研究者詳細 - 田中　啓文

論文 - 田中　啓文

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7-Methylquinolinium Iodobismuthate Memristor: Exploring Plasticity and Memristive Properties for Digit Classification in Physical Reservoir Computing 査読有り国際誌

Abdi G., Karacali A., Zaman A.S.K., Gryl M., Sławek A., Szkudlarek A., Tanaka H., Szaciłowski K.

Advanced Electronic Materials 2025年01月

記述言語：英語掲載種別：研究論文（学術雑誌）

This study explores 7-methylquinolinium halobismuthates (I, Br, and Cl) with a focus on: (1) the impact of halide composition on their structural and semiconducting properties, and (2) their memristive behavior and plasticity for neuromorphic and reservoir computing. Crystallographic analysis reveals that halide substitution leads to the formation of low-dimensional bismuth-based frameworks. Optical bandgaps, measured via diffuse reflectance spectroscopy, correlate well with density functional theory calculations. Due to solubility constraints, only bismuth iodide complexes are integrated into electronic devices. Current–voltage measurements reveal pinched hysteresis loops, indicative of memristive behavior. Conductivity versus temperature analysis suggests both ionic and electronic conduction pathways. Given their ability to function as synaptic analogs, further tests on transient conductance (potentiation–depression) and spike-time-dependent plasticity are performed. The observed nonlinearity and fading memory characteristics highlight their potential for physical reservoir computing. To evaluate system-level behavior, a device with 16 gold electrodes (1 input, 15 outputs) is fabricated on a silicon substrate coated with the target compound. The device is assessed through benchmark tasks including waveform generation, NARMA-2, memory capacity, and noise response under DC/AC signals. Finally, the system demonstrates 82.26% accuracy in MNIST digit classification and 82% accuracy in spoken digit “2” recognition across six different speakers.

DOI： 10.1002/aelm.202500049

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=105011273025&origin=inward

A label-free liquid–crystal-droplet based optical sensing platform for the detection of Neisseria gonorrhoeae 査読有り国際誌

Kumar R., Sumana G., Sood S., Pandey S.S., Tanaka H., Rajesh

Journal of Molecular Liquids 415 2024年12月

記述言語：英語掲載種別：研究論文（学術雑誌）

An oligonucleotide decorated liquid crystal (LC) droplet platform was studied for the detection of sexually transmitted disease (STD) caused by bacterium Neisseria gonorrhoeae. Homeotropically aligned nematic LC droplets were patterned on the silane modified glass plates and were utilized as sensing platform using an oligonucleotide probe (ssDNAprobe) sequence specific for N. gonorrhoeae. The developed LC-droplets platform could detect the synthetic complementary DNA (ssDNAtarget) and genomic DNA of N. gonorrhoeae with dark polarizing optical microscopy (POM) images of homeotropic LC alignment up to the lowest detectable limit of 10 pM and 50 pM, respectively. The DNA hybridization event was further monitored by zeta potential (ζ) measurement of LC droplets using dynamic light scattering technique to understand the sensing mechanism of ssDNAprobe hybridization with ssDNAtarget. The zeta potential response showed a linear relationship to ssDNAtarget over a concentration range of 10 pM to 100 nM and a limit of detection of 10 pM, which is nearly close to limit of detection (LOD) obtained with LC optical response measurement. These results indicated a similar kind of sensing mechanism with LC-droplets in both aqueous medium as well as on a glass substrate. The specificity of the LC droplet platform was investigated with various levels of mismatched synthetic DNA sequences and non-specific genomic DNA isolated from other bacteria. The homeotropic LC optical response with genomic DNA of N. gonorrhoeae in the presence of potential interferents showed that LC-droplet platform is highly selective for N. gonorrhoeae, suggesting a simple, rapid and reliable label-free detection platform.

