The Trail of Challenges: Autobiographical Notes of Hiroaki Misawa

Abstract

Published as part of The Journal of Physical Chemistry C special issue “Hiroaki Misawa Festschrift”. When Prof. Kosei Ueno (Hokkaido University), the guest editor of this Festschrift, invited me to write an autobiographical note, I felt a bit perplexed. However, I realized that reflecting on the circumstances of that era, and how I conceived and pursued my research themes within those circumstances, is crucial for determining the future direction of my ongoing research. Thus, from this perspective, I decided to write this autobiographical note. Let me begin by recounting the early stages of my life. I was born in 1955 in Chofu City, Tokyo, as the eldest son of my father, Sukeo Misawa, and my mother, Toshie. My father was a public school teacher, and both of my parents were enthusiastic about educating their children. I was raised in such an environment with my younger brother Naoaki, who is two years my junior. Though we were a middle-class family, our parents encouraged us to pursue our interests. We lived in a nature-rich area near the Tama River, where I often played with my brother and friends during my early elementary school years. In the upper grades of elementary school, students interested in science from several local schools, about ten from each, gathered once a month in the science room of a representative school to participate in a science club and conduct various experiments. In middle school, my science teacher provided fascinating and easily understandable explanations, which fostered my interest in pursuing a career in science. In high school, I was fortunate to have two excellent teachers who were passionate about teaching physics and chemistry. The numerous experiments I experienced in physics classes had a significant impact on my future academic and career choices. When choosing my major in university, I was torn between physics and chemistry. Ultimately, I decided to major in chemistry and enrolled in the Faculty of Engineering at Tokyo Metropolitan University. For my fourth-year graduation research, I wanted to deepen my understanding of molecular reaction dynamics. Believing that studying photochemistry and/or excited state chemistry would be ideal, I sought the guidance of Prof. Haruo Inoue, who was conducting photochemistry research in Prof. Mitsuhiko Hida’s lab at the time. Under Prof. Inoue’s mentorship, I conducted a year-long research project on the photochromism of anthraquinone derivatives. Through Prof. Inoue’s meticulous guidance, I cultivated foundational knowledge in photochemistry and the basis of my logical thinking in science. Even now, I continue to discuss with Prof. Inoue the reaction mechanisms of water splitting using visible light, through strong coupling between plasmons and nano-optical resonators, which I am currently researching. After graduating from Tokyo Metropolitan University, I continued my photochemistry research at the graduate school of Tsukuba University, joining the lab of Prof. Katsumi Tokumaru. Under his supervision, my master’s research focused on elucidating the singlet-sensitized photodecomposition mechanism of benzoyl peroxide and studying the photoelectrochemical oxidation reactions of olefin compounds using semiconductor electrodes. During my doctoral course, I researched the mechanisms of electron transfer reactions from the excited triplet states of organic dyes. At that time, Prof. Tokumaru’s lab was equipped with nanosecond time-resolved single-photon counting equipment and a nanosecond time-resolved absorption measurement apparatus, both of which were rare in Japan. Having access to these instruments allowed me to study the dynamics of short-lived excited states and reaction intermediates, which was extremely fortunate for me. Additionally, many renowned photochemistry researchers from overseas visited Prof. Tokumaru, and listening to their lectures was highly inspiring. In the final year of my doctoral course, I married Sayoko. After obtaining my Ph.D., I wanted to continue my research at a university but was somewhat apprehensive about the financial instability of a postdoctoral researcher. However, Sayoko strongly encouraged me, and I decided to pursue a postdoctoral position. Without her support, I do not think I would have been able to continue my research at the university to this day. In 1984, I had the opportunity to work as a postdoctoral researcher under Prof. Richard A. Caldwell at the University of Texas at Dallas, where I conducted research on the excited triplet states of cyclic olefins. At UT Dallas, I synthesized various cyclic olefins and took them to the Center for Fast Kinetics Research (CFKR) at UT Austin, where I measured the dynamics of twisted cyclic olefins in their excited triplet states using nanosecond and picosecond transient absorption equipment. During my stay in the United States as a postdoctoral researcher, in 1985, my eldest