SOC Effect Research Articles

A comparative spin orbit coupling DFT study of opto-electronic properties of [formula omitted] and [formula omitted] bulk crystal

Bi2Se3 and Bi2Te3 are the ideal candidate for spintronics and many other novel applications due to their strong opto-electronic properties. These materials are regarded as topological insulator as they portray band inversion which is considered to be a key signature of topology. Moreover, because of their superior opto-electronic qualities, Bi2Se3 and Bi2Te3 are intriguing in the realm of optical and electronic applications. This paper compares the optical and electronic characteristics of Bi2Te3 and Bi2Se3 in the framework of density functional theory taking PBE-GGA and mBJ-GGA as exchange correlation potential. The analysis of band structure and density of states (DOS) confirms the gapped nature without and with SOC calculation. The introduction of SOC gives the accurate result which matches with the experimental figure. Optical properties including reflectivity, absorption coefficient, energy loss function, refractive index, extinction coefficient, and optical conductivity are analyzed without and with SOC. We have also calculated birefringence, dichroism, and the optical skin depth which has not been reported yet for those compounds. The spectroscopic limited maximum efficiency (SLME), which theoretically determines the power conversion efficiency (PCE) of solar cells is also calculated. Based on the optical and electronic properties, possible uses of Bi2Se3 and Bi2Te3 are discussed without and with SOC effect.

First-principles screening of optoelectronics and thermoelectric response of XAcTe2 (X=K, Rb) full Heusler alloys: mBJ+SOC effect

Structural geometry, Electronic, optical, and thermoelectric attributes of XAcTe2 (X=K,Rb) full Heuser alloys were investigated theoretically via density functional theory (DFT). Structural optimization yielded optimized lattice parameters along with obtained negative formation energies (Ef) revealed the thermodynamically stable cubic geometries of alloys under investigation. For both alloys, the computed electronic band dispersions exhibit semiconductor behavior with a direct band gap. The band gap value of KAcTe2 is 1.59 eV, and 1.66 eV for RbAcTe2. The analysis of optical response shows maximum absorption α (ω) in the ultraviolet (UV) region, validating their quality for photovoltaic devices. The investigation of thermoelectric characteristics showed that both alloys display higher electrical conductivities and lower thermal conductivities.

The quantum spin Hall insulator with large bandgap in functionalized AlBi monolayer

The quantum spin Hall (QSH) insulator exhibits various interesting physical properties. Therefore, researchers have been seeking QSH insulators with large bandgaps suitable for room temperature applications. Here, based on first-principles calculations, we predict that the chlorine atom functionalized AlBi monolayer forms a topological insulator with a large bandgap (Eg = 0.215 eV). Chlorination and SOC effect induce AlBi(Cl)2 band inversion, and phonon spectra calculations demonstrate excellent dynamic stability for AlBi(Cl)2. The Z2 topological invariants, as well as the topological nontrivial edge states further confirm these findings. In addition, we applied the biaxial strains ranging from −5% to 5% to the monolayer, revealing a topological phase transition at −3%, resulting in the emergence of a normal insulator. These interesting features suggest that chlorinated AlBi is a promising material for room temperature spintronic devices.

A Multiconfigurational Wave Function Theoretical Study on Electronic Structure and Magnetic Susceptibility of Dilanthanide Single Molecule Magnet.

Single molecule magnets (SMMs) have been a promising material for next-generation high-density information storage and molecular spintronics. N23--bridged dilanthanide complexes, {[(Me3Si)2N]2Ln(THF)(μ-η2:η2-N2)(THF)Ln[(Me3Si)2N]2}1-, exhibit high blocking temperatures and have been one of the promising candidates for future application. Rational understanding should be established between the magnetic properties and electronic structure. However, the theoretical study is still challenging due to the complexities in their electronic structures. Here, we theoretically studied the magnetic susceptibility of dilanthanide SMMs based on the state-of-the-art multistate-complete active space self-consistent field and perturbation theory at the second order and restricted active space state interaction with spin-orbit coupling calculations. Temperature dependence of the magnetic susceptibility (χmT-T curve) was quantitatively reproduced by the theoretical calculations. The complexities in the electronic states of these dilanthanide complexes originate from significantly strong static electron correlations in the lanthanide 4f and N2 π* orbitals and the SOC effect. The temperature dependence of the magnetic susceptibility results from the energy levels and magnetic properties of the low-lying excited state. The χmT values below 50 K are dominated by the ground state, while thermal distribution in the low-lying excited state affects the χmT values over 50 K. Saturation magnetization at low temperatures was also evaluated, and the result agrees with the experimental observation.

