基本情報

所属

• 電子科学研究所　物質科学研究部門

職名

• 助教

学位

• 博士（理学）（2020年03月 大阪市立大学）

科研費研究者番号

• 40888608

ORCID ID

•  https://orcid.org/0000-0002-8764-3951

J-Global ID

• 202101012703910183

研究分野

• ナノテク・材料 / 基礎物理化学
• ナノテク・材料 / ナノ構造化学
• ナノテク・材料 / ナノ材料科学

研究活動情報

論文

• Highly Luminescent and Stable Halide Perovskite Nanocrystals by Interfacial Defect Passivation and Amphiphilic Ligand Capping.

  Sushant Ghimire, Most Farida Khatun, Bhagyashree M Sachith, Takuya Okamoto, Jeladhara Sobhanan, Ch Subrahmanyam, Vasudevanpillai Biju

  ACS applied materials & interfaces 15 34 41081 - 41091 2023年08月30日 

  Halide vacancies cause lattice degradation and nonradiative losses in halide perovskites. In this study, we strategically fill bromide vacancies in CsPbBr3 perovskite nanocrystals with NaBr, KBr, or CsBr at the organic-aqueous interface for hydrophobic ligand-capped nanocrystals or in a polar solvent (2-propanol) for amphiphilic ligand-capped nanocrystals. Energy-dispersive X-ray spectra, powder X-ray diffraction data, and scanning transmission electron microscopy images help us confirm vacancy filling and the structures of samples. The bromide salts increase the photoluminescence quantum yield (98 ± 2%) of CsPbBr3 by decreasing the nonradiative decay rate. Single-particle studies show the quantum yield increase originates from the poorly luminescent nanocrystals becoming highly luminescent after filling vacancies. Furthermore, we tune the optical band gap (ultraviolet-visible-near-infrared) of the hydrophobic ligand-capped nanocrystals by halide exchange at the toluene-water interface using saturated NaCl or NaI solutions, which completes in about 60 min under continuous mixing. In contrast, the amphiphilic ligand accelerates the halide exchange in 2-propanol, suggesting ambipolar functional groups speed up the ion-exchange reaction. The bromide vacancy-filled or halide-exchanged samples in a toluene-water biphasic solvent show higher stability than amphiphilic ligand-capped samples in 2-propanol. This strategy of defect passivation, ion exchange, and ligand chemistry to improve quantum yields and tune band gaps of halide perovskite nanocrystals can be promising for designing stable and water-soluble perovskite samples for solar cells, light-emitting diodes, photodetectors, and photocatalysts.
• Thermodynamically and Kinetically Controlled Nucleation and Growth of Halide Perovskite Single Crystals

  Dong Zhang, Takuya Okamoto, Vasudevanpillai Biju

  Small 19 48 2023年07月25日 

  Abstract Halide perovskites are ideal for next‐generation optical devices and photovoltaics. Although perovskite single‐crystals show reproducible optoelectronic properties, significant variations in the crystal size, anisotropy, density, defects, photoluminescence (PL), and carrier lifetime affect the sample properties and device performances. Homogenous size and shape FA/MAPbBr₃ single microcrystals (MCs) with controlled edge lengths, crystal densities, PL lifetimes, and PL intensities are prepared by thermodynamically controlling and kinetically separating the crystal nucleation‐growth processes using optimum N‐cyclohexyl‐2‐pyrrolidone (CHP) concentration. The crystal growth kinetics at different CHP concentrations and temperatures are estimated spectroscopically by measuring the concentration of Pb (II). High‐density cubic MCs with a homogenous size distribution, high PL intensities, and long PL lifetimes are obtained within minutes at high temperatures by the controlled addition of the pyrrolidone derivative. Conversely, the crystal size nonlinearly increases with time at low temperatures. The isotropically grown high‐density single crystals at controlled nucleation‐growth rates at 190 °C with 20% CHP show the highest PL intensity and the longest PL lifetimes. This method offers thermodynamic and kinetic control of perovskite single‐crystal growth with shape control.
• Slipping-Free Halide Perovskite Supercrystals from Supramolecularly-Assembled Nanocrystals.

