Monolayer Modification of VTe<sub>2</sub> and Its Charge Density Wave

Coelho, Paula Mariel; Lasek, Kinga; Cong, Kien Nguyen; Li, Jing‐Feng; Niu, Wei; Liu, Wenqing; Oleynik, Ivan; Batzill, Matthias

doi:10.1021/acs.jpclett.9b01949

Cited by 52 publications

(62 citation statements)

References 39 publications

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“…The formation of such ordered intercalation compounds may also explain some controversial results regarding possible distorted lattices for ultrathin TMDC-films formed by direct MBE growth at elevated growth temperatures. 22,23,26,44 Transformation of layered chalcogenides into a different compositional phase by chalcogen-desorption induced by annealing or electron beam irradiation has been reported previously for other systems. 45,46,47,48,49 Thus, the transformations observed here fall into the same general category of phase engineering of layered materials and demonstrates that post-growth processing of ultrathin layered materials is a common approach for synthesizing new van der Waals materials.…”

Section: Discussionsupporting

confidence: 53%

Compositional Phase Change of Early Transition Metal Diselenide (VSe₂ and TiSe₂) Ultrathin Films by Postgrowth Annealing

Bonilla

Kolekar

et al. 2020

Adv Materials Inter

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The transition metal selenides M 1+y Se 2 (M=V, Ti) have intriguing quantum properties, which make them target materials for controlling properties by thinning them to the ultrathin limit. An appropriate approach for the synthesis of such ultrathin films is by molecular beam epitaxy. Here we show that such synthesized V-and Ti-Se 2 films can undergo a compositional change by vacuum annealing. Combined scanning tunneling and photoemission spectroscopy was used to determine compositional and structural changes of ultrathin films as a function of annealing temperature. Loss of selenium from the film is accompanied by a morphology change of monolayer height islands to predominantly bi-layer height. In addition, crystal periodicity and atomic structure changes are observed. These changes are consistent with a transition from a layered transition metal dichalcogenide (TMDC) to ordered intercalation compounds with V or Ti intercalated in between two layers of their respective TMDCs. These observations may clear up misconception of the nature of previously reported high temperature grown transition metal selenides. More significantly, the demonstrated control of the formation of intercalation compounds is a key step towards modifying properties in van der Waals systems and towards expanding materials systems for van der Waals heterostructures.

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Section: Discussionsupporting

confidence: 53%

Compositional Phase Change of Early Transition Metal Diselenide (VSe₂ and TiSe₂) Ultrathin Films by Postgrowth Annealing

Bonilla

Kolekar

et al. 2020

Adv Materials Inter

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“…Room-temperature ferromagnetism has been observed in VTe2 nanoplates 2 . However, FM order was absent in monolayer VTe2 according to 3 / 18 recent experimental studies 36,37 . The interplay between the long-range charge and spin orders in monolayer VTe2 is yet unknown.Here we investigate the different CDW phases in monolayer VTe2 by STM/STS and DFT calculations.…”

mentioning

confidence: 87%

Multimorphism and gap opening of charge-density-wave phases in monolayer VTe2

Liu

et al. 2020

Nano Res.

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Vanadium dichalcogenides have attracted increasing interests for the charge density wave phenomena and possible ferromagnetism. Here, we report on the multiphase behavior and gap opening in monolayer VTe2 grown by molecular beam epitaxy. Scanning tunneling microscopy (STM) and spectroscopy study revealed the (4×4) metallic and gapped (2√3×2√3) charge-density wave (CDW) phases with an energy gap of ~40 meV. Through the in-plane condensation of vanadium atoms, the typical star-of-David clusters and truncated triangle-shaped clusters are formed in the (4×4) and (2√3×2√3) phases respectively, resulting in different surface morphologies and electronic structures as confirmed by density functional theory (DFT) calculations with on-site Coulomb repulsion. The CDW-driven reorganization of the atomic structure weakens the ferromagnetic superexchange coupling and strengthens the antiferromagnetic exchange coupling on the contrary, suppressing the long-range magnetic order in monolayer VTe2.The electron correlation is found to be important to explain the gap opening in the (2√3×2√3) phase. / 18Two-dimensional (2D) transition-metal dichalcogenides (TMDs) are recently attracting great attention for their diverse physical properties such as ferromagnetism 1,2 , Mott-insulator phase 3,4 , quantum Hall effect 5-7 , superconductivity and charge density wave (CDW) [8][9][10][11] . CDW is a periodic symmetry-lowering redistribution of charge in a material, accompanied with periodic modulation of the atomic lattice and electronic densities. The CDW transition in the group VB dichalcogenides, such as VS2, VSe2, NbSe2, TaS2, TaSe2 and TaTe2, has been extensively studied [12][13][14][15][16][17][18][19][20] . The phase transition exhibits a layer-dependent behavior, for instance, VSe2 and NbSe2 have increased CDW transition temperatures as the thicknesses reduce down to a few monolayers. In monolayer VSe2 and NbSe2, the TCDW can be enhanced to 140 K and 145 K compared to 110 K and 33 K of the bulk TCDW respectively [21][22][23][24] . The intricate interplay between CDW and other collective electronic states such as superconductivity has also been explored in NbSe2 and TaS2 25,26 . While the driving mechanisms of CDW in twodimensional TMDs consisting of Fermi surface nesting 27,28 , saddle point singularities 29,30 and electron-phonon coupling [31][32][33][34] have been proposed, a consistent picture on the CDW formation is still to emerge.As for VTe2, CDW phase transition has been observed in VTe2 thin films as the change of resistance at 240 K and 135 K, which can be driven by an electric field due to local Joule heating 35 . When the thickness reduces from multilayer to single layer, the absence of interlayer interaction result in the structural transition from a monoclinic distorted 1Tʹ structure to a hexagonal 1T structure 36 . The 1Tʹ structure has a (3×1) double zigzag chain-like modulation of V atoms, which arise from the in-plane metal coordination through d orbital hybridization. As the temperature is cooled below TCDW, the mo...

