京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第20406号 / 工博第4343号 / 新制||工||1673(附属図書館) / 京都大学大学院工学研究科高分子化学専攻 / (主査)教授 大北 英生, 教授 辻井 敬亘, 教授 竹中 幹人 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

The foundation of vacuum nanoelectronics was laid as early as in 1961 when Kenneth Shoulders proposed the development of vertical field-emission micro-triodes. After years of conspicuous stagnancy in the field much interest has reemerged for the vacuum nanoelectronics in recent years. Electron field emission under high electric field from conventional and exotic nanoemitters, which have now been made possible with the use of modern day technology, has been the driving force behind this renewal of interest in vacuum nanoelectronics. In the research reported in this thesis self-assembled silicon nanostructures were studied as a potential source of field emission for vacuum nanoelectronic device applications. Whiskerlike protruding silicon nanostructures were grown on untreated n- and p-type silicon surfaces using electron-beam annealing under high vacuum. The electrical transport characteristics of the silicon nanostructures were investigated using conductive atomic force microscopy (C-AFM). Higher electrical conductivities for the nanostructured surface compared to that for the surrounding planar silicon substrate region were observed. Non-ideal diode behaviour with high ideality factors were reported for the individual nanostructure-AFM tip Schottky nanocontacts. This demonstration, indicative of the presence of a significant field emission component in the analysed current transport phenomena was also detailed. Field emission from these nanostructures was demonstrated qualitatively in a lift-mode interleave C-AFM study. A technique to fabricate integrated field emission diodes using silicon nanostructures in a CMOS process technology was developed. The process incorporated the nanostructure growth phase at the closing steps in the process flow. Turn-on voltages as low as ~ 0.6 V were reported for these devices, which make them good candidates for incorporation into standard CMOS circuit applications. Reproducible I V characteristics exhibited by these fabricated devices were further studied and field emission parameters were extracted. A new consistent and reliable method to extract field emission parameters such as effective barrier height, field conversion factor, and total emitting area at the onset of the field emission regime was developed and is reported herein. The developed parameter extraction method used a unified electron emission approach in the transition region of the device operation. The existence of an electron-supply limited current saturation region at very high electric field was also confirmed. Both the C-AFM and the device characterization studies were modelled and simulated using the finite element method in COMSOL Multiphysics. The experimental results – the field developed at various operating environments – are explained in relation to these finite element analyses. Field enhancements at the atomically sharp nanostructure apexes as suggested in the experimental studies were confirmed. The nanostructure tip radius effect and sensitivity to small nanostructure height variation were investigated and mathematical relations for the nanostructure regime of our interest were established. A technique to optimize the cathode-opening area was also demonstrated. Suggestions related to further research on field emission from silicon nanostructures, optimization of the field emission device fabrication process, and fabrication of field emission triodes are elaborated in the final chapter of this thesis. The experimental, modelling, and simulation works of this thesis indicate that silicon field emission devices could be integrated into the existing CMOS process technology. This integration would offer goods from both the worlds of vacuum and solid-sate nanoelectronics – fast ballistic electron transport, temperature insensitivity, radiation hardness, high packing density, mature technological backing, and economies of scale among other features.

