The Photopolymer Science and Technology Award No. 201100, the Outstanding Achievement Award 2020 was presented to Dr. Masao Tomikawa for his outstanding achievements in photo definable polyimides science and technology including the photo reaction mechanism of the Ionic-bonded-photosensitive polyimide, and the pioneering development of positive photo definable polyimide by partial esterification of poly(amic acid) for semiconductor stress buffer and for the organic light emitting diode (OLED) displays. In addition, he contributed the Cu compatibility study for the improvement to long time reliability of the polyimide and Cu interconnection.

The Photopolymer Science and Technology Award No. 202100, the Best Paper Award 2020, was presented to Yukinori Yamauchi^a, Naoki Doi^b, Shin-ichi Kondo^b, Yasushi Sasai^b, and Masayuki Kuzuya^c (^aMatsuyama University, ^bGifu Pharmaceutical University, ^cChubu Gakuin University) for their outstanding contribution published in Journal of Photopolymer Science and Technology, 32, (2019) 505-510, entitled “Development of A Novel Polymeric Prodrug Synthesized Using Plasma-induced Radicals of Polycrystalline Carbohydrates”.

The Photopolymer Science and Technology Award No. 202200, the Best Paper Award 2020, was presented to Kevin Wylie, Yuta Nabae, and Teruaki Hayakawa (Department of Materials Science and Technology, Tokyo Institute of Technology) for their outstanding contribution published in Journal of Photopolymer Science and Technology, 32, (2019) 395-400, entitled “Altering the Self-Assembly of Poly(styrene-block-methyl methacrylate) by Introduction of Strongly Dissimilar Molecules at the Block Interface”.

Photopolymer materials have been widely used in some advanced industries owing to their practicability, low-cost, and ecological advantage. One of the key components of these photopolymer materials is a molecule that releases acidic species upon a photon trigger (known as Photo-acid generators, PAGs). Recently, PAGs have attracted much attention with novel technologies such as near-infrared CTP imaging, 3D printing, and EUV lithography, and are required to have various functions and sophisticated features. This review article summarizes recent advances in the molecular design and function of PAGs, which are required to respond to the increasing applications of the photopolymer materials in advanced industries.

The aim of this study was to investigate the effect of different light curing units and light modes on the amount of residual monomers eluted from different resin-based composites. Initially, a total of 96 composite samples (N=24/group) were prepared from 3 bulk-fill composites with different characteristics and a nanohybrid composite using a mold (diameter: 5 mm, height: 4 mm). Then, each group was divided into 4 subgroups (n=6). Polymerization of the resin composites was performed using a halogen light source (Hilux 250), a 2nd generation LED device (Elipar DeepCure –S) and a 3rd generation LED device (Valo, standard and ultra modes). Samples were stored in 75% ethanol solution and residual monomers eluted in the solution were analyzed with HPLC after 1 day and 1 month. Monomer concentrations corresponding to the peak areas in chromatograms were calculated in ppm to obtain data for statistical analysis. The study data were analyzed using One Way ANOVA (p=0.05) and post-hoc Tukey tests. The type of the light-curing unit significantly affected the amount of residual monomer released in all composite groups (p<0.05). Except the Fill-Up composite groups, the least monomer elution was detected in the groups cured with Elipar DeepCure-S. Residual monomer amounts detected after 30 days were significantly increased in comparison to those eluted after 1 day in all groups. In light of these findings, it was concluded that the light curing units might have an impact on the monomer elution from different composites.

Gigaphoton Inc. has been developing a CO₂-Sn-LPP (LPP: Laser Produced Plasma) extreme ultraviolet (EUV) light source system for high-volume manufacturing (HVM) semiconductor lithography. Key components of the source include a high-power CO₂ laser with 15 ns pulse duration and 100 kHz repetition frequency, a solid-state pre-pulse laser with 10 ps pulse duration, a high speed Sn-droplet generator, a high-speed and high accuracy shooting system, and a magnetic field debris mitigation system. To achieve an in-band power of 330 W with long collector mirror lifetime and stable output, we improved the performance of key system components. We achieved an in-band power of 250 W under DC operation and demonstrated a power scalability up to 330 W. This paper presents the key technology update of our EUV light source.