  Takuya Okamoto, Vasudevanpillai Biju

  Small (Weinheim an der Bergstrasse, Germany) e2303496  2023年05月12日 

  Supramolecularly assembled high-order supercrystals (SCs) help control the dielectric, electronic, and excitonic properties of semiconductor nanocrystals (NCs) and quantum dots (QDs). Ligand-engineered perovskite NCs (PNCs) assemble into SCs showing shorter excitonic lifetimes than strongly dielectric PNC films showing long photoluminescence (PL) lifetimes and long-range carrier diffusion. Monodentate to bidentate ligand exchange on ≈ 8 nm halide perovskite (APbX3 ; A:Cs/MA, X:Br/I) PNCs generates mechanically stable SCs with close-packed lattices, overlapping electronic wave functions, and higher dielectric constant, providing distinct excitonic properties from single PNCs or PNC films. From Fast Fourier Transform (FFT) images, time-resolved PL, and small-angle X-ray scattering, structurally and excitonically ordered large SCs are identified. An Sc shows a smaller spectral shift (<35 meV) than a PNC film (>100 meV), a microcrystal (>100 meV), or a bulk crystal (>100 meV). Also, the exciton lifetime (<10 ns) of an SC is excitation power-independent in the single exciton regime 〈N〉<1, comparable to an isolated PNC. Therefore, bidentate-ligand-assisted SCs help overcome delayed exciton or carrier recombination in halide perovskite nanocrystal assemblies or films.
• Photoinduced interfacial electron transfer from perovskite quantum dots to molecular acceptors for solar cells.

  Bhagyashree Mahesha Sachith, Zhijing Zhang, Palyam Subramanyam, Challapalli Subrahmanyam, Akihiro Furube, Naoto Tamai, Takuya Okamoto, Hiroaki Misawa, Vasudevanpillai Biju

  Nanoscale 15 17 7695 - 7702 2023年05月04日 

  Bandgap-engineered inorganic and hybrid halide perovskite (HP) films, nanocrystals, and quantum dots (PQDs) are promising for solar cells. Fluctuations of photoinduced electron transfer (PET) rates affect the interfacial charge separation efficiencies of such solar cells. Electron donor- or acceptor-doped perovskite samples help analyze PET and harvest photogenerated charge carriers efficiently. Therefore, PET in perovskite-based donor-acceptor (D-A) systems has received considerable attention. We analyzed the fluctuations of interfacial PET from MAPbBr3 or CsPbBr3 PQDs to classical electron acceptors such as 7,7,8,8-tetracyanoquinodimethane (TCNQ) and 1,2,4,5-tetracyanobenzene (TCNB) at single-particle and ensemble levels. The significantly negative Gibbs free energy changes of PET estimated from the donor-acceptor redox potentials, the donor-acceptor sizes, and the solvent dielectric properties help us clarify the PET in the above D-A systems. The dynamic nature of PET is apparent from the decrease in photoluminescence (PL) lifetimes and PL photocounts of PQDs with an increase in the acceptor concentrations. Also, the acceptor radical anion spectrum helps us characterize the charge-separated states. Furthermore, the PL blinking time and PET rate fluctuations (108 to 107 s-1) provide us with single-molecule level information about interfacial PET in perovskites.
• Self-assembled halide perovskite quantum dots in polymer thin films showing temperature-controlled exciton recombination

  Most Farida Khatun, Takuya Okamoto, Vasudevanpillai Biju

  Chemical Communications 59 93 13831 - 13834 2023年 

  Spontaneous assembly formation and thermal dissociation of self-assemblies of lead halide perovskite quantum dots embedded in a polymer host reversibly modulate the photoluminescence color, spectral maxima, and lifetime.
• Halide Perovskite Single Crystals and Nanocrystal Films as Electron Donor-Acceptor Heterojunctions

  M. D. Shahjahan, Takuya Okamoto, Lata Chouhan, Bhagyashree Mahesha Sachith, Narayan Pradhan, Hiroaki Misawa, Vasudevanpillai Biju

  ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 2022年12月 

  Halide perovskites are materials for future optical displays and solar cells. Electron donor-acceptor perovskite heterostructures with distinguishing halide compositions are promising for transporting and harvesting photogenerated charge carriers. Combined e-beam lithography and anion exchange are promising to develop such heterostructures but challenging to prepare multiple heterojunctions at desired locations in single crystals. We demonstrate swift laser trapping-assisted band gap engineering at the desired locations in MAPbBr(3) microrods, microplates, or nanocrystal thin films. The built-in donor-acceptor double and multi-heterojunction structures let us transport and trap photogenerated charge carriers from wide-band gap bromide to narrow-band gap iodide domains. We discuss the charge carrier transport and trapping mechanisms from the viewpoints of engineered bands and band continuity. This work offers a convenient method for designing single-, double- and multi-heterojunction donor-acceptor halide perovskites for photovoltaic, photonic, and electronic applications.
• Mechano-optical Modulation of Excitons and Carrier Recombination in Self-Assembled Halide Perovskite Quantum Dots

  Zhijing Zhang, Sushant Ghimire, Takuya Okamoto, Bhagyashree Mahesha Sachith, Jeladhara Sobhanan, Challapalli Subrahmanyam, Vasudevanpillai Biju

  ACS NANO 2022年01月 

  Mechanically modulating optical properties of semiconductor nanocrystals and organic molecules are valuable for mechano-optical and optomechanical devices. Halide perovskites with excellent optical and electronic properties are promising for such applications. We report the mechanically changing excitons and photoluminescence of self-assembled formamidinium lead bromide (FAPbBr(3)) quantum dots. The as-synthesized quantum dots (3.6 nm diameter), showing blue emission and a short photoluminescence lifetime (2.6 ns), form 20-300 nm 2D and 3D self-assemblies with intense green emission in a solution or a film. The blue emission and short photoluminescence lifetime of the quantum dots are different from the delayed (ca. 550 ns) green emission from the assemblies. Thus, we consider the structure and excitonic properties of individual quantum dots differently from the self-assemblies. The blue emission and short lifetime of individual quantum dots are consistent with a weak dielectric screening of excitons or strong quantum confinement. The red-shifted emission and a long photoluminescence lifetime of the assemblies suggest a strong dielectric screening that weakens the quantum confinement, allowing excitons to split into free carriers, diffuse, and trap. The delayed emission suggests nongeminate recombination of diffusing and detrapped carriers. Interestingly, the green emission of the self-assembly blueshifts by applying a lateral mechanical force (ca. 4.65 N). Correspondingly, the photoluminescence lifetime decreases by 1 order of magnitude. These photoluminescence changes suggest the mechanical dissociation of the quantum dot self-assemblies and mechanically controlled exciton splitting and recombination. The mechanically changing emission color and lifetime of halide perovskite are promising for mechano-optical and optomechanical switches and sensors.
• Long-Range Interfacial Charge Carrier Trapping in Halide Perovskite-C-60 and Halide Perovskite-TiO2 Donor-Acceptor Films

  Bhagyashree Mahesha Sachith, Takuya Okamoto, Sushant Ghimire, Tomokazu Umeyama, Yuta Takano, Hiroshi Imahori, Vasudevanpillai Biju

  JOURNAL OF PHYSICAL CHEMISTRY LETTERS 12 35 8644 - 8651 2021年09月 

  Interfacial electron transfer across perovskite-electron acceptor heterojunctions plays a significant role in the power-conversion efficiency of perovskite solar cells. Thus, electron donor-acceptor thin films of halide perovskite nanocrystals receive considerable attention. Nevertheless, understanding and optimizing distance- and thickness-dependent electron transfer in perovskite-electron acceptor heterojunctions are important. We reveal the distance-dependent and diffusion-controlled interfacial electron transfer across donor-acceptor heterojunction films formed by formamidinium or cesium lead bromide (FAPbBr(3)/CsPbBr3) perovskite nanocrystals with TiO2/C-60. Self-assembled nanocrystal films prepared from FAPbBr(3) show a longer photoluminescence lifetime than a solution, showing a long-range carrier migration. The acceptors quench the photoluminescence intensity but not the lifetime in a solution, revealing a static electron transfer. Conversely, the electron transfer in the films changes from dynamic to static by moving toward the donor-acceptor interface. While radiative recombination dominates the electron transfer at 800 mu m or farther, the acceptors scavenge the photogenerated carriers within 100 mu m. This research highlights the significance of interfacial electron transfer in perovskite films.
• Shape-Dependent Kinetics of Halide Vacancy Filling in Organolead Halide Perovskites

