Thesis (Ph. D.)--University of Missouri-Columbia, 2005. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on October 18, 2007) Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 239-244).

The isolation of single layer graphene in 2004 by Geim and Novoselov introduced a method that researchers could extend to other van der Waals materials. Interesting and new properties arise when we reduce a crystal to two dimensions where they are often different from their bulk counterpart. Due to the van der Waals bonding between layers, these single sheets of crystal can be combined and stacked with diferent sheets to create novel materials. With the goal to study the interesting physics associated to these stacks, the focus of this work is on the fabrication and characterization of van der Waals heterostructures. In this work, we first present a brief history of 2D materials, the fabrication of heterostructures, and the various tools used to characterize these materials. We then give a description of the custom-built instrument that was used to assemble various 2D heterostructures followed by the findings associated with the optimization of the cleanliness of the stack's interface and surface. Finally, we discuss the results related to the twisting of adjacent layers of stacked MoS2 and its relation to the interlayer coupling between said layers.

No description available.

Actuellement, les recherches sur la fonctionnalisation des surfaces sont en pleine effervescence. Dans ce manuscrit, nous proposons une approche innovante pour mesurer l’efficacité de cette fonctionnalisation. Cette approche est basée sur l’utilisation d’un microscope à force atomique, opérant dans un mode dit de « modulation de fréquence ». Cet outil couplé aux pointes greffées d’un nanotube de carbone, que nous appellerons « sonde », permet d’obtenir des mesures qu’il serait impossible d’effectuer avec des pointes standards. En métrologie, afin d’assurer une bonne reproductibilité des mesures, nous avons besoin d’avoir des sondes ayant des caractéristiques les plus similaires possibles. Ceci a nécessité la mise en oeuvre d’une méthode pour optimiser la fabrication des sondes, ainsi qu’une définition de critères pour les classer dans différents grades de qualités. L’incertitude de répétabilité et de reproductibilité des mesures effectuées avec des sondes de grade « A » a été quantifiée. Ces mesures ont démontré que ces sondes sont compatibles en termes de robustesse et de sensibilité pour la caractérisation de surfaces fonctionnalisées, dont l’épaisseur est supérieure à la monocouche. Des mesures de cartographie effectuées sur de deux types de surfaces fonctionnalisées ont permis de dissocier la mesure de topographie de la réponse mécanique du nanotube en interaction avec la surface. / At present, the researches on the surface functionalization are in full effervescence. In this manuscript, we propose an innovative approach to measure the efficiency of this functionalization. This approach is based on the use of an atomic force microscope, operating in a mode called "frequency modulation". This tool coupled with the grafted tips with a carbon nanotube, which we will call "probe", allows to obtain measurements which would be impossible to make with standard tips. However, in metrology, in order to ensure good reproducibility of the measurements, we need to have probes with characteristics that are as similar as possible. This required the implementation of a method to optimize the manufacture of the probes, as well as a definition of criteria to classify them in different grades of qualities. The uncertainty of repeatability and reproducibility of the measures made with probes of rank "A" were quantified. These measurements have demonstrated that these probes are compatible in terms of robustness and sensitivity for the characterization of functionalized surfaces, whose thickness is superior to the monolayer. Mapping measurements carried out on two types of functionalized surfaces enable to dissociate the topography measurement from the mechanical response of the nanotube in interaction with the surface.

No description available.