DOI： 10.1016/j.molliq.2024.126410

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85208033794&origin=inward

固体電解質を用いた物理リザバー査読有り

長谷川剛, 田中啓文

表面と真空 ( 公益社団法人日本表面真空学会 ) 67 ( 11 ) 521 - 526 2024年11月

担当区分：最終著者記述言語：日本語掲載種別：研究論文（学術雑誌）

<p>A solid electrolyte-based physical reservoir utilizes ions’ diffusion and their redox reactions to achieve nonlinear transformation of input and its short-term memorization. One of the major advantage in using a solid electrolyte is easy fabrication of a recurrent neural network with a large number of ‘nodes’, which enables various functions unique to the material-based physical reservoir such as in-sensor computing.</p>

DOI： 10.1380/vss.67.521

その他リンク： https://www.jstage.jst.go.jp/article/vss/67/11/67_20181362/_pdf

導電性高分子ネットワークを用いたマテリアルリザバー演算査読有り

宇佐美雄生, 琴岡匠, 松本卓也, 田中啓文

表面と真空 ( 公益社団法人日本表面真空学会 ) 67 ( 11 ) 527 - 532 2024年11月

担当区分：最終著者,　責任著者記述言語：日本語掲載種別：研究論文（学術雑誌）

<p>Artificial intelligence (AI) has rapidly advanced and is being utilized across a wide range of fields by developing artificial neural network (ANN). However, constructing large-scale ANNs requires significant power consumption. In the field of materials and device engineering, “physical reservoir computing (physical RC)” is gaining attention to perform ANN computations with low power consumption. Unlike traditional ANNs, physical RC leverages physical properties for computation, resulting in energy efficiency. Conductive polymers such as polyaniline are expected to exhibit excellent performance in in-materio physical reservoir computing (IMRC) due to their superior environmental stability and reversible doping behavior. This paper introduces about utilizing the mixed polaron-ion conductivity of sulfonated polyaniline (SPAN), evaluating changes in electrical properties with humidity adjustments, and exploring its potential application in IMRC by investigating the correlation between the electrical properties and computational ability.</p>

DOI： 10.1380/vss.67.527

その他リンク： http://id.ndl.go.jp/bib/033827434

ナノマテリアルランダムネットワークを利用した物理リザバー演算素子とそのセンシング応用招待有り査読有り

田中啓文, アズハリサマン, バナジーディープ, 君塚紘喜, 田中悠一朗, 宇佐美雄生

表面と真空 ( 公益社団法人日本表面真空学会 ) 67 ( 9 ) 428 - 432 2024年09月

担当区分：筆頭著者,　責任著者記述言語：日本語掲載種別：研究論文（学術雑誌）

<p>The rapid advancement of software-based deep learning has led to a surge in AI applications, yet hardware limitations in silicon CMOS technology hinder performance. Consequently, interest is growing in hardware technologies and new materials for artificial neural networks (ANNs) and neuromorphic systems. Exploiting nanomaterials nonlinearity caused by spontaneous physical phenomena holds promise of reducing power consumption in AI hardware. Reservoir computing devices, derived from recurrent neural networks, play a crucial role, with material reservoir devices showcasing “material intelligence.” Tailored nanomaterials for reservoir devices hold potential for revolutionizing AI, especially in robotics. As research progresses, focusing on device functionalization and applications, recent findings underline the significance of integrating nanomaterials into AI hardware for enhanced computational capabilities and energy efficiency.</p>

DOI： 10.1380/vss.67.428

その他リンク： https://www.jstage.jst.go.jp/article/vss/67/9/67_20181334/_pdf

A new physical reservoir using the complex dynamics of electric fields in type-II superconductors containing pinning centers interacting with quantized magnetic flux lines 査読有り国際誌

Arita K., Ueda T., Otabe E.S., Usami Y., Tanaka H., Matsuno T.

