Femtosecond Laser‐Driven Phase Engineering of WS₂ for Nano‐Periodic Phase Patterning and Sub‐ppm Ammonia Gas Sensing

Abstract

Laser‐driven phase transition of 2D transition metal dichalcogenides has attracted much attention due to its high flexibility and rapidity. However, there are some limitations during the laser irradiation process, especially the unsatisfied surface ablation, the inability of nanoscale phase patterning, and the unexploited physical properties of new phase. In this work, the well‐controlled femtosecond (fs) laser‐driven transformation from the metallic 2M‐WS2 to the semiconducting 2H‐WS2 is reported, which is confirmed to be a single‐crystal to single‐crystal transition without layer thinning or obvious ablation. Moreover, a highly ordered 2H/2M nano‐periodic phase transition with a resolution of ≈435 nm is achieved, breaking through the existing size bottleneck of laser‐driven phase transition, which is attributed to the selective deposition of plasmon energy induced by fs laser. It is also demonstrated that the achieved 2H‐WS2 after laser irradiation contains rich sulfur vacancies, which exhibits highly competitive ammonia gas sensing performance, with a detection limit below 0.1 ppm and a fast response/recovery time of 43/67 s at room temperature. This study provides a new strategy for the preparation of the phase‐selective transition homojunction and high‐performance applications in electronics.

Coexisting Phases in Transition Metal Dichalcogenides: Overview, Synthesis, Applications, and Prospects

“…This approach has resulted in the creation of coexisting phases in TMDCs without thinning layers or significant ablation. 72 Electron Beam Irradiation. The highest precision achieved by both PMMA masks and laser irradiation techniques, as mentioned before, is limited to the nanometer scale.…”

“…However, this issue has recently been improved through the application of femtosecond (fs) laser irradiation. This approach has resulted in the creation of coexisting phases in TMDCs without thinning layers or significant ablation …”

“…Theoretical calculations have already evaluated the phase transitions induced by electric fields, light, and stress to show that coexisting phases have highly potential applications in fields such as electric control, ultrafast phase transitions, and flexible electronics. Experimental investigation of various synthesis methods, along with the in-depth study of the structural phases of TMDCs, have been developed to achieve coexisting phases, including laser induction, − electric-field-driving, ,, gate voltage modulation, ,, plasma bombardment, − thermal treatment, ,− chemical intercalation, ,, CVD, − and solvothermal methods. ,− These methods for preparing coexisting phases can be mainly categorized into two types: localized patterning and randomly formed coexisting phases.…”

Fabrication of Highly Sensitive YCeO Chemo-resistive Gas Sensor for Selective Detection of CO2

“…The Ohmic contact structure encompasses chemi-resistive kinetics between the oxidizing (CO 2 ) and active materials, while the Schottky structure originates from both the chemical sensitivity of the metal oxide semiconductor and the Schottky type sensitivity of the metal-semiconductor junction. [66][67][68] When exposed to air, YCeO sensor adsorbed oxygen molecules, capturing free electrons from the conduction band to form chemisorbed oxygen species resulting in an increase in effective potential barrier height as shown Fig. 10a.…”

Controllable superconducting to semiconducting phase transition in topological superconductor 2M-WS2

“…In the past decade, notable progress in structural phase transitions between 2H and 1T or 1T ′ phases in 2D MX 2 atomic layers has been achieved through different techniques, including temperature [36,37], strain [38][39][40], laser irradiation [41,42], and electrostatic doping [43][44][45], etc. However, phase transitions between topological superconducting and semiconducting phases (figure 1(a)) or other phases in 2D TMDs are still rare [46,47]. As a result, investigating structural phase transitions in 2D superconductors is crucial for deepening our understanding of their fundamental physical properties and unlocking potential applications in future quantum devices.…”