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/cm 3

3. BET (Brunauer, Emmett and Teller) 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.

4. X-ray Diffraction FOR CONSTRUCTIVE INTERFERENCE Bragg’s Law 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

7. Titania

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

9. 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.

10. 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. Field emission point source accelerated to required level (200-300KeV)

11. 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.

12. THE END