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Articles 1 - 22 of 22
Full-Text Articles in Physics
Synthesis Of Nanocomposites By Laser Ablation, Stephen Mutisya
Synthesis Of Nanocomposites By Laser Ablation, Stephen Mutisya
Theses and Dissertations
Immunoglobulin E (IgE)-conjugated gold nanoparticles were produced via in situ conjugation of gold nanoparticles with immunoglobulin E by laser ablation of Au in a liquid solution. The colloidal stability and the size distribution of the resulting bio-nanoconjugates were examined with UV-Visible spectroscopy (UV-Vis), dynamic light scattering (DLS), and transmission electron microscopy (TEM). These techniques showed that the Au nanoparticles in aqueous solutions were highly monodispersed spherical particles with a very narrow size distribution. The particles net diameter using TEM, was found to be D5 =3.8±0.9nm and D10 =4.7±1.3nm while the hydrodynamic diameter obtained with DLS was found to be h5 …
Aging Effect In The Wettability Of Nickel Nanorod Arrays, Nahla Albarakati
Aging Effect In The Wettability Of Nickel Nanorod Arrays, Nahla Albarakati
Theses and Dissertations
The time-dependent wettability of nickel nanorod arrays was studied by measuring their water contact angles as a function of "aging" time in air. The nickel nanorod arrays were deposited on silicon substrates by DC magnetron sputtering using an oblique angle of 85° with respect to the substrate normal. By changing the deposition time from 10 to 90 min., the diameter, height, and separation of the nanorods were varied. The water contact angles of each sample were then periodically measured from a minimum aging time of 30 min. after deposition and exposure to air, up to a maximum aging time of …
The Effect Of Ambient On Photoluminescence From Gan, Iwona Ruchala
The Effect Of Ambient On Photoluminescence From Gan, Iwona Ruchala
Theses and Dissertations
The effect of ambient on photoluminescence (PL) from GaN was studied. We found that the PL intensity in vacuum was nearly four times higher than in air. The PL intensity also increased after etching the sample in Aqua Regia and BOE to remove the native oxide layer. After etching, the PL intensity was very stable in vacuum, but substantially degraded in air ambient. In HCl vapor (low pH), the PL intensity increased as compared to air ambient, while in NH3 vapor (high pH) it decreased. The quantum efficiency of the exciton and blue luminescence bands increased significantly with increasing excitation …
Inducing Active Sites In Clusters: Reactivity Of Al13ix- And Al14iy- (X=0-2, Y=2-4) With Methanol, Christopher Powell
Inducing Active Sites In Clusters: Reactivity Of Al13ix- And Al14iy- (X=0-2, Y=2-4) With Methanol, Christopher Powell
Theses and Dissertations
Size selective reactivity has been observed in pure aluminum cluster anions as a result of Lewis acid and base pairs. Using this a starting point, the goal of this study has been to explore how reactivity is affected with the addition of one or more ligand, which may induce active sites on the surface of the metal clusters. To study this, a theoretical investigation was undertaken on Al13Ix- and Al14Iy- (x=0-2, y=2-4) and their reactivity with methanol. The hypothesis was that iodine can induce a Lewis base site on the opposite side of the cluster, which may enhance reactivity. In …
Stability And Spectroscopic Properties Of Negative Ions, Swayamprabha Behera
Stability And Spectroscopic Properties Of Negative Ions, Swayamprabha Behera
Theses and Dissertations
Negative ions play an important role in chemistry as building blocks of salts and oxidizing agents. Halogen atoms, due to their ability to attract electrons, readily form negative ions. Considerable interest exists in the design and synthesis of new negative ions called superhaogens whose electron affinities are much higher than those of halogen atoms. This thesis deals with the design of such species. Using density functional theory I have studied two classes of superhalogens. First one involves d1 transition metal (Sc, Y, La) atoms surrounded by Cl while the second one involves simple metals (Na, Mg, Al) surrounded by pseudohalogens …
