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A simple substrate decoupling method with optimized growth conditions enables a high-quality synthetic monolayer semiconductor.

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Scanning probe lithography is used to directly pattern monolayer transition metal dichalcogenides (TMDs) without the use of a sacrificial resist. Using an atomic force microscope, a negatively biased tip is brought close to the TMD surface. By inducing a water bridge between the tip and the TMD surface, controllable oxidation is achieved at the sub-100 nm resolution. The oxidized flake is then submerged into water for selective oxide removal which leads to controllable patterning. In addition, by changing the oxidation time, thickness tunable patterning of multilayer TMDs is demonstrated. This resist-less process results in exposed edges, overcoming a barrier in traditional resist-based lithography and dry etch where polymeric byproduct layers are often formed at the edges. By patterning monolayers into geometric patterns of different dimensions and measuring the effective carrier lifetime, the non-radiative recombination velocity due to edge defects is extracted. Using this patterning technique, we show that selenide TMDs exhibit lower edge recombination velocity as compared to sulfide TMDs. The work highlights the utility of scanning probe lithography towards understanding material dependent edge recombination losses without significantly normalizing edge behaviors due to heavy defect generation, while allowing for eventual exploration of edge passivation schemes which is of profound interest for nanoscale electronics and optoelectronics.

Monolayer 2D transition metal dichalcogenides (TMDCs) have shown great promise for optoelectronic applications due to their direct bandgaps and unique physical properties. In particular, they can possess photoluminescence quantum yields (PL QY) approaching unity at the ultimate thickness limit, making their application in light-emitting devices highly promising. Here, large-area WS 2 grown via chemical vapor deposition is synthesized and characterized for visible (red) light-emitting devices. Detail optical characterization of the synthesized films is performed, which show peak PL QY as high as 12%. Electrically pumped emission from the synthetic WS 2 is achieved utilizing a transient-mode electroluminescence device structure, which consists of a single metal-semiconductor contact and alternating gate fields to achieve bipolar emission. Utilizing this aforementioned structure, a centimeter-scale (≈0.5 cm 2 ) visible (640 nm) display is demonstrated, fabricated using TMDCs to showcase the potential of this material system for display applications.absorbed, and is a key figure of merit as it directly dictates the final efficiency when the materials are made into light-emitting devices or photovoltaics. Various microscale light-emitting devices have been demonstrated using TMDCs. [13][14][15][16] However, a challenge has been the requirement for simultaneous formation of low-resistance contacts to both electrons and holes in the same device. In one specific architecture, we recently demonstrated efficient bipolar carrier injection using transientmode operation through a single Schottky contact. [17] The device effectively acts as a light-emitting capacitor, with minimal dependence on the contact metal to the semiconductor. This device structure was shown to work with exfoliated monolayers of MoS 2 , WS 2 , MoSe 2 , and WSe 2 . Furthermore, large-area (3 mm × 2 mm) emission was demonstrated using WSe 2 monolayers grown by chemical vapor deposition (CVD). Although the WSe 2 devices were bright, their emission is in the near-infrared regime (750 nm peak emission). Recently, millimeter-scale WS 2 devices operated in the visible wavelength regime were demonstrated using a vertical architecture with quantum dots and polymers as electron/hole injection layers, but a more efficient device is still demanded. [18] In this regard, we report a centimeter-scale, bright, visible light-emitting device based on WS 2 monolayers synthesized via CVD [19][20][21] using a simple capacitor structure. The CVD-synthesized material exhibits a respectable peak PL QY of approximately 10%, without a droop at high injection levels. Using this material, we fabricate a transient-electroluminescence (t-EL) device and characterize its performance; in particular, its efficient light emission at high injection levels. Finally, we also fabricate a sixteen-pixel display with bright red EL emission (640 nm, peak output power 14 µW cm −2 ), which is visible in ambient room lighting. Figure 1a shows the PL spectra of the synthesized WS 2 measured over a p...

High-performance monolayer MoS 2 field-effect transistor with large-scale nitrogen-doped graphene electrodes for Ohmic contact Applied Physics Letters 115, 012104 (2019);

We appreciate the reviewers for their time and insightful questions. Please find the responses to their comments below.

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