Showing papers on "Scattering published in 2002"

Scattering, Absorption, and Emission of Light by Small Particles

Abstract: Preface Acknowledgements Part I. Basic Theory of Electromagnetic Scattering, Absorption, and Emission: 1. Polarization characteristics of electromagnetic radiation 2. Scattering, absorption, and emission of electromagnetic radiation by an arbitrary finite particle 3. Scattering, absorption and emission by collections of independent particles 4. Scattering matrix and macroscopically isotropic and mirror-symmetric scattering media Part II. Calculation and Measurement of Scattering and Absorption Characteristics of Small Particles: 5. T-matrix method and Lorenz-Mie theory 6. Miscellaneous exact techniques 7. Approximations 8. Measurement techniques Part III. Scattering and Absorption Properties of Small Particles and Illustrative Applications: 9. Scattering and absorption properties of spherical particles 10. Scattering and absorption properties of nonspherical particles Appendices References Index.

Photothermal imaging of nanometer-sized metal particles among scatterers.

Abstract: Ambient optical detection of labeled molecules is limited for fluorescent dyes by photobleaching and for semiconducting nanoparticles by “blinking” effects. Because nanometer-sized metal particles do not optically bleach, they may be useful optical labels if suitable detection signals can be found. We demonstrate far-field optical detection of gold colloids down to diameters of 2.5 nanometers with a photothermal method that combines high-frequency modulation and polarization interference contrast. The photothermal image is immune to the effects of scattering background, which limits particle imaging through Rayleigh scattering to diameters larger than 40 nanometers.

Neutrons, X-rays and light : scattering methods applied to soft condensed matter

Abstract: Part I. Using general principles 1. Introduction to scattering experiments (P.N. Pusey) 2. Scattering experiments: Experimental aspects, initial data reduction and absolute calibration (P. Lindner) 3. General theorems in small-angle scattering (O. Spalla) 4. The inverse scattering problem in small angle scattering (O. Glatter) 5. Fourier transformation and deconvolution (O. Glatter) Part II. Methods 6. Instrumentation for small-angle x-ray and neutron scattering and instrumental smearing effects (J.S. Pedersen) 7. Contrast and contrast variaion in neutron, x-ray and light scatering (P. Schurtenberger) 8. Static light scattering of large systems (O. Glatter) 9. Dynamic light scattering (P.N. Pusey) 10.Inelastic neutron scattering: Dynamics of polymers (R. Zorn) Part III. Revealing microstructures of soft condensed matter 11. Static properties of polymers (P. Schurtenberger) 12. Surfactant micelles and bilayers: Shapes and interactions (G. Porte) 13. Scattering by microemulsions (Th. Zemb) 14. Interacting colloidal suspensions (R. Klein) 15. Monte Carlo simulation techniques applied in the analysis of small-angle scattering data from colloids and polymer system (J.S. Pedersen) 16. Modelling of small-angle scattering data from colloids and polymer systems (J.S. Pedersen) Part IV. Special Applications 17. Scattering experiments under external constraints: SANS and Shear flow (P. Lindner) 18. Using synchrotron radiation to study structure development in polymer processing (A.J.Ryan) 19. Biological applications of small-angle neutron scattering (R.P. May) 20. Light scattering in turbid suspensions, a tutorial (J. Ricka) 21. Use of scattering methods in chemical industr - SAXS an SANS from fibers and films (J. Rieger) Subject Index

Organo luminescent semiconductor nanocrystal probes for biological applications and process for making and using such probes

Abstract: A semiconductor nanocrystal compound is described capable of linking to an affinity molecule. The compound comprises (1) a semiconductor nanocrystal capable of emitting electromagnetic radiation and/or absorbing energy, and/or scattering or diffracting electromagnetic radiation—when excited by an electromagnetic radiation source or a particle beam; and (2) at least one linking agent, having a first portion linked to the semiconductor nanocrystal and a second portion capable of linking to an affinity molecule. The compound is linked to an affinity molecule to form a semiconductor nanocrystal probe capable of bonding with a detectable substance. subsequent exposure to excitation energy will excite the semiconductor nanocrystal in the probe causing the emission of electromagnetic radiation. Further described are processes for respectively: making the luminescent semiconductor nanocrystal compound; making the semiconductor nanocrystal probe; and using the probe to determine the presence of a detectable substance in a material.

