Angle-resolved cathodoluminescence imaging polarimetry

Cathodoluminescence spectroscopy (CL) allows characterizing light emission in bulk and nanostructured materials and is a key tool in fields ranging from materials science to nanophotonics. Previously, CL measurements focused on the spectral content and angular distribution of emission, while the polarization was not fully determined. Here we demonstrate a technique to access the full polarization state of the cathodoluminescence emission, that is the Stokes parameters as a function of the emission angle. Using this technique, we measure the emission of metallic bullseye nanostructures and show that the handedness of the structure as well as nanoscale changes in excitation position induce large changes in polarization ellipticity and helicity. Furthermore, by exploiting the ability of polarimetry to distinguish polarized from unpolarized light, we quantify the contributions of different types of coherent and incoherent radiation to the emission of a gold surface, silicon and gallium arsenide bulk semiconductors. This technique paves the way for in-depth analysis of the emission mechanisms of nanostructured devices as well as macroscopic media.Comment: 8 figures. Includes supplementary informatio

Experimental Verification of \u3cem\u3en\u3c/em\u3e = 0 Structures for Visible Light

We fabricate and characterize a metal-dielectric nanostructure with an effective refractive index n=0 in the visible spectral range. Light is excited in the material at deep subwavelength resolution by a 30-keV electron beam. From the measured spatially and angle-resolved emission patterns, a vanishing phase advance, corresponding to an effective ϵ=0 and n=0, is directly observed at the cutoff frequency. The wavelength at which this condition is observed can be tuned over the entire visible or near-infrared spectral range by varying the waveguide width. This n=0 plasmonic nanostructure may serve as a new building block in nanoscale optical integrated circuits and to control spontaneous emission as experimentally demonstrated by the strongly enhanced radiative optical density of states over the entire n=0 structure

Light emission intensities of luminescent Y2O3:Eu and Gd2O3:Eu particles of various sizes

There is great technological interest in elucidating the effect of particle size on the luminescence efficiency of doped rare earth oxides. This study demonstrates unambiguously that there is a size effect and that it is not dependent on the calcination temperature. The Y2O3:Eu and Gd2O3:Eu particles used in this study were synthesized using wet chemistry to produce particles ranging in size between 7 nm and 326 nm and a commercially available phosphor. These particles were characterized using three excitation methods: UV light at 250 nm wavelength, electron beam at 10 kV, and X-rays generated at 100 kV. Regardless of the excitation source, it was found that with increasing particle diameter there is an increase in emitted light. Furthermore, dense particles emit more light than porous particles. These results can be explained by considering the larger surface area to volume ratio of the smallest particles and increased internal surface area of the pores found in the large particles. For the small particles, the additional surface area hosts adsorbates that lead to non-radiative recombination, and in the porous particles, the pore walls can quench fluorescence. This trend is valid across calcination temperatures and is evident when comparing particles from the same calcination temperature

Plasmonic excitation and manipulation with an electron beam

When an electron beam passes through or near a metal structure, it will excite surface plasmons, providing a unique way to access surface plasmon behavior at the nanoscale. An electron beam focused to nanometer dimensions thus functions as a point source that is able to probe the local plasmonic mode structure at deep-subwavelength resolution. In this article, we show how well-controlled coupling between an electron beam and surface plasmons, combined with a far-field detection system, allows characterization and manipulation of plasmons on a variety of plasmonic devices. By mapping the spatial profile of inelastic scattering to resonant modes, the dispersion and losses of surface plasmons are resolved. The technique further allows probing of the confinement of plasmons within cavities and measuring the angular emission profile of nanoantennas. The coupling of electrons to surface plasmons allows the use of the electron beam as a dipole emitter that can be positioned at will. The beam position thereby can select between modes with different symmetries. This effect can be used to exert forces on plasmonic structures on the nanometer length scale with great control. © 2012 Materials Research Society.This work is part of the research program of the “Stichting voor Fundamenteel Onderzoek der Materie (FOM),” which is financially supported by the “Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO).” P.E.B. acknowledges financial support from the Basic Energy Sciences Division of the US Department of Energy, Award #DE-SC0005132. J.A. acknowledges financial support from the project FIS2010-19609-C02-01 of the Spanish Ministery of Science and A.R.C. acknowledges Consejo Nacional de Ciencia y Tecnología of Mexico and Benemérita Universidad Autónoma de Puebla.Peer Reviewe

