Band Engineering and Van Hove Singularity on HfX₂ Thin Films (X = S, Se, or Te)

Abstract

Two-dimensional transition metal dichalcogenides (TMDs) have become well-known due to their versatile and tunable physical properties for potential applications, specifically on low-power and optical devices. Here, we explored the structural stability and electronic properties of bulk and thin-film (from 1 up to 6 layers) structures of hafnium dichalcogenides (HfX 2 , X = S, Se, or Te) using first-principles calculations. Our calculations reveal that the most stable phase is 1T for both thin films and bulk. The bulk and thin-film structures of HfTe 2 are semimetallic, while those of HfS 2 and HfSe 2 are insulating. Both HfS 2 and HfSe 2 thin films exhibit a decreasing band gap with increasing thickness, while HfTe 2 thin films remain semimetallic with increasing number of layers. Moreover, van Hove singularity (vHs), due to the contribution of the p z orbital from S atoms, is observed in 3L-HfS 2 at the valence band maximum, which can be further enhanced by applying an in-plane biaxial strain, suggesting possible superconductivity. Finally, the bulk and monolayer band structures of HfTe 2 , under HSE06 and GGA + U with the effective Hubbard U parameter of 4.6 eV, are in good agreement with the experimental ARPES data. Our results indeed show that HfX 2 have sensitive and tunable electronic properties through film thickness control and strain for future potential applications.

High-pressure structural phase transitions and metallization in layered HfS2under different hydrostatic environments up to 42.1 GPa

“…Among them, 1T-HfS 2 has been reported to be the most simple and stable polytype. [7][8][9][10] Previous investigations have disclosed that the pressure is a crucial factor in modulating the high-pressure crystalline and electronic structures of hafnium dichalcogenides, thus leading to the occurrences of structural transition and metallization under high pressure. 8,[11][12][13][14][15] Despite some available high-pressure phase stability and structural transition studies for HfSe 2 and HfTe 2 , the relevant research on HfS 2 has to date been rather rare.…”

Nontrivial Topology in Monolayer MA2Z4 (M = Ti, Zr, or Hf; A = Si or Ge; and Z = N, P, As, Sb, or Bi)

“…Among them, graphene, which is renowned for its exceptional electronic properties such as high electron mobility and remarkable mechanical strength, is the first 2D material discovered to have a nontrivial topological phenomenon . Since graphene was obtained experimentally, thousands of new 2D materials have been proposed, − and many have been synthesized. − Beyond graphene, the other reported two-dimensional topological materials possessing honeycomb structures are III–V buckled honeycombs, , MXenes, − transition metal dichalcogenides (TMD), − Janus materials, , ternary transition metal chalcogenides, , functionalized Bi/Sb, arsenene oxide, and RuClBr . Additionally, other 2D topological compounds in different structures such as copper sulfide, Zintl compounds, , half-Heusler compounds, and ilmenite oxidizes also exist.…”

Pressure-induced phase transition and electronic structure evolution in layered semimetal HfTe2

“…[1][2][3][4][5][6] In particular, more and more interests have been paid to the Hafnium dichalcogenides HfX 2 (X = S, Se, and Te), a typical group of layered TMDs with exotic electronic structures, showing an important application in optoelectronic and electronic. [7][8][9][10] HfX 2 adopts the well-known 1T trigonal structure (P 3m1, Z = 1), consisting of the X-Hf-X sandwich layers along the c-axis direction with weak van der Waals (vdW) interactions. [11] Both HfS 2 and HfSe 2 have been manifested to be narrow band-gap semiconductors and possessed higher electron mobility and current density, which make they are favorable candidates for high performance field-effect transistor components, optoelectronic devices, and photovoltaic cells.…”