Since the discovery of graphene, a new era of physics called "Two Dimensional (2D)Materials" has emerged. Group IV and Group III Selenides such as SnSe and InSe arepromising members of the 2D family. Structure of Group IV selenides is unique and highlysensitive to pressure and temperature. To further tweaking their properties by structuralchanges, thorough understanding of how the structure relates to the electronic bands is veryimportant. Based on the results from DFT calculations, I carefully analyzed electronic bandstructures of layered SnSe with various interlayer stacking. The first part of this dissertationdiscussed the possible stacking-dependent indirect-direct transition of bilayer SnSe.By further analysis, these results reveal that the directionality of interlayer interactionsdetermine the critical features of their electronic band structures. Further, it demonstratedthat such changes can be achieved by substitutional chemical doping. Using a multi-scalemodeling approach by combining the result of DFT and Boltzmann Transport Theory, Idiscussed the electron transport properties of co-doped SnSe, a class of thermodynamicallyand dynamically stable structures. The second part discussed on charge transfer across InSe/Gas interface, which showsbi-polar transport properties. This finding is in a good agreement with the recent experimentalobservations. Fundamental understanding of charge transfer in few-layer InSe /gasinterfaces at the atomic level is expected to pave the path for designing gas sensing devices.

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A series of oxide materials were modified with different nanoparticles (NPs). Novel cobalt@H4Nb6O17 nanopeapod structures were fabricated and magnetic NPs modified oxide nanosheets and nanoscrolls were prepared. Both aqueous method and two-phase method were applied to prepare gold NPs onto oxide nanosheets, nanoscrolls and other nanocrystals. The combination of H4Nb6O17 nanoscrolls and cobalt NPs generate a novel method to fabricate nanopeapod structures. Cobalt NPs were synthesized in the presence of exfoliated H4Nb6O17 nanosheets and the resulting magnetic chain structures, formed due to the dipole-dipole interaction, were captured within scrolled lamella. The yield of peapod structures can be improved by using proper reagents and reaction temperatures. As similar method with iron oxide NPs also produced peapod-like structures in a low yield. Exfoliated Dion-Jacobson phase layered perovskite HLaNb2O7 (HLN), its organic derivate propoxyl-HLaNb2O7 (pHLN), Ruddlesden-Popper phase perovskite H2SrTa2O7 (HSTO) and Aurivillius phase perovskite H2W2O7 (HWO) were synthesized and functionalized with gold NPs by in-situ methods. Gold NPs were prepared by both an aqueous method and two-phase method. The size of NPs can be adjusted by different reaction times. Overall, the latter method shows a narrower size distribution and better dispersion. In addition, most gold NPs prepared by the two-phase method were attached on the surface of nanosheets and almost no free gold NPs were observed in solution. This approach should be applicable to most layered perovskites. The aqueous and two-phase methods were also applied on the preparation of gold NPs onto H4Nb6O17 nanosheets and nanoscrolls. H4Nb6O17 nanosheets were prepared by two approaches and showed similar gold NPs attachment. LiNbO3 nanocrystals can be also modified with gold NPs by the two-phase method though free gold NPs were observed. Further studies involved the functionalization of layered perovskites and related compounds with magnetic NPs. Iron oxide and cobalt NPs were synthesized in the presence of layered perovskite and modified perovskite nanosheets were obtained.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第23911号 / 工博第4998号 / 新制||工||1780(附属図書館) / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 阿部 竜, 教授 陰山 洋, 教授 藤田 晃司 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Since 2016 there are world-wide more mobile phone contracts than people on the planet, and in all these devices critical raw materials (CRMs) are incorporated.[1] For instance, commonly used silicon-based transistors are limited in their chemical modularity. Inorganic materials for solar cells and photocatalysis suffer from critical raw elements content, low apparent quantum efficiencies and photodegradation. Hence, considerable research interest in recent years is focused on development of new high-performance devices for optical and electronic applications that avoid CRMs entirely. To address all these problems materials chemists are exploring for new pathways towards making more sustainable and reliable materials. In that respect, porous organic π- conjugated polymers (POPs) are among the most promising candidates and have gained tremendous attention in materials research over the last decade, especially in the fields of photocatalysis, opto- and electrochemical sensorics, and microelectronics. Synthetic diversity, chemical and physical stability, as well as comparatively low production costs and scalability enable POPs to overcome the drawbacks of inorganic materials. Moreover, the absence of rare earth elements in the purely organic structure of POPs makes these materials more environmentally...