  Takuya Okamoto, Md Shahjahan, Vasudevanpillai Biju

  ADVANCED OPTICAL MATERIALS 2021年06月 

  Halide perovskites show high photoluminescence quantum yields and tunable bandgap. While perovskites' optical properties significantly degrade due to the ionic and electronic defects, a correlation among their structure, size, defects, and degradation rate remains concealed. The authors report the crystal shape- and halide vacancy-dependent stability of methylammonium lead bromide single crystals. The vacancies are filled in the cubic-, plate-, and rod-shaped crystals by the halide-soaking and light-soaking processes. The differences in the stability, photoluminescence intensity, lifetime, and vacancy filling rates in these geometrical shapes derive from their specific surface-to-volume ratios. The shape-dependent vacancy filling helps to correlate the electron microscope images, elemental compositions, and the photoluminescence intensity and lifetime.
• Heterojunction Perovskite Microrods Prepared by Remote-Controlled Vacancy Filling and Halide Exchange

  Md Shahjahan, Ken-ichi Yuyama, Takuya Okamoto, Vasudevanpillai Biju

  ADVANCED MATERIALS TECHNOLOGIES 6 2 2021年02月 

  Anion exchange reaction tunes the band gap of halide perovskites, which proceeds by the migration of the ions through the halide vacancies. This study reports the preparation of the heterojunction perovskite microrods by optically controlled localized halide vacancy filling, and halide exchange leading to color tuning in the MAPbBr(3) microrod crystals. The exchange reaction is homogeneously suppressed by treating the crystal with a halide precursor solution, whereas the reaction is locally inhibited at the specific site of a crystal by filling the halide vacancies using a tightly focused beam of a near-infrared laser. By controlling the density of halide vacancies at the specific site of the crystal, the rate of nonradiative recombination of charge carriers in the crystal is controlled. This halide vacancy filling by the remote-controlled reaction helps to locally control the crystal quality and photoluminescence for designing perovskite-based high-quality photovoltaic and optoelectronic devices.
• Synthesis of iron-based nanoparticles from ferrocene by femtosecond laser irradiation: Suppression of the particle growth in a mixture of water and hexane

  Yuki Horikawa, Takuya Okamoto, Takahiro Nakamura, Yuhei O. Tahara, Makoto Miyata, Shingo Ikeda, Kenji Sakota, Tomoyuki Yatsuhashi

  CHEMICAL PHYSICS LETTERS 750 2020年07月 

  Iron-based nanoparticles show unique magnetic properties, and their syntheses from metal complex solution by pulsed lasers have been widely studied; however, the aggregation of nanoparticles is unavoidable in homogeneous solution. We report the production of water-dispersible iron-based nanoparticles in a mixture of water and ferrocene n-hexane solution by femtosecond laser irradiation without using any additive agents. The mean diameter of iron-based nanoparticles (ca. 7 nm) is independent on the concentration of ferrocene and laser irradiation time. We propose that hexane microdroplets dispersed in water act as reaction vessels and reduce the opportunity of aggregation of primary nanoparticles.
• Effects of Ligand and Solvent on the Synthesis of Iron Oxide Nanoparticles from Fe(acac)(3) Solution by Femtosecond Laser Irradiation

  Takuya Okamoto, Takahiro Nakamura, Yuhei O. Tahara, Makoto Miyata, Kenji Sakota, Tomoyuki Yatsuhashi

  CHEMISTRY LETTERS 49 1 75 - 78 2020年01月 

  Synthesis of iron oxide nanoparticles (Fe-O NPs) from iron(III)acetylacetonate solution by femtosecond laser irradiation is reported. Fe-O NPs and carbon are agglomerated in nhexane, while single-nanometer-sized dispersed Fe-O NPs are obtained in water. We propose that the choice of ligands and solvent determines the primary particle size distribution and dispersion states of NPs as well as carbon contaminants in laser-assisted synthesis using metal complexes as reactants.
• Synthesis of Single-Nanometer-Sized Gold Nanoparticles in Liquid-Liquid Dispersion System by Femtosecond Laser Irradiation

