Stabilizing Metastable Polymorphs of van der Waals Solid MoS₂ on Single Crystal Oxide Substrates: Exploring the Possible Role of Surface Chemistry and Structure

Abstract

In this work we address the question of growth of thin films of a soft van der Waals solid (2D MoS 2 ) on a hard, crystalline metal oxide substrates. Thus, MoS 2 thin films are grown on different single-crystal metal oxide substrates (SrLaAlO 4 , c-Al 2 O 3 , SrTiO 3 , LaAlO 3 ) by pulsed laser deposition (PLD) and characterized by different techniques to confirm and quantify their phase constitution (2H, 1T′). We observe that, on the SrLaAlO 4 (001) substrate, a mixed 1T′+2H phase of MoS 2 grows with a dominant (∼75%) 1T′ phase, while on c-Al 2 O 3 (0001) pure 2H phase grows. On the SrTiO 3 and LaAlO 3 substrates also the mixed phase grows, but with a much lesser component of the 1T′. Higher 1T′ contribution in SLAO and STO points to the chemical role of strontium in the early growth. It is also noted that, with increased film thickness on SrLaAlO 4 , the contribution of the pure 2H phase is enhanced, indicating the pivotal role of lattice strain in stabilizing the initial layer(s). The mixed 1T′+2H phase in the ultrathin film shows significantly lower room temperature resistivity (∼2 mΩ cm) with respect to that of the pure 2H phase (∼14 mΩ cm). The substrate selective polymorphism with distinct electronic features could invite multiple application interests.

Semiconductor–Semimetal 2D/3D MoS2/SrRuO3(111) TMD/TMO Heterojunction-Based ReRAM Devices

“…The splitting energy values of both components are apart by 1.1 eV corresponding to strong spin–orbit coupling in FL and BL MoS 2 . The slight shift in both the cases can be consequence of the strain effect in FL and its absence in the BL MoS 2 heterostructures, which thereby correlates to the change in bond length and angle …”

“…We therefore suggest that the initial MoS 2 layer which is strongly bound with Ru of SRO must therefore have a 1T phase. The transformation into the metallic character of initial layers of MoS 2 in the heterojunction system is the consequence of a small percentage (1.9%) of lattice mismatch instigating the Jahn–Teller structural distortion in the MoS 2 layer causing the removal of the degeneracy of the nested Fermi surface for 1T MoS 2 with a gap opening of ≤100 meV …”

“…The transformation into the metallic character of initial layers of MoS 2 in the heterojunction system is the consequence of a small percentage (1.9%) of lattice mismatch instigating the Jahn−Teller structural distortion in the MoS 2 layer causing the removal of the degeneracy of the nested Fermi surface for 1T MoS 2 with a gap opening of ≤100 meV. 27 This results in decreased conductivity (discussed ahead in the electronic transport section) for the thinner (few-layer) MoS 2 on the SRO film. The observed strong interface coupling has an impact on the vibrational modes of MoS 2 layers.…”

“…The Mo 3d core (Figure 2A) shows the expected spin−orbit coupling (SOC) of 3.11 and 3.13 eV for few-layer and BL MoS 2 /SRO heterostructures, respectively, commensurate with the reported values. 27 The SOC in the Mo 3d core is based on the number of layers (even and odd) and breaking of inversion symmetry or, in other words, interlayer coupling, which is responsible for the splitting of valence and conduction bands at the first Brillouin zone and Mo 3d degeneracy-lifted orbitals. 13 The peaks located at 232. energy is quite natural as the electronegativity of S (2.58) is higher than that of Ru (2.2), reflecting the strong influence of MoS 2 layers.…”

Modulated Photoluminescence of Single‐Layer MoS2 via Nanostructured SrTiO3 Surface

“…[21][22][23][24][25][26][27][28][29][30][31][32] On the one hand, distinct substrate materials can induce different charge separation at the interfaces and establish varied dipole fields at the corresponding heterojunctions, which strictly depends on the actual components as well as the atomic structures of the interfaces. [33,34] On the other hand, additional tuning effects can be obtained via nanostructuring the substrate surface, which has provided a more-open strategy for tuning the transportation and luminescence properties of MoS 2 . [35][36][37][38][39][40][41][42][43][44] However, in the latter case, the substrate surfaces were usually prepared through complicated and expensive processes such as nanosphere or electron beam lithographies.…”