Surface and Materials Analysis Techniques


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Surface and Materials Analysis Techniques

  1. 1. Surface and Materials Analysis Techniques Nanotechnology Foothill College
  2. 2. Your Instructor <ul><li>Robert Cormia </li></ul><ul><li>Associate Professor, Foothill College </li></ul><ul><li>Engineering and Nanotechnology </li></ul><ul><li>Background in surface chemistry and surface modification, materials analysis, </li></ul><ul><li>Contact info </li></ul><ul><ul><li> ph. 650.747.1588 </li></ul></ul>
  3. 3. Overview <ul><li>Why characterize? </li></ul><ul><li>Techniques </li></ul><ul><li>Approaches </li></ul><ul><li>Examples </li></ul><ul><li>Where to learn more </li></ul>
  4. 4. Why Characterize? <ul><li>Nanostructures are unknown </li></ul><ul><li>QA/QC of fabrication process </li></ul><ul><li>Failure analysis of products </li></ul><ul><li>Materials characterization </li></ul><ul><li>Process development / optimization </li></ul>
  5. 5. Characterization Techniques <ul><li>Surface analysis </li></ul><ul><li>Image analysis </li></ul><ul><li>Organic analysis </li></ul><ul><li>Structural analysis </li></ul><ul><li>Physical properties </li></ul>
  6. 6. Types of Approaches <ul><li>Failure analysis </li></ul><ul><li>Problem solving </li></ul><ul><li>Materials characterization </li></ul><ul><li>Process development </li></ul><ul><li>QA/QC </li></ul>
  7. 7. Industry Examples <ul><li>Semiconductors and MEMS </li></ul><ul><li>Bionanotechnology </li></ul><ul><li>Self Assembled Monolayers (SAMs) </li></ul><ul><li>Thin film coatings </li></ul><ul><li>Plasma deposited films </li></ul>
  8. 8. Surface Techniques <ul><li>AES – Auger Electron Spectroscopy </li></ul><ul><li>XPS – X-ray Photoelectron Spectroscopy </li></ul><ul><li>SSIMS – Static Secondary Ion Spectroscopy </li></ul><ul><li>TOF-SIMS – Time-Of-Flight SIMS </li></ul><ul><li>LEEDS – Low Energy Electron Diffraction </li></ul>
  9. 9. Surface Analysis <ul><li>Electron Spectroscopies </li></ul><ul><ul><li>XPS: X-ray Photoelectron Spectroscopy </li></ul></ul><ul><ul><li>AES: Auger Electron Spectroscopy </li></ul></ul><ul><ul><li>EELS: Electron Energy Loss Spectroscopy </li></ul></ul><ul><li>Ion Spectroscopies </li></ul><ul><ul><li>SIMS: Secondary Ion Mass Spectrometry </li></ul></ul><ul><ul><li>SNMS: Sputtered Neutral Mass Spectrometry </li></ul></ul><ul><ul><li>ISS: Ion Scattering Spectroscopy </li></ul></ul><ul><ul><li>RBS: Rutherford Back Scattering </li></ul></ul>The Study of the Outer-Most Layers of Materials (<100A)
  10. 10. XPS/AES Analysis Volume
  11. 11. AES - Auger <ul><li>Surface sensitivity </li></ul><ul><li>Microbeam </li></ul><ul><li>Depth profiling </li></ul><ul><li>Elemental composition </li></ul><ul><li>Some chemical bonding </li></ul>
  12. 12. Why the Odd Name?
  13. 13. Surface Sensitivity <ul><li>Escape depth of electrons limits the sample information volume. </li></ul><ul><li>For AES and XPS, this is ~40 Angstroms. </li></ul><ul><li>Angle of sample to detector can be varied to change the surface sensitivity. </li></ul>
  14. 14. Auger Data Formats Raw Data Differentiated Data
  15. 15. Auger Instrumentation PHI Model 660 Scanning Auger Microprobe
  16. 16. Sputtering (Ion Etching) of Samples
  17. 17. Al/Pd/GaN Thin Film Example (cross section)
  18. 18. Al/Pd/GaN Profile Data
  19. 19. Al/Pd/GaN Atomic Concentration Data
  20. 20. XPS / ESCA <ul><li>Surface sensitivity </li></ul><ul><li>Microbeam resolution </li></ul><ul><li>Depth profiling </li></ul><ul><li>Elemental composition </li></ul><ul><li>Some chemical bonding </li></ul>
  21. 21. What is XPS / ESCA? X-ray Photoelectron Spectroscopy (XPS), also known as Electron Spectroscopy for Chemical Analysis (ESCA) is a widely used technique to investigate the chemical composition of surfaces.