Physica C: Superconductivity and its Applications 622 2024年07月

記述言語：英語掲載種別：研究論文（学術雑誌）

Reservoir computing, which takes advantage of physical phenomena with nonlinearities, is attracting a lot of attention. Therefore, it is expected to focus on superconductivity, a physical phenomenon with nonlinearities between the output electric field and the input current density. Compared to other physical phenomena used in reservoirs, it is considered that with superconductivity, the nonlinearity can easily be adjusted spatially by pin placement to produce dynamics suitable for reservoirs. The nonlinearity between the electric field generated by the motion of the quantized magnetic flux lines and the input current density was used to perform a reservoir computing task. Three waveform generation tasks, a NARMA2 task and a nonlinear-memory task were performed, and all tasks were generally successful. It was found that the electromagnetic phenomenon in superconductors can be used as a physical reservoir.

DOI： 10.1016/j.physc.2024.1354522

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85194199384&origin=inward

High-Density, Nonvolatile, Flexible Multilevel Organic Memristor Using Multilayered Polymer Semiconductors 査読有り国際誌

Sharma S., Pandey M., Nagamatsu S., Tanaka H., Takashima K., Nakamura M., Pandey S.S.

ACS Applied Materials and Interfaces 16 ( 17 ) 22282 - 22293 2024年05月

記述言語：英語掲載種別：研究論文（学術雑誌）

Nonvolatile organic memristors have emerged as promising candidates for next-generation electronics, emphasizing the need for vertical device fabrication to attain a high density. Herein, we present a comprehensive investigation of high-performance organic memristors, fabricated in crossbar architecture with PTB7/Al-AlOx-nanocluster/PTB7 embedded between Al electrodes. PTB7 films were fabricated using the Unidirectional Floating Film Transfer Method, enabling independent uniform film fabrication in the Layer-by-Layer (LbL) configuration without disturbing underlying films. We examined the charge transport mechanism of our memristors using the Hubbard model highlighting the role of Al-AlOx-nanoclusters in switching-on the devices, due to the accumulation of bipolarons in the semiconducting layer. By varying the number of LbL films in the device architecture, the resistance of resistive states was systematically altered, enabling the fabrication of novel multilevel memristors. These multilevel devices exhibited excellent performance metrics, including enhanced memory density, high on-off ratio (>108), remarkable memory retention (>105 s), high endurance (87 on-off cycles), and rapid switching (∼100 ns). Furthermore, flexible memristors were fabricated, demonstrating consistent performance even under bending conditions, with a radius of 2.78 mm for >104 bending cycles. This study not only demonstrates the fundamental understanding of charge transport in organic memristors but also introduces novel device architectures with significant implications for high-density flexible applications.

DOI： 10.1021/acsami.4c03111

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85191165281&origin=inward

Effect of nonlinearity induced by atomic switch in Ag/Ag<inf>2</inf>S nanoparticles on performance of in-materio reservoir computing 査読有り国際誌

Dang T.T., Srikimkaew O., Banerjee D., Azhari S., Usami Y., Tanaka H.

Applied Physics Letters 124 ( 9 ) 2024年02月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

A random network of Ag/Ag2S nanoparticles (NPs) was used as a physical system in reservoir computing (RC) because the network has nonlinear and dynamical characteristics. Ag/Ag2S NPs were synthesized by the modified Brust-Schiffrin method. Atomic switching among the NPs caused nonlinear dynamical behavior of the random network. The Fourier transform of output signals indicated that the generated harmonics were far higher with a larger amplitude of the input sine wave because the atomic switching occurred only at high bias voltages. Higher accuracy was achieved in the Boolean logic RC task because of the nonlinearity originating from switching. These findings suggest that nonlinearity plays a fundamental role in the design and implementation of RC devices.

DOI： 10.1063/5.0169067

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85186372242&origin=inward

Volatile and Nonvolatile Dual-Mode Switching Operations in an Ag-Ag<inf>2</inf>S Core-Shell Nanoparticle Atomic Switch Network 査読有り国際誌

Srikimkaew O., Ricci S., Porzani M., Dang T.T., Nakaoka Y., Usami Y., Ielmini D., Tanaka H.

