Search query: Band-Edge Orbital Engineering

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abstract: Lead (Pb) halide perovskites have achieved great success in recent years because of their excellent optoelectronic properties, which is largely attributed to the lone pair s orbital derived antibonding states at the valence band edge. Guided by the key band edge orbital character, a series of ns2 containing (i.e. Sn2+ Sb3+ and Bi3+ Pb free perovskite alternatives have been explored as potential photovoltaic candidates. On the other hand, based on the band edge orbital components (i.e. M2+ s and p/X p orbitals) a series of strategies have been proposed to optimize their optoelectronic properties by modifying the atomic orbitals and orbital interactions. Therefore, understanding the band edge electronic features from the recently reported halide perovskites is essential for future material design and device optimization. This Perspective first attempts to establish the band edge orbital property relationship using a chemically intuitive approach and then rationalizes their superior properties and explains the trends in electronic properties. We hope that this Perspective will provide atomic level guidance and insights toward the rational design of perovskite semiconductors with outstanding optoelectronic properties.
author_names: Gang Tang

Philippe Ghosez
title: Band Edge Orbital Engineering of Perovskite Semiconductors for Optoelectronic Applications.
venue: The journal of physical chemistry letters
year: 2021

abstract: The effects of ferroic distortion and biaxial strain on the band gap and band edges of SrTiO(3) are calculated by using density functional theory and many body perturbation theory. Anisotropic strains are shown to reduce the gap by breaking degeneracies at the band edges. Ferroic distortions are shown to widen the gap by allowing new band edge orbital mixings. Compressive biaxial strains raise band edge energies, while tensile strains lower them. To reduce the SrTiO(3) gap, one must lower the symmetry from cubic while suppressing ferroic distortions. Our calculations indicate that, for engineered orientation of the growth direction along [111] the SrTiO(3) gap can be controllably and considerably reduced at room temperature.
author_names: Robert F Berger

Craig J Fennie

Jeffrey B Neaton
title: Band gap and edge engineering via ferroic distortion and anisotropic strain: the case of SrTiO(3)
venue: Physical review letters
year: 2011

abstract: Abstract The effect of edge passivation with non metallic atoms was evaluated on some structural and electronic properties of MoS2 nanoribbons. It was observed that at Na 12 and above, the band gap is less oscillating and converges to 0.58 eV. By reducing the dimensionality, the band gap value changed dramatically. We found that d orbital of Mo atom greatly affects the density of states. All passivation processes were performed with H and X atoms, where X is a non metallic atom. The hybridization of p and s orbitals of X and Mo atoms plays an important role in changing the electronic properties of AMoS2NR. It was found that after passivation the largest band gap change is related to the most stable structure. Our studies suggest that the band gap of AMoS2NR H X depends on two factors: the nanoribbon width and the hybridization of Mo X orbitals.
author_names: Huang Jing
title: Increasing stability of MoS2 nanoribbons by edge engineering
year: 2021

abstract: Two dimensional electron dispersions with peculiar band crossings provide a platform for realizing topological phases of matter. Here we theoretically show that the eg orbital manifold of honeycomb layered transition metal compounds accommodates a plethora of peculiar band crossings, such as multiple Dirac point nodes, quadratic band crossings, and line nodes. From the tight binding analysis, we find that the band topology is systematically changed by the orbital dependent transfer integrals on the honeycomb network of edge sharing octahedra, which can be modulated by distortions of the octahedra as well as chemical substitutions. The band crossings are gapped out by the spin orbit coupling, which brings about a variety of topological phases distinguished by the spin Chern numbers. The results provide a comprehensive understanding of the previous studies on various honeycomb compounds. We also propose another candidate materials by ab initio calculations.
author_names: Yusuke Sugita

Yukitoshi Motome
title: M ay 2 01 8 Engineering of Band Crossings in Honeycomb layered Transition Metal Compounds
year: 2018

abstract: Two dimensional electron dispersions with peculiar band crossings provide a platform for realizing topological phases of matter. Here we theoretically show that the $e_g$ orbital manifold of honeycomb layered transition metal compounds accommodates a plethora of peculiar band crossings, such as multiple Dirac point nodes, quadratic band crossings, and line nodes. From the tight binding analysis, we find that the band topology is systematically changed by the orbital dependent transfer integrals on the honeycomb network of edge sharing octahedra, which can be modulated by distortions of the octahedra as well as chemical substitutions. The band crossings are gapped out by the spin orbit coupling, which brings about a variety of topological phases distinguished by the spin Chern numbers. The results provide a comprehensive understanding of the previous studies on various honeycomb compounds. We also propose another candidate materials by ab initio calculations.
author_names: Yusuke Sugita

Yukitoshi Motome
title: Engineering of Band Crossings in Honeycomb layered Transition Metal Compounds
year: 2018

abstract: We calculate the band structure and the conductance of periodic edge corrugated graphene nanoribbons within the framework of the tight binding p orbital model. We consider corrugated structures based on host ribbons with armchair and zigzag edges and three different types of corrugations (armchair edges, zigzag edges, as well as a rectangular corrugation) We demonstrate that for armchair host ribbons, depending on the type of corrugation, a band gap or low velocity minibands appear near the charge neutrality point. For higher energies the allowed Bloch state bands become separated by ministopbands. By contrast, for corrugated ribbons with the zigzag host, the corrugations introduce neither band gaps nor stopbands (except for the case of the rectangular corrugations) The conductances of finite edge corrugated ribbons are analyzed on the basis of the corresponding band structures. For a sufficiently large number of corrugations the conductance follows the number of the corresponding propagating Bloch states and shows pronounced oscillations due to the Fabry Perot interference within the corrugated segments. Finally we demonstrate that edge disorder strongly affects the conductances of corrugated ribbons. Our results indicate that observation of miniband formation in corrugated ribbons would require clean, edge disorder free samples, especially for the case of the armchair host lattice.
author_names: S Ihnatsenka

