First-principles study of the impact of chemical doping and functional groups on the absorption spectra of graphene

Abstract The rational design of the electronic band structures and the associated properties (e.g., optical) of advanced materials has remained challenging for crucial applications in optoelectronics, solar desalination, advanced manufacturing technologies, etc. In this work, using first-principles calculations, we studied the prospects of tuning the absorption spectra of graphene via defect engineering, i.e., chemical doping and oxidation. Our computational analysis shows that graphene functionalization with single hydroxyl and carboxylic acid fails to open a band gap in graphene. While single epoxide functionalization successfully opens a bandgap in graphene and increases absorptivity, however, other optical properties such as reflection, transmission, and dielectric constants are significantly altered. Boron and nitrogen dopants lead to p- and n-type doping, respectively, while fluorine dopants or a single-carbon atomic vacancy cannot create a significant bandgap in graphene. By rigorously considering the spin-polarization effect, we find that titanium, zirconium, and hafnium dopants can create a bandgap in graphene via an induced flat band around the Fermi level as well as the collapse of the Dirac cone. In addition, silicon, germanium, and tin dopants are also effective in improving the optical characteristics. Our work is important for future experimental work on graphene for laser and optical processing applications.

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A first-principles study of the properties of two novel Si3P4 phases

International Journal of Modern Physics B ◽

10.1142/s0217979218502442 ◽

2018 ◽

Vol 32 (22) ◽

pp. 1850244 ◽

Cited By ~ 1

Author(s):

Ruike Yang ◽

Bao Chai ◽

Qun Wei ◽

Dongyun Zhang

Keyword(s):

Optical Properties ◽

Young’S Modulus ◽

Absorption Spectra ◽

First Principles ◽

Phonon Dispersion ◽

Young's Modulus ◽

Dielectric Constants ◽

Loss Functions ◽

Deformation Ability ◽

Two Phases

The structural, elastic, electronic and optical properties of two novel phases Si3P4 with tetragonal and orthorhombic structures are studied by first-principles calculations according to density function theory (DFT). For novel structures t-Si3P4 and o-Si3P4, the elastic constants results show that they are mechanically stable. The phonon dispersion spectra confirm that they are dynamically stable. The forming enthalpies prove their thermodynamic stability. The mechanical properties, such as the bulk modulus B, shear modulus G, Pugh ratio k, Young’s modulus E and Poisson’s ratios [Formula: see text] are calculated. The results show that t-Si3P4 has better anti-deformation ability than o-Si3P4, and t-Si3P4 is harder than o-Si3P4. The Poisson’s ratio values of t-Si3P4 and o-Si3P4 are 0.16 and 0.35, and the Pugh ratio values, k, are 0.88 and 0.33. For t-Si3P4, the Pugh ratio k [Formula: see text] 0.57 indicates that it behaves in a brittle manner. For o-Si3P4, it owns the better plasticity. The directional dependence of the Young’s modulus indicates that o-Si3P4 is more anisotropic than t-Si3P4. The calculated band structures show that the two novel phases are semiconductors, and the narrow indirect bandgaps are 1.847 and 0.158 eV by using PBE0. The densities of states (DOS) indicate that the P ‘p’ and Si ‘p’ play major roles in two phases total DOS. The results of the optical properties, such as the dielectric functions, absorption spectra, loss functions, refractive index, and so on are given. The static dielectric constants are 5.493 and 12.206, the starting positions of the absorption spectra are approximately at 1.815 and 0.140 eV, and the peaks of loss functions are at 15.503 and 11.763 eV, for t-Si3P4 and o-Si3P4, respectively.

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Flat-Band in Pyrochlore Oxides: A First-Principles Study

Nanomaterials ◽

10.3390/nano9060876 ◽

2019 ◽

Vol 9 (6) ◽

pp. 876

Author(s):

Izumi Hase ◽

Takashi Yanagisawa ◽

Kenji Kawashima

Keyword(s):

Ground State ◽

First Principles ◽

Flat Band ◽

Magnetic Element ◽

Electronic Band ◽

Flat Bands ◽

Spin Polarized ◽

Pyrochlore Oxides ◽

Carrier Doping ◽

A Site

Using a first-principles electronic band calculation, we obtained a quasi flat-band near the Fermi level for the six pyrochlore oxides, A2B2O7. These quasi flat-bands are mostly characterized by the s-orbitals of the A-site. The band structures of these oxides are well described by the non-interacting Mielke model. Spin-polarized calculations showed that the ground state of these compounds was ferromagnetic after appropriate carrier doping, despite the absence of the magnetic element.

