Recently there have been many research breakthroughs in two-dimensional (2D) materials including graphene, boron nitride (h-BN), black phosphors (BPs), and transition-metal dichalcogenides (TMDCs). The unique electrical, optical, and thermal properties in 2D materials are associated with their strictly defined low dimensionalities. These materials provide a wide range of basic building blocks for next-generation electronics. The chemical vapor deposition (CVD) technique has shown great promise to generate high-quality TMDC layers with scalable size, controllable thickness, and excellent electronic properties suitable for both technological applications and fundamental sciences. The capability to precisely engineer 2D materials by chemical approaches has also given rise to fascinating new physics, which could lead to exciting new applications. In this Review, we introduce the latest development of TMDC synthesis by CVD approaches and provide further insight for the controllable and reliable synthesis of atomically thin TMDCs. Understanding of the vapor-phase growth mechanism of 2D TMDCs could benefit the formation of complicated heterostructures and novel artificial 2D lattices.

Electrical and optical properties of lateral monolayer WSe2–MoS2 p–n heterojunctions were characterized to demonstrate a high responsivity of 0.26 A W−1 with an excellent omnidirectional photodetection capability. The heterojunction functioning as a diode exhibits a prominent gate-tuning behavior with an ideality factor of 1.25. In addition, ultrafast photoresponse, low-light detectability, and high-temperature operation have been achieved. These unique characteristics pave a way for the future development of sub-nano semiconductor devices.

作者：Henan, L.;  Mei Er, P.;  Yumeng, S.*; Hui Ying, Y.*

发表杂志：FlatChem 卷 4 页 48-53

Abstract

The unique electrical and optical properties in atomically thin two-dimensional (2D) transitionmetal dichalcogenides (TMDCs) have recently attracted huge research interests. Synthetic methods, such as chemical vapor deposition (CVD), provide scalable way to produce 2D TMDCs layers with good controllability for optoelectronics applications. However, intricate defects including point defects, dislocations, grain boundaries, and type of edges are inevitably formed during the synthetic reactions. The TMDCs monolayers grown by CVD method could incorporate structure defects such as chalcogen and metal vacancies to determine their electrical and optical properties. In this review, we present the recent development in the structure defects characterization and repairing. We further provide insights into the crystal lattices and their optical properties in the TMDCs layers. Based on these fundamental understanding of thephotoluminescence (PL) evolution, monolayer lattice structures and chemical compositions are being established. A better understanding on the generation, control and passivation of defects lead to the field of so called defect engineering in TMDCs layers.

作者：Huizhen, Y.;  Li, L.;  Wuyou, F.;  Haibin, Y.*; Yumeng, S.*

发表杂志：FlatChem 卷 3 页 1-7

Abstract

The hybrid structure of Fe2O3 nanothorns/TiO2 nanosheets photoanodes is reported in the work for the first time. Two-dimensional TiO2 nanosheets array films are grown on transparent conductive fluorinedoped tin oxide glass substrate by simple hydrothermal method. The Fe2O3nanothorns uniformly deposited on the TiO2 backbone are prepared by chemical bath deposition followed by annealing. The phase structure, morphology and optical properties of the heterogeneous composite films are characterized by X-ray diffraction pattern, scanning electron microscopy and UV-visible spectroscopy. Different nanostructured Fe2O3/TiO2 heterostructures are also investigated by controlling the reaction time of the chemical bath deposition. The two-dimensional TiO2 nanosheets provide an extremely porous matrix and high-activity area required for deposition of Fe2O3 sensitizer. The optimal photocurrent density of Fe2O3/TiO2 film reaches 2.50 mA/cm(2) and the photoconversion efficiency is 1.25%, which is more than six times higher than that of bare TiO2 film (0.2%). The results indicate that the photogenerated carriers can separate and transfer more easily in Fe2O3/TiO2 films due to the type-Il band structures formed at the interface between TiO2 and Fe2O3. The Fe2O3/TiO2 heterogeneous films have potential applications in photoelectrochemical solar cells or water splitting.