  22. 22. X-ray Photoelectron Spectroscopy Small Area Detection X-ray Beam X-ray penetration depth ~1  m. Electrons can be excited in this entire volume. X-ray excitation area ~1x1 cm 2 . Electrons are emitted from this entire area Electrons are extracted only from a narrow solid angle. 1 mm 2 10 nm
  23. 23. The Photoelectric Process <ul><li>XPS spectral lines are identified by the shell from which the electron was ejected (1s, 2s, 2p, etc.). </li></ul><ul><li>The ejected photoelectron has kinetic energy: </li></ul><ul><li>KE=hv-BE-  </li></ul><ul><li>Following this process, the atom will release energy by the emission of an Auger Electron. </li></ul>Conduction Band Valence Band L2,L3 L1 K Fermi Level Free Electron Level Incident X-ray Ejected Photoelectron 1s 2s 2p
  24. 24. Auger Relation of Core Hole <ul><li>L electron falls to fill core level vacancy (step 1). </li></ul><ul><li>KLL Auger electron emitted to conserve energy released in step 1. </li></ul><ul><li>The kinetic energy of the emitted Auger electron is: </li></ul><ul><li>KE=E(K)-E(L2)-E(L3). </li></ul>Conduction Band Valence Band L2,L3 L1 K Fermi Level Free Electron Level Emitted Auger Electron 1s 2s 2p
  25. 25. Surface Analysis Tools SSX-100 ESCA on the left, Auger Spectrometer on the right
  26. 26. XPS Spectrum of Carbon <ul><li>XPS can determine the types of carbon present by shifts in the binding energy of the C(1s) peak. These data show three primary types of carbon present in PET. These are C-C, C-O, and O-C=O </li></ul>
  27. 27. Surface Treatments <ul><li>Control friction, lubrication, and wear </li></ul><ul><li>Improve corrosion resistance (passivation) </li></ul><ul><li>Change physical property, e.g., conductivity, resistivity, and reflection </li></ul><ul><li>Alter dimension (flatten, smooth, etc.) </li></ul><ul><li>Vary appearance, e.g., color and roughness </li></ul><ul><li>Reduce cost (replace bulk material) </li></ul>
  28. 28. Surface Treatment of NiTi Biomedical Devices and Biomedical Implants – SJSU Guna Selvaduray
  29. 29. Surface Treatment of NiTi Biomedical Devices and Biomedical Implants – SJSU Guna Selvaduray
  30. 30. <ul><li>XPS spectra of the Ni(2p) and Ti(2p) signals from Nitinol undergoing surface treatments show removal of surface Ni from electropolish, and oxidation of Ni from chemical and plasma etch. Mechanical etch enhances surface Ni. </li></ul>Surface Treatment of NiTi Biomedical Devices and Biomedical Implants – SJSU Guna Selvaduray
  31. 32. Molecular Self Assembly Figure1: 3D diagram of a lipid bilayer membrane - water molecules not represented for clarity <ul><li>Figure 2: Different lipid model </li></ul><ul><li>top : multi-particles lipid molecule </li></ul><ul><li>bottom: single-particle lipid molecule </li></ul>
  32. 33. Self Assembled Monolayers <ul><li>SAMS – Self Assembled Monolayers </li></ul><ul><li>Cast a film onto a surface from a liquid </li></ul><ul><li>You can also use a spray technique </li></ul><ul><li>Films spontaneously ‘order’ / ‘reorder’ </li></ul><ul><li>Modifying surface properties yields materials with a bulk strength but modified surface interaction phase </li></ul>
  33. 34. The Self-Assembly Process The self-assembly process. An n -alkane thiol is added to an ethanol solution (0.001 M). A gold (111) surface is immersed in the solution and the self-assembled structure rapidly evolves. A properly assembled monolayer on gold (111) typically exhibits a lattice. A schematic of SAM ( n -alkanethiol CH 3 (CH 2 ) n SH molecules) formation on a Au(111) sample.
