Yao Yao's research while affiliated with City University of Hong Kong and other places

Unconventional 1T′-phase transition metal dichalcogenides (TMDs) have aroused tremendous research interest due to their unique phase-dependent physicochemical properties and applications. However, due to the metastable nature of 1T′-TMDs, the controlled synthesis of 1T′-TMD monolayers (MLs) with high phase purity and stability still remains a challenge. Here we report that 4H-Au nanowires (NWs), when used as templates, can induce the quasi-epitaxial growth of high-phase-purity and stable 1T′-TMD MLs, including WS2, WSe2, MoS2 and MoSe2, via a facile and rapid wet-chemical method. The as-synthesized 4H-Au@1T′-TMD core–shell NWs can be used for ultrasensitive surface-enhanced Raman scattering (SERS) detection. For instance, the 4H-Au@1T′-WS2 NWs have achieved attomole-level SERS detections of Rhodamine 6G and a variety of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike proteins. This work provides insights into the preparation of high-phase-purity and stable 1T′-TMD MLs on metal substrates or templates, showing great potential in various promising applications.

2D heterostructures are emerging as alternatives to conventional semiconductors, such as silicon, germanium, and gallium nitride, for next‐generation electronics and optoelectronics. However, the direct growth of 2D heterostructures, especially for those with metastable phases still remains challenging. To obtain 2D transition metal dichalcogenides (TMDs) with designed phases, it is highly desired to develop phase‐controlled synthetic strategies. Here, a facile chemical vapor deposition method is reported to prepare vertical 1H/1T′ MoS2 heterophase structures. By simply changing the growth atmosphere, semimetallic 1T′‐MoS2 can be in situ grown on the top of semiconducting 1H‐MoS2, forming vertical semiconductor/semimetal 1H/1T′ heterophase structures with a sharp interface. The integrated device based on the 1H/1T′ MoS2 heterophase structure displays a typical rectifying behavior with a current rectifying ratio of ≈10³. Moreover, the 1H/1T′ MoS2‐based photodetector achieves a responsivity of 1.07 A W⁻¹ at 532 nm with an ultralow dark current of less than 10⁻¹¹ A. The aforementioned results indicate that 1H/1T′ MoS2 heterophase structures can be a promising candidate for future rectifiers and photodetectors. Importantly, the approach may pave the way toward tailoring the phases of TMDs, which can help us utilize phase engineering strategies to promote the performance of electronic devices.

Ongoing advances in superconductors continue to revolutionize technology thanks to the increasingly versatile and robust availability of lossless supercurrents. In particular, high supercurrent density can lead to more efficient and compact power transmission lines, high-field magnets, as well as high-performance nanoscale radiation detectors and superconducting spintronics. Here, we report the discovery of an unprecedentedly high superconducting critical current density (17MA/cm2 at 0 T and 7MA/cm2 at 8 T) in 1T′−WS2, exceeding those of all reported two-dimensional superconductors to date. 1T′−WS2 features a strongly anisotropic (both in- and out-of-plane) superconducting state that violates the Pauli paramagnetic limit signaling the presence of unconventional superconductivity. Spectroscopic imaging of the vortices further substantiates the anisotropic nature of the superconducting state. More intriguingly, the normal state of 1T′−WS2 carries topological properties. The band structure obtained via angle-resolved photoemission spectroscopy and first-principles calculations points to a Z2 topological invariant. The concomitance of topology and superconductivity in 1T′−WS2 establishes it as a topological superconductor candidate, which is promising for the development of quantum computing technology.

Phase transition with band gap modulation of materials has gained intensive research attention due to its various applications, including memories, neuromorphic computing, and transistors. As a powerful strategy to tune the crystal phase of transition-metal dichalcogenides (TMDs), the phase transition of TMDs provides opportunities to prepare new phases of TMDs for exploring their phase-dependent property, function, and application. However, the previously reported phase transition of TMDs is mainly irreversible. Here, we report a reversible phase transition in the semimetallic 1T'-WS2 driven by proton intercalation and deintercalation, resulting in a newly discovered semiconducting WS2 with a novel unconventional phase, denoted as the 1T'd phase. Impressively, an on/off ratio of >106 has been achieved during the phase transition of WS2 from the semimetallic 1T' phase to the semiconducting 1T'd phase. Our work not only provides a unique insight into the phase transition of TMDs via proton intercalation but also opens up possibilities to tune their physicochemical properties for various applications.

Although two-dimensional (2D) materials have been widely explored for data storage and neuromorphic computing, the construction of 2D material-based memory devices with optoelectronic responsivity in the short-wave infrared (SWIR) region for in-sensor reservoir computing (RC) at the optical communication band still remains a big challenge. In this work, we report an electronic/optoelectronic memory device enabled by tellurium-based 2D van der Waals (vdW) heterostructure, where the ferroelectric CuInP2S6 and tellurium channel endow this device with both the long-term potentiation/depression by voltage pulses and short-term potentiation by 1550-nm laser pulses (a typical wavelength in the conventional fiber optical communication band). Leveraging the rich dynamics, we demonstrate a fully memristive in-sensor RC system that can simultaneously sense, decode and learn messages transmitted by optical fibers. The reported 2D vdW heterostructure-based memory featuring both the long-term and short-term memory behaviors using electrical and optical pulses in SWIR region has not only complemented the wide spectrum of applications of 2D materials family in electronics/optoelectronics but also paves the way for future smart signal processing systems at the edge. This article is protected by copyright. All rights reserved