Article
Nanoscience & Nanotechnology
Hongwu Tang, Fang Luo, Ziru Cui, Yang Xiao, Wei Xu, Zhihong Zhu, Shula Chen, Xiao Wang, Yanping Liu, Jinbin Wang, Gang Peng, Shiqiao Qin, Mengjian Zhu
Summary: Facile control of the wavelength of light emitters is crucial for optoelectronics and photonics applications. In this study, by utilizing the Joule heating effect, the refractive index of silicon-based waveguides can be modulated for reconfigurable nanophotonic circuits. The authors demonstrate electrically controlled wavelength-tunable photoluminescence from vertical van der Waals heterostructures combined by graphene and 2D-TMDCs. The electric control of the PL wavelength and the bandgap reduction of TMDCs are reversible and can be achieved by applying a moderate electric field to the graphene substrate.
ACS APPLIED MATERIALS & INTERFACES
(2022)
Article
Chemistry, Multidisciplinary
Andrey Yu Klokov, Nikolay Yu Frolov, Andrey Sharkov, Sergey N. Nikolaev, Maxim A. Chernopitssky, Semen Chentsov, Mikhail Pugachev, Aliaksandr Duleba, Alexey Shupletsov, Vladimir S. Krivobok, Aleksandr Yu Kuntsevich
Summary: This study explores the mechanical properties of layered crystals in the few layer limit using picosecond ultrasonic technique. By measuring the temporal variation of the reflection coefficient of an Al film covering heterostructures, the mechanical parameters and rigidity of the interfaces can be evaluated. The results demonstrate the potential of van der Waals heterostructures for nanoacoustical applications.
Article
Chemistry, Multidisciplinary
Jinkun Han, Xiaofei Yue, Yabing Shan, Jiajun Chen, Borgea G. M. Ekoya, Laigui Hu, Ran Liu, Zhijun Qiu, Chunxiao Cong
Summary: Two-dimensional (2D) materials and their van der Waals stacked heterostructures (vdWH) are rising candidates in flexible nanoelectronics and optoelectronic industry. Strain engineering provides an efficient way to modulate their band structure. This study focuses on strain engineering on monolayer WSe2 and graphene/WSe2 heterostructure, and found that pre-strain process improves the interface contacts and reduces the residual strain, resulting in comparable shift rate of the neutral exciton and trion. These findings are important in guiding the use of 2D materials and their vdWH in flexible and wearable devices.
Article
Chemistry, Multidisciplinary
Jamie M. Fitzgerald, Joshua J. P. Thompson, Ermin Malic
Summary: The study provides microscopic insights into moire exciton polaritons by combining an excitonic density matrix formalism with a Hopfield approach. The coupling between exciton and light, polariton energy, and even the number of polariton branches can be controlled via the twist angle. These new hybrid light-exciton states become delocalized relative to the constituent excitons.
Article
Nanoscience & Nanotechnology
Maria Ramos, Francisco Marques-Moros, Dorye L. Esteras, Samuel Manas-Valero, Eudomar Henr iquez-Guerra, Marcos Gadea Jose, Jose J. Baldovi, Josep Canet-Ferrer, Eugenio Coronado, M. Reyes Calvo
Summary: This study investigates the photoluminescence properties of a stacked structure of single-layer MoS2 and van der Waals FePS3. The results demonstrate the outstanding performance of this heterostructure in terms of energy band alignment and charge transfer, providing potential for rational design of van der Waals heterostructures with advanced optoelectronic properties.
ACS APPLIED MATERIALS & INTERFACES
(2022)
Article
Nanoscience & Nanotechnology
Yunjeong Hwang, Taehun Kim, Naechul Shin
Summary: The study reveals that the interlayer energy transfer in transition-metal dichalcogenide/graphene vdW heterostructures strongly depends on the interlayer distance, and the h-BN interlayer can modulate exciton energy transfer, affecting the generation of photocurrent.
ACS APPLIED NANO MATERIALS
(2021)
Article
Chemistry, Multidisciplinary
Hugh Ramsden, Soumya Sarkar, Yan Wang, Yiru Zhu, James Kerfoot, Evgeny M. Alexeev, Takashi Taniguchi, Kenji Watanabe, Sefaattin Tongay, Andrea C. Ferrari, Manish Chhowalla
Summary: van der Waals heterostructures (vdW-HSs) integrate dissimilar materials to form complex devices, relying on the manipulation of charges at multiple interfaces. Conductive mode and cathodoluminescence scanning electron microscopy (CM-SEM and SEM-CL) were used to investigate the trapping of charges in vdW-HSs during electron irradiation, which can adversely affect the performance of the devices. The results showed that up to 70% of beam electrons are deposited into the vdW-HS, leading to dynamic doping of 1L-WSe2 and reducing its cathodoluminescence efficiency. CM-SEM and SEM-CL provide a toolkit for nanoscale characterization of vdW-HS devices, allowing for the correlation of electrical and optical properties.
