Vibrational spectroscopies using infrared radiation, Raman scattering, neutrons, low-energy electrons and inelastic electron tunnelling are powerful techniques that can analyse bonding arrangements, identify chemical compounds and probe many other important properties of materials. The spatial resolution of these spectroscopies is typically one micrometre or more, although it can reach a few tens of nanometres or even a few ångströms when enhanced by the presence of a sharp metallic tip. If vibrational spectroscopy could be combined with the spatial resolution and flexibility of the transmission electron microscope, it would open up the study of vibrational modes in many different types of nanostructures. Unfortunately, the energy resolution of electron energy loss spectroscopy performed in the electron microscope has until now been too poor to allow such a combination. Recent developments that have improved the attainable energy resolution of electron energy loss spectroscopy in a scanning transmission electron microscope to around ten millielectronvolts now allow vibrational spectroscopy to be carried out in the electron microscope. Here we describe the innovations responsible for the progress, and present examples of applications in inorganic and organic materials, including the detection of hydrogen. We also demonstrate that the vibrational signal has both high- and low-spatial-resolution components, that the first component can be used to map vibrational features at nanometre-level resolution, and that the second component can be used for analysis carried out with the beam positioned just outside the sample--that is, for 'aloof' spectroscopy that largely avoids radiation damage.

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Although the majority of glasses in use in technology are complex mixtures of oxides or chalcogenides, there are numerous examples of pure substances-'glassformers'-that also fail to crystallize during cooling. Most glassformers are organic molecular systems, but there are important inorganic examples too, such as silicon dioxide and elemental selenium (the latter being polymeric). Bulk metallic glasses can now be made; but, with the exception of Zr50Cu50 (ref. 4), they require multiple components to avoid crystallization during normal liquid cooling. Two-component 'metglasses' can often be achieved by hyperquenching, but this has not hitherto been achieved with a single-component system. Glasses form when crystal nucleation rates are slow, although the factors that create the slow nucleation conditions are not well understood. Here we apply the insights gained in a recent molecular dynamics simulation study to create conditions for successful vitrification of metallic liquid germanium. Our results also provide micrographic evidence for a rare polyamorphic transition preceding crystallization of the diamond cubic phase.

International audienceA detailed nuclear magnetic resonance and Raman study of GexSe1−x glasses indicate that the glass structure is composed of intertwined microdomains of GeSe2 and Sen. Static nuclear magnetic resonance spectra of glasses ranging from 0≤x≤1/3 reveal the absence of Ge-Se-Se fragments in the structure. High temperature nuclear magnetic resonance showing considerable line narrowing confirms this observation. More importantly, the fraction of Se-Se-Se obtained by integration of nuclear magnetic resonance lines matches closely the percentage predicted for a bimodal phase model and is not consistent with the existence of Ge-Se-Se fragments. Raman spectra collected on the same glass also confirm the existence of GeSe2 domains up to high selenium concentrations. The mobility of the Sen phase observed at high temperature while the GeSe2 phase remains rigid is consistent with their respective underconstrained and overconstrained structural nature. The proposed bimodal phase percolation model is consistent with the original Phillips and Thorpe theory however it is clearly at odds with the intermediate phase model which predicts large amounts of Ge-Se-Se fragments in the structure. A calorimetric study performed over a wide range of cooling/heating rates shows a narrow composition dependence centered at ⟨r⟩=2.4 in contrast with the wide reversibility window observed by Modulated Differential Scanning Calorimetry. This suggests that the observation of the reversibility window associated with the intermediate phase in Ge-Se glasses could be an experimental artifact resulting from the use of a single modulation frequency

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