作者：Jiang, J. Z.;  Wong, C. P. Y.;  Zou, J.;  Li, S. S.;  Wang, Q. X.;  Chen, J. Y.;  Qi, D. Y.;  Wang, H. Y.;  Eda, G.;  Chua, D. H. C.;  Shi, Y. M.；Zhang, W. J.*

发表杂志：2D Materials 卷 4 期 2 页 9

Abstract

Recent findings about ultrahigh thermoelectric performances in SnSe single crystals have stimulated research on this binary semiconductor material. Furthermore, single-layer SnSe is an interesting analogue of phosphorene, with potential applications in two-dimensional (2D) nanoelectronics. Although significant advances in the synthesis of SnSe nanocrystals have been made, fabrication of well-defined large-sized single-layer SnSe flakes in a facile way still remains a challenge. The growth of single-layer rectangular SnSe flakes with a thickness of similar to 6.8 angstrom and lateral dimensions of about 30 mu m x 50 mu m is demonstrated by a two-stepsynthesis method, where bulk rectangular SnSe flakes were synthesized first by a vapor transport deposition method followed by a nitrogen etching technique to fabricate single-layer rectangularSnSe flakes in an atmospheric pressure system. The as-obtained rectangular SnSe flakes exhibited a pure crystalline phase oriented along the a-axis direction. Field-effect transistor devices fabricated on individual single-layer rectangular SnSe flakes using gold electrodes exhibited p-doped ambipolar behavior and a hole mobility of about 0.16 cm(2) V-1 s(-1). This two-step fabricationmethod can be helpful for growing other similar 2D large-sized single-layer materials.

作者：Juang, Z.-Y.;  Tseng, C.-C.;  Shi, Y.;  Hsieh, W.-P.;  Ryuzaki, S.;  Saito, N.;  Hsiung, C.-E.;  Chang, W.-H.;  Hernandez, Y.;  Han, Y.;  Tamada, K.; Li, L.-J*.

发表杂志：Nano Energy 卷 38 页 385-391

Abstract

Monolayer graphene exhibits impressive in-plane thermal conductivity (> 1000 W m(-1) K-1). However, the out-of-plane thermal transport is limited due to the weak van der Waals interaction, indicating the possibility of constructing a vertical thermoelectric (TE) device. Here, we propose across-plane TE device based on the vertical heterostructures of few-layer graphene and gold nanoparticles (AuNPs) on Si substrates, where the incorporation of AuNPs further inhibits the phonon transport and enhances the electrical conductivity along vertical direction. A measurable Seebeck voltage is produced vertically between top graphene and bottom Si when the device is put on a hot surface and the figure of merit ZT is estimated as 1 at room temperature from the transient Harman method. The polarity of the output voltage is determined by the carrier polarity of the substrate. The device concept is also applicable to a flexible and transparent substrate as demonstrated.

作者：Tsai, M.-L.;  Li, M.-Y.;  Shi, Y.;  Chen, L.-J.*;  Li, L.-J.; He, J.-H*.

发表杂志：Nanoscale Horizons 卷 2 期 1 页 37-42

Abstract

Electrical and optical properties of lateral monolayer WSe2-MoS2 p-n heterojunctions were characterized to demonstrate a high responsivity of 0.26 A W-1 with an excellent omnidirectionalphotodetection capability. The heterojunction functioning as a diode exhibits a prominent gate-tuning behavior with an ideality factor of 1.25. In addition, ultrafast photoresponse, low-light detectability, and high-temperature operation have been achieved. These unique characteristics pave a way for the future development of sub-nano semiconductor devices.

作者：Zhao, C.;  Ng, T. K.;  Tseng, C.-C.;  Li, J.;  Shi, Y.;  Wei, N.;  Zhang, D.;  Consiglio, G. B.;  Prabaswara, A.;  Alhamoud, A. A.;  Albadri, A. M.;  Alyamani, A. Y.;  Zhang, X. X.;  Li, L.-J.; Ooi, B. S*

发表杂志：RSC Advances 卷 7 期 43 页 26665-26672

Abstract

The recent study of a wide range of layered transition metal dichalcogenides (TMDCs) has created a new era for device design and applications. In particular, the concept of van der Waals epitaxy(vdWE) utilizing layered TMDCs has the potential to broaden the family of epitaxial growth techniques beyond the conventional methods. We report herein, for the first time, the monolithic high-power, droop-free, and wavelength tunable InGaN/GaN nanowire light-emitting diodes (NW-LEDs) on large-area MoS2 layers formed by sulfurizing entire Mo substrates. MoS2 serves as both a buffer layer for high-quality GaN nanowires growth and a sacrificial layer for epitaxy lift-off. The LEDs obtained on nitridated MoS2 via quasi vdWE show a low turn-on voltage of similar to 2 V and light output power up to 1.5 mW emitting beyond the "green gap", without an efficiency droop up to the current injection of 1 A (400 A cm(-2)), by virtue of high thermal and electrical conductivities of the metal substrates. The discovery of the nitride/layered TMDCs/metal heterostructure platform also ushers in the unparalleled opportunities of simultaneous high-quality nitrides growth for high-performance devices, ultralow-profile optoelectronics, energy harvesting, as well as substrate reusability for practical applications.