Bulletin of the American Physical Society
2005 Joint New England Sections of APS and AAPT Spring Meeting
Friday–Saturday, April 1–2, 2005; Cambridge, MA
Session PO: Poster Session |
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Room: Stata Center 5:00pm - 6:30pm |
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PO.00001: Electromigration characterization of semiconductor devices Narahara Dingari, Brian Setlik, David Heskett Insuring the reliability of metal interconnects has become one of the most serious issues in the design and fabrication of integrated circuits. Electromigration is an important failure mechanism which affects the functionality and lifetime of integrated circuits. The addition of relatively small amounts of copper has repeatedly been shown to improve device lifetimes. Through the use of Scanning Electron Microscope (SEM) with Energy Dispersive Spectroscopic (EDS) capabilities we have measured the copper concentration as a function of length for interconnects after several accelerated stress time periods. We observe a migration of copper atoms from the cathode to the anode side of the interconnect as a function of stressing time. A pileup of copper near the middle of the interconnect indicates a blocking of copper diffusion and creates a site for interconnect failure. [Preview Abstract] |
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PO.00002: Absolute and Relative Time John M. Kulick Relative time is defined as the time interval that separates points in spacetime as expressed by the speed of light. Absolute time, also called ``Cosmic'' or ``historical'' time demarcates a point's temporal location relative to the beginning of time. A hypothetical geometric relationship between the two dimensions of time allows all relative or local measures of time remain proportionally the same but from a historical perspective, relative time is slowing down. Gravitational relationships observed in the past would appear to be moving too fast for the amount of matter observed within the system. The effect of gravity becomes temporally dependant. [Preview Abstract] |
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PO.00003: Angular Dependent Interaction of $\mathrm{He}_{2}^{*}$ ON $\mathrm{He}_{N}$ Droplet Surfaces Raghuram Petluri, Jan Northby A Metastable helium molecule is produced in a helium nanodroplet by electron bombardment and rise to the droplet surface. After equilibration, absorption of an infrared photon detaches it from the droplet surface. It is subsequently detected when it reaches a nearby metal surface and emits an electron. The spectral peaks studied in the region of the $a ^{3} \Sigma_{u}^{+} \rightarrow c ^{3} \Sigma_{g}^{+}$ transition are found to be shifted by $\sim\mathrm{2.6 cm}^{-1}$ from their corresponding free molecular transition values. In addition the lines are sharp, well resolved, and highly structured as a result of the interaction of the molecule with the droplet surface. We propose a model to explain the spectral shifts and line shapes on the basis of perturbation theory and Frank-Condon principle. [Preview Abstract] |
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PO.00004: The Lorentz Force Law and Spacetime Symmetries Richard Shurtleff Assume that arc length is measured with the flat spacetime metric. Then, for the most general Poincare group representation for translating 4-vectors, curves with parallel translated tangent vectors must have accelerations that are the scalar product of the tangent vector with an antisymmetric tensor. Such curves are the paths of charged particles in an electromagnetic field. [Preview Abstract] |
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PO.00005: A Symbolic and Graphical Computer Representation of Dynamical Systems Laurence I. Gould, Christopher J. Mahar AUTONO is a Macsyma/Maxima program, designed at the University of Hartford, for solving autonomous systems of differential equations as well as for relating Lagrangians and Hamiltonians to their associated dynamical equations. AUTONO can be used in a number of fields to decipher a variety of complex dynamical systems with ease, producing their Lagrangian and Hamiltonian equations in seconds. These equations can then be incorporated into VisSim, a modeling and simulation program, which yields graphical representations of motion in a given system through easily chosen input parameters. The program, along with the VisSim differential-equations graphical package, allows for resolution and easy understanding of complex problems in a relatively short time; thus enabling quicker and more advanced computing of dynamical systems on any number of platforms---from a network of sensors on a space probe, to the behavior of neural networks, to the effects of an electromagnetic field on components in a dynamical system. A flowchart of AUTONO, along with some simple applications and VisSim output, will be shown. [Preview Abstract] |
