Tham khảo tài liệu 'nanomaterials for nanoscience and nanotechnology part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Transmission Electron Microscopy and Spectroscopy of Nanoparticles 73 ratio image will be obtained which reflects the distribution of valence state across the specimen. It must be pointed out that the thickness effect has been removed in the L3 L2 image. A partially oxidized CoO specimen that contains CoO and CO3O4 grain structure was chosen for this study 67 . The CoO and CO3O4 phases are separated by clear boundaries and it is an ideal specimen for testing the optimum resolution. Figure 3-33 shows a group of energy-filtered TEM image from a triple point in the COO-CO3O4 specimen. The energy-filtered images using the L3 and L2 lines and the post L2 line region Figures 3-33a-c show distinctly difference in contrast distribution due to a difference in the relative white line intensities. From these three images the L3 L2 is calculated after subtracting the contribution from the continuous energy-loss region that is due to single atom scattering and the image clearly displays the distribution of cobalt oxides having different valence states Figure 3-33e where the diffraction contrast disappears. The region with lower oxidation state Co2 shows stronger contrast and the ones with high oxidation states show darker contrast see the L3 L2 ratio displayed in Figure 3-29a . The O Co image was calculated from the images recorded from the O-K edge and the L3 L2 white lines for an energy window width of A 24 eV. Although the energy-filtered O-K edge image exhibit some diffraction contrast and the thickness effect the O Co compositional ratio image greatly reduces the effect. The high intensity region in the O Co image indicates the relative high local concentration in oxygen . higher Co oxidation states the low intensity region contain relatively less oxygen . lower Co valence state entirely consistent with the information provided by the L3 L2 image. A spatial resolution of 2 nm has been achieved. This is remarkable in comparison to any existing techniques. Energy
