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Articles 1 - 20 of 20
Full-Text Articles in Physics
Photoluminescence From Bulk Gan Substrates, Marrwa Alrrshedan
Photoluminescence From Bulk Gan Substrates, Marrwa Alrrshedan
Theses and Dissertations
Photoluminescence (PL) has been studied from different types of bulk GaN samples grown by hydride vapor phase epitaxy technique at Kyma Technologies. Point defects in bulk and at the surface affect the electrical and optical properties of GaN and could be analyzed by PL. The surface of the samples was polished with different techniques: one is chemical mechanical polish (CMP) and another is mechanical polish (MP). PL data from MP and CMP surfaces show that PL intensity from the CMP-treated surface is much higher than that from the MP-treated surface. This can be explained by defects formed during the process …
Preferentially Orienting Ag Nanoparticles Using Caf2 Nanorods, Mathias Auer
Preferentially Orienting Ag Nanoparticles Using Caf2 Nanorods, Mathias Auer
Theses and Dissertations
A study was done to examine the effect of surface orientation as well as heterogeneous epitaxy at an interface between two materials with a large lattice mismatch. Silver nanoparticles of different diameters were grown in an effort to study methods of preferentially orienting the geometry of metal nanoparticles. Arrays of calcium fluoride nanorods were grown on silicon substrates using oblique angle thermal vapor deposition. The chamber operated at an ultra high vacuum pressure of 10^-10 Torr during the deposition of the rods and an oblique angle of 75° was kept between the silicon substrate normal and the direction of incident …
Finite-Difference Time-Domain Modeling Of Nickel Nanorods, Joseph Steele Parris
Finite-Difference Time-Domain Modeling Of Nickel Nanorods, Joseph Steele Parris
Theses and Dissertations
Theoretical and experimental plasmonics is a growing field as a method to create near fields at sub-wavelength distances. In this thesis, a finite-difference time-domain method is used to simulate electromagnetic waves onto a thin film that present of nickel nanorods with sharp apexes. The absorbed, transmitted, and reflected fields were shown to depend linearly on silver film thickness and nanotip length. The electric field is visualized along the tip to show strong charge density along the base of the tip’s apex and how that density changes for wavelength, metal, and source tilt. Lastly, the study shows gold film on the …
Mechanical Characterization Of Patterned Silver Columnar Nanorods With The Atomic Force Microscope., Sean Kenny
Mechanical Characterization Of Patterned Silver Columnar Nanorods With The Atomic Force Microscope., Sean Kenny
Theses and Dissertations
Patterned silver (Ag) columnar nanorods were prepared by the glancing angle physical vapor deposition method. The Ag columnar nanorods were grown on a Si (100) substrate patterned with posts in a square “lattice” of length 1 μm. An electron beam source was used as the evaporation method, creating the deposition flux which was oriented 85˚ from the substrate normal. A Dimension Icon with NanoScope V controller atomic force microscope was used to measure the spring constant in 10 nm increments along the long axis of five 670 nm long Ag nanorod specimens. The simple beam bending model was used to …
Fabrication Of Anisotropic Sol-Gel Materials By Photo-Crosslinking, Charles Wingfield
Fabrication Of Anisotropic Sol-Gel Materials By Photo-Crosslinking, Charles Wingfield
Theses and Dissertations
This is a report on the fabrication and characterization of anisotropic, porous materials: functionally graded cellular and compositionally anisotropic aerogels. This new class of materials was fabricated by photopolymerization of selected regions of a homogeneous monolith using visible light. Visible light is not significantly absorbed and not significantly scattered by organic molecules and oxide nanoparticles in wet gels and it allows fabrication of deeply penetrating, well-resolved patterns. Simple variations of the exposure geometry allowed fabrication of a wide variety of anisotropic materials without requiring layers or bonding.