Octastanene Halogenide: A Family of Two-dimensional Nodal Line Semimetals and Topological Insulators

With the first principle calculation and k-p model, we find that the Octastanene halogenide is a node line semimetal(NLs) without spin-orbit coupling(soc), forming a fermi ring centered on point G and protected by mirror symmetry. The band simulated by the k-p model fits well with the band calculated by GGA-PBE at point G, and the energy dispersion calculated by the Hamiltonian of the model explains well the formation of node rings. Under the SOC effect, NLs become a two dimensional Topological Insulators(TIs). With the increase of atomic number, the large band gap reaches about 0.16 ev, and the clear spiral edge state of the quantum spin hall effect is obtained. The phonon spectra of the two structures show that they are dynamically stable. These findings provide a new two dimensional material series for the future design and manufacture of NLs and TIs.

Surface-functionalization induced spintronic and photocatalytic features in group-III monochalcogenide monolayers: A first-principles study

In this paper, based on first principles calculations, we propose functionalization of group-III monochalcogenides with halogen atoms to form Janus MXY (M = Al, Ga, In; X = Se, Te; Y = Br, I) monolayers with enhanced physical properties. Using phonon dispersion, formation energy and AIMD simulations, nine MXY monolayers are found to be highly stable. The proposed MXY structures are shown to be direct/indirect semiconductors with bandgaps in the range of 1.13 and 3.34 eV. With regard to SOC effect, large Rashba spin splitting is observed at the Γ-point of conduction band in all Janus MXY monolayers with the largest coefficient of 1.021 eVÅ for GaTeBr. Moreover, we apply vertical electric field and biaxial strain as methods to tune the electronic and spintronic properties of MXY monolayers and improve their potential applications in the future devices. Investigating band edge positions, we find that six MXY monolayers fulfil the band alignment requirement for overall water splitting. Finally, Optical absorption, spatial charge separation and Gibbs free energy profile as other factors to assess the efficiency of MXY photocatalysts are studied. We believe that our research can pave a solid way to tune the physical properties of group-III monochalcogenides for a wider range of applications.

Tunable valley polarization and magneto-crystal anisotropy in two-dimensional VI3/WSe2 Van der Waals heterostructure

In this work, the effects of magnetic proximity coupling on electronic structures, valley polarization and magneto-crystal anisotropy of VI3/WSe2 heterostructure are studied in detail based on density functional theory. The results show that the spin-valley polarization characters of WSe2 monolayer can be induced by the proximity effect of ferromagnetic VI3 monolayer. Based on the effective Hamiltonian [Formula: see text] model, a large valley polarization of 8.7[Formula: see text]meV is observed, which is mainly contributed by the SOC effect and not magnetic exchange field. Meanwhile, the magneto-crystal anisotropy of VI3 layer is also obviously altered from the [100] to [001] magnetic axis compared to the isolated VI3 monolayer. The reduction in the interlayer space strengths the W–V atomic coupling, resulting in a significant increase in the spin and valley polarization. Compression strain shows weakening effect on the valley polarization, while the tensile strain largely enhances the valley polarization of VI3/WSe2 heterostructure, which can reach the maximum value of 29.1[Formula: see text]meV at the tensile strain of 8%. The V spin direction ([Formula: see text]) has significant effect on valley polarization of WSe2 layer, which is positively correlated with the magnetization strength of V atom in the vertical direction. Furthermore, constructing the VI3/WSe2/VI3 sandwich heterostructure can induce a larger valley polarization, which can reach a maximum value of 32.4[Formula: see text]meV. These results indicate that the VI3/WSe2 heterostructure is a potential candidate for valleytronics.

