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High-Resolution Electron Microscopy
01 Dec 2013-
TL;DR: In this article, the authors present a list of symbols for high-resolution images of Crystals and their defects, including Stem and Z-Contrast, Wave Optics, and Coherence and Fourier Optics.
Abstract: Preface Acknowledgements List of Symbols 1. Preliminaries 2. Electron Optics 3. Wave Optics 4. Coherence and Fourier Optics 5. High-Resolution Images of Crystals and their Defects 6. HREM in Biology, Organic Crystals and Radiation Damage 7. Image Processing and Superresolution Schemes 8. Stem and Z-Contrast 9. Electron Sources and Detectors 10. Measurement of Electron-optical Parameters Affecting High-Resolution Images 11. Instabilities and the Microscope Environment 12. Experimental Methods 13. Associated Techniques Appendix 1 Appendix 2 Appendix 3 Appendix 4 Appendix 5
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TL;DR: These studies by transmission electron microscopy reveal that individual graphene sheets freely suspended on a microfabricated scaffold in vacuum or air are not perfectly flat: they exhibit intrinsic microscopic roughening such that the surface normal varies by several degrees and out-of-plane deformations reach 1 nm.
Abstract: Graphene — a recently isolated one-atom-thick layered form of graphite — is a hot topic in the materials science and condensed matter physics communities, where it is proving to be a popular model system for investigation. An experiment involving individual graphene sheets suspended over a microscale scaffold has allowed structure determination using transmission electron microscopy and diffraction, perhaps paving the way towards an answer to the question of why graphene can exist at all. The 'two-dimensional' sheets, it seems, are not flat, but wavy. The undulations are less pronounced in a two-layer system, and disappear in multilayer samples. Learning more about this 'waviness' may reveal what makes these extremely thin carbon membranes so stable. Investigations of individual graphene sheets freely suspended on a microfabricated scaffold in vacuum or in air reveal that the membranes are not perfectly flat, but exhibit an intrinsic waviness, such that the surface normal varies by several degrees, and out-of-plane deformations reach 1 nm. The recent discovery of graphene has sparked much interest, thus far focused on the peculiar electronic structure of this material, in which charge carriers mimic massless relativistic particles1,2,3. However, the physical structure of graphene—a single layer of carbon atoms densely packed in a honeycomb crystal lattice—is also puzzling. On the one hand, graphene appears to be a strictly two-dimensional material, exhibiting such a high crystal quality that electrons can travel submicrometre distances without scattering. On the other hand, perfect two-dimensional crystals cannot exist in the free state, according to both theory and experiment4,5,6,7,8,9. This incompatibility can be avoided by arguing that all the graphene structures studied so far were an integral part of larger three-dimensional structures, either supported by a bulk substrate or embedded in a three-dimensional matrix1,2,3,9,10,11,12. Here we report on individual graphene sheets freely suspended on a microfabricated scaffold in vacuum or air. These membranes are only one atom thick, yet they still display long-range crystalline order. However, our studies by transmission electron microscopy also reveal that these suspended graphene sheets are not perfectly flat: they exhibit intrinsic microscopic roughening such that the surface normal varies by several degrees and out-of-plane deformations reach 1 nm. The atomically thin single-crystal membranes offer ample scope for fundamental research and new technologies, whereas the observed corrugations in the third dimension may provide subtle reasons for the stability of two-dimensional crystals13,14,15.
4,653 citations
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...04 Monolayer [0–110] Bilayer [0–110] About 50 layers 0....
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TL;DR: Assessment of the potential role that electron microscopy of liquid samples can play in areas such as energy storage and bioimaging is assessed.
Abstract: This article reviews the use of electron microscopy in liquids and its application in biology and materials science.
821 citations
TL;DR: The observation of the photon-induced near-field effect in ultrafast electron microscopy demonstrates the potential for many applications, including those of direct space-time imaging of localized fields at interfaces and visualization of phenomena related to photonics, plasmonics and nanostructures.
