Bandgap modulation of MoS₂monolayer by thermal annealing and quick cooling

Abstract

We developed a non-mechanical straining method to simultaneously modulate the bandgap and photoluminescence (PL) quantum efficiency of a synthesized molybdenum disulfide (MoS) monolayer on SiO, by vacuum annealing and subsequent quick cooling in ethanol. Influences of the thermal treatments at different temperatures from 100 °C to 600 °C on the PL and Raman spectra of the MoS monolayers are reported. A maximum PL peak intensity, twice that of the untreated counterparts under the same measurement conditions, was observed at the treating temperature of 200 °C. At the same time, approximately permanent tensile strains were induced, due to the quick cooling from high temperatures, which led to a red-shift of the direct optical bandgap. Modulation of the bandgap was achieved by changing the treating temperatures; nearly linear PL and Raman frequency shifts of ∼3.82 meV per 100 °C and ∼-0.28 cm/100 °C for A exciton photoluminescence and Raman E mode frequency were observed, respectively. The proposed thermal modulation promises a wide range of applications in functional 2D nanodevices and semiconductors. To our knowledge, our findings constitute the first demonstration of thermal engineering by combinational manipulation of annealing and quick cooling of the 2D transition-metal dichalcogenides.

Enhancement of photoluminescence efficiency in GeSe ultrathin slab by thermal treatment and annealing: experiment and first-principles molecular dynamics simulations

“…When the temperature is higher than 200 °C, the intensity of the spectrum is no longer continue to be increased. Similarly, our previous work about the thermal treatments of MoS 2 thin film under temperatures from 100 °C to 600 °C obtained a maximum value of double PL peak intensity under 200 °C 20 . After 200 °C, it was found that the exciton peak intensity in MoS 2 sample is decreased linearly.…”

“…It was also found that the PL intensity of WSe 2 ultrathin slab was increased three times under thermal treatment and annealing 19 . We previously reported that the quantum efficiency of MoS 2 ultrathin slab under thermal treatments can be increased twice of that under room temperature (RT) 20 .…”

Long‐Term Stability Control of CVD‐Grown Monolayer MoS2

“…PL enhancement by thermal treatment occurs at temperatures that are lower than the oxidation or decomposition temperature of MoS 2 with specific treatment durations. After the oxidation temperature or long process times, the PL intensity begins to decrease …”

Band Structure and Photoelectric Characterization of GeSe Monolayers

“…Because of the absence of bandgaps in graphene, recent research focused on searching of alternative 2D semiconductors . Monolayer transition metal dichalcogenide (TMDC), represented by MoS 2 and WSe 2 , have attracted extensive interests due to their intrinsic bandgaps and exciting features of indirect to direct bandgap transitions as the materials are thinned down to few‐layers . However, even though devices based on monolayer TMDCs have shown high on/off ratios and photosensitivities, their carrier mobilities are still much lower than graphene .…”