Добірка наукової літератури з теми "Metallic and polymeric nanowire arrays"

In this short review, we report the facile fabrication of various interesting multi-component nanostructures including arrays of core-shell nanowires, multiwall nanotubes, segmented nanowires and multilayer stacked nanodisks, using anodized alumina membrane (AAM). We demonstrate that metallic (Cu, Ni and Au) and polymeric (PPV and PPy) one-dimensional (1D) arrays can be readily prepared by electrochemical deposition into the AAM. By optimizing the experimental design and conditions, we developed techniques to produce various multi-component nanostructures such as polymer/metal or metal/metal core-shell nanowires as well as nanotubes, with reasonably good control over both the length and the shell thickness of the nanostructures. Furthermore, we extend this method to make segmented nanowires as well as multilayer stacked nanodisks. Selective functionalization of the segmented nanowires resulted in end-on or side-on adhesion of nanowires during assembly. We illustrate the possibility of utilizing these 1D arrays to present patterns with luminescent and/or magnetic properties at this length scale.

One-dimensional metallic nanostructures such as nanowires, rods, and tubes have drawn much attention for electrocatalytic applications due to potential advantages that include fewer diffusion impeding interfaces with polymeric binders, more facile pathways for electron transfer, and more effective exposure of active surface sites. 1D nanostructured electrodes have been fabricated using a variety of methods, typically showing improved current response which has been attributed to improved CO tolerance, enhanced surface activity, and/or improved transport characteristics. A template wetting approach was used to fabricate an array of platinum nanotubules which were examined electrochemically with regard to the electrooxidation of formic acid. Arrays of 100 and 200 nm nanotubules were compared to a traditional platinum black catalyst, all of which were found to have similar surface areas. Peak formic acid oxidation current was observed to be highest for the 100 nm nanotubule array, followed by the 200 nm array and the Pt black; however, CO tolerance of all electrodes was similar, as were the onset potentials of the oxidation and reduction peaks. The higher current response was attributed to enhanced mass transfer in the nanotubule electrodes, likely due to a combination of both the more open nanostructure as well as the lack of a polymeric binder in the catalyst layer.

We demonstrate a scalable method to create metallic nanowire arrays and meshes over square-centimeter-areas with tunable sub-100 nm dimensions and geometries using the shear alignment of block copolymers.

Single Metallic Nanowire Arrays (Ni, Au and Cu etc) and superlattice nanowire arrays (Ni/Au, Ni/Cu) were synthesized through template-directed electrochemical deposition method. The dual-bath technique was employed in fabrication of superlattice nanowire arrays. Anodized alumina membrane (AAM) and Ion Track-etched Polycarbonate Membrane was used as the fabrication templates. The specific electrode making technique and electrochemical deposition procedures were described in detail. Scanning electron microscope (SEM) performed all sample characterization. Vibrating sample magnetometer (VSM) and ferromagnetic resonance (FMR) were utilized to investigate the magnetic properties of single Ni nanowire arrays of different lengths and Ni/Cu superlattice nanowire arrays. The VSM data exhibited that the magnetic easy axis of samples is parallel to the nanowire axis direction and the nanowire arrays have obvious shape anisotropy. The FMR spectra indicated that the resonant field value is angular and aspect ratio dependence.