The complex phenomenon of indentation deformation is studied using finite element analysis for both homogeneous and layered materials. For the homogeneous materials, the elastic-plastic deformation at large indentation depth is studied. The variation of the load-displacement curves as well as the variation of the energy ratio with the applied indentation depth for different strain hardening indices is presented. The power law relation between the indentation load and depth for shallow indentation becomes invalid for deep indentation. The ratio of plastic energy to total mechanical work is a linear function of the ratio of residual indentation depth and maximum indentation depth. For the layered materials (film-substrate systems), the elastic deformation under an indenter is studied. Various material parameters are investigated, including film thickness and modulus. A generalized power law equation is presented for characterizing the indentation load-displacement responses of film-substrate structures.

The goal of the dissertation was to optimize synthetic parameters to tune the properties of two layered materials, MoS2 and MnO2 for applications such as antibacterial, energy storage and water remediation. Two aspects of the materials were investigated. Firstly, the synthetic parameters were tuned to prepare material with different morphologies and then the effect of morphology and structure on interaction with bacterial cells was studied. In the second part, the research was focused on tuning the synthetic parameters to improve the intrinsic conductivity of the material for electrocatalytic applications. This dissertation work primarily focuses on understanding the catalytic and antibacterial activity of layered MnO2 and MoS2. One research effort was focused on the antibacterial mode of action of layered nanosheets of MnO2 and MoS2 toward Gram-positive and Gram-negative bacteria. Bacillus subtilis and Escherichia coli bacteria were chosen as model organisms, which were treated individually with randomly oriented and vertically aligned nanosheets. Viability measurements of bacteria, by flow cytometry and fluorescence imaging, showed that vertically aligned MnO2 and MoS2 nanosheets revealed the highest antimicrobial activity and that Gram-positive bacteria showed a higher loss in membrane integrity, compared to Gram-negative bacteria. Moreover, scanning electron microscopy images suggested that the nanosheets compromised the cell wall upon interaction, which led to significant bacterial morphological changes. We propose that the peptidoglycan mesh in the bacterial wall is likely the primary target of the 2D layered nanomaterials. Another focus of the dissertation research investigated the effect of structural and geometrical changes of layered materials on the properties which affect the intrinsic conductivity of material. In the first study, the electrocatalytic activity of layer-by-layer (LbL) deposited 1T'-MoS2 (metallic phase) on a fluorine-doped tin oxide (FTO) substrate was investigated for the hydrogen evolution reaction (HER) as a function of layer number. Conversion of the deposited 1T'-MoS2 to the semiconducting 2H-MoS2 phase via exposure to 532 nm wavelength light, confirmed by Raman spectroscopy and scanning tunneling spectroscopy (STS), allowed a direct comparison of the HER activity of the two phases at a constant mass loading and surface area on the same substrate. The morphology, thickness and roughness of the deposited MoS2 layers as a function of the number of deposition cycles were investigated using atomic force microscopy (AFM) and scanning electron microscopy (SEM). The results showed that the average roughness of the surface increased with the number of deposition cycles, indicating that the thickness of the deposited layered material became heterogeneous with increasing cycle number. For a given number of deposition cycles (i.e., similar mass loading), 1T'-MoS2 exhibited a lower overpotential for the HER than the 2H-MoS2 phase. For example, at a sample thickness of 19.7 ± 2.8 nm (20 LbL cycle) the overpotentials for the HER for 1T'-MoS2 and 2H-MoS2 were 0.54 and 0.61 V, respectively (at a current density of -2 mA/cm2). Overall, the overpotential for HER associated with both MoS2 phases decreased as the mass loading increased. Our study revealed the heterogenous formation of few layer 1T'-MoS2 on the surface, providing a novel approach to improve HER activity towards water splitting applications. A further research effort studied birnessite, focusing on the activity of exfoliated birnessite and the role of birnessite defects for water oxidation. The catalytic activity of layered MnO2 has been studied widely. Birnessite has the lowest oxygen evolution reaction (OER) activity in alkaline media compared to other manganese oxide phases. A motivation for the study was to investigate the OER activity of exfoliated-restacked birnessite sheets which can lead to a better understanding of the birnessite catalytic performance. Synthesized birnessite was exfoliated into monolayer sheets via a cation exchange method. Characterization of the birnessite monolayer sheets using AFM and scanning tunneling microscopy (STM) revealed the presence of the holes and point defects. The phase and conductivity of monolayer sheets were measured by STS. Electrochemical characterizations of exfoliated birnessite have shown that nanosheets of birnessite expose a great number of active sites and exhibit facile electrode kinetics as a result of the defective sheets. In particular, the overpotential of exfoliated birnessite synthesized at 400°C was 450 mV compared to 550 mV for the exfoliated birnessite synthesized at 1000°C. The results indicate that the defective exfoliated sheets have higher conductivity and higher OER activity compared to defect free exfoliated sheets. Additional research of birnessite focused on its activity for the arsenite (i.e., As(III)) oxidation reaction. Birnessite polytypes were synthesized by decomposition of KMnO4 at different temperatures, and three polytypes including two-layer orthogonal (2O), two-layer hexagonal (2H) and three-layer rhombohedral (3R) were identified in the samples. The synthetic temperature controlled the phase formation and heterogeneity of the phases. Birnessite synthesized at 600°C contained 2H/3R phases which showed the highest activity with first order rate constant of the 0.741 h-1 which is 3.6 and 24 times higher than Birnessite synthesized at 800 and 1000°C, respectively. The structural change of the polytype birnessite after As(III) oxidation was studied by pair distribution function experiment. Results indicated that Mn4+ in the birnessite was reduced to Mn3+ and that this reduced species migrated from the in-layer position to the interlayer region. Furthermore, we report the results of in-situ AFM of birnessite sheets exposed to arsenite which provides a detailed understanding of the arsenite oxidation reaction at the birnessite surface. The reductive dissolution of birnessite was shown to be more active on the edges compared to the basal plane of birnessite. Our findings have important implications for material design aimed at removal of arsenite in purification processes. / Chemistry

