京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19898号 / 工博第4214号 / 新制||工||1651(附属図書館) / 32975 / 京都大学大学院工学研究科材料化学専攻 / (主査)教授 木村 俊作, 教授 瀧川 敏算, 教授 今堀 博 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

Yes / The application of photoelectrochemical methods presents the researcher with a powerful set of versatile tools by which photoactive materials, such as semiconductor quantum dots, at conductive interfaces may be interrogated. While the range of photoelectrochemical techniques available is quite large, it is surprising that very few have found their way into common usage within the nanoparticle community. Here a number of photoelectrochemical techniques and the principles upon which they are based are introduced. A short discussion on the criticality of ensuring the nanoparticles are reliably anchored to the substrate is followed by an introduction to the basic set of equipment required in order to enable the investigator to undertake such experiments. Subsequently the four techniques of transient photocurrent response to square wave illumination, photocurrent spectroscopy, intensity modulated photocurrent spectroscopy (IMPS) and intensity modulated photovoltage spectroscopy (IMVS) are introduced. Finally, the information that can be acquired using such techniques is provided with emphasis being placed on a number of case studies exemplifying the application of photoelectrochemical techniques to nanoparticles at interfaces, in particular optically transparent electrodes.

No description available.

In recent years a great deal of interest has been focused on the synthesis of transitional metal (e.g. Ag, Cu, Fe, Au) nanosystems at the surface to sub-surface regions of Si and SiO2 matrices for fundamental understanding of their structures as well as for development of technological applications with enhanced electronic and optical properties. The applications of the metal nanoparticle or nanocluster (NC) systems range from plasmonics, photovoltaic devices, medical, and biosensors. In all of these applications; the size, shape and distribution of the metallic NCs in the silicon matrix play a key role. Low energy ion implantation followed by thermal annealing (in vacuum or gas environment) is one of the most suitable methods for synthesis of NCs at near surfaces to buried layers below the surfaces of the substrates. This technique can provide control over depth and concentration of the implanted ions in the host matrix. The implanted low energy metal ions initially amorphizes the Si substrates while being distributed at a shallow depth near the substrate surface. When subject to thermal annealing, the implanted ions agglomerate to form clusters of different sizes at different depths depending upon the fluence. However, for the heavier ions implanted with high fluences (~1×1016 - 1×1017 atoms/cm2), there lies challenges for accurately predicting the distribution of the implanted ions due to sputtering of the surface as well as redistribution of the implants within the host matrix. In this dissertation, we report the investigation of the saturation of the concentration of the implanted ion species in the depth profiles with low energies (< 80 keV) metal ions (Ag and Au) in Si (100), while studying the dynamic changes during the ion implantation. Multiple low energies (30-80 keV) Ag ions with different fluences were sequentially implanted into commercially available Si wafers in order to facilitate the formation of Ag NCs with a wide ion distributions range. The light absorption profile according to different sizes of NCs at the near-surface layers in Si were investigated. We have investigated the formation of Ag NCs in the Si matrix as a function of implantation and thermal annealing parameters. The absorbance of light is increased in Ag implanted Si with a significant increase in the current collection in I-V (current-voltage) photo switching measurements. The experimental photovoltaic cells fabricated with the Ag implanted Si samples were optically characterized under AM (air mass) 1.5 solar radiation conditions (~1.0 kW/m2). An enhancement in the charge collection were measured in the annealed samples, where prominent Ag NCs were formed in the Si matrix compared to the as-implanted samples with the amorphous layer. The characterization techniques such as Rutherford Backscattering Spectroscopy, XPS-depth profiling, transmission electron microscopy, optical absorption, and I-V (current-voltage) photo switching measurements were employed to understand the underlying science in the observed properties. The results of these investigations are discussed in this research.

