1 / 66

Characterization of Nanomaterials…

Characterization of Nanomaterials…. And the magnification game!. During today’s notes, there will be a picture every other slide. Try to guess what common household item you’re looking at (it has been magnified quite a bit!!!). 1.

curryj
Download Presentation

Characterization of Nanomaterials…

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Characterization of Nanomaterials… And the magnification game!

  2. During today’s notes, there will be a picture every other slide. Try to guess what common household item you’re looking at (it has been magnified quite a bit!!!)

  3. 1

  4. Observations and Measurement:Studying physical properties related to nanometer size Needs: • Extreme sensitivity • Extreme accuracy • Atomic-level resolution http://www.viewsfromscience.com/ documents/webpages/nanocrystals.html

  5. 2

  6. Characterization Techniques • Structural Characterization • Scanning electron microscopy (SEM) • Transmission electron microscopy (TEM) • X-ray diffraction (XRD) • Scanning probe microscopy (SPM) (includes AFM) • Chemical Characterization • Optical spectroscopy • Electron spectroscopy

  7. 3

  8. Structural Characterization • Techniques are already used for crystal structures • X-Ray Diffraction • Many techniques are already used for studying the surfaces of bulk material (They provide topographical images) • Scanning Probe Microscopy (AFM & STM) • Electron Microscopes DEMO: Lattice model & laser/skewer

  9. 4

  10. Electron Microscopes • Are used to count individual atoms What can electron microscopes tell us? • Morphology • Size and shape • Topography • Surface features (roughness, texture, hardness) • Crystallography • Organization of atoms in a lattice

  11. 5

  12. Crystallography • Crystals have atoms in ordered lattices • Amorphous: no ordering of atoms Crystallography affects properties

  13. 6

  14. Microscopes: History • Light microscopes • 500 X to 1500 X magnification • Resolution of 0.2 µm • Limits reached by early 1930s • Optical microscopes have a resolution limit of 200 nm, meaning they cannot be used to measure objects smaller than 200 nm. (wavelength of visible light ~400 nm). • Electron Microscopes • Use focused beam of electrons instead of light * Transmission Electron Microscope (TEM) * Scanning Electron Microscope (SEM)

  15. 7

  16. Electron Microscopy Steps to form an image: • Stream of electrons formed by an electron source and accelerated toward the specimen • Electrons confined and focused into thin beam • Electron beam focused onto sample • Electron beam affected as interacts with sample • Interactions / effects are detected • Image is formed from the detected signals

  17. 8

  18. Electron Microscopes • Electron Beam • Accelerated and focused using deflection coils • Energy: 200 - 1,000,000 eV • Sample • TEM: conductive, very thin! • SEM: conductive • Detection • TEM: transmitted e- • SEM: emitted e- Source: Virtual Classroom Biology

  19. 9

  20. EM Resolution • Resolution dependent on: • wavelength of electrons () • NA of lens system • Wavelength dependent on: • Electron mass (m) • Electron charge (q) • Potential difference to accelerate electrons (V)

  21. 10

  22. Transmission EM • Magnification: ~50X to 1,000,000X • E-beam strikes sample and is transmitted through film • Scattering occurs • Unscattered electrons pass through sample and are detected http://www.hk-phy.org/atomic_world/tem/tem04_e.html Source: Wikipedia

  23. 11

  24. Scanning EM • Magnification: ~10X to 300,000X • E-beam strikes sample and electron penetrate surface • Interactions occur between electrons and sample • Electrons and photons emitted from sample • Emitted e- or photons detected http://virtual.itg.uiuc.edu/training/EM_tutorial/#segment 1_6 Source: Wikipedia

  25. 12

  26. SEM: Electron Beam Interactions valence e- + + core e- + + • Valence electrons • Inelastic scattering • Can be emitted from sample “secondary electron” Atomic nuclei • Elastic scattering • Bounce back - “backscattered electrons” Core electrons • Core electron ejected from sample; atom excited • To return to ground state, x-ray photon or Auger electron emitted + + nucleus

  27. Electron Spectroscopy • e- or photon strikes atom; ejects core e- • e- from outer shell fills inner shell hole • Energy is released as X-ray or Auger electron EDS: Energy Dispersive X-ray Spectroscopy AES: Auger Electron Spectroscopy Auger e- X-ray Energy Relaxes to ground state Ground state e- emitted; excited state