Malgré l'enthousiasme croissant pour les nanotechnologies, les nanoparticules (NPs) peuvent interagir avec les systèmes biologiques et affecter leur comportement, et pourraient ainsi présenter un danger pour les écosystèmes et l’Homme. Il est donc essentiel de connaître leurs mécanismes d'interactions afin non seulement de prévenir leurs risques potentiels, mais également de bénéficier de leurs propriétés uniques, par exemple dans la conception des biocapteurs. Dans ce contexte, nous étudions la cytotoxicité des NPs de silice, de tailles et charges diverses, sur les propriétés des bactéries Escherichia coli et Bacillus subtilis, au moyen de la microscopie à force atomique et des tests de viabilité. Les NPs chargées négativement (NPs-) de diamètre inférieur à un diamètre critique φc, 50 - 80 nm, (i) mènent à l'isolation des bactéries E. coli, (ii) induisent une "sphérification" de la cellule initialement en bâtonnet, (iii) provoquent des lésions dans la membrane externe et une réorganisation de sa structure. Pour la bactérie B. subtilis, seule la dégradation de la structure du peptidoglycane a été observée. Cependant, pour les deux souches, une activité antibactérienne a été démontrée pour les NPs- en dessous de φc, qui peuvent conduire à la lyse cellulaire tandis que, au-dessus de φc, les NPs- n’ont aucun effet sur la population, la morphologie ou la structure bactérienne. En ce qui concerne les NPs chargées positivement, elles conduisent, quel que soit leur diamètre, à une forte agrégation des cellules, en raison des interactions électrostatiques, et tendent à favoriser la formation d'invaginations membranaires, ne menant pas nécessairement à la lyse cellulaire. Cette étude fondamentale a mené au développement d’un biocapteur électrochimique pour la détection de bactéries, application notable pour des problèmes biomédicaux, environnementaux et de défense. Les NPs, intégrées à ces outils, offrent un mode de détection rapide, très sensible et peu coûteux. Expérimentalement, une multicouche de polyélectrolytes a été utilisée pour immobiliser des NPs inoffensives (φ = 100 nm), auxquelles sont ensuite fixés des anticorps spécifiques, afin d'améliorer la détection finale de la bactérie E. coli. L’ensemble des étapes a été optimisé par le procédé du spin coating et étudié à l'aide de mesures de microbalance à quartz et de voltametrie cyclique. L’intégration de NPs au biocapteur a permis une détection linéaire et non saturée des bactéries E. coli dans une large gamme de concentration (jusqu’à 10^9 CFU/mL) pour une limite de détection de 10^6 CFU/mL. / Despite the growing enthusiasm for nanotechnologies, nanoparticles (NPs) might put environmental safety and human health at risk, as they can interact with biological systems and affect their behavior. It is therefore essential to know their mechanisms of interactions in order not only to prevent their potential risks but also to benefit from their unique properties, such as in biosensors design. In this context, we study the cytotoxicity of silica NPs, with diverse sizes and charges, on the properties of Escherichia coli and Bacillus subtilis bacteria, by means of atomic force microscopy and viability tests. Negatively charged NPs (NPs-) with a diameter φ lower than a critical diameter φc, 50 - 80 nm, (i) lead to the isolation of E. coli bacteria, (ii) induce a "spherification" of the cell initially rod shaped, and (iii) cause the formation of pore-like lesions in the outer membrane and a reorganization of its structure. For B. subtilis bacteria, only the degradation of the peptidoglycane’s structure was observed. Though, for both strains, an antibacterial activity was shown for NPs- below φc, which potentially lead to the cell lysis whereas, above φc, NPs- have no effect on population, morphology or bacterial structure. As positively charged NPs are concerned, whatever their diameter, they lead to a strong aggregation of the cells, due to electrostatic interactions, and tend to favor the formation of membrane invaginations, not necessarily involving cell lysis. This fundamental study has been used to develop an electrochemical biosensor for bacteria, which are of great importance for biomedical, environmental and defense issues. NPs involved in such tools offer a fast, high-sensitive and low-cost way of detection. A polyelectrolyte multilayer was used to immobilize harmless NPs (φ = 100 nm), which are, then, functionalized with specific antibodies, in order to enhance the final detection of E. coli bacteria. All steps were optimized by a spin coating process and studied through quartz microbalance and cyclic voltametry measurements. Integrating NPs in this biosensor resulted in a linear and unsaturated detection of E. coli bacteria in a wide range of concentration (until 10^9 CFU/mL) and a limit of detection of 10^6 CFU/mL.

