1 / 12

CHAPTER 8 (Chapter 11 in text) Characterization of Nanomaterials

CHAPTER 8 (Chapter 11 in text) Characterization of Nanomaterials. Global Methods of Characterization. SURFACE AREA. Assuming spherical particle shape, Surface are per gram (specific surface area), A is given by:. Assuming a density of 3.5g/cm 3.

bcoe
Télécharger la présentation

CHAPTER 8 (Chapter 11 in text) 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. CHAPTER 8 (Chapter 11 in text) Characterization of Nanomaterials

  2. Global Methods of Characterization SURFACE AREA Assuming spherical particle shape, Surface are per gram (specific surface area), A is given by: Assuming a density of 3.5g/cm3

  3. What if it is possible to coat the individual particles with a monolayer of gas molecules? If we knew how much of the gas was adsorbed (physisorped), we can measure the surface area. BET (Brunauer, Emmett and Teller)

  4. X-ray Diffraction • X-ray striking atom = • interaction with electrons • vibrate with frequency of x-ray  re-radiate X-rays of the same frequency (scattered) Constructive interference when angle of incidence = angle of reflection FOR CONSTRUCTIVE INTERFERENCE Bragg’s Law

  5. Titania

  6. Peak width at half height Constant (0.89-1.39)

  7. ELECTRON MICROSCOPY Lowest resolved feature is half of the wavelength of the illuminating waves In light optical systems: (short wavelengths applied 400nm) This leads to 200nm min resolved features. Electron waves have much shorter wavelengths that can be controlled by the accelerating voltage.

  8. Field emission point source accelerated to required level (200-300KeV) Selects electrons of narrow energy band) Focuses electrons at the specimen Picture enlarged Limit electron beam (can adjust brightness and contrast) Some in elastic scatter electrons lose energy to below allowed amount, hence chromatic correction.

  9. Primary electrons hit specimen and majority pass through the sample (after elastic scattering or diffraction). Electrons interacting with specimen transfer parts of their energy to electrons in the specimen, resulting in the emission of: - Secondary electrons - X-rays - Auger electrons - Inelastic scattered electrons passing through the specimen Electrons hit the atom and lose energy Which in turn excites atom and emit x-ray photon Both characteristic of the specimen Auger electron: For low atomic number (Z) specimens, emitted x-ray photon pushes out electron of low energy, electron has energy characteristic of the atom. The higher the energy of the primary x-ray photon (equivalent to higher atomic number), the lower the probability of emission of Auger electron.

  10. THE END

More Related