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VSe2 is trigonal omega structured and crystallizes in the trigonal P-3m1 space group. The structure is two-dimensional and consists of one VSe2 sheet oriented in the (0, 0, 1) direction. V4+ is bonded to six equivalent Se2- atoms to form edge-sharing VSe6 octahedra. All V–Se bond lengths are 2.50 Å. Se2- is bonded in a 3-coordinate geometry to three equivalent V4+ atoms.
Na(VSe2)2 is MAX Phase-like structured and crystallizes in the trigonal R3m space group. The structure is two-dimensional and consists of three Na(VSe2)2 sheets oriented in the (0, 0, 1) direction. Na1+ is bonded in a 6-coordinate geometry to six Se2- atoms. There are three shorter (2.99 Å) and three longer (3.00 Å) Na–Se bond lengths. There are two inequivalent V+3.50+ sites. In the first V+3.50+ site, V+3.50+ is bonded to six Se2- atoms to form edge-sharing VSe6 octahedra. There are three shorter (2.52 Å) and three longer (2.59 Å) V–Se bond lengths. In the second V+3.50+ site, V+3.50+ is bonded to six Se2- atoms to form edge-sharing VSe6 octahedra. There are three shorter (2.52 Å) and three longer (2.59 Å) V–Se bond lengths. There are four inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to three equivalent Na1+ and three equivalent V+3.50+ atoms to form a mixture of face, edge, and corner-sharing SeNa3V3 octahedra. In the second Se2- site, Se2- is bonded in a distorted T-shaped geometry to three equivalent V+3.50+ atoms. In the third Se2- site, Se2- is bonded to three equivalent Na1+ and three equivalent V+3.50+ atoms to form a mixture of distorted face, edge, and corner-sharing SeNa3V3 pentagonal pyramids. The corner-sharing octahedral tilt angles are 41°. In the fourth Se2- site, Se2- is bonded in a distorted T-shaped geometry to three equivalent V+3.50+ atoms.
Na(VSe2)2 crystallizes in the monoclinic Pm space group. The structure is three-dimensional. Na1+ is bonded in a 6-coordinate geometry to six Se2- atoms. There are a spread of Na–Se bond distances ranging from 2.98–3.10 Å. There are two inequivalent V+3.50+ sites. In the first V+3.50+ site, V+3.50+ is bonded to six Se2- atoms to form edge-sharing VSe6 octahedra. There are a spread of V–Se bond distances ranging from 2.48–2.59 Å. In the second V+3.50+ site, V+3.50+ is bonded to six Se2- atoms to form edge-sharing VSe6 octahedra. There are a spread of V–Se bond distances ranging from 2.47–2.59 Å. There are four inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to two equivalent Na1+ and three V+3.50+ atoms to form distorted SeNa2V3 square pyramids that share corners with five equivalent SeNa2V3 trigonal bipyramids, corners with four SeNaV3 trigonal pyramids, edges with two equivalent SeNa2V3 square pyramids, edges with two equivalent SeNa2V3 trigonal bipyramids, and edges with four SeNaV3 trigonal pyramids. In the second Se2- site, Se2- is bonded to one Na1+ and three V+3.50+ atoms to form distorted SeNaV3 trigonal pyramids that share corners with two equivalent SeNa2V3 square pyramids, corners with two equivalent SeNa2V3 trigonal bipyramids, corners with six SeNaV3 trigonal pyramids, edges with two equivalent SeNa2V3 square pyramids, edges with two equivalent SeNa2V3 trigonal bipyramids, and an edgeedge with one SeNaV3 trigonal pyramid. In the third Se2- site, Se2- is bonded to two equivalent Na1+ and three V+3.50+ atoms to form distorted SeNa2V3 trigonal bipyramids that share corners with five equivalent SeNa2V3 square pyramids, corners with four SeNaV3 trigonal pyramids, edges with two equivalent SeNa2V3 square pyramids, edges with two equivalent SeNa2V3 trigonal bipyramids, and edges with four SeNaV3 trigonal pyramids. In the fourth Se2- site, Se2- is bonded to one Na1+ and three V+3.50+ atoms to form distorted SeNaV3 trigonal pyramids that share corners with two equivalent SeNa2V3 square pyramids, corners with two equivalent SeNa2V3 trigonal bipyramids, corners with six SeNaV3 trigonal pyramids, edges with two equivalent SeNa2V3 square pyramids, edges with two equivalent SeNa2V3 trigonal bipyramids, and an edgeedge with one SeNaV3 trigonal pyramid.
We report epitaxial growth of vanadium diselenide (VSe₂) thin films in the octahedrally coordinated (1T) structure on GaAs(111)B substrates by molecular beam epitaxy. Film thickness from a single monolayer (ML) up to 30 ML is demonstrated. Structural and chemical studies using x-ray diffraction, transmission electron microscopy, scanning tunneling microscopy, and x-ray photoelectron spectroscopy indicate high-quality thin films. Further studies show that monolayer VSe₂ films on GaAs are not air stable and are susceptible to oxidation within a matter of hours, which indicates that a protective capping layer should be employed for device applications. This work demonstrates that VSe₂, a candidate van der Waals material for possible spintronic and electronic applications, can be integrated with III-V semiconductors via epitaxial growth for two- and three-dimensional hybrid devices.
Here, we study the surface electronic structure of 1T-VSe 2 by means of angle resolved photoemission spectroscopy and uncover a dispersion-less emission located in the vicinity of the Fermi level. Its crystal momentum dependency reveals that it occupies large portions of the Brillouin zone (BZ), where no bulk band is expected. Upon electron doping (deposition of Rb-atoms), the system evolves in a surprising way. Besides the expected down-shifting of the bands, a splitting of both bulk and dispersion-less emission is observed. This peculiar behavior strongly suggests the intrinsic nature of the dispersion-less emission. Its characterization may therefore be relevant to a deeper understanding of the physics of transition metal dichalcogenides.
Three metastable compounds predicted to be kinetically stable using an “island” approach were successfully synthesized from designed modulated elemental reactants. Fe0.8V0.2Se2 was synthesized by depositing ultrathin elemental layers in a V|Fe|Se sequence to control the local composition. An alloyed rock salt structured Pb3Mn2Se5 constituent layer, which does not exist as a bulk compound, was synthesized in the heterostructure (Pb3Mn2Se5)0.6VSe2 by depositing a precursor with a V|Se|Pb|Se|Mn|Se|Pb|Se|Mn|Se|Pb|Se sequence of elemental layers that mimicked the compositional profile of the targeted heterostructure. The heterostructure (PbSe)1+δ(FeSe2)2 was prepared by depositing a precursor with a repeating layering sequence of Fe|Pb|Fe|Se, where each sequence contains the number of atoms required to form a single unit cell. In all three systems, the local compositions in the layer sequence kinetically favored the nucleation and growth of the targeted products during the deposition. The diffusion lengths to form the targeted compounds were short, and the diffusion was limited by postdeposition low temperature annealing to favor the growth of the targeted compounds and avoid the decomposition into a mixture of thermodynamically stable compounds.