Article
Nanoscience & Nanotechnology
Chung-Che Huang, He Wang, Yameng Cao, Ed Weatherby, Filipe Richheimer, Sebastian Wood, Shan Jiang, Daqing Wei, Yongkang Dong, Xiaosong Lu, Pengfei Wang, Tomas Polcar, Daniel W. Hewak
Summary: We have developed a fabrication process for uniform large-scale MoS2, WS2 monolayers, and their heterostructures using van der Waals epitaxy. The resulting materials have been successfully deposited on various substrates, and their band alignment and large-scale uniformity have been evaluated.
ACS APPLIED MATERIALS & INTERFACES
(2022)
Article
Nanoscience & Nanotechnology
Daniele Nazzari, Jakob Genser, Masiar Sistani, Maximilian G. Bartmann, Xavier Cartoixa, Riccardo Rurali, Walter M. Weber, Alois Lugstein
Summary: 2D materials provide a rapidly expanding platform for the observation of novel physical phenomena and the realization of cutting-edge optoelectronic devices. In addition to their individual characteristics, 2D materials can be stacked into complex van der Waals heterostructures, greatly expanding their potential. Moreover, strain can be used as a powerful control knob to tune or boost many of their properties, thanks to their excellent stretchability.
Article
Nanoscience & Nanotechnology
Carla Boix-Constant, Samuel Manas-Valero, Rosa Cordoba, Eugenio Coronado
Summary: This work demonstrates the integration of 2D materials between 2D superconductors in Van der Waals heterostructures (vdWHs). The vertical vdWHs based on NbSe2/TaS2/NbSe2 stacks exhibit phase transitions such as 1T-TaS2 charge density wave and NbSe2 superconductivity. The study also shows an enhancement of vdWH resistance due to Andreev reflections in NbSe2 superconducting state.
ADVANCED ELECTRONIC MATERIALS
(2021)
Article
Nanoscience & Nanotechnology
Chuan He, Ruowei Wu, Mei Qi, Yuanyuan Huang, Yixuan Zhou, Sujuan Zhang, Qiyi Zhao, Xinlong Xu
Summary: The dispersion property and SHG pattern of novel 2D van der Waals heterostructures are crucial for characterizing material symmetry and understanding nonlinear photophysical phenomena. Different types of vdWHs exhibit distinct SHG responses due to processes like charge transfer and charge separation, with more nonlinear effects observed under oblique incidence.
ACS APPLIED MATERIALS & INTERFACES
(2021)
Article
Chemistry, Physical
Joanna Jadczak, Joanna Kutrowska-Girzycka, Janina J. Schindler, Joerg Debus, Kenji Watanabe, Takashi Taniguchi, Ching-Hwa Ho, Leszek Bryja
Summary: The study reveals the interlayer electron-phonon coupling in heterostructures composed of TMDs monolayers and hBN layers, leading to a significant increase in emission intensity and preservation of helicity in the exciting light.
Article
Chemistry, Multidisciplinary
Haonan Ling, Jacob B. Khurgin, Artur R. Davoyan
Summary: Layered van der Waals materials provide unique atomic-void channels with subnanometer dimensions, offering opportunities for advanced applications such as sensing and quantum information. Theoretical limits of light guiding in these channels show that materials with strong resonances, excitonic and polaritonic properties are ideal for deeply subwavelength light guiding. Transition metal dichalcogenides with excitonic properties can concentrate over 70% of optical power within them.
Article
Nanoscience & Nanotechnology
Boyu Wang, Jing Ning, Jincheng Zhang, Dong Wang, Yue Hao
Summary: The study investigated the effect of adjusting the spontaneous polarization direction of 2D GaN layer on the electronic properties of MoS2/GaN heterostructures, showing the potential to achieve conversion between type-I and type-II band alignments and enhance optical absorption.
PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES
(2022)
Review
Chemistry, Multidisciplinary
Xiangdong Guo, Wei Lyu, Tinghan Chen, Yang Luo, Chenchen Wu, Bei Yang, Zhipei Sun, F. Javier Garcia de Abajo, Xiaoxia Yang, Qing Dai
Summary: 2D monolayers can be vertically stacked in van der Waals heterostructures to support a wide range of confined polaritons. This offers advantages in terms of controlling the constituent layers, stacking sequence, and twist angles. These heterostructures have extended the performance and functions of polaritons, and potential applications include nanophotonic integrated circuits.
