Showing papers on "Scattering published in 2008"
TL;DR: Measurements show that mobilities higher than 200 000 cm2/V s are achievable, if extrinsic disorder is eliminated and a sharp (thresholdlike) increase in resistivity observed above approximately 200 K is unexpected but can qualitatively be understood within a model of a rippled graphene sheet in which scattering occurs on intraripple flexural phonons.
Abstract: We have studied temperature dependences of electron transport in graphene and its bilayer and found extremely low electron-phonon scattering rates that set the fundamental limit on possible charge carrier mobilities at room temperature. Our measurements show that mobilities higher than 200 000 cm2/V s are achievable, if extrinsic disorder is eliminated. A sharp (thresholdlike) increase in resistivity observed above approximately 200 K is unexpected but can qualitatively be understood within a model of a rippled graphene sheet in which scattering occurs on intraripple flexural phonons.
3,100 citations
TL;DR: It is shown that electron-acoustic phonon scattering is indeed independent of n, and contributes only 30 Omega to graphene's room-temperature resistivity, and its magnitude, temperature dependence and carrier-density dependence are consistent with extrinsic scattering by surface phonons at the SiO2 substrate.
Abstract: The linear dispersion relation in graphene gives rise to a surprising prediction: the resistivity due to isotropic scatterers, such as white-noise disorder or phonons, is independent of carrier density, n. Here we show that electron-acoustic phonon scattering is indeed independent of n, and contributes only 30 Omega to graphene's room-temperature resistivity. At a technologically relevant carrier density of 1 x1012 cm-2, we infer a mean free path for electron-acoustic phonon scattering of >2 microm and an intrinsic mobility limit of 2 x 105 cm2 V-1 s-1. If realized, this mobility would exceed that of InSb, the inorganic semiconductor with the highest known mobility ( approximately 7.7 x 104 cm2 V-1 s-1; ref. 9) and that of semiconducting carbon nanotubes ( approximately 1 x 105 cm2 V-1 s-1; ref. 10). A strongly temperature-dependent resistivity contribution is observed above approximately 200 K (ref. 8); its magnitude, temperature dependence and carrier-density dependence are consistent with extrinsic scattering by surface phonons at the SiO2 substrate and limit the room-temperature mobility to approximately 4 x 104 cm2 V-1 s-1, indicating the importance of substrate choice for graphene devices.
2,947 citations
TL;DR: Sherpa as discussed by the authors is a general-purpose tool for the simulation of particle collisions at high-energy colliders and contains a very flexible tree-level matrix-element generator for the calculation of hard scattering processes within the Standard Model and various new physics models.
Abstract: In this paper the current release of the Monte Carlo event generator Sherpa, version 1.1, is presented. Sherpa is a general-purpose tool for the simulation of particle collisions at high-energy colliders. It contains a very flexible tree-level matrix-element generator for the calculation of hard scattering processes within the Standard Model and various new physics models. The emission of additional QCD partons off the initial and final states is described through a parton-shower model. To consistently combine multi-parton matrix elements with the QCD parton cascades the approach of Catani, Krauss, Kuhn and Webber is employed. A simple model of multiple interactions is used to account for underlying events in hadron--hadron collisions. The fragmentation of partons into primary hadrons is described using a phenomenological cluster-hadronisation model. A comprehensive library for simulating tau-lepton and hadron decays is provided. Where available form-factor models and matrix elements are used, allowing for the inclusion of spin correlations; effects of virtual and real QED corrections are included using the approach of Yennie, Frautschi and Suura.
1,911 citations
TL;DR: This work directly image the atomic density profiles as a function of time, and finds that weak disorder can stop the expansion and lead to the formation of a stationary, exponentially localized wavefunction—a direct signature of Anderson localization.
