scholarly journals Uniaxially Strained Graphene: Structural Characteristics and G-Mode Splitting

Materials ◽  
2021 ◽  
Vol 15 (1) ◽  
pp. 67
Author(s):  
George Kalosakas ◽  
Nektarios N. Lathiotakis ◽  
Konstantinos Papagelis
Keyword(s):  
Density Functional ◽  
Structural Characteristics ◽  
Strain Engineering ◽  
Graphene Monolayer ◽  
Mode Splitting ◽  
Zigzag Direction ◽  
Strained Graphene ◽  
Out Of Plane ◽  
Frequency Split ◽  
Analytical Relations

The potential use of graphene in various strain engineering applications requires an accurate characterization of its properties when the material is under different mechanical loads. In this work, we present the strain dependence of the geometrical characteristics at the atomic level and the Raman active G-band evolution in a uniaxially strained graphene monolayer, using density functional theory methods as well as molecular dynamics atomistic simulations for strains that extend up to the structural failure. The bond length and bond angle variations with strain, applied either along the zigzag or along the armchair direction, are discussed and analytical relations describing this dependence are provided. The G-mode splitting with strain, as obtained by first principles’ methods, is also presented. While for small strains, up to around 1%, the G-band splitting is symmetrical in the two perpendicular directions of tension considered here, this is no longer the case for larger values of strains where the splitting appears to be larger for strains along the zigzag direction. Further, a crossing is observed between the lower frequency split G-mode component and the out-of-plane optical mode at the Γ point for large uniaxial strains (>20%) along the zigzag direction.

scholarly journals Highly Selective Adsorption on SiSe Monolayer and Effect of Strain Engineering: A DFT Study

Sensors ◽  
2020 ◽  
Vol 20 (4) ◽  
pp. 977 ◽  
Author(s):  
Quan Zhou ◽  
Lian Liu ◽  
Qipeng Liu ◽  
Zeping Wang ◽  
Chenshan Gao ◽  
...  
Keyword(s):  
Compressive Stress ◽  
Adsorption Energy ◽  
Density Functional ◽  
Selective Adsorption ◽  
Physical Adsorption ◽  
Co Adsorption ◽  
Energy Charge ◽  
Strain Engineering ◽  
Zigzag Direction ◽  
Gas Molecules

The adsorption types of ten kinds of gas molecules (O2, NH3, SO2, CH4, NO, H2S, H2, CO, CO2, and NO2) on the surface of SiSe monolayer are analyzed by the density-functional theory (DFT) calculation based on adsorption energy, charge density difference (CDD), electron localization function (ELF), and band structure. It shows high selective adsorption on SiSe monolayer that some gas molecules like SO2, NO, and NO2 are chemically adsorbed, while the NH3 molecule is physically adsorbed, the rest of the molecules are weakly adsorbed. Moreover, stress is applied to the SiSe monolayer to improve the adsorption strength of NH3. It has a tendency of increment with the increase of compressive stress. The strongest physical adsorption energy (−0.426 eV) is obtained when 2% compressive stress is added to the substrate in zigzag direction. The simple desorption is realized by decreasing the stress. Furthermore, based on the similar adsorption energy between SO2 and NH3 molecules, the co-adsorption of these two gases are studied. The results show that SO2 will promote the detection of NH3 in the case of SO2-NH3/SiSe configuration. Therefore, SiSe monolayer is a good candidate for NH3 sensing with strain engineering.