daughter, Tomoyo, was born. Sayoko chose to give birth in Texas rather than returning to Japan. We were very grateful for the assistance of Sayoko’s sister, Toshiko, who came to help for three months around the time of the birth, and for the kindness of the two Japanese families living nearby who helped take care of Sayoko and Tomoyo. Shortly after Tomoyo’s birth, Prof. Tokumaru offered me a position as a technical staff member in his laboratory. I returned to Japan in 1986 and became an Assistant Professor a year later. In Prof. Tokumaru’s lab, I conducted research on one-way photoisomerization, the photochemical process first discovered by Prof. Tokumaru. During this time, Prof. Thomas W. Ebbesen, now a professor at the University of Strasbourg in France, was a visiting researcher. We had many stimulating discussions about photochemical research. I still maintain a friendship with Prof. Ebbesen, and I am grateful for the valuable advice he has given me for my research. In 1987, my son Takahiro was born, and our family of four settled in Tsukuba. In December 1988, just as my daughter Tomoyo turned three and just before my son Takahiro turned one, I resigned from Tsukuba University to join the “Microphotoconversion Project” of the ERATO program at the Japan Science and Technology Agency (JST), led by Prof. Hiroshi Masuhara, as a full-time researcher. The research was conducted in Kyoto. Although the project period was only five years, the funding was ample. For a young researcher of 33 like me, it was an extremely attractive project. Prof. Masuhara did not assign a specific research theme but encouraged me to tackle new research challenges involving light and matter. For the ten years since my graduation, I had been conducting research in photochemistry. However, I felt somewhat uncomfortable that much of the research in photochemistry focused on the electronic structure of excited molecules. During this decade, the pulse width of lasers entered the femtosecond range, making their high-power output possible. Amid these technological innovations in light sources, I began to think it might be possible to develop a new field of photochemistry focusing on light rather than molecules. Around that time, I decided to attend a lecture by a researcher with my colleague, Dr. Keiji Sasaki, who specializes in optics. The lecture was on biophysics, a field entirely different from our specializations. The lecture was fascinating and presented the work of Dr. Arthur Ashkin from Bell Laboratories in the United States. Dr. Ashkin reported that focusing laser light on micrometer-sized transparent materials could generate radiation pressure to noncontact trap these materials─a technique known as “Laser Trapping”. He also suggested that in the future, it might be possible to trap biological materials such as proteins without contact using laser light. When I heard this, I immediately thought, “This could be used for the new photochemistry I am considering!” However, as a chemist, I did not know how to assemble an instrument like this. After the lecture, I talked with Dr. Sasaki about Laser Trapping and learned that he was also very interested in it. When I consulted with him about the possibility of assembling a Laser Trapping instrument, he enthusiastically confirmed that it could be done with a CW laser, an optical microscope, and optical elements. I still vividly remember how happy I was to hear that. I immediately spoke with Dr. Noboru Kitamura, the project’s technical advisor, about conducting research on the scientific applications of Laser Trapping. He agreed, as did Prof. Masuhara. We prepared the necessary equipment, including a CW YAG Laser, an optical microscope, and optical components for Laser Trapping. Once assembled, we began constructing the Laser Trapping instrument. Although the assembly did not take long, adjusting the optical system was a bit challenging. By the second day of work, we successfully trapped polystyrene microparticles with a diameter of a few micrometers dispersed in water using Laser Trapping, which was incredibly thrilling. Subsequently, we arranged multiple polymer particles in the interference fringes of the laser light, and Dr. Sasaki also succeeded in drawing letters with multiple particles by rapidly moving the trapping laser beam using a galvano mirror. Our achievements were recognized, and in 1992, the four of us─Masuhara, Kitamura, Misawa, and Sasaki─were honored with the Moet Hennessy Louis Vuitton International Science Award. After attending an international conference in August 1990, I had the opportunity to visit Bell Laboratories with Dr. Kitamura and Dr. Sasaki and meet Dr. Ashkin. Additionally, it was a great honor to hear about Dr. Ashkin’s recent research results and to share our Laser Trapping research findings with him. As you may know, Dr. Ashkin was awarded the Nobel Prize in Physics in 2018, and we were very pleased by this recognition. As my research shifted significantly toward