Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session X20: Dielectric and Optical Phenomena |
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Sponsoring Units: DMP Chair: Eric Shirley, NIST Room: LACC 407 |
Friday, March 25, 2005 8:00AM - 8:12AM |
X20.00001: Optical Response of Graded Films Joseph T.A. Kwok, K.W. Yu Graded materials have quite different physical properties from the homogeneous materials. Recently, it has been found that graded thin films may have better dielectric properties than a single-layer film. The materials properties of graded films can vary continuously in space. These materials have attracted much interest in various engineering applications. However, the traditional theories fail to deal with the composites of graded inclusions. Recently, for treating these composites, we presented a first-principles approach [1] and differential effective dipole approximation [2]. In this work, we adopt a graded multilayer model by putting together infinite planes of square lattices. We adopted the Drude dielectric gradation profile for the polarizability of the spherical metallic particles. An external electric field is applied to the multilayer and the local field inside the multilayer has been calculated by Lekner summation method [3]. The effect of the boundary condition has also been examined. From this, the effective polarizability and hence the optical absorption as well as optical nonlinearity of the film can be obtained. Such theoretical studies on the dielectric properties of graded composite materials will be useful in diverse applications. [1]. L. Dong, G. Q. Gu, and K. W. Yu, Phys. Rev. B 67, 224205 (2003). [2]. J. P. Huang, K. W. Yu, G. Q. Gu, and M. Karttunen, Phys. Rev. E 67, 051405 (2003). [3]. S. V. Lishchuk, Mol. Phys. 100, 3789 (2002). [Preview Abstract] |
Friday, March 25, 2005 8:12AM - 8:24AM |
X20.00002: Effects of Incident Electron Fluence and Energy on the Electron Yield Curves and Emission Spectra of Dielectrics Alec Sim, J.R. Dennison, Clint Thomson We present an experimental study of evolution of electron emission yields and spectra as a result of internal charge build up due to electron dose. Reliable total, backscattered and secondary yield curves and electron emission spectra for un-charged insulators using a low fluence, pulsed electron beam ($\le $5 $\mu $sec at $\le $ 3 nA/mm$^{2}$ or =10$^{5}$ e/mm$^{2}$ per pulse) with low energy electron and UV flooding to neutralize the charging between pulses. Quantifiable changes in yield curves are observed due to $<$100 fC/mm$^{2}$ fluences for several excellent dielectric thin film materials. We find good agreement with a phenomenological argument based on insulator charging predicted by the yield curve; this includes an approximately linear decrease in the magnitude of the yield as incident energies approach the crossover energies and an exponential decrease in yield as accumulated internal charge reduces the landing energy to asymptotically approach a steady state surface charge and unity yield. We also find that the exponential decay of yield curves with fluence exhibit an energy dependant decay constant, $\alpha $(E), over a broad range of incident energies below, between and above the crossover energies. Finally, we present some preliminary physics-based models for this energy dependence and relate our charging measurements to the physics of charge deposition, trapping, transport and emission from insulators. [Preview Abstract] |
Friday, March 25, 2005 8:24AM - 8:36AM |
X20.00003: The scattering of X-rays and the induction phenomenon Rama Mohanty This paper discusses the well-established Faraday’s Law of Induction and the associated Lenz’s law and compares these laws with a similar law which appears to exist in the triplet production process achieved by bombardment of emulsion with 0-9- Mev X-ray. This comparison shows that an induction-like process occurs during triplet production, leading to the supposition that a force which may be called the ``Matteromotive force'' exists for triplet production. An associated Lenz’s-law-like law also appears to exist in this process. For this study, 1935 triplets were observed in 54433 fields of view of the microscopes; out of these, 1872 triplets were measured in the energy interval of 2-90 Mev. In addition, the angular distribution of recoil electrons was observed, and is presented here. [Preview Abstract] |
Friday, March 25, 2005 8:36AM - 8:48AM |
X20.00004: Refractive-Index Dispersion Formulas, Old and New Carrie E. Black, William Karstens, David Y. Smith A multitude of dispersion formulas, many empirical, have been proposed to approximate the refractive index of transparent materials. The commonly used Cauchy and Sellmeier formulas are based on classical elastic models. They also follow from more fundamental linear-response theory: The generalized Cauchy formula follows from expansion of the Kramers-Kronig relations in a Laurent series. It is exact, but may involve many terms. In contrast, the Sellmeier formula follows from approximating the continuous ir and uv absorptions of the material with a spectrum of isolated lines. A superior representation involves a partial series expansion of the dispersion relations followed by approximation of the remainder using a discrete spectrum. The distinction between this and prior formulations is that the isolated-absorption approximation is made at the last possible step. We have tested this new dispersion formula on typical optical glasses and found it gives an improved representation of the index. [Preview Abstract] |
Friday, March 25, 2005 8:48AM - 9:00AM |
X20.00005: An attempt to intuitively understand intrinsic birefringence Eric L. Shirley In recent years, intrinsic birefringence has grown from being a topic of curiosity to a symmetric-breaking effect on the optical properties of cubic-symmetry materials. In many cubic systems, light propagating along the (1,1,0) direction has different refractive indices for polarization along (0,0,1) versus (1,-1,0). This has been important in consideration of calcium, barium and strontium fluoride as refractive elements in deep- ultraviolet lithography. Largely, the most successful theoretical prediction of the magnitude or even sign of the birefringence relies on first-principles calculations, the results of which are difficult to predict beforehand. This talk presents an attempt to correlate the birefringence with other properties of a material, such as whether a given ion species is surrounded by an octahedral or cubic cage of near-neighbor ions. [Preview Abstract] |