Experimental and Theoretical (ab initio and DFT) Analysis of UV-Vis Spectra, Thermodynamic Functions and Non-linear Optical Properties of 2-Chloro-3,4-Dimethoxybenzaldehyde

2015 ◽  
Vol 8 (2) ◽  
pp. 2122-2134
Author(s):  
Sarvendra Kumar ◽  
Rajesh Kumar ◽  
Jayant Teotia ◽  
M. K. Yadav
Keyword(s):  
Thermodynamic Functions ◽  
Title Compound ◽  
Density Functional ◽  
Structural Characteristics ◽  
Basis Sets ◽  
Ultraviolet Absorption Spectrum ◽  
Non Linear ◽  
Different Temperatures ◽  
Linear Optical Properties ◽  
Linear Optical

In the present work, UV- Visible spectra of 2-Chloro-3,4-Dimethoxybenzaldehyde (2,3,4-CDMB) compound  have been carried out experimentally and theoretically. The ultraviolet absorption spectrum of title compound in three solvents (Acetone, Diethyl Ether, CCl4) of different polarity were examined in the range of 200–500 nm. The structure of the molecule was optimized and the structural characteristics were determined by HF and DFT (B3LYP) methods with 6-31+G(d,p) and 6-311++G(d,p) as basis sets. The excitation energy, wavelength corresponds to absorption maxima () and oscillator strength (f) are calculated by Time-Dependent Density Functional Theory (TD-DFT) using B3LYP/6-31+G(d,p) and B3LYP/6-311++G(d,p) as basis sets. The electric dipole moment (μ), polarizability (α) and the first hyperpolarizability (β ) have been computed to evaluate the non-linear optical (NLO) response of the investigated compound by HF and DFT (B3LYP) with already mentioned basis sets. Thermodynamic functions of the title compound at different temperatures were also calculated.

scholarly journals Phonons in Short-Period GaN/AlN Superlattices: Group-Theoretical Analysis, Ab initio Calculations, and Raman Spectra

Nanomaterials ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 286
Author(s):  
Valery Davydov ◽  
Evgenii Roginskii ◽  
Yuri Kitaev ◽  
Alexander Smirnov ◽  
Ilya Eliseyev ◽  
...  
Keyword(s):  
Theoretical Analysis ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Raman Spectra ◽  
Density Functional ◽  
Structural Characteristics ◽  
Vibrational Modes ◽  
Phonon Modes ◽  
Short Period ◽  
Group Theoretical Analysis

We report the results of experimental and theoretical studies of phonon modes in GaN/AlN superlattices (SLs) with a period of several atomic layers, grown by submonolayer digital plasma-assisted molecular-beam epitaxy, which have a great potential for use in quantum and stress engineering. Using detailed group-theoretical analysis, the genesis of the SL vibrational modes from the modes of bulk AlN and GaN crystals is established. Ab initio calculations in the framework of the density functional theory, aimed at studying the phonon states, are performed for SLs with both equal and unequal layer thicknesses. The frequencies of the vibrational modes are calculated, and atomic displacement patterns are obtained. Raman spectra are calculated and compared with the experimental ones. The results of the ab initio calculations are in good agreement with the experimental Raman spectra and the results of the group-theoretical analysis. As a result of comprehensive studies, the correlations between the parameters of acoustic and optical phonons and the structure of SLs are obtained. This opens up new possibilities for the analysis of the structural characteristics of short-period GaN/AlN SLs using Raman spectroscopy. The results obtained can be used to optimize the growth technologies aimed to form structurally perfect short-period GaN/AlN SLs.

scholarly journals Strain Investigation on Spin-Dependent Transport Properties of γ-Graphyne Nanoribbon Between Gold Electrodes

2021 ◽  
Vol 16 (1) ◽  
Author(s):  
Yun Li ◽  
Xiaobo Li ◽  
Shidong Zhang ◽  
Liemao Cao ◽  
Fangping Ouyang ◽  
...  
Keyword(s):  
Transport Properties ◽  
High Performance ◽  
Density Functional ◽  
Strain Engineering ◽  
Molecular Junctions ◽  
Spin Splitting ◽  
Functional Theory ◽  
Spin Dependent Transport ◽  
The Density Functional Theory ◽  
Dependent Transport