Abstract: Anderson localization (AL) is a phenomenon in wave physics, occurring when interference between multiple scattering paths causes diffusion to cease. Experimentally, localization has been reported for light waves, microwaves, sound waves and electron gases, but there has been no direct observation of AL for matter waves of any type. The paper reports AL in a Bose–Einstein condensate as it expands in a one-dimensional disordered optical potential. The authors image directly the atomic density profiles as a function of time, and find that weak disorder can stop the expansion and lead to the formation of a stationary exponentially localized wave function — a direct signature of AL. The method can be extended to localization of atomic quantum gases in higher dimensions, and with controlled interactions. In 1958, Anderson predicted the localization1 of electronic wavefunctions in disordered crystals and the resulting absence of diffusion. It is now recognized that Anderson localization is ubiquitous in wave physics2 because it originates from the interference between multiple scattering paths. Experimentally, localization has been reported for light waves3,4,5,6,7, microwaves8,9, sound waves10 and electron gases11. However, there has been no direct observation of exponential spatial localization of matter waves of any type. Here we observe exponential localization of a Bose–Einstein condensate released into a one-dimensional waveguide in the presence of a controlled disorder created by laser speckle12. We operate in a regime of pure Anderson localization, that is, with weak disorder—such that localization results from many quantum reflections of low amplitude—and an atomic density low enough to render interactions negligible. We directly image the atomic density profiles as a function of time, and find that weak disorder can stop the expansion and lead to the formation of a stationary, exponentially localized wavefunction—a direct signature of Anderson localization. We extract the localization length by fitting the exponential wings of the profiles, and compare it to theoretical calculations. The power spectrum of the one-dimensional speckle potentials has a high spatial frequency cutoff, causing exponential localization to occur only when the de Broglie wavelengths of the atoms in the expanding condensate are greater than an effective mobility edge corresponding to that cutoff. In the opposite case, we find that the density profiles decay algebraically, as predicted in ref. 13. The method presented here can be extended to localization of atomic quantum gases in higher dimensions, and with controlled interactions.
1,357 citations
TL;DR: In this paper, a systematic study of the influence of scattering from impurities on the peculiar electronic properties of graphene is conducted by monitoring changes in electronic characteristics of initially clean graphene, by depositing potassium atoms onto its surface in ultrahigh vacuum.
Abstract: Valuable insight into the influence of scattering from impurities on the peculiar electronic properties of graphene are gained by a systematic study of how its conductivity changes with increasing concentration of potassium ions deposited on its surface. Since the initial demonstration of the ability to experimentally isolate a single graphene sheet1, a great deal of theoretical work has focused on explaining graphene’s unusual carrier-density-dependent conductivity σ(n), and its minimum value (σmin) of nearly twice the quantum unit of conductance (4e2/h) (refs 1, 2, 3, 4, 5, 6). Potential explanations for such behaviour include short-range disorder7,8,9,10, ‘ripples’ in graphene’s atomic structure11,12 and the presence of charged impurities7,8,13,14,15,16,17,18. Here, we conduct a systematic study of the last of these mechanisms, by monitoring changes in electronic characteristics of initially clean graphene19 as the density of charged impurities (nimp) is increased by depositing potassium atoms onto its surface in ultrahigh vacuum. At non-zero carrier density, charged-impurity scattering produces the widely observed linear dependence1,2,3,4,5,6 of σ(n). More significantly, we find that σmin occurs not at the carrier density that neutralizes nimp, but rather the carrier density at which the average impurity potential is zero15. As nimp increases, σmin initially falls to a minimum value near 4e2/h. This indicates that σmin in the present experimental samples1,2,3,4,5,6 is governed not by the physics of the Dirac point singularity20,21, but rather by carrier-density inhomogeneities induced by the potential of charged impurities6,8,14,15.
1,287 citations
TL;DR: Simulations for various other models of Nafion, including Gierke's cluster and the polymer-bundle model, do not match the scattering data, and a recently introduced algorithm can explain important features of Nafeon, including fast diffusion of water and protons through Nafions and its persistence at low temperatures.
