Presented by:                                                                                                       Zaahir...
Background 1905 Photoelectric effect      discovered by Albert      Einstein        Nobel Prize 1961   Photoemission as an...
X-Rays Irradiate the sample surface, hitting        The core e-s are local close to the nucleus and                      ...
X-Rays Irradiate the sample surface, hitting        The core e-s are local close to the nucleus and                      ...
Spectroscopy Spectroscopy- the study of the light from an object. Spectrometer- an instrument which spreads out light ma...
Working Equation Because the energy of an X-ray  with particular wavelength is  known, the electron binding  energy of ea...
XPS Instrument                                                       XPS is also known as ESCA                           ...
 XPS works by irradiating atoms of a surface of  any solid material with X-Ray while  simultaneously measuring the kineti...
XPS Instrument     X-Ray Source             Ion Source     SIMS AnalyzerSample introductionChamber    University of Texas ...
Sample Introduction Chamber The sample will be introduced  through a chamber that is in  contact   with  the   outside  e...
Diagram of the Side View of XPS System                              X-Ray source                                         I...
How Does XPS Technology Work? A monoenergetic x-ray beam        Ultrahigh vacuum environment  emits photoelectrons from ...
Why Does XPS Need UHV? Contamination of surface    XPS is a surface sensitive technique.         Contaminates will prod...
X-Rays on the Surface               Electron without collision   X-Ray               Electron with collisionThe noise sign...
What e-s can the Cylindrical Mirror            Analyzer Detect? The CMA not only can detect electrons from the irradiatio...
X-Rays and Auger Electrons When the core electron leaves a vacancy an electron of higher energy will     move down to occ...
Cylindrical Mirror Analyzer (CMA)                                                     Electron Pathway through the CMA    ...
KE versus BE                                                    Noise                                                     ...
XPS Spectrum   The XPS peaks are sharp.   In a XPS graph it is possible to see Auger electron peaks.   The Auger peaks ...
Identification of XPS Peaks The plot has characteristic peaks for each element found in the surface  of the sample. Ther...
Use of XPS Technology   Elements and the quantity of those elements that are present within the top 1-12 nm of the sample...
References Dr.William Durrer for explanations on XPS  technique, Department of Physics at UTEP. www.uksaf.com www.casax...
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Xps (x ray photoelectron spectroscopy)

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X-RAY PHOTO ELECTRON SPECTROSCOPY

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Xps (x ray photoelectron spectroscopy)

