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Articles 1 - 11 of 11
Full-Text Articles in Physics
Theoretical Study Of Deep-Defect States In Bulk Pbte And In Thin Films, Khang Hoang, S. D. Mahanti, Puru Jena
Theoretical Study Of Deep-Defect States In Bulk Pbte And In Thin Films, Khang Hoang, S. D. Mahanti, Puru Jena
Physics Publications
The nature of neutral defect states in PbTe, a narrow band-gap semiconductor, has been studied using density functional theory and supercell models. We find that the defect states associated with different substitutional impurities and native point defects found in bulk PbTe are preserved in the film geometry, but get modified as one goes from the surface to the subsurface layers and then to the bulklike layers. These modifications, which usually occur in the neighborhood of the band gap, will impact the transport properties of the films. Energetic studies of different impurities and native defects embedded in bulk PbTe and in …
Ab Initio Study Of Electronic And Magnetic Properties Of The C-Codoped Ga1−Xmnxn (101¯0) Surface, Q. Wang, Q. Sun, Puru Jena
Ab Initio Study Of Electronic And Magnetic Properties Of The C-Codoped Ga1−Xmnxn (101¯0) Surface, Q. Wang, Q. Sun, Puru Jena
Physics Publications
First principles calculations based on gradient corrected density functional theory have been carried out to study the magnetic coupling between Mn atoms in pure and carbon doped Ga1−xMnxN thin films. We show that the ground state of Mn-doped GaN (101¯0) thin film, with Mn replacing the Ga sites, is antiferromagnetic but becomes ferromagnetic when it is codoped with C. The interaction between the Mn spins via the delocalized holes introduced by codoping of C at N sites is responsible for this transition. The overlap between Mn 3d and C 2p in the spin-up band renders half-metallic character to the C …
Ground State Structures And Photoelectron Spectroscopy Of [Co-M(Coronene)](-) Complexes, Anil K. Kandalam, Boggavarapu Kiran, Puru Jena, Xiang Li, Andrej Grubisic, Kit H. Bowen
Ground State Structures And Photoelectron Spectroscopy Of [Co-M(Coronene)](-) Complexes, Anil K. Kandalam, Boggavarapu Kiran, Puru Jena, Xiang Li, Andrej Grubisic, Kit H. Bowen
Physics Publications
A synergistic approach involving theory and experiment has been used to study the structure and properties of neutral and negatively charged cobalt-coronene [Com(coronene)] complexes. The calculations are based on density functional theory with generalized gradient approximation for exchange and correlation potential, while the experiments are carried out using photoelectron spectroscopy of mass selected anions. The authors show that the geometries of neutral and anionic Co(coronene) and Co2(coronene) are different from those of the corresponding iron-coronene complexes and that both the Co atom and the dimer prefer to occupy η2-bridge binding sites. However, the magnetic coupling between the Co atoms remains …
On The Structural And Energetic Properties Of The Hydrogen Absorber Li2mg(Nh)2, C. Moysés Araújo, Ralph H. Scheicher, Puru Jena, Rajeev Ahuja
On The Structural And Energetic Properties Of The Hydrogen Absorber Li2mg(Nh)2, C. Moysés Araújo, Ralph H. Scheicher, Puru Jena, Rajeev Ahuja
Physics Publications
The authors have performed density functional theory based calculations of several possible conformations for the crystal structure of Li2Mg(NH)2 and they confirm the α phase, resolved from both x-ray and neutron diffraction data, as the ground-state configuration. It is also found that although the N–H bond is stronger in Li2Mg(NH)2 than in Li2NH, hydrogen release from Li2Mg(NH)2/LiH mixture displays more favorable thermodynamics than that from the Li2NH∕LiH mixture. The insights gained from this seemingly counterintuitive result should prove helpful in the search for promising hydrogen storage materials.
First-Principles Study Of Magnetic Properties In V-Doped Zno, Qian Wang, Qiang Sun, Puru Jena, Zheng Hu, R. Note, Y. Kawazoe
First-Principles Study Of Magnetic Properties In V-Doped Zno, Qian Wang, Qiang Sun, Puru Jena, Zheng Hu, R. Note, Y. Kawazoe
Physics Publications
A comprehensive theoretical study of electronic and magnetic properties of V-doped ZnO in bulk as well as (112¯0)thin films has been performed using density functional theory. Vanadium atoms substituted at Zn sites show very little selectivity of site occupancy. More importantly, different geometries with ferromagnetic, ferrimagnetic, and antiferromagnetic configurations are found to be energetically nearly degenerate both in Zn1−xVxO bulk and subsurface layers of the thin film. On the other hand, V atoms couple ferromagnetically when they occupy surface sites of the thin film. The diverse magnetic behaviors in V-doped ZnO account for the many reported conflicting experimental results.
