Large Scattering Cross Section Research Articles

How Far Can We Probe by SERS?

Surface-enhanced Raman spectroscopy (SERS) has gained paramount importance in the recent past due to its widespread applications in biodetection, monitoring chemical reactions, small molecule protein interactions, etc. It is believed that SERS is a distance-dependent phenomenon and is effective within 1 nm from the nanoparticle surface. In this work, we have investigated this distance dependence of SERS as a function of nanoparticle size. Earlier attempts have made use of flexible separators, like DNA and chemical molecules, between nanoparticle and analyte to vary the distance. We have used silica coating to vary the distance, without ambiguity, of the analyte from the silver nanoparticle surface. Our results suggest that SERS is observed up to a distance of 1 nm for 20 nm silver nanoparticles juxtaposed to 5 nm in the case of 90 nm silver nanoparticles. This is due to large scattering cross sections and increased radiative damping in the case of the larger nanoparticles. This study gives direct correlat...

Neutron Radiography of Condensation and Evaporation of Hydrogen in a Cryogenic Condition

The condensation and evaporation of hydrogen under cryogenic conditions is visualized by using neutron imaging at the BT-2 Beam Facility at the National Institute of Standards and Technology (NIST). The condensation and evaporation are controlled by adjusting temperature (20 K ~ 23 K) and pressure (1.3 ~ 1.95 bar absolute). The hydrogen contained in the aluminum test cell inside the cryostat has a large attenuation coefficient due to its large scattering cross section. The high sensitivity of neutron radiography to hydrogen allows the visualization of a meniscus and a contact line of evaporating hydrogenated cryogenic propellants. The graphic represents the temperature, pressure and corresponding images of liquid hydrogen in the test cell. The test cell is made of Aluminum 6061 with an inner diameter of 12 mm. The captured images are then median filtered and post-processed in order to find the volume of liquid hydrogen in the test cell as a function of time. The condensation/evaporation rates obtained from neutron imaging along with corresponding temperature and pressure are used to validate the evaporation model being developed by the authors.

Cloaking resonant scatterers and tuning electron flow in graphene

We consider resonant scatterers with large scattering cross sections in graphene that are produced by a gated disk or a vacancy, and show that a gated ring can be engineered to produce an efficient electron cloak. We also demonstrate that this same scheme can be applied to tune the direction of electron flow. Our analysis is based on a partial-wave expansion of the electronic wave functions in the continuum approximation, described by the Dirac equation. Using a symmetrized version of the massless Dirac equation, we derive a general condition for the cloaking of a scatterer by a potential with radial symmetry. We also perform tight-binding calculations to show that our findings are robust against the presence of disorder in the gate potential.

Quasi-Classical Gravity Effect on Neutrino Oscillations in a Gravitational Field of a Heavy Astrophysical Object

In the framework of quantum field theory, a graviton interacts locally with a quantum state having definite mass, that is, the gravitational mass eigenstate, while a weak boson interacts with a state having definite flavor, that is, the flavor eigenstate. An interaction of a neutrino with an energetic graviton may trigger the collapse of the neutrino to a definite mass eigenstate with probability expressed in terms of PMNS mixing matrix elements. Thus, gravitons would induce quantum decoherence of a coherent neutrino flavor state similarly to how weak bosons induce quantum decoherence of a neutrino in a definite mass state. We demonstrate that such an essentially quantum gravity effect may have strong consequences for neutrino oscillation phenomena in astrophysics due to relatively large scattering cross sections of relativistic neutrinos undergoing large angle radiation of energetic gravitons in gravitational field of a classical massive source (i.e., the quasi-classical case of gravitational Bethe-Heitler scattering). This graviton-induceddecoherenceis compared todecoherencedue to propagation in the presence of the Earth matter effect. Based on this study, we propose a new technique for the indirect detection of energetic gravitons by measuring the flavor composition of astrophysical neutrinos.