Advanced Electronic Materials 10 ( 10 ) 2024年01月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

This paper proposes a nanoparticle-based atomic switch network memristive device, capable of both volatile and nonvolatile switching operations, which have not been previously reported for this material. The operational modes can be determined by altering the compliance current, demonstrating high stability over 100 cycles. Analysis of the conduction mechanism using I–V curves reveals switching characteristics consistent with space-charge-limited current conduction during the set process and ohmic behavior in the reset state. Furthermore, this study analyzes these dual-operational modes in devices with varying electrode spacings. The results indicate that a wider spacing necessitated a higher compliance current for the volatile-to-nonvolatile transition, underscoring the significance of interconnection. These findings facilitate the integration of neuron and synapse functions within a single atomic switch network device, thereby advancing neuromorphic systems.

DOI： 10.1002/aelm.202300709

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85197746392&origin=inward

Short-Term and Long-Term Memory Functionality of a Brain-Like Device Built from Nanoparticle Atomic Switch Networks 査読有り国際誌

Srikimkaew O., Azhari S., Banerjee D., Usami Y., Tanaka H.

Advanced Electronic Materials 10 ( 12 ) 2024年01月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

The synaptic plasticity of the Ag-Ag2S nanoparticle-based volatile memristor system is demonstrated. The nanoparticles self-assemble into a network with over 103 interconnected atomic switch interfaces. Short-term plasticity is identified by spontaneous conductance relaxation, attributed to the memristor's volatility. The conductance of the network is enhanced when a subsequent stimulus pulse arrives shortly after the previous one, analogous to the paired-pulse facilitation in biological synapses. Furthermore, repeated pulse stimulation is used to achieve the transition from short-term plasticity to long-term potentiation, a process related to learning and memory formation. Remarkably, the result reveals that the lifetime of long-term potentiation for 100-pulse stimulation is 40 min, indicating that the device can forget newly acquired information after prolonged storage, akin to human memories. The findings provide insight into the the learning and memory abilities of atomic switch network memristors, facilitating the development of hardware-implemented artificial neural networks.

DOI： 10.1002/aelm.202400360

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85203194268&origin=inward

Enhancing Optoelectronic Anisotropy in Highly Oriented Thin Films by Fluorine Substitution in Novel Semiconducting Polymers 査読有り国際誌

Sharma S., Desu M., Chen G.L., Tseng K.W., Gaurav K.V., Liu Z.Y., Cheng K.H., Pradhan S., Ranganathan P., Liu P.H., Chiu X.L., Tanaka H., Chen J.C., Chen C.T., Dai C.A., Wang L., Pandey S.S.

ACS Applied Materials and Interfaces 16 ( 38 ) 51229 - 51240 2024年01月

記述言語：英語掲載種別：研究論文（学術雑誌）

The recent past has witnessed remarkable progress in organic electronics, driven by the quest for flexible, lightweight, and cost-effective electronic devices. Semiconducting polymers (SCPs) have emerged as key materials in this field, offering unique electronic and optoelectronic properties along with mechanical flexibility. This study focuses on designing, synthesizing, and utilizing novel donor-acceptor (D-A) copolymer-based SCPs introducing a difluorothiophene moiety in the polymeric backbone. The importance of fluorine substitution for backbone planarity was verified by density functional theory calculations, comparing it with a nonfluorine substituted counterpart. Through the Unidirectional Floating Film Transfer Method (UFTM), we fabricated highly oriented thin films, resulting in increased optical anisotropy with dichroic ratios reaching 19.3 in PC20-FT thin films, one of the highest optical anisotropy observed for solution processable SCP thin films. X-ray diffraction and atomic force microscopy results validated the increase in the crystallinity and domain size with the increasing alkyl chain length. Finally, we elucidate these findings in the context of electrical applications by fabricating organic field-effect transistors revealing anisotropic charge transport achieving a promising mobility of 1.24 cm2V-1s-1 and mobility anisotropy of 39.5. This study offers insights into the design principles and performance optimization of SCP-based devices, paving the way for advancements in plastic electronics.