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Dans le cadre de certaines applications militaires ou méthodologiques, on peut chercher à rendre un objet « invisible » vis-à-vis des ondes acoustiques. Différentes méthodes passives ont été proposées ces dernières années pour éviter ou atténuer la diffraction d'ondes acoustiques sur des obstacles rigides. Ces techniques reposent sur des phénomènes purement acoustiques, avec par exemple la présence de multiples résonateurs ou d'objets diffractants. L'étude présentée ici s'intéresse pour sa part aux effets que l'on pourrait obtenir au moyen d'un revêtement multicouche élastique fixé à un cylindre que l'on souhaite rendre indétectable. Le comportement vibro-acoustique d'un tel revêtement est d'abord modélisé. Par optimisation, on détermine les caractéristiques mécaniques et dimensionnelles des couches permettant une atténuation omnidirectionnelle de la diffraction. Des configurations réalistes de revêtements composés d'une couche orthotrope et d'une couche isotrope sont dégagées dans le cas d'un milieu extérieur constitué d'air. On montre que de tels dispositifs permettent d'atténuer la diffraction à une fréquence donnée ou sur une bande de fréquence. Le problème de la caractérisation expérimentale de ces revêtements est également abordé. Dans un second temps, le cas d'un milieu extérieur constitué d'eau est étudié. On met alors en évidence une réduction de la diffraction avec des revêtements composés de deux couches isotropes. L'influence des différents paramètres de la couche intérieure est analysée. Enfin, des exemples montrent que la bande de fréquence sur laquelle a lieu l'atténuation de la diffraction peut être élargie en augmentant le nombre de couches. / Making an object invisible to acoustic waves could prove useful for military applications or measurements in confined space. Different passive methods have been proposed in recent years to avoid acoustic scattering from rigid obstacles.These techniques are exclusively based on acoustic phenomena, and use for instance multiple resonators or scatterers. This thesis deals with a different method and studies the effects in terms of scattering reduction of an elastic multi-layered coating fixed to the object to conceal. Vibrations of the coating subject to acoustic waves are first modelled to compute the scattered pressure in the external fluid. Mechanical and dimensional properties of the layers leading to omnidirectional scattering reduction are optimised. Considering an external fluid consisting of air, realistic configurations of coatings emerge, composed of a thick internal orthotopic layer and a thin external isotropic layer. These coatings are shown to enable scattering reduction at a precise frequency or on a larger frequency band. The problem of experimental characterisation is also addressed.The study then focuses on a cylinder immersed in water. Bi-layer isotropic coatings can be used in such configuration. A parametric study is led on the characteristics of the internal layer. Finally, significant scattering reduction is achieved for alarger frequency range by increasing the number of layers. Examples of four-layer isotropic coatings are presented to highlight this result.

The diploma thesis deals with electrode materials for lithium-ions accumulators, concretely layered materials prepared via new methods. The main objective of this work is dealing with new procedures prepare electrodes of newly developed layered electrode materials and subsequently their measure. Another challenge was a theoretical analysis of newly developed layered electrode materials for positive and negative electrodes and their preparation of new procedures. In this work the detailed procedures for the preparation of individual electrodes, electrolytes and other issues associated with these preparations. There were describing batteries of general, primary and secondary lithium cells, fuel cells, Lithium-ion batteries, layered materials forming the electrodes and of course the history these cells. Practical work is focused on separate measurements layered electrode materials prepared by new processes and assessment of results for individual layered materials. In the practical part has been made that the newly prepared layered electrode materials offer higher capacity and voltage.