In-line holography in the transmission electron microscope is a versatile technique, which provides real-space phase information that can be used for the correction of imaging aberrations, as well as for measuring electric and magnetic fields and strain distributions. It is able to recover high-spatial-frequency contributions to the phase effectively but suffers from the weak transfer of low-spatial-frequency information, as well as from incoherent scattering. Here, we combine gradient flipping and phase prediction in an iterative flux-preserving focal series reconstruction algorithm with incoherent background subtraction that gives extensive access to the missing low spatial frequencies. A procedure for optimizing the reconstruction parameters is presented, and results from MgO cubes, and Fe-filled C nanospheres are compared with phase images obtained using off-axis holography.
The surface plasmon excitation is one of the popular field of research due to their high potential to be applicable in sensor 1 or information technologies 2 , cancer research 3 etc. These coherent delocalized electron oscillations are common in metal-dielectric interfaces. However, recent studies show they also exist in highly doped semiconductors, conducting oxide system or graphene, in summary mostly the systems with high carrier mobility. The next question can be asked for the insulator interfaces. Bismuth Selenide became popular material system due to its recently discovered topological insulator property, in which it behaves as an insulator in the bulk state and metallic at the surface state. This also makes Bi 2 Se 3 as a potential candidate for surface plasmons,so that the first example of Dirac plasmons on Bi 2 Se 3 was observed in 2013 in 0.5 -1 eV energy loss region 4 . The Dirac state is not the only reason of the existence of a plasmon resonance in Bi 2 Se 3 . It is a highly anisotropic with hypabolic dispersion Tetradymites crystal structure, which also makes the dielectric properties highly anisotropic which can allow the plasmon excitation 5 . In this study we would like to show energy filtered transmission electron microscopy (EFTEM) and a finite-difference frequency-domain (FDTD) study for investigating Bi 2 Se 3 nanoplates and try to find an explanation for the existing plasmon excitations. For the experimental observation of Hyporbolic dispersion in Bi 2 Se 3 , EFTEM study was carried out using FEG-TEM Sub-Electron-Volt-Sub-Ångstrom-Microscope (Zeiss SESAM) in the 200 kV equipped with an electrostatic monochromator and the in-column MANDOLINE filter with 0.2 eV slit width. As shown in Fig. 1 localized excitations exist at surface of Bi 2 Se 3 crystal and they show different collective modes in different energies. These results supported by FDTD simulations to be able to explain the interplay between the edge plasmons and surface plasmons.The research leading to these results has received funding from the European Union Seventh Framework Programme [FP7/2007[FP7/ -2013 under grant agreement n°312483 (ESTEEM2). W. V. d. B. acknowledges the Carl Zeiss Foundation.
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