We examined the synthesis, physical properties, and resist properties of the various polymers and an oligomer containing fixed hole derived from calixarenes. By the condensation reaction of p-t-butylcalix[n]arene (n = 4 and 8) with 1,4-dichloro-2-oxabutane (DCB) and 2,5-dibromoacetyloxy-2,5-dimethylhexane (DBH), the soluble polymers poly(BCA[8]-co-DCB), poly(BCA[8]-co-DBH), and poly(BCA[4]-co-DCB), and an oligomer BCA[4]-DBH were obtained. They have good physical properties (solubility, film-forming ability, high thermal stability), excellent thickness loss property, and good acid-deprotection reactivity upon ultra-violet (UV) irradiation. The resist-sensitivity in an extreme ultraviolet (EUV) exposure tool indicated that poly(BCA[8]-co-DBH) and BCA[4]- DBH were good candidate to offer higher resolution resist pattern, i.e., E₀ = 5.0 mJ/cm² [poly(BCA[8]-co-DBH] and 0.8 mJ/cm² (BCA[4]-DBH).

A stochastic simulation of the pattern formation process for negative-type chemically amplified resists in extreme ultraviolet (EUV) lithography has been performed. The initial structures of the resist polymers are formed by randomly bonding monomers. The deposited energy distribution in the resist by EUV light exposure is calculated by Monte Carlo simulation of the photoelectron scattering. The activation of acid generators is introduced according to the deposited energy distribution. Acid diffusion and the polymer crosslinking reactions during the post-exposure bake (PEB) are then simulated. Development of the resist is modeled by removing the polymers with a polymerization degree below the threshold value from the resist. The effects of EUV light exposure and PEB conditions on the pattern shapes are investigated by the simulation.

A feasibility study of the focus monitoring method with sub-wavelength grating is computationally performed. Instead of non-180° phase shifter which is commonly used for focus monitors, sub-wavelength grating with depth of 180° phase shifter is adopted to produce effective non-180° phase shifting. The result shows that the 180° sub-wavelength grating successfully produces an asymmetric light intensity distribution on wafer with both on-axis and off-axis illuminations in a same manner as typical focus monitors with 90° phase shifter. This indicates that the sub-wavelength grating is a focus monitoring pattern which can be embedded on standard phase shift masks with 180° phase shifter contrary to commonly used phase shift focus monitors.

Photomechanical behaviors of the films of 4-[bis(9,9-dimethylfluoren-2-yl)amino]-4'-cyanoazobenzene (CN-BFlAB) and 4-[bis(9,9-dimethylfluoren-2-yl)amino]-4'-nitroazobenzene (NO₂-BFlAB) fabricated on the surface of agar gel have been investigated. Two-stage process including striped pattern formation and the subsequent band-like structure formation was observed upon irradiation with a linearly polarized laser beam with 488 nm, being similar to the result for the film of the parent compound, 4-[bis(9,9-dimethylfluoren-2-yl)amino]azobenzene (BFlAB). The rate of such structural change for CN-BFlAB was almost similar to or somewhat slower than that for BFlAB film. On the other hand, the rate for NO₂-BFlAB was considerably slower than those for BFlAB and CN-BFlAB. The results suggested that the photochromic reactivity of the molecule in the amorphous film plays a role for the present photomechanical behaviors.

Fluorescence, color, and morphological changes of fluorescent nanostructures consisting of azobenzene-containing chromophores were investigated under successive visible light irradiation. Compared with spheres composed of a chromophore showing sufficient photoisomerization, fluorescent nanofibers assembled from a molecule showing a very small amount of photoisomerization had a slow response to light. Successive visible light irradiation of the nanofibers led to changes in fluorescence intensity and color, whereas the one-dimensional morphology was hardly affected. UV-visible absorption spectroscopy, optical microscopy (OM), scanning electron microscopy (SEM), and fluorescence optical microscopy (FOM) were employed to confirm the light-responsive properties. Our observations suggest that sufficient photoisomerization plays a key role in realizing fast and efficient light response of self-assembled structures.

Liquid crystalline polymers (LCPs) have attracted much attention because of their macroscopic deformation to external stimuli such as heat or light-irradiation. Among them, thermal responsible polymers, in which their macroscopic structures are controlled by heat treatment, are one of the most attractive materials. Although the thermal responsive materials by thermal phase transition were developed in wide for the application to the electronic devices and sensors, few examples have been applied to practical uses because of their high transition temperatures. In this paper, the development of LCPs with low deformation temperatures was investigated aiming for the application to functional fibers responding to body temperature. The phase transition temperature was found to depend on the content of crosslinking unit, and the film deformation was controlled by the one-side photo-irradiation to change the degree of crosslinking between two sides.

