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In-plane anisotropic and ultra-low-loss polaritons in a natural van der Waals crystal

In-plane anisotropic and ultra-low-loss polaritons in a natural van der Waals crystal, Published online: 24 October 2018; doi:10.1038/s41586-018-0618-9

Observation of the anisotropic propagation of polaritons along the surface of layered, semiconducting α-MoO3 confirms the existence of this phenomenon in natural materials.

Advanced Materials, EarlyView.

Heterojunctions are essential building blocks for modern electronic and optoelectronic devices. The recent discovery of two-dimensional semiconductors offers an opportunity to build these heterojunctions with atomic sharp interfaces by van der Waals interaction. Here we fabricated MoS 2 –black phosphorus (BP) heterojunction devices. Due to the narrow band-gap and unpinned Fermi level of BP, this heterojunction could be tuned to either p–n or n–n by the electrostatic gating. The current rectification behaviors were observed in both p–n and n–n junctions. The current rectification of the MoS 2 –BP n–n junction was attributed to the energy barrier formed at the interface of wide band-gap MoS 2 and narrow band-gap BP. The gate dependence of forward current, reverse current and current rectification properties of the heterojunction at different thickness scale were systematically studied, suggesting the electrical properties of the heterojunction could be c...

Ever-increasing energy demands and the depletion of fossil fuels are compelling humanity toward the development of suitable electrochemical energy conversion and storage devices to attain a more sustainable society with adequate renewable energy and zero environmental pollution. In this regard, supercapacitors are being contemplated as potential energy storage devices to afford cleaner, environmentally friendly energy. Recently, a great deal of attention has been paid to two-dimensional (2D) nanomaterials, including 2D graphene and its inorganic analogues (transition metal double layer hydroxides, chalcogenides, etc), as potential electrodes for the development of supercapacitors with high electrochemical performance. This review provides an overview of the recent progress in using these graphene-based 2D materials as potential electrodes for supercapacitors. In addition, future research trends including notable challenges and opportunities are also discussed.

We perform an optical spectroscopy study to investigate the properties of different artificial MoS 2 bi- and trilayer stacks created from individual monolayers by a deterministic transfer process. These twisted bi- and trilayers differ from the common 2H stacking in mineral MoS 2 in the relative stacking angle of adjacent layers and the interlayer distance. The combination of Raman spectroscopy, second-harmonic-generation microscopy and photoluminescence measurements allows us to determine the degree of interlayer coupling in our samples. We find that even for electronically decoupled artificial structures, which show the same valley polarization degree as the constituent MoS 2 monolayers at low temperatures, there is a resonant energy transfer between individual layers which acts as an effective luminescence quenching mechanism.

Nature Materials. doi:10.1038/nmat4064

Authors: Chunming Huang, Sanfeng Wu, Ana M. Sanchez, Jonathan J. P. Peters, Richard Beanland, Jason S. Ross, Pasqual Rivera, Wang Yao, David H. Cobden & Xiaodong Xu

Heterojunctions between three-dimensional (3D) semiconductors with different bandgaps are the basis of modern light-emitting diodes, diode lasers and high-speed transistors. Creating analogous heterojunctions between different 2D semiconductors would enable band engineering within the 2D plane and open up new realms in materials science, device physics and engineering. Here we demonstrate that seamless high-quality in-plane heterojunctions can be grown between the 2D monolayer semiconductors MoSe2 and WSe2. The junctions, grown by lateral heteroepitaxy using physical vapour transport, are visible in an optical microscope and show enhanced photoluminescence. Atomically resolved transmission electron microscopy reveals that their structure is an undistorted honeycomb lattice in which substitution of one transition metal by another occurs across the interface. The growth of such lateral junctions will allow new device functionalities, such as in-plane transistors and diodes, to be integrated within a single atomically thin layer.