Abstract: In materials science and biology, optical near-field microscopies enable spatial resolutions beyond the diffraction limit, but they cannot provide the atomic-scale imaging capabilities of electron microscopy. Given the nature of interactions between electrons and photons, and considering their connections through nanostructures, it should be possible to achieve imaging of evanescent electromagnetic fields with electron pulses when such fields are resolved in both space (nanometre and below) and time (femtosecond). Here we report the development of photon-induced near-field electron microscopy (PINEM), and the associated phenomena. We show that the precise spatiotemporal overlap of femtosecond single-electron packets with intense optical pulses at a nanostructure (individual carbon nanotube or silver nanowire in this instance) results in the direct absorption of integer multiples of photon quanta (nhomega) by the relativistic electrons accelerated to 200 keV. By energy-filtering only those electrons resulting from this absorption, it is possible to image directly in space the near-field electric field distribution, obtain the temporal behaviour of the field on the femtosecond timescale, and map its spatial polarization dependence. We believe that the observation of the photon-induced near-field effect in ultrafast electron microscopy demonstrates the potential for many applications, including those of direct space-time imaging of localized fields at interfaces and visualization of phenomena related to photonics, plasmonics and nanostructures.
583 citations
TL;DR: In this paper, a detailed transmission electron microscopy and electron diffraction study of the thinnest possible membrane, a single layer of carbon atoms suspended in vacuum and attached only at its edges, is presented.
575 citations
Cites background from "High-Resolution Electron Microscopy..."
...While the total (integrated) intensities within each Bragg reflection agree quite well with the model of a flat membrane, the actual shape and widths of the peaks show striking deviations from the standard diffraction behaviour of 3D crystals [20,21]....
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TL;DR: On a clean single-layer graphene membrane, adsorbates such as atomic hydrogen and carbon can be seen as if they were suspended in free space, and directly image such individual adatoms, along with carbon chains and vacancies, and investigate their dynamics in real time, opening a way to reveal dynamics of more complex chemical reactions or identify the atomic-scale structure of unknown adsorbate.
Abstract: Scanning tunnelling microscopes made it possible to image atomic-scale features on a solid-state surface. But they have limitations in terms of sample conductivity, cleanliness and data acquisition rate. An older technology, the transmission electron microscope (TEM), meanwhile evolved to be able to image individual heavy atoms. But lighter atoms remained beyond its range because of their low contrast. Enter graphene, the one-atom-thick sheet of carbon atoms packed in a dense two-dimensional honeycomb lattice. Meyer et al. show that atoms as small as carbon and even hydrogen adsorbed onto graphene can be imaged using standard TEM technology. Ultrathin graphene is an ideal support, either invisible or, if the lattice is resolved at high resolution, its contribution to the imaging signal is easily removed. This approach brings atomic resolution to biomolecules as well as to graphene itself. The cover shows hydrogen atoms (purple) on a graphene sheet (red), with a carbon atom (yellow tipped) near left centre. Yellow peaks are amorphous carbon. Detecting individual low-atomic-number atoms is extremely challenging using conventional transmission electron microscopy. This paper reports the direct imaging in a transmission electron microscope (TEM) of atomic carbon and hydrogen using graphene as a substrate which provides a near-invisible background. The approach could be used for the direct study at the atomic level of organic species such as biomolecules. Observing the individual building blocks of matter is one of the primary goals of microscopy. The invention of the scanning tunnelling microscope1 revolutionized experimental surface science in that atomic-scale features on a solid-state surface could finally be readily imaged. However, scanning tunnelling microscopy has limited applicability due to restrictions in, for example, sample conductivity, cleanliness, and data acquisition rate. An older microscopy technique, that of transmission electron microscopy (TEM)2,3, has benefited tremendously in recent years from subtle instrumentation advances, and individual heavy (high-atomic-number) atoms can now be detected by TEM4,5,6,7 even when embedded within a semiconductor material8,9. But detecting an individual low-atomic-number atom, for example carbon or even hydrogen, is still extremely challenging, if not impossible, via conventional TEM owing to the very low contrast of light elements2,3,10,11,12. Here we demonstrate a means to observe, by conventional TEM, even the smallest atoms and molecules: on a clean single-layer graphene membrane, adsorbates such as atomic hydrogen and carbon can be seen as if they were suspended in free space. We directly image such individual adatoms, along with carbon chains and vacancies, and investigate their dynamics in real time. These techniques open a way to reveal dynamics of more complex chemical reactions or identify the atomic-scale structure of unknown adsorbates. In addition, the study of atomic-scale defects in graphene may provide insights for nanoelectronic applications of this interesting material.
502 citations