Impurity Complexes And Conductivity Of Ga-Doped Zno, D. O. Demchenko, B. Earles, H. Y. Liu, Vitaliy Avrutin, N. Izyumskaya, Ü. Özgür, Hadis Morkoç
Impurity Complexes And Conductivity Of Ga-Doped Zno, D. O. Demchenko, B. Earles, H. Y. Liu, Vitaliy Avrutin, N. Izyumskaya, Ü. Özgür, Hadis Morkoç
Physics Publications
Using hybrid functional theory together with experimental measurements, we investigate the influence of gallium impurities and their complexes on electrical properties of ZnO. In contrast to the behavior of isolated Ga impurities and native defects, the calculated formation energies of Ga complexes are consistent with our experimental data. We show that for high levels of Ga doping the acceptor behavior of GaZn-VZn and GaZn-Oi complexes explains the conductivity measurements and compensation levels in ZnO. The computed binding energies of these complexes are also consistent with the binding energies obtained from the measurements of the temperature dependence of carrier mobility. Our …
Tunable And Abrupt Thermal Quenching Of Photoluminescence In High-Resistivity Zn-Doped Gan, Michael A. Reshchikov, Alexander A. Kvasov, Marilyn F. Bishop, Tom Mcmullen, Alexander Usikov, Vitali Soukhoveev, Vladimir A. Dmitriev
Tunable And Abrupt Thermal Quenching Of Photoluminescence In High-Resistivity Zn-Doped Gan, Michael A. Reshchikov, Alexander A. Kvasov, Marilyn F. Bishop, Tom Mcmullen, Alexander Usikov, Vitali Soukhoveev, Vladimir A. Dmitriev
Physics Publications
Tunable and abrupt thermal quenching of photoluminescence by increasing temperature has been observed for the blue band in high-resistivity Zn-doped GaN. The photoluminescence intensity dropped by several orders of magnitude within a few Kelvins, and the temperature at which that drop occurred could be tuned by changing the incident light intensity. Modeling the system with rate equations for competing electron-hole recombination flows through three defect species, one of which is a nonradiative deep donor, gives results consistent with these observations.
Structures And Photoelectron Spectroscopy Of Cu-N(Bo2)(M) - (N, M=1, 2) Clusters: Observation Of Hyperhalogen Behavior, Yuan Feng, Hong-Guang Xu, Weijun Zheng, Hongmin Zhao, Anil K. Kandalam, Puru Jena
Structures And Photoelectron Spectroscopy Of Cu-N(Bo2)(M) - (N, M=1, 2) Clusters: Observation Of Hyperhalogen Behavior, Yuan Feng, Hong-Guang Xu, Weijun Zheng, Hongmin Zhao, Anil K. Kandalam, Puru Jena
Physics Publications
The electronic structures of CuBO2 −, Cu(BO2)2 −, Cu2(BO2)−, and Cu2(BO2)2 − clusters were investigated using photoelectron spectroscopy. The measured vertical and adiabatic detachment energies of these clusters revealed unusual properties of Cu(BO2)2 cluster. With an electron affinity of 5.07 eV which is larger than that of its BO2 superhalogen (4.46 eV) building-block, Cu(BO2)2 can be classified as a hyperhalogen. Density functional theory based calculations were carried out to identify the ground stategeometries and study the …
Gas Phase Analogs Of Stable Sodium-Tin Zintl Ions: Anion Photoelectron Spectroscopy And Electronic Structure, W.-J. Zheng, O. C. Thomas, J. M. Nilles, K. H. Bowen Jr., A. C. Reber, S. N. Khanna
Gas Phase Analogs Of Stable Sodium-Tin Zintl Ions: Anion Photoelectron Spectroscopy And Electronic Structure, W.-J. Zheng, O. C. Thomas, J. M. Nilles, K. H. Bowen Jr., A. C. Reber, S. N. Khanna
Physics Publications
Mass spectrometry and photoelectron spectroscopy together with first principles theoretical calculations have been used to study the electronic and geometric properties of the following sodium-tin, cluster anion/neutral cluster combinations, (NanSn4)−/(NanSn4), n = 0–4 and (NaSnm)−/(NaSnm), m = 4–7. These synergistic studies found that specific Zintl anions, which are known to occur in condensed Zintl phases, also exist as stable moieties within free clusters. In particular, the cluster anion, (Na3Sn4)− is very stable and is characterized as (Na+) …
Interactions Of A Mn Atom With Halogen Atoms And Stability Of Its Half-Filled 3d-Shell, Kalpataru Pradhan, Gennady L. Gutsev, Charles A. Weatherford, Purusottam Jena
