Topological structures of transition metal dichalcogenides: A review on fabrication, effects, applications, and potential

Abstract

Transition metal dichalcogenides (TMDs) have received tremendous attention owing to their potential for optoelectronic applications. Topological structures, such as wrinkles, folds, and scrolls, have been generated on TMDs, thereby exhibiting novel physical properties with improved optoelectronic performance, making them attractive prospects for both basic understanding and advanced applications in optoelectronics. In this review, the methods for fabricating wrinkles, folds, and scrolls on TMDs are outlined, including modification of the fabrication and transfer processes, and manipulation via auxiliary polymers. The effects on their physical and electronic properties are also discussed, with particular paid to the energy band structure, single‐photon sources, second harmonic generation (SHG), and interlayer coupling. In comparison to pristine TMDs, these topologies exhibit great advantages in optoelectronic devices, such as field‐effect transistors and photodetectors. Finally, existing challenges and opportunities of wrinkled, folded, and scrolled TMDs are outlined and an outlook is presented.

Paraffin-Enabled Compressive Folding of Two-Dimensional Materials with Controllable Broadening of the Electronic Band Gap

“…Compared with unfolded monolayer MoS 2 , folded bilayer by PCF exhibited blue-shifts in characteristic Raman modes of E 2g 1 and A 1g with much higher intensity (Figures 3a and S10, Supporting Information), which are completely opposite with most changes (red-shifts) using the strain engineering methods. 12,36 This abnormal blue-shift and stiffening indicated compressive strain and accumulation of photons on the folded bilayer using the PCF strategy. Because E 2g…”

“…Topology engineering such as making wrinkles and folds on 2D materials was predicted to tune band gap efficiently in theory. , For example, due to weak interlayer coupling in adjacent layers, multilayer MoS 2 folded or wrinkled from the monolayer exhibits direct gap transition with increased light absorption, which will be beneficial to optoelectronic devices. , However, in the experiment, fabrication of wrinkles/folds has been mostly achieved on graphene, − and there were only a few reports available on transition-metal dichalcogenides (TMDs), in particular on large-scale CVD-grown TMDs. Based on exfoliated MoS 2 , wrinkles and folds were obtained by releasing the pre-stretched substrate ,− and heating substrate, , and some some wrinkles and folds may also form during the transfer process .…”

Recent Progress on Two-Dimensional Materials

“…57f). However, the biggest challenges for semiconducting 2D materials to be really applicable in flexible electronics are a feasible synthetic strategy of large-area and high-quality materials, and a mature technique for processing these materials into devices on plastic or elastomeric substrates 1476,[1485][1486][1487] . Although MoS2 ranks the most studied TMDs, achieving centimeter scale and uniform monolayer MoS2 by CVD and transfer on to flexible substrates is still not easy.…”

Stretchable MoS2 Artificial Photoreceptors for E‐Skin

“…[ 33 ] It should be noted that the broader full width at half maximum (FWHM) at tetralayer MoS 2 is due to interlayer coupling and faster interband electron relaxation, and the disappearance of B exciton peak on elastic substrates is attributed to the release of strain. [ 34,35 ] To understand the strain dependence of bandgap for MoS 2 with different layer number, we performed the density functional theory (DFT) calculations including vdW correction on band structures of monolayer and tetralayer MoS 2 upon strains (Figure 2g,h; Figure S8, Supporting Information). [ 36–41 ] It shows that the decrease in direct bandgap of the monolayer MoS 2 (380 meV) is more significant than that of the tetralayer MoS 2 (325 meV) when the strain rate increases from 0% to 3.2%.…”