radiation pressure research, my second daughter, Momoko, was born in 1992. While Sayoko was busy raising our three children, we were fortunate to reside in an annex of her parents’ house, where we received detailed support from them in child-rearing. I believe that the rapid achievement of Laser Trapping in a short period since the project’s inception was due to the project’s team being composed of researchers from various specialized fields who regularly discussed their respective research topics. This also demonstrates that Prof. Masuhara was an excellent mentor in nurturing young researchers. Based on this successful experience, I believe that young researchers and students should actively engage in discussions with researchers from different fields, absorb various knowledge, and create new research ideas beyond their own specializations. We introduced pulsed laser light coaxially with the trapping laser light into the optical microscope used for Laser Trapping. We reported various research findings in academic journals, including creating holes in micrometer-sized polymer particles trapped by Laser Trapping, bonding multiple particles with light to form structures, and rotating them. However, we were unable to control photochemical reactions using radiation pressure as initially intended. Before the project ended in 1993, Prof. Masuhara introduced me to Prof. Tsutomu Araki of the Department of Mechanical Engineering at Tokushima University. Prof. Araki subsequently hired me as an associate professor. As a chemist, I was somewhat hesitant to become an associate professor in the Department of Mechanical Engineering. At that time, microchemistry and nanochemistry had not yet become established fields in Japan, and there were very few chemistry departments hiring researchers in these areas. However, research on micromachines was becoming a trending field in mechanical engineering, so I decided to become an associate professor in the Department of Mechanical Engineering. Upon my appointment, Prof. Araki told me to conduct any research I wanted freely, but to secure the necessary research funding on my own. I understood this as a suggestion to establish my independent laboratory. I still remember the mixed feelings of joy and tension I experienced. At Tokushima University, I chose the following two research topics: 1) controlling chemical reactions using radiation pressure and 2) three-dimensional processing using focused femtosecond pulsed lasers. About a year before moving to Tokushima University, I discovered that focusing a pulsed laser on the inside of a slide glass changed the refractive index near the focal point. I wanted to research this phenomenon. At the beginning of my tenure at Tokushima University, I continued the research on using single trapped microparticles as Whispering Gallery Mode (WGM) resonators, which I had studied in the Microphotoconversion Project. When I first joined Tokushima University, we had a Laser Trapping setup but no pulsed laser. With the significant help of Prof. Araki and Prof. Satake, we were able to introduce a picosecond pulsed laser into the lab in 1994. Setting up these laser systems and establishing the lab was greatly supported by Dr. Toshimasa Takahashi, who was a student at the time and the first to earn a Ph.D. in my lab, and Dr. Masufumi Miwa, who is now an associate professor at Tokushima University. In 1995, I was promoted to full Professor at Tokushima University. In 1996, I became a member of the Satellite Venture Business Laboratory (SVBL) established at Tokushima University. As part of this initiative, we introduced a femtosecond laser system equipped with a regenerative amplifier. Additionally, Dr. Hong-Bo Sun from China joined our lab as a postdoctoral researcher. His ideas were innovative, and he worked diligently on research topics, producing numerous excellent research results. One such study focused on the creation of three-dimensional photonic crystals using two-photon processing of UV-curable resin with a near-infrared focused femtosecond laser. This research (1) has been cited over 500 times, making it my most cited paper. He is currently a full Professor at Tsinghua University in China and one of the most successful researchers who have been part of my lab. Afterward, Dr. Shigeki Matsuo from the Institute for Molecular Science in Japan joined our lab as an assistant professor, and Dr. Saulius Juodkazis from Lithuania joined as a postdoctoral researcher. Dr. Vygantas Mizeikis and Dr. Andrius Marcinkevicius from Lithuania, as well as Dr. Akira Yamaguchi from Tohoku University, joined our lab as postdoctoral researchers. Through the efforts of these researchers and students, we achieved many research results related to research topic 2. For the control of chemical reactions using radiation pressure (research topic 1), we synthesized microrods of poly(N-isopropylacrylamide) gel, which undergoes volume phase transition around 38 °C. We found that