The effect of giving influenza vaccination to general practitioners: a controlled trial [NCT00221676]

BACKGROUND: No efficacy studies of influenza vaccination given to GPs have yet been published. Therefore, our purpose was to assess the effect of an inactivated influenza vaccine given to GPs on the rate of clinical respiratory tract infections (RTIs) and proven influenza cases (influenza positive nose and throat swabs and a 4-fold titre rise), while adjusting for important covariates. METHODS: In a controlled trial during two consecutive winter periods (2002–2003 and 2003–2004) we compared (77 and 100) vaccinated with (45 and 40) unvaccinated GPs working in Flanders, Belgium. Influenza antibodies were measured immediately prior to and 3–5 weeks after vaccination, as well as after the influenza epidemic. During the influenza epidemic, GPs had to record their contact with influenza cases and their own RTI symptoms every day. If they became ill, the GPs had to take nose and throat swabs during the first 4 days. We performed a multivariate regression analysis for covariates using Generalized Estimating Equations. RESULTS: One half of the GPs (vaccinated or not) developed an RTI during the 2 influenza epidemics. During the two influenza periods, 8.6% of the vaccinated and 14.7% of the unvaccinated GPs had positive swabs for influenza (RR: 0.59; 95%CI: 0.28 – 1.24). Multivariate analysis revealed that influenza vaccination prevented RTIs and swab-positive influenza only among young GPs (ORadj: 0.35; 95%CI: 0.13 – 0.96 and 0.1; 0.01 – 0.75 respectively for 30-year-old GPs). Independent of vaccination, a low basic antibody titre against influenza (ORadj 0.57; 95%CI: 0.37 – 0.89) and the presence of influenza cases in the family (ORadj 9.24; 95%CI: 2.91 – 29) were highly predictive of an episode of swab-positive influenza. CONCLUSION: Influenza vaccination was shown to protect against proven influenza among young GPs. GPs, vaccinated or not, who are very vulnerable to influenza are those who have a low basic immunity against influenza and, in particular, those who have family members who develop influenza

Nanoscale Structural and Emission Properties within - Russian Doll- - Type InGaN/AlGaN Quantum Wells

Due to the increasing desire for nanoscale optoelectronic devices with green light emission capability and high efficiency, ternary III- N- based nanorods are extensively studied. Many efforts have been taken on the planar device configuration, which lead to unavoided defects and strains. With selective- area molecular- beam epitaxy, new - Russian Doll- - type InGaN/AlGaN quantum wells (QWs) have been developed, which could largely alleviate this issue. This work combines multiple nanoscale characterization methods and k- p theory calculations so that the crystalline structure, chemical compositions, strain effects, and light emission properties can be quantitatively correlated and understood. The 3D structure and atomic composition of these QWs are retrieved with transmission electron microscopy and atom probe tomography while their green light emission has been demonstrated with room- temperature cathodoluminescence experiments. k- p theory calculations, with the consideration of strain effects, are used to derive the light emission characteristics that are compared with the local measurements. Thus, the structural properties of the newly designed nanorods are quantitatively characterized and the relationship with their outstanding optical properties is described. This combined approach provides an innovative way for analyzing nano- optical- devices and new strategies for the structure design of light- emitting diodes.The chemical components of the nanorods, shape effects and strain effects given by this unique - Russian Doll- - type geometry of InGaN/AlGaN quantum wells are quantitatively related with the optical properties. This combined approach reported here provides an innovative way for analyzing nano- optical- devices and new strategies for the structure design of light- emitting diodes.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/162759/3/adom202000481_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/162759/2/adom202000481.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/162759/1/adom202000481-sup-0001-SuppMat.pd