Quantum spin hall charge pumping characterized by symmetry in 2D topological Sb2S3 insulator

The quantum spin hall (QSH) insulator in a hexagonal lattice motivates the future searching for novel two-dimensional (2D) materials due to the potential applications caused by the dissipationless helical edges located in the band gap on spintronic devices, in which the symmetry of crystals has a significant effect on topological properties. Here, we investigate the topological property of the Sb2S3 monolayer by means of the group theory and symmetries based on first principle calculations. Our results demonstrate that the Sb2S3 monolayer is a Z2 insulator with a huge bulk band gap of 252 meV in the presence of SOC effect. The characterization of topological non-trivial band gap is the irreducible representation of the conduction band and valence band undergoes a reversal when crossing the path along the band gap under the operation of crystal point groups, resulting in the band inversion. This result is convinced by the evolution of the wave-functions. Our finding deepens the insight into the quantum hall effects and provides some theoretical ideas for a deeper knowledge on topological non-trivial band.

A theoretical study on the influence of N-containing heterocyclic ligands on the luminescence mechanisms (phosphorescence or TADF) of Au (III) complexes

Au (III) complexes display remarkable emission properties in OLEDs materials due to the high-performance emitters in recent years. Explaining microscopic mechanisms of the luminescence process clearly remain a challenge. The intersystem crossing between the singlet excited state and the triplet excited state in the metal complexes systems plays a central role in determining the fate of excitons and various luminescence pathways. For the planar tridentate coordination complexes of Au (III), it remains unclear what are the key factors that affect the luminescent pathways and thus the quantum efficiency. This work uncovers the relationship between the intersystem crossing processes (include ISC and RISC) and electronic structures of chelated ligands in the Au ( III ) complexes, which is supported by the quantum-chemical calculations. It is found that the modification of strong electron-donating groups (such as –NMe 2 , -NPh 2 ) may reduce the vibration coupling effect and energy gap (Δ E ST ), then open the thermal equilibrium channel, and finally obtain higher quantum yield TADF emitter through the fluorescence process. But the complex that has carbazole group in the auxiliary ligand still can't undergo the RISC process. These may be caused by the various electron delocalization and transition type result from different auxiliary ligands mediated by the N 2 atom. Moreover, the vibration analyses for the phosphorescence emision show that the vibration modes, which make significantly contribute to the reorganization energy, mainly come from the CˆNˆC ligand. While for TADF emission, that is from the auxiliary ligand. This work presents a deep insight into the luminescent mechanism and the key factors affected by the regulation of the ligands in the Au (III) complexes, and provides valuable theoretical basis and reference for the synthesis and design of TADF materials. • The higher SOC effect does not necessarily lead to the TADF process. • The modification of strong electron-donating may reduce the vibration coupling effect and energy gap Δ E ST , finally obtain higher quantum yield TADF emitter through the fluorescence process. • Adding the carbazole group in the auxiliary ligand can enhance the contribution of the CˆNˆC ligand on the reorganization energy.

New families of quantum spin Hall insulators with rashba effect in functionalized InBi monolayers

Because quantum spin Hall (QSH) insulators with dissipative electron transport properties have broad application prospect in the field of quantum devices, QSH insulators have aroused great research enthusiasm and many ideal QSH insulators are predicted successfully. Based on density functional calculations, we predict that new families of functionalized InBi monolayers, H–InBi-X (X = F, Cl, Br, I), to be QSH insulators. We find that the pristine InBi monolayer that is simultaneously hydrogenated and halogenated has a maximum band gap of 0.49 eV while preserving the untrivial topological properties, which is large enough for room-temperature applications. Because of the absence of inversion symmetry, the Rashba SOC effect occurs in the band structure and the SOC not only opens the bandgaps but also leads to the band inversion. In addition, the topological properties of these monolayers can survive a wide range of external strain from −6% to 6%. Our findings enrich the inversion-asymmetry topological materials and provide a reliable reference for designing QSH insulators at room temperature.

Rashba states localized to InSe layer in InSe/GaTe(InTe) heterostructure

The zero potential gradient in 2D III-VI chalcogenides NX (N = Ga, In; X = S, Se, Te) monolayers hinders the Rashba spin splitting (RSS), which limits their application in spintronics. Here, we construct InSe/GaTe and InSe/InTe van der Waals (vdW) heterostructures and investigate their Rashba SOC effect on the basis of first-principles calculations. The occurrence of internal electric field in the heterostructures induces spin splitting conduction band minimum (CBM). Rashba characteristic of the spin splitting can be confirmed through the band structures and spin textures. The projected energy bands suggest that the RSS state in both heterostructures mainly roots in InSe layers. Furthermore, in-plane strain, vertical strain, and the external electric field are all proved to be effective methods to regulate the RSS. When an in-plane strain of 6% is exerted, the Rashba coefficient can become as high as 1.33 eV Å and 1.26 eV Å for InSe/GaTe and InSe/InTe, respectively. The occurrence of controllable RSS at CBM makes the both heterostructures become potential candidate materials for spintronic devices.