Abstract: The structure of the Nafion ionomer used in proton-exchange membranes of H(2)/O(2) fuel cells has long been contentious. Using a recently introduced algorithm, we have quantitatively simulated previously published small-angle scattering data of hydrated Nafion. The characteristic 'ionomer peak' arises from long parallel but otherwise randomly packed water channels surrounded by partially hydrophilic side branches, forming inverted-micelle cylinders. At 20 vol% water, the water channels have diameters of between 1.8 and 3.5 nm, with an average of 2.4 nm. Nafion crystallites (approximately 10 vol%), which form physical crosslinks that are crucial for the mechanical properties of Nafion films, are elongated and parallel to the water channels, with cross-sections of approximately (5 nm)(2). Simulations for various other models of Nafion, including Gierke's cluster and the polymer-bundle model, do not match the scattering data. The new model can explain important features of Nafion, including fast diffusion of water and protons through Nafion and its persistence at low temperatures.
1,239 citations
Journal Article•
1,119 citations
TL;DR: Experimental evidence of sharp spectral features in the optical response of 2D arrays of gold nanorods is presented, and a simple coupled dipole model is used to describe the main features of the observed spectral line shape.
Abstract: We present experimental evidence of sharp spectral features in the optical response of 2D arrays of gold nanorods. A simple coupled dipole model is used to describe the main features of the observed spectral line shape. The resonance involves an interplay between the excitation of plasmons localized on the particles and diffraction resulting from the scattering by the periodic arrangement of these particles. We investigate this interplay by varying the particle size, aspect ratio, and interparticle spacing, and observe the effect on the position, width, and intensity of the sharp spectral feature.
963 citations
TL;DR: In this paper, the authors developed fundamental design principles for increasing the efficiency of solar cells using light trapping by scattering from metal nanoparticles, and showed that cylindrical and hemispherical particles lead to much higher path length enhancements than spherical particles, due to enhanced near-field coupling, and that the path length enhancement for an electric point dipole is even higher than the Lambertian value.
Abstract: We develop fundamental design principles for increasing the efficiency of solar cells using light trapping by scattering from metal nanoparticles. We show that cylindrical and hemispherical particles lead to much higher path length enhancements than spherical particles, due to enhanced near-field coupling, and that the path length enhancement for an electric point dipole is even higher than the Lambertian value. Silver particles give much higher path length enhancements than gold particles. The scattering cross section of the particles is very sensitive to the thickness of a spacer layer at the substrate, which provides additional tunability in the design of particle arrays.
824 citations
TL;DR: Nanoshell arrays have recently been found to possess ideal properties as a substrate for combining surface enhanced raman scattering (SERS) and surface enhanced infrared absorption (SEIRA) spectroscopies, with large field enhancements at the same spatial locations on the structure.
Abstract: Nanoshell arrays have recently been found to possess ideal properties as a substrate for combining surface enhanced raman scattering (SERS) and surface enhanced infrared absorption (SEIRA) spectroscopies, with large field enhancements at the same spatial locations on the structure. For small interparticle distances, the multipolar plasmon resonances of individual nanoshells hybridize and form red-shifted bands, a relatively narrow band in the near-infrared (NIR) originating from quadrupolar nanoshell resonances enhancing SERS, and a very broadband in the mid-infrared (MIR) arising from dipolar resonances enhancing SEIRA. The large field enhancements in the MIR and at longer wavelengths are due to the lightning-rod effect and are well described with an electrostatic model.
768 citations
TL;DR: It is shown that, despite experimental imperfections, optical phase conjugation can force a transmitted light field to retrace its trajectory through a biological target and recover the original light field.
