In recent decades two-dimensional (2D) layered materials have attracted intense interest because of their unique mechanical, electronic and optical attributes that emerge from the exotic quantum collective behaviors of electrons confined within the atomically thin layers. By exploiting the 2D structural feature and unique material properties, 2D materials and their heterostructures have been explored as promising candidates for the applications in electronics, optoelectronics, sensing, catalysis, biomedicine, etc. In the fields of both fundamental research and practical applications in the 2D materials, surface and interface play crucial roles in modulating material properties and improving devices performance. Significant efforts have been directed towards the surface and interface engineering that is extremely important no matter the 2D materials are fabricated through the bottom-up or top-down processes. These endow emerging new properties of the 2D materials and enhanced performance of bespoken devices.
The scope of this focus issue in Frontiers of Physics would cover the aspects on the surface and interface of 2D materials from experimental synthesis, characterizations, theoretical calculations, device applications, etc. Articles reporting on the latest progress in the controllable growth of surface and interface of 2D materials and the exploitation of them towards innovative and practical devices are expected. Research works addressing approaches to regulate surface and interface of 2D materials from both experimental and theoretical points of view are also welcome.
We are looking for high profile scientists from China and overseas to contribute Review, Mini-Review, Perspective, or Research Article in the foresaid areas. Please feel free to choose a striking topic that best fits the issue. Co-authorship is welcome. There is no strict length limit for each article, and for each review at least 15 pages length is highly expected.
The sample article (TEX template) can be downloaded via http://journal.hep.com.cn/fop/EN/column/column15258.shtml and the new manuscript can be submitted online through http://mc.manuscriptcentral.com/fop. All PDFs of the special issue will be open accessed, and a copy of the volume will be mailed to all participants.
Sincerely,
Lijun Zhang, Jilin University, China, lijun_zhang@jlu.edu.cn
Dongchen Qi, Queensland University of Technology, Australia, dongchen.qi@qut.edu.au
Ming Yang, The Hong Kong Polytechnic University, Hong Kong, kevin.m.yang@polyu.edu.hk
Kai Zhang, Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academy of Sciences, China, kzhang2015@sinano.ac.cn
The low-dimensional light source shows promise in photonic integrated circuits. Stable layered van der Waals material that exhibits luminescence in the near-infrared optical communication waveband is an essential component in on-chip light sources. Herein, the tunable near-infrared photoluminescence (PL) of the air-stable layered titanium trisulfide (TiS3) is reported. Compared with iodine particles as a transport agent, TiS3 grown by chemical vapor transport using sulfur powder as a transport agent has fewer sulfur vacancies, which increases the luminescence intensity by an order of magnitude. The PL emission wavelength can be regulated in the near-infrared regime by thickness control. In addition, we observed an interesting anisotropic strain response of PL in layered TiS3 nanoribbon: a blue shift of PL was achieved when the uniaxial tensile strain was applied along the b-axis, while a negligible shift was observed when the strain was applied along the a-axis. Our work reveals the tunable near-infrared luminescent properties of TiS3 nanoribbons, suggesting their potential applications as near-infrared light sources in photonic integrated circuits.
We examine the electronic and transport properties of a new phase PdSe monolayer with a puckered structure calculated by first-principles and Boltzmann transport equation. The spin−orbit coupling is found to play a negligible effect on the electronic properties of PdSe monolayer. The lattice thermal conductivity of PdSe monolayer exhibits remarkable anisotropic characteristic due to anisotropic phonon group velocity along different directions and its intrinsic structure anisotropy. The compromised electronic mobility despite a relatively low thermal conduction results in a moderate ZT value but significantly anisotropic thermoelectric performance in single-layer PdSe. The present work suggests that the remarkable thermal transport anisotropy of PdSe monolayer can be used for thermal management, and enhance the scope of possibilities for heat flow manipulation in PdSe based devices. The sizeable puckered cages and wiggling lattice implies it an ideal platform for ionic and molecular engineering for thermoelectronic applications.
Two-dimensional (2D) heterostructures have shown great potential in advanced photovoltaics due to their restrained carrier recombination, prolonged exciton lifetime and improved light absorption. Herein, a 2D polarized heterostructure is constructed between Janus MoSSe and MoTe2 monolayers and is systematically investigated via first-principles calculations. Electronically, the valence band and conduction band of the MoSSe−MoTe2 (MoSeS−MoTe2) are contributed by MoTe2 and MoSSe layers, respectively, and its bandgap is 0.71 (0.03) eV. A built-in electric field pointing from MoTe2 to MoSSe layers appears at the interface of heterostructures due to the interlayer carrier redistribution. Notably, the band alignment and built-in electric field make it a direct z-scheme heterostructure, benefiting the separation of photogenerated electron-hole pairs. Besides, the electronic structure and interlayer carrier reconstruction can be readily controlled by reversing the electric polarization of the MoSSe layer. Furthermore, the light absorption of the MoSSe/MoTe2 heterostructure is also improved in comparison with the separated monolayers. Consequently, in this work, a new z-scheme polarized heterostructure with polarization-controllable optoelectronic properties is designed for highly efficient optoelectronics.