La thèse commence le 1er octobre 2012. IL s'agit pour cette première année de thèse de synthétiser différents complexes de coordination a base du Ruthénium, Fer, Manganèse et de Cobalt à ligands polypyridinique. Ces complexes seront ensuite assemblés par lien covalent. Nous proposons d'utiliser entre autre les techniques d'electrochimie pour induire ces couplages. On cherchera aussi a immobiliser les assemblages sur surface. La principale difficulté attendue dans cette etape du travail concerne la fonctionalisation dissymétrique des ligands pour l'obtention de triade. / This thesis deals with the synthesis and characterization of inorganic triads for photoinduced charge separation. A range of photosensitizers will be studied, and the effect of the donor and acceptor will be assesed as well. These systems will be studied in solution and immobalized on surfaces. Cette thèse traite de la synthèse et la caractérisation des triades inorganiques pour la séparation de charge photoinduite. Une gamme de photosensibilisateurs seront étudiées, et l'effet du donneur et accepteur sera ainsi étudié. Ces systèmes seront étudiés en solution et immobalizes sur les surfaces.

This thesis deals with the study of the lifetime of charge carriers in perovskite single crystals. The principle of perovskite solar cells is formulated, their main structures are characterized and the history of the development of perovskite solar cells is summarized, especially in terms of efficiency. The properties of perovskite single crystals with perovskite solar cells are compared. For measurement purposes, transient methods, impedance spectroscopy, load characteristics and the dependence of sensitivity and photocurrent on the wavelength of incident radiation are described. The practical part deals with the method of measuring and evaluating the lifetime of charge carriers in the investigated perovskite single crystals.

Dans le contexte de la recherche sur l’amélioration des performances et la réduction des coûts des cellules solaires à base de silicium, nous nous sommes intéréssés dans cette thèse aux hétérojonctions entre le silicium amorphe hydrogéné (a-Si:H) et le silicium cristallin (c-Si). Nous avons étudié d’une part l’application de la technique de mesure du PhotoCourant Modulé (MPC) comme outil de caractérisation de l’interface a-Si:H/c-Si et que nous avons couplé à la technique de mesure de PhotoLuminescence Modulée (MPL) déjà largement utilisée pour étudier la qualité de passivation de l’interface. Nous avons alors caractérisé par ces deux techniques une série d'échantillons composées de (p)a-Si:H/(i)a-Si:H/(n)c-Si d'épaisseur de (i)a-Si:H allant de 2 à 50 nm. Une partie importante de cette étude a été réalisée par simulations numériques en 2D afin d’interpréter nos résultats expérimentaux. Une cohérence dans l'estimation de la densité d'état de défauts à l'interface a-Si:H/c-Si a été obtenue par les deux techniques. Nous avons conçu d’autre part un outil de couplage des simulations électriques et optiques pour le design de cellules à base de nanofils à hétérojonction. Grâce à cet outil nous avons réalisé une étude plus réaliste et plus complète qu'auparavant où ces deux simulations étaient effectuées de manière séparée. Nous montrons notamment comment les conditions sur les contacts électriques des nanofils affectent les performances de la cellule solaire. / In the context of the research on improving performances and reducing costs of silicon-based solar cells, we focused on heterojunctions between hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si). On the one hand, we studied the application of the Modulated PhotoCurrent technique (MPC) as a tool for characterizing the a-Si:H/c-Si interface and which we coupled to the Modulated PhotoLuminescence technique (MPL) widely used to study the quality of interface passivation. We characterized by these two techiques a serie of samples composed of (p)a-Si:H/(i)a-Si:H/(n)c-Si with a thickness of (i)a-Si:H going from 2 to 50 nm. An important part of this study was made by 2D numerical simulations in order to interpret our experimental results. We showed that both techniques give the same estimation of the density of interface defects between (i)a-Si:H and (n)c-Si. On the other hand, we developped a tool for coupling electrical and optical simulations for the design of nanowire-based solar cells with a radial heterojunction. Formerly, these simulations were most of the time performed separately and therefore were not allowing for a complete study of these kind of structures. We then made a study showing how the conditions of electrical contacts of nanowires affect the performances of these solar cells.

