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Series

2001

Physics Publications

Articles 1 - 12 of 12

Full-Text Articles in Physics

On Misorientation Distribution Evolution During Anisotropic Grain Growth, Elizabeth A. Holm, Gregory N. Hassold, Mark A. Miodownik Sep 2001

On Misorientation Distribution Evolution During Anisotropic Grain Growth, Elizabeth A. Holm, Gregory N. Hassold, Mark A. Miodownik

Physics Publications

In order to study the development of texture and boundary character during annealing, three-dimensional grain crystallography and crystallographically mediated grain boundary properties were incorporated into a finite temperature Monte Carlo model for grain growth. Randomly textured microstructures evolve normally, with growth exponent n=0.96. While texture remains random, the steady-state boundary misorientation distribution favors low-angle boundaries. To first order, low-angle boundaries increase by lengthening, not by proliferating. In contrast, microstructures with a strong single-component texture develop four-grain junctions and highly curved grain boundaries, which alter evolution. The boundary misorientation distribution narrows and shifts to low angles, and no steady state …

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Reply To “Comment On ‘Photodetachment In Combined Static And Dynamic Electric Fields’”, A. R. P. Rau, Chitra Rangan Jan 2001

Reply To “Comment On ‘Photodetachment In Combined Static And Dynamic Electric Fields’”, A. R. P. Rau, Chitra Rangan

Physics Publications

While distortion of the initial negative-ion state by a strong static electric field can have observable effects, the effect attributed by the authors of the preceding Comment [Phys. Rev. A 64, 037401 (2001)] to a cross term between the detaching laser field and the static field is spurious, an artifact of their procedures. Other points of dispute are also clarified.

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Optimally Shaped Terahertz Pulses For Phase Retrieval In A Rydberg-Atom Data Register, Chitra Rangan, P.H. Bucksbaum Jan 2001

Optimally Shaped Terahertz Pulses For Phase Retrieval In A Rydberg-Atom Data Register, Chitra Rangan, P.H. Bucksbaum

Physics Publications

A terahertz pulse was designed to implement a search algorithm on a quantum data register. Phase information stored in a Rydberg wave packet was optimally retrieved through the interaction with the pulse. Careful attention was paid to the smooth switch on and switch off of the terahertz pulse. Furthermore, the possibility of designing an optimal pulse that can achieve not only a desired target state of an atom, but also implement a desired algorithm was shown.

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Quantum Phase Retrieval Of A Rydberg Wave Packet Using A Half-Cycle Pulse, J. Ahn, D.N. Hutchinson, Chitra Rangan, P.H. Bucksbaum Jan 2001

Quantum Phase Retrieval Of A Rydberg Wave Packet Using A Half-Cycle Pulse, J. Ahn, D.N. Hutchinson, Chitra Rangan, P.H. Bucksbaum

Physics Publications

The half-cycle pulse (HCP) was used to search for information stored as phase in a Rydberg wave packet. Phase information coded in a Rydberg quantum register was retrieved through the impulsive interaction of HCP. In general, results of the study point to the use of HCPs as general tools for analysis for unknown wave packet.

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Measurement Of The Hyperfine Structure Of The 4d2d 3/2,5/2 Levels And Isotope Shifts Of The 4p2p 3/2 ? 4d2d3/2 And 4p2p 3/2 ? 4d2d5/2 Transitions In Gallium 69 And 71, Steven J. Rehse, W.M. Fairbank Jr., S.A. Lee Jan 2001

Measurement Of The Hyperfine Structure Of The 4d2d 3/2,5/2 Levels And Isotope Shifts Of The 4p2p 3/2 ? 4d2d3/2 And 4p2p 3/2 ? 4d2d5/2 Transitions In Gallium 69 And 71, Steven J. Rehse, W.M. Fairbank Jr., S.A. Lee

Physics Publications

The hyperfine structure of the 4d2D3/2,5/2 levels of 69,71Ga is determined. The 4p2P3/2 ? 4d2D3/2 (294.50-nm) and 4p2P3/2 ? 4d2D5/2 (294.45-nm) transitions are studied by laser-induced fluorescence in an atomic Ga beam. The hyperfine A constant measured for the 4d2D5/2 level is 77.3 ± 0.9 MHz for 69Ga and 97.9 ± 0.7 MHz for 71Ga (3s errors). The A constant measured for the 4d2D3/2 level is -36.3 ± 2.2 MHz for 69Ga and -46.2 ± 3.8 MHz for 71Ga. These measurements correct sign errors in the previous determination of these constants. For 69Ga the hyperfine B constants measured for the …

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Lamb Shift In He+: Resolution Of A Discrepancy Between Theory And Experiment, A. Van Wijngaarden, F. Holuj, Gordon W. F. Drake Jan 2001

Lamb Shift In He+: Resolution Of A Discrepancy Between Theory And Experiment, A. Van Wijngaarden, F. Holuj, Gordon W. F. Drake

Physics Publications

The Lamb shift in helium ions were investigated to verify or remove a discrepancy between theory and experiment by the anisotropy method. The method was used for the elimination of residual polarization sensitivity of the photon detectors. The results showed that the experimental value of a Lamb shift were in agreement with the theoretical values.