  Takuya Okamoto, Takahiro Nakamura, Kenji Sakota, Tomoyuki Yatsuhashi

  LANGMUIR 35 37 12123 - 12129 2019年09月 

  Gold nanoparticles (AuNPs) show unique optical properties and catalytic activities, and their synthesis from gold ions has been widely studied. One of the additive-reagent-free and noncontact production procedures is the reduction of gold ions in solution by femtosecond laser pulses; however, the aggregation of AuNPs is unavoidable in homogeneous solution. Here, we report the synthesis of single-nanometer-sized AuNPs in a mixture of aqueous HAuCl4 solution and n-hexane (the mixture) and in aqueous HAuCl4 solution (the aqueous solution) by femtosecond laser irradiation in the absence of any additive reagents. Transmission electron microscopy revealed that circlelike colonies consisting of well-separated AuNPs were obtained from the mixture, while highly stacked and agglomerated AuNPs were obtained from the aqueous solution. The mean size of AuNPs in the mixture was nearly independent of the laser irradiation time, whereas that obtained in aqueous solution was gradually shifted to smaller size by laser irradiation period. We propose that the adsorption of primary AuNPs on the surface of hexane microdroplets and the fragmentation of large AuNPs in water by successive laser pulses retain single-nanometer-sized AuNPs in the mixture. The use of liquid-liquid interface on hexane microdroplets in aqueous solution provides a simple and useful environment to synthesize small AuNPs without the aid of surfactants or capping agents.
• Synthesis of Bare Iron Nanoparticles from Ferrocene Hexane Solution by Femtosecond Laser Pulses

  Takuya Okamoto, Takahiro Nakamura, Ryo Kihara, Tsuyoshi Asahi, Kenji Sakota, Tomoyuki Yatsuhashi

  CHEMPHYSCHEM 19 19 2480 - 2485 2018年10月 

  Iron-based nanoparticles (FeNPs) have unique and attractive properties such as superparamagnetism, biocompatibility, and catalytic activity. Although the synthesis of precious metal NPs from a metal in liquid and/or metal salt solution by a pulsed laser has been investigated, comparably little effort has been devoted to examine the production of FeNPs. Here we report the synthesis of carbon-shell free spherical NPs of iron oxide (magnetite) from ferrocene hexane solution by femtosecond near infrared laser pulses. Nanosecond UV laser pulses are used to compare the evolution of the particle size distribution as a function of laser irradiation time. The size of NPs remains constant even for extended exposure to femtosecond laser pulses, whereas it grows with exposure to nanosecond laser pulses. The primary particles are generated by photochemical reactions regardless of pulse duration; however, the fragmentation of NPs by successive femtosecond laser pulses regulates the particle size.
• Precipitation of dichloromethane as low-chlorine carbon nanoparticles from water by femtosecond laser pulses

  Takuya Okamoto, Erina Miyasaka, Koji Mitamura, Kimihiro Matsukawa, Tomoyuki Yatsuhashi

  JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY 344 178 - 183 2017年07月 

  We report on the transformation of dichloromethane to low-chlorine carbon nanoparticles by the exposure of aqueous dichloromethane solution and/or dichloromethane/water biphasic solution to femtosecond laser pulses. The pH of either solution immediately decreased due to the reduction of dichloromethane by hydrated electrons. The time evolution of transmittance revealed that particle formation was suppressed when the initial pH was low because protons scavenge hydrated electrons. The size and morphology of nanoparticles was independent of the initial pH and the reaction solution used. The analysis of the elemental composition of carbon particles showed that the Cl/C atomic ratio was, independent on the initial pH values, greatly reduced to 0.06. We propose that the violent destruction of dichloromethane and elimination of chlorine atoms not only as Cl- but also Cl-2 excludes chlorine atoms from the carbon network construction processes toward the formation of carbon nanoparticles. (C) 2017 Elsevier B.V. All rights reserved.
• Synthesis of Fluorine-Doped Hydrophilic Carbon Nanoparticles from Hexafluorobenzene by Femtosecond Laser Pulses