  34. 35. SAM Technology Platform <ul><li>SAM reagents are used for electrochemical, optical and other detection systems. Self-Assembled Monolayers (SAMs) are unidirectional layers formed on a solid surface by spontaneous organization of molecules. </li></ul><ul><li>Using functionally derivatized C10 monolayer, surfaces can be prepared with active chemistry for binding analytes. </li></ul>
  35. 36. SAM Surface Derivatization <ul><li>Biomolecules (green) functionalized with biotin groups (red) can be selectively immobilized onto a gold surface using a streptavidin linker (blue) bound to a mixed biotinylated thiol / ethylene glycol thiol self-assembled monolayer. </li></ul>
  36. 37. SAMs C10 Imaging with AFM
  37. 38. AES vs. XPS? <ul><li>AES – needs an electrically conductive substrate – metals and semiconductors </li></ul><ul><li>XPS – can analyze polymers and metals </li></ul><ul><li>AES – very small area imaging </li></ul><ul><li>XPS – somewhat small area imaging </li></ul><ul><li>Depth profiling of thin films, faster by AES, but only for conductive materials </li></ul>
  38. 39. Image Analysis <ul><li>AFM </li></ul><ul><ul><li>Atomic Force Microscopy </li></ul></ul><ul><li>SEM - EDX </li></ul><ul><ul><li>Scanning Electron Microscopy </li></ul></ul><ul><ul><li>Energy Dispersive Wavelength X-Ray </li></ul></ul><ul><li>TEM </li></ul><ul><ul><li>Transmission Electron Microscope </li></ul></ul>
  39. 40. Seeing the Nano World <ul><li>Because visible light has wavelengths that are hundreds of nanometers long we can not use optical microscopes to see into the nano world. Atoms are like boats on a sea compared to light waves. </li></ul>
  40. 41. AFM <ul><li>Atomic Force Microscope (AFM) </li></ul><ul><li>Scanning Tunneling Microscope (STM) </li></ul><ul><li>Scanning Probe Microscopy (SPM) </li></ul><ul><li>Magnetic Force Microscopy (MFM) </li></ul><ul><li>Lateral Force Microscopy (LFM) </li></ul>
  41. 42. AFM Instrumentation PNI Nano-R AFM Instrumentation as used at Foothill College
  42. 43. What is an SPM? <ul><li>An SPM is a mechanical imaging instrument in which a small, < 1 µm, probe is scanned over a surface. By monitoring the motion of the probe, the surface topography and/or images of surface physical properties are measured with an SPM . </li></ul>z y z
  43. 44. A Family of Microscopes AFM SPM (air, liquid, vacuum) STM Topography Spectroscopy Lithography EChem. BEEM SNOM(NSOM) Aperture Aperatureless Reflection Transmission Contact Modes Topography LFM, SThM Lithography AC Modes Topography MFM, EFM SKPM Others EChem
  44. 45. Many Imaging Modes <ul><li>AC – Close Contact Mode - Soft Samples - Sharp Probe <20nm </li></ul>DC – Contact Mode - Hard Samples - Probes > 20 nm Material Sensing Modes Lateral Force Vibrating Phase
  45. 46. Crystal Scanner <ul><li>Point and Scan™ </li></ul><ul><ul><ul><li>Crystal Sensor </li></ul></ul></ul><ul><ul><ul><li>Stage Automation </li></ul></ul></ul><ul><ul><ul><li>Software </li></ul></ul></ul>
  46. 47. AFM Stage Assembly AFM Stage for sample orientation, with scanner and optics Z Motion Control xyz scanner XY Motion Control AFM Force Sensor Optic
  47. 48. AFM Light Lever – Force Sensor Signal out Sample When the cantilever moves up and down, the position of the laser on the photo detector moves up and down. Differential Amplifier
  48. 49. High Resolution Video Microscope Scanner Sample Puck X-Y Stage (in granite block) Light Lever Crystal Nano-R™ Stage
  49. 50. High Resolution Video Microscope Software control of video microscope functions Optical Microscope
  50. 51. Easy Sample Load Load and Unload Sample Positions Sample Puck
  51. 52. Video Optical Microscope Laser Alignment Feature Location
  52. 53. Information Technology – DVD
  53. 54. Consumer – Razor Blade Cutting edge of razor blade 4 X 4 µ
  54. 55. Consumer Applications 100 X 100 µ AFM is used to understand the glossing characteristics of paper surfaces