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Absorption Spectra and Electron-Vibration Coupling of Ti:Sapphire From First Principles

Journal of Heat Transfer ◽

10.1115/1.4032177 ◽

2016 ◽

Vol 138 (4) ◽

Cited By ~ 3

Author(s):

Hua Bao ◽

Xiulin Ruan

Keyword(s):

Optical Properties ◽

Absorption Spectra ◽

First Principles ◽

Electronic Band Structure ◽

Stokes Shift ◽

First Principles Calculation ◽

Band Structure Calculation ◽

Crystal Field Theory ◽

Electronic Band ◽

Vibration Coupling

First-principles calculations are performed to study the absorption spectra and electron-vibration coupling of titanium-doped sapphire (Ti:Al2O3). Geometry optimization shows a local structure relaxation after the doping of Ti. Electronic band structure calculation shows that five additional dopant energy bands are observed around the band gap of Al2O3, and are attributed to the five localized d orbitals of the Ti dopant. The optical absorption spectra are then predicted by averaging the oscillator strength during a 4 ps first-principles molecular dynamics (MD) trajectory, and the spectra agree well with the experimental results. Electron-vibration coupling is further investigated by studying the response of the ground and excited states to the Eg vibrational mode, for which a configuration coordinate diagram is obtained. Stokes shift effect is observed, which confirms the red shift of emission spectra of Ti:sapphire. This work offers a quantitative understanding of the optical properties and crystal-field theory of Ti-doped sapphire. The first-principles calculation framework developed here can also be followed to predict the optical properties and study the electron-vibration coupling in other doped materials.

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Electronic Structure and X-ray Absorption Spectra of Rutile TiO2 Using First-Principles Calculations

Korean Journal of Metals and Materials ◽

10.3365/kjmm.2014.52.12.1025 ◽

2014 ◽

Vol 52 (12) ◽

pp. 1025-1029

Author(s):

Min-Wook Oh ◽

Tae-Gu Kang ◽

Byungki Ryu ◽

Ji Eun Lee ◽

Sung-Jae Joo ◽

...

Keyword(s):

Electronic Structure ◽

Absorption Spectra ◽

First Principles ◽

First Principles Calculations ◽

Rutile Tio2 ◽

X Ray ◽

X Ray Absorption

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Temperature effects on the electronic band structure of PbTe from first principles

Physical Review Materials ◽

10.1103/physrevmaterials.3.055405 ◽

2019 ◽

Vol 3 (5) ◽

Cited By ~ 9

Author(s):

José D. Querales-Flores ◽

Jiang Cao ◽

Stephen Fahy ◽

Ivana Savić

Keyword(s):

Band Structure ◽

First Principles ◽

Temperature Effects ◽

Electronic Band Structure ◽

Electronic Band

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The effect of ionic defect interactions on the hydration of yttrium-doped barium zirconate

Physical Chemistry Chemical Physics ◽

10.1039/d0cp06587k ◽

2021 ◽

Author(s):

Sebastian Eisele ◽

Fabian M. Draber ◽

Steffen Grieshammer

Keyword(s):

Monte Carlo ◽

Monte Carlo Simulations ◽

First Principles ◽

Barium Zirconate ◽

First Principles Calculations ◽

Defect Interactions ◽

The Impact ◽

Ionic Defect

First principles calculations and Monte Carlo simulations reveal the impact of defect interactions on the hydration of barium-zirconate.

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Electronic and optical properties of vacancy ordered double perovskites A2BX6 (A = Rb, Cs; B = Sn, Pd, Pt; and X = Cl, Br, I): a first principles study

Scientific Reports ◽

10.1038/s41598-021-86145-x ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Muhammad Faizan ◽

K. C. Bhamu ◽

Ghulam Murtaza ◽

Xin He ◽

Neeraj Kulhari ◽

...