Abstract: Elastic optical scattering, the dominant light-interaction process in biological tissues, prevents tissues from being transparent. Although scattering may appear stochastic, it is in fact deterministic in nature. We show that, despite experimental imperfections, optical phase conjugation (λ = 532 nm) can force a transmitted light field to retrace its trajectory through a biological target and recover the original light field. For a 0.69-mm-thick chicken breast tissue section, we can enhance point-source light return by a factor of ~5 x 10^3 and achieve a light transmission enhancement factor of 3.8 within a collection angle of 29°. Additionally, we find that the reconstruction's quality, measured by the width of the reconstructed point source, is independent of tissue thickness (up to a thickness of 0.69 mm). This phenomenon may be used to enhance light transmission through tissue, enable measurement of small tissue movements, and form the basis of new tissue imaging techniques.
TL;DR: It is shown experimentally that reflection from an array of nanoparticles can be completely suppressed at certain wavelengths, and metal nanostructures exhibit pi-jump for the phase of the reflected light.
Abstract: We experimentally demonstrate extremely narrow plasmon resonances with half-width of just several nanometers in regular arrays of metallic nanoparticles. These resonances are observed at Rayleigh's cutoff wavelengths for Wood anomalies and based on diffraction coupling of localized plasmons. We show experimentally that reflection from an array of nanoparticles can be completely suppressed at certain wavelengths. As a result, our metal nanostructures exhibit pi-jump for the phase of the reflected light.
TL;DR: It is shown that the interaction between trapped electromagnetic modes can lead to scattering resonances with practically zero width, which are the bound states in the radiation continuum first discovered in quantum systems by von Neumann and Wigner.
Abstract: With examples of two parallel dielectric gratings and two arrays of thin parallel dielectric cylinders, it is shown that the interaction between trapped electromagnetic modes can lead to scattering resonances with practically zero width. Such resonances are the bound states in the radiation continuum first discovered in quantum systems by von Neumann and Wigner. Potential applications of such photonic systems include: large amplification of electromagnetic fields within photonic structures and, hence, enhancement of nonlinear phenomena, biosensing, as well as perfect filters and waveguides for a particular frequency, and impurity detection.
TL;DR: In this paper, the authors measured carrier relaxation times in epitaxial graphene layers grown on SiC wafers and found that an initial fast relaxation transient in the 70-120fs range is followed by a slower relaxation process in the 0.4-1.7ps range.
Abstract: Using ultrafast optical pump-probe spectroscopy, we have measured carrier relaxation times in epitaxial graphene layers grown on SiC wafers. We find two distinct time scales associated with the relaxation of nonequilibrium photogenerated carriers. An initial fast relaxation transient in the 70–120fs range is followed by a slower relaxation process in the 0.4–1.7ps range. The slower relaxation time is found to be inversely proportional to the degree of crystalline disorder in the graphene layers as measured by Raman spectroscopy. We relate the measured fast and slow time constants to carrier-carrier and carrier-phonon intraband and interband scattering processes in graphene.
TL;DR: A microscopic theory of the transmission through subwavelength hole arrays is derived, by considering the elementary processes associated with scattering of surface-plasmon-polariton (SPP) modes by individual one-dimensional chains of subwa wavelength holes, and derives analytical expressions for all the transmission spectrum characteristics.
Abstract: The phenomenon of extraordinary light transmission through metallic films perforated by nanohole arrays at optical frequencies was first observed a decade ago and initiated important further experimental and theoretical work. In view of potential applications of such structures--for example, subwavelength optics, optoelectronics devices, and chemical sensing--it is important to understand the underlying physical processes in detail. Here we derive a microscopic theory of the transmission through subwavelength hole arrays, by considering the elementary processes associated with scattering of surface-plasmon-polariton (SPP) modes by individual one-dimensional chains of subwavelength holes. Using a SPP coupled-mode model that coherently gathers these elementary processes, we derive analytical expressions for all the transmission spectrum characteristics--such as the resonance wavelength, the peak transmission and the anti-resonance. Further comparisons of the model predictions with fully vectorial computational results allow us quantitatively to check the model accuracy and to discuss the respective impacts of SPP modes and of other electromagnetic fields on producing the extraordinary transmission of light. The model greatly expands our understanding of the phenomenon and may affect further engineering of nanoplasmonic devices.
