Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第14104号 / 工博第2968号 / 新制||工||1440(附属図書館) / 26392 / UT51-2008-L159 / 京都大学大学院工学研究科高分子化学専攻 / (主査)教授 金谷 利治, 教授 伊藤 紳三郎, 教授 瀧川 敏算 / 学位規則第4条第1項該当

Carbon Nanotubes (CNTs) are used extensively in various applications where substrate are required to be possessing higher surface area, porosity and electrical and thermal conductivity. Such properties can be enhanced to target a particular gas and biochemical for efficient detection when CNT matrix is functionalized with Nanoparticles (NPs). Conventional functionalization involves harsh oxidation repeated washing, filtration and sonication, which induce defects. The defects lead to hindered mobility of carriers, unwanted doping and also fragmentation of the CNTs in some cases. In this document we demonstrate functionalization of CNT with Au nanoparticles on a macro scale under dry and ambient condition using Xenon ash induced solid-state dewetting. A sputtered thin film was transformed into nanoparticles which were confirmed to be in a state of thermodynamic equilibrium. We worked on 3 nm, 6 nm, 9 nm, 15 nm, 30 nm initial thickness of thin films. Xenon ash parameters of energy, number of pulse, duration of pulse, duration of gap between consecutive pulses were optimized to achieve complete dewetting of Au thin films. 3 nm deposition was in the form of irregular nano-islands which were transformed into stable nanoparticles with a single shot of 10 J/cm2 of 2 ms duration. 6 nm and 9 nm deposition was in form of continues film which was also dewetted into stable nanoparticles with a single pulse but with an increased energy density of 20 J/cm2 and 35 J/cm2 respectively. In case of 15 nm and 30 nm deposition the thin film couldn't be dewetted with a maximum energy density of 50 J/cm2, it was observed that 3 and 4 pulses of 2 ms pulse duration and 2 ms gap duration with an energy density of 50 J/cm2 were required to completely dewet the thicker films. However irregularity was induced in the sizes of the NPs due to Ostwald ripening phenomenon which causes smaller particle within a critical difiusion length to combine and form a larger particle during or after dewetting process. For comparison, the Au thin films were also dewetted by a conventional process involving annealing of samples until the thin film was fully transformed into NPs and the size of NPs seized to grow. Scanning electron microscope (SEM) was used to characterize the samples. Thermodynamic stability of the particles was confirmed with statistical analyses of size distribution after every additional pulse.

The ability to fabricate structures and engineer materials on the nanoscale leads to the development of new devices and the study of exciting phenomena. Nanostructures attached to the surface of a substrate, in a manner that renders them immobile, have numerous potential applications in a diverse number of areas. Substrate-supported nanostructures can be fabricated using numerous modalities; however the easiest and most inexpensive technique to create a large area of randomly distributed particles is by the technique of thermal dewetting. In this process a metastable thin film is deposited at room temperature and heated, causing the film to lower its surface energy by agglomerating into droplet-like nanostructures. The main drawbacks of nanostructure fabrication via this technique are the substantial size distributions realized and the lack of control over nanostructure placement. In this doctoral dissertation, a new pathway for imposing order onto the thermal dewetting process and for manipulating the size, placement, shape and composition of preformed templates is described. It sees the confinement of substrate-supported thin films or nanostructure templates by the free surface of a metal film or a second substrate surface. Confining the templates in this manner and heating them to elevated temperatures leads to changes in the characteristics of the nanostructures formed. Three different modalities are demonstrated which alters the preformed structures by: (i) subtracting atoms from the templates, (ii) adding atoms to the template or (iii) simultaneously adding and subtracting atoms. The ability to carry out such processes depends on the choice of the confining surface and the nanostructured templates used. A subtractive process occurs when an electroformed nickel mesh is placed in conformal contact with a continuous gold film while it dewets, resulting in the formation of a periodic array of gold microstructures on an oxide substrate surface. When heated the gold beneath the grid selectively attaches to it due to the surface energy gradient which drives gold from the low surface energy oxide surface to the higher surface energy nickel mesh. With this process being confined to areas adjacent to and in contact with the grid surface the film ruptures at well-defined locations to form isolated islands of gold and subsequently, a periodic array of microstructures. The process can be carried out on substrates of different crystallographic orientations leading to nanostructures which are formed epitaxially and have orientations based on underlying substrate orientations. The process can be extended by placing a metallic foil of Pt or Ni over preformed templates, in which case a reduction in the size of the initial structures is observed. Placing a foil on structures with random placement and a wide size distribution results, not only in a size reduction, but also a narrowed size distribution. Additive processes are carried out by using materials which possess high vapor pressures much below the sublimation temperature of the template materials. In this case a germanium substrate was used as a source of germanium adatoms while gold or silver nanostructures were used as heterogeneous nucleation sites. At elevated temperatures the adatoms collect in sufficient quantities to transform each site into a liquid alloy which, upon cooling, phase separates into elemental components sharing a common interface and, hence, resulting in the formation of heterodimers and hollowed metal nanocrescents upon etching away the Ge. A process which combined aspects of the additive and subtractive process was carried out by using a metallic foil with a high vapor pressure and higher surface energy than the substrate surface (in this case Pd foil). This process resulted in the initial preformed gold templates being annihilated and replaced by nanostructures of palladium, thereby altering their chemical composition. The assembly process relies on the concurrent sublimation of palladium and gold which results in the complete transfer of the templated gold from the substrate to the foil, but not before the templates act as heterogeneous nucleation sites for palladium adatoms arriving to the substrate surface. Thus, the process is not only subtractive, but also additive due to the addition of palladium and removal of gold. / Mechanical Engineering