Tunable electronic structure and Rashba spin splitting of WSe2/WS2 van der Waals heterostructure via strain and electric-field

Suitable band structure, effective carrier separation and spin-charge locking are critical for further development and application of nanoscale spintronic devices. In this work, the effects of in-plane biaxial strain and electric field on the electronic structures and Rashba spin splitting of WSe 2 /WS 2 van der Waals heterostructure are investigated by the first principles calculations. The results show that considering the SOC effect, an observable Dresselhaus spin splitting of 424.5 meV and Rashba spin splitting can be observed at the K and Γ point in the valence band, respectively. At the same time, unexpected circle-type Berry curvature occurs due to a broken mirror structure for the WSe 2 /WS 2 heterostructure. A largest Rashba parameter α R with 0.503 eV Å can be achieved at the strain of −4% and the positive electronic field tend to weaken the strength of Rashba spin splitting. The linear Rashba spin splitting strength of WSe 2 /WS 2 heterostructure is tried to clarify, and coexistence of valley-contrasting property and Rashba effect enables spintronics and valleytronics application can be achieved. These results provide a way to engineer the electronic structure and Rashba spin splitting of WSe 2 /WS 2 heterostructure and open up the possibilities for exploring spin logic electronic devices as well as valleytronic devices. • Effects of strain and electric field on the electronic structures of WSe2/WS2van der Waals heterostructure are studied. • The WSe 2 /WS 2 heterostructure exhibits type-II band alignment and tunable Rashba spin splitting. • Unexpected circle-type Berry curvature occurs due to broken mirror structure. • A largest Rashba parameter α R of 0.507 eV Å can be obtained at the strain of −4%.

Exploring the stability and physical properties of double perovskite Cs2SnI6 by doping the Cl/Br atom: A DFT study

In recent years, it is of great interest to develop stable and high efficiency lead-free perovskite materials. Double perovskite Cs2SnX6 (X = Cl, Br, I) shows excellent stability and tunable band gap. The stability, electronic, and optical properties of three mixed halide double perovskites Cs2SnI4Cl2, Cs2SnI4ClBr, and Cs2SnI4Br2 are studied in this work. The stability of three mixed halide compounds is slightly lower than that of Cs2SnI6. The trend of phase separation is found for the studied compounds. Compared with CsSnX3, the SOC effect is negligible for Cs2SnX6. Cs2SnI4Cl2 and Cs2SnI4ClBr have the same band gaps with 1.75 eV, while Cs2SnI4Br2 shows an optimum band gap with 1.56 eV. Although these mixed halide compounds display stronger absorption coefficients than Cs2SnI6 from 300 to 450 nm, the lower light absorption capacity is observed between 450 and 800 nm.

First-principles study of the structural, electronic and optical properties of Zn1-xHgxSe (x = 0, 0.25, 0.50, 0.75, 1)

The structural, electronic and optical properties of Zn1-xHgxSe alloys with different Hg concentrations (x = 0, 0.25, 0.50, 0.75, 1) are studied through first-principles calculations. The stability of three Zn1-xHgxSe ternary alloys is proved by calculating phonon spectrum. It is found that the SOC effect on the band gap is less than 0.2 eV. In addition, the HSE06 functional underestimates the band gap of ZnSe, so the PBE0 functional is employed to calculate the electronic and optical properties of Zn1-xHgxSe alloys. The tunable band gap can be realized by Hg doping from 2.5 to 0 eV Zn0.75Hg0.25Se and Zn0.50Hg0.50Se have suitable band gaps (1.0–1.8 eV) for solar cells. Zn0.50Hg0.50Se shows wider and higher absorption coefficient than that of Zn0.75Hg0.25Se in the visible light range.