  1. 1. Presented by: Zaahir salam M.Tech NS &TUniversity of Texas at El Paso, Physics DepartmentFront view of the Phi 560 XPS/AES/SIMS UHV System
  2. 2. Background 1905 Photoelectric effect discovered by Albert Einstein Nobel Prize 1961 Photoemission as an analytical tool demonstrated by Kai Siegbahn (Electron Spectroscopy for Chemical Analysis – ESCA) Nobel Prize
  3. 3. X-Rays Irradiate the sample surface, hitting The core e-s are local close to the nucleus and have binding energies characteristic of their the core electrons (e-) of the atoms. particular element. The X-Rays penetrate the sample to a The core e-s have a higher probability of matching the energies of AlK and MgK. depth of the order of a micrometer. Valence e- Core e- Atom Useful e- signal is obtained only from a depth of around 10 to 100 Å on the surface. The X-Ray source produces photons with certain energies:  MgK photon with an energy of 1253.6 eV  AlK photon with an energy of 1486.6 eV
  4. 4. X-Rays Irradiate the sample surface, hitting The core e-s are local close to the nucleus and have binding energies characteristic of their the core electrons (e-) of the atoms. particular element. The X-Rays penetrate the sample to a The core e-s have a higher probability of matching the energies of AlK and MgK. depth of the order of a micrometer. Valence e- Core e- Atom Useful e- signal is obtained only from a depth of around 10 to 100 Å on the surface. The X-Ray source produces photons with certain energies:  MgK photon with an energy of 1253.6 eV  AlK photon with an energy of 1486.6 eV
  5. 5. Spectroscopy Spectroscopy- the study of the light from an object. Spectrometer- an instrument which spreads out light making a spectra. Spectra- range of electromagnetic energy separated by wavelength.
  6. 6. Working Equation Because the energy of an X-ray with particular wavelength is known, the electron binding energy of each of the emitted electrons can be determined by using an equation that is based on the work of Ernest Rutherford (1914): KE=hv-BE-Ø where BE is the binding energy of the electron, hv is the energy of the X-ray photons being used, KE is the kinetic energy of the electron as measured by the instrument and φ is the work function of the spectrometer (not the material).
  7. 7. XPS Instrument  XPS is also known as ESCA (Electron Spectroscopy for Chemical Analysis).  It is a quantitative spectroscopic technique that measures the  Elemental composition  Empirical formula  Chemical state  Electronic state  The technique is widely used because it is very simple to use and the data is easily analyzed. University of Texas at El Paso, Physics DepartmentFront view of the Phi 560 XPS/AES/SIMS UHV System
  8. 8.  XPS works by irradiating atoms of a surface of any solid material with X-Ray while simultaneously measuring the kinetic energy and number of electrons that escape from the top 1 to 10 nm of the material being analyzed The XPS is controlled by using a computer system. The instrument uses different pump systems to reach the goal of an Ultra High Vacuum (UHV) environment. The Ultra High Vacuum environment will prevent contamination of the surface and aid an accurate analysis of the sample. University of Texas at El Paso, Physics Department Front view of the Phi 560 XPS/AES/SIMS UHV System and the computer system that controls the XPS.
  9. 9. XPS Instrument X-Ray Source Ion Source SIMS AnalyzerSample introductionChamber University of Texas at El Paso, Physics DepartmentSide view of the Phi 560 XPS/AES/SIMS UHV System
  10. 10. Sample Introduction Chamber The sample will be introduced through a chamber that is in contact with the outside environment It will be closed and pumped to low vacuum. After the first chamber is at low vacuum the sample will be introduced into the second chamber in which a UHV environment exists. First Chamber Second Chamber UHV
  11. 11. Diagram of the Side View of XPS System X-Ray source Ion source Detector SIMS Analyzer Axial Electron GunSample introduction Chamber Sample Holder sample CMA Roughing Pump Slits Ion Pump
  12. 12. How Does XPS Technology Work? A monoenergetic x-ray beam  Ultrahigh vacuum environment emits photoelectrons from the to eliminate excessive surface surface of the sample. contamination. The X-Rays either of two  Cylindrical Mirror Analyzer energies: (CMA) measures the KE of  Al Kα (1486.6eV) emitted e-s.  Mg Kα(1253.6 eV)  The spectrum plotted by the The x-ray photons The computer from the analyzer penetration about a micrometer signal. of the sample The XPS spectrum contains  The binding energies can be information only about the top determined from the peak 10 - 100 Ǻ of the sample. positions and the elements present in the sample identified.
  13. 13. Why Does XPS Need UHV? Contamination of surface  XPS is a surface sensitive technique.  Contaminates will produce an XPS signal and lead to incorrect analysis of the surface of composition. The pressure of the vacuum system is < 10-9 Torr Removing contamination  To remove the contamination the sample surface is bombarded with argon ions (Ar+ = 3KeV).  heat and oxygen can be used to remove hydrocarbons
  14. 14. X-Rays on the Surface Electron without collision X-Ray Electron with collisionThe noise signal comesfrom the electrons thatcollide with otherelectrons of differentlayers. The collisionscause a decrease inenergy of the electronand it no longer willcontribute to thecharacteristic energy ofthe element.
  15. 15. What e-s can the Cylindrical Mirror Analyzer Detect? The CMA not only can detect electrons from the irradiation of X-Rays, it can also detect electrons from irradiation by the e- gun. The e- gun it is located inside the CMA while the X-Ray source is located on top of the instrument. The only electrons normally used in a spectrum from irradiation by the e- gun are known as Auger e-s. Auger electrons are also produced by X- ray irradiation.
  16. 16. X-Rays and Auger Electrons When the core electron leaves a vacancy an electron of higher energy will move down to occupy the vacancy while releasing energy by:  photons  Auger electrons Each Auger electron carries a characteristic energy that can be measured. 2 e- of high energy that Free e- 3 will occupy the vacancy of the core levele-released toanalyze 4 1 e- gun e- Vacancy 1, 2, 3 and 4 are the order of steps in which the e-s will move in the atom when hit by the e- gun.
  17. 17. Cylindrical Mirror Analyzer (CMA) Electron Pathway through the CMA Slit The electrons ejected will pass X-Rays through a device called a CMA. Source 0V 0V The CMA has two concentric metal cylinders at different voltages. +V +V +V +V One of the metal cylinders will have a positive voltage and the Sample Holder other will have a 0 voltage. This will 0V 0V create an electric field between the two cylinders. The voltages on the CMA for XPS and Auger e-s are different.
  18. 18. KE versus BE Noise N = noise No. of electronsNo. of electrons N4 N3 N2 N1 Binding energy Binding energy (eV) Ntot= N1 + N2 + N3 + N4 KE can be plotted depending on BE e- will collide with other e- from top Each peak represents the amount of layers, decreasing its energy to e-s at a certain energy that is contribute to the noise, at lower characteristic of some element. kinetic energy than the peak . BE increase from right to left The background noise increases with BE because the SUM of all 1000 eV 0 eV noise is taken from the beginning of the analysis. KE increase from left to right
  19. 19. XPS Spectrum The XPS peaks are sharp. In a XPS graph it is possible to see Auger electron peaks. The Auger peaks are usually wider peaks in a XPS spectrum. Aluminum foil XPS Spectrum Auger Spectrum O 1s Characteristic of Auger graphsO Auger The graph goes up as KE increases. O because of Mg source C Al Al O 2s
  20. 20. Identification of XPS Peaks The plot has characteristic peaks for each element found in the surface of the sample. There are tables with the KE and BE already assigned to each element. After the spectrum is plotted you can look for the designated value of the peak energy from the graph and find the element present on the surface.
  21. 21. Use of XPS Technology Elements and the quantity of those elements that are present within the top 1-12 nm of the sample surface. Detects all elements with an atomic number (Z) of 3 (lithium) and above. It cannot detect hydrogen (Z = 1) or helium (Z = 2) because the diameter of these orbitals is so small, reducing the catch probability to almost zero. Chemical state analysis of the surface of polymers readily reveals the presence or absence of the chemical states of carbon known as: carbide (C 2-), hydrocarbon (C-C), alcohol (C-OH), ketone (C=O), organic ester (COOR), carbonate (CO3), fluoro-hydrocarbon (CF2-CH2), trifluorocarbon (CF3). Is routinely used to analyze  Inorganic compounds.  Metal alloys.  Semiconductors.  Polymers.  Catalysts, glasses, ceramics, paints, papers, inks, woods, plant parts, make-up, teeth, bones, medical implants, bio-materials, viscous oils, glues, ion modified materials and many others. Organic chemicals are not routinely analyzed by XPS because they are readily degraded by either the energy of the X-rays or the heat from non-monochromatic X-ray sources.
  22. 22. References Dr.William Durrer for explanations on XPS technique, Department of Physics at UTEP. www.uksaf.com www.casaxps.com www.nwsl.net XPS instrument from the Physics Department.
  23. 23. Thank You
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