Igor V Zozoulenko

George Kirczenow
title: Band gap engineering and ballistic transport in edge corrugated graphene nanoribbons
year: 2009

abstract: A series of trigonal planar N O and S dopant atoms incorporated along the convex protrusion lining the edges of bottom up synthesized chevron graphene nanoribbons (cGNRs) induce a characteristic shift in the energy of conduction and valence band edge states along with a significant reduction of the band gap of up to 0.3 eV per dopant atom per monomer. A combination of scanning probe spectroscopy and density functional theory calculations reveals that the direction and the magnitude of charge transfer between the dopant atoms and the cGNR backbone are dominated by inductive effects and follow the expected trend in electronegativity. The introduction of heteroatom dopants with trigonal planar geometry ensures an efficient overlap of a p orbital lone pair centered on the dopant atom with the extended p system of the cGNR backbone effectively extending the conjugation length. Our work demonstrates a widely tunable method for band gap engineering of graphene nanostructures for advanced electronic applications.
author_names: Rebecca A Durr

Danny Haberer

Yea-Lee Lee

Raymond Blackwell

Alin Miksi Kalayjian

Tomas Marangoni

Jisoon Ihm

Steven G Louie

Felix R Fischer
title: Orbitally Matched Edge Doping in Graphene Nanoribbons.
venue: Journal of the American Chemical Society
year: 2018

abstract: The effects of in plane biaxial strain on the electronic structure of a photofunctional material, single layer SnS2, were systematically investigated using hybrid density functional calculations. The bonding diagram for the band gap was firstly proposed based on the crystal orbital overlap population analysis. The conduction band edge of single layer SnS2 is determined by the anti bonding interaction between Sn 5s and S 3p orbitals, while the valence band edge comes from the anti bonding between the neighboring S atoms. It is found that the compressive strain not only decreases the indirect band gap of single layer SnS2, but also effectively promotes the band edges of the conduction band to realize the overall water splitting. Besides, the dispersion of the valence band of single layer SnS2 becomes weaker with increasing tensile strain which is beneficial for the photo excitation through direct transitions.
author_names: Wei Zhou

Naoto Umezawa
title: Insight into the band structure engineering of single layer SnS2 with in plane biaxial strain.
venue: Physical chemistry chemical physics PCCP
year: 2016

abstract: PdCl3 belongs to a novel class of Dirac materials with Dirac spin gapless semiconducting characteristics. In this paper based, on first principles calculations, we have systematically investigated the effect of adatom adsorption, vacancy defects, electric field, strain, edge states and layer thickness on the electronic and magnetic properties of PdCl3 (palladium trichloride) Our results show that when spin orbital coupling is included, PdCl3 exhibits the quantum anomalous Hall effect with a non trivial band gap of 24 meV. With increasing number of layers, from monolayer to bulk, a transition occurs from a Dirac half metal to a ferromagnetic metal. On application of a perpendicular electrical field to bilayer PdCl3, we find that the energy band gap decreases with increasing field. Uniaxial and biaxial strain, significantly modifies the electronic structure depending on the strain type and magnitude. Adsorption of adatom and topological defects have a dramatic effect on the electronic and magnetic properties of PdCl3. In particular, the structure can become a metal (Na) half metal (Be, Ca, Al, Ti, V, Cr, Fe and Cu with, respective, 0.72, 9.71, 7.14, 6.90, 9.71, 4.33 and 9.5 mB magnetic moments) ferromagnetic metal (Sc, Mn and Co with 4.55, 7.93 and 2.0 mB) spin glass semiconductor (Mg, Ni with 3.30 and 8.63 mB) and dilute magnetic semiconductor (Li, K and Zn with 9.0, 9.0 and 5.80 mB magnetic moment, respectively) Single Pd and double Pd Cl vacancies in PdCl3 display dilute magnetic semiconductor characteristics, while with a single Cl vacancy, the material becomes a half metal. The calculated optical properties of PdCl3 suggest it could be a good candidate for microelectronic and optoelectronics devices.
author_names: Asadollah Bafekry

Catherine Stampfl

Francois M Peeters
title: Dirac half metallicity of Thin PdCl3 Nanosheets: Investigation of the Effects of External Fields, Surface Adsorption and Defect Engineering on the Electronic and Magnetic Properties
venue: Scientific Reports
year: 2020

abstract: Density functional theory calculations were carried out for Ni1 xMgxO alloys using both GGA+U method and hybrid exchange correlation functional HSE06. We find that the band gap of Ni1 xMgxO is a nonlinear function of MgO concentration with a strong bowing behavior at high Mg content. Band edge alignment is determined using heterojunction superlattice models. The valence band maximum of Ni1 xMgxO is shown to be tunable within a range of 0.90 eV. By comparing with the highest occupied molecular orbital levels of some of the most widely used dye molecules, we propose that Ni1 xMgxO is a promising alternate to replace NiO photocathode in dye sensitized solar cells with an enhanced open circuit voltage and transparency of cathode films.
author_names: Junkai Deng

Majid Mortazavi

Nikhil V Medhekar

Jefferson Z Liu
title: Band engineering of Ni1 xMgxO alloys for photocathodes of high efficiency dye sensitized solar cells
year: 2012