A Novel 19$\sqrt {19} $ × 19$\sqrt {19} $ Superstructure in Epitaxially Grown 1T‐TaTe₂

Abstract

The spontaneous formation of electronic orders is a crucial element for understanding complex quantum states and engineering heterostructures in 2D materials. A novel 19$\sqrt {19} $ ×19$\sqrt {19} $ charge order in few‐layer‐thick 1T‐TaTe2 transition metal dichalcogenide films grown by molecular beam epitaxy, which has not been realized, is report. The photoemission and scanning probe measurements demonstrate that monolayer 1T‐TaTe2 exhibits a variety of metastable charge density wave orders, including the 19$\sqrt {19} $ × 19$\sqrt {19} $ superstructure, which can be selectively stabilized by controlling the post‐growth annealing temperature. Moreover, it is found that only the 19$\sqrt {19} $ × 19$\sqrt {19} $ order persists in 1T‐TaTe2 films thicker than a monolayer, up to 8 layers. The findings identify the previously unrealized novel electronic order in a much‐studied transition metal dichalcogenide and provide a viable route to control it within the epitaxial growth process.

Realization of Multiple Charge-Density Waves in NbTe2 at the Monolayer Limit

“…Instead, as shown in Figure S10, our spectroscopic data and spatial conductance mappings firmly support the CDW nature of both 19 × 19 and 28 × 28 superstructures. Note that the 19 × 19 structure was recently observed in the ML 1 T -TaTe 2, showing STM morphology features nearly identical with ours and has been unambiguously confirmed as an enlarged star of David CDW. , The 28 × 28 structure was also found to be a CDW order according to our private communications with C. G. Zeng et. al.…”

“…Note that the × 19 19 structure was recently observed in the ML 1T-TaTe 2, showing STM morphology features nearly identical with ours and has been unambiguously confirmed as an enlarged star of David CDW. 13,39 The × 28 28 structure was also found to be a CDW order according to our private communications with C. G. Zeng et. al.…”

Metastable Polymorphic Phases in Monolayer TaTe2

“…The existence of CDWs has been reported for other ditellurides (VTe 2 , [ 32 ] TiTe 2 , [ 33 ] NbTe 2 [ 34 ] ), and demonstrated for 1T‐TaTe 2 film thickness up to 8 ML. [ 21 ] We, therefore, tentatively attribute these superperiodicities to the presence of CDWs at RT. The average step height of the octahedral islands is 732 ± 40 pm, obtained by averaging over 40 profiles acquired with different bias voltages across different sample preparations (see Section S3, Supporting Information, for details).…”

“…The rest is assigned to the octahedral areas, which reveal different superstructures, as seen in panels (b–d). The flower‐like structure in Figure 4b, also observed at RT, has recently been attributed to the $$(\sqrt {19} \; \times \sqrt {19} )$$ CDW [ 21 ] originally reported in bulk TaTe 2 . [ 19,20 ] An alternative explanation identifies this superstructure as a chalcogen‐deficient stoichiometric phase, like the one reported for Mo 5 Te 8 .…”

“…The first molecular beam epitaxy (MBE) growth of thin films of TaTe 2 on bilayer graphene/SiC was recently reported. [ 21 ] The authors observed a 1T phase (rather than the distorted 1T′) for thicknesses up to 8MLs, and irreversible CDW transitions in the ML as a function of the substrate annealing temperature. For high substrate temperatures and thicknesses above the ML, the most stable superstructure was found to be the $$(\sqrt {19} \times \sqrt {19} )$$ CDW.…”