applying radiation pressure induced volume phase transition at temperatures more than 10 °C lower than the conventional transition temperature. We believe this occurs because the radiation pressure disrupts the molecular fluctuations, leading to a volume phase transition at a lower temperature. (2) However, we were unable to control (photo)chemical reactions themselves using radiation pressure, so we decided to suspend this research topic. The resolution of multiphoton processing with focused femtosecond lasers can achieve sizes below the wavelength, but significantly improving the resolution is challenging. To achieve further improvements in processing resolution, I realized that it would be necessary to explore entirely different ideas for photoprocessing methods. I then conceived the idea that if multiphoton processing using “quantum correlated photons”, which are utilized in quantum information communication, could be realized, it might improve processing resolution. However, I was not certain about this idea, so I discussed the potential use of quantum correlated photons in processing with Dr. Keiji Sasaki, who at that time had become a full professor at the Research Institute for Electronic Science at Hokkaido University and was also conducting research on quantum information. We consolidated this idea and proposed it in 2001 under the title “Development of Nanofabrication Technology by Entangled Photon Beams” to the Core Research for Evolutional Science and Technology (CREST) program of JST. The proposal was accepted after passing the document review and interview. The research period for this project was five years, during which we acquired necessary equipment and hired postdoctoral researchers. In 2003, during the CREST research period, I moved from Tokushima University to the Research Institute for Electronic Science at Hokkaido University as a full professor. Alongside the CREST research theme, this move to Hokkaido University provided me with a strong desire to construct reaction fields that interact strongly with weak light, such as sunlight, and induce specific photochemical reactions. At the Research Institute for Electronic Science, in addition to my research, I was involved in the design of the clean room for the newly established Nanotechnology Research Center, selecting electron beam lithography equipment for the center and maintaining the environment for the stable operation of the equipment. From 2006 to 2009, I served as the Head of the Nanotechnology Research Center. In 2007, the center was selected as one of the core centers for the Nanotechnology Network Project promoted by the Ministry of Education, Culture, Sports, Science and Technology (MEXT). I worked to introduce many nanotechnology-related equipment needed by researchers inside and outside Hokkaido University and to share them. From 2009 to 2013, I served as the director of the Research Institute for Electronic Science, and I actively promoted collaboration with departments related to nanotechnology research within Hokkaido University, centered around the Nanotechnology Research Center. Additionally, I participated in the Nanotechnology Platform Project, which MEXT initiated in 2013, allowing us to enhance our nanotechnology-related equipment, including electron beam lithography systems that enable high processing resolution and high throughput and time-resolved photoemission electron microscopy (time-resolved PEEM). During this period, we also introduced two aberration-corrected electron microscopes, which Hokkaido University lacked at the time. One was installed at the Research Institute for Electronic Science, and the other was placed in the Faculty of Engineering, where there were many electron microscope users. Regarding the research conducted under the CREST program, generating quantum correlated photons at high densities with the light sources available at that time was difficult, and we did not achieve material processing. However, the group of Professor Sasaki, a team member, verified that the interference fringes of quantum correlated photons would be half the wavelength, confirming our idea’s validity. I began to consider various designs for reaction fields that could interact strongly with light and efficiently induce photochemical reactions using weak light. The small absorption cross-section of typical molecules and their extremely weak interaction with light is usually not a concern when performing bulk photochemical reactions by irradiating solutions in test tubes with light from conventional light sources such as mercury lamps. However, to efficiently induce photochemical reactions by allowing molecules to effectively absorb weak light, it is essential to develop methodologies for localizing photons in nanometer-sized spatial regions, matching the size of the molecules. To localize light, photonic crystals or localized surface plasmon resonance (LSPR) exhibited in nanoparticles of gold or silver are effective. I