Ab-initio investigation of preferential triangular self-formation of oxide heterostructures of monolayer $$\hbox {WSe}_{2}$$

Abstract

Triangular growth patterns of pristine two-dimensional (2D) transition metal dichalcogenides (TMDs) are ubiquitous in experiments. Here, we use first-principles calculations to investigate the growth of triangular shaped oxide islands upon layer-by-layer controlled oxidation in monolayer and few-layer $$\hbox {WSe}_{2}$$ WSe 2 systems. Pristine 2D TMDs with a trigonal prismatic geometry prefer the triangular growth morphology due to structural stability arising from the edge chalcogen atoms along its three sides. Our ab-initio energetics and thermodynamic study show that, since the Se atoms are more susceptible to oxygen replacement, the preferential oxidation happens along the Se zigzag lines, producing triangular islands of transition metal oxides. The thermodynamic stability arising from the preferential triangular self-formation of TMD based oxide heterostructures and their electronic properties opens a new avenue for their exploration in advanced electronic and optoelectronic devices.

Morphotaxy of Layered van der Waals Materials

“…In particular, Das et al considered the growth of oxides on WSe 2 with ab initio calculations, noting that trigonal prismatic TMDCs lead to preferential triangular growth of oxide islands. 73 These authors further showed that oxygen preferentially substitutes at selenium zigzag edges and is energetically more stable in a triangular, rather than a rectangular island. The triangular oxide islands have been predicted to function as embedded quantum dots in WSe 2 , suggesting further innovations in TMDC−TMO heterostructures.…”

“…First-principles calculations also play an essential role in explaining and predicting experimental results. In particular, Das et al considered the growth of oxides on WSe 2 with ab initio calculations, noting that trigonal prismatic TMDCs lead to preferential triangular growth of oxide islands . These authors further showed that oxygen preferentially substitutes at selenium zigzag edges and is energetically more stable in a triangular, rather than a rectangular island.…”

“…These authors further showed that oxygen preferentially substitutes at selenium zigzag edges and is energetically more stable in a triangular, rather than a rectangular island. The triangular oxide islands have been predicted to function as embedded quantum dots in WSe 2 , suggesting further innovations in TMDC–TMO heterostructures . In related work, Xu et al utilized WO x as contacts in bilayer WSe 2 FETs, where they argued that the substoichiometric, high work function WO 2.57 offered decreased contact resistance and enhanced channel current, with conductivities as high as 2600 S m –1 .…”

“…The triangular oxide islands have been predicted to function as embedded quantum dots in WSe 2 , suggesting further innovations in TMDC−TMO heterostructures. 73 In related work, Xu et al utilized WO x as contacts in bilayer WSe 2 FETs, where they argued that the substoichiometric, high work function WO 2.57 offered decreased contact resistance and enhanced channel current, with conductivities as high as 2600 S m −1 . 74 In line with these experimental results, DFT calculations showed that the substoichiometric oxide formed through air exposure gives rise to a defect band near the Fermi energy, resulting in gapstate-assisted carrier transport and enhanced conductivities.…”