Liquid crystals (LCs) are the innovative materials that can control their molecular orientation using an optical field with a laser beam. However, the molecular orientation has been explored only by a polarized laser beam. In this study, we report the molecular reorientation of oligothiophene-doped LCs by an irradiation with a focused depolarized laser beam that has a spatial polarization pattern. Two self-diffraction rings occurred by nonlinear molecular reorientation induced by the irradiation with the focused depolarized laser beam. The threshold intensities measured by the focused depolarized laser beam were two times higher than that of the linearly polarized laser beam.

Understanding the three-dimensional deformation of soft materials is needed for development of soft robots and flexible devices. In particular, “strain” is an important indicator reflecting the deformation of materials as it could be measured accurately. Although electrical sensors have been commonly used for investigating strain, local internal strain analysis remains a challenge due to difficulty of external connections. In this work, local internal strain in polydimethylsiloxane (PDMS) induced by stretching is quantitatively measured via the selective reflection of a cholesteric liquid crystal (CLC) sensor. The results reveal that the out-of-plane strain in the stretched PDMS films occurs by approximately 17% at tensile strain of 50%. Out-of-plane strains show the same value in near-surface and center of PDMS films. Understanding of the deformation behavior of soft materials such as PDMS could accelerate the development of soft robots and flexible devices.

Photo-irradiation responsible resins have attracted intense interest in research area of photolithographic technology because of their application for semiconductors and organic EL displays. Although photosensitive resins including photoacid generators, which emit acidic moieties by photo-irradiation, have been developed, their utilization are limited because of corrosion of metals and resins due to residual acid. On the other hand, for the fabrication of materials available in long-term, resins containing photobase generators are focused because of prevention of the corrosions. However, there is no example of photobase generator in which strong bases are prepared. For the development of photobase generators, we purposed the investigation of basicity control based on the complexation of photo-isomerization of a diarylethene derivative (BDAE) having boronate ring and 1,8-diazabicyclo[5.4.0]-7-undecene (DBU). Although decomposed products were obtained after UV-irradiation to an open-formed isomer of BDAE probably because of oxidative reaction, it was found that the basicity of a solution of a mixture of BDAE and DBU decreased due to complexation of DBU and phenylboronic acid produced by the decomposition of BDAE.

Acetylenes are the first monomer to polymerize by the energy deposited by ionizing radiations. Herein we report an extremely efficient solid state polymerization of ethynyl-substituted 9,9'-spirobi[9H-fluorene]s (SBFs) via a unique nano-fabrication technique referred to as Single Particle Trigged Linear Polymerization (STLiP) initiated by high energy charged particles. The resulted nanowires of polymerized/crosslinked SBFs show a gradual transformation from flexible to rigid rod-like with an increase in the reaction efficiency mediated by the ethynyl substitution. The overall efficiency of initiation/propagation/crosslinking reactions is remarkably high even in comparison with the primary yield of ionization events in the radiation chemical processes, marking up to G > 80 (100 eV)^－1, which is suggestive of efficient chain reactions in the propagation steps. The present results demonstrate efficient solid-state polymerization reactions, which are neither topochemical polymerization reactions nor acid/base catalyzed reactions, expand the versatility of STLiP technique to fabricate 1D nanomaterials based on a variety of organic compounds.

Inverted-type polymer solar cells with semiconducting polymers based on PTzNTz have attracted attention because of its high power conversion efficiency (PCE) and thermal stability. In recent years, the PCE of the polymer solar cells has been remarkably improved. However, the effect of these hole transport layers (HTLs) on PTzNTz solar cells have not yet been completely clarified. Here, we report operand electron spin resonance (ESR) spectroscopy of the PTzNTz layered samples to investigate the deterioration mechanism of the PTzNTz solar cells at a molecular level. We have observed monotonic increases in the ESR intensity of the PTzNTz layered samples, where the increases in the ESR intensity of PTzNTz active layers with WO_x HTL are smaller than those with MoO_x HTL. The present results would be useful to develop further highly efficient and durable polymer solar cells.

To improve the efficiency of organic photovoltaics (OPVs), the trapping of incident light with surface nanostructures, such as moth eye structures, is a highly useful strategy for enhancing absorption in the photoactive layer. Nanoimprint lithography is a widely used technique to produce large-area nanostructures cost effectively. However, the moth eye texture fabricated by the nanoimprint process necessarily contains a spatial clearance between adjacent cones, which could degrade the antireflective property of the textured surface. In this study, we perform optical simulations for the OPVs with moth eye coating to explore the effects of the spatial clearance in the moth eye array as well as its geometric pattern on the photocurrent generation. We show that the photocurrent level decreases significantly and superlinearly with increases in the size of the spatial clearance in moth eye, suggesting the importance of sufficiently narrowing the clearance size. Furthermore, we experimentally measure the performance of the OPV cell incorporated with the moth eye structure having a near-optimal geometric pattern with reduced clearance size to verify the simulation results.