Dans ce projet, nous avons exploité la modification de surface d’électrodes avec des films minces de silice mésoporeuse à porosité verticalement orientée, générés par une méthode d'auto-assemblage assisté par électrochimie. La membrane de silice présente des pores étroits d'un diamètre d'environ 2-3 nm, et une épaisseur de l’ordre de 50-150 nm, susceptible d’être utilisée en tant que moule pour la préparation d’ensembles métalliques et organiques de faible dimension sur des surfaces conductrices. Nous avons combiné les caractéristiques du film mince de silice mésoporeuse avec l'électrochimie pour obtenir des motifs nanométriques à la surface de l’électrode. Un film de silice mésoporeuse mécaniquement stable et adhérent bien à la surface de l’électrode peut être obtenu sur des supports portant des fonctions hydroxydes de surface, par exemple l'oxyde mixte d'indium-étain (ITO). Cependant, l'adhésion et la stabilité mécanique du film mince de silice mésoporeuse sont faibles sur les électrodes à base de métaux nobles tels que l'or (Au). Pour assurer une couverture uniforme de la surface et une bonne adhésion du film de silice à la surface de l'or, il a été nécessaire d'utiliser un réactif (3-mercaptopropyl) triméthoxysilane (MPTMS) en tant que "colle moléculaire", dont la fonctionnalité thiol est capable de se lier au substrat d'or et dont la partie alcoxysilane peut se condenser avec le matériau silicique. La couche de MPTMS a cependant eu un effet important sur la perméabilité du film aux sondes redox. L'adsorption de MPTMS doit être suffisamment longue pour assurer une bonne adhésion du film mais pas trop longue afin d'éviter un blocage de la surface ou des défauts dans le film. En outre, les expériences de dépôt sous-potentiel de cuivre (UPD) ont révélé que la membrane de silice affectait de manière notoire le processus d'UPD, suggérant un certain effet de barrière de la membrane poreuse, mais l'interface Au/MPTMS/silice n'est pas suffisamment dense que pour empêcher la formation d’un dépôt métallique entre le substrat d'or et le film mince de silice. Dans la deuxième partie de la thèse, des films minces de silice mésoporeuse de deux diamètres de pores distincts (2,0 et 2,9 nm), générés sur électrodes d’ITO ont été utilisés comme moule pour la croissance électrochimique contrôlée de réseaux de nanofils de polyaniline (PANI). Afin d'assurer une bonne adhésion du PANI à la surface du support d’ITO, des entités d'aniline sont d'abord fixés de manière covalente au fond des mésocanaux par électrogreffage de cations aminophényle-diazonium, dont on se servira dans un second temps en tant que précurseurs pour la croissance du PANI par électropolymérisation de l'aniline à travers les mésocanaux de silice. Les fils de PANI restent attachés à l'ITO après extraction de la membrane de silice, confirmant l'importance de l'électrogreffage initial. Tant le PANI à l'intérieur du gabarit de silice que les réseaux de nanofils de PANI libres sont électroactifs. L'étude spectroélectrochimique a révélé un comportement électrochrome présentant une réponse rapide et une stabilité élevée de cyclage de ces réseaux de nanofils de PANI. Dans la dernière partie du projet, quelques tentatives préliminaires ont été faites pour le co-dépôt électrochimique de réseaux de nanofils bimétalliques Cobalt/Platine (CoPt) sur une électrode ITO recouverte de films de silice mésoporeuse. La présence de Co et de Pt dans les dépôts a été confirmée par analyse de surface au moyen de méthodes spectroscopiques et par caractérisation électrochimique
In this project we exploited surface modification of electrodes with vertically oriented mesoporous silica thin films, generated by electrochemically assisted self-assembly method. The silica scaffold offers narrow pores diameter around 2-3 nm and 50-150 nm film thickness, a competitive hard template material for the preparation of low dimensional metallic and organic nanopatterns on conducting surfaces. We combined the wealth of mesoporous silica thin film with electrochemistry to obtain surface nanopatterning of the underlying support. Well-adhered and mechanically stable mesoporous silica film is formed on electrodes bearing hydroxyl moieties on their surface, for example indium tin oxide (ITO). However, the adhesion and mechanical stability of mesoporous silica thin film is poor on noble metals such as gold (Au). To ensure uniform surface coverage and good adhesion of the silica film to the Au surface, it was necessary to use a (3-mercaptopropyl) trimethoxysilane (MPTMS) reagent to act as a “molecular glue” thanks to its thiol functionality, which is able to bind to the gold substrate and to its alkoxysilane moieties enabling condensation with the silica material. The MPTMS layer had, however, a significant effect on film permeability to redox probes, depending on the MPTMS treatment time. MPTMS adsorption should be long enough to ensure proper adhesion of the film but not too long to avoid surface blocking or film defects. In addition, Cu underpotential deposition (UPD) experiments revealed that the silica membrane significantly affected the UPD process, suggesting some barrier effect of the porous membrane, but the interface Au/MPTMS/silica is not sharp and allowed metal UPD between the gold substrate and the silica thin film. In the second part of the thesis, mesoporous silica thin films, with two distinct pore diameters (2.0 and 2.9 nm), covered ITO electrodes were used as hard template for the control electrochemical growth of polyaniline (PANI) nanowire arrays. To ensure proper adhesion of PANI to the underlying ITO surface, aniline moieties are first covalently attached to the bottom of mesochannels via electrografting of aminophenyl diazonium cations, serving in a second step as precursors for PANI growth by electropolymerization of aniline through the silica mesochannels. PANI wires remain attached to ITO after removal of the silica membrane, confirming the importance of initial electrografting. Both PANI inside silica template and the free PANI nanowire arrays were electroactive. Spectroelectrochemical study revealed fast electrochromic behavior and cycling stability of PANI nanowire arrays. In last part of the project, some preliminary attempts were made for the electrochemical co-deposition of bimetallic Cobalt/Platinum (CoPt) nanowire arrays onto ITO electrode covered with mesoporous silica films. The presence of Co and Pt in the deposits was confirmed from surface analysis by spectroscopic methods and electrochemical characterization