  Takuya Okamoto, Koji Mitamura, Tomoyuki Hamaguchi, Kimihiro Matsukawa, Tomoyuki Yatsuhashi

  CHEMPHYSCHEM 18 9 1007 - 1011 2017年05月 

  We report on the preparation and characterization of fluorine-doped hydrophilic carbon nanoparticles by the exposure of hexafluorobenzene or a water/hexafluorobenzene bilayer solution to femtosecond laser pulses. Uniform atom distributions are achieved not only on the particle surface but also inside the particles. The semi-ionic character of C-F bonds and the non-aggregating feature of the nanoparticles play key roles in the water-dispersible character of fluorine-doped carbon nanoparticles. We suggest the following building-up process of carbon nanoparticles: the fragmentation of hexafluorobenzene initiated by the electrons generated in laser-induced plasma followed by the reconstruction of a carbon framework of nanoparticles.
• Synthesis of Hydrophilic and Hydrophobic Carbon Nanoparticles from Benzene/Water Bilayer Solution with Femtosecond Laser Generated Plasma Filaments in Water

  Tomoyuki Hamaguchi, Takuya Okamoto, Koji Mitamura, Kimihiro Matsukawa, Tomoyuki Yatsuhashi

  BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 88 2 251 - 261 2015年02月 

  We synthesized hydrophilic and hydrophobic carbon nanoparticles (CNPs) by femtosecond laser (0.8 mu m, 40 fs) irradiation of the water layer of an aerated benzene/water (B/W) bilayer solution. Focusing intense femtosecond laser pulses onto water creates a high density of reactive species such as hydroxyl radicals in a well-confined volume; i.e., plasma filament. The properties of the particle surface were controlled simply by adjusting the laser focusing position, the duration between the preparation of B/W bilayer solution and the laser irradiation. The hydrophobic CNPs appeared to be nearly identical in size and morphology to hydrophilic CNPs. Raman spectroscopy revealed that both particles had a graphitic and disordered structure; however, ER. spectroscopy clearly showed that the hydroxy group is the origin of the hydrophilicity. The time evolution of particle formation, products in water, and benzene dissolution behavior in water reveals that the surface properties are determined by the concentration of benzene in water. The diluted aqueous benzene solution gave hydrophilic particles; however, the density of particles was much smaller than that formed in B/W bilayer solution. We concluded that the production of denser hydrophilic CNPs in B/W bilayer was achieved by limiting the concentration of benzene in water layer by B/W interface, and by continuously supplying benzene into water layer through B/W interface. We discuss the subsequent reaction mechanism leading to CNPs of different surface characters.

その他活動・業績

• Lead-Free Halide Perovskite Materials and Optoelectronic Devices: Progress and Prospective

  Iago López-Fernández, Donato Valli, Chun Yun Wang, Subarna Samanta, Takuya Okamoto, Yi Teng Huang, Kun Sun, Yang Liu, Vladimir S. Chirvony, Avijit Patra, Juliette Zito, Luca De Trizio, Deepika Gaur, Hong Tao Sun, Zhiguo Xia, Xiaoming Li, Haibo Zeng, Iván Mora-Seró, Narayan Pradhan, Juan P. Martínez-Pastor, Peter Müller-Buschbaum, Vasudevanpillai Biju, Tushar Debnath, Michael Saliba, Elke Debroye, Robert L.Z. Hoye, Ivan Infante, Liberato Manna, Lakshminarayana Polavarapu Advanced Functional Materials 2023年 

