Janus MSiGeN4 (M = Zr and Hf) monolayers derived from centrosymmetric β-MA2Z4: A first-principles study

2021 ◽  
Vol 42 (12) ◽  
pp. 122002
Author(s):  
Xiaoshu Guo ◽  
Sandong Guo
Keyword(s):  
Band Gap ◽  
Tensile Strain ◽  
Compressive Strain ◽  
Valence Band Maximum ◽  
Spin Splitting ◽  
Piezoelectric Response ◽  
Generalized Gradient ◽  
Thermal Stabilities ◽  
Out Of Plane ◽  
Indirect Band Gap

Abstract A two-dimensional (2D) MA2Z4 family with and phases has been attracting tremendous interest, the MoSi2N4 and WSi2N4 of which have been successfully fabricated ( Science 369, 670 (2020)). Janus monolayers have been achieved in many 2D families, so it is interesting to construct a Janus monolayer from the MA2Z4 family. In this work, Janus MSiGeN4 (M = Zr and Hf) monolayers are predicted from -MA2Z4, which exhibit dynamic, mechanical and thermal stabilities. It is found that they are indirect band-gap semiconductors by using generalized gradient approximation (GGA) plus spin-orbit coupling (SOC). With biaxial strain from 0.90 to 1.10, the energy band gap shows a nonmonotonic behavior due to a change of conduction band minimum (CBM). A semiconductor to metal transition can be induced by both compressive and tensile strains, and the phase transformation point is about 0.96 for compressive strain and 1.10 for tensile strain. The tensile strain can change the positions of CBM and valence band maximum (VBM), and can also induce the weak Rashba-type spin splitting near CBM. For MSiGeN4 (M = Zr and Hf) monolayers, both an in-plane and out-of-plane piezoelectric response can be produced, when a uniaxial strain in the basal plane is applied, which reveals the potential as piezoelectric 2D materials. The high absorption coefficients in the visible light region suggest that MSiGeN4 (M = Zr and Hf) monolayers have potential photocatalytic applications. Our works provide an idea to achieve a Janus structure from the MA2Z4 family, and can hopefully inspire further research exploring Janus MA2Z4 monolayers.

STRAIN-TUNABLE BAND GAP OF BC3 SHEET: A FIRST-PRINCIPLES INVESTIGATION

2013 ◽  
Vol 27 (15) ◽  
pp. 1350110 ◽  
Author(s):  
GANG LIU ◽  
MU SHENG WU ◽  
CHU YING OUYANG ◽  
BO XU
Keyword(s):  
Band Gap ◽  
Electronic Properties ◽  
First Principles ◽  
Density Functional ◽  
Tensile Strain ◽  
Compressive Strain ◽  
Valence Band Maximum ◽  
Functional Theory ◽  
Band Maximum ◽  
Tunable Band Gap

The effect of strain on the electronic properties of BC 3 sheet was studied by using first-principles density functional theory. It is found that the band gap of BC 3 sheet increases gradually when the applied tensile strain ranges from 0% to 12.5%. While the band gap decreases as the compressive strain is applied, especially resulting in the semiconductor-metal transition at some strain. Further analysis shows that the change of band gap mainly results from the variation of the energy of valence band maximum (VBM), which is related to the strength of the bonding state. The proposed mechanical control of the electronic properties will widen the application of BC 3 sheet in future nanotechnology.

First-principles study on the band structure, magnetic and elastic properties of half-metallic Cr2MnAl

2015 ◽  
Vol 29 (24) ◽  
pp. 1550139 ◽  
Author(s):  
Santao Qi ◽  
Chuan-Hui Zhang ◽  
Bao Chen ◽  
Jiang Shen
Keyword(s):  
Band Structure ◽  
Band Gap ◽  
Elastic Properties ◽  
Density Functional ◽  
Stable State ◽  
Generalized Gradient ◽  
Half Metallic ◽  
Text Type ◽  
Calculation Results ◽  
Indirect Band Gap