Resonance raman spectra of linear polymer molecule

The present paper summarizes the characteristics of resonance Raman spectra of the linear polymer molecule, and its relations with the molecular structure, including: electronic spectra(ultraviolet-visible absorption spectrum), Raman spectra characteristics and its relations with external field; Modulation relation between the electron energy gap and CC atom vibration; Several experimental results were obtained: The UV-visible absorption spectra are red-shifted with decreasing temperature, increasing solvent density and reducing solution concentration, and because the linear polymer molecule has high structured order, decreasing pi electron energy gap; extended pi electronic delocalization, large effective conjugation length, large intensity of the Raman activity, Ramrnan spectrum are red-shifted, with large scattering cross section. "Am plitude modes" are the ideal theory models to study the linear polymer molecule.

Microstructure and Millimeter-Wave Attenuation Performance of Exfoliated Graphite with Different Expanding Volume

Exfoliated graphite with different expanding volume (EV) was prepared by two-step intercalation, in which the mixture of nitric acid and phosphoric acid, and that of nitric acid and acetic acid were employed as intercalating agent step by step, and potassium permanganate was used as oxidant. Its microstructure was analyzed by scanning electron microscope, and its millimeter-wave attenuation performance was measured by a static method. The results show that the exfoliated graphite forms more microcellular structures and its layers become thinner with the increasing of EV, the interlayers are fully opened and there are more tiny graphite flakes with size distribution between several microns and several ten microns. The millimeter-wave attenuation performance enhances with the increasing of EV, and the 3mm wave attenuation value rises from 5.7dB to 8.68dB When EV increases from 233ml/g to 450ml/g, which is mainly attributed to the full expansion of exfoliated graphite to form larger scattering cross section and the absorption of more tiny graphite flakes with size distribution between several microns and several ten microns.

Photothermal diffuse reflectance: a new tool for spectroscopic investigation of scattering samples

A new method named photothermal diffuse reflectance (PTDR) is presented. This method combines the diffuse reflectance spectroscopy with the photothermal technique and is particularly suited for the investigation of strongly scattering samples. This method takes advantage of the high spectral selectivity and absorption of the mid-infrared region with the larger scattering cross section and high detector sensitivity available in the near-infrared. A model describing the PTDR method is proposed and supported with experimental results. The potential of the PTDR technique is illustrated by experimental signals obtained from various scattering media like polymers, liquids and powders.

Evidence of sympathetic cooling of Na+ions by a Na magneto-optical trap in a hybrid trap

A hybrid ion-neutral trap provides an ideal system to study collisional dynamics between ions and neutrals. This system provides a general cooling method that can be applied to optically inaccessible species and can also potentially cool internal degrees of freedom. The long range polarization potentials ($V\propto-\alpha/r^4$) between ions and neutrals result in large scattering cross sections at cold temperatures, making the hybrid trap a favorable system for efficient sympathetic cooling of ions by collisions with neutral atoms. We present experimental evidence of sympathetic cooling in a hybrid trap of \ce{Na+} ions, which are closed shell and therefore do not have a laser induced atomic transition, by equal mass cold Na atoms in a magneto-optical trap (MOT).

Light neutralino dark matter in the pMSSM

Three dark matter direct detection experiments have reported possible signals which can be interpreted as due to the interaction of light WIMPs with large scattering cross section. In this paper we investigate the viability of SUSY scenarios with light neutralino using high statistics scans in the pMSSM. We identify several scenarios which give rise to very light neutralinos with large direct detection scattering cross sections. We apply constraints from dark matter relic density, direct detection, indirect detection, as well as flavour physics, electroweak precision tests, LEP and Tevatron limits, LHC limits on SUSY, Higgs and monojet searches. In particular we require the Higgs boson mass to be in the range 122.5<M h <127.5 GeV. We study how the combination of these constraints largely reduces the number of viable scenarios. MSSM solutions with a light neutralino and an almost degenerate lightest scalar bottom quark emerge as the scenario in agreement with all these constraints. We study their characteristics in relation to the LHC missing E T searches.

Structure of different grades of nuclear graphite

Owing to its low neutron absorption cross-section, large scattering cross section and thermal and chemical stability, graphite is a key component of operational nuclear reactors where it is used as a moderator, reflector and as major structural component for 90% of current UK nuclear plants. It is also of interest for use in developing the future high temperature gas-cooled reactors. The properties of the nuclear graphite are influenced by its structural characteristics, which change as a function of neutron irradiation, temperature and oxidation. The principal structural changes during neutron irradiation that affect the integrity and dimensions of nuclear graphite components, thereby affecting service lifetime, are that the a-axis contracts and the c-axis expands in the crystallites. Characterization of virgin graphite structure and of the damage evolution after irradiation of nuclear graphite has an important role to play in the understanding and development of materials used in current and future nuclear reactors, respectively.