Phonons and electron-phonon scattering in carbon nanotubes

Abstract: Electron-phonon scattering is studied within an effective-mass theory. A continuum model for acoustic phonons is introduced and electron-phonon interaction due to modification of band structure is derived as well as a normal deformation potential. In a metallic nanotube, the deformation potential does not participate in electron scattering and a metallic nanotube becomes nearly a one-dimensional ballistic conductor even at room temperature. A resistivity determined by small band-structure interaction depends on the chirality at low temperatures. A magnetic field perpendicular to the axis induces electron scattering by the deformation potential, giving rise to huge positive magnetoresistance.

Essential physics of carrier transport in nanoscale MOSFETs

Abstract: The device physics of nanoscale MOSFETs is explored by numerical simulations of a model transistor. The physics of charge control, source velocity saturation due to thermal injection, and scattering in ultrasmall devices are examined. The results show that the essential physics of nanoscale MOSFETs can be understood in terms of a conceptually simple scattering model.

Electrodynamics of Solids: Optical Properties of Electrons in Matter

Abstract: 1. Introduction Part I. Concepts and Properties: 2. The interaction of radiation with matter 3. General properties of the optical constants 4. The medium: correlation and response functions 5. Metals 6. Semiconductors 7. Broken-symmetry states of metals Part II. Methods: 8. Techniques: general considerations 9. Propagation and scattering of electromagnetic waves 10. Spectroscopic principles 11. Measurement configurations Part III. Experiments: 12. Metals 13. Semiconductors 14. Broken-symmetry states of metals Appendix A. Fourier and Laplace transformation Appendix B. Medium of finite thickness Appendix C. k.p perturbation theory Appendix D. Sum rules Appendix E. Non-local response Appendix F. Dielectric response in reduced dimensions Appendix G. Important constants and units.

Imaging Quasiparticle Interference in Bi2Sr2CaCu2O8+δ

Abstract: Scanning tunneling spectroscopy of the high-Tc superconductor Bi2Sr2CaCu2O8+delta reveals weak, incommensurate, spatial modulations in the tunneling conductance. Images of these energy-dependent modulations are Fourier analyzed to yield the dispersion of their wavevectors. Comparison of the dispersions with photoemission spectroscopy data indicates that quasiparticle interference, due to elastic scattering between characteristic regions of momentum-space, provides a consistent explanation for the conductance modulations, without appeal to another order parameter. These results refocus attention on quasiparticle scattering processes as potential explanations for other incommensurate phenomena in the cuprates. The momentum-resolved tunneling spectroscopy demonstrated here also provides a new technique with which to study quasiparticles in correlated materials.

Photon and gluon emission in relativistic plasmas

Abstract: We recently derived, using diagrammatic methods, the leading-order hard photon emission rate in ultra-relativistic plasmas This requires a correct treatment of multiple scattering effects which limit the coherence length of emitted radiation (the Landau-Pomeranchuk-Migdal effect) In this paper, we provide a more physical derivation of this result, and extend the treatment to the case of gluon radiation

Three-nucleon forces from chiral effective field theory

Abstract: We perform the first fully consistent analysis of $\mathrm{nd}$ scattering at next-to-next-to-leading order in chiral effective field theory including the corresponding three-nucleon force and extending our previous work, where only the two-nucleon interaction has been taken into account. The three-nucleon force appears first at this order in the chiral expansion and depends on two unknown parameters. These two parameters are determined from the triton binding energy and $\mathrm{nd}$ doublet scattering length. We find an improved description of various scattering observables in relation to the next-to-leading order results especially at moderate energies ${(E}_{\mathrm{lab}}=65\mathrm{MeV}).$ It is demonstrated that the long-standing ${A}_{y}$ problem in $\mathrm{nd}$ elastic scattering is still not solved by the leading 3NF, although some visible improvement is observed. We discuss possibilities of solving this puzzle. The predicted binding energy for the $\ensuremath{\alpha}$ particle agrees with the empirical value.

IsGISAXS: a program for grazing‐incidence small‐angle X‐ray scattering analysis of supported islands

Abstract: This paper describes a Fortran program, IsGISAXS, for the simulation and analysis of grazing-incidence small-angle X-ray scattering (GISAXS) of islands supported on a substrate. As is usual in small-angle scattering of particles, the scattering cross section is expressed in terms of an island form factor and interference function. However, the emphasis is placed on the specificity of the grazing-incidence geometry, in particular in the evaluation of the island form factor in the distorted-wave Born approximation. A library of simple geometrical shapes is available. A full account of size and possible shape distributions is given in the decoupling approximation, where sizes and positions are not correlated, and in the local monodisperse approximation. Two types of island repartitions on the substrate are considered: disordered systems characterized by their particle–particle pair correlation functions, and bidimensional crystalline or paracrystalline systems of particles.