abstract: The atomic force microscope (AFM) is capable of directly probing the mechanics of samples with length scales from single molecules to tissues and force scales from pico to micronewtons. In particular, AFM is widely used as a tool to measure the elastic modulus of soft biological samples by collecting force-indentation relationships and fitting these to classic elastic contact models. However, the analysis of raw force-indentation data may be complicated by mechanical heterogeneity present in biological systems. An analytical model of an elastic indentation on a bonded two-layer sample was solved. This may be used to account for substrate effects and more generally address experimental design for samples with varying elasticity. This model was applied to two mechanobiology systems of interest. First, AFM was combined with confocal laser scanning fluorescence microscopy and finite element analysis to examine stiffness changes during the initial stages of invasion of MDA-MB-231 metastatic breast cells into bovine collagen I matrices. It was determined that the cells stiffen significantly as they invade, the amount of stiffening is correlated with the elastic modulus of the collagen gel, and inhibition of Rho-associated protein kinase reduces the elastic modulus of the invading cells. Second, the elastic modulus of cancer cell nuclei was investigated ex situ and in situ. It was observed that inhibition of histone deacetylation to facilitate chromatin decondenstation result in significantly more morphological and stiffness changes in cancerous cells compared to normal cells. The methods and results presented here offer novel strategies for approaching biological systems with AFM and demonstrate its applicability and necessity in studying cellular function in physiologically relevant environments. / Dissertation/Thesis / Doctoral Dissertation Physics 2015

abstract: Cell adhesion is an important aspect of many biological processes. The atomic force microscope (AFM) has made it possible to quantify the forces involved in cellular adhesion using a technique called single cell force spectroscopy (SCFS). AFM based SCFS offers versatile control over experimental conditions for probing directly the interaction between specific cell types and specific proteins, surfaces, or other cells. Transmembrane integrins are the primary proteins involved in cellular adhesion to the extra cellular matix (ECM). One of the chief integrins involved in the adhesion of leukocyte cells is αMβ2 (Mac-1). The experiments in this dissertation quantify the adhesion of Mac-1 expressing human embryonic kidney (HEK Mac-1), platelets, and neutrophils cells on substrates with different concentrations of fibrinogen and on fibrin gels and multi-layered fibrinogen coated fibrin gels. It was shown that multi-layered fibrinogen reduces the adhesion force of these cells considerably. A novel method was developed as part of this research combining total internal reflection microscopy (TIRFM) with SCFS allowing for optical microscopy of HEK Mac-1 cells interacting with bovine serum albumin (BSA) coated glass after interacting with multi-layered fibrinogen. HEK Mac-1 cells are able to remove fibrinogen molecules from the multi-layered fibrinogen matrix. An analysis methodology for quantifying the kinetic parameters of integrin-ligand interactions from SCFS experiments is proposed, and the kinetic parameters of the Mac-1 fibrinogen bond are quantified. Additional SCFS experiments quantify the adhesion of macrophages and HEK Mac-1 cells on functionalized glass surfaces and normal glass surfaces. Both cell types show highest adhesion on a novel functionalized glass surface that was prepared to induce macrophage fusion. These experiments demonstrate the versatility of AFM based SCFS, and how it can be applied to address many questions in cellular biology offering quantitative insights. / Dissertation/Thesis / Doctoral Dissertation Physics 2016

