Selective Chemical Vapor Deposition Growth of WS2/MoS2 Vertical and Lateral Heterostructures on Gold Foils

Electronic and Optoelectronic Monolayer WSe2 Devices via Transfer-Free Fabrication Method

Monolayer transition metal dichalcogenides (TMDs) have drawn significant attention for their potential applications in electronics and optoelectronics. To achieve consistent electronic properties and high device yield, uniform large monolayer crystals are crucial. In this report, we describe the growth of high-quality and uniform monolayer WSe₂ film using chemical vapor deposition on polycrystalline Au substrates. This method allows for the fabrication of continuous large-area WSe₂ film with large-size domains. Additionally, a novel transfer-free method is used to fabricate field-effect transistors (FETs) based on the as-grown WSe₂. The exceptional metal/semiconductor interfaces achieved through this fabrication method result in monolayer WSe₂ FETs with extraordinary electrical performance comparable to those with thermal deposition electrodes, with a high mobility of up to ≈62.95 cm² V^-1 s^-1 at room temperature. In addition, the as-fabricated transfer-free devices can maintain their original performance after weeks without obvious device decay. The transfer-free WSe₂-based photodetectors exhibit prominent photoresponse with a high photoresponsivity of ~1.7 × 10⁴ A W^-1 at V_ds = 1 V and V_g = -60 V and a maximum detectivity value of ~1.2 × 10¹³ Jones. Our study presents a robust pathway for the growth of high-quality monolayer TMDs thin films and large-scale device fabrication.

Extremely Reduced Dielectric Constant and Band Gap Enhancement in Few-Layered Tungsten Disulfide Nanosheets

Highly crystalline few-layered tungsten disulfide (WS₂) nanosheets were synthesized via a cost-effective, low-temperature hydrothermal route. X-ray diffraction and HR-TEM analysis confirmed the formation of hexagonal nanosheets with thickness of ∼6-8 nm. Raman analysis and AFM results confirmed the few-layered 2H phase of WS₂ nanosheets. The UV-vis study shows absorption peaks at 219 and 271 nm with large band gap value of ∼3.12 eV for WS₂ nanosheets. Surprisingly, WS₂ nanosheets show a dielectric constant of approximately ε' ≈ 5245, whereas bulk WS₂ material exhibits a dielectric constant of 7482373. An almost 1426-fold decrease in the value of dielectric constant for the WS₂ nanosheet is observed. Such an extreme reduction in dielectric constant and observance of large band gap in WS₂ nanosheet were observed for the first time. The present study reveals the excellent and unusual optical and dielectric properties for their potential application in optoelectronic, dielectric, solar, phosphor, and various nanoelectronic devices.