Prediction of nodal-line semimetals in 2D ScX (X = P, As) with high stability and considerable fermi velocities

• New nodal–line ternary semimetals of ScX (X = P, As) are proposed. • Fully optimized structures still keep good structural integrity at high temperature of 1000 K. • The SOC effect and physical biaxial strain are negligible for the nodal-line of ScX. • The considerable Fermi velocities which are the same order of magnitude as graphene. • The elastic constants and transport properties of ScX (X = P, As) show nice anisotropy. The nodal–line structure provides higher carrier mobility, massless and special features in which the conduction band and the valence band cross at the Fermi level. The anisotropic nodal–line structure has the advantage of anisotropic Fermi velocity for novel 2D quantum device. Here we report two binary monolayers with anisotropic nodal–line based on first-principles calculation. Fully optimized ScX (X = P, As) structure can still keep good structural integrity at high temperature of 1000 K in ab initio molecular dynamics simulation. Besides, we analyze structural symmetry and wave function to illustrate the existence of nodal–line, the Young’s modulus and Poisson’s ratio of ScX show nice anisotropy. The Fermi velocities of ScX are larger than 10 5 m/s, which are the same order of magnitude as graphene. This work provides novel candidates of nodal–line semimetals for massless and stable quantum devices.

Large Gap Two-Dimensional Topological Insulators with the Significant Rashba Effect in Ethynyl and Methyl Functionalized PbSn Monolayers.

Two-dimensional (2D) topological insulators (TIs) have recently attracted a great deal of attention due to their nondissipation electron transmission, stable performance, and easy device integration. However, a primary obstacle to influencing 2D TIs is the small bandgap, which limits their room-temperature applications. Here, we adopted first-principles to predict inversion-asymmetric group IV monolayers, PbSn(C2H)2 and PbSn(CH3)2, to be quantum spin Hall (QSH) insulators with large topological gaps of 0.586 and 0.481 eV, respectively. The nontrivial band topologies, which can survive in a wide range of strain, are characterized by topological invariants Z2, gapless edge states, and the Berry curvature. Another intriguing characteristic is the significant Rashba SOC effect which can also be tuned by feasible compressive and tensile strains. Meanwhile, the hexagonal boron nitride (h-BN) provides a suitable substrate for growth of these films without influencing their topological phases. These novel materials are expected to accelerate the development of advanced quantum devices.

Large gap two-dimensional topological insulators with prominent Rashba effect in ethynyl functionalized Ⅲ-Bi Buckled-Honeycomb monolayers

Recently, two-dimensional topological insulators have attracted extensive attention because of their excellent electronic transport performance and easy integration into electronic devices. However, the small bandgap limits their room-temperature application. Based on first-principles calculations, we predict that the ethynyl functionalized GaBi/InBi monolayers are topological insulators with large bandgap ( E g = 0.512 e V ) and significant Rashba SOC effect ( α R = 2.819 eVÅ ). The topological phases, which originate from s-p x,y band inversion induced by chemical bonding, can be maintained within the large-range biaxial strain. Additionally, the h -BN is found to be an ideal substrate for the growth of these QSH insulators. These findings indicate that the ethynyl functionalized Ⅲ-Bi monolayers are expected to be candidate materials for spintronics and quantum computing . These findings indicate that the ethynyl functionalized Ⅲ-Bi monolayers are expected to be candidate materials for spintronics and quantum computing. • We predict that the ethynyl functionalized GaBi/InBi monolayers are topological insulators with large bandgap ( E g = 0.512 eV ) and significant Rashba SOC effect ( α R = 2.819 eVÅ ) . • We research the strain engineering and explain the change in topology phase through evolution of orbitals. • We study the significant Rashba SOC effect and the electric field impact. • The h -BN is found to be an ideal substrate for the growth of these QSH insulators.

Insight into elastic anisotropy, mechanical and dynamical stability, electronic properties, bonding and weak interactions analysis of LuAuSn Half-Heusler

Despite their great interest showing that LuAuSn half-Heusler is a topologically trivial semimetal, most of information about its physical behaviors seem rather remote from completion for the fact that several of its physical properties remain still unknown. Therefore, we try to outline, going into much specific details, a study on elastic anisotropy, mechanical and dynamical stability, electronic properties as well as the analysis of bonding and weak interactions. The lattice parameter value obtained by GGA-WC is very close to the experimental one, therefore, this functional has been chosen to carry out the rest of this work. The detailed study of the elastic behavior has revealed the mechanical stability of this compound, it results that its structure resists to slight strains. The obtained results also indicate a large elastic anisotropy of LuAuSn. Electronic results obtained by TB-mBJ(SOC) have confirmed its semimetallic behavior as well as being topologically trivial. This last property has been confirmed not only by the absence of band overlap but also by the absence of band inversion by the analysis of fat bands with and without SOC effect. The analysis of bonding and weak interactions has shown that the covalent character is predominant with the presence of weak repulsive interactions in cage regions and strong repulsive interactions between Lu and Sn. The vibrational study has revealed the dynamical stability of LuAuSn in the ground state, which indicates that this compound keeps its half-Heusler structure even at very low temperatures. Also, its zone center phonon modes have been determined and analyzed in detail by showing their frequencies and polarizations.