Interactions Of A Mn Atom With Halogen Atoms And Stability Of Its Half-Filled 3d-Shell, Kalpataru Pradhan, Gennady L. Gutsev, Charles A. Weatherford, Purusottam Jena
Physics Publications
Using density functional theory with hybrid exchange-correlation potential, we have calculated the geometrical and electronic structure, relative stability, and electron affinities of MnX ncompounds (n = 1–6) formed by a Mn atom and halogen atoms X = F, Cl, and Br. Our objective is to examine the extent to which the Mn–X interactions are similar and to elucidate if/how the half-filled 3d-shell of a Mn atom participates in chemical bonding as the number of halogen atoms increases. While the highest oxidation number of the Mn atom in fluorides is considered to be +4, the maximum …
Photoelectron Spectroscopic Study Of Iron-Pyrene Cluster Anions, Xiang Li, Kit H. Bowen Jr., Puru Jena, Anil K. Kandalam
Photoelectron Spectroscopic Study Of Iron-Pyrene Cluster Anions, Xiang Li, Kit H. Bowen Jr., Puru Jena, Anil K. Kandalam
Physics Publications
Iron-pyrene cluster anions, [Fem(pyrene)n]− (m = 1–2, n = 1–2) were studied in the gas phase by photoelectron spectroscopy, resulting in the determination of their electron affinity and vertical detachment energy values. Density functional theory calculations were also conducted, providing the structures and spin multiplicities of the neutral clusters and their anions as well as their respective electron affinity and vertical detachment energy values. The calculated magnetic moments of neutral Fe1(pyrene)1 and Fe2(pyrene)1 clusters suggest that a single pyrene molecule could be a suitable template on which to deposit …
Sc-Phthalocyanine Sheet: Promising Material For Hydrogen Storage, Kun Lü, Jian Zhou, Le Zhou, Qian Wang, Qiang Sun, Puru Jena
Sc-Phthalocyanine Sheet: Promising Material For Hydrogen Storage, Kun Lü, Jian Zhou, Le Zhou, Qian Wang, Qiang Sun, Puru Jena
Physics Publications
It has been a long-standing dream to have high surface area materials with isolated and exposed transition-metal ions for hydrogen storage. The flexible synthesis procedure proposed recently by M. Abel, et al. [J. Am. Chem. Soc. 133, 1203 (2011)] and A. Sperl et al. [J. Am. Chem. Soc. 133, 11007 (2011)] provides a different pathway to achieve this goal. Using first-principles theory and grand canonical Monte Carlo simulation, we carry out a systematic study of 3d transition metals (Sc to Zn)-phthalocyanine porous sheets and find that Sc-phthalocyanine can store 4.6 wt. % hydrogen at 298 K and 100 …
Double Exchange Mediated Ferromagnetic Coupling Between Co Atoms In Dicobalt Complex, Kalpataru Pradhan, Purusottam Jena
Double Exchange Mediated Ferromagnetic Coupling Between Co Atoms In Dicobalt Complex, Kalpataru Pradhan, Purusottam Jena
Physics Publications
Realization of the full technological potential of molecular magnets requires a fundamental understanding of the origin of magnetic coupling in molecular systems. Using gradient corrected density functional theory and Cl as a ligand we show that the magnetic coupling between Co sites in a di-cobalt complex can be manipulated. While the ferromagnetic states of Co2Cl6 and Co2Cl7 are 0.07 eV and 0.20 eV lower in energy than their respective antiferromagnetic states, they are nearly degenerate in Co2Cl8. The origin of ferromagnetic coupling is explained using the double exchange model caused …
Stability And Electronic Structure Of Bilayer Graphone, J. Zhou, Q. Wang, Q. Sun, Puru Jena
Stability And Electronic Structure Of Bilayer Graphone, J. Zhou, Q. Wang, Q. Sun, Puru Jena
Physics Publications
Stability, reconstruction, and electronic structure of a bilayer graphone have been studied, where the most stable configuration undergoes a (1×2)surface reconstruction. An energy barrier of 1.83 eV separates this structure from the nonbonded state. The stability of the reconstructed bilayer at room temperature is confirmed by both frequency calculation and molecular dynamics simulation. Unlike the graphone sheet, the bilayer graphone is nonmagnetic but remains metallic due to the existence of delocalized π orbital on the zigzag sp2carbon chains, which are stable against Peierls instability. The metallicity is also stable under gate external electric field.
