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EELS and EDS Analysis


Figure 6: Colorized elemental maps of Ti in green, Sr in red, Mn in blue, and La in purple acquired using a) EELS and b) EDS.


the upper region of the ADF STEM image in Figure 1 . T e EELS and EDS maps were acquired using the method outlined in the previous section. Figure 7 shows the Ti, O, Mn, and La composition maps obtained using EELS, as well as a Sr composition map obtained using EDS. T ese elemental maps were combined to generate the composite color map in Figure 8 that shows the distribution of each element (oxygen is omitted for clarity). T e intermixing across the interface that is also observed in the EELS compositional maps in Figures 3 and 6a , can now be further investigated by looking at changes in the fi ne structure of Ti, O, and Mn that occur across the interface region. Figure 9 shows high-energy resolution EELS spectra of


the Ti L 2,3 -edges, O K-edge, and Mn L 2,3 -edges extracted from the selected regions in Figure 8 across the STO/LMO/ STO interfaces. Each spectrum is normalized to the same maximum and then vertically shifted for better visualization. Changes in the fine structure can be observed in every spectrum, although they are quite strong in the case of the O K-edge in Figure 9b . Here, the shape goes from that typical of SrTiO 3 to something intermediate with that of LaMnO 3 . The pre-peak in the O K edge at 529 eV is due to the excitation of the electrons from the O 1s state to the partially filled O 2p state, which can be partially hybridized with 3D states of the transition metal. The size of this pre-peak is related to the strength of the hybridization with the transition metal, which varies as a result of different coordinations of the bonded atoms. In this case, O atoms in the same column are bonded to both Mn and Ti atoms. The effects of such intermixing can be seen in the O K-edge fine structure at the interface.


As shown in Figure 9a the Ti L2,3-edges in the EELS spectrum splits into two sets of different peaks between


50


Figure 7: Ti, O, Mn, La, and Sr. a) EELS using the Ti L2,3-edge at 456 eV; b) EELS using O K-edge at 532 eV; c) EELS using the Mn L2,3-edges at 640 eV; d) EELS using the La M4,5-edges at 832 eV; and e) EDS using the Sr L at 1.81 keV. Here the EELS spectrometer was set up with high dispersion in order to increase the energy resolution for the fi ne structure analysis. As a result, the fi eld of view is reduced and extends up to 900 eV. Thus, the Sr L2,3-edges at 1,940 eV are out of the fi eld of view.


456 eV and 466 eV that can be labeled as L 3 - and L 2 -edges, respectively. They correspond to electronic transitions from the 2p3/2 and 2p1/2 core levels to a 3D excited state. Both edges are divided into t 2g and e g bands whose relative intensities reflect the different distortions of the local coordination environment, and, coupled with simulations, they can be used to detect crystal distortion or changes in the oxidation state. As shown in Figure 9a there is the presence of Ti across the entire LMO layer, but the shape of Ti L 2,3 - edges remains largely unchanged showing the features typical of Ti 4+. This indicates that the Ti atoms tend to keep their configuration largely unchanged going from the STO to the LMO layers. As mentioned above, the ZLP was used to correct for energy drift effects that usually occur as result of microscope or environmental instabilities. In this way the


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