We explore a specific small geometry containing a single thin bounded grain on a substrate with a hole at its center. By employing a mathematical model based on surface diffusion, no flux boundary conditions, and prescribed contact angles, we study the evolution of the hole as well as the exterior surface of the grain, based on energetic considerations and dynamic simulations. Our results regarding the formation and evolution of holes in thin films in small geometries shed light on various nonlinear phenomena associated with wetting and dewetting.

Various techniques of fabricating surface patterns of small scales have been widely studied due to the potential applications of surface patterns in a variety of areas. It is a challenge to fabricate well-ordered surface area efficiently and economically. Evaporation-induced surface patterning is a promising approach to fabricate well-ordered surface patterns over a large area at low cost. In this study, the evaporation-induced surface patterns with controllable geometrical characteristics have been constructed. The dewetting kinetics on deformable substrate is also investigated. Using simple templates to control the geometry and the evaporation behavior of a droplet of volatile solvent, various gradient surface patterns, such as concentric rings, multiple straight stripes formed with a straight copper wire, etc. have been constructed on PMMA films. The wavelength and amplitude are found to decreases with the decrease of the distance to the objects used in templates. There is also a nearly linear relation between the amplitude and wavelength. The effects of several experimental parameters on the geometrical characteristics of the surface structures are studied, i.e. dimensions of the template, film thickness (solution concentration), substrate temperature, etc. The wavelength and amplitude increase with the increase of the film thickness (solution concentration), with the increase of the dimension of the template. However with the increase of the substrate temperature, the wavelength increases, while the amplitude decrease. Hexagonal network in pre-cast PMMA film have been fabricated by a “breath figure” approach at low humidity and low substrate temperature. The dimensions of the hexagonal holes are dependent on the template size and film thickness. The kinetics of the evaporative dewetting of a liquid (toluene) film on a deformable substrate (PMMA film) with the confinement of a circular copper ring is also studied. The liquid film first dewets from the outside towards the copper ring. When a critical volume is reached, an internal contact line appears, which dewets from the center to the copper ring smoothly with a constant velocity, then switches to a “stick-slip” motion. The average velocity of the smooth motion increases with the increase of the copper ring size and film thickness.

