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AFM

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AFM

  1. 1. Get to the point!
  2. 2. AFM - atomic force microscopy A 'new' view of structure (1986) AlGaN/GaN quantum well waveguideCD stamper polymer growth surface atoms on Si single crystal See Vocabulary of Surface Crystallography, Journal of Applied Physics 35, 1306 (1964), by Elizabeth A. Wood
  3. 3. AFM - atomic force microscopy How does the microscope work? Si3N4 tip laser diode photodiode sample mirror Tip scans sample Up and down movement of tip recorded by position sensing photodiode
  4. 4. AFM - atomic force microscopy How does the microscope work? Si3N4 tip laser diode photodiode sample mirror Tip scans sample Up and down movement of tip recorded by position sensing photodiode
  5. 5. AFM - atomic force microscopy How does the microscope work? Si3N4 tip laser diode photodiode sample mirror Two modes of operation
  6. 6. AFM - atomic force microscopy How does the microscope work? Contact mode - short-range interactions (Å) - interatomic forces Tip: 5-20 nm radius, 10-25 µm high, on 50-400 µm cantilever beam
  7. 7. AFM - atomic force microscopy How does the microscope work? Detector system can measure deflections in nm range Tip: 5-20 nm radius, 10-25 µm high, on 50-400 µm cantilever beam Cantilever: low stiffness - can't deform surface Tip contacts surface Tip scans surface: either tip or specimen moved by piezoelectric positioning system over x and y Contact mode - short-range interactions (Å) - interatomic forces
  8. 8. AFM - atomic force microscopy How does the microscope work? Contact mode - short-range interactions (Å) - interatomic forces Two ways - 'constant force' ……. feedback system moves tip in z direction to keep force constant 'constant height'……. no feedback system - usually used when surface roughness small higher scan speeds possible
  9. 9. AFM - atomic force microscopy How does the microscope work? Tapping mode - long-range forces - van der Waals, electrostatic, magnetic Tip vibrates (105 Hz) close to specimen surface (50-150 Å) with amplitude 10-100 nm May at times lightly contact surface Suitable for soft materials
  10. 10. AFM - atomic force microscopy How does the microscope work? Tapping mode Tip vibrates (105 Hz) close to specimen surface (50-150 Å) with amplitude 10-100 nm May at times lightly contact surface When near or on surface, oscillation is damped - tip z position corrected so that vibration amplitude stays constant Tip height Amplitude
  11. 11. AFM - atomic force microscopy From force-distance plot, can get: range & magnitude of attractive & repulsive forces elastic modulus & adhesion energy

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