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Articles 1 - 11 of 11

Full-Text Articles in Physics

Transmission Electron Goniometry And Its Relation To Electron Tomography For Materials Science Apoplications, Peter Moeck, P. Fraundorf Nov 2006

Transmission Electron Goniometry And Its Relation To Electron Tomography For Materials Science Apoplications, Peter Moeck, P. Fraundorf

Physics Faculty Publications and Presentations

Aspects of transmission electron goniometry are discussed. Combined with high resolution phase contrast transmission electron microscopy (HRTEM) and atomic resolution scanning TEM (STEM) in the atomic number contrast (Z-STEM) or the phase contrast bright field mode, transmission electron goniometry offers the opportunity to develop dedicated methods for the crystallographic characterization of nanocrystals in three dimensions. The relationship between transmission electron goniometry and electron tomography for materials science applications is briefly discussed. Internet based java applets that facilitate the application of transmission electron goniometry for cubic crystals with calibrated tilt-rotation and double-tilt specimen holders/goniometers are mentioned. The so called cubic-minimalistic ...


A Transmission Electron Microscope For Lecture Demonstrations, J. A. Panitz, Gertrude Rempfer Nov 2006

A Transmission Electron Microscope For Lecture Demonstrations, J. A. Panitz, Gertrude Rempfer

Physics Faculty Publications and Presentations

A simple transmission electron microscope (TEM) suitable for lecture demonstrations is described. In this TEM electrons are created in a glow discharge between two parallel electrodes in air at a reduced pressure. The electrons are collimated by a small hole in theanode, focused by a solenoid that acts as an electromagnetic lens, and imaged on a thin layer of phosphor deposited inside an Erlenmeyer flask. An image of a biological sample placed between the source and the lens can be magnified about 20 times. The microscope uses inexpensive components that can be quickly assembled during a demonstration. The TEMprovides a ...


Relativistic Corrections To A Generalized Sum Rule, P.T. Leung, H. Sinky Sep 2006

Relativistic Corrections To A Generalized Sum Rule, P.T. Leung, H. Sinky

Physics Faculty Publications and Presentations

Relativistic corrections to a previously established generalized sum rule are obtained using the Foldy-Wouthysen transformation. This sum rule derived previously by Wang [Phys. Rev. A 60, 262 (1999)] for a nonrelativistic system contains both the well-known Thomas-Reiche-Kuhn and Bethe sum rules, for which relativistic corrections have been obtained in the literature. Our results for the generalized formula will be applied to recover several results obtained previously in the literature, as well as to another sum rule whose relativistic corrections will be obtained.


Two-Photon Spectroscopy Of Rubidium Using A Grating-Feedback Diode Laser, Abraham J. Olson, Evan J. Carlson, Shannon K. Mayer Mar 2006

Two-Photon Spectroscopy Of Rubidium Using A Grating-Feedback Diode Laser, Abraham J. Olson, Evan J. Carlson, Shannon K. Mayer

Physics Faculty Publications and Presentations

We describe an experiment for investigating the 5S1/2→5D5/2 two-photon transition in rubidium using a single grating-feedback diode laser operating at 778.1nm (385 THz). Continuous tuning of the laser frequency over 4GHz allows for the clear resolution of the Doppler-free spectral features and allows accurate measurement of the hyperfine ground-state splitting. A direct comparison between Doppler-broadened and Doppler-free spectral features is possible because both are distinctly evident in the two-photon spectra. By independently modifying the polarization state of the two laser fields, the impact of electric dipole selection rules on the two-photon transition spectra is ...


Nonlocal Effects On Optical And Molecular Interactions With Metallic Nanoshells, P.T. Leung, Railing Chang Mar 2006

Nonlocal Effects On Optical And Molecular Interactions With Metallic Nanoshells, P.T. Leung, Railing Chang

Physics Faculty Publications and Presentations

Theoretical studies of the optical response of metallic nanoshells have been carried out, where quantum effects are partially accounted for through the application of a nonlocal response model for shells of mesoscopic dimensions. Both far field and near field interactions are considered, with the incident source being a plane wave and an emitting molecular dipole, respectively. It is found that these nonlocal effects can lead to significant deviations from macroscopic electrodynamic theory, for shells of ultrasmall dimensions (<10 >nm) or ultrathin thickness (~1 nm), and are particularly significant for processes involving higher multipolar responses of the nanoshells. It is further concluded ...