Friday, March 25, 2005 9:00AM - 9:12AM |
X20.00006: Negative Refraction in Gyrotropic Media by Polaritons Vladimir Agranovitch, Anvar Zakhidov We discuss the negative refraction in isotropic gyrotropic (chiral) Materials (having natural optical activity) from the point of view of crystal optics with account of a spatial dispersion, i.e. the linear dependence of the dielectric tensor $\varepsilon (\omega $,k) on the k-vector. We show that in the media with high enough rotatory power, (such as polylactic acid),negative refraction can be observed at optical frequencies for additional waves. We make computer modeling of lensing effect in naturally gyrotropic rectangular lenses and compare our results of spatial dispersion, polaritonic approach with those, demonstrated recently by J.B. Pendry (Science,v.306, p.1353) for a negative refraction near electrical dipole resonance. [Preview Abstract] |
Friday, March 25, 2005 9:12AM - 9:24AM |
X20.00007: Complex Permittivity Measurements of Dielectrics and Semiconductors in Millimeter-Wave Range with High Power Sources Konstantin Korolev, Mohammed Afsar, Lakshmi Subramanian, Igor Tkachov We present complex dielectric permittivity measurements of various semiconductor and dielectric materials, including highly absorbing substances, in $Q$-, $V$- and $W$-band frequencies. The measurements have been done using broad-band quasi-optical millimeter-wave system with a backward-wave oscillator as a high power source of radiation. Frequency dependencies of real and imaginary parts of dielectric permittivity are calculated from the transmittance spectra. Refractive index data, obtained using both waveguide bridge technique and free space measurements have been compared with previously published data. The work was supported by US Army contracts. [Preview Abstract] |
Friday, March 25, 2005 9:24AM - 9:36AM |
X20.00008: Dynamics and Spectral Weights in Transition-Metal K-edge Resonant Inelastic X-ray Scattering Michel van Veenendaal, Ken Ahn, Art Fedro We discuss the trends in resonant inelastic x-ray scattering (RIXS) at the transition-metal K-edge for metals, semiconductors, and strongly correlated systems. We find that the inelastic spectral weight is not determined by the total energy of the shake-up structure, as is expected from simple considerations, but by the excitonic nature of the core hole and the valence electrons. The asymmetry between electron and hole excitations is emphasized and shown to be important in explaining the RIXS spectrum. The results differ significantly from lowest-order perturbation theory results that predict that the probability of exciting a certain shake-up structure depends only on its total energy. [Preview Abstract] |
Friday, March 25, 2005 9:36AM - 9:48AM |
X20.00009: Frequency-Dependent Dielectric Behavior in ER Fluid Stephen Tsui, Feng Chen, Jason Shulman, Yuyi Xue, C.W. Chu, Weijia Wen It is well accepted that the electrorheology (ER) of a fluid is directly related to the change of its dielectric constant $\varepsilon $. We investigate the frequency dependency of $\varepsilon $ in the giant ER fluid consisting of urea-coated Ba$_{0.8}$Rb$_{0.4}$TiO(C$_{2}$O$_{4})_{2 }$nanoparticles suspended in silicone oil. The data show a step around 2 kHz, similar to those seen in other composite systems, which is typically interpreted via the Maxwell-Wagner polarization. Upon extending the measurement down to lower frequencies, the data suggest the existence of multiple relaxation processes in the ER fluid, some of which occur with characteristic time scales from 10$^{-4}$ to 10$^{2}$ s. The related microstructures are examined through impedance spectroscopy, and a comparison to other composite systems, including biological suspensions, will be discussed. [Preview Abstract] |
Friday, March 25, 2005 9:48AM - 10:00AM |
X20.00010: Negative Static Dielectric Constant Under Electrical Field Feng Chen, Stephen Tsui, Jason Shulman, Yuyi Xue, C. W. Chu, W. J. Wen We report the sign change of the dielectric constant ($\epsilon^\prime$) for the Ba-Ti-O based giant electrorheological (ER) fluid under the electrical field ($E$) up to 5 kV/mm. The data that extend to low frequency suggest that the static $\epsilon^\prime$ changes from positive to negative under the dc bias. Models that were suggested for the left-handed materials (LHM), e.g. resonance models and plasmon models, are examined. Our analysis suggests that the self- assembled nanostructures under the electrical field and a large suppression of carrier collisions play key roles. The great potential for application of this phenomena will be discussed. [Preview Abstract] |
Friday, March 25, 2005 10:00AM - 10:12AM |
X20.00011: Theoretical Calculations of Nonlinear Optical Response F. Vila, Y. Takimoto, J.J. Rehr Nonlinear optical (NLO) devices play a key role in many applications. A systematic approach for the design and synthesis of materials with desirable NLO properties has been difficult to achieve, and hence theoretical methods are desirable. Usually systems with sizable NLO properties are large, limiting the theoretical methods that can be used. Here we examine two approaches for calculating the polarizabilities and first hyperpolarizabilities of large systems. First, we discuss the applicability of density functional theory (DFT), with special attention to difficulties of applying it in systems where non-locality can be important. Results are presented for "push-pull" molecules, which have some of the largest hyperpolarizabilities reported to date. Second, we present a self-consistent real space multiple scattering approach for calculating both linear and nonlinear response of large systems. The approach is illustrated with sample calculations including C60 and other large molecules. [Preview Abstract] |
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