliation: pre-processing of pristine antimony, solvent selection based on Hansen solubility parameters and ultrasound conditions. Moreover, exhaustive characterization by means of turbidimetry, XRD, Raman spectroscopy, XPS, AFM, SEM, XEDS and TEM has been carried out. Indeed, we achieved concentration values of ca. 0.368 g L−1 (∼yield of 37 wt%), up to ∼30 times higher compared to the highest value so far reported, with ca. 50% of the nanolayers with heights between 2 and 10 nm and lateral dimensions in the 40-300 nm range. Furthermore, it has been demonstrated that the yield of the process can be enhanced up to ∼90 wt% by recycling the sediment to perform a maximum of 7 cycles. Moreover, we have illustrated the usefulness of this approach by characterizing the electrochemical behaviour of antimonene as a catalyst for the hydrogen evolution reaction (HER). This study provides important insights into the LPE and electrochemical properties of antimonene, allowing its large-scale production and paving the way for its application in fields of utmost importance such as energy storage and conversion or catalysis

Supramolecular networks stabilise and functionalise black phosphorus

The limited stability of the surface of black phosphorus (BP) under atmospheric conditions is a significant constraint on the exploitation of this layered material and its few layer analogue, phosphorene, as an optoelectronic material. Here we show that supramolecular networks stabilised by hydrogen bonding can be formed on BP, and that these monolayer-thick films can passivate the BP surface and inhibit oxidation under ambient conditions. The supramolecular layers are formed by solution deposition and we use atomic force microscopy to obtain images of the BP surface and hexagonal supramolecular networks of trimesic acid and melamine cyanurate (CA.M) under ambient conditions. The CA.M network is aligned with rows of phosphorus atoms and forms large domains which passivate the BP surface for more than a month, and also provides a stable supramolecular platform for the sequential deposition of 1,2,4,5-tetrakis(4-carboxyphenyl)benzene to form supramolecular heterostructures

Liquid exfoliation of solvent-stabilized few-layer black phosphorus for applications beyond electronics

Few-layer black phosphorus (BP) is a new two-dimensional material which is of great interest for applications, mainly in electronics. However, its lack of environmental stability severely limits its synthesis and processing. Here we demonstrate that high-quality, few-layer BP nanosheets, with controllable size and observable photoluminescence, can be produced in large quantities by liquid phase exfoliation under ambient conditions in solvents such as N-cyclohexyl-2-pyrrolidone (CHP). Nanosheets are surprisingly stable in CHP, probably due to the solvation shell protecting the nanosheets from reacting with water or oxygen. Experiments, supported by simulations, show reactions to occur only at the nanosheet edge, with the rate and extent of the reaction dependent on the water/oxygen content. We demonstrate that liquid-exfoliated BP nanosheets are potentially useful in a range of applications from ultrafast saturable absorbers to gas sensors to fillers for composite reinforcement

2D Black Phosphorus: from Preparation to Applications for Electrochemical Energy Storage

Black phosphorus (BP) is rediscovered as a 2D layered material. Since its first isolation in 2014, 2D BP has triggered tremendous interest in the fields of condensed matter physics, chemistry, and materials science. Given its unique puckered monolayer geometry, 2D BP displays many unprecedented properties and is being explored for use in numerous applications. The flexibility, large surface area, and good electric conductivity of 2D BP make it a promising electrode material for electrochemical energy storage devices (EESDs). Here, the experimental and theoretical progress of 2D BP is presented on the basis of its preparation methods. The structural and physiochemical properties, air instability, passivation, and EESD applications of 2D BP are discussed systemically. Specifically, the latest research findings on utilizing 2D BP in EESDs, such as lithium‐ion batteries, supercapacitors, and emerging technologies (lithium–sulfur batteries, magnesium‐ion batteries, and sodium‐ion batteries), are summarized. On the basis of the current progress, a few personal perspectives on the existing challenges and future research directions in this developing field are provided

High electron mobility, quantum Hall effect and anomalous optical response in atomically thin InSe

A decade of intense research on two-dimensional (2D) atomic crystals has revealed that their properties can differ greatly from those of the parent compound. These differences are governed by changes in the band structure due to quantum confinement and are most profound if the underlying lattice symmetry changes. Here we report a high-quality 2D electron gas in few-layer InSe encapsulated in hexagonal boron nitride under an inert atmosphere. Carrier mobilities are found to exceed 103cm2V-1s-1and 104cm2V-1s-1at room and liquid-helium temperatures, respectively, allowing the observation of the fully developed quantum Hall effect. The conduction electrons occupy a single 2D subband and have a small effective mass. Photoluminescence spectroscopy reveals that the bandgap increases by more than 0.5eV with decreasing the thickness from bulk to bilayer InSe. The band-edge optical response vanishes in monolayer InSe, which is attributed to the monolayer's mirror-plane symmetry. Encapsulated 2D InSe expands the family of graphene-like semiconductors and, in terms of quality, is competitive with atomically thin dichalcogenides and black phosphorus.EU, EPSRC. The Royal Societ