In this study, we have investigated the structural, electronic, magnetic and elastic properties of the full-Heusler [Formula: see text] alloy in the framework of density functional theory with generalized gradient approximation (GGA). The calculated results showed that [Formula: see text] was stable in ferrimagnetic configuration and crystallized in the [Formula: see text]-type structure. From the band structure and density of states calculation results, we concluded that [Formula: see text] belongs to a kind of half-metallic compound with an indirect band gap of 0.37 eV. Immediately thereafter, we have analyzed the origin of half-metallic band gap. The total magnetic moment of [Formula: see text] at the stable state is [Formula: see text] per formula unit, obeying the Slater–Pauling rule [Formula: see text]. In addition, various mechanical properties have been obtained and discussed based on the three principle elastic tensor elements [Formula: see text] and [Formula: see text] for the first time in the present work. We expect that our calculated results may trigger the application of [Formula: see text] in future spintronics field.

Theoretical Investigation on Electronic Properties of ZnO Crystals Using DFT-Based Calculation Method

2015 ◽  
Vol 1112 ◽  
pp. 41-44 ◽  
Author(s):  
Yudi Darma ◽  
Freddy Giovanni Setiawan ◽  
Muhammad Aziz Majidi ◽  
Andrivo Rusydi
Keyword(s):  
Band Gap ◽  
Valence Band ◽  
Density Functional ◽  
Electronic Band Structure ◽  
Valence Band Maximum ◽  
Band Gaps ◽  
Generalized Gradient ◽  
Strong Electron ◽  
Electronic Band ◽  
Rocksalt Structure

We study the electronic band structure and density of states (DOS) on ZnO material in various crystal structures : wurtzite (W), zincblende (ZB), and rocksalt (RS) phases. Calculations are based on Density Functional Theory (DFT) with Generalized Gradient Approximation (GGA) for exchange-correlation functional and Hubbard correction to consider the strong electron correlations in 3d orbitals. After structural optimization, GGA results show that wurtzite and zincblende structures have a direct band gap of 0.749 eV and 0.637 eV, respectively, whereas rocksalt structure has an indirect band gap of 0.817 eV. Symmetrical shape of total DOS for spin up and spin down electrons indicates a zero total magnetic moment. For all ZnO structures, the upper valence band is formed by hybridization among O 2p and Zn 3d orbitals, while lower valence and conduction band are primarily filled by O 2s and Zn 4s, respectively. The GGA+U approach is found to improve the calculated band gaps and correct the position of Zn 3d state below Valence Band Maximum (VBM). From GGA+U, the band gaps for W-ZnO, ZB-ZnO, and RS-ZnO are 1.12 eV, 1.00 eV, and 1.11 eV, respectively.

Electronic State and Piezoresistivity Analysis of Zinc Oxide Nanowires for Force Sensing Devices

2015 ◽  
Vol 644 ◽  
pp. 16-21 ◽  
Author(s):  
Koichi Nakamura
Keyword(s):  
Band Gap ◽  
Compressive Strain ◽  
Force Sensing ◽  
Wall Structure ◽  
Direct Band Gap ◽  
Direct Band ◽  
The Difference ◽  
Piezoresistance Coefficient ◽  
Indirect Band Gap ◽  
P Type

The piezoresistivity for force sensing in wurtzite-ZnO nanowires with [0001] orientation has been simulated on the basis of the first-principles calculations of model structures. According to the difference in wall structure, our devised nanowire models can be divided into three groups by their conductivities; no band-gap conducting models, direct band-gap semiconducting models, and indirect band-gap semiconducting models. The strain responses to carrier conductivity of n-or p-doped semiconducting wurtzite-ZnO[0001] nanowire models were calculated using band carrier densities and their corresponding effective masses derived from the one-dimensional band diagram by our original procedure for a small amount of carrier occupation. The conductivities of p-type direct band-gap models change drastically due to longitudinal uniaxial strain in the simulation: the longitudinal piezoresistance coefficient is 120 × 10–11 Pa–1 for p-type (ZnO)24 nanowire model with 1% compressive strain at room temperature.