Thermal Quenching Of Photoluminescence From Gan, Anita Olsen
Thermal Quenching Of Photoluminescence From Gan, Anita Olsen
Theses and Dissertations
GaN is a III-V semiconductor that is a promising material used in production of light emitting devices and high power/high frequency electronics. The electronic and optical properties of GaN are subdued by defects that occur during the growth processes of this material. The emitted photoluminescence (PL) from optically excited GaN gives insight into the origins and effects of point defects within the crystal lattice structure of GaN. In this study, PL spectroscopy is used to examine and analyze the point defects that occur in Zn-doped GaN. The blue luminescence band seen in undoped and Zn-doped GaN have identical fine structure …
Adsorption Of Oxygen-Containing Functional Groups On Free And Supported Graphene Using Point Contact, Qian Wang, D. X. Ye, Y. Kawazoe, Puru Jena
Adsorption Of Oxygen-Containing Functional Groups On Free And Supported Graphene Using Point Contact, Qian Wang, D. X. Ye, Y. Kawazoe, Puru Jena
Physics Publications
First-principles electronic structure calculations based on spin-polarized density functional theory were carried out to study the adsorption of oxygen-containing functional groups -OH, -CHO, and -COOH on a two-dimensional (2D) infinite graphene sheet without edge states and defects. We find that the energy gain of adsorption can be significantly improved when the graphene sheet is supported via a point contact, a prototype for graphene sheet supported by catalysts, nanoparticles or nanopillars, or a surface with steps, edges, adatoms, or defects. This was modeled by placing a single atom of Fe, Co, and Ni under the graphene surface. Thus supported graphene not …
Two-Step Thermal Quenching Of Photoluminescence In Zn-Doped Gan, Michael A. Reshchikov
Two-Step Thermal Quenching Of Photoluminescence In Zn-Doped Gan, Michael A. Reshchikov
Physics Publications
We observed tunable two-step thermal quenching of photoluminescence in high-resistivity Zn-doped GaN. The characteristic temperatures of the first and second steps increase with increasing excitation intensity. The effect is explained within a phenomenological model involving shallow donors, nonradiative deep donors, and two types of acceptors.
Tuning Magnetic Properties Of Graphene Nanoribbons With Topological Line Defects: From Antiferromagnetic To Ferromagnetic, Min Kan, Jian Zhou, Qiang Sun, Qiang Wang, Yoshiyuki Kawazoe, Puru Jena
Tuning Magnetic Properties Of Graphene Nanoribbons With Topological Line Defects: From Antiferromagnetic To Ferromagnetic, Min Kan, Jian Zhou, Qiang Sun, Qiang Wang, Yoshiyuki Kawazoe, Puru Jena
Physics Publications
Zigzag-edged graphene nanoribbons are antiferromagnetic in cross-edge coupling and unsuitable for spintronics applications. Two new strategies of tuning antiferromagnetism (AFM) to ferromagnetism (FM) in graphene nanoribbons are introduced through topological line defects composed of pentagonal and octagonal rings, and their ability to induce magnetic transition is probed by using density functional theory. The resulting exchange energy is found to be large enough for ferromagnetism to be observed at room temperature. Both strategies are experimentally feasible, and the results suggest that defect engineering may provide a novel path to manipulate the magnetic properties of graphene nanoribbons.
Determination Of The Absolute Internal Quantum Efficiency Of Photoluminescence In Gan Co-Doped With Si And Zn, M. A. Reshchikov, M. Foussekis, J. D. Mcnamara, A. Behrends, A. Bakin, A. Waag
Determination Of The Absolute Internal Quantum Efficiency Of Photoluminescence In Gan Co-Doped With Si And Zn, M. A. Reshchikov, M. Foussekis, J. D. Mcnamara, A. Behrends, A. Bakin, A. Waag
Physics Publications
The optical properties of high-quality GaN co-doped with silicon and zinc are investigated by using temperature-dependent continuous-wave and time-resolved photoluminescence measurements. The blue luminescence band is related to the ZnGa acceptor in GaN:Si,Zn, which exhibits an exceptionally high absolute internal quantum efficiency (IQE). An IQE above 90% was calculated for several samples having different concentrations of Zn. Accurate and reliable values of the IQE were obtained by using several approaches based on rate equations. The concentrations of the ZnGa acceptors and free electrons were also estimated from the photoluminescence measurements.
