The fabrication and tunable optical properties of 2D transition metal dichalcogenides heterostructures by adjusting the thickness of Mo/W films

Multilayered Vertical Heterostructures Comprised of MoS2 and WS2 Nanosheets for Optoelectronics

“…According to the growth, characterizations, and discussions of these specific multilayered vertical HSs, we can infer that the growth temperature and difference in the evaporation temperature of metallic Mo (or W) foil and WO 3 (or MoO 3 ) powder play a crucial role in the formation of these HSs with different layer numbers and stacking sequences. Generally, vertically stacked TMDC HSs prefer to grow at high temperatures (≥850 °C), while lateral heterojunctions are usually carried out at temperatures lower than 800 °C. ,,,, Meanwhile, the evaporation temperature of different kinds of precursors can influence the evaporation sequence of precursors and the growth sequence of target materials. In this regard, we have realized the growth of MoS 2 /WS 2 , WS 2 /MoS 2 , MoS 2 /WS 2 /WS 2 , MoS 2 /MoS 2 /WS 2 /WS 2 , and MoS 2 /MoS 2 /MoS 2 /WS 2 vertical HSs through two opposite routes via a combination of the selection of source materials and manipulation of the growth temperature.…”

“…The emergence of nanoscale two-dimensional (2D) layered materials has opened prospective pathways to develop low-dimensional physics as the sample thickness is scaled down to nanometers and to construct multifunctional devices with superior performance and unique functionalities. − On the basis of the thickness-dependent fundamental features of 2D layered materials, a handful of 2D materials, including semiconducting transition-metal dichalcogenides (TMDCs), hexagonal boron nitride, and black phosphorus, have been attained via diverse materials preparation strategies. − Meanwhile, most of the known 2D materials, possessing thickness-dependent indirect–direct band-gap transitions, various band-gap values, and spin and valley physics, can be utilized as promising building blocks for ultrathin optoelectronic devices, for example, tunneling devices, light-emitting diodes, photodetectors, energy harvesting, and so on. ,− So far, substantial efforts have been devoted to identifying, synthesizing, and characterizing various one-layer (1L) 2D materials and exploiting the corresponding potential applications in flexible optoelectronic devices. However, isolated 2D 1L materials suffer from low light absorption efficiency, extraordinarily short exciton lifetime, and rapid valley depolarization, leading to the restriction of the external quantum efficiency/detectivity of optoelectronic devices and implementation of spin and valley devices. , …”

“…Moreover, 2D vdW HSs have been demonstrated to exhibit manifold attractive characteristics, such as tunable band gaps, enhanced light absorption, remarkable interlayer excitons, and ultrafast interlayer charge transfer, which ensure fascinating applications in detection, water splitting, photovoltaics, and devices requiring ultrafast carrier transport . Accordingly, multifarious two-layer TMDC–TMDC vdW HSs, including MoS 2 /WS 2 , ,,, MoSe 2 /WSe 2 , WSe 2 /MoS 2 , MoS 2 /MoSe 2 , ReS 2 /WS 2 , WTe 2 /MoS 2 , WS 2 /WSe 2 , WS 2 /Mo 1– x W x S 2 (0 ≤ x ≤ 1), ,,,, and so forth, have been attained through mechanical exfoliation, one/two-step or multistep chemical vapor deposition (CVD), or a combination of CVD and the transfer strategy. It is well-known that the physical properties of 2D TMDCs can be manipulated through tuning of the compositions, layer number, stacking sequence, and relative stacking angles.…”

Advances in Liquid‐Phase and Intercalation Exfoliations of Transition Metal Dichalcogenides to Produce 2D Framework

“…[18,43,82,86] TMDCs are transpired in a variety of structural phases, which derive from interaction of different coordination spheres of transitional metal atoms; ordinarily encountered polymorphs are trigonal, hexagonal, and rhombohedral, lyrics as 1T, 2H, and 3R respectively (Figure 3c,d). [82,87,88] These are normally restricted to chemical elements of groups IVB (Ti, Zr, and Hf), group VB (V, Nb, and Ta), and group VIB (Mo, and W), group VIIB (Tc and Re), group X referred as noble transition metals (Pt and Pd), and chalcogens (S, Se, and Te); varies their behavior from semiconductor to superconductors for example semiconductor group contains MoS 2 and WS 2 , in the class of semimetals WTe 2 and TiSe 2 are potential candidates, but VSe 2 and NbS 2 are considered as true metals in TMDCs, NbSe 2 , and TaS 2 are able of donating superconductivity near low temperatures (0.8 K) (see Figure 3b). [17,38,[89][90][91][92][93][94][95][96] TMDCs parade exclusive tunable optical and physical properties evolve from quantum size effect, surface defects, and their nanosized thickness.…”

Stoichiometry-Modulated Resonant Raman Spectroscopy of WS2(1–x)Se2x-Alloyed Monolayer Nanosheets

“…Meanwhile, the excitonic energies, carrier type, and concentration can be further modulated in a wide range. In recent years, a handful of alloyed TMDs, such as WS 2 x Se 2–2 x , − MoS 2(1– x ) Se 2 x , Mo 1– x W x S 2 , − Mo 1– x W x Se 2 , MoSe 2(1– x ) Te 2 x , WSe 2(1– x ) Te 2 x , ReS 2(1– x ) Se 2 x , , etc., have been synthesized and various devices using these alloyed TMDs have been prepared. These progresses greatly fascinate the design and manufacturing of novel ultrathin devices with advanced optoelectronic properties.…”