Presentation on X-ray Photoelectron Spectroscopy.pptx
- 2. It is also known as electron spectroscopy for chemical analysis ( ESCA). It is generally regarded as most important key technique for surface characterisation and analysis of biomedical polymers. It is one of the most widely used surface techniques which allows determination of atomic composition of sample in non destructive manner. It gives chemical information such as binding constants , oxidation states and speciation . It provides a total element analysis except for hydrogen and helium .
- 3. XPS is used to characterise the surfaces of diverse materials such as inorganic compounds, semiconductors , organic compounds and thin films and coatings on natural and engineered materials. XPS is application of photoelectric effect described by Einstein in 1905. XPS are obtained by irradiating a solid surface with a beam of X rays and measuring kinetic energy of electrons that are emitted from the top 1-10 nm of material. Spectrum is recorded by counting ejected electrons over a range of Kinetic energies. The energies and intensities of photoelectron peaks enable identification and qualification of all surface elements.
- 4. Based on irradiation of sample to soft X rays and then analysing energy of released electrons. Penetrating depth of these photons is restricted to few microns. XPS spectrum contains information about only top 10-100 augnstron. This interaction between soft photons and surface atoms occur resulting in emission of photoelectrons. Ultrahigh vacuum eliminates excessive surface contamination Energy analyzer measures the K.E of emitted es. Core electrons eject with kinetic energy K.E are ejected by incident X ray. The K.E of these ejected electrons can be calculated by using following relation:
- 5. Ekinetic = Ephoton (ﾎ) - Ebinding - Energy diagram demonstrating the energetics of the photoelectron effect
- 6. Spectrum plotted by the computer from the analyzer signal. The binding energies can be determined from peak position and elements present in sample identified.
- 7. The main components of XPS system are: Source of X ray( usually Al k alpha or M g K alpha anode radiation is used) Ultrahigh vacuum chamber with mu- magnetic shielding Electron collection lens Electron energy analyzer Electron detector system Sample introduction chamber Sample mounts Sample stage with ability to heat and cool Set of stage manipulators
- 9. Limited for mapping the composition of a surface It has little lateral resolution across a surface because diameter of X ray is relatively large to distance of importance in surface mapping. It is also not effective in obtaining depth profiles because it must be combined with ion sputtering to remove layers of material and date acquisition is slow.
- 10. Non-destructive analysis of materials. Ability to detect all elements except for H and He. XPS surveys will obtain inventories of all elements present on material surfaces. Small shifts in binding energies can be measured (~0.1 eV) that provides information about the bound state of elements present. these data are obtained by collecting spectra over limited energy range to reveal the fine structure of XPS spectra for a given element. Surface-sensitive analysis to determine composition of material surfaces a few atomic layers thick (~ 10 nm). Surface contaminants are usually easily removed using ion (Ar) beam sputtering methods. Semi-quantitative analyses can be obtained within 賊 10% atomic concentration.
- 11. XPS is widely used in characterization of both natural and engineered materials. Studies of surface-mediated reactions such as sorption, catalysis, REDOX, dissolution/preciptitation Material Science Polymers Medical Devices Thin Films and Coatings Microelectronic Devices Medical and Biological Samples Geologic materials