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Chinedu Ekuma

Bio: Chinedu Ekuma is an academic researcher from Lehigh University. The author has contributed to research in topics: Band gap & Direct and indirect band gaps. The author has an hindex of 16, co-authored 73 publications receiving 817 citations. Previous affiliations of Chinedu Ekuma include Louisiana State University & United States Naval Research Laboratory.


Papers
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Journal ArticleDOI
TL;DR: In this paper, the electronic structure of monoclinic CuO was obtained from first principles calculations utilizing density functional theory plus effective Coulomb interaction (DFT + U) method.
Abstract: We report the electronic structure of monoclinic CuO as obtained from first principles calculations utilizing density functional theory plus effective Coulomb interaction (DFT + U) method. In contrast to standard DFT calculations taking into account electronic correlations in DFT + U gave antiferromagnetic insulator with energy gap and magnetic moment values in good agreement with experimental data. The electronic states around the Fermi level are formed by partially filled Cu 3d x²−y² orbitals with significant admixture of O 2p states. Theoretical spectra are calculated using DFT + U electronic structure method and their comparison with experimental photoemission and optical spectra show very good agreement.

82 citations

Journal ArticleDOI
TL;DR: In this article, optical properties of PbTe and PbSe were obtained from first-principles calculations with the Tran-Blaha modified Becke-Johnson potential.
Abstract: We report optical properties of PbTe and PbSe as obtained from first-principles calculations with the Tran-Blaha modified Becke-Johnson potential The results are discussed in relation to existing experimental data, particularly in relation to the temperature dependence of the band gap

66 citations

Journal Article
TL;DR: In this paper, optical properties of PbTe and PbSe were obtained from first-principles calculations with the Tran-Blaha modified Becke-Johnson potential.
Abstract: We report optical properties of PbTe and PbSe as obtained from first-principles calculations with the Tran-Blaha modified Becke-Johnson potential. The results are discussed in relation to existing experimental data, particularly in relation to the temperature dependence of the band gap.

58 citations

Journal ArticleDOI
TL;DR: In this paper, self-consistent electronic energy bands of rutile TiO2 are reported within the local density functional approximation (LDA) potential and the linear combination of atomic orbitals (LCAO).
Abstract: Ab-initio, self-consistent electronic energy bands of rutile TiO2 are reported within the local density functional approximation (LDA). Our first principle, non-relativistic and ground state calculations employed a local density functional approximation (LDA) potential and the linear combination of atomic orbitals (LCAO). Within the framework of the Bagayoko, Zhao, and Williams (BZW) method, we solved self-consistently both the Kohn-Sham equation and the equation giving the ground state charge density in terms of the wave functions of the occupied states. Our calculated band structure shows that there is significant O2p-Ti3d hybridization in the valence bands. These bands are well separated from the conduction bands by an indirect band gap of 2.95 eV, from {\Gamma} to R. Consequently, this work predicts that rutile TiO2 is an indirect band gap material, as all other gaps from our calculations are larger than 2.95 eV. We found a slightly larger, direct band gap of 3.05 eV, at the {\Gamma} point, in excellent agreement with experiment. Our calculations reproduced the peaks in the measured conduction and valence bands densities of states, within experimental uncertainties. We also calculated electron effective mass. Our structural optimization led to lattice parameters of 4.65 A and 2.97 A for a_{0} and c_{0}, respectively with a u parameter of 0.3051 and a bulk modulus of 215 GPa.

50 citations

Journal ArticleDOI
TL;DR: In this article, self-consistent electronic energy bands of rutile TiO2 are reported within the local density functional approximation (LDA) potential and the linear combination of atomic orbitals (LCAO).
Abstract: Ab-initio, self-consistent electronic energy bands of rutile TiO2 are reported within the local density functional approximation (LDA). Our first principle, non-relativistic and ground state calculations employed a local density functional approximation (LDA) potential and the linear combination of atomic orbitals (LCAO). Within the framework of the Bagayoko–Zhao–Williams (BZW) method, we solved self-consistently both the Kohn–Sham equation and the equation giving the ground state charge density in terms of the wave functions of the occupied states. Our calculated band structure shows that there is significant O 2p–Ti 3d hybridization in the valence bands. These bands are well separated from the conduction bands by an indirect band gap of 2.95 eV, from Γ to R. Consequently, this work predicts that rutile TiO2 is an indirect band gap material, as all other gaps from our calculations are larger than 2.95 eV. We found a slightly larger, direct band gap of 3.05 eV, at the Γ point, in excellent agreement with experiment. Our calculations reproduced the peaks in the measured conduction and valence bands densities of states, within experimental uncertainties. We also calculated electron effective mass. Our structural optimization led to lattice parameters of 4.65 and 2.97 A for a0 and c0, respectively with a u parameter of 0.3051 and a bulk modulus of 215 GPa.

49 citations


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Book
01 Jan 1957

1,574 citations

Journal ArticleDOI
TL;DR: This review aims to comprehensively summarize the state-of-the-art strategies for the realization of high-performance thermoelectric materials and devices by establishing the links between synthesis, structural characteristics, properties, underlying chemistry and physics.
Abstract: The long-standing popularity of thermoelectric materials has contributed to the creation of various thermoelectric devices and stimulated the development of strategies to improve their thermoelectric performance. In this review, we aim to comprehensively summarize the state-of-the-art strategies for the realization of high-performance thermoelectric materials and devices by establishing the links between synthesis, structural characteristics, properties, underlying chemistry and physics, including structural design (point defects, dislocations, interfaces, inclusions, and pores), multidimensional design (quantum dots/wires, nanoparticles, nanowires, nano- or microbelts, few-layered nanosheets, nano- or microplates, thin films, single crystals, and polycrystalline bulks), and advanced device design (thermoelectric modules, miniature generators and coolers, and flexible thermoelectric generators). The outline of each strategy starts with a concise presentation of their fundamentals and carefully selected examples. In the end, we point out the controversies, challenges, and outlooks toward the future development of thermoelectric materials and devices. Overall, this review will serve to help materials scientists, chemists, and physicists, particularly students and young researchers, in selecting suitable strategies for the improvement of thermoelectrics and potentially other relevant energy conversion technologies.

951 citations

01 Jan 1952

748 citations

Journal Article
TL;DR: In this paper, a few and single-layered BN nanoribbons, mostly terminated with zigzag edges, can be produced under unwrapping multi-walled Bn nanotubes through plasma etching.
Abstract: Inspired by rich physics and functionalities of graphenes, scientists have taken an intensive interest in two-dimensional (2D) crystals of h-BN (analogue of graphite, so-called "white" graphite). Recent calculations have predicted the exciting potentials of BN nanoribbons in spintronics due to tunable magnetic and electrical properties; however no experimental evidence has been provided since fabrication of such ribbons remains a challenge. Here, we show that few- and single-layered BN nanoribbons, mostly terminated with zigzag edges, can be produced under unwrapping multiwalled BN nanotubes through plasma etching. The interesting stepwise unwrapping and intermediate states were observed and analyzed. Opposed to insulating primal tubes, the nanoribbons become semiconducting due to doping-like conducting edge states and vacancy defects, as revealed by structural analyses and ab initio simulations. This study paves the way for BN nanoribbon production and usage as functional semiconductors with a wide range of applications in optoelectronics and spintronics.

577 citations