Revival of Prism-Based TIR Microscopy - Versatile Tracking of Fluorescent and Scattering Probes with NM-Precision

Current single-molecule microscopy experiments mostly rely on the fluorescence signal of fluorescent proteins, organic dyes or quantum dots attached to proteins of interest. However, these probes suffer from certain limitations, namely limited number of photons before photobleaching, photon blinking, and fluorescence saturation. Consequently, the temporal and spatial resolution by which single molecules can be tracked is limited. Promising candidates for replacing fluorescent probes are gold nanoparticles (GNPs). GNPs exhibit a large scattering cross section in the optical spectrum due to plasmon resonance, provide long-term stability and allow for versatile surface chemistry. Furthermore, because generation of photons relies on elastic scattering, their emission rate does not saturate.Here, we present a camera-based wide-field imaging technique for GNP-labeled proteins using a novel parabolic prism-type total-internal reflection (TIR) microscope. We demonstrate the advantages of GNPs over commonly used fluorescent probes and discuss the pros and cons of prism-type versus objective-type TIR microscopy. We demonstrate that prism-based TIR microscopy allows imaging of fluorescent and scattering probes with high signal-to-noise, excellent control over a wide range of incidence angles, and even illumination intensities within a field of view. When tracking surface-immobilized GNPs (40 nm diameter) we obtained two-dimensional localization precisions as good as 5 angstrom within 30 ms exposure time. We demonstrate localization experiments of kinesin-1 motors labeled with GNPs walking on surface-immobilized microtubules. When GNPs where bound to the tail or motor domains of kinesin-1 we found localization precisions of 3.6 nm and 1.9 nm within 30 ms exposure time, respectively. Furthermore GNP-loaded motors showed 8 nm stepping along microtubules at 3 μM MgATP within image acquisition times of 15 ms. Our method allows for precise localization of biomolecules within short acquisition times over long time scales.

LIGHT SUPERSYMMETRIC DARK MATTER

The neutralino in a singlet extension of the minimal supersymmetric standard model and the mixed sneutrino in a supersymmetric model with right-handed neutrinos are two possible light dark matter candidates. Both can have a large scattering cross section on nuclei thus being compatible with recent results in direct detection experiments. A brief overview of the properties of light supersymmetric dark matter scenarios is presented.

Existence of an exceptional reaction pathway for H3+ formation observed in collision-induced dissociation of methane ions at 1000 eV

Dissociation of CH(4)(+) ions at 1000 eV induced by collision with Ar atoms was investigated by measuring the kinetic energies of the ionized fragments. At small scattering angles, including zero, H(+), H(2)(+), H(3)(+), CH(3)(+), CH(2)(+), CH(+), and C(+) fragments were observed. The attractive part of the potential in the CH(4)(+)-Ar collision system played an important role in the formation of the ionized fragments. Rainbow scattering, leading to a large scattering cross section, was shown to be responsible for the increased formation of H(3)(+). It is proposed that on collision-induced dissociation of CH(4)(+), its three hydrogen atoms, which form a triangle, simultaneously react and move together to form H(3)(+).

CDMS II result and light Higgs boson scenario of the MSSM

The CDMS Collaboration has reported two candidate events for dark matter. If the events are due to the elastic scattering of dark matter, the dark matter would be a WIMP dark matter with its mass of the order of 10-100GeV and its scattering cross section with a nucleon is about 10−44-10−43 cm2. We show that such a dark matter is properly realized as a neutralino dark matter in the light higgs boson scenario of the MSSM. The lightest higgs boson mass can be lighter than 114.4GeV in the scenario because of a suppressed interaction between higgs boson and Z bosons. As a result, a large scattering cross section between the dark matter and ordinary matter is obtained.