TL;DR: A one-step homogeneous immunoassay for the detection of a prostate cancer biomarker, free-PSA (prostate specific antigen), was developed using gold nanoparticle probes coupled with dynamic light scattering (DLS) measurements.
Abstract: A one-step homogeneous immunoassay for the detection of a prostate cancer biomarker, free-PSA (prostate specific antigen), was developed using gold nanoparticle probes coupled with dynamic light scattering (DLS) measurements. A spherical gold nanoparticle with a core diameter around 37 nm and a gold nanorod with a dimension of 40 by 10 nm were first conjugated with two different primary anti-PSA antibodies and then used as optical probes for the immunoassay. In the presence of antigen f-PSA in solution, the nanoparticles and nanorods aggregate together into pairs and oligomers through the formation of a sandwich type antibody−antigen−antibody linkage. The relative ratio of nanoparticle-nanorod pairs and oligomers versus individual nanoparticles was quantitatively monitored by DLS measurement. A correlation can be established between this relative ratio and the amount of antigen in solution. The light scattering intensity of nanoparticles and nanoparticle oligomers is several orders of magnitude higher tha...
TL;DR: In this article, a theory for the enhancement of the thermoelectric properties of semiconductor materials with metallic nanoinclusions is presented, which is based on the concept of band bending at metal/semiconductor interfaces as an energy filter for electrons.
Abstract: Based on the concept of band bending at metal/semiconductor interfaces as an energy filter for electrons, we present a theory for the enhancement of the thermoelectric properties of semiconductor materials with metallic nanoinclusions. We show that the Seebeck coefficient can be significantly increased due to a strongly energy-dependent electronic scattering time. By including phonon scattering, we find that the enhancement of $ZT$ due to electron scattering is important for high doping, while at low doping it is primarily due to a decrease in the phonon thermal conductivity.
TL;DR: Multilayer epitaxial graphene is investigated using far infrared transmission experiments in the different limits of low magnetic fields and high temperatures, finding the well-defined Landau level quantization up to room temperature at magnetic fields below 1 T, a phenomenon unusual in solid state systems.
Abstract: Multilayer epitaxial graphene is investigated using far infrared transmission experiments in the different limits of low magnetic fields and high temperatures. The cyclotron-resonance-like absorption is observed at low temperature in magnetic fields below 50 mT, probing the nearest vicinity of the Dirac point. The carrier mobility is found to exceed 250,000 cm2/(V x s). In the limit of high temperatures, the well-defined Landau level quantization is observed up to room temperature at magnetic fields below 1 T, a phenomenon unusual in solid state systems. A negligible increase in the width of the cyclotron resonance lines with increasing temperature indicates that no important scattering mechanism is thermally activated.
TL;DR: In this article, the Yang-Mills equations are solved in an AdS4-Schwarzschild background with superconductivity, where the order parameter is a vector and the conductivities are strongly anisotropic.
Abstract: We construct black hole solutions to the Yang-Mills equations in an AdS4-Schwarzschild background which exhibit superconductivity. What makes these backgrounds p-wave superconductors is that the order parameter is a vector, and the conductivities are strongly anisotropic in a manner that is suggestive of a gap with nodes. The low-lying excitations of the normal state have a relaxation time which grows rapidly as the temperature decreases, consistent with the absence of impurity scattering. A numerical exploration of quasinormal modes close to the transition temperature suggests that p-wave backgrounds are stable against perturbations analogous to turning on a p+ip gap, whereas p+ip-wave configurations are unstable against turning into pure p-wave backgrounds.
TL;DR: An improved method for determining lipid areas helps to reconcile long-standing differences in the values of lipid areas obtained from stand-alone x-ray and neutron scattering experiments and poses new challenges for molecular dynamics simulations.