Thermal conduction in doped single-crystal silicon films

Abstract: This work measures the thermal conductivities along free-standing silicon layers doped with boron and phosphorus at concentrations ranging from 1×1017 to 3×1019 cm−3 at temperatures between 15 and 300 K. The impurity concentrations are measured using secondary ion mass spectroscopy (SIMS) and the thermal conductivity data are interpreted using phonon transport theory accounting for scattering on impurities, free electrons, and the layer boundaries. Phonon-boundary scattering in the 3-μm-thick layers reduces the thermal conductivity of the layers at low temperatures regardless of the level of impurity concentration. The present data suggest that unintentional impurities may have strongly reduced the conductivities reported previously for bulk samples, for which impurity concentrations were determined from the electrical resistivity rather than from SIMS data. This work illustrates the combined effects of phonon interactions with impurities, free electrons, and material interfaces, which can be particularly...

MATLAB Functions for Mie Scattering and Absorption

Abstract: A set of Mie functions has been developed in MATLAB to compute the four Mie coefficients an, bn, cn and dn, efficiencies of extinction, scattering, backscattering and absorption, the asymmetry parameter, and the two angular scattering functions S1 and S2. In addition to the scattered field, also the absolute-square of the internal field is computed and used to get the absorption efficiency in a way independent from the scattered field. This allows to test the computational accuracy. This first version of MATLAB Mie Functions is limited to homogeneous dielectric spheres without change in the magnetic permeability between the inside and outside of the particle. Required input parameters are the complex refractive index, m= m’+ im”, of the sphere (relative to the ambient medium) and the size parameter, x=ka, where a is the sphere radius and k the wave number in the ambient medium. 1 Equation on p. 16 corrected, April 2006

Surface characterization techniques for determining the root-mean-square roughness and power spectral densities of optical components

Abstract: Surface topography and light scattering were measured on 15 samples ranging from those having smooth surfaces to others with ground surfaces. The measurement techniques included an atomic force microscope, mechanical and optical profilers, confocal laser scanning microscope, angle-resolved scattering, and total scattering. The samples included polished and ground fused silica, silicon carbide, sapphire, electroplated gold, and diamond-turned brass. The measurement instruments and techniques had different surface spatial wavelength band limits, so the measured roughnesses were not directly comparable. Two-dimensional power spectral density (PSD) functions were calculated from the digitized measurement data, and we obtained rms roughnesses by integrating areas under the PSD curves between fixed upper and lower band limits. In this way, roughnesses measured with different instruments and techniques could be directly compared. Although smaller differences between measurement techniques remained in the calculated roughnesses, these could be explained mostly by surface topographical features such as isolated particles that affected the instruments in different ways.

Wavelength Dependence of the Absorption of Black Carbon Particles: Predictions and Results from the TARFOX Experiment and Implications for the Aerosol Single Scattering Albedo

Abstract: Measurements are presented of the wavelength dependence of the aerosol absorption coefficient taken during the Tropical Aerosol Radiative Forcing Observational Experiment (TARFOX) over the northern Atlantic. The data show an approximate lamda(exp -1) variation between 0.40 and 1.0 micrometers. The theoretical basis of the wavelength variation of the absorption of solar radiation by elemental carbon [or black carbon (BC)] is explored. For a wavelength independent refractive index the small particle absorption limit simplifies to a lambda(exp -1) variation in relatively good agreement with the data. This result implies that the refractive indices of BC were relatively constant in this wavelength region, in agreement with much of the data on refractive indices of BC. However, the result does not indicate the magnitude of the refractive indices. The implications of the wavelength dependence of BC absorption for the spectral behavior of the aerosol single scattering albedo are discussed. It is shown that the single scattering albedo for a mixture of BC and nonabsorbing material decreases with wavelength in the solar spectrum (i.e., the percentage amount of absorption increases). This decease in the single scattering albedo with wavelength for black carbon mixtures is different from the increase in single scattering allied for most mineral aerosols (dusts). This indicates that, if generally true, the spectral variation of the single- scattering albedo can be used to distinguish aerosol types. It also highlights the importance of measurements of the spectral variation of the aerosol absorption coefficient and single scattering albedo.