In vivid structural coloration in the natural world, melanin plays an important role. For example, the coloring of peacock feathers is based on the periodic microstructure formed by melanin granules. Melanin, which has the ability to absorb light, not only builds a microstructure but also absorbs scattered light to produce highly visible structural colors. We focus on polydopamine as a mimic of melanin and the production of structural color materials from a biomimetic perspective. This review paper focuses on our recent findings on structural color materials using artificial melanin particles made of polydopamine and describes the research trends.

Imaging utilizing the near-infrared (NIR) light has attracted numerous attention due to the possibility in the deep tissue penetration as it can overcome the light scattering and absorption of tissue components. The ultraviolet (UV) unlikely penetrates the skin, while the visible (VIS) light can be scattered or absorbed by tissue components. This penetration likely improves as the wavelength shifts beyond 1000 nm region (also called NIR-II). Fat tissues are ascribed to the scattering of UV or VIS, while others such as water, melanin, hemoglobin are greatly attributed to absorbing light. Using NIR over 1000 nm (OTN-NIR) is currently considered as a critical approach for real-time dynamical visualization of the structure and functional features of tissues anatomically with refrained effects of fatty scattering and water absorption. However, the attempts to image anatomical structure by OTN-NIR is laborious and time-consuming. Then, for facile human applying, magnetic resonance imaging (MRI) is used as a guiding technique to localize the sites of interest. MRI is considered the most beneficial imaging technique without ionizing radiation which provides images with high resolution, preeminent tissue contrast. MRI also can visualize a large volume such as the human body to the few millimeter objects with great signal-to-noise ratio as well as contrast-to-noise ratio. This review highlights the design of imaging probe for multimodal NIR/MR imaging, including the potential applications.

Tissue adhesives are greatly employed as surgical sealants for wound-healing patches and hemostatic dressing. However, achieving strong adhesion of wet tissues is still challenging because the bonding strength of biomedical adhesives is generally weakened by physiological fluids due to their high dielectric and ionic strengths. To overcome this challenge, bioinspired approaches have been adopted to enhance the wet adhesion of biocompatible polymers. Here, we synthesized a series of chitosan functionalized with bioinspired phenolic groups, i.e., phenol, catechol, and gallol, with similar modification rates. The bonding and sealing strengths of wet tissues by this functionalized chitosan were compared under similar conditions. We observed that the gallol group was the most effective in enhancing the tissue adhesion property of chitosan.

The field of self-reporting materials is gaining increased attention recently. These materials can convey the forces applied to them without the need to integrate external devices. The ability to report strain exerted onto polymers is especially important, as it might give indication of high levels of force that may damage the material. These materials could also be applied to in-dwelling medical devices such as artificial tendons and heart valves. In this work, we designed a self-reporting system based on energy transfer (ET) between rare earth-doped ceramic nanoparticles (RED-CNPs). When external strain and heat are applied, the efficiency of the ET changes, resulting in changes in the emission spectra. We chose particles that are excited by 808 nm radiation and emit in the over-thousand-nanometer near infrared, since this range offers high penetration to biological tissues. Nanoparticles (NPs) were synthesized using the thermal decomposition method and then extensively characterized. X- ray diffraction analysis revealed that the doped NaYF₄ crystals are in the β-phase, while inductively coupled plasma emission spectrometry demonstrated the existence of two types of NPs: NaYF₄: Nd³⁺, Yb³⁺ and NaYF₄: Er³⁺. The absorption and emission of the particles showed no ET between the two kinds of NPs when simply mixed together. In order to reduce the interparticle distance and allow ET, RED-CNPs were coated with polydopamine (PDA) and then conjugated with a polymeric linker. Scanning electron microscopy, dynamic light scattering and absorption analysis showed the successful coating with PDA and the creation of interconnected NP networks. Emission from the conjugated system showed evidence of ET, while changes in the emission lifetime of Yb as measured by time-gated imaging further suggested ET between Yb and Er. Finally, the conjugated system was integrated into poly(dimethylsiloxane) and it was shown that as strain or heat are exerted onto it, the emission spectra under 808 nm excitation is varied.