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“…Since the late 1950s, both CDW and magnetic orderings have been separately reported in VTe 2 of various thicknesses;15–19,21 in the former studies, however, the powder and thin film‐based VTe 2 materials showed conflicting features regarding their lattice structure at room temperature 19,20,22. Recent studies of thin VTe 2 films show that the interlayer interaction plays a role for the structural changes 18,23,24. However, no study on possible polymorphic quantum states from high‐quality VTe 2 single crystals has been performed.…”

Section: Electrical Properties Of the Types 1 And 2 Cdw Phases In Vtementioning

confidence: 99%

Polymorphic Spin, Charge, and Lattice Waves in Vanadium Ditelluride

et al. 2020

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Lattice distortion, spin interaction, and dimensional crossover in transition metal dichalcogenides (TMDs) have led to intriguing quantum phases such as charge density waves (CDWs) and 2D magnetism. However, the combined effect of many factors in TMDs, such as spin–orbit, electron–phonon, and electron–electron interactions, stabilizes a single quantum phase at a given temperature and pressure, which restricts original device operations with various quantum phases. Here, nontrivial polymorphic quantum states, CDW phases, are reported in vanadium ditelluride (VTe2) at room temperature, which is unique among various CDW systems; the doping concentration determines the formation of either of the two CDW phases in VTe2 at ambient conditions. The two CDW polymorphs show different antiferromagnetic spin orderings in which the vanadium atoms create two different stripe‐patterned spin waves. First‐principles calculations demonstrate that the magnetic ordering is critically coupled with the corresponding CDW in VTe2, which suggests a rich phase diagram with polymorphic spin, charge, and lattice waves all coexisting in a solid for new conceptual quantum state‐switching device applications.

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Monolayer Modification of VTe₂ and Its Charge Density Wave

Cited by 52 publications

References 39 publications

Compositional Phase Change of Early Transition Metal Diselenide (VSe₂ and TiSe₂) Ultrathin Films by Postgrowth Annealing

Compositional Phase Change of Early Transition Metal Diselenide (VSe₂ and TiSe₂) Ultrathin Films by Postgrowth Annealing

Multimorphism and gap opening of charge-density-wave phases in monolayer VTe2

Polymorphic Spin, Charge, and Lattice Waves in Vanadium Ditelluride

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Monolayer Modification of VTe2 and Its Charge Density Wave

Cited by 52 publications

References 39 publications

Compositional Phase Change of Early Transition Metal Diselenide (VSe2 and TiSe2) Ultrathin Films by Postgrowth Annealing

Compositional Phase Change of Early Transition Metal Diselenide (VSe2 and TiSe2) Ultrathin Films by Postgrowth Annealing

Multimorphism and gap opening of charge-density-wave phases in monolayer VTe2

Polymorphic Spin, Charge, and Lattice Waves in Vanadium Ditelluride

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Monolayer Modification of VTe₂ and Its Charge Density Wave

Compositional Phase Change of Early Transition Metal Diselenide (VSe₂ and TiSe₂) Ultrathin Films by Postgrowth Annealing

Compositional Phase Change of Early Transition Metal Diselenide (VSe₂ and TiSe₂) Ultrathin Films by Postgrowth Annealing