Electron energy loss spectroscopy slides
- 2. Introduction It is an analytic technique based on the inelastic scattering of fast moving electrons into a thin specimen. It provides structural and chemical information about the specimen using TEM (Tunneling electron microscope. It provides information with high spatial resolution.
- 3. Introduction Each type of interaction between the electron beam and thin specimen produces a characteristic change in energy and angular distribution of scattered electrons. Electron energy-loss spectroscopy offers unique possibilities for advanced materials analysis.
- 4. Every primary electron has one of three possibilities in terms of its interactions with atoms of the specimen.
- 6. Electron Energy Loss Spectrum Three regions Each region arises due to a different group of electron/sample interactions. Region 1 (0 to 10 eV) is the zero-loss region. Region 2 (10 to 60 eV) is the low- loss region. Region 3 (>60 eV), the core-loss region
- 7. EEL Spectrum The zero loss peak It is the main feature in EELS spectra of thin specimens. Originates from electrons that have lost NO energy Width of the zero-loss peak: energy spread of the electron source. Less analytical information about the sample Used to calibrate the Energy scale What is phonon? -- Phonons are lattice vibrations, which are equal to heating the specimen. This effect may lead to a damage of the sample.
- 8. EEL Spectrum Low Loss Area It reflects excitation of plasmons and interband transitions. What is plasmons: Plasmons are longitudinal oscillations of free electrons, which decay either in photons or phonons. It is caused by weakly bonded. It depends on local density of the weakly bonded electrons. The typical lifetime of plasmons is about 10-15 s.
- 9. EEL Spectrum Low Loss Area In the EELS spectra, Plasmon losses always occur, except the ultra-thin specimens. Used to estimate the thickness of the sample. However, when the specimen is quite thick, multiple Plasmon losses will make the straightforward analysis impossible. Thin Thick
- 10. EEL Spectrum Low Loss Area Interband transition: the transition between the conduction and valence bands (electrons and holes) Intraband transitions: the transitions between the quantized levels within the conduction or valence band
- 11. EEL Spectra High Loss Region The most important region of the EELS spectrum for microanalysis. The signal in the core-loss region is very weak relative to that in the zero-loss and low-loss regions. Therefore, the core-loss region of the spectrum is often amplified 50 to 100 times. The peaks, or edges, arise because of interactions between the incident electrons and the inner-shell electrons of atoms in the specimen. When an incident electron ionizes an atom, it produced a specific amount of energy. The amount of energy lost in ionizing the target atoms is the electron energy loss.
- 12. EEL Spectroscopy Magnetic Spectrometer Discriminates the energy loss electrons on the basis of their absolute energy. The signal from the electron energy loss spectrometer can be used to generate an EELS spectrum The spectrometer can be used to produce a compositional map
- 13. Examples Diamond, graphite and fullerene all consist of only carbon. All of these specimens have absorption peaks around 284 eV in EELS corresponding to the existence of carbon atoms. From the fine structure of the absorption peak, the difference in bonding state and local electronic state can be detected.
- 14. Conclusion Within last decade, TEM based EELS has gone a lot of development . EELS very efficient and high sensitivity to most elements. EELS imaging and spectroscopy offers many new opportunities to study fundamental questions of material science atomic resolution. The energy resolution of present-day spectrometers is as high as 1 meV.