DOI： 10.1021/acsami.4c08566

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85204382304&origin=inward

Development in memristor-based spiking neural network 査読有り国際誌

Abdi Gisya, Karacali Ahmet, Tanaka Hirofumi

Nonlinear Theory and Its Applications, IEICE ( 一般社団法人電子情報通信学会 ) 15 ( 4 ) 811 - 823 2024年01月

担当区分：最終著者記述言語：英語掲載種別：研究論文（学術雑誌）

<p>The field of neuromorphic computing has experienced remarkable growth driven by the need to overcome the limitations of traditional von Neumann architecture in handling big data, IoT, and AI tasks. This paper provides an overview of recent advancements in brain-inspired computing, particularly focusing on the integration of various memristive materials, including metal oxides, perovskites, and 2D materials, into neuromorphic hardware. The evolution of artificial neural network (ANN) technology, ranging from perceptron to deep neural networks (DNNs) and spiking neural networks (SNNs), is discussed, emphasizing the potential of SNNs for energy-efficient hardware implementation. Challenges in integrating memristors, especially 2D material-based memristors, into SNNs are highlighted, along with recent developments in neuromorphic hardware utilizing memristors and complementary metal-oxide-semiconductor (CMOS) technology. Through simulations and experimental demonstrations, researchers have shown the feasibility of using memristors for implementing artificial neurons and synapses, paving the way for efficient and scalable neuromorphic computing systems.</p>

DOI： 10.1587/nolta.15.811

その他リンク： https://www.jstage.jst.go.jp/article/nolta/15/4/15_811/_pdf

Special Section on Recent Progress in Neuromorphic AI Hardware 国際誌

Tanaka Hirofumi

Nonlinear Theory and Its Applications, IEICE ( 一般社団法人電子情報通信学会 ) 15 ( 4 ) 784 - 784 2024年01月

Object recognition and grasping point detection using carbon nanotube - polydimethylsiloxane nanocomposite sensor 査読有り国際誌

Tokuno Shoshi, Kimizuka Kouki, Tanaka Yuichiro, Usami Yuki, Tanaka Hirofumi, Tamukoh Hakaru

Nonlinear Theory and Its Applications, IEICE ( 一般社団法人電子情報通信学会 ) 15 ( 4 ) 883 - 898 2024年01月

記述言語：英語掲載種別：研究論文（学術雑誌）

<p>This paper presents a system for processing tactile information using a carbon nanotube (CNT)-polydimethylsiloxane (PDMS) nanocomposite sensor designed for robotic applications. This study introduces an approach for recognizing objects and detecting optimal grasping points using tactile data from a sensor-equipped robotic hand. The sensor is expected to be more efficient than a computerized implementation using sensor dynamics directly in the computation. The experiments demonstrated the system's ability to classify nine types of objects with an accuracy of 83.56% and to discern two grasping points on four object types, achieving a 71.7% success rate.</p>

DOI： 10.1587/nolta.15.883

その他リンク： https://www.jstage.jst.go.jp/article/nolta/15/4/15_883/_pdf

Mel-frequency cepstral coefficients feature extracted voice recognition task using atomic switch Ag/Ag<sub>2</sub>S device-based time-delayed reservoir computing 査読有り国際誌

Karacali Ahmet, Nakao Yusuke, Srikimkaew Oradee, Abdi Gisya, Szacilowski Konrad, Usami Yuki, Tanaka Hirofumi

Nonlinear Theory and Its Applications, IEICE ( 一般社団法人電子情報通信学会 ) 15 ( 4 ) 871 - 882 2024年01月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