Dehydrogenation From 3d-Transition-Metal-Doped Naalh4: Prediction Of Catalysts, A. Blomqvist, C. Moysés Araújo, Puru Jena, R. Ahuja
Dehydrogenation From 3d-Transition-Metal-Doped Naalh4: Prediction Of Catalysts, A. Blomqvist, C. Moysés Araújo, Puru Jena, R. Ahuja
Physics Publications
A fundamental understanding of the role of catalysts in improving the kinetics and thermodynamics of hydrogen sorption in NaAlH4 is the key for using this material in hydrogen storage. The authors present a systematic theoretical study of energies needed to desorb hydrogen in 3dtransition metal (Sc–Cu)-doped NaAlH4. They show that Cr and Fe atoms can be far more effective catalysts than Ti in desorbing hydrogen. The role of the 3d metal atoms in improving the thermodynamics of dehydrogenation is attributed to a significant shortening of the bond length with neighboring Al atoms.
Local Electronic And Optical Behaviors Of A-Plane Gan Grown Via Epitaxial Lateral Overgrowth, J. C. Moore, V. Kasliwal, A. A. Baski, X. Ni, Ü. Özgür, Hadis Morkoç
Local Electronic And Optical Behaviors Of A-Plane Gan Grown Via Epitaxial Lateral Overgrowth, J. C. Moore, V. Kasliwal, A. A. Baski, X. Ni, Ü. Özgür, Hadis Morkoç
Physics Publications
Conductive atomic force microscopy and near-field optical microscopy (NSOM) were used to study the morphology, conduction, and optical properties of a-plane GaNfilmsgrown via epitaxial lateral overgrowth (ELO) by metal organic chemical vapor deposition. The AFM images for the coalesced ELOfilms show undulations, where the window regions appear as depressions with a high density of surface pits. At reverse bias below 12V, very low uniform conduction (2pA) is seen in the window regions. Above 20V, a lower-quality sample shows localized sites inside the window regions with significant leakage, indicating a correlation between the presence of surface pits and leakage sites. Room …
Magnetic Endohedral Metallofullerenes With Floppy Interiors, Meichun Qian, Stephen V. Ong, Shiv N. Khanna, Mark B. Knickelbein
Magnetic Endohedral Metallofullerenes With Floppy Interiors, Meichun Qian, Stephen V. Ong, Shiv N. Khanna, Mark B. Knickelbein
Physics Publications
It is shown that Gd3N@C80 is a highly magnetic and very stable motif that allows enhanced contrast magnetic resonance imaging and electric dipole moment with potential for cancer treatment. Using a synergistic approach combining Stern-Gerlach experiments in beams and first-principles electronic structure studies, it is demonstrated that an isolated Gd3N has a ground state spin moment of 23μBfollowed by a noncollinear state of 17.2μB only 88meV above the ground state. The large moment is largely due to localized f electrons. As a Gd3N is embedded inside a C80 cage, the localized felectrons maintain the magnetic character while the hybridization between …
Ferromagnetic To Ferrimagnetic Crossover In Cr-Doped Gan Nanohole Arrays, Q. Wang, Q. Sun, Puru Jena, Y. Kawazoe
Ferromagnetic To Ferrimagnetic Crossover In Cr-Doped Gan Nanohole Arrays, Q. Wang, Q. Sun, Puru Jena, Y. Kawazoe
Physics Publications
Using spin-polarized density-functional theory with exchange and correlation potential, approximated by both the generalized gradient approximation (GGA) and the GGA+U methods, we show that the coupling between a pair of Cr atoms substituted in GaN nanoholes is ferromagnetic. The interaction between the two Cr atoms, each carrying an average magnetic moment of around 2.5μB, is short ranged and mediated by the neighboring N atom. As the concentration of Cr increases, clustering ensues and the coupling changes from ferromagnetic to ferrimagnetic resulting in a significant reduction in the average magnetic moment per Cr atom.
Structure Of Siau(16): Can A Silicon Atom Be Stabilized In A Gold Cage?, Qiang Sun, Qian Wang, Gang Chen, Puru Jena
Structure Of Siau(16): Can A Silicon Atom Be Stabilized In A Gold Cage?, Qiang Sun, Qian Wang, Gang Chen, Puru Jena
Physics Publications
Nanostructures of Au and Si as well as Au–Si hybrid structures are topics of great current interest from both scientific and technological points of view. Recent discovery of Au clusters having fullerenelike geometries and the possibility of endohedral complexes with Si atoms inside the Au cage opens new possibilities for designing Au–Si nanostructures. Using ab initio simulated annealing method we have examined the stability of Si–Au16 endohedral complex. Contrary to what we believed, we find that the endohedral configuration is metastable and the structure where Si atom binds to the exterior surface of the Au16 cage is the lowest energy …
An Ab Initio Investigation On The Endohedral Metallofullerene Gd 3 N – C 80, M. C. Qian, S. N. Khanna
An Ab Initio Investigation On The Endohedral Metallofullerene Gd 3 N – C 80, M. C. Qian, S. N. Khanna
Physics Publications
First-principles electronic structure studies on the ground state geometry and electronic and magnetic properties of bare and hydrogen coated metallofullerene Gd3N–C80 have been carried out within a density functional formalism. The correlation effects are incorporated either through a generalized gradient corrected functional or through an on-site Coulomb interaction (LDA+U). It is shown that the bare Gd3N–C80 possess a ferromagnetic ground state with a large spin moment of 21μB that is highly stable against spin fluctuations. The simulated Raman spectrum shows that the low-energy peaks are contributed by the floppy movement of N atom. As to the effect of addition of …