TL;DR: This Feature Article examines recent advances in chemical analyte detection and optical imaging applications using gold and silver nanoparticles, with a primary focus on the authors' own work.
TL;DR: In this paper, the energy-critical focusing non-linear wave equation with data in the energy space, in dimensions 3, 4 and 5, was studied and it was shown that for Cauchy data of energy smaller than the one of the static solution W which gives the best constant in the Sobolev embedding, the following alternative holds.
Abstract: We study the energy-critical focusing non-linear wave equation, with data in the energy space, in dimensions 3, 4 and 5. We prove that for Cauchy data of energy smaller than the one of the static solution W which gives the best constant in the Sobolev embedding, the following alternative holds. If the initial data has smaller norm in the homogeneous Sobolev space H1 than the one of W, then we have global well-posedness and scattering. If the norm is larger than the one of W, then we have break-down in finite time.
TL;DR: Tailoring the longitudinal surface plasmon wavelengths (LSPWs), scattering, and absorption cross sections of gold nanorods has been demonstrated by combining anisotropic shortening and transverse overgrowth and judiciously choosing starting Au nanorod samples.
Abstract: Tailoring the longitudinal surface plasmon wavelengths (LSPWs), scattering, and absorption cross sections of gold nanorods has been demonstrated by combining anisotropic shortening and transverse overgrowth and judiciously choosing starting Au nanorods. Shortening yields Au nanorods with decreasing lengths but a fixed diameter, while overgrowth produces nanorods with increasing diameters but a nearly unchanged length. Two series of Au nanorods with LSPWs varying in the same spectral range but distinct extinction coefficients are thus obtained. The systematic changes in the LSPW and extinction for the two series of Au nanorods are found to be in good agreement with those obtained from Gans theory. Dark-field imaging performed on two representative nanorod samples with similar LSPWs shows that the scattering intensities of the overgrown nanorods are much larger than those of the shortened nanorods. The experimental results are found to be in very good agreement with those obtained from finite-difference tim...
TL;DR: It is reported that the metal film induces a polarization to the single nanoparticle light scattering, resulting in a doughnut-shaped point spread function when imaged in the far-field.
Abstract: We present an experimental analysis of the plasmonic scattering properties of gold nanoparticles controllably placed nanometers away from a gold metal film. We show that the spectral response of this system results from the interplay between the localized plasmon resonance of the nanoparticle and the surface plasmon polaritons of the gold film, as previously predicted by theoretical studies. In addition, we report that the metal film induces a polarization to the single nanoparticle light scattering, resulting in a doughnut-shaped point spread function when imaged in the far-field. Both the spectral response and the polarization effects are highly sensitive to the nanoparticle−film separation distance. Such a system shows promise in potential biometrology and diagnostic devices.
Journal Article•
TL;DR: In this paper, a theory for the enhancement of the thermoelectric properties of semiconductor materials with metallic nanoinclusions is presented, which is based on the concept of band bending at metal/semiconductor interfaces as an energy filter for electrons.
Abstract: Based on the concept of band bending at metal/semiconductor interfaces as an energy filter for electrons, we present a theory for the enhancement of the thermoelectric properties of semiconductor materials with metallic nanoinclusions. We show that the Seebeck coefficient can be significantly increased due to a strongly energy-dependent electronic scattering time. By including phonon scattering, we find that the enhancement of $ZT$ due to electron scattering is important for high doping, while at low doping it is primarily due to a decrease in the phonon thermal conductivity.
TL;DR: In this article, the authors obtained global well-posedness, scattering, and global L 10 spacetime bounds for energy-class solutions to the quintic defocusing Schrodinger equa- tion in R 1+3, which is energy-critical.