Transition properties among Ω states originating from X 2Π, A 2Σ+, B 2Π, C 2Σ+, a 4Π, b 4Σ+, c 4Δ, and d 4Σ– states of SiP molecule

The potential energy curves of X 2Π, A 2Σ+, B 2Π, C 2Σ+, a 4Π, b 4Σ+, c 4Δ, and d 4Σ– states of SiP molecules and the transition dipole moments of the transitions between these states were calculated using the CASSCF method, followed by the icMRCI approach. The radiative lifetimes of the first 16 vibrational levels were 0.27 – 66 and 1.5 – 2.38 × 104 ms for the A 2Σ+ and b 4Σ+ states, respectively. Those were 146 – 497, 93 – 254, 23.9 – 30.3, and 0.85 – 1.1 µs for the B 2Π, c 4Δ, d 4Σ–, and C 2Σ+ states, rspectively. The spin–orbit coupling constants of the X 2Π, B 2Π, a 4Π, and b 4Σ+ states were evaluated. Including the spin–orbit coupling effect, the radiative lifetimes of the A 2Σ+1/2, B 2П1/2, B 2П3/2, C 2Σ+1/2, a 4П–1/2, a 4П1/2, a 4П3/2, a 4П5/2, b 4Σ+1/2, and b 4Σ+3/2 states were calculated. The lifetimes of the first 16 levels were 0.35 – 0.42, 3.1 – 5.5, 1.3 – 5.8, and 30 – 57 s for the a 4П–1/2, a 4П1/2, a 4П3/2, and a 4П5/2 states, respectively. And those were 2.3 – 268 and 2.6 – 257 ms for the b 4Σ+1/2 and b 4Σ+3/2 states, respectively. The SOC effect made the radiative lifetimes of the A 2Σ+, B 2Π, and C 2Σ+ states become longer. Among the spontaneous emissions between these Ω states, those from the C 2Σ+1/2 state to the X 2П3/2, X 2П1/2, and A 2Σ+1/2 states were the strongest. The results indicated that the strong emissions originated from the lower levels of the C 2Σ+1/2 state. Furthermore, almost all of these strong emissions were in the visible region. All emissions generating from the a 4П–1/2, a 4П1/2, a 4П3/2, and a 4П5/2 states are extremely weak. The radiative–lifetime distribution of each level υ versus the rotational quantum number J was evaluated for several Ω states.

Optical properties of molybdenum disulfide on different substrates affected by spin-orbit coupling

Molybdenum disulfide (MoS 2 ) films have been widely used in many optical devices owing to their excellent optical properties. In this paper, inch-scale MoS 2 films were grown on sapphire substrates through chemical vapor deposition (CVD) and transferred to SiO 2 /Si substrates. Analysis of Raman spectroscopy shows the transfer process releases uniaxial stress and introduces weak n-type doping. Using spectroscopic ellipsometry to analyze the refractive index, extinction coefficient and the dielectric function of monolayer MoS 2 on sapphire substrates and SiO 2 /Si substrates, the electron transition energies were calculated on this basis. Combined with the first principle calculation based on density functional theory (DFT), the physical origins of electron transition peak were obtained. Computational and experimental tests show that monolayer MoS 2 on sapphire substrates show spin-orbit coupling phenomena, which leads to the splitting of an electron-jumping peak, while MoS 2 on SiO 2 /Si substrates did not exhibit spin-orbit coupling. This work can provide a reference for the application of MoS 2 on different substrates. • Inch-scale monolayer MoS 2 films on different substrates were prepared by CVD. • Optical constants of MoS 2 films were explored by spectroscopic ellipsometry. • Origins of electron transition peaks were obtained combined with theoretical calculations. • The variation of dielectric function on different substrates is due to the SOC effect.