decided to pursue research on reaction fields using LSPR, which can reduce the mode volume to the size of molecules. This was an entirely new and challenging research topic for me, but Dr. Kosei Ueno, who joined my lab as a postdoctoral researcher in 2004 and is now a full professor in the Department of Chemistry at Hokkaido University, agreed to this research project and energetically advanced the research. He designed reaction fields with significant near-field enhancement using FDTD simulations and fabricated the gold nanostructures based on these designs using techniques such as electron beam lithography. He conducted studies on multiphoton reactions and surface-enhanced Raman scattering (SERS). His strong determination to create a new academic field and his dedicated efforts led to our notable publications on LSPR. (3−5) Additionally, Dr. Yoshiaki Nishijima, who became a postdoctoral researcher after obtaining his Ph.D. in my lab (currently an associate professor at Yokohama National University), used electron beam lithography to fabricate plasmonic electrodes by placing gold nanostructures on single-crystal titanium dioxide. He was the first to observe the generation of photocurrent using water as an electron source and the accompanying production of oxygen. (6,7) These papers have been highly cited, and using this research as a starting point, we further advanced our studies on decomposing water using visible light with LSPR. Moreover, Dr. Xu Shi, who was a doctoral student in my lab at the time (currently an associate professor at the Creative Research Institution of Hokkaido University), successfully enhanced electron injection efficiency by selecting the thickness of thin-film titanium oxide electrodes loaded with gold nanoparticles to produce constructive interference at the LSPR wavelength of the incident light. (8) This research led to the creation of electrodes with strong coupling that combine thin-film titanium oxide electrodes with Fabry-Pérot nanocavity functionality and LSPR, achieving a significant enhancement in photoelectric conversion efficiency. (9) Mr. Yoshiki Suganami, a doctoral student, expanded this research on strong coupling electrodes. By using gold–silver alloy nanoparticles instead of gold nanoparticles, he found that the quantum yield of photocurrent generation using water as an electron source increased to 2.4 times that of gold nanoparticles. This was due to the ultrastrong coupling with larger splitting energy. (10) Additionally, Dr. Yuqing Zhong, who was a doctoral student in my lab at the time, developed a new system that generates oxygen and hydrogen from different sides of single-crystal strontium titanate by loading gold nanoparticles on one side and platinum on the other. (11) Furthermore, Dr. Tomoya Oshikiri, who was an Assistant Professor in my lab at the time (currently an Associate Professor at the Institute of Multidisciplinary Research for Advanced Materials, Tohoku University), undertook the synthesis of ammonia using water as an electron source with plasmonic electrodes. By devising the cathode, he succeeded in selectively synthesizing ammonia. (12,13) He also elucidated the detailed mechanism. (14) Dr. Oshikiri advanced the creation of strong coupling cathodes using nickel oxide, a p-type semiconductor, and succeeded in significantly surpassing the hydrogen generation efficiency of conventional plasmonic cathodes. (15) From the time I began research on the photodecomposition of water using LSPR, I believed it was necessary to understand the initial processes immediately after LSPR excitation for enhancing efficiency. Dr. Quan Sun, who was a postdoctoral researcher in my lab and later became an Assistant Professor (currently deputy director at Yangtze Delta Institute of Optoelectronics, Peking University), has energetically worked on the maintenance and improvement of time-resolved PEEM since 2012. We received significant support from Prof. Atsushi Kubo of the Department of Physics at Tsukuba University, who has extensive knowledge of time-resolved PEEM. Using PEEM, we were able to obtain information on the spatial distribution of the near field, near-field spectra, and dephasing times. Dr. Sun advanced the research on time-resolved PEEM with Dr. Han Yu, who was a doctoral student at the time, and Dr. Jinghuan Yang and Dr. Yaolong Li, who were visiting researchers from Peking University. Through this research, we discovered important insights, such as Fano resonance between LSPRs, strong coupling between LSPRs, and the ability to control the dephasing time of LSPR through strong coupling with propagating plasmons. Measurements using PEEM have also made it possible to quantitatively discuss plasmonic reaction fields. (16−20) In addition to these papers, time-resolved PEEM has significantly contributed to our lab’s research. Additionally, femtosecond time-resolved absorption measurements have played an important role in evaluating the electron injection efficiency