Electrical Transition Of (3,3) Carbon Nanotube On Patterned Hydrogen Terminated Si(001)-2 X 1 Driven By Electric Field, Bikash C. Gupta, Shyamal Konar, Puru Jena
Electrical Transition Of (3,3) Carbon Nanotube On Patterned Hydrogen Terminated Si(001)-2 X 1 Driven By Electric Field, Bikash C. Gupta, Shyamal Konar, Puru Jena
Physics Publications
Structure, energetics, and electrical properties of (3,3) carbon nanotube(CNT) supported on patterned hydrogen terminated Si(001): 2 × 1 surface are studied using density functional theory. Our investigation reveals that an otherwise metallic (3,3) CNT when supported becomes semiconducting with a band gap of ≈0.5 eV due to its strong interaction with the surface. During adsorption, Si-C bonds form at the interface and charges transfer from Si surface to CNT. The Si-C bonds at the interface are partially covalent and partially ionic in nature. Under the application of an external electric field, the bandgap of the supported CNT reduces to zero, …
Magnetism Of Electrons In Atoms And Superatoms, Victor Medel, J. Ulises Reveles, Shiv N. Khanna
Magnetism Of Electrons In Atoms And Superatoms, Victor Medel, J. Ulises Reveles, Shiv N. Khanna
Physics Publications
The quantum states of electrons in small symmetric metallic clusters are grouped into shells similar to the electronic shells in free atoms, leading to the conceptual basis for defining superatoms. The filling of the electronic shells in clusters, however, do not follow Hund's rule and usually result in non-magnetic species. It is shown that by embedding a transition metal in group II atoms, one can stabilize superatoms with unpaired electronic supershells. We demonstrate this intriguing effect through electronic structure studies of MnSrn (n = 6-12) clusters within first principles generalized gradient calculations. The studies identify an unusually stable magnetic …
Ferromagnetism In Li Doped Zno Nanoparticles: The Role Of Interstitial Li, Saif Ullah Awan, S. K. Hasanain, Massimo F. Bertino, G. Hassnain Jaffari
Ferromagnetism In Li Doped Zno Nanoparticles: The Role Of Interstitial Li, Saif Ullah Awan, S. K. Hasanain, Massimo F. Bertino, G. Hassnain Jaffari
Physics Publications
ZnO nanoparticles doped with Li (Zn1−yLiyO, y ≤ 0.1) have been investigated with emphasis on the correlation between their magnetic, electronic, and structural properties. In particular, defects such as interstitial Li and Zn atoms, substitutional Li atoms, and oxygen vacancies have been identified by X-ray photoelectron spectroscopy(XPS) and their respective roles in stabilization of the magnetic moment are discussed. X-ray diffraction(XRD) and XPS give clear evidence of Li presence at both substitutional and interstitial sites. XPS studies further show that the amount of substitutional Li defects (Lizn) and interstitial Li defects (Lii) …
Structural Changes Of Pd-13 Upon Charging And Oxidation/Reduction, J. Ulises Reveles, A. M. Köster, P. Calaminici, S. N. Khanna
Structural Changes Of Pd-13 Upon Charging And Oxidation/Reduction, J. Ulises Reveles, A. M. Köster, P. Calaminici, S. N. Khanna
Physics Publications
First-principle generalized gradient corrected density functional calculations have been performed to study the stability of cationic and anionic Pd13 +/−, and neutral Pd13O2 clusters. It is found that while cationic Pd13 + favors a C s geometry similar to the neutral Pd13, both anionic Pd13 − and neutral Pd13O2 favor a compact ∼I h structure. A detailed analysis of the electronic structure shows that the stabilization of the delocalized 1P and 2P cluster orbitals, and the hybridization of the 1D orbitals with the oxygen atomic p orbitals …
Evolution Of Superhalogen Properties In Ptcln Clusters, Jorly Joseph, Kalpataru Pradhan, Purusottam Jena, Haopeng Wang, Xinxing Zhang, Yeon Jae Ko, Kit H. Bowen Jr.
Evolution Of Superhalogen Properties In Ptcln Clusters, Jorly Joseph, Kalpataru Pradhan, Purusottam Jena, Haopeng Wang, Xinxing Zhang, Yeon Jae Ko, Kit H. Bowen Jr.