In this work, we have explored 2D semiconducting transition metal dichalcogenides (TMDs), black phosphorus (BP), and graphene for various applications using liquid and mechanical exfoliation routes. The topical areas of interest that motivate our work include considering factors such as device integration, stability, doping, and the effect of gasses to modulate the electronic transport characteristics of the underlying 2D materials. In the first area, we have integrated solution-processed transparent conducting oxides (TCOs), specifically indium-doped tin oxide (ITO) with BP, which is a commonly used TCO for solar cell devices. Here we have found surface treatment of glass substrates with a plasma before spin-coating the solution-processed ITO, to be effective in improving coverage and uniformity of the ITO film by promoting wettability and film adhesion. The maximum transmittance obtained was measured to be ~75% in the visible region, while electrical measurements made on BP/ITO heterostructures showed improved transport characteristics compared to the bare ITO film. Within the integration realm, inkjet-printing of BP and MoS2 p-n hetero-junctions on standard ITO glass substrates in a vertical architecture was also demonstrated. To address the issue of stability which some 2D materials such as BP face, we experimented with ionic liquids (ILs) to passivation the hydrophilic surface of BP to minimize its oxidative degradation. The enhanced stability of BP was inferred through Raman spectroscopy and scanning probe microscopy techniques, where no observable changes in the A1g and A2g Raman vibrational modes were observed for the BP films passivated with ILs over time under ambient conditions. On the other hand, a blue-shift in these Raman modes was evident for unpassivated samples. Atomic force microscopy measurements on the unpassivated samples clearly revealed the difference in surface characteristics through localized regions of degradation that intensified with time which was absent in IL passivated BP samples. The electronic device measurements for IL coated BP devices showed a more stabilized Ids−Vds characteristic in the 5.4 K to 335 K temperature range. Prototypical demonstrations of stabilized ILs/BP devices at ambient printed on flexible polyimide substrates were also successfully made. At the same time, doping is one of the essential steps required for the modulation of carrier density and electronic transport in electronic and optoelectronic devices, which is the third topical area we have addressed in this work with semiconducting TMDs. Of the conventional approaches used to dope 3D semiconductors, ion-implantation is commonly adopted but given the ultra-thin nature of 2D materials, this approach is not feasible as it causes severe damage to the delicate crystalline lattice of ultra-thin 2D membranes. Instead, we have used plasma-based doping routes with UV-ozone treatement and solution processing using 1,2 dichloroethane, to characterize the temperature-dependent two-terminal and three-terminal electronic and optoelectronic transport of mechanically exfoliated 2D MoS2 and WSe2. A significant difference was seen in the optoelectronic properties between the two dopants, owing to differences in their respective doping mechanisms and the intrinsic structural attributes of the exfoliated flakes. A significant reduction in barrier height was evident after doping using both techniques in MoS2, while an increase in barrier height after soaking in 1,2 dichloroethane was seen in WSe2. Lastly, in the fourth topical area for sensing devices, we have studied the effect of gas-flow in inkjet-printed and spin-coated graphene and MoS2 to modulate the electronic transport for the 2D materials since their increased surface area is an ideal platform to observe interactions with external stimuli, in this case, in-coming gas species. Here, the chamber pressure and change in current with flow of gas was measured in the steady-state, as well as time-dependent dynamic transport toward nitrogen and carbon dioxide. We observed significant differences in the electrical response of mono-elemental graphene and binary MoS2, owing to differences in microstructure and joule heating response to the ambient gas. In conclusion, the findings obtained from our work will provide an important framework to help guide strategies in further improving integration schemes, stability, doping and sensing behavior driven by the unique structural attributes inherent to 2D materials for high-performance devices in the future.

Methods for testing commercial off-the-shelf (COTS) digital devices at varying levels of complexity is presented and discussed as well as the results for testing a COTS SRAM, FRAM, and SoC using these methodologies in a pulsed dose rate environment at Little Mountain Test Facility (LMTF) and neutron testing at Los Alamos Neutron Science Center (LANSCE). Investigations at LMTF revealed a dependence in all three devices on the integrated dose of a single pulse of radiation, implying that the duration of radiation plays a significant role in the response. The test infrastructure necessary to dynamically access an FRAM at LMTF and time the access with the pulse of radiation allowed for the discovery of a new FRAM failure mode where an entire word of the FRAM becomes corrupted as well as selecting between two different failure modes based on the timing of the pulse. A novel component-based testing methodology for testing complicated SoCs is presented and used to report on the cross-sections of several components on the Xilinx MPSoC, including its DMA which has not previously been reported.