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PO.00006: Study of Phonon Propagation in GaN Riccardo Schmid, Madeleine Msall We have studied the propagation of heat in GaN crystals using phonon imaging. GaN is commonly used in semiconductor technology and our experiments can help understand how the material transports heat. Such information would enable the development of more efficient integrated circuits, critical in the construction of powerful computer components. Phonon creation is achieved by laser pulse heating. A thin superconducting bolometer measures the changes in the temperature after phonons have propagated through the crystal. The experiments are carried out at the superconducting critical temperature of the bolometer kept constant in a superfluid He bath ($T < 2.17^{\circ}$K) by vacuum pumping. The data collected measures phonon flux with time for different crystal directions. The fastest phonon pulses reach the detector in $\sim 40 $ns, in agreement with calculated group velocities. We were able to observe phonon focusing for particular crystal directions. GaN crystals generally abound in imperfections due to the development of stacking dislocations during growth processes. Our experiments are carried out on thin crystals ($\sim 200 \mu$m), with dislocation density $\sim 5 \times 10^{6} / \mathrm{cm}^{2}$. The effects of imperfections on phonon propagation are evident from our observation of strong phonon scattering and enable us to quantify phonon defect interactions including angular dependance. [Preview Abstract] |
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PO.00007: Isospin Equilibrium in Heavy Ion Reactions Malgorzata Zielinska-Pfabe, Darcy Lambert, Alexis Knaub, Virgil Baran, Maria Colonna, Massimo di Toro, Hermann Wolter The BUU approach with density fluctuations was used to study the density dependence of the asymmetry term in the nuclear equation of state (EOS.) The knowledge of the nuclear mean field potential is of crucial importance for nuclear binding, stabilization of neutron stars, and dynamics of supernovae explosions. To gain information about the density dependence of the asymmetry term we study isospin equilibration in the reactions between projectile and target with different isospin asymmetry. In these cases, the asymmetry term in the nuclear EOS provides diffusive forces which drive the isospin equilibration process. It is important to use observables which are sensitive to the stiffness of the asymmetry term. The isospin imbalance parameter which measures the degree of ispospin equilibration seems to be sensitive to the density dependence of the asymmetry term in the nuclear equation of state. We have calculated this parameter for the asy-soft and asy-stiff EOS for the semi-peripheral (b=6fm) reactions of Sn+Sn at 50 MeV/u and present a comparison of our results with experiment. [Preview Abstract] |
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PO.00008: Variational formulation of self-consistent ponderomotive effects in unmagnetized plasmas Alain Brizard, Christopher Scilla The variational formulation of self-consistent ponderomotive effects in unmagnetized plasmas is investigated. In particular, we show how ponderomotive effects can assist in generating quasi-static magnetic fields. [Preview Abstract] |
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PO.00009: Separation of Wave and Particle Fluctuations to Higher Orders Norma M. Chase By extending Einstein's separation of wave and particle parts of the second order thermal fluctuation to encompass ``generalized'' fluctuations in any Bose field, P. E. Gordon proposed alternative definitions for nth order coherence and nth order coherent states. This paper proves the equivalence of Gordon's coherence conditions to those of Glauber. We then examine some of the physical implications of extending duality to higher orders. [Preview Abstract] |
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PO.00010: Dielectrophoretic control of semiconductor nanostructure growth and assembly Alexander Wissner-Gross, Charles Lieber The rational growth and assembly of one-dimensional semiconductor nanostructures may have significant applications to superlattice electronics and large scale integration. The electrostatics of doped semiconductor nanowires capped with metallic catalysts, under nonuniform electric fields and at elevated temperatures, are analyzed and the feasibility of dielectrophoretically-controlled growth is explored. For post- growth control, positive dielectrophoretic assembly of silicon nanowires into simple devices is experimentally demonstrated and the devices are characterized. [Preview Abstract] |
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PO.00011: Many-Body Decay Quantified by a Complex Chemical Potential George Cragg, Arthur Kerman For species having negative s-wave scattering lengths, atomic condensation is impossible above some critical number of atoms. Nevertheless, for some species, Feshbach resonance coupling to a molecular state enables the effective scattering length, $a$, to be tuned to positive values, where it is believed to then result in stability. However, a many-body analysis of the resonant system reveals that while the ground state remains unstable against collapse, the usual low-density dependencies occur in an excited state with a complex chemical potential. Physically, the imaginary part quantifies the time of decay into collective phonon excitations of the collapsing ground state, thus revealing a unique decay rate dependency on both the scattering length and the density, $\sim ~a^{5/2}\rho^{3/2}$, which can be experimentally tested. Using our predicted rate, there is good agreement with the overall lifetime observed in $^{85}$Rb. [Preview Abstract] |