from gold nanoparticles to the conduction band of titanium dioxide. The electrodes with strong coupling between LSPR and optical nanocavities exhibit an internal quantum yield for photocurrent generation using water as an electron source, which is approximately 1.5 times higher than that of conventional plasmonic electrodes. Mr. Yen-En Liu, a current doctoral student, used electron beam lithography to fabricate strong coupling electrodes with varying number densities of gold nanodisks per unit area. He found that the quantum yield of electron injection from gold nanodisks to titanium dioxide increased with the number density. This suggested that the enhancement of the quantum yield is due to the presence of quantum coherence between multiple LSPRs through the optical nanocavity. This research is the result of a collaborative effort with Prof. Hajime Ishihara of the Department of Materials Engineering Science at Osaka University and Prof. Keiji Sasaki of the Research Institute for Electronic Science at Hokkaido University. (21) Furthermore, Mr. En Cao, a current doctoral student, clarified that the quantum yield of electron injection into the titanium dioxide under strong coupling conditions depends on the thickness of the titanium metal layer, which is the adhesion layer between the gold nanodisks and titanium dioxide, and that the quantum yield reaches its maximum when the titanium metal layer is 5 nm thick. We concluded that this is due to the excitation of d-band electrons in the titanium metal layer by the near-field induced on the surface of the gold nanodisks, generating high-energy hot electrons that can be more easily injected into the titanium dioxide. (22) Additionally, Mr. Yoshiki Suganami, a doctoral student in my lab, successfully applied the quantum coherence of ultrastrong coupling electrodes to SERS, obtaining high-sensitivity and spatially uniform SERS signals. Currently, I have been awarded the research grant I applied for, and since 2023, I have been conducting research to elucidate the mechanism of quantum yield enhancement through quantum coherence. In January 2024, I moved to the Research Institute for Interdisciplinary Sciences at Okayama University as a specially appointed professor, where I am conducting research in a new environment. The existence of quantum coherence in natural photosynthesis has been discussed through various ultrafast measurements and theoretical calculations. It may become a new factor in enhancing quantum yield in artificial photosynthesis. For the time being, I want to continue enjoying the research on “how God plays dice with quantum coherence”. Throughout my career, I have been captivated by photochemistry and photonics, and I have pursued my research with free and unrestricted ideas. I would like to express my heartfelt gratitude to the staff and students of my lab and to all my collaborators for making this research possible. I also want to thank Ms. Saeko Endo (née Hase), my secretary at Tokushima University, and Ms. Yumiko Yamaguchi, my current secretary at Okayama University and Hokkaido University, for handling all the administrative work in the lab. Their support has allowed me to focus on my research. Due to limited space, I could not mention the names of everyone involved in my research, but I would like to extend my gratitude to all of you. In closing, I would like to express my deep gratitude to my long-time friends who organized this Festschrift and served as guest editors: Prof. Ueno (Hokkaido University), Prof. Hong-Bo Sun (Tsinghua University), Prof. Paul Mulvaney (University of Melbourne), Prof. Stephan Link (University of Illinois Urbana–Champaign), and Prof. Johan Hofkens (KU Leuven). Furthermore, I extend my thanks to all my friends who contributed articles to this special issue. The friendships and mutual respect we have developed through our scientific endeavors, while being excited by each other’s discoveries and sharing those thrilling moments, are invaluable and irreplaceable. I hope these bonds will last forever. Finally, I would also like to express my deep gratitude to my wife Sayoko and our three children Tomoyo, Takahiro, and Momoko. My gratitude also extends to my daughter-in-law Asuka, Takahiro’s wife; my son-in-law Takaki, husband of Momoko (née Misawa, now Kato)”; and my first granddaughter Hana, the daughter of Momoko and Takaki. All of them have always been a source of support for me. The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.jpcc.4c05539. List of colleagues of Hiroaki Misawa (PDF) Curriculum vitae of Hiroaki Misawa (PDF) Publications of Hiroaki Misawa (PDF) The Trail of Challenges: Autobiographical Notes of Hiroaki Misawa 4 views 0 shares 0 downloads Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html. Views expressed in this editorial are those of the author and not necessarily the views of the ACS. This article references 22 other publications. This article has not yet been cited by other publications.