Longitudinal and transverse modulation of electron wave function with light, and its application to electron microscopy

Conventional electron microscopy operates with flat electron wave fronts. Employing attenuative or electrostatic phase plates allows transversally modulating the wave front, enhancing cross-sections of particular scattering channels. Utilization of light from coherent ultrafast sources allows modulating electrons phase both transversally and longitudinally. This results in a plethora of phenomena, as well as conceptually new techniques such as non-local electron holography of light fields and generation of ultrafast electron vortex beams, which we present in this contribution.

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Gabriele Berruto, Fabrizio Carbone, Ido Kaminer, Ivan Madan, Enrico Pomarico, Giovanni Maria Vanacore
IEEE, 2021
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https://infoscience.epfl.ch/record/292047?ln=fr

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A protocol for preparing GFP-labeled neurons previously imaged in vivo and in slice preparations for light and electron microscopic analysis

Graham Knott, Egbert Welker

In vivo imaging of green fluorescent protein (GFP)-labeled neurons in the intact brain is being used increasingly to study neuronal plasticity. However, interpreting the observed changes as modifications in neuronal connectivity needs information about synapses. We show here that axons and dendrites of GFP-labeled neurons imaged previously in the live mouse or in slice preparations using 2-photon laser microscopy can be analyzed using light and electron microscopy, allowing morphological reconstruction of the synapses both on the imaged neurons, as well as those in the surrounding neuropil. We describe how, over a 2-day period, the imaged tissue is fixed, sliced and immuno-labeled to localize the neurons of interest. Once embedded in epoxy resin, the entire neuron can then be drawn in three dimensions (3D) for detailed morphological analysis using light microscopy. Specific dendrites and axons can be further serially thin sectioned, imaged in the electron microscope (EM) and then the ultrastructure analyzed on the serial images.

2009

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Imaging green fluorescent protein-labeled neurons using light and electron microscopy

Graham Knott

The ability to observe axons and dendrites with transmission electron microscopy (EM) after they have been previously imaged live with laser-scanning microscopy is a useful technique to study their synaptic connectivity. This protocol provides a detailed method by which neurons that were imaged in a live brain or slice culture can be reimaged using EM. First, brain tissue expressing green fluorescent protein (GFP) is chemically fixed. Then, an immunocytochemistry process is used to render the fluorescent protein electron dense so that it can first be located using light microscopy and then serial thin-sectioned for EM so that the ultrastructure of specific parts of neurites can be analyzed in three dimensions. Patterns of blood vessels observed in the live brain are used to locate the previously imaged neurons. The method described here allows for a complete three-dimensional (3D) reconstruction to be made of the imaged structures from serial electron micrographs.

2013

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Nanocrystalline Low-Refractive Magnesium Fluoride Films Deposited by Reactive Magnetron Sputtering: Optical and Structural Properties

Stefan Mertin, Paul Muralt, Silviu Cosmin Sandu, Jean-Louis Scartezzini

In this work, we study MgF2 thin-film synthesis by reactive pulsed DC magnetron sputtering from a metallic magnesium target in a gas mixture of argon, oxygen, and carbon tetrafluoride (CF4). Nanocrystalline films on silicon and glass substrates with excellent properties for optical application are achieved. The plasma discharge is analyzed with a differentially pumped mass spectrometer before and during the deposition process. Without breaking the vacuum, monochromatic photoelectron spectroscopy (XPS) is performed for in situ determination of the atomic C and O concentration. Film microstructure, topography, and thickness are investigated by electron microscopy (SEM and TEM), atomic force microscopy (AFM), and X-ray diffraction (XRD). The optical constants n and k are determined by spectroscopic ellipsometry and spectrophotometry: a consistent parametric fit of the ellipsometric angles and spectral transmittance and reflectance based on three Lorentz oscillators to determine n and k is achieved for a wide spectral range (300–2 300 nm). At 550 nm, a refractive index of 1.382 and near-zero absorption is obtained, which is in excellent agreement with n = 1.383 of polycrystalline MgF2. The measured light reflection at 760 nm is reduced by 3% for a quarter-wave nanocrystalline MgF2 coating on glass compared to the uncoated glass substrate.

Wiley-Blackwell2015

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Microscopie électronique en transmission

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Microscope électronique

thumb|Microscope électronique construit par Ernst Ruska en 1933.thumb|Collection de microscopes électroniques anciens (National Museum of Health & Medicine). Un microscope électronique (ME) est un ty