AbstractStrain engineering has become one of the effective methods to tune the electronic structures of materials, which can be introduced into the molecular junction to induce some unique physical effects. The various γ-graphyne nanoribbons (γ-GYNRs) embedded between gold (Au) electrodes with strain controlling have been designed, involving the calculation of the spin-dependent transport properties by employing the density functional theory. Our calculated results exhibit that the presence of strain has a great effect on transport properties of molecular junctions, which can obviously enhance the coupling between the γ-GYNR and Au electrodes. We find that the current flowing through the strained nanojunction is larger than that of the unstrained one. What is more, the length and strained shape of the γ-GYNR serves as the important factors which affect the transport properties of molecular junctions. Simultaneously, the phenomenon of spin-splitting occurs after introducing strain into nanojunction, implying that strain engineering may be a new means to regulate the electron spin. Our work can provide theoretical basis for designing of high performance graphyne-based devices in the future.

scholarly journals Unlocking surface octahedral tilt in two-dimensional Ruddlesden-Popper perovskites

2022 ◽  
Vol 13 (1) ◽  
Author(s):  
Yan Shao ◽  
Wei Gao ◽  
Hejin Yan ◽  
Runlai Li ◽  
Ibrahim Abdelwahab ◽  
...  
Keyword(s):  
Density Functional ◽  
Carrier Transport ◽  
Plane Surface ◽  
Structural Phase ◽  
Density Functional Theory Calculations ◽  
Spin Splitting ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Out Of Plane ◽  
Inversion Asymmetry

AbstractMolecularly soft organic-inorganic hybrid perovskites are susceptible to dynamic instabilities of the lattice called octahedral tilt, which directly impacts their carrier transport and exciton-phonon coupling. Although the structural phase transitions associated with octahedral tilt has been extensively studied in 3D hybrid halide perovskites, its impact in hybrid 2D perovskites is not well understood. Here, we used scanning tunneling microscopy (STM) to directly visualize surface octahedral tilt in freshly exfoliated 2D Ruddlesden-Popper perovskites (RPPs) across the homologous series, whereby the steric hindrance imposed by long organic cations is unlocked by exfoliation. The experimentally determined octahedral tilts from n = 1 to n = 4 RPPs from STM images are found to agree very well with out-of-plane surface octahedral tilts predicted by density functional theory calculations. The surface-enhanced octahedral tilt is correlated to excitonic redshift observed in photoluminescence (PL), and it enhances inversion asymmetry normal to the direction of quantum well and promotes Rashba spin splitting for n > 1.

Generating large out-of-plane piezoelectric properties of atomically thin MoS2 via the defect engineering

2021 ◽  
Author(s):  
Li-Ren Ng ◽  
Guan-Fu Chen ◽  
Shi-Hsin Lin
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Piezoelectric Properties ◽  
Two Dimensional ◽  
Defect Engineering ◽  
Functional Theory ◽  
Out Of Plane

We calculated the piezoelectric properties of asymmetrically defected MoS2 with density functional theory. By creating uneven numbers of defects on the either sides of two-dimensional MoS2, the out-of-plane centrosym- metry...

Tunable electronic properties of the dynamically stable layered mineral Pt2HgSe3 (Jacutingaite)

2020 ◽  
Vol 22 (42) ◽  
pp. 24471-24479 ◽  
Author(s):  
Asadollah Bafekry ◽  
Catherine Stampfl ◽  
Chuong Nguyen ◽  
Mitra Ghergherehchi ◽  
Bohayra Mortazavi
Keyword(s):  
Density Functional Theory ◽  
Electric Field ◽  
Electronic Properties ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Biaxial Strain ◽  
Functional Theory ◽  
Structural And Electronic Properties ◽  
Out Of Plane ◽  
Strain Layer

Density functional theory calculations are performed in order to study the structural and electronic properties of monolayer Pt2HgSe3. Effects of uniaxial and biaxial strain, layer thickness, electric field and out-of-plane pressure on the electronic properties are systematically investigated.

scholarly journals DFT Prediction of Factors Affecting the Structural Characteristics, the Transition Temperature and the Electronic Density of Some New Conjugated Polymers