Recent experimental studies of electron dephasing in metal and semiconductor mesoscopic structures

Abstract: In this review, we discuss the results of recent experimental studies of the low-temperature electron dephasing time (τφ) in metal and semiconductor mesoscopic structures. A major focus of this review is on the use of weak localization, and other quantum-interference-related phenomena, to determine the value of τφ in systems of different dimensionality and with different levels of disorder. Significant attention is devoted to a discussion of three-dimensional metal films, in which dephasing is found to predominantly arise from the influence of electron–phonon (e–ph) scattering. Both the temperature and electron mean free path dependences of τφ that result from this scattering mechanism are found to be sensitive to the microscopic quality and degree of disorder in the sample. The results of these studies are compared with the predictions of recent theories for the e–ph interaction. We conclude that, in spite of progress in the theory for this scattering mechanism, our understanding of the e–ph interaction remains incomplete. We also discuss the origins of decoherence in low-diffusivity metal films, close to the metal–insulator transition, in which evidence for a crossover of the inelastic scattering, from e–ph to ‘critical’ electron–electron (e–e) scattering, is observed. Electron– electron scattering is also found to be the dominant source of dephasing in experimental studies of semiconductor quantum wires, in which the effects of both large- and small-energy-transfer scattering must be taken into account. The latter, Nyquist, mechanism is the stronger effect at a few kelvins, and may be viewed as arising from fluctuations in the electromagnetic background, generated by the thermal motion of electrons. At higher temperatures, however, a crossover to inelastic e–e scattering typically occurs; and evidence for this large-energy-transfer process has been found at temperatures as high as 30 K. Electron–electron interactions are also thought to play an important role in dephasing in ballistic quantum dots, and the results of recent experiments in this area are reviewed. A common feature of experiments, in both dirty metals 3 Authors to whom any correspondence should be addressed.

Phase function effects on oceanic light fields.

Abstract: Numerical simulations show that underwater radiances, irradiances, and reflectances are sensitive to the shape of the scattering phase function at intermediate and large scattering angles, although the exact shape of the phase function in the backscatter directions (for a given backscatter fraction) is not critical if errors of the order of 10% are acceptable. We present an algorithm for generating depth- and wavelength-dependent Fournier-Forand phase functions having any desired backscatter fraction. Modeling of a comprehensive data set of measured inherent optical properties and radiometric variables shows that use of phase functions with the correct backscatter fraction and overall shape is crucial to achieve model-data closure.

Protein dynamics studied by neutron scattering.

Abstract: This review of protein dynamics studied by neutron scattering focuses on data collected in the last 10 years. After an introduction to thermal neutron scattering and instrumental aspects, theoretical models that have been used to interpret the data are presented and discussed. Experiments are described according to sample type, protein powders, solutions and membranes. Neutron-scattering results are compared to those obtained from other techniques. The biological relevance of the experimental results is discussed. The major conclusion of the last decade concerns the strong dependence of internal dynamics on the macromolecular environment.

Monte Carlo Study of Supernova Neutrino Spectra Formation

Abstract: The neutrino flux and spectra formation in a supernova core is studied by using a Monte Carlo code. The dominant opacity contribution for nu_mu and nu_tau is elastic scattering on nucleons. In addition we switch on or off a variety of processes which allow for the exchange of energy or the creation and destruction of neutrino pairs, notably nucleon bremsstrahlung, the e^+ e^- pair annihilation process and nu_e-bar nu_e -> nu_{mu,tau} nu_{mu,tau}-bar, recoil and weak magnetism in elastic nucleon scattering, elastic scattering on electrons and positrons and elastic scattering on electron neutrinos and anti-neutrinos. The least important processes are neutrino-neutrino scattering and e^+ e^- annihilation. The formation of the spectra and fluxes of nu_mu is dominated by the nucleonic processes, i.e. bremsstrahlung and elastic scattering with recoil, but also nu_e nu_e-bar annihilation and nu_mu e^\pm scattering contribute significantly. When all processes are included, the spectral shape of the emitted neutrino flux is always ``pinched,'' i.e. the width of the spectrum is smaller than that of a thermal spectrum with the same average energy. In all of our cases we find that the average nu_mu-bar energy exceeds the average nu_e-bar energy by only a small amount, 10% being a typical number. Weak magnetism effects cause the opacity of nu_mu to differ slightly from that of nu_mu-bar, translating into differences of the luminosities and average energies of a few percent. Depending on the density, temperature, and composition profile, the flavor-dependent luminosities L_{nu_e}$, L_{nu_e-bar}, and L_{nu_mu} can mutually differ from each other by up to a factor of two in either direction.