<p>Neuromorphic devices have diverse potential applications, such as brain-inspired computers and promising high-performance arithmetic systems with power saving. Reservoir computing (RC), a type of recurrent neural network (RNN), achieves learning by adjusting the weights between the intermediate and output layers. Time-delay reservoir computing introduces a delay and creates virtual nodes within the middle layer. The Ag/Ag<sub>2</sub>S nanoparticles function as nonlinear electrical devices, following the atomic switch principles of the time-delay system. Voice recognition was performed with 87.81% accuracy when six different people pronounced the same number, and 80.18% when the same person pronounced ten different numbers.</p>

DOI： 10.1587/nolta.15.871

その他リンク： https://www.jstage.jst.go.jp/article/nolta/15/4/15_871/_pdf

Thermally Stable Ag<inf>2</inf>Se Nanowire Network as an Effective In-Materio Physical Reservoir Computing Device 査読有り国際誌

Kotooka T., Lilak S., Stieg A.Z., Gimzewski J.K., Sugiyama N., Tanaka Y., Kawabata T., Karacali A., Tamukoh H., Usami Y., Tanaka H.

Advanced Electronic Materials 10 ( 12 ) 2024年01月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

The artificial intelligence (AI) paradigm shifts from software to implementing general-purpose or application-specific hardware systems with lower power requirements. This study explored a material physical reservoir consisting of a material random network, called in-materio physical reservoir computing (RC) to achieve efficient hardware systems. The device, made up of a random, highly interconnected network of nonlinear Ag2Se nanojunctions as reservoir nodes, demonstrated the requisite characteristics of an in-materio physical reservoir, including but not limited to nonlinear switching, memory, and higher harmonic generation. The power consumption of the in-materio physical reservoir is 0.07 nW per nanojunctions, confirming its highly efficient information processing system. As a hardware reservoir, the devices successfully performed waveform generation tasks. Finally, a voice classification by an in-materio physical reservoir is achieved over 80%, comparable to an RC software simulation. In-materio physical RC with rich nonlinear dynamics has huge potential for next-generation hardware-based AI.

DOI： 10.1002/aelm.202400443

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85210391008&origin=inward

Haptic In-Sensor Computing Device Based on CNT/PDMS Nanocomposite Physical Reservoir 査読有り国際誌

Kimizuka K., Azhari S., Tokuno S., Karacali A., Usami Y., Ikemoto S., Tamukoh H., Tanaka H.

Advanced Intelligent Systems 7 ( 3 ) 2024年01月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

The importance of haptic in-sensor computing devices has been increasing. Herein, a haptic sensor with a hierarchical structure is successfully fabricated via the sacrificial template method, using carbon nanotube-polydimethylsiloxane (CNT-PDMS) nanocomposites for in-sensor computing applications. The CNT-PDMS nanocomposite sensors, with different sensitivities, are obtained by varying the amount of CNTs. The input stimuli are transformed into higher-dimensional information, enabling a new path for the CNT-PDMS nanocomposite application, which is implemented on a robotic hand as an in-sensor computing device by applying a reservoir computing paradigm. The nonlinear output data obtained from the sensors are trained using linear regression and used to classify nine different objects used in everyday life with an object recognition accuracy of >80% for each object. This approach can enable tactile sensation in robots while reducing the computational cost.

DOI： 10.1002/aisy.202400640

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85210097770&origin=inward

High Performance of an In-Material Reservoir Computing Device Achieved by Complex Dynamics in a Nanoparticle Random Network Memristor 査読有り国際誌

Srikimkaew O., Banerjee D., Azhari S., Usami Y., Tanaka H.