  Halide perovskites, in the form of thin films and colloidal nanocrystals, have recently taken semiconductor optoelectronics research by storm, and have emerged as promising candidates for high-performance solar cells, light-emitting diodes (LEDs), lasers, photodetectors, and radiation detectors. The impressive optical and optoelectronic properties, along with the rapid increase in efficiencies of solar cells and LEDs, have greatly attracted researchers across many disciplines. However, most advances made so far in terms of preparation (colloidal nanocrystals and thin films), and the devices with highest efficiencies are based on Pb-based halide perovskites, which have raised concerns over their commercialization due to the toxicity of Pb. This has triggered the search for lower-toxicity Pb-free halide perovskites and has led to significant progress in the last few years. In this roadmap review, researchers of different expertise have joined together to summarize the latest progress, outstanding challenges, and future directions of Pb-free halide perovskite thin films and nanocrystals, regarding their synthesis, optical spectroscopy, and optoelectronic devices, to guide the researchers currently working in this area as well as those that will join the field in the future.
• レーザーを用いた微粒子作製と応用展開 液-液界面を利用する均一粒径金属ナノ粒子のレーザー合成

  八ッ橋知幸, 岡本拓也, 堀川雄輝 光学 51 (2) 2022年
• Bottom-up Synthetic Approaches to Carbon Nanomaterial Production in Liquid Phase by Femtosecond Laser Pulses

  Tomoyuki Yatsuhashi, Takuya Okamoto High-Energy Chemistry and Processing in Liquids 331 -356 2022年
• フェムト秒レーザーによる液相化学反応およびナノ材料創成

  岡本拓也, 中島信昭, 八ッ橋知幸 レーザー研究 45 (5) 2017年

共同研究・競争的資金等の研究課題

• ペロブスカイト結晶-ナノ共振器を用いた低閾値かつ狭帯域ナノレーザーの開発

  日本学術振興会：科学研究費助成事業 若手研究

  研究期間 : 2021年04月 -2024年03月 

  代表者 : 岡本 拓也
• 光圧による局所濃縮を利用したハロゲン混合ペロブスカイト単一ナノ結晶形成機構の解明

  日本学術振興会：科学研究費助成事業 特別研究員奨励費

  研究期間 : 2020年04月 -2023年03月 

  代表者 : 岡本 拓也
• 微小プラズマと微小液滴を融合したナノ粒子生成：微小反応場の特異性の解明

  日本学術振興会：科学研究費助成事業 特別研究員奨励費

  研究期間 : 2018年04月 -2020年03月 

  代表者 : 岡本 拓也

   

  本研究は微小反応場におけるナノ粒子の生成、成長、そして凝集について基礎的な知見を得ることを目的とした。本年度は金属錯体の溶液試料と貧溶媒を撹拌試料して生じる微小液滴がナノ粒子の形態および粒子径に及ぼす効果の解明、およびマイクロ流路によりサイズを制御した液滴中での微小プラズマ発生について研究活動を行った。ヘキサン/塩化金酸水溶液、およびフェロセンヘキサン溶液/水の撹拌により水中油滴型のエマルションを形成し、原料が水に溶解する条件と有機溶媒に溶解する条件にてフェムト秒レーザーをそれぞれ照射した。ヘキサン/塩化金酸水溶液の水中油滴型エマルションへのレーザー照射では、キャッピング剤を用いることなく直径10 nm未満の大きさの金ナノ粒子の生成に成功した。レーザー照射時間にかかわらず平均粒子径は5 nm程度で一定であった。さらに、乾燥により金ナノ粒子は円形状に濃縮されつつも凝集しないことが分かった。金ナノ粒子の1次粒子が液滴表面に捕捉されることで粒子成長が抑制されると結論した。なお、この研究に基づいた論文はアメリカ化学会のLangmuirに掲載された。一方、フェロセンヘキサン溶液/水の水中油滴型エマルションへのレーザー照射では、油相側に原料分子が溶解しているにもかかわらず、レーザー照射後の水相において10 nm未満の鉄ナノ粒子が分散して得られることを見出した。また、原料濃度を10倍にしても、レーザーの照射時間にかかわらず、平均粒子径は10 nm未満のままであった。フェロセンを溶解したヘキサン液滴が微小な反応場として機能し、粒子および鉄原子の凝集が抑制されると結論した。さらに、市販のシリコン樹脂製マイクロ流路を用いて液滴のサイズ制御条件の検討を行った。微小液滴内でのナノ粒子生成に向けて、レーザー照射系の構築や、マイクロ流路内における各試料の流速条件およびレーザー照射条件の最適化を行った。