Phonon wave-packet dynamics at semiconductor interfaces by molecular-dynamics simulation

Abstract: We directly observe phonon wave packets of well-defined frequency and polarization scattering at a coherent semiconductor interface using molecular-dynamics simulations. We find that in the low-frequency limit the transmission coefficients of both longitudinal and transverse acoustic phonons agree well with those predicted by the continuum-level based acoustic mismatch model. However, the transmission coefficients rapidly decrease close to the cutoff frequency, a result that can be understood within a simple one-dimensional discrete atomic-chain model. We also find that the transmission coefficient for transverse acoustic phonons depends strongly on the relative orientation of the polarization and the Si-Si bonds in the diamond lattice structure.

Structures of high and low density amorphous ice by neutron diffraction.

Abstract: Neutron diffraction with isotope substitution is used to determine the structures of high (HDA) and low (LDA) density amorphous ice. Both "phases" are fully hydrogen bonded, tetrahedral networks, with local order similarities between LDA and ice Ih, and HDA and liquid water. Moving from HDA, through liquid water and LDA to ice Ih, the second shell radial order increases at the expense of spatial order. This is linked to a fifth first neighbor "interstitial" that restricts the orientations of first shell waters. This "lynch pin" molecule which keeps the HDA structure intact has implications for the nature of the HDA-LDA transition that bear on the current metastable water debate.

Dynamical diffraction explanation of the anomalous transmission of light through metallic gratings

Abstract: In this paper, it is pointed out that the light transmission anomalies observed for thin-film metallic gratings can be explained entirely in terms of dynamical diffraction theory. Surface plasmons are an intrinsic component of the diffracted wave field and, as such, play no independent causal role in the anomalies, as has been implied by others. The dynamical scattering matrix for the Bloch-wave modes of the diffracted photon wave field (E, H) is derived for a three-dimensionally periodic medium with arbitrary dielectric constant. A new theoretical treatment and numerical results are presented for a one-dimensional array of slits. In model metallic slit arrays, with negative dielectric constant, 100% and 0% transmission is possible at different wavelengths in the zero-order beam. In slit arrays, both propagating and evanescent modes (traditional surface plasmons) are strongly excited at both the peak and the minimum transmission conditions.

Broadband absorption spectroscopy in turbid media by combined frequency-domain and steady state methodologies

Abstract: A technique for measuring broadband near-infrared absorption spectra of turbid media (12) uses a combination of frequency-domain and steady-state reflectance methods Most of the wavelengths coverage is provided by steady-state measurement using a white light (21) and a spectrograph (22) The frequency-domain data are acquired at a few selected wavelengths using laser diodes (13) and an avalanche photodiode unit (16) Coefficients of absorption and reduced scattering derived from the frequency-domain data are used to calibrate the intensity of the steady-state measurements and to determine the reduced scattering coefficient at all wavelengths in the spectral window of interest, The absorption coefficient spectrum is determined by comparing the steady-state reflectance values with the predictions of diffusion theory, wavelength by wavelength Absorption spectra of a turbid phantom and of human breast tissue in vivo, derived with the combined frequency-domain and steady-state technique, agree well with expected reference values

Resonant light scattering from individual Ag nanoparticles and particle pairs

Abstract: Light scattering by individual Ag nanoparticles and structures have been studied spectroscopically. Individual particles were selected and manipulated with a micromanipulator installed inside a scanning electron microscope (SEM). With typical particle dimensions of some 100 nm, the plasma resonances of particles and the coupled modes of particle pairs were observed in the visible region. The polarization dependence of the resonance frequencies strongly reflects the shape anisotropy; the effect that would be averaged out for experiments on ensembles. With a simple approximation to take the glass substrate into account, the results are in good agreement with the analytical calculations by Mie scattering, and with numerical calculations by the finite-difference time-domain method, both of which are performed with the morphological parameters obtained from the SEM observation for the corresponding particle or particle pair.