Dans cette thèse, nous étudions deux systèmes désordonnés du point de vue du de la transition de dépiégeage (depinning). Dans les deux cas, la dynamique est régie par la compétition entre un paysage aléatoire qui tend à induire des fluctuations et des interactions élastiques qui tendent à les limiter. Dans la première partie, nous développons un modèle mésoscopique simplifié qui vise à rendre compte des propriétés génériques de la plasticité des matériaux amorphes. La déformation plastique des matériaux amorphes présente une phénoménologie qui rappelle les propriétés critiques observées au voisinage d'une transition de dépiégeage: émergence d'un seuil critique (ici la contrainte plastique), dynamique d'avalanches, etc. L'interaction élastique à l'oeuvre dans ce modèle de plasticité dérive directement de la solution élastique d'Eshelby associée à la présence d'une inclusion plastique dans une matrice élastique. Nous montrons que cette interaction anisotrope et à longue portée est caractérisée par la présence de modes mous. ces derniers ont un impact dramatique sur la localisation et les fluctuations de déformation plastique qui augmentent de manière diffusive. Cette phénoménologie n'est pas présente dans le dépiégeage tel qu'il est souvent traité, par exemple avec une approche champ moyen. Nous montrons que les bandes de cisaillement sont des modes mous de l'intéraction d'Eshelby et affectent aussi bien la localisation que les propriétés universelles. Par ailleurs, en testant deux cas extrèmes, nous avons trouvé que les détails du paysage désordonné n'ont pas d'impact particulier sur les propriétés universelles. En application de ce travail, nous montrons que le renforcement des matériaux amorphes par des inclusions dures est relié à la percolation des bandes de cisaillement entre les inclusions. Dans la deuxième partie, nous étudions la morphologie d'une ligne de démouillage en recul sur des surfaces inhomogènes. Contrairement aux modèles de dépiégeage standard, nous développons ici une méthode permettant de décrire le régime de grandes déformations de la ligne de contact et le déchirement de la couche. Nous montrons l'existence d'une concentration seuil des inhomogeneités. Au delà de cette concentration, la ligne s'arrête à une distance finie et autour de la concentration critique, présente des propriétés de type critique. / In the present thesis, two disordered systems are investigated from the depinning perspective. In both of them, the dynamics is governed by the competition between elastic interactions and a disordered landscape. In the first part, we use a simplified mesoscopic model to investigate the generic properties of amorphous plasticity. The yielding of amorphous materials shows universal properties similar to the depinning transition. As such, it is often described by mean field approaches. Here we show that the soft modes present in the interaction kernel (based on the Eshelby solution for a plastic inclusion in an elastic matrix) have a dramatic impact on localization and result in diffusively increasing plastic strain fluctuations. This additional phenomenology is absent in standard depinning and, despite its important consequences, is disregarded in mean field descriptions. We show that shear bands are soft modes of the Eshelby interaction kernel and, besides localization, they affect the universal properties as well. At the same time, we found by testing two extreme cases that the form of the disordered landscape has no considerable impact on the universal properties. As an application, we show that the reinforcement of amorphous materials by hard inclusions is related to the percolation of shear bands in between the inclusions. In the second part of the thesis, we study the morphology of a receding dewetting line on inhomogeneous surfaces. Unlike in standard depinning models, here we developed a method suitable to describe the large deformation regime of the contact line and tearing up of the layer. We show the existence of a threshold concentration of inhomogeneities. Above this concentration the line stops within at finite distance, and around the critical concentration it features critical-like properties.

In an age in which the microchip is ubiquitous, the rewards for novel methods of microfabrification are great, and the vast possibilities of nanotechnology lie just a little ahead. Various methods of microlithography offer differing benefits, and even as older techniques such as optical lithography are being refined beyond what were once considered their upper limits of resolution, new techniques show great promise for going even further once they reach their technological maturity. Recent developments in optical lithography may allow it to break the 100-nm limit even without resorting to x-rays.

A dehydrogen is an ‘under-wrapped’ hydrogen bond in a protein that is purported to be a hot spot for binding due to the favorable replacement of water with hydrocarbon upon binding of another protein. A model at the level of dielectric constants is used to test the validity of the claim that moving a hydrogen bond from high dielectric (i.e. a dehydron) to low dielectric (i.e. after binding of another protein) is actually a thermodynamically favorable process. In simulation, several proteins have been shown to undergo a dewetting transition when fixed components are separated a small distance. A new atomic-level hydrophobicity scale is combined with topographical information to characterize protein interfaces. The relationship between hydrophobicity and topography for protein surfaces known to be involved in binding is examined. This framework is then applied to identify surface characteristics likely to have an affect on the occurrence of a dewetting transition. Cadmium selenide (CdSe) nanoparticles form nanospheres or nanorods when grown in solutions of varying concentrations of the surfactants hexylphosphonic acid (HPA) and trioctylphosphine oxide (TOPO). Relative binding free energies are calculated for HPA and TOPO to the solvent-accessible faces of CdSe crystals. Binding free energies calculated with a Molecular Mechanics-Generalized Born model are used to identify a set of low free energy structures for which the solvation free energy is refined with the solution to the Poisson equation. These relative binding free energies provide information about the relative growth rates of these crystal faces in the presence of surfactants. Relative growth rates are then used to help understand why nanoparticles form certain shapes in the presence of specific surfactants. / text