Extremely High Absolute Internal Quantum Efficiency Of Photoluminescence In Co-Doped Gan:Zn,Si, Michael A. Reshchikov, A. G. Willyard, A. Behrends, A. Bakin, A. Waag
Extremely High Absolute Internal Quantum Efficiency Of Photoluminescence In Co-Doped Gan:Zn,Si, Michael A. Reshchikov, A. G. Willyard, A. Behrends, A. Bakin, A. Waag
Physics Publications
We report on the fabrication of GaN co-doped with silicon and zinc by metalorganic vapor phase epitaxy and a detailed study of photoluminescence in this material. We observe an exceptionally high absolute internal quantum efficiency of blue photoluminescence in GaN:Zn,Si. The value of0.93±0.04 has been obtained from several approaches based on rate equations.
Tuning The Band Gap And Magnetic Properties Of Bn Sheets Impregnated With Graphene Flakes, M. Kan, J. Zhou, Q. Wang, Q. Sun, Puru Jena
Tuning The Band Gap And Magnetic Properties Of Bn Sheets Impregnated With Graphene Flakes, M. Kan, J. Zhou, Q. Wang, Q. Sun, Puru Jena
Physics Publications
The BN sheet is a nonmagnetic wide-band-gap semiconductor. Using density functional theory, we show that these properties can be fundamentally altered by embedding graphene flakes. Not only do graphene flakes preserve the two-dimensional (2D) planar structure of the BN sheet, but by controlling their shape and size, unexpected electronic and magnetic properties also emerge. The electronic band structure can be tuned from a direct gap to an indirect gap, the energy gap can be further modulated by changing the bonding patterns, and both hole injecting or electron injecting can be achieved by tailoring the triangular embedding pattern. Furthermore, the Lieb …
Closed-Shell To Split-Shell Stability Of Isovalent Clusters, Victor M. Medel, J. Ulises Reveles, A. C. Reber, Shiv N. Khanna, A. W. Castleman Jr.
Closed-Shell To Split-Shell Stability Of Isovalent Clusters, Victor M. Medel, J. Ulises Reveles, A. C. Reber, Shiv N. Khanna, A. W. Castleman Jr.
