Case Study: Electron Motion Control And Imaging

1768 Words 8 Pages
Electron Motion Control and Imaging
M. Th. Hassan
Electron motion in atomic systems, which happens on timescales of attoseconds (10-18s), is at the heart of all phenomena in nature. For instance, the motion of electrons in the chemical bonds determines the structure change in the molecules. Therefore, controlling this fast electron motion, in turn, allows to control the molecular structure change. Additionally, recording snapshots of the electron motion will provide real-time access to all microscopic motions outside the atomic core and radically change our insight into the workings of the microcosm, which will improve our understanding of chemistry.
Moreover, sometimes revealing the electron dynamics by time-resolved spectroscopy measurements
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1b) is exploited to generate sub-femtosecond electron pulses (Fig. 2a). This technique is based on photon-electron coupling on a nanostructure3. This leads to the gain or loss of photon quanta via electron packets, when the electrons and the photons are temporally overlapping on the nanostructure surface. That can be resolved in the electron energy spectrum as discrete peaks on the higher and lower energy sides of the zero loss peak (ZLP) separated by multiples of photon energy (nћω) (Fig. 2b).3 In this case, the optical attosecond pulse acts as a temporal gate for the electron pulses. Therefore, the electrons that only gain energy due to the coupling (shaded area in Fig. 2b), emulate the optical attosecond pulse duration, have effectively sub-femtosecond resolution4.
The optically-gated electrons are filtered out and utilized to probe and image the ultrafast electron dynamics triggered by a second optical pulse, as is schematically illustrated in Fig. 2c. That will pave the way for establishing the field of “Attomicroscopy”, which will have numerous applications in imaging the electron dynamics of
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It consists of two biopolymer strands coiled around each other to form a double helix6. DNA is a highly polymorphic molecule and adopts a conformation that is the most favorable with respect to the surrounding physicochemical environment. DNA exists in many possible conformations that include A-DNA, B-DNA, and Z-DNA forms (Fig.3). One of the most characteristic of the DNA molecule is the flexibility of its backbone. Therefore, the DNA conformation can be transferred from a form to another by just a few kcal/mol9. The primary DNA structure is connected by strong covalent bonds while the overall 3-D folding is determined by much weaker forces including hydrogen bonds, van der Waals, electrostatic and hydrophobic interactions. These weaker forces, being comparable in order of magnitude to the average kinetic energy of molecules at physiologically relevant temperatures, account for most of the molecular interplay, structural equilibria and reorganizations inside the

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