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Large-area, continuous monolayer WS2 exhibits great potential for future micro-nanodevice applications due to its special electrical properties and mechanical flexibility. In this work, the front opening quartz boat is used to increase the amount of sulfur (S) vapor under the sapphire substrate, which is critical for achieving large-area films during the chemical vapor deposition processes. COMSOL simulations reveal that the front opening quartz boat will significantly introduce gas distribute under the sapphire substrate. Moreover, the gas velocity and height of substrate away from the tube bottom will also affect the substrate temperature. By carefully optimizing the gas velocity, temperature, and height of substrate away from the tube bottom, a large-scale continues monolayered WS2 film was achieved. Field-effect transistor based on the as-grown monolayer WS2 showed a mobility of 3.76 cm2V−1 s−1 and ON/OFF ratio of 106. In addition, a flexible WS2/PEN strain sensor with a gauge factor of 306 was fabricated, showing great potential for applications in wearable biosensors, health monitoring, and human–computer interaction. [ABSTRACT FROM AUTHOR]

The structural and electronic properties of high work function metal atoms (Au and Pd) and low work function metal atoms (Ti and In) adsorbed WS2 monolayers are systematically studied using first-principles calculations. Due to the weak interaction between Au and S atoms, high Schottky barriers may be formed at the interface. Using the metal Pd contact, p-type ohmic contact may be fabricated, but the localized and sparse partial charge densities decrease the electronic transparency and increase the contact resistance. For the low work function metal In, the delocalized n-type conduction interface states form in the bandgap; however, the wide and high electrostatic potential barrier suppresses the electron-transition probability. Strikingly different from Au, Pd, and In, the strongest interaction between Ti and S atoms induces the delocalized n-type conduction interface states with the highest electronic states near the Fermi level. The delocalized and high partial charge densities, as well as the narrowest and lowest electrostatic potential barrier, would enhance the electronic transparency and form the n-type ohmic contact. Furthermore, the results of the multilayer metal contacts are consistent with those of the atom-adsorbed systems. These investigations offer valuable resources for the design and fabrication of two-dimensional nanodevices. [ABSTRACT FROM AUTHOR]

• The large-area Ag nanoprism array with well-matched resonance was prepared. • Ag/WS 2 plasmonic hybrid structure with compact contact was fabricated. • The Ag nanoprism array has a better enhancement effect on the neutral exciton of monolayer WS 2. • The intensity of feature modes and A 1g of WS 2 is greatly enhanced by a factor of 3 and 4, respectively. Monolayer transition metal dichalcogenides (TMDs) usually have weak optical emission due to the poor light absorption as being atomically thin. Enhancing their optical properties by surface plasmon resonance is attractive for applying atomically thin TMDs in optoelectronic and photonic devices. Here, Ag/WS 2 hybrid structure was fabricated by transferring monolayer WS 2 grown via chemical vapor deposition (CVD) onto optimized periodic Ag nanoprism array with well-matched resonance by controlling the mask geometry and etching time of polystyrene (PS) nanospheres. Significant enhanced photoluminescence (PL) emission and Raman scattering were successfully achieved. Especially, the higher enhancement is realized for neutral excitons of monolayer WS 2. Theoretical calculations reveal that the plasmonic enhancement mainly results from the highly enhanced local electric field and the charge transfer. This work explores the feasibility of exciton emission and Raman scattering enhancement for TMDs with plasmonic nanostructures fabricated by low-cost and easily-manipulated nanosphere lithography (NSL), which paves a way towards the applications of plasmon-enhanced TMD sensors, emitters, and photodetectors. [ABSTRACT FROM AUTHOR]