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MicroscopyInnovations


T e GLAD plasmonic grating platform can improve the SNR and precision of current localization microscopy techniques such as stochastic optical reconstruction microscopy (STORM) and photo-activated localization microscopy (PALM). T is enables the imaging of a wider range of fl uoro- phore concentrations. T e nano-protrusions on GLAD gratings enable simultaneous imaging of large sample areas without using point-by-point scanning techniques, reducing image collection time and minimizing photobleaching. T e enhancement provided by the GLAD grating also enables the imaging of single-molecule fl uorescence with less expensive systems such as the simple epifl uorescence microscopes available in most labs.


Scanning Helium Microscope (SHeM) University of Newcastle, Australia Developer: Paul Dastoor


Scanning helium microscopy (SHeM) is based on helium atom scattering (HAS), an established technique for investigating surface structure. In a typical HAS experiment, monochromatic, very-low-energy (10–300 meV) helium atoms are scattered from a surface, under vacuum conditions, and detected in a


tuned mass spectrometer. HAS is a sensitive, non-perturbing probe of surface morphology that can be used to analyze metals, insulators, semiconductors, and organic materials. T e SHeM operates analogously to a scanning electron microscope (SEM) but with the electron beam replaced with a beam of neutral helium atoms. T e beam of helium atoms (created via free-jet expansion in the source chamber) emerges through a small pinhole to strike the sample surface, and refl ected helium atoms are collected in the detector chamber. By rastering the sample back and forth, an image of the surface is constructed. The very-low-energy (a few meV) neutral helium atoms cannot penetrate the surface at all, but rather they backscatter from the outermost electronic corrugation of the sample, giving the technique absolute surface sensitivity. The SHeM is able to exploit both electron-atom (elastic- scattering) and electron-phonon-atom (inelastic-scattering) interactions to deliver both topological and chemical contrast simultaneously. Moreover, the chemical sensitivity is still apparent even under several atomic layers of adsorbed contaminant.


A range of material systems remains diffi cult to image with conventional light and electron microscopies: transparent, fragile, weakly-bonded, insulating, very rough, and magnetic samples. T ese delicate structures (such as biological samples, organic fi lms for polymer electronics, and adsorbate layers) suff er degradation under the energetic probes of traditional microscopies. Furthermore, the charged nature of certain probes presents diffi culties when imaging insulating materials without the addition of a conductive coating. SHeM is able to


2017 September • www.microscopy-today.com


image such structures completely non-destructively since the neutral helium beam is a chemically, electrically, and magnetically inert probe of the sample surface. Applications of SHeM include the investigation of new explosives and the imaging of organic electronic materials and circuits in operando without damaging or influencing the operation of the circuitry. Thus, the SHeM enables a wide range of surfaces to be studied for the first time.


STEM Method for Observing Magnetic Ordering with Atomic Resolution


Oak Ridge National Laboratory and University of Uppsala, Sweden


Developers: Juan Carlos Idrobo and Ján Rusz


Energy-loss (or electron) magnetic circular dichroism (EMCD) is a spectroscopic method used to measure the magnetic properties of materials in scanning transmission electron microscopy (STEM). Until now, classical EMCD measurements were performed either in diffraction mode or by using small convergence-


angle electron probes. These two approaches intrinsically limit the spatial resolution of the measurements. A recent experiment demonstrated that the poor spatial resolution of previous EMCD measurements can be overcome by using aberrated electron probes. In recent years, much effort has been directed toward correcting aberrations in electron beams to achieve high-resolution imaging and analysis. Rather than eliminating the aberrations in the electron microscope to achieve a smaller probe size, this new method intentionally introduces a non-cylindrical aberration and then uses this aberrated electron probe to acquire atomically resolved electron energy-loss spectra. The acquired spectra then can be analyzed to reveal the magnetic ordering of a material. The original work used a four-fold astigmatism aberration (because the material had four-fold crystal symmetry), but different aberrations can be selected depending on the crystal symmetry of the material. This “aberrated-probe method” is based on electron energy- loss spectrometry, and thus the technique also reveals the chemical nature of a magnetic phase, which is not achievable via Lorentz microscopy.


The new method demonstrates that phases in electron probes can be used in ways analogous to polarization of light and X-rays. Neither light nor X-ray synchrotrons, however, can achieve the spatial resolution of an electron microscope, and therefore electron microscopy has a special capability for studying chiral properties of materials at atomic resolution. This new analysis method allows the study of magnetic phases in materials at a new level of precision. For instance, magnetic domains in magnetic storage hard drives could be investigated at the atomic level. The method is not


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