A novel strategy to investigate interfaces relevant to chromatographic separations is presented. The strategy in this dissertation relies on three key ideas: 1) design and fabrication of appropriate model of chromatographic interface, 2) use of forced dewetting to separate interfacial constituent of mobile phase from its bulk component yet preserves the interface, and 3) use of IR spectroscopy and ellipsometry to investigate the structure and thickness of isolated interface.Stratified structures of ultrathin (< 10 nm thick) silica films on gold using gold oxide as adhesive layer and wetting control agent are used as model solid phase. Such design provides chemical environment of bulk silica surface, does not introduce significant spectral background, is suitable for reflection-based spectroscopies, and allow for easy modification to mimic wide range of silica - solvent interfaces. Bare silica-water models capillary electrophoresis interfaces; water-methanol mixture at octadecylsilane-modified silica represents reversed phase liquid chromatography interfaces.Forced dewetting is used to decouple interfacial constituent of mobile phase from its bulk component; yet, the integrity of interface is preserved. This approach, combined with the use of IR spectroscopy and ellipsometry, allowed for ambient atmosphere characterization of these interfacial layers in terms of their structure, composition, and thickness for water at bare silica. Hydrogen bonding was probed in case of complex water-methanol binary mixture at octadecylsilane-modified silica surface.The analysis of residual water layers formed by forced dewetting at bare silica as a function of bulk solution pH shows that the structure of the interfacial layer is highly ordered compared to bulk, and is also pH dependent. Further, thicknesses of interfacial layers were found to be pH dependent and vary from ~6 (pH 1) to ~9 nm (pH 9). Gouy-Chapman-Stern double layer was found to be inadequate to satisfactorily describe observed trends. In addition, surface enhanced infrared absorbance phenomenon was also observed that aided increased quality of resulting IR spectra.The analysis of residual water-methanol layers formed by forced dewetting at octadecylsilane-modified silica surface as a function of gas phase atmosphere shows that the structure of the interfacial layer is highly dependent on the composition of gas phase. The observed changes indicate that condensation of methanol from gas phase into residual layer and/or evaporation of water from residual layer into gas phase may occur in used experimental setup used in this dissertation. For that reason, more precise quantification of relative amounts of water and methanol in residual layers was precluded. Yet, regardless of investigational conditions, two different hydrogen bonding environments for methanol were distinctively observed.

The process of forcibly dewetting a solid substrate from a bulk liquid so as to leave a thin residual layer on the surface is referred to as forced dewetting. This novel experimental approach helps to investigate interfacial species by minimizing the interference of the bulk liquid when coupled with spectroscopy. In this work, the scope of liquids investigating using this approach has been expanded from simple fluids to one type of complex fluid, a nematic liquid crystal, 4-n-pentyl-4'-cyanobiphenyl (5CB).In order to better understand the interfacial behavior of the simple fluids, water, chloroform, and n-pentane vapors were adsorbed onto omega-terminated SAM-modifed Ag (11-mercaptoundecanoic acid, 11-mercaptoundenanol, and undecanethiol) surfaces under vapor-saturated conditions. The kinetics of solvent adsorption on each of these surfaces were investigated and the thicknesses of the adsorbed layer were compared to predictions from Lifshitz theory of long-range van der Waals interactions. Although the predicted thicknesses do not match the experimental values for adsorbed films, the predicted thicknesses do match those observed experimentally using forced dewetting. The correlation between these predicted and observed thicknesses implies that residual film formation under the conditions of forced dewetting used in this laboratory is dictated by interfacial forces alone.The surface adsorption behavior of 5CB was investigated using surface-enhanced Raman spectroscopy with the aid of localized surface plasmon resonances-surface plasmon polaritron coupling. The results clearly indicate that 5CB is adsorbed to smooth Ag surface in a facial orientation with pi-d orbital interaction suggested.Finally, forced dewetting studies of bare, -NH2-temintaed SAM, and -CH3-temintaed SAM modified-SiO2 substrates from 5CB were undertaken. Residual layer thicknesses were monitored as a function of substrate velocity. The transition from the regime in which interfacial forces dictate residual layer thickness to the regime in which fluid dynamic forces dictate thickness was observed for the first time and was evaluated in terms of the average 5CB director orientation. Unlike simple fluids, 5CB has strong interfacial interactions from surface anchoring depending on the chemical nature of the substrate, which makes the residual layer thicknesses at least 100 times larger than observed in simple fluids.