Physics Publications
We have systematically calculated the ground state geometries, relative stability, electronic structure, and spectroscopic properties of PtCl n (n = 1–7) clusters. The bonding in these clusters is dominated by covalent interaction. In neutral clusters, chlorine atoms are chemically bound to Pt up to n = 5. However, in neutral PtCl6 and PtCl7 clusters, two of the chlorine atoms bind molecularly while the remaining bind as individual atoms. In the negative ions, this happens only in the case of PtCl7 cluster. The geometries of both neutral and anionic clusters can be considered as fragments of an …
Temperature-Dependent Kelvin Probe Measurements Of Band Bending In P-Type Gan, M. Foussekis, J. D. Mcnamara, A. A. Baski, Michael A. Reshchikov
Temperature-Dependent Kelvin Probe Measurements Of Band Bending In P-Type Gan, M. Foussekis, J. D. Mcnamara, A. A. Baski, Michael A. Reshchikov
Physics Publications
The band bending in a Mg-doped, p-type GaN film grown by hydride vapor phase epitaxy was studied at various temperatures. At 295 K, the band bending in dark was calculated to be approximately −1.5 eV. However, when the sample was heated to 600 K for 1 h in dark before performing a measurement at 295 K, the calculated value of band bending in dark became about −2.0 eV. These results are explained by the fact that increasing the sample temperature exponentially increases the rate at which the band bending restores and allows for a more accurate value of band …
Origin Of The Anomalous Magnetic Behavior Of The Fe13+ Cluster, M. Wu, A. K. Kandalam, G. L. Gutsev, Puru Jena
Origin Of The Anomalous Magnetic Behavior Of The Fe13+ Cluster, M. Wu, A. K. Kandalam, G. L. Gutsev, Puru Jena
Physics Publications
By using density functional theory, we show that the exceptionally low value of the total magnetic moment of Fe13+ observed in an experiment [Phys. Rev. Lett. 108, 057201 (2012)] is not due to antiferromagnetic coupling between the spins of the core and surface atoms as hypothesized but is due to the symmetry-driven quenching of the local spin moments of all atoms with the largest quenching observed for the central atom. Our study of Fe12+, Fe13+, Fe14+, and their neutral parents reveals that the total magnetic moment of Fe13+ decreases by 9μB with respect to that of neutral Fe13, …
Quantum Spin Transport Through Magnetic Superatom Dimer (Cs8v-Cs8v), Lin Zhu, Shiv N. Khanna
Quantum Spin Transport Through Magnetic Superatom Dimer (Cs8v-Cs8v), Lin Zhu, Shiv N. Khanna
Physics Publications
Theoretical studies of the spin transport through a magnetic superatom dimer (Cs8V)-(Cs8V) have been carried out within a density functional theory combined with nonequilibrium Green's-function formalism. It is shown that the electronic transport is sensitive to the binding site as well as the contact distance between the dimer and the electrode, and that the conductance at zero bias exhibits an oscillatory behavior as a function of the contact distance. The conductance in ferromagnetic state shows an unusually high spin polarization that exceeds 80% at large separations. The I–V curve shows negative differential resistance for …
The Effects Of Diffusion On An Exonuclease/Nanopore-Based Dna Sequencing Engine, Joseph E. Reiner, Arvind Balijepalli, Joseph W. F. Robertson, Bryon S. Drown, Daniel L. Burden, John J. Kasianowicz
The Effects Of Diffusion On An Exonuclease/Nanopore-Based Dna Sequencing Engine, Joseph E. Reiner, Arvind Balijepalli, Joseph W. F. Robertson, Bryon S. Drown, Daniel L. Burden, John J. Kasianowicz
Physics Publications
Over 15 years ago, the ability to electrically detect and characterize individual polynucleotides as they are driven through a single protein ion channel was suggested as a potential method for rapidly sequencing DNA, base-by-base, in a ticker tape-like fashion. More recently, a variation of this method was proposed in which a nanopore would instead detect single nucleotides cleaved sequentially by an exonuclease enzyme in close proximity to one pore entrance. We analyze the exonuclease/nanopore-based DNA sequencing engine using analytical theory and computer simulations that describe nucleotide transport. The available data and analytical results suggest that the proposed method will be …
Metallic And Molecular Orbital Concepts In Xmg8 Clusters, X = Be-F, Victor M. Medel, Arthur C. Reber, J. Ulises Reveles, Shiv N. Khanna
Metallic And Molecular Orbital Concepts In Xmg8 Clusters, X = Be-F, Victor M. Medel, Arthur C. Reber, J. Ulises Reveles, Shiv N. Khanna
Physics Publications
The electronic structure and stability of the XMg8 clusters (X = Be, B, C, N, O, and F) are studied using first principles theoretical calculations to understand the variation in bonding in heteroatomic clusters which mix simple divalent metals with main group dopants. We examine these progressions with two competing models, the first is a distorted nearly free electron gas model and the second is a molecular orbital picture examining the orbital overlap between the dopant and the cluster. OMg8 is found to be the most energetically stable cluster due to strong bonding of O with the Mg …