  28. 13

  29. Electron Spectroscopy Emitted energy is characteristic of a specific type of atom Each atom has its own unique electronic structure and energy levels • AES is a surface analytical technique <1.5 nm deep • AES can detect almost all elements • EDS only detects elements Z > 11 • EDS can perform quantitative chemical analysis

  30. 14

  31. SEM and TEM Comparison • SEM makes clearer images than TEM • SEM has easier sample preparation than TEM • TEM has greater magnification than SEM • SEM has large depth of field • SEM is often paired with detectors for elemental analysis (chemical characterization)

  32. SEM and TEM Data Images • Ag thin film deposited on Si substrate (thermal or e-beam evaporation) • TCNQ (7,7,8,8-tetracyanoquinodimethane) powder and Ag thin film are enclosed in a vacuum glass tube, then heated in a furnace. http://nami.eng.uci.edu/projects/Agtcnq.htm

  33. 15

  34. Chemical Characterization • Optical Spectroscopy • Absorption and Emission • Photoluminescence (PL) • Infrared Spectroscopy (IR or FTIR) • Raman Spectroscopy • Electron Spectroscopy • Energy-Dispersive X-ray Spectroscopy (EDS) • Auger Electron Spectroscopy (AES)

  35. Optical Spectroscopy:Absorbance/Transmittance • Absorbance:electron excited from ground to excited state • Emission:electron relaxed from excited state to ground state • Transmittance:“opposite” of absorbance: A = -log(T) Radiation only penetrates ~50 nm N&N Fig. 8.10

  36. 16

  37. Scanning Probe Microscopy (SPM) • AFM & STM • Measure forces • Many types of forces (dependent on tip) • Electrostatic Force Microscopy • Distribution of electric charge on surface • Magnetic Force Microscopy • Magnetic material (iron) coated tip • magnetized along tip axis • Scanning Thermal Microscopy • Scanning Capacitance Microscopy • Capacity changes between tip and sample

  38. 17

  39. Scanning Tunneling Microscopy (STM) • Developed by Binnig and Rohrer in 1982 • Tunneling • Very dependent on distance between the two metals or semiconductors • By making the distance 1 nm smaller, tunneling will increase 10X

  40. Scanning Tunneling Microscopy (STM) Instrument: Scanning Tip • Extremely sharp • Metal or metal alloys (Tungsten); Conductive • Mounted on a stage that controls position of tip in all three dimensions • Typically kept 0.2 - 0.6 nm from surface Tunneling Current: ~ 0.1 - 10 nA Resolution: 0.01 nm (in X and Y directions) 0.002 nm in Z direction Source: Univ. of Michigan

  41. 18

  42. Scanning Tunneling Microscopy (STM) Constant Current Mode: • As tip moves across the surface, it constantly adjusts height to keep the tunneling current constant • Uses a feedback mechanism • Height is measured at each point Constant Height Mode: • As tip moves across surface, it keeps height constant • Tunneling current is measured at each point

  43. 19

  44. Atomic Force Microscopy (AFM) • Can be used for most samples • Measures: • Small distances: • Van der Waals interactions • Larger distances: • Electrostatic interactions (attraction, repulsion) • Magnetic interactions • Capillary forces (condensation of water between sample and tip) Source: photonics.com Source: Nanosurf

  45. Atomic Force Microscopy (AFM) • Scan tip across surface with constant force of contact • Measure deflections of cantilever http://virtual.itg.uiuc.edu/training/AFM_tutorial/

  46. Scanning Probe Techniques Other tip-surface force microscopes: • Magnetic force microscope • Scanning capacitance microscope • Scanning acoustic microscope Some instruments combine STM and AFM Uses: • Imaging of surfaces • Measuring chemical/physical properties of surfaces • Fabrication/Processing of nanostructures • Nanodevices http://virtual.itg.uiuc.edu/training/AFM_tutorial/

  47. Summary: Techniques used to study nanostructures • Bulk characterization techniques • Information is average for all particles • Surface characterization techniques • Information about individual nanostructures

  48. Mosquito Eye 1

  49. Salt & Pepper 2

  50. Deer Tick Head 3

More Related