Similarity-Based Constitutive Relations For Local Mass Fluxes In Incompressible Mixing Layers, John D. Ramshaw Feb 2006

Similarity-Based Constitutive Relations For Local Mass Fluxes In Incompressible Mixing Layers, John D. Ramshaw

Physics Faculty Publications and Presentations

The local concentrations of the two fluids within a mixing layer produced by an interfacial instability are determined by their individual continuity equations. Solution of these equations requires constitutive relations for the local mass fluxes of the two fluids. We derive explicit analytical expressions for these fluxes in planar incompressible mixing layers characterized by a single integral length scale h(t), which is presumed to be provided by a suitable mix or turbulence model. Elementary scaling arguments imply that in mixing layers of this type, the mean volume fraction profile α(x,t) depends on x and t only through ...


Quantum Phase Transitions In The Transverse One-Dimensional Ising Model With Four-Spin Interactions, O. F. De Alcantara Bonfim, J. Florencio Jan 2006

Quantum Phase Transitions In The Transverse One-Dimensional Ising Model With Four-Spin Interactions, O. F. De Alcantara Bonfim, J. Florencio

Physics Faculty Publications and Presentations

In this work we investigate the quantum phase transitions at zero temperature of the one-dimensional transverse Ising model with an extra term containing four-spin interactions. The competition between the energy couplings of the model leads to an interesting zero-temperature phase diagram. We use a modified Lanczos method to determine the ground state and the first excited state energies of the system, with sizes of up to 20 spins. We apply finite size scaling to the energy gap to obtain the boundary region where ferromagnetic to paramagnetic transition takes place. We also find the critical exponent associated with the correlation length ...


Exact And Approximate Energy Spectrum For The Finite Square Well And Related Potentials, O. F. De Alcantara Bonfim, David J. Griffiths Jan 2006

Exact And Approximate Energy Spectrum For The Finite Square Well And Related Potentials, O. F. De Alcantara Bonfim, David J. Griffiths

Physics Faculty Publications and Presentations

We investigate the problem of a quantum particle in a one-dimensional finite square well. In the standard approach the allowed energies are determined implicitly as the solutions to a transcendental equation. We obtain the spectrum analytically as the solution to a pair of parametric equations and algebraically using a remarkably accurate approximation to the cosine function. The approach is also applied to a variety of other quantum wells.


Lattice Fringe Fingerprinting In Two Dimensions With Database Support, Peter Moeck, B. Seipel, R. Bjorge, P. Fraundorf Jan 2006

Lattice Fringe Fingerprinting In Two Dimensions With Database Support, Peter Moeck, B. Seipel, R. Bjorge, P. Fraundorf

Physics Faculty Publications and Presentations

A brief introduction to lattice fringe fingerprinting in two dimensions (2D) with database support is given. The method is employed for the identification of the crystal phase of a small ensemble of nanocrystals. The enhanced viability of this method in aberration-corrected transmission electron microscopes (TEMs) and scanning TEMs (STEMs) is also illustrated.


Image-Based Nanocrystallography With Online Database Support, Peter Moeck, Ján Zahornadsky, Boris Dusek Jan 2006

Image-Based Nanocrystallography With Online Database Support, Peter Moeck, Ján Zahornadsky, Boris Dusek

Physics Faculty Publications and Presentations

The crystallographic phase and morphology of many materials change with the crystal size so that new needs arise to determine the crystallography of nanocrystals. Direct space high-resolution phase-contrast transmission electron microscopy (HRTEM) and atomic resolution scanning TEM (STEM) when combined with tools for image-based nanocrystallography in two (2D) and three (3D) dimensions possess the capacity to meet these needs. After a concise discussion of lattice-fringe visibility spheres and maps, this paper discusses lattice-fringe fingerprinting in 2D and tilt protocol applications. On-line database developments at Portland State University (PSU) that support image-based nanocrystallography are also mentioned.


Probing Nanoscale Ferroelectricity By Ultraviolet Raman Spectroscopy, Dmitri Tenne, A. Bruchhausen, N. D. Lanzillotti-Kimura, A. Fainstein, R. S. Katiyar, A. Cantarero, A. Soukiassian Jan 2006

Probing Nanoscale Ferroelectricity By Ultraviolet Raman Spectroscopy, Dmitri Tenne, A. Bruchhausen, N. D. Lanzillotti-Kimura, A. Fainstein, R. S. Katiyar, A. Cantarero, A. Soukiassian

Physics Faculty Publications and Presentations

We demonstrate that ultraviolet Raman spectroscopy is an effective technique to measure the transition temperature, Tc, accurately in ferroelectric ultrathin films and superlattices. We show that one-unit-cell thick BaTiO3 layers in BaTiO3/SrTiO3 superlattices are not only ferroelectric (Tc as high as 250 K), but also polarize the quantum paraelectric SrTiO3 layers adjacent to them. Tc was tuned by ~ 500 K by varying the thicknesses of BaTiO3 and SrTiO3 layers, revealing the essential roles of electrical and mechanical boundary conditions for nanoscale ferroelectricity.