ADVANCED MATERIALS
(2023)
Article
Physics, Applied
Mina Maruyama, Yanlin Gao, Nguyen Thanh Cuong, Susumu Okada
Summary: A two-dimensional magnetic carbon allotrope with hexagonally arranged fused pentagons is theoretically predicted. It has ferromagnetic and antiferromagnetic phases as its respective ground and metastable states, with similar energy levels. The magnetic properties come from the polarized electron spins distributed in the hexagonal network structure.
APPLIED PHYSICS EXPRESS
(2022)
Article
Physics, Applied
Kaoru Hisama, Yanlin Gao, Mina Maruyama, Ryo Kitaura, Susumu Okada
Summary: The study shows that the Fermi level of Nb-doped WSe2 can be tuned by an external electric field, thus controlling its electronic structure. Regardless of Nb concentration and arrangement, the electric field simply shifts the Fermi level, resulting in a constant quantum capacitance under all conditions.
JAPANESE JOURNAL OF APPLIED PHYSICS
(2022)
Article
Physics, Multidisciplinary
Susumu Okada, Nguyen Thanh Cuong, Yanlin Gao, Mina Maruyama
Summary: This study investigates the geometric and electronic structures of a two-dimensional covalent network composed of [5.5.5.5]-fenestratetraene and cyclooctatetraene frameworks. The research reveals that this two-dimensional carbon allotrope possesses a metallic electronic structure and exhibits thermal stability and high total energy.
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN
(2022)
Article
Nanoscience & Nanotechnology
Taishi Nishihara, Akira Takakura, Masafumi Shimasaki, Kazunari Matsuda, Takeshi Tanaka, Hiromichi Kataura, Yuhei Miyauchi
Summary: Assemblies of single-walled carbon nanotubes with specific chiral structures are highly promising optofunctional materials due to their strong light-matter coupling and selectivity in optical resonances. However, the lack of research on the complex optical spectra of single-chirality carbon nanotube assemblies has hindered their application in device design. In this study, we experimentally determine the broadband complex refractive index spectra of single-chirality carbon nanotube assemblies, providing valuable insights for the design of photonic devices using carbon nanotubes as the material.
Article
Chemistry, Multidisciplinary
Masafumi Shimasaki, Taishi Nishihara, Kazunari Matsuda, Takahiko Endo, Yuhei Takaguchi, Zheng Liu, Yasumitsu Miyata, Yuhei Miyauchi
Summary: This study demonstrates directional exciton-energy transport in tungsten diselenide-molybdenum diselenide lateral heterostructures. The transport is driven by the built-in asymmetry of the exciton-energy landscape with respect to the heterojunction interface, allowing for efficient energy transfer in a specific direction.
Article
Spectroscopy
Kenya Tanaka, Taishi Nishihara, Akira Takakura, Yasutomo Segawa, Kazunari Matsuda, Yuhei Miyauchi
Summary: In this study, polarized Raman spectroscopy was used to investigate the topological semimetal Co3Sn2S2. The results revealed that the Raman signals at low and high wave numbers are related to phonon modes with different symmetries. The high wave number A1g mode showed an asymmetric peak feature, indicating a Fano resonance with the continuous electronic background. These findings not only serve as fingerprints for verifying the crystal structure of Co3Sn2S2, but also highlight the importance of Raman spectroscopy as an effective tool to study low energy excitations and their interactions in this material.
JOURNAL OF RAMAN SPECTROSCOPY
(2023)
Article
Physics, Applied
Masafumi Shimasaki, Taishi Nishihara, Naoki Wada, Zheng Liu, Kazunari Matsuda, Yasumitsu Miyata, Yuhei Miyauchi
Summary: We demonstrate anisotropic exciton drift-diffusion in a WS2x Se(2-2x) alloy monolayer with a gradually changing exciton energy caused by the spatial variation in the chalcogen composition ratio. The photoluminescence (PL) images under isotropic laser excitation are extended toward the lower exciton energy side. Moreover, the degree of asymmetry in the PL image increases at the positions with a steep exciton energy gradient. The anisotropy in the PL images and its correlation with the exciton energy gradient are reproduced considering the exciton kinetics obeying a drift-diffusion equation.
APPLIED PHYSICS EXPRESS
(2023)
Article
Physics, Applied
Hui Zhang, Mina Maruyama, Yanlin Gao, Susumu Okada
Summary: The electronic structure of covalent networks of triangular graphene flakes embedded in hexagonal boron nitride depends on the arrangements of the flakes and border atom species. Heterostructures comprising a copolymer of triangular graphene flakes exhibit flat dispersion bands near the Fermi level. A heterostructure made of [3]triangulene is a semiconductor with a moderate direct gap of 0.7 eV and flat band nature throughout the Brillouin zone, attributed to the hybridization between non-bonding states of the triangulene and p(z) orbitals of border B and N atoms.