Light neutralinos with large scattering cross sections in the minimal supersymmetric standard model

Motivated by recent data from CoGeNT and the DAMA annual modulation signal, we discuss collider constraints on the minimal supersymmetric standard model neutralino dark matter with mass in the 5--15 GeV range. The lightest superpartner (LSP) would be a bino with a small Higgsino admixture. Maximization of the dark matter nucleon scattering cross section for such a weakly interacting massive particle requires a light Higgs boson with $\mathrm{tan}\ensuremath{\beta}$ enhanced couplings. Limits on the invisible width of the $Z$ boson, combined with the rare decays ${B}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\rightarrow}\ensuremath{\tau}\ensuremath{\nu}$, and the ratio $B\ensuremath{\rightarrow}D\ensuremath{\tau}\ensuremath{\nu}/B\ensuremath{\rightarrow}D\ensuremath{\ell}\ensuremath{\nu}$, constrain cross sections to be below ${\ensuremath{\sigma}}_{n}\ensuremath{\lesssim}5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}42}\text{ }\text{ }{\mathrm{cm}}^{2}$. This indicates a higher local dark matter density than is usually assumed by a factor of roughly 6 necessary to explain the CoGeNT excess. This scenario also requires a light charged Higgs boson, which can give substantial contributions to rare decays such as $b\ensuremath{\rightarrow}s\ensuremath{\gamma}$ and $t\ensuremath{\rightarrow}b{H}^{+}$. We also discuss the impact of Tevatron searches for Higgs bosons at large $\mathrm{tan}\ensuremath{\beta}$.

Structure of aluminum alloys irradiated with reactor neutrons

Samples of the CAB-1 alloy in the initial state and irradiated with fast neutrons at an fluence of 2 × 1021 neutrons/cm2 have been studied by small-angle neutron scattering. It has been demonstrated that the observed large scattering cross sections are associated with the presence of nanosized pores with radii R ∼ 5–50 nm in the alloy, whereas for possible inclusions of the Mg2Si and Si phases, the contrast factors and limiting volume fractions lead to the estimated cross sections that are two orders of magnitude smaller than those observed in the experiment. As a result of the irradiation, the volume fraction of scattering objects (pores) 40–50 nm in radius decreases by a factor of more than two. This is compensated, to a large extent, by an increase in the total fraction of particles with radii of 5–8 and 20–25 nm as the total surface area of the scattering objects increases by 40%.

Neutralino dark matter in light Higgs boson scenario

Phenomenology of neutralino dark matter in the minimal supersymmetric model is discussed for a scenario where the lightest Higgs boson mass is lighter than 114.4 GeV. We show that the scenario is consistent not only with many collider experiments but also with the observed relic abundance of dark matter. The allowed region may be probed by experiments of Bs→μ+μ− in near future. The scenario predicts a large scattering cross section between the dark matter and ordinary matter and thus it may be tested in present direct detection experiments of dark matter.

Plasmonic Enhancement of Molecular Fluorescence

Metallic nanoparticles are known to dramatically modify the spontaneous emission of nearby fluorescent molecules and materials. Here we examine the role of the nanoparticle plasmon resonance energy and nanoparticle scattering cross section on the fluorescence enhancement of adjacent indocyanine green (ICG) dye molecules. We find that enhancement of the molecular fluorescence by more than a factor of 50 can be achieved for ICG next to a nanoparticle with a large scattering cross section and a plasmon resonance frequency corresponding to the emission frequency of the molecule.

Application of the boundary-element method to the interaction of light with single and coupled metallic nanoparticles.

The boundary-element method is applied to the interaction of light with resonant metallic nanoparticles. At a certain wavelength, excitation of a surface plasmon takes place, which leads to a resonantly enhanced near-field amplitude and a large scattering cross section. The resonance wavelength for different scatterer geometries is determined. Alteration of the scattering properties in the presence of other metallic nanoparticles is discussed. To treat this problem, a novel formulation of the boundary-element method is presented that solves the interaction problem for all the coupled particles.

Synchronous electron-nuclear vibrations in a π-conjugated nanopoly(acetylene) chain

An unusual behavior was observed for the spontaneous Raman spectra in the range of the passband of trans-poly(acetylene) nanoparticles. The following phenomena are observed for the stretching carbon-carbon vibrations: large scattering cross section; high anti-Stokes-to-Stokes ratio; no correlation between the absorption spectra of trans-nanopoly(acetylene) and the Raman excitation spectrum. A qualitative model is proposed for synchronous weakly damping electron-nuclear vibrations in the ordered poly(acetylene) chain.