Le rayonnement synchrotron et la microscopie à sondes locales (SPM) sont deux des techniques les plus utilisées pour étudier les propriétés physiques et chimiques de nanostructures. Le couplage de ces deux techniques est prometteur pour les nanosciences en leur ouvrant de nouveaux horizons. D'un point de vue expérimental ce couplage est un défi exaltant et a déjà prouvé ses capacités par la combinaison de la Microscopie à Force Atomique (AFM) et de la diffraction de Rayons-X pendant le projet X-tip, qui, grâce au développement d'un microcope à force atomique embarqué sur une lugne de lumière synchrotron a permis l'étude du module de Young de microplots de germanium en procédant simulatanément à son indentation et à son analyse par diffraction. Cependant, cette configuration ne permet pas de manipuler en trois dimensions (3D). Le but ultime, pour notre nano-manipulateur est de manipuler en 3D avec un contrôle permanent des nano-forces exercées sur l'objet sous un faisceau d'analyse (rayon X, LASER). Le premier chapitre s'attarde donc sur les senseurs qui devront rendre compte des interactions à l'échelle nanométrique et permettre la saisie d'un objet individuel. Après un tour d'horizon de différentes techniques de micro/nanomanipulation disponibles à ce jour (micro-préhenseurs mécaniques basés sur la technologie MEMS, pinces optiques, préhenseurs basés sur la microscopie à force atomique conventionnelle) et devant les contraintes qu'implique le couplage d'un tel système avec les expériences synchrotron, le choix des oscillateurs à quartz (Diapason et LER) en tant que senseurs est expliqué. La microscopie à force atomique en générale et le fonctionnement particulier de ces oscillateurs sont décrits. Dans le second chapitre le développement instrumental de notre station de nanomanipulation est détaillé et notamment : Comment mettre en place ce type de résonateurs et la pointe associée pour réaliser à la fois l'imagerie AFM de l'échantillon et la préhension de l'objet? Comment contrôler le positionnement grossier et fin des trois éléments d'une nanomanipulation? Enfin le système haptique ERGOS et son couplage avec notre montage est décrit. Dans le dernier chapitre, deux types d'expériences sont présentés : le premier ne fait intervenir que notre montage piloté classiquement par ordinateur et montre ses capacités à réaliser la préhension d'objets micrométriques de manière contrôlée. Le second fait intervenir le couplage entre notre montage et le système haptique pour réaliser l'exploration rapide d'un échantillon ainsi que la localisation et la reconnaissance de forme d'objet sub-micronique. Ces expériences rendent compte des capacités de ce couplage à transmettre directement à un utilisateur les interactions à l'échelle nanométrique ainsi que la possibilité par l'intermédiaire de cette interface de réaliser des tâches complexes : manipulation sur une surface, reconnaissance de forme, et suivi de contour. / The synchrotron radiation and scanning probe microscopy (SPM) are the (two) most used techniques to study the physical and chimical properties of nanostructures. Coupling these two techniques is promising for the nanosciences by opening news horizons. From an experimental point of view, this coupling is an exciting challenge and has already proven its skills with the combination of Atomic Force Microscopy (AFM) and X-Ray diffraction during the X-tip project, which, thanks to the development of an atomic force microscope embended on a synchrotron beamline, has permitted to study Young's modulus of germanium microplots proceeding simultaneously with its indentation and its diffraction analysis. However, this configuration doesn't permit a three dimension (3D) manipulation. The ultimate goal, for our nano-manipulator, is to manipulate in 3D with a permanent control of nano-forces exerted on the object undcer a scanning beam (X-Ray, laser). The first chapter therefore focuses on the sensors which measure the interactions at a nanometer scale and permit the seizure of an individual object. After an overview of the differents techniques of micro/nano-manipulation available today ( mechanical micro-grippers based on MEMS technology, optic tweezers, grippers based on conventionnal atomic force microscopy), and in front of the constraints implied by the coupling of this kind of system with the synchrotron experiments, the choice of quartz oscillators (Tunning fork and LER) as sensors is explained. The atomic force microscopy in general and the particular behavior of these oscillators is described. In the second chapter, the instrumental development of our nano-manipulation station is detailed and especially : How to implement this type of resonators and the associated tip to achieve both AFM imaging of the sample and gripping of the object ? How to control the coarse and fine positionning of the three elements of a nano-manipulation ? Finally, the haptic system ERGOS et its coupling with our assembly is describe. In the last chapter, two types of experiments are presented : the first involves only our assembly piloted classically with a computer and show its skills in the achievement of gripping of micrometric objects in a controled way. The second involves the coupling between our assembly and the haptic system to achieve the fast exploration of a sample and also the location and shape recognition of sub-micronic objects. These experiments reflect the capacities of this coupling to directly transmit to an user the interactions at a nanometer scale and also the possibility using this interface to achieve complex tasks : manipulation on a surface, shape recognition and contour tracking.