Esta tese teve por objetivo, desde seu in&iacute;cio, investigar as propriedades el&eacute;tricas de um dispositivo ITO/PEDOT:PSS/P3HT:PCBM/Ca/Al, o qual &eacute; uma estrutura bem conhecida de c&eacute;lula solar org&acirc;nica do tipo de heterojun&ccedil;&atilde;o de volume (bulk-heterojunction &ndash; BHJ), e com isso dar uma contribui&ccedil;&atilde;o &agrave; melhora de seu desempenho. Por&eacute;m, o primeiro passo foi introduzir no Grupo de Pol&iacute;meros Bernhard Gross, um m&eacute;todo eficaz de produzir c&eacute;lulas solares do tipo BHJ com boa efici&ecirc;ncia e reprodutibilidade. Esse primeiro desafio foi alcan&ccedil;ado com sucesso. A efici&ecirc;ncia (&eta;) de um dispositivo fotovoltaico de multicamadas depende de muitos fatores. Dentre eles, uma boa superposi&ccedil;&atilde;o entre o espectro solar e a curva de absor&ccedil;&atilde;o da camada absorvedora, uma excelente convers&atilde;o da energia luminosa em portadores de carga, um eficiente processo de condu&ccedil;&atilde;o e uma perda m&iacute;nima por recombina&ccedil;&atilde;o e armadilhamento de portadores. Al&eacute;m disso, a compatibilidade eletr&ocirc;nica entre as interfaces tem um papel fundamental na defini&ccedil;&atilde;o na tens&atilde;o de circuito aberto (VOC), no valor da corrente de curto-circuito (JSC), e no fator de preenchimento (FF). Baseado nesses efeitos, realizamos uma s&eacute;rie de medidas experimentais, que auxiliado por um modelo te&oacute;rico proporcionaram um estudo detalhado da evolu&ccedil;&atilde;o em fun&ccedil;&atilde;o da temperatura da mobilidade dos portadores (&mu;) e de seu tempo de vida (&tau;). Os principais experimentos nessa tese foram realizados em diferentes temperaturas (entre 100 e 340 K). Foram eles: medidas de fotocorrente - Jph(V), a t&eacute;cnica de foto-CELIV, e medidas de transiente de fotovoltagem (TPV). Em paralelo, desenvolvemos o modelo te&oacute;rico para a descri&ccedil;&atilde;o anal&iacute;tica de Jph(V)&nbsp;que assumiu contatos n&atilde;o-injetores e que o livre caminho m&eacute;dio (w = &mu;&tau;F) de el&eacute;trons e buracos eram iguais (F &eacute; o campo el&eacute;trico). Nos ajustes te&oacute;rico/experimental usamos a probabilidade de dissocia&ccedil;&atilde;o dos estados de transfer&ecirc;ncia de carga (P) e o produto &mu;&tau;&nbsp;como par&acirc;metros de ajuste. A condi&ccedil;&atilde;o na qual o livre caminho m&eacute;dio &eacute; maior que a espessura da amostra (w &gt;&gt; L) reproduz a corrente de satura&ccedil;&atilde;o reversa, Jsat = qGPLG &eacute; a taxa de gera&ccedil;&atilde;o dos &eacute;xcitons. Para w &lt;&lt; L, a fotocorrente varia linearmente com o livre caminho m&eacute;dio, ou seja, J(F) = qGP&mu;&tau;F. A compara&ccedil;&atilde;o entre os resultados experimentais e os te&oacute;ricos permitiram, al&eacute;m da obten&ccedil;&atilde;o da evolu&ccedil;&atilde;o das grandezas &mu; e &tau;&nbsp;com a temperatura, estabelecer uma rela&ccedil;&atilde;o efetiva entre os par&acirc;metros da c&eacute;lula (&eta;, JSC, e FF) e as propriedades el&eacute;tricas da camada ativa P3HT:PCBM. As medidas termo-mec&acirc;nicas (DMA) forneceram informa&ccedil;&otilde;es adicionais sobre mudan&ccedil;as estruturais da camada ativa, as quais foram correlacionadas com varia&ccedil;&otilde;es dos par&acirc;metros da c&eacute;lula e com fatores de perda. Finalmente, medidas de tempo-de-voo (TOF) e de CELIV foram realizadas para estudos mais detalhados sobre mecanismos de transporte ao longo da camada ativa, a efeitos de inje&ccedil;&atilde;o pelos eletrodos, e para o