Physics Publications
Metallic clusters containing 2, 8, 18, and 20 electrons are now known to exhibit enhanced stability that can be reconciled because of filled 1S, 1P, 1D, and 2S electronic shells within a simplified confined nearly free electron (NFE) gas. Here, we present first-principles studies on three isovalent clusters, i.e., ZnMg8, CuMg8−, and AuMg8−, each with 18 valence electrons. All the clusters exhibit local energetic stability but with differing origins. Although the stability of ZnMg8 can be reconciled within the conventional confined NFE picture with filled 1S2, 1P6, and 1D10shells, CuMg8− and AuMg8− are shown to be stable despite the unfilled …
Electronic Structures And Bonding Of Graphyne Sheet And Its Bn Analog, Jian Zhou, Kun Lv, Qian Wang, X. S. Chen, Qiang Sun, Puru Jena
Electronic Structures And Bonding Of Graphyne Sheet And Its Bn Analog, Jian Zhou, Kun Lv, Qian Wang, X. S. Chen, Qiang Sun, Puru Jena
Physics Publications
Using density functional theory and generalized gradient approximation for exchange and correlation, we present theoretical analysis of the electronic structure of recently synthesized graphyne and its boron nitride analog (labeled as BN-yne). The former is composed of hexagonal carbon rings joined by C-chains, while the latter is composed of hexagonal BN rings joined by C-chains. We have explored the nature of bonding and energy band structure of these unique systems characterized by sp and sp 2 bonding. Both graphyne and BN-yne are found to be direct bandgap semiconductors. The bandgap can be modulated by changing the size of hexagonal ring …
A Systematic Study Of Neutral And Charged 3d-Metal Trioxides And Tetraoxides, Kalpataru Pradhan, Gennady L. Gutsev, Charles A. Weatherford, Puru Jena
A Systematic Study Of Neutral And Charged 3d-Metal Trioxides And Tetraoxides, Kalpataru Pradhan, Gennady L. Gutsev, Charles A. Weatherford, Puru Jena
Physics Publications
Using density functional theory with generalized gradient approximation, we have performed a systematic study of the structure and properties of neutral and charged trioxides (MO3) and tetraoxides (MO4) of the 3d-metal atoms. The results of our calculations revealed a number of interesting features when moving along the 3d-metal series. (1) Geometrical configurations of the lowest total energy states of neutral and charged trioxides and tetraoxides are composed of oxo and/or peroxo groups, except for CuO3 − and ZnO3 − which possess a superoxo group, CuO4 + and ZnO4 + which possess two …
Superhalogen Properties Of Cumcln Clusters: Theory And Experiment, Y. J. Ko, H. Wang, K. Pradhan, P. Koirala, A. K. Kandalam, K. H. Bowen, P. Jena
Superhalogen Properties Of Cumcln Clusters: Theory And Experiment, Y. J. Ko, H. Wang, K. Pradhan, P. Koirala, A. K. Kandalam, K. H. Bowen, P. Jena
Physics Publications
Using a combination of density functional theory and anion photoelectron spectroscopy experiment, we have studied the structure and electronic properties of CuCl n − (n = 1–5) and Cu2Cl n − (n = 2–5) clusters. Prominent peaks in the mass spectrum of these clusters occurring at n = 2, 3, and 4 in CuCl n − and at n = 3, 4, and 5 in Cu2Cl n − are shown to be associated with the large electron affinities of their neutral clusters that far exceed the value of Cl. While CuCl n(n …
Cooperative Effects In The Oxidation Of Co By Palladium Oxide Cations, Arthur C. Reber, Shiv N. Khanna, Eric C. Tyo, Christopher L. Harmon, A. W. Castleman Jr
Cooperative Effects In The Oxidation Of Co By Palladium Oxide Cations, Arthur C. Reber, Shiv N. Khanna, Eric C. Tyo, Christopher L. Harmon, A. W. Castleman Jr
Physics Publications
Cooperative reactivity plays an important role in the oxidation of CO to CO2 by palladium oxide cations and offers insight into factors which influence catalysis. Comprehensive studies including guided-ion-beam mass spectrometry and theoretical investigations reveal the reaction products and profiles of PdO2 + and PdO3 + with CO through oxygen radical centers and dioxygen complexes bound to the Pd atom. O radical centers are more reactive than the dioxygen complexes, and experimental evidence of both direct and cooperative CO oxidation with the adsorption of two CO molecules are observed. The binding of multiple electron withdrawing CO molecules …
Potential Candidates For Hyperhalogens: A Comparative Study Of Bo2, Alo2, And Vo3 Species, Kalpataru Pradhan, Purusottam Jena
Potential Candidates For Hyperhalogens: A Comparative Study Of Bo2, Alo2, And Vo3 Species, Kalpataru Pradhan, Purusottam Jena
Physics Publications
Recent work has shown that BO2 which is a superhalogen with an electron affinity of 4.46 eV, can be used as building block of a new class of molecules/clusters whose electron affinities can exceed that of BO2. This class of molecules was named hyperhalogens and the concept was illustrated by focusing on Au(BO2)2. Here we explore other superhalogens besides BO2 to see if they too can be used to form hyperhalogens. We have chosen to focus on AlO2 which is valence isoelectronic with BO2 as well as VO3 which …