ACS Applied Electronic Materials 6 ( 2 ) 688 - 695 2023年12月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

An in-material reservoir computing (RC) device with an Ag-Ag2S core-shell nanoparticle (NP) network is proposed. Network-wide nonlinear sine-wave outputs of higher frequencies and varying phases were produced from the different Ag+ ion diffusion rates and filament formation caused by the heterogeneous NP size in the thiol layer. Such emergent dynamics of multiple information regimes enabled the reconstruction of Fourier waves, with a maximum accuracy of 99% achieved only for trained outputs with mixed spatiotemporal complexities. Additionally, the device showed stable retrieval of past information with a two-times-step delay and successfully computed a two-step time-series prediction task with 87% accuracy.

DOI： 10.1021/acsaelm.3c01046

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85181823293&origin=inward

High field-effect mobility in oriented thin films of D-A type semiconducting polymers by engineering stable interfacial system 査読有り国際誌

Sharma S., Vats A.K., Tang L., Kaishan F., Toyoda J., Nagamatsu S., Ando Y., Tamagawa M., Tanaka H., Pandey M., Pandey S.S.

Chemical Engineering Journal 469 2023年08月

記述言語：英語掲載種別：研究論文（学術雑誌）

Conjugated polymers (CPs) have emerged as excellent organic semiconducting materials for flexible electronic applications. CPs exhibit a notably fast carrier transport along their main π-conjugated backbone followed by inter-chain hopping compelling the need to form large and ordered domains in thin films. Therefore, the formation of larger domains, along with their orientation, is critical in controlling the electrical properties of CP-based organic electronic devices. However, controlling the molecular ordering along with the formation of large aggregates is a challenge. In this work, the unidirectional floating film transfer method (UFTM) has been utilized to prepare oriented thin films of CPs, which is a highly facile, cost-effective and material utilization efficient technique. We have demonstrated that extent and direction of molecular orientation in the fabricated thin films can be tuned along with the higher degree of aggregation. The rheological aspects, especially viscosity, play a significant role in determining molecular ordering along with the formation of these large aggregates. Active control of viscosity to achieve a stable interfacial viscous system is paramount to achieving this, resulting in a very high mobility of 12.4 cm2V−1s−1.

DOI： 10.1016/j.cej.2023.143932

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85161350728&origin=inward

Visualizing Ribbon-to-Ribbon Heterogeneity of Chemically Unzipped Wide Graphene Nanoribbons by Silver Nanowire-Based Tip-Enhanced Raman Scattering Microscopy 査読有り国際誌

T. Inose, S. Toyouchi, S. Hara, S. Sugioka, P. Walke, R. Oyabu, B. Fortuni, W. Peeters, Y. Usami, K. Hirai, S. De Feyter, Y. Fujita, H. Uji-i, H. Tanaka

Small ( Wiley ) 20 ( 3 ) 2023年08月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

Graphene nanoribbons (GNRs), a quasi-one-dimensional form of graphene, have gained tremendous attention due to their potential for next-generation nanoelectronic devices. The chemical unzipping of carbon nanotubes is one of the attractive fabrication methods to obtain single-layered GNRs (sGNRs) with simple and large-scale production. The authors recently found that unzipping from double-walled carbon nanotubes (DWNTs), rather than single- or multi-walled, results in high-yield production of crystalline sGNRs. However, details of the resultant GNR structure, as well as the reaction mechanism, are not fully understood due to the necessity of nanoscale spectroscopy. In this regard, silver nanowire-based tip-enhanced Raman spectroscopy (TERS) is applied for single GNR analysis and investigated ribbon-to-ribbon heterogeneity in terms of defect density and edge structure generated through the unzipping process. The authors found that sGNRs originated from the inner walls of DWNTs showed lower defect densities than those from the outer walls. Furthermore, TERS spectra of sGNRs exhibit a large variety in graphitic Raman parameters, indicating a large variation in edge structures. This work at the single GNR level reveals, for the first time, ribbon-to-ribbon heterogeneity that can never be observed by diffraction-limited techniques and provides deeper insights into unzipped GNR structure as well as the DWNT unzipping reaction mechanism.

DOI： 10.1002/smll.202301841

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85169170888&origin=inward

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