Keyword(s):

Optical Properties ◽

Band Gap ◽

First Principles ◽

Density Functional ◽

Perovskite Solar Cells ◽

Dielectric Constants ◽

Maximum Efficiency ◽

Exchange Potential ◽

Double Perovskites ◽

Electronic And Optical Properties

AbstractThe highly successful PBE functional and the modified Becke–Johnson exchange potential were used to calculate the structural, electronic, and optical properties of the vacancy-ordered double perovskites A2BX6 (A = Rb, Cs; B = Sn, Pd, Pt; X = Cl, Br, and I) using the density functional theory, a first principles approach. The convex hull approach was used to check the thermodynamic stability of the compounds. The calculated parameters (lattice constants, band gap, and bond lengths) are in tune with the available experimental and theoretical results. The compounds, Rb2PdBr6 and Cs2PtI6, exhibit band gaps within the optimal range of 0.9–1.6 eV, required for the single-junction photovoltaic applications. The photovoltaic efficiency of the studied materials was assessed using the spectroscopic-limited-maximum-efficiency (SLME) metric as well as the optical properties. The ideal band gap, high dielectric constants, and optimum light absorption of these perovskites make them suitable for high performance single and multi-junction perovskite solar cells.

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Phase-selective active sites on ordered/disordered titanium dioxide enable exceptional photocatalytic ammonia synthesis

Chemical Science ◽

10.1039/d1sc03223b ◽

2021 ◽

Author(s):

Jinsun Lee ◽

Xinghui Liu ◽

Ashwani Kumar ◽

Yosep Hwang ◽

Eunji Lee ◽

...

Keyword(s):

Titanium Dioxide ◽

Active Sites ◽

Rational Design ◽

Ammonia Synthesis ◽

Reduction Reaction ◽

Band Structures ◽

Electronic Band ◽

Defect Sites ◽

Electronic Band Structures ◽

Reaction Routes

This work highlights the importance of a rational design for more energetically suitable nitrogen reduction reaction routes and mechanisms by regulating the electronic band structures with phase-selective defect sites.

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New physically based model for thermal induced initial stress in 3D for silicon germanium films after deposition

COMPEL The International Journal for Computation and Mathematics in Electrical and Electronic Engineering ◽

10.1108/compel-11-2013-0390 ◽

2014 ◽

Vol 33 (6) ◽

pp. 2121-2138 ◽

Cited By ~ 1

Author(s):

Abderrazzak El Boukili

Keyword(s):

Thermal Expansion ◽

Initial Stress ◽

Silicon Germanium ◽

Rate Of Change ◽

Thermal Mismatch ◽

Electronic Band ◽

Physically Based Model ◽

Content Type ◽

Physically Based ◽

Pmos Transistor

Purpose – The purpose of this paper is to provide a new three dimension physically based model to calculate the initial stress in silicon germanium (SiGe) film due to thermal mismatch after deposition. We should note that there are many other sources of initial stress in SiGe films or in the substrate. Here, the author is focussing only on how to model the initial stress arising from thermal mismatch in SiGe film. The author uses this initial stress to calculate numerically the resulting extrinsic stress distribution in a nanoscale PMOS transistor. This extrinsic stress is used by industrials and manufacturers as Intel or IBM to boost the performances of the nanoscale PMOS and NMOS transistors. It is now admitted that compressive stress enhances the mobility of holes and tensile stress enhances the mobility of electrons in the channel. Design/methodology/approach – During thermal processing, thin film materials like polysilicon, silicon nitride, silicon dioxide, or SiGe expand or contract at different rates compared to the silicon substrate according to their thermal expansion coefficients. The author defines the thermal expansion coefficient as the rate of change of strain with respect to temperature. Findings – Several numerical experiments have been used for different temperatures ranging from 30 to 1,000°C. These experiments did show that the temperature affects strongly the extrinsic stress in the channel of a 45 nm PMOS transistor. On the other hand, the author has compared the extrinsic stress due to lattice mismatch with the extrinsic stress due to thermal mismatch. The author found that these two types of stress have the same order (see the numerical results on Figures 4 and 12). And, these are great findings for semiconductor industry. Practical implications – Front-end process induced extrinsic stress is used by manufacturers of nanoscale transistors as the new scaling vector for the 90 nm node technology and below. The extrinsic stress has the advantage of improving the performances of PMOSFETs and NMOSFETs transistors by enhancing mobility. This mobility enhancement fundamentally results from alteration of electronic band structure of silicon due to extrinsic stress. Then, the results are of great importance to manufacturers and industrials. The evidence is that these results show that the extrinsic stress in the channel depends also on the thermal mismatch between materials and not only on the material mismatch. Originality/value – The model the author is proposing to calculate the initial stress due to thermal mismatch is novel and original. The author validated the values of the initial stress with those obtained by experiments in Al-Bayati et al. (2005). Using the uniaxial stress generation technique of Intel (see Figure 2). Al-Bayati et al. (2005) found experimentally that for 17 percent germanium concentration, a compressive initial stress of 1.4 GPa is generated inside the SiGe layer.

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