Increased Malleability in Tetragonal Zrx Ti1−x O2 Ternary Alloys: First-Principles Approach

2017 ◽  
Vol 72 (6) ◽  
pp. 567-572
Author(s):  
F. Ayedun ◽  
P.O. Adebambo ◽  
B.I. Adetunji ◽  
V.C. Ozebo ◽  
J.A. Oguntuase ◽  
...  
Keyword(s):  
Band Gap ◽  
First Principles ◽  
Density Functional ◽  
Ternary Alloys ◽  
Generalized Gradient ◽  
Functional Theory ◽  
Direct Band ◽  
Indirect Band Gap ◽  
Projector Augmented Wave ◽  
Alloying Effects

AbstractTetragonal phase of ZrxTi1−xO2ternary alloys is studied using generalized gradient approximation (GGA) projector augmented wave-based density functional theory (DFT). The calculations are used to characterize alloying effects of Zr substituting Ti in tutile TiO2. Band gap calculations show a direct band gap atx=0, while at other concentrations, an indirect band gap is observed. Electronic structure analysis shows that Zr alloying is capable of lowering the band gap transition of ZrxTi1−xO2atx=1 by the presence of an impurity state of transition metal Zr 5S2on the upper edge of the valence band. The addition of Zr also results in the corresponding increment in lattice constant with the material becoming more ductile and malleable.

scholarly journals Modeling and simulation of mechanical and physical properties of Barium orthotitanate (Ba2TiO4) composite by Materials Studio ( MS)

2018 ◽  
Vol 22 (11) ◽  
pp. 61
Author(s):  
Najat A. Dahham1 ◽  
Abdullah Hamoud Fares2 ◽  
Khaled Abdullah Najem1
Keyword(s):  
Physical Properties ◽  
Band Gap ◽  
Mechanical Stability ◽  
Linear Method ◽  
Young Modulus ◽  
Generalized Gradient ◽  
Lame Constant ◽  
Structure Density ◽  
Indirect Band Gap ◽  
Materials Studio

This research including a study of mechanical ,physical properties (band structure, density of states)  and the elasticity constants of the Barium Ortho titanate by using Materials studio software. The calculations were based on the generalized gradient approximation  (GGA) by linear method. The calculated equilibrium lattice constants of monoclinic barium orthotitanate were: a = 0.612nm, b = 0.77nm, c = 1.05nm,calculated bulk modulus =42.3021 GPa, young modulus= 40.29 GPa, share modulus = 15.97 GPa, lame constant (λ)= 142.56 GPa ,and energy band gap=3.435eV which is indirect band gap and the composite is insulator and the electronic properties where be calculated in first Brillion zone. According the mechanical stability conditions the composite is stable mechanically. These results were calculated by Materials studio software. 

Not your familiar two dimensional transition metal disulfide: structural and electronic properties of the PdS2monolayer

2015 ◽  
Vol 3 (37) ◽  
pp. 9603-9608 ◽  
Author(s):  
Yu Wang ◽  
Yafei Li ◽  
Zhongfang Chen
Keyword(s):  
Transition Metal ◽  
Band Gap ◽  
Electronic Properties ◽  
Structural Properties ◽  
Tensile Strain ◽  
Two Dimensional ◽  
Structural And Electronic Properties ◽  
High Carrier ◽  
Indirect Band Gap

The PdS2monolayer has distinguished structural properties from other transition metal disulfides, and also has rather high carrier mobilities. It is semiconducting with a moderate indirect band gap, which could be effectively tuned by applying a tensile strain.

scholarly journals Strain effects on electronic, optical properties and carriers mobility of Cs2SnI6 double perovskite: A promising photovoltaic material

2021 ◽  
Author(s):  
B. Rezini ◽  
T. Seddik ◽  
R. Mouacher ◽  
Tuan Vu ◽  
Mohammed Batouche ◽  
...  
Keyword(s):  
Optical Properties ◽  
Band Gap ◽  
Carrier Mobility ◽  
Tensile Strain ◽  
Compressive Strain ◽  
Double Perovskite ◽  
Band Gap Energy ◽  
Exchange Potential ◽  
Photovoltaic Properties ◽  
Strain Effects