Polymers ◽  
2020 ◽  
Vol 12 (6) ◽  
pp. 1207
Author(s):  
Quoc-Trung Vu ◽  
Thi-Thuy-Duong Tran ◽  
Thuy-Chinh Nguyen ◽  
Thien Vuong Nguyen ◽  
Hien Nguyen ◽  
...  
Keyword(s):  
Phase Transition ◽  
Transition Temperature ◽  
Conjugated Polymers ◽  
Bond Length ◽  
Density Functional ◽  
Structural Characteristics ◽  
Side Chain ◽  
Electronic Density ◽  
Energy Field ◽  
Energy Bandgap

Conjugated polymers are promising materials for various cutting-edge technologies, especially for organic conducting materials and in the energy field. In this work, we have synthesized a new conjugated polymer and investigated the effect of distance between bond layers, side-chain functional groups (H, Br, OH, OCH3 and OC2H5) on structural characteristics, phase transition temperature (T), and electrical structure of C13H8OS using Density Functional Theory (DFT). The structural characteristics were determined by the shape, network constant (a, b and c), bond length (C–C, C–H, C–O, C–S, C–Br and O–H), phase transition temperatures, and the total energy (Etot) on a base cell. Our finding shows that the increase of layer thickness (h) of C13H8OS–H has a negligible effect on the transition temperature, while the energy bandgap (Eg) increases from 1.646 eV to 1.675 eV. The calculation of bond length with different side chain groups was carried out for which C13H8OS–H has C–H = 1.09 Å; C13H8OS–Br has C–Br = 1.93 Å; C13H8OS–OH has C–O = 1.36 Å, O–H = 0.78 Å; C13H8OS–OCH3 has C–O = 1.44 Å, O–H =1.10 Å; C13H8OS–OC2H5 has C–O = 1.45 Å, C–C = 1.51Å, C–H = 1.10 Å. The transition temperature (T) for C13H8OS–H was 500 K < T < 562 K; C13H8OS–Br was 442 K < T < 512 K; C13H8OS–OH was 487 K < T < 543 K; C13H8OS–OCH3 was 492 K < T < 558 K; and C13H8OS–OC2H5 was 492 K < T < 572 K. The energy bandgap (Eg) of Br is of Eg = 1.621 eV, the doping of side chain groups H, OH, OCH3, and OC2H5, leads to an increase of Eg from 1.621 eV to 1.646, 1.697, 1.920, and 2.04 eV, respectively.

scholarly journals Magnetic anisotropy of graphene quantum dots decorated with a ruthenium adatom

2013 ◽  
Vol 4 ◽  
pp. 441-445 ◽  
Author(s):  
Igor Beljakov ◽  
Velimir Meded ◽  
Franz Symalla ◽  
Karin Fink ◽  
Sam Shallcross ◽  
...  
Keyword(s):  
Magnetic Anisotropy ◽  
Density Functional ◽  
Magnetic Transition ◽  
Graphene Quantum Dots ◽  
Magnetic Storage ◽  
Magnetic Anisotropy Energy ◽  
Magnetization Direction ◽  
Storage Devices ◽  
Out Of Plane ◽  
Graphene Edge

The creation of magnetic storage devices by decoration of a graphene sheet by magnetic transition-metal adatoms, utilizing the high in-plane versus out-of-plane magnetic anisotropy energy (MAE), has recently been proposed. This concept is extended in our density-functional-based modeling study by incorporating the influence of the graphene edge on the MAE. We consider triangular graphene flakes with both armchair and zigzag edges in which a single ruthenium adatom is placed at symmetrically inequivalent positions. Depending on the edge-type, the graphene edge was found to influence the MAE in opposite ways: for the armchair flake the MAE increases close to the edge, while the opposite is true for the zigzag edge. Additionally, in-plane pinning of the magnetization direction perpendicular to the edge itself is observed for the first time.

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