Abstract: We obtain global well-posedness, scattering, and global L 10 spacetime bounds for energy-class solutions to the quintic defocusing Schrodinger equa- tion in R 1+3 , which is energy-critical. In particular, this establishes global existence of classical solutions. Our work extends the results of Bourgain (4) and Grillakis (20), which handled the radial case. The method is similar in spirit to the induction-on-energy strategy of Bourgain (4), but we perform the induction analysis in both frequency space and physical space simultaneously, and replace the Morawetz inequality by an interaction variant (first used in (12), (13)). The principal advantage of the interaction Morawetz estimate is that it is not localized to the spatial origin and so is better able to handle nonradial solutions. In particular, this interaction estimate, together with an almost-conservation argument controlling the movement of L 2 mass in fre- quency space, rules out the possibility of energy concentration.
TL;DR: This work identifies a design principle for the effective suppression of reflective losses, based on the ratio of the nondiffusive absorption and diffusive scattering lengths, and demonstrates successful suppression of the hemispherical diffuse reflectance of InP nanowires to below that of the corresponding transparent effective medium.
Abstract: We experimentally investigate the optical properties of layers of InP, Si, and GaP nanowires, relevant for applications in solar cells. The nanowires are strongly photonic, resulting in a significant coupling mismatch with incident light due to multiple scattering. We identify a design principle for the effective suppression of reflective losses, based on the ratio of the nondiffusive absorption and diffusive scattering lengths. Using this principle, we demonstrate successful suppression of the hemispherical diffuse reflectance of InP nanowires to below that of the corresponding transparent effective medium. The design of light scattering in nanowire materials is of large importance for optimization of the external efficiency of nanowire-based photovoltaic devices.
TL;DR: Through acoustic scattering theory, the mass density and bulk modulus of a spherical shell that can eliminate scattering from an arbitrary object in the interior of the shell are derived--in other words, a 3D acoustic cloaking shell.
Abstract: Through acoustic scattering theory we derive the mass density and bulk modulus of a spherical shell that can eliminate scattering from an arbitrary object in the interior of the shell—in other words, a 3D acoustic cloaking shell. Calculations confirm that the pressure and velocity fields are smoothly bent and excluded from the central region as for previously reported electromagnetic cloaking shells. The shell requires an anisotropic mass density with principal axes in the spherical coordinate directions and a radially dependent bulk modulus. The existence of this 3D cloaking shell indicates that such reflectionless solutions may also exist for other wave systems that are not isomorphic with electromagnetics.
TL;DR: A technique based on moment-analysis for the measurement of the average number of molecules and brightness in each pixel in fluorescence microscopy images is described, which reveals binding dynamics at the focal adhesions with pixel resolution and provides a picture of the binding and unbinding process.
TL;DR: In this paper, first-order equations to interpret absorption spectra of the transit spectrum of the exoplanet HD 189733b have been developed, and the observed slope of the absorption as a function of wavelength is characteristic of extinction proportional to the inverse of the fourth power of the wavelength (∝λ −4 ).
Abstract: The transit spectrum of the exoplanet HD 189733b has recently been obtained between 0.55 and 1.05 µm. Here we present an analysis of this spectrum. We develop first-order equations to interpret absorption spectra. In the case of HD 189733b, we show that the observed slope of the absorption as a function of wavelength is characteristic of extinction proportional to the inverse of the fourth power of the wavelength (∝λ −4 ). Assuming an extinction dominated by Rayleigh scattering, we derive an atmospheric temperature of 1340 ± 150 K. If molecular hydrogen is responsible for the Rayleigh scattering, the atmospheric pressure at the planetary characteristic radius of 0.1564 stellar radius must be 410 ± 30 mbar. However the preferred scenario is scattering by condensate particles. Using the Mie approximation, we find that the particles must have a low value for the imaginary part of the refraction index. We identify MgSiO3 as a possible abundant condensate whose particle size must be between ∼10 −2 and ∼10 −1 µm. For this condensate, assuming solar abundance, the pressure at 0.1564 stellar radius is found to be between a few microbars and few millibars, and the temperature is found to be in the range 1340–1540 K, and both depend on the particle size.