Evolution of the Electronic Properties of ZrX₂ (X = S, Se, or Te) Thin Films under Varying Thickness

Abstract

Probing the effects of thin-film thickness on transition metal dichalcogenides offer novel insights into their electronic properties and tunability, which leads to a new avenue of research and applications. A comprehensive first-principles study on thickness-dependent structural stabilities and electronic properties of ZrX2 (X = S, Se, or Te) thin films from 1 layer (L) to 6L and bulk was performed. The calculated formation energies show that ZrX2 adopts the 1T phase as the most stable structure. Furthermore, 1T-ZrS2 and ZrSe2 thin films and bulk are indirect semiconductors and their band gaps decrease as the number of layers is increased up to 6L, while 1T-ZrTe2 thin films and bulk are semimetallic. Interestingly, we demonstrate that the surface band structure of bulk and monolayer ZrTe2 under generalized gradient approximation + U and HSE06 methods is in excellent agreement with the angle-resolved photoelectron spectroscopy measurement. Finally, we discover the existence of van Hove singularities in strained 2L and unstrained 3L 1T-ZrS2 thin films, implying the existence of superconductivity in these thin films. These results showcase the tunable electronic properties of ZrX2 thin films because of thickness dependence and strain.

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

“…This discovery indicates the sensitivity and possibility of modulation of the vHs peaks through thickness dependence and determination of the critical thickness, respectively. For thin-film HfS 2 , a critical thickness of 3 layers exists, which agrees well with previous studies about the relationship between thickness and vHs, 13,69 although no existing critical thickness was found for the HfSe 2 and HfTe 2 thin films.…”

“…This behavior, decreasing system band gap with increasing thickness, is also manifested in other thickness dependence studies. 10,12,13,17 This robustness in indirect system band gaps is also shown experimentally in thin-film HfSe 2. 33 The calculated system band gaps of 1L-HfX 2 under GGA, GGA + U using U eff of 4.6 eV, and HSE06 are tabulated in Table S2 and included in Figure 3a.…”

“…This trend is consistent with other semimetallic systems, PtTe 2 , 10 PdTe 2, 12 and ZrTe 2. 13 Moreover, from the DOS in Figures 4−6, we noticed that the Hf atom (denoted by magenta lines) dominates the contribution in the conduction bands above the Fermi level, whereas the chalcogen atom (denoted by cyan lines) dominates the valence bands below the Fermi level.…”

“…Compressive strain, on the other hand, leads to the destabilization of the vHs by shifting the p z orbital further below the Fermi level, resulting in the disappearance of the vHs DOS peak. Based on these results, the interplay between the critical thickness due to the quantum confinement effect 69 and straining is the crucial factor that affects the presence and stability of the vHs near the Fermi level, which was also observed in Pt 10 and Zr 13 TMDs. Our results show that the existence and stability of vHs can be engineered through controlling the thickness and strain.…”

Effects of 3d transition metal impurities and vacancy defects on electronic and magnetic properties of pentagonal Pd2S4 : Competition between exchange splitting and crystal fields

“…In addition, one of the most significant magnetization methods is doping the material with transition elements of different periods of the periodic table. Some of the works performed in this area are noted in the following [16][17][18][19][20][21][22][23][24][25][26][27][28] . Octa et al 17 created the T and H-phase conditions on an extensive range of TMCs and investigated the magnetization conditions on the structures.…”