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A prerequisite for widespread applications of atomically thin transition metal dichalcogenides in future electronics is to achieve reliable electrical contacts, which is of considerable challenge due to the difficulties in selectively doping and inevitable physical damages of these atomically thin materials during typical metal integration process. Here, we report the in situ growth of ultrathin metallic NiSe single crystals on WSe2 in which the metallic NiSe nanosheets function as the contact electrodes to WSe2, creating an interface that is essentially free from chemical disorder. The NiSe/WSe2 heterostructures also exhibit well-aligned lattice orientation between the two layers, forming a periodic Moiré pattern. Electrical transport studies demonstrate that the NiSe nanosheets exhibit an excellent metallic feature, as evidenced by the extra-high electrical conductivity of up to 1.6×106 S·m−1. The WSe2 transistors with the NiSe contact show field-effect mobilities (μFE) more than double that with Cr/Au electrodes. This study demonstrates an effective pathway to achieve reliable electrical contacts to the atomically thin 2D materials, and maybe readily extended for fabricating 2D/2D low-resistance contacts for a variety of transition metal dichalcogenides. [ABSTRACT FROM AUTHOR]

The mixed-dimensional integration of two-dimensional (2D) materials with non-2D materials can give rise to prominent advances in performance or function. To date, the mixed-dimensional one-dimensional (1D)/2D heterostructures have been fabricated using various physical assembly approaches. However, direct epitaxial growth method which has notable advantages in preparing large-scale products and obtaining perfect interfaces is rarely investigated. Herein, we demonstrate for the first time the direct synthesis of the 1D/2D mixed-dimensional heterostructures by sequential vapor-phase growth of Sb2Se3 nanowires on WS2 monolayers. X-ray diffraction (XRD) pattern and Raman spectrum confirm the composition of the Sb2Se3/WS2 heterostructures. Transmission electron microscope (TEM) measurement demonstrates high quality of the heterostructures. Electrical transport characterization reveals that Sb2Se3 nanowire exhibits p-type characteristic and that WS2 monolayer exhibits n-type behavior, and that the p-n diode from 1D/2D mixed-dimensional Sb2Se3/WS2 heterostructure possesses obvious current rectification behavior. Optoelectronic measurements of the heterostructures show apparent photovoltaic response with an open-circuit voltage of 0.19 V, photoresponsivity of 1.51 A/W (Vds = 5 V) and fast response time of less than 8 ms. The van der Waals epitaxial growth mode of Sb2Se3 nanowires on WS2 monolayers is verified by stripping the Sb2Se3 nanowire from the heterostructures using tape. Together, the direct van der Waals epitaxy opens a facile pathway to 1D/2D mixed-dimensional heterostructures for functional electronic and optoelectronic devices. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) van der Waals (vdWs) metal-semiconductor heterostructures with atomically sharp interface and matched work functions have recently attracted great attention due to their unique electronic and optoelectronic properties. Here we report the vapor phase epitaxial growth of large-scale vertical Sb/WSe2 metal-semiconductor vdWs heterostructures with uniform stacking orientation. Compared with the growth on SiO2/Si substrate, the thickness of Sb nanosheet on WSe2 can be reduced effectively to monolayer. We construct Sb-WSe2-Au asymmetric electrodes photodiode based on the Sb/WSe2 heterostructures. Electrical transport measurements indicate that the photodiode show obvious rectifying effect. Optoelectronic characterizations show prominent photoresponse with a high photoresposivity of 364 mA/W, a fast response time of less than 8 ms, a large open-circuit voltage of 0.27 V and a maximum electrical power output of 0.11 nW. The direct growth of high-quality metal-semiconductor vdWs heterostructures may open up new realms in 2D functional electronics and optoelectronics. [ABSTRACT FROM AUTHOR]