Cette thèse concerne une nouvelle méthode chimique de croissance par germes qui peut produire des assemblés de nanostructures métalliques epitaxiées sur des surfaces macroscopiques cristallines qui agissent comme germes. Cette approche permet d’obtenir des assemblés bien organisées en échelle centimétrique de nanofils métalliques de Co, qui sontmonocristallins, monodisperses de diamètres inferieurs à 10nm et qui ont une orientation perpendiculaire. Ils ont une anisotropie magnétique perpendiculaire et sont intéressantes pour des applications d’enregistrement magnétique à très haute densité. L’extension de cette méthode au fer donne des films nanostructurés de fer. L’orientation des nanostructures sur le support solide dépend de l’orientation cristallographique du substrat, alors que leur morphologie est dictée par la composition de la solution. Cet objectif a été atteint grâce à des études parallèles sur le mécanisme de croissance de nano-cristaux de cobalt en solution qui ont révélées une influence inattendue de la procédure de préparation de la solution mère sur la morphologie des nanocristaux. En plus,l’utilisation des germes nanoscopiques pour la croissance de Co et de Fe a rendu des nanofils longs de Co et des altères de Co-Fe et elle a contribué à la définition et l’amélioration des conditions expérimentales pour la croissance par germes de Co et de Fe sur les substrats solides
This thesis concerns a new wet chemical seeded growth method that can produce arrays of metal nanostructures epitaxially grown on crystalline macroscopic surfaces which act as seeds. This approach produces wafer-scale organized 2D hexagonal arrays of perpendicularly oriented, monodisperse and monocrystalline metallic Co nanowires with diameters below 10 nm which exhibit perpendicular magnetic anisotropy and are interesting for applications in ultra high density magnetic recording. Extension of this approach to iron gives rise to nanostructured iron films. The orientation of the nanostructures on the solid substrate depends on the substrate crystallographic orientation, whereas their morphology is dictated by the solution composition. This objective was attained through parallel studies on the growth mechanism of cobalt nano-crystals in solution which revealed an unexpected influence of the stock solution preparation procedure on the nanocrystal morphology. In addition, the use of nanoscopicseeds for the overgrowth of cobalt and iron gave rise to long Co nanowires and Co-Fe dumbbells and contributed to the definition and the improvement of the experimental conditions for the seeded growth of Co and Fe on the solid substrates

We develop a method for direct measurement of thermal conductivity of nanowires, consisting of a microelectrothermal test device and a complementary parameter estimation algorithm. Simulations of a simplified version of the problem show how differential measurements can address the problem of parasitic heat loss, and examine several different parameter estimation schemes. As reported elsewhere, measurements have been performed on aluminum nanowire arrays, with excellent results. Several design modifications are required to accommodate semiconducting samples. A device design for silicon nanowire arrays is presented. A simulation study suggests that these devices will also perform extremely well.

Understanding the structure and properties of metal nanowires is critical for the atomic-scale manipulation, design and application of those materials. Currently, active research on structure and behavior of various metallic nanowires has been carried out by computer simulation. Much experimental work has been done for synthesizing various metal nanowires by many different methods. To experimentally explore the mechanism of the behavior of and the development of structures in the nanowires, it is desirable to have the capability of synthesis various metal nanowires with controlled size, length, uniformity and aspect ratio. It is also desirable to further process those metal nanowires to engineer their properties. In our study, a template assisted fabrication method has been employed to fabricate various metal nanowire arrays, including cobalt, iron and nickel. This fabrication method offers us command over the size and length of the nanowires with excellent uniformity. Heat treatments were used to further process the metal nanowires. The structure of cobalt nanowire array has been investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Mechanical properties of the metal nanowire array will be investigated through nanoindentation and atomic force microscopy (AFM).