Magnetic-Field- and Temperature-Dependent Characteristics of Fe/Cu Granular Films Produced by Sputter- and Cluster-Beam-Deposition(Research in High Magnetic Fields)

The magnetoresistance (MR) and magnetization (M) have been measured as functions of temperature, T, and magnetic field, H, in sputter(SP)- and cluster-beam(CB)-deposited Fe_XCu_ alloys. The MR for the SP-deposited Fe_Cu_ film exhibits a maximum at around the Curie temperature (T_C=150 K) and increases rapidly below 100 K owing to a spin-glass transition. For the CB-deposited granular Fe-Cu films with low Fe content, the MR is also enhanced at low temperatures being attributable to a cluster-glass behavior of small fcc Fe clusters. At low temperatures, moreover, a T^ dependence is found for both MR and M versus T curves. For the SP-deposited Fe_Cu_ sample, the T^ coefficient of the MR roughly corresponds with that of the M. For the CB-deposited Fe_Cu_ sample, however, they are inconsistent each other. These results originate from different status of the Fe atoms : the Fe atoms are rather randomly dispersed in the Cu matrices in the SP-deposited sample, while they form clusters in the CB-deposited one

Compositional partition in Ag-Nb alloy clusters produced by a plasma-gas-condensation cluster source

We have produced Ag-Nb clusters by a facing-target type plasma-gas-condensation cluster source as our first step toward alloy cluster formation. The Ag-Nb clusters have been deposited on substrates and examined by a transmission electron microscope with a nano-beam energy dispersive X-ray analysis. We have obtained Ag-Nb alloy clusters with the sizes range between 5 and 10 nm in diameter. Their chemical compositions are broadly dispersed and partitioned into Ag-rich and Nb-rich ones, being consistent with the immiscible type equilibrium phase diagram. This result suggests that alloy cluster formation is driven by the alloy phase stability. (C) 2000 Acta Metallurgica Inc

Functionalization of Multi-Walled Carbon Nanotubes with Polymers

Cette thèse traite de la modification de surface des nanotubes de carbone avec des polymères Le chapitre I présente l'état de l'art des matériaux hybrides associant des liquides ioniques avec des nanotubes de carbone (NTC) ou du graphenes. Le chapitre II commence par un aperçu général de l'adsorption non-covalente de polymères sur la surface de NTC, suivi d'une description détaillée de l'étude réalisée sur la fonctionnalisation non covalente des nanotubes de carbone avec divers liquides ioniques polymérisable (LIP) à base d'imidazolium. Dans ce cadre, nous avons comparé deux méthodes expérimentales: la polymérisation in situ et le mélange en solution. Une des applications les plus importantes des NTC se situe dans le domaine des nanocomposites polymères/NTC. Le chapitre III décrit la formation de composites polyetherimide/NTC à partir des NTC-LIP obtenue dans la chapitre II. La préparation des composites en utilisant la méthode dite solvent casting est détaillée. Les NTC bruts, oxydés à l'acide nitrique et fonctionnalisé par le LIP ont été comparés. Des mesures mécaniques, thermiques et électriques de ces composées ont été aussi réalisées. Le dernier chapitre, divisé en deux sections, traite de la fonctionnalisation covalente des nanotubes de carbone avec une variété de polymères en utilisant deux approches différentes: "grafting from" et "grafting to". En utilisant la première approche, nous avons réalisé la croissance de chaînes de polyamide (PA) à partir de la surface de nanotubes de carbone fonctionnalisés avec le caprolactame par polymérisation anionique par ouverture de cycle. Les propriétés de traction des composites à base de PA ainsi préparées ont été étudiées. La polymérisation radicalaire de monomères vinyliques à base de LI de type imidazolium greffés à la surface de NTC est également présentée dans cette partie. Dans la deuxième partie du chapitre IV, nous présentons plusieurs stratégies de fonctionnalisation, y compris l'addition radicalaire et le greffage sur les défauts de NTC, pour la préparation des NTC fonctionnalisés de manière covalente avec des polymères compatibles avec des matrices époxyThis thesis deals with the surface modification of multi-walled carbon nanotubes with polymers with the aim to achieve a high level of dispersion in polymer matrices. Chapter I gives a comprehensive review of the state of the art of hybrids of ionic liquids with carbon nanomaterials, particularly, nanotubes and more recently, graphene. Chapter II starts with a general overview of the non-covalent adsorption of polymers onto the CNT surfaces followed by a detailed description of the study carried out on the non-covalent functionalization of CNTs with various imidazolium based polymerized ionic liquids (PIL). For this purpose, we further compare the two experimental methods: in situ polymerization and solution mixing. One of the most important applications of CNT is in polymer/CNT composites. Chapter III describes the formation of polyetherimide/CNT composites starting from PIL-CNT hybrids obtained in Chapter II. The preparation and characterization of composites using solvent casting methods have been detailed. Pristine, acid oxidized and PIL functionalized CNTs have been compared. Mechanical, thermal and electrical property measurements on these composites have also been described. The last chapter Chapter IV, divided into two sections, discusses the covalent functionalization of CNTs with a variety of polymers using two main approaches: grafting from and grafting to . Using the first approach we have grown polyamide (PA) chains from the surface of caprolactam grafted CNTs by anionic ring opening polymerization. The tensile properties of the PA based composites prepared therefrom containing pristine, amine- and PA-functionalized CNTs have been investigated. The radical polymerization of vinyl imidazolium based IL monomers attached to the activated CNT surface is also given in this section. In the second part of Chapter IV, we have reported several grafting to functionalization strategies including radical addition and defect site grafting used for the preparation of CNTs covalently attached with polymers intended to blend well with epoxy matricesTOULOUSE-INP (315552154) / SudocSudocFranceF

Co cluster coalescence behavior observed by electrical conduction and transmission electron microscopy

We deposited monodispersed Co clusters with mean diameters d = 6, 8.5, and 13 nm on quartz and microgrid substrates using a plasma-gas-condensation-type cluster beam deposition system. The cluster-cluster coalescence behavior of the Co cluster assemblies was investigated by in situ electrical conductivity measurements and ex situ transmission electron microscopy (TEM). The electrical conductivity measurement indicates that, below temperature T approximate to 100 degreesC, the Co clusters with d=8.5 nm maintain their original size as deposited at room temperature, while the cluster-cluster coalescence takes place at their interface at T > 100 degreesC. The TEM observation indicates that the morphology of the cluster distribution shows no marked change at substrate temperatures T-s < 250 degreesC. Above T-s = 300 degreesC, the interfacial area of coalesced clusters is crystalline, and has its own orientation, different from that of two connected cluster cores. (C) 2001 American Institute of Physics

Full potential LAPW calculation of electron momentum density and related properties of Li

Electron momentum density and Compton profiles in Lithium along $$,$$, and $$ directions are calculated using Full-Potential Linear Augmented Plane Wave basis within generalized gradient approximation. The profiles have been corrected for correlations with Lam-Platzman formulation using self-consistent charge density. The first and second derivatives of Compton profiles are studied to investigate the Fermi surface breaks. Decent agreement is observed between recent experimental and our calculated values. Our values for the derivatives are found to be in better agreement with experiments than earlier theoretical results. Two-photon momentum density and one- and two-dimensional angular correlation of positron annihilation radiation are also calculated within the same formalism and including the electron-positron enhancement factor.Comment: 11 pages, 7 figures TO appear in Physical Review