Abstract This thesis is dedicated to realizations and physical understanding of electronic and photocatalytic properties after decorating transition metals to the semiconducting molybdenum disulfide. Synthesized via facile wet chemical methods, the MoS₂-Au, MoS₂-Au-Ni and MoS₂-Ag-Ni composites were formed as binary or ternary compounds. The Au nanoparticles are stably joined to the MoS₂ matrix without deteriorating layered structures of the host. After introducing the Au nanoglue as a common buffer, a metallic contact is reached between Ni and MoS₂, and attributed to new electron migration channel via MoS₂ edge contact. Adapting the Ag as the buffer element can attach the Ni to the basal plane of the MoS₂ beside edge contact. The Ni-Ag-MoS₂ composite effectively splits water under visible light irradiation and produce hydrogen. The excellent photocatalytic activity is attributed to effective charge migration through dangling bonds at the MoS2-Ag-Ni alloy interface and the activation of MoS₂ basal planes. / Original papers The original publications are not included in the electronic version of the dissertation. W. Cao, V. Pankratov, M. Huttula, X. Shi, S. Saukko, Z. Huang, M. Zhang. Gold nanoparticles on MoS2 layered crystal flakes. Materials Chemistry and Physics, 158, 89−95 (2015). DOI: 10.1016/j.matchemphys.2015.03.041 X. Shi, S. Posysaev, M. Huttula, V. Pankratov, J. Hoszowska, J.-Cl. Dousse, F. Zeeshan, Y. Niu, A. Zakharov, T. Li, O. Miroshnichenko, M. Zhang, X. Wang, Z. Huang, S. Saukko, D. L. González, S. van Dijken, M. Alatalo, W. Cao. Metallic contact between MoS₂ and Ni via Au nanoglue. Small, 14, 1704526 (2018). DOI: 10.1002/smll.201704526 http://jultika.oulu.fi/Record/nbnfi-fe2018060525279 X. Shi, M. Huttula, V. Pankratov, J. Hoszowska, J.-Cl. Dousse, F. Zeeshan, Y. Niu, A. Zakharov, Z. Huang, G. Wang, S. Posysaev, O. Miroshnichenko, M. Alatalo, W. Cao. Quantification of bonded Ni atoms for Ni-MoS₂ metallic contact through X-ray photoemission electron microscopy. Microscopy and Microanalysis, 24, 458−459 (2018). DOI: 10.1017/S1431927618014526 http://jultika.oulu.fi/Record/nbnfi-fe2018082834233 X. Shi, M. Zhang, W. Cao, X. Wang, M. Huttula. Efficient photocatalytic hydrogen evolution via activated multilayer MoS₂. Manuscript. X. Shi, Z. Huang, M. Huttula, T. Li, S. Li, X. Wang, Y. Luo, M. Zhang, W. Cao. Introducing magnetism into 2D nonmagnetic inorganic layered crystals: a brief review from first-principles aspects. Crystals, 8, 24 (2018). DOI: 10.3390/cryst8010024 http://jultika.oulu.fi/Record/nbnfi-fe201802153441

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Supramolecular electronics aims to construct and investigate the optoelectronic properties of tailored supramolecular nanoarchitectures. The aim of this thesis is to get control over the organization of organic molecular systems and correlate their structure with the electrical properties, with particular attention at the nanoscale properties. The exploited strategies require a focused molecular design, the balancing of intermolecular and interfacial interactions, a control on the kinetics of the processes and possibly the exploitation of external forces. The presented results showed that understanding the local properties of a material on a nanoscale basis is a huge fundamental challenge to bring solutions to both scientific and technological issues, since in electronic devices the performances are strongly dependent on the order at the supramolecular level.

L'électronique supramoléculaires vise à construire et à étudier les propriétés optoélectroniques des architectures supramoléculaires à l'échelle nanométrique. L'objectif de cette thèse est d'obtenir le contrôle de l'organisation des systèmesmoléculaires organiques et de corréler leur structure avec les propriétés électriques, avec une attention particulière sur les propriétés à l'échelle nanométrique. Les stratégies exploitées nécessitent un design chimique adapté, un équilibre desinteractions intermoléculaires et d'interface, un contrôle sur la cinétique des processus et, éventuellement, l'exploitation des forces extérieures. Les résultats présentés montrent que la compréhension des propriétés locales d'un matériau sur une base à l'échelle nanométrique est un énorme défi fondamental vise à apporter des solutions à des questions scientifiques et technologiques, puisque les performances dans les appareils électroniques sont fortement dépendante de l'ordre au niveau supramoléculaire. / Supramolecular electronics aims to construct and investigate the optoelectronic properties of tailored supramolecular nanoarchitectures. The aim of this thesis is to get control over the organization of organic molecular systems and correlate their structure with the electrical properties, with particular attention at the nanoscale properties. The exploited strategies require a focused molecular design, the balancing of intermolecular and interfacial interactions, a control on the kinetics of the processes and possibly the exploitation of external forces. The presented results showed that understanding the local properties of a material on a nanoscale basis is a huge fundamental challenge to bring solutions to both scientific and technological issues, since in electronic devices the performances are strongly dependent on the order at the supramolecular level.

科学研究費補助金 研究種目:基盤研究(A)(2) 課題番号:13305005 研究代表者:近藤 博基 研究期間:2001-2004年度