Van der Waals (vdW) heterostructures are the fundamental blocks for two-dimensional (2D) electronic and optoelectronic devices. In this work, a high-quality 2D metal–semiconductor NiTe2/MoS2 heterostructure is prepared by a two-step chemical vapor deposition (CVD) growth. The back-gated field-effect transistors (FETs) and photodetectors based on the heterostructure show enhanced electronic and optoelectronic performance than that of a pristine MoS2 monolayer, owing to the better heterointerface in the former device. Especially, this photodetector based on the metal–semiconductor heterostructure shows 3 orders faster rise time and decay time than that of the pristine MoS2 under the same fabrication procedure. The enhancement of electronic behavior and optoelectronic response by the epitaxial growth of metallic vdW layered materials can provide a new method to improve the performance of optoelectronic devices.

lattice along the [001] direction, induced by the twist angles among different layers, yielded quadratically enhanced layerdependent second-harmonic generation (SHG) properties, [4][5][6][7] which is different from the decreasing oscillations in the odd and even layers that are observed with increasing the number of 2H stacked TMDs. [8,9] Moreover, conductive atomic force microscopy (c-AFM) studies have revealed that the vertical resistance of spiral MoS 2 nanosheets is much lower than that of mechanically exfoliated layered MoS 2 nanosheets, owing to the helical current along the screw dislocation direction. [10] The extraordinary nonlinear optical properties and unusual conductivity suggest that spiral TMDs are very promising for applications in optical, electronic, and optoelectronic devices.To extend the application of TMDs to a broader range of wavelengths, bandgap engineering can be used for developing novel electronic, optical, and optoelectronic devices at various wavelengths. By forming alloy-layered structures, novel TMD monolayers and multilayers with tunable bandgaps can be prepared. Recently, ternary-alloy TMDs have been successfully synthesized using the CVD, [11][12][13][14] PVD, [15][16][17] chemical vapor transport (CVT), [18,19] and molecular beam epitaxy (MBE) [20,21] methods. In these materials, the bandgap varies with the chemical composition. Atomically resolved spherical aberration-corrected scanning transmission electron microscopy (CS-STEM) and scanning tunneling microscopy (STM) studies revealed that atoms in these alloy TMDs are randomly distributed on nano sheets. [14,15,22,23] Bandgap-modulated alloy TMDs have extensive applications in many fields, such as heterogeneous catalysts, field-effect transistors (FETs), [15,17,24,25] photodetectors, [11,[26][27][28] and gas sensors. [29] In these fabricated devices, electron scattering in the ternary-alloy TMD monolayer is supposed to decrease the carrier mobility in FETs [17,24,25] and lower the photocurrent and responsivity of photodetectors. [24] Alloy bandgap engineering of TMDs has made significant strides. Nevertheless, most studies have focused on the preparation and characterization of alloy monolayers. To date, no synthesis of 3R stacked, alloy spiral TMDs has been reported. On the other hand, although many researchers have noticed that the defects and the interfaces between different domains are important for Electronic properties at the interfaces between different-composition domains of 2D-alloys are key for their optical, electronic, and optoelectronic applications. Understanding the interfacial electronic structures and carrier dynamics is essential for designing and fabricating devices that use these alloys. Here, WS 2x Se 2−2x spiral nanosheets are prepared using the physical vapor deposition method, and the nonlinear optical and electronic properties, as well as the carrier dynamics at the interfaces between the WS and WSe domains, are studied. Second-harmonic generation tests demonstrate that these nanosheets exhibit a very...

Twisted two-dimensional transition metal dichalcogenide (TMD) moirésuperlattices provide an additional degree of freedom to engineer electronic and optical properties. Nevertheless, controllable synthesis of marginally twisted homo TMD moireś uperlattices is still a challenge. Here, physical vapor deposition grown spiral WS 2 nanosheets are demonstrated to be a marginally twisted moirésuperlattice using scanning tunneling microscopy and spectroscopy. Periodic moirésuperlattices are found on the third layer (3L) and 4L of the spiral WS 2 nanosheet owing to the marginally twisted alignment between two neighboring layers, resulting in a highly localized flat band near the valence band maximum. Their bandgap depends on atomic stacking configurations, which gives a good interpretation for split moiréexcitons using photoluminescence at 77 K. This work can benefit the development of twisted homo TMD moirésuperlattices and could promote the profound research of twisted TMDs in the prospective field, such as strongly correlated physics and twistronics.