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Reactivity And Electronic Structure Of Aluminum Clusters: The Aluminum-Nitrogen System, B. D. Leskiw, A. W. Castleman Jr., C. Ashman, S. N. Khanna Jan 2001

Reactivity And Electronic Structure Of Aluminum Clusters: The Aluminum-Nitrogen System, B. D. Leskiw, A. W. Castleman Jr., C. Ashman, S. N. Khanna

Physics Publications

The stability of anionic aluminum–nitrogen clusters has been examined and Al2N−, Al3N−2,Al5N−2, Al6N−3, Al8N−3, and Al9N−2 are found to be particularly stable. Theoreticaldensity functional calculations on neutral and anionic AlnN (n=1–8) clusters were performed and the stability and reaction energetics with oxygen examined. Clusters requiring less than 5.7 eV to remove an electron and an Al atom are shown to be resistant to the reaction with oxygen.

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Geometry, Electronic Structure, And Energetics Of Copper-Doped Aluminum Clusters, S. N. Khanna, C. Ashman, B. K. Rao, P. Jena Jan 2001

Geometry, Electronic Structure, And Energetics Of Copper-Doped Aluminum Clusters, S. N. Khanna, C. Ashman, B. K. Rao, P. Jena

Physics Publications

Using density functional theory and generalized gradient approximation for exchange-correlation potential, we have calculated the equilibrium geometries and energetics of neutral and negatively charged AlnCu (n=11,12,13,14) clusters. Unlike the alkali atom-doped aluminum clusters in the same size range, the copper atom resides inside the aluminum cluster cage. Furthermore, the 3d and 4s energy levels of Cu hybridize with the valence electrons of Al causing a redistribution of the molecular orbital energy levels of the Aln clusters. However, this redistribution does not affect the magic numbers of AlnCu clusters that could be derived by assuming that Cu donates one electron to …

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Electronic Structure And Chemical Bonding Of 3d-Metal Dimers Scx, X=Sc-Zn, G. L. Gutsev, P. Jena, B. K. Rao, S. N. Khanna Jan 2001

Electronic Structure And Chemical Bonding Of 3d-Metal Dimers Scx, X=Sc-Zn, G. L. Gutsev, P. Jena, B. K. Rao, S. N. Khanna

Physics Publications

The electronic and geometrical structures of the ground and excited states of the homonuclear Sc2, mixed ScTi, ScV, ScCr, ScMn, ScFe, ScCo, ScNi, ScCu, and ScZn 3d-metal dimers and their anions have been calculated using the density functional theory with generalized gradient approximation for the exchange-correlation potential. The ground states of the neutral dimers are found to be 5Σ−u (Sc2), 6Σ+ (ScTi), 7Σ+ (ScV), 4Σ+ (ScCr), 3Σ+ (ScMn), 2Δ(ScFe), 1Σ+ (ScCo), 2Σ+ (ScNi), 3Δ(ScCu), and 4Σ+ (ScZn). A natural bond analysis reveals an antiferrimagnetic spin coupling in the ground states of ScCr, ScMn, and ScFe. This is due to the …

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Energetics And Electronic Structure Of Carbon Doped Aluminum Clusters, B. K. Rao, P. Jena Jan 2001

Energetics And Electronic Structure Of Carbon Doped Aluminum Clusters, B. K. Rao, P. Jena

Physics Publications

The energetics and the electronic structure of AlnC clusters (n=3, 4, 5; 11, 12, 13) have been studied by a global optimization of their geometry without any symmetry constraint. The total energies of these clusters both in neutral and charged states are calculated using an all-electron basis and the generalized gradient approximation to the density functional theory. While Al4C and Al12C clusters share some characteristic features of closed shell structures, namely enhanced stability and low electron affinity compared to their neighboring sizes, their ionization potentials exhibit different behavior. These decrease steadily from Al3C to Al5C while that of Al12C is …

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Electronic Structure Of Chromium Oxides, Cron- And Cron (N=1-5) From Photoelectron Spectroscopy And Density Functional Theory Calculations, G. L. Gutsev, P. Jena, Hua-Jin Zhai, Lai-Sheng Wang Jan 2001

Electronic Structure Of Chromium Oxides, Cron- And Cron (N=1-5) From Photoelectron Spectroscopy And Density Functional Theory Calculations, G. L. Gutsev, P. Jena, Hua-Jin Zhai, Lai-Sheng Wang

Physics Publications

The electronic structure of CrO−n and CrOn (n=1–5) was investigated using anion photoelectron spectroscopy and density functional theory. Photoelectron spectra of CrO−n were obtained at several photon energies and yielded electron affinities, vibrational and electronic structure information about the neutral CrOn species. Density functional theory calculations were carried out for both the neutrals and anions and were used to interpret the experimental spectra. Several low-lying electronic states of CrO were observed and assigned from photodetachment of the CrO− ground state(6∑+) and an excited state (4∏), which is only 0.1 eV higher. The main spectral features of CrO−2 were interpreted based …

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Investigation Of Inversion Domains In Gan By Electric-Force Microscopy, K. M. Jones, P. Visconti, F. Yun, A. A. Baski, Hadis Morkoç Jan 2001

Investigation Of Inversion Domains In Gan By Electric-Force Microscopy, K. M. Jones, P. Visconti, F. Yun, A. A. Baski, Hadis Morkoç

Physics Publications

Inversion domains in III-nitride semiconductors degrade the performance of devicesfabricated in them. Consequently, it is imperative that we understand their electrostatic manifestation, the growth conditions under which such domains form, and an effective means of their identification. In what is nominally referred to as Ga-polarity samples, N-polarity domains have a polarization that is reversed with respect to the remainder of the surface, and therefore, have a different potential under strain. We have used surface-potential electric-force microscopy (SP-EFM) to image the electrostaticsurface potential of GaNgrown on sapphire, which is strained due to the thermal mismatch between the substrate and GaN. Employing …

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