  55. 56. Metrology of Metals <ul><li>AFM can be used to understand surface morphology. </li></ul><ul><li>This material was prepared using a spray / cast technique. </li></ul>
  56. 57. Metrology of Structures <ul><li>The pattern and depth of this micro lens can be determined using an AFM. </li></ul><ul><li>This helps in both development and process control. </li></ul>
  57. 58. NanoMechanics- MEMS
  58. 59. SEM Techniques <ul><li>Scanning Electron Microscopy (SEM) </li></ul><ul><li>Wavelength Dispersive X-Ray (WDX) </li></ul><ul><li>Primary electron imaging </li></ul><ul><li>Secondary electron imaging </li></ul><ul><li>X-ray (WDX) elemental mapping </li></ul>
  59. 60. SEM Principles of Operation <ul><li>In an electron microscope, electrons are accelerated in a vacuum until their wavelength is extremely short. The higher the voltage the shorter the wavelengths. </li></ul><ul><li>Beams of these fast-moving electrons are focused on an object and are absorbed or scattered by the object so as to form an image on an electron-sensitive photographic plate </li></ul>
  60. 61. <ul><li>Electron beam </li></ul><ul><li>Electron gun </li></ul><ul><li>Anode </li></ul><ul><li>Magnetic lens </li></ul><ul><li>Scanning coils </li></ul><ul><li>Secondary electron detector </li></ul><ul><li>Stage and specimen </li></ul> SEM Principles of Operation
  61. 62. SEM Principles of Operation
  62. 63. SEM Principles of Operation
  63. 64. SEM Imaging <ul><li>Imaging of microscopic scale objects in high resolution </li></ul>
  64. 65. SEM Instrument
  65. 66. SEM – AFM Comparison SEM AFM Wide range of sample roughness True 3D image Operated in low to high vacuum Vacuum, Air or Liquid
  66. 67. Imaging Applications <ul><li>Imaging individual atoms. </li></ul><ul><li>Imaging of surface materials. </li></ul><ul><li>Imaging of nanotubes. </li></ul>
  67. 68. TEM Diagram <ul><li>The TEM works like a slide projector. A beam of electron is shined though the surface with the transmitted electrons projector on a screen. </li></ul>
  68. 69. TEM in Use <ul><li>The drawback is the sample must be very thin for the electrons to pass through and the sample has to be able to withstand the high energy electrons and a strong vacuum. </li></ul>
  69. 70. X-Ray Diffraction <ul><li>X-Ray diffraction is an important tool in the characterization of nanostructures. </li></ul><ul><li>It is the principle means by which the atomic structure of materials can be determined. </li></ul>
  70. 71. Summary of Techniques <ul><li>Surface techniques </li></ul><ul><ul><li>AES </li></ul></ul><ul><ul><li>ESCA / XPS </li></ul></ul><ul><li>Deeper techniques </li></ul><ul><ul><li>RBS and PIXE </li></ul></ul><ul><li>Ion techniques </li></ul><ul><ul><li>SIMS </li></ul></ul>
  71. 72. Materials Analysis Review <ul><li>What is it you need to know? </li></ul><ul><li>What volume of material? </li></ul><ul><li>Elemental information? </li></ul><ul><li>Chemical information? </li></ul><ul><li>Molecular information? </li></ul><ul><li>Structural information? </li></ul>
  72. 73. Analyst Skills <ul><li>Instrument skills </li></ul><ul><li>Analytical reasoning ability </li></ul><ul><li>Materials science </li></ul><ul><li>Process knowledge </li></ul><ul><li>Industry knowledge </li></ul>
  73. 74. Commercial Laboratories <ul><li>Evans Analytical Group </li></ul><ul><li>Nanolab Technologies </li></ul><ul><li>Center for Microanalysis of Materials </li></ul><ul><li>Stanford Nanofabrication Facility </li></ul><ul><li>Exponent </li></ul><ul><li>Balaz Analytical Laboratories </li></ul>
  74. 75. Summary <ul><li>Nanostructures are very small </li></ul><ul><li>You need tools that ‘characterize atoms’ and the world (neighborhood) of an atom </li></ul><ul><li>Composition and chemistry </li></ul><ul><li>Molecular bonding information </li></ul><ul><li>Structural information </li></ul><ul><li>Film thickness especially </li></ul>