JAPANESE JOURNAL OF APPLIED PHYSICS
(2023)
Article
Physics, Applied
Yanlin Gao, Haruna Nakajima, Mina Maruyama, Takashi Taniguchi, Kenji Watanabe, Ryo Kitaura, Susumu Okada
Summary: We investigated the energetics and electronic structure of monolayer MoS2 with periodic structural corrugations using density functional theory. The corrugated MoS2 sheet showed a slight increase in total energy with increasing corrugation height, indicating the presence of intrinsic and extrinsic nanometer-scale structural corrugations. The corrugation induced shifts in the valence and conduction band edges due to local strain at the wrinkle peak. By injecting holes through an external electric field, the corrugated MoS2 sheet exhibited a one-dimensional conducting channel. This suggests that corrugation can be used to control the dimensionality of electrons and holes in two-dimensional materials without implementing one-dimensional boundary conditions.
JAPANESE JOURNAL OF APPLIED PHYSICS
(2023)
Article
Chemistry, Multidisciplinary
Shuhong Li, Tomonori Nishimura, Mina Maruyama, Susumu Okada, Kosuke Nagashio
Summary: The adsorbed oxygen on the surface of MoS2 assists in sulfur vacancy formation, causing defects in the material. At high temperatures, the sulfur atoms dissociate from MoS2 with the help of adsorbed oxygen, while at even higher temperatures, direct sulfur desorption dominates. A preannealing treatment effectively removes adsorbed oxygen and prevents defect formation.
NANOSCALE ADVANCES
(2023)
Article
Physics, Applied
Nadia Sultana, Mina Maruyama, Yanlin Gao, Susumu Okada
Summary: Based on density functional theory (DFT), the electronic structure of multilayer graphene under perpendicular electric field was investigated. DFT calculations showed that the number of layers and stacking arrangement have a significant impact on the electronic structure of multilayer graphene under perpendicular electric field. Multilayer graphene with AB stacking exhibits metallic or semi-metallic properties based on the odd or even number of layers when an electric field is applied. Multilayer graphene with ABC stacking is a semiconductor with a flat band at the valence- and conduction-band edges under electric field, regardless of the number of layers. The electronic structure near the Fermi level of multilayer graphene with AA stacking is insensitive to the external electric field.
JAPANESE JOURNAL OF APPLIED PHYSICS
(2023)
Article
Nanoscience & Nanotechnology
Mina Maruyama, Nanami Ichinose, Yanlin Gao, Zheng Liu, Ryo Kitaura, Susumu Okada
Summary: Using the metal-organic chemical vapor deposition technique, a bilayer lateral heterostructure of MoS2 and WS2 was synthesized, showing complex type-II band edge alignments. The bilayer heterostructure exhibited gate-induced trans-dimensionality in carrier injection behavior, with carrier distributions varying from zero-to two-dimensional based on the applied gate voltage. This tunable carrier dimensionality has potential applications in various electronics fields.
ACS APPLIED NANO MATERIALS
(2023)
Article
Engineering, Electrical & Electronic
Masato Takei, Mihiro Takeuchi, Hiroshi Suga, Takatsugu Wakahara, Katsunori Wakabayashi, Susumu Okada, Kazuhito Tsukagoshi
Summary: Electromechanical switching was achieved in fullerene C-60 nanochains using a C-60 pyrrolidine tris-acid(CPTA) film in nanogap electrodes. A conductive C(60) chain formed spontaneously in the nanogap without electron beam irradiation. The switching operation from a high-resistance state to a low-resistance state was reproducible and could be executed at room temperature.
ACS APPLIED ELECTRONIC MATERIALS
(2023)
Article
Physics, Applied
Yanlin Gao, Susumu Okada
Summary: Using density functional theory and the effective screening medium method, we studied the energetics and electronic structure of bilayer Janus WSSe, focusing on their interlayer stacking arrangement. The energetics are sensitive to the interlayer stacking orientation and interface atomic arrangements, resulting from orbital hybridization between chalcogen atoms at the interfaces. The unique electronic structure of bilayer Janus WSSe is determined by the dipole moment arrangement of the constituent WSSe layers.
APPLIED PHYSICS EXPRESS
(2023)
Article
Materials Science, Multidisciplinary
Tomonari Mizoguchi, Yanlin Gao, Mina Maruyama, Yasuhiro Hatsugai, Susumu Okada
Summary: We study characteristic electronic structures in an extended martini lattice model by investigating the minimal tight-binding model, and propose its materialization in pi-electron networks constructed by designated chemisorption on graphene and silicene. Remarkably, the unconventional gapless semiconductor with a flat band at the Fermi level can be realized by designated chemisorption or chemical substitution on graphene and silicene, and the electronic structure near the Fermi level is tunable by the choice of the atomic species of adsorbed atoms. Our results open the way to search exotic electronic structures and their functionalities induced by an extended martini lattice.