Owing to the fascinating optoelectronic and photovoltaic properties, perovskite halide materials have attracted much attention for solar cells applications. Using the first-principles approaches, we present here results of calculations of the strain effects on electronic and optical properties as well as carriers mobility of CsSnI double perovskite. The calculated band gap energy of unstrained CsSnI is about 1.257 eV when using Tran-Blaha modified Becke Johnson (mBJ) exchange potential that is in fair agreement with experimental measurements. Under the applied strains, this band gap value increases up to 1.316 eV for -4% compressive strain and decreases till 1.211 eV for 4% tensile strain. This effect is mainly due to the fact that the conduction band minimum shifts under compressive and tensile strains. From carrier mobility calculations, we notice that under tensile strain both hole and electron carrier mobilitiy diminishes, whereas the carrier mobility increases by 25.7 % for electron and by 15 % for holes under -4% compressive strain. Moreover, the optical analysis reveals that applied strain can affect the optical properties of CsSnI perovskite.

scholarly journals Strain and Electric Field Modulated Indirect to Direct Band Transition of Monolayer GaInS2

2021 ◽  
Author(s):  
Atanu Betal ◽  
Jayanta Bera ◽  
Satyajit Sahu
Keyword(s):  
Optical Properties ◽  
Electric Field ◽  
Band Gap ◽  
Density Functional ◽  
Compressive Strain ◽  
Direct Band Gap ◽  
Td Dft ◽  
Direct Band ◽  
Band Transition ◽  
Indirect Band Gap

Abstract Strain and electric field dependent electronic and optical properties have been calculated using density functional theory (DFT) and time-dependent DFT (TD-DFT) for GaInS2 monolayer. GaInS2 monolayer shows an indirect band gap of 1.79 eV where valance band maxima (VBM) and conduction band maxima (CBM) rest between K and Γ point and at Γ point, respectively. Under a particular tensile strain (8%), a phase change from semiconductor to semimetal has been noticed. While at 4% compressive strain, the material changes from indirect to direct band gap of 2.22 eV having VBM and CBM at Γ point. With further increase in compressive strain, CBM shifted from Γ to M point, which leads to an indirect band gap again. The electric field also affects the band structure of monolayer GaInS2 and shows the transition between indirect to direct band gap at positive electric field of 4 V/nm, which acts normal to the surface. The strain-dependent optical properties are also calculated, which suggests that the absorption coefficient increases with compressive strain.

scholarly journals Structural fluctuations cause spin-split states in tetragonal (CH3NH3)PbI3 as evidenced by the circular photogalvanic effect

2018 ◽  
Vol 115 (38) ◽  
pp. 9509-9514 ◽  
Author(s):  
Daniel Niesner ◽  
Martin Hauck ◽  
Shreetu Shrestha ◽  
Ievgen Levchuk ◽  
Gebhard J. Matt ◽  
...  
Keyword(s):  
Band Gap ◽  
Tetragonal Phase ◽  
High Efficiency ◽  
Polarized Light ◽  
Spin Splitting ◽  
Rashba Effect ◽  
Photogalvanic Effect ◽  
Circularly Polarized Light ◽  
Structural Fluctuations ◽  
Indirect Band Gap

Lead halide perovskites are used in thin-film solar cells, which owe their high efficiency to the long lifetimes of photocarriers. Various calculations find that a dynamical Rashba effect could significantly contribute to these long lifetimes. This effect is predicted to cause a spin splitting of the electronic bands of inversion-symmetric crystalline materials at finite temperatures, resulting in a slightly indirect band gap. Direct experimental evidence of the existence or the strength of the spin splitting is lacking. Here, we resonantly excite photocurrents in single crystalline (CH3NH3)PbI3 with circularly polarized light to clarify the existence of spin splittings in the band structure. We observe a circular photogalvanic effect, i.e., the photocurrent depends on the light helicity, in both orthorhombic and tetragonal (CH3NH3)PbI3. At room temperature, the effect peaks for excitation photon energies ΔE=110 meV below the direct optical band gap. Temperature-dependent measurements reveal a sign change of the effect at the orthorhombic–tetragonal phase transition, indicating different microscopic origins in the two phases. Within the tetragonal phase, both ΔE and the amplitude of the circular photogalvanic effect increase with temperature. Our findings support a dynamical Rashba effect in this phase, i.e., a spin splitting caused by thermally induced structural fluctuations which break inversion symmetry.

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