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PO.00012: Prospects for Observing Gravitational Lensing by Supermassive Black Holes in Galaxy Cores Judd Bowman The properties of supermassive black holes (SMBHs) in galaxy cores have emerged as important probes into understanding the history of galaxy and structure formation in the universe. Detecting SMBHs, however, is difficult and has been achieved typically using stellar kinematics in the very central regions of galaxies. Strong galaxy-galaxy gravitational lensing offers a compelling mechanism to discover new SMBHs and explore the relationships between the properties of SMBHs and their host galaxies at cosmologically significant redshifts. The presence of an SMBH in a galaxy core is predicted to produce two primary observable effects depending on the lens configuration, either blocking an otherwise predicted image of the background galaxy, or adding an extra, highly demagnified image. Examination of these gravitational lenses under proper circumstances may yield the mass of the SMBH, information on the inner mass-density profile of the host galaxy, and the total mass of the galaxy simultaneously. A serious observational campaign to detect and study these faint images should be practical when the next generation of radio telescope technology is operational. [Preview Abstract] |
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PO.00013: \textbf{Upconversion Luminescence of Novel Ceramic } \textbf{Laser Materials of Er-doped PLZT} Naota Nakayama, Leanne Lortie, Isabella Pi-Ling Huang, Xuesheng Chen The purpose of this research is to examine upconversion luminescence properties of Erbium-doped PLZT, a novel, new ceramic laser material. We investigate how the upconversion properties are affected by doping the ceramic host material PLZT with the Erbium concentrations of 0.5{\%} and 2 {\%}. Using an infrared laser at about 975nm to excite the sample, upconversion luminescence spectra are taken in range of 400 to 750 nm at different temperatures ranging from about 28K to 300K. Upconversion processes are discussed for the temperature and concentration dependence of the visible luminescence under the excitation of the infrared light. This is part of an ongoing joint project with industry funded by National Science Foundation that will lead to high power laser applications using this new ceramic laser material. We would like to acknowledge the support from NSF and collaboration with Boston Applied Technologies, Inc., which developed the material, and Wheaton Research Participation Program. [Preview Abstract] |
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PO.00014: Optical Studies of Newly-developed Nd doped Ceramic Laser Materials Nicholas apRoberts-Warren, Xuesheng Chen A major focus in recent laser research is to develop new laser materials for making high-power and efficient lasers, for which transparent ceramic laser materials have great potentials. In this research project, newly-developed tranparent ceramic laser materials are examined for their optical properties. They are PLZT doped with Nd ions of 0.5{\%}, 1{\%}, and 2{\%}. Absorption and luminescence spectra of these materials are investigated in the wavelength range from 350 to 1100 nm at different temperatures. The implications of these results are very important. The absorption peaks reveals what wavelengths the materials absorb well, which is critical in knowing what kinds of pump lasers to use. The luminescence results establish what Nd ion concentration gives off strong emission at certain wavelengths for potential lasing wavelength choices. Results will be discussed in details. We would like to acknowledge the support from NSF and Wheaton Research Participation Program and collaboration with BATI. [Preview Abstract] |
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PO.00015: Fluctuations in Heavy Ion Collisions Malgorzata Zielinska-Pfabe, Darcy Lambert, Alexis Knaub, Virgil Baran, Maria Colonna, Massimo di Toro, Hermann Wolter Collisions between heavy ions are investigated within the semi-classical mean field formalism (BUU/BNV.) The influence of neglected higher order terms is considered as a fluctuation of the distribution function. Without fluctuations the widths of calculated mass and charge distributions are too narrow compared to experiment. We discuss the implementation and the effects of fluctuations on mean field dynamics and fragmentation. We consider two methods of including fluctuations. In one method we assume a local thermal equilibrium, determine the variances of density, and introduce density fluctuations according to these variances. In a second approach, a gauged numerical noise serves as an origin of fluctuations. The way in which the mean field evolves the fluctuation depends on the stability of the system. We consider the central (b=2fm) and semi-peripheral (b=6fm and b=8fm) collisions of the Sn+Sn system at 50 MeV and use both approaches to study the time evolution of the average number of fragments, their charge distribution, the distribution of the number of fragments, their isospin asymmetry and the velocity correlations. We conclude that both ways of implementation of fluctuations lead to quite similar results for fragmentation and isospin distributions. [Preview Abstract] |
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