Quasi-two-dimensional (2D) Ruddlesden‒Popper (RP) halide perovskites, as a kind of emerged two-dimensional layered materials, have recently achieved great attentions in lasing materials field owing to their large exciton binding energy, high emission yield, large optical gain, and wide-range tuning of optical bandgap. This review will introduce research progresses of RP halide perovskites for lasing applications in aspects of materials, photophysics, and devices with emphasis on emission and lasing properties tailored by the molecular composition and interface. The materials, structures and fabrications are introduced in the first part. Next, the optical transitions and amplified spontaneous emission properties are discussed from the aspects of electronic structure, exciton, gain dynamics, and interface tailoring. Then, the research progresses on lasing devices are summarized and several types of lasers including VCSEL, DFB lasers, microlasers, random lasers, plasmonic lasers, and polariton lasers are discussed. At last, the challenges and perspectives would be provided.
The effective modulation of the thermal conductivity of halide perovskites is of great importance in optimizing their optoelectronic device performance. Based on first-principles lattice dynamics calculations, we found that alloying at the B and X sites can significantly modulate the thermal transport properties of 2D Ruddlesden−Popper (RP) phase halide perovskites, achieving a range of lattice thermal conductivity values from the lowest (
Atomically thin two-dimensional (2D) transition metal dichalcogenides (TMDCs) have stimulated enormous research interest due to rich phase structure, high theoretical carrier mobility and layer-dependent bandgap. In view of the close correlation between defects and properties in 2D TMDCs, more attentions have been paid on the defect engineering in recent years, however the mechanism is still unclear. Herein, we review the critical progress of defect engineering and provide an extensive way to modulate the properties depressed by defects. To insight into the defect engineering, we firstly introduce two common kinds of defects during the growth progress of TMDCs and the possible distribution of energy levels those defects could induce. Then, various methods to improve point defects and grain boundaries during the period of growth are discussed intensively, with the assistance of which more large-area TMDCs films can be obtained. Considering the defects in TMDCs are inevitable regardless of concentration, we also highlight strategies to heal the defects after growth. Through dry methods or wet methods, the chalcogen vacancies can be repaired and thus, the performance of electronic device would be significantly enhanced. Finally, we propose the challenges and prospective for defect engineering in 2D TMDCs materials to support the optimization of device and lead them to wide applied fields.
As a two-dimensional material with a hollow hexatomic ring structure, Néel-type anti-ferromagnetic (AFM) GdI3 can be used as a theoretical model to study the effect of electron doping. Based on first-principles calculations, we find that the Fermi surface nesting occurs when more than 1/3 electron per Gd is doped, resulting in the failure to obtain a stable ferromagnetic (FM) state. More interestingly, GdI3 with appropriate Mg/Ca doping (1/6 Mg/Ca per Gd) turns to be half-metallic FM state. This AFM−FM transition results from the transfer of doped electrons to the spatially expanded Gd-5d orbital, which leads to the FM coupling of local half-full Gd-4f electrons through 5d−4f hybridization. Moreover, the shortened Gd−Gd length is the key to the formation of the stable ferromagnetic coupling. Our method provides new insights into obtaining stable FM materials from AFM materials.
Two-dimensional layered materials (2DLMs) have attracted growing attention in optoelectronic devices due to their intriguing anisotropic physical properties. Different members of 2DLMs exhibit unique anisotropic electrical, optical, and thermal properties, fundamentally related to their crystal structure. Among them, directional heat transfer plays a vital role in the thermal management of electronic devices. Here, we use density functional theory calculations to investigate the thermal transport properties of representative layered materials: β-InSe, γ-InSe, MoS2, and h-BN. We found that the lattice thermal conductivities of β-InSe, γ-InSe, MoS2, and h-BN display diverse anisotropic behaviors with anisotropy ratios of 10.4, 9.4, 64.9, and 107.7, respectively. The analysis of the phonon modes further indicates that the phonon group velocity is responsible for the anisotropy of thermal transport. Furthermore, the low lattice thermal conductivity of the layered InSe mainly comes from low phonon group velocity and atomic masses. Our findings provide a fundamental physical understanding of the anisotropic thermal transport in layered materials. We hope this study could inspire the advancement of 2DLMs thermal management applications in next-generation integrated electronic and optoelectronic devices.