entendimento de efeitos de degrada&ccedil;&atilde;o pela a&ccedil;&atilde;o do oxig&ecirc;nio. / This thesis aims to investigate electrical characteristics of an ITO/PEDOT:PSS/P3HT:PCBM/Ca/Al device, which is a well-known structure of a bulk-heterojunction (BHJ) organic solar cell, and to contribute to improve its performance. However, the first step was to introduce in the Group of Polymer Bernhard Gross an effective method for producing BHJ solar cells, manufacturing thus devices exhibiting excellent performance and reproducibility. This thesis aims to investigate electrical characteristics of an ITO/PEDOT:PSS/P3HT:PCBM/Ca/Al device, which is a well-known structure of a bulk-heterojunction (BHJ) organic solar cell, and to contribute to improve its performance. However, the first step was to introduce in the Group of Polymer Bernhard Gross an effective method for producing BHJ solar cells, manufacturing thus devices exhibiting excellent performance and reproducibility. This goal was successfully achieved. The good efficiency (&eta;) of a multilayer photovoltaic cell depends on many factors, including good overlap between the solar spectrum and the light absorbing layer, an excellent conversion of the absorbed light energy in pairs of electronic carriers, efficient charge transport and the minimum losses by recombination or by the action of deep traps for the carriers. Furthermore, the compatibility between electronic interfaces plays a crucial role in defining the open-circuit voltage (VOC) and the value of short-circuit current (JSC), and on the fill factor (FF). Anchored on these effects, we carried out a series of experiments, aided by a theoretical modeling, which provided a detailed study of the temperature evolution of fundamental electric quantities such as carrier mobility (&mu;) and its lifetime (&tau;). These studies were performed with the help of different experiments: photocurrent in function of the applied voltage&nbsp;&nbsp;Jph(V), Photo-CELIV technique, and Transient Photovoltage (TPV) measurements, which were carried out at several temperatures in the 100 to 340 K range. In parallel, we developed an analytical model for Jph(V)&nbsp;that assumed non-injecting contacts and equal mean-free-paths for electrons and holes. The theoretical/experimental entities used as fitting parameters were the charge-transfer-state dissociation probability (P) and the &mu;&tau;&nbsp;product. The condition in which the mean-free-path (w = &mu;&tau;F) is higher the sample thickness (L), the model reproduces the experimental reverse saturation current, Jsat = qGPL, which is coincident with the experimental value. F is the internal electric field and G is the generation rate of excitons by the absorbed light. When w &lt;&lt; L, J(F) = qGP&mu;&tau;F, which is also coincident with experimental behavior. The confrontation between the experimental results and the theoretical model provided, in addition to the study of the evolution of &mu;&nbsp;and &tau;&nbsp;with temperature, to establish a more effective relationship between the parameters (&eta;, JSC, e FF) of the cell and the electrical properties of the P3HT:PCBM active layer. Thermomechanical analysis (DMA) provided additional information of structural changes of active layer, which can be correlated with change in the loss factor and in the cell parameters. Finally, Time-of-Flight (TOF) and CELIV techniques were used in the more accurate study of charge transport along the active layers, effects of injection by the electrodes, and the degradation effect caused by oxygen.