atomic force microscopy AFM
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Atomic force microscopy (AFM) is a technique used to image surfaces at the nanoscale. The document outlines the history, components, operating modes, applications, and limitations of AFM. It discusses how AFM works by scanning a sample with a sharp tip attached to a flexible cantilever, measuring deflections to construct 3D surface images. Three common modes are contact, non-contact, and tapping mode. AFM can image a variety of materials and is useful for measuring surface roughness, adhesion, and other nanoscale properties. While resolution is limited by tip size, continued improvements aim to develop sharper tips and less damaging probes.
atomic force microscopy AFM
- 1. Prepared by Amare Worku (MSC in Tex. Eng.) November 2015 Seminar Title on: Atomic Force Microscopy (AFM)
- 3. Contents/ Outlines 1. Background and History 2. General Applications 3. How Does AFM Work? 4. Parts of AFM 5. THREE Modes: Contact mode, Non-contact mode, Tapping Mode
- 4. Contents/ Outlines 6. What are the limitations of AFM? 7. Advantages and Disadvanteges of AFM 8. The future of AFM
- 5. 1. Background and History Scanning tunneling microscopy 1981 – Swiss scientists Gerd Binnig and Heinrich Rohrer Atomic resolution, simple 1986 – Nobel prize
- 6. 2. General Applications 1 Materials Investigated: Thin and thick film coatings, ceramics, composites, glasses, synthetic and biological membranes, metals, polymers, and semiconductors. 3 AFM can image surface of material in atomic resolution and also measure force at the nano-Newton scale. 2 Used to study phenomena of: Abrasion, corrosion, etching (scratch), friction, lubricating, plating, and polishing.
- 8. 3. How Does AFM Work?
- 9. Tip vibrates (105 Hz) close to specimen surface (50-150 Å) with amplitude 10-100 nm, May at times lightly contact surface 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. 3. Continued…
- 11. Hooke’s Law x= the vertical displacement of the end of the cantilever. k = the cantilever spring constant F = the force acting On the cantilever F = -kx Hooke’s Law
- 12. 3. 1 Experimental Procedures Sample preparation Thin layer of wax on steel disk Measuring 3-D Imaging Manipulating/Analyzing
- 14. Scanning the Sample/measure Tip brought within nanometers of the sample (van der Waals) Radius of tip limits the accuracy of analysis/ resolution Stiffer cantilevers protect against sample damage because they deflect less in response to a small force This means a more sensitive detection scheme is needed
- 15. Data Analysis Morphology Characterization/ Sub microscopic level Surface roughness quantification Physical properties/ Swelling, cohesiveness, smoothness Will be analyzed
- 16. AFM Tips
- 17. 4. Parts of AFM 1. Laser – deflected off cantilever 2. Mirror –reflects laser beam to photo detector 3. Photo detector –dual element photodiode that measures differences in light intensity and converts to voltage 4. Amplifier 5. Register 6. Sample 7. Probe –tip that scans sample made of Si 8. Cantilever –moves as scanned over sample and deflects laser beam
- 19. 1. Z-Piezo Calibration: by scanning a sample of known height (calibration grating) In contact mode 2. Cantilever deflection calibration 3. Cantilever stiffness, k, calibration Calibration Every month
- 20. 5. THREE Modes: Contact mode, Non-contact, mode, Tapping Mode A.Contact Mode Mode; hard, stable samples in air or liquid B. Non-Contact Mode: non- invasive sampling. C. Tapping (Intermittent contact): No shear and damaging samples
- 21. A. Contact Mode Measures repulsion between tip and sample Force of tip against sample remains constant Feedback regulation keeps cantilever deflection constant Voltage required indicates height of sample Problems: excessive tracking forces applied by probe to sample
- 22. B. Non-Contact Mode Measures attractive forces between tip and sample Tip doesn’t touch sample Van der Waals forces between tip and sample detected Problems: Can’t use with samples in fluid Used to analyze semiconductors Doesn’t degrade or interfere with sample- better for soft samples
- 23. C. Tapping (Intermittent- Contact) Mode Tip vertically oscillates between contacting sample surface and lifting of at frequency of 50,000 to 500,000 cycles/sec. Oscillation amplitude reduced as probe contacts surface due to loss of energy caused by tip contacting surface Advantages: overcomes problems associated with friction, adhesion, electrostatic forces More effective for larger scan sizes
- 25. 6. What are the limitations of AFM? AFM imaging is not ideally sharp
- 26. 7. Advantages and Disadvanteges of AFM
- 27. Comparison b/n AFM vs. SEM
- 28. 8. The future of AFM Sharper tips by improved micro-fabrication processes: (tip – sample interaction tends to distort or destroy soft biological molecules ) development of more flexible cantilever springs and less damaging and non-sticky probes needed
- 29. Nano-Identification on Fiber surface MMF Viscose Rayon Cotton
- 30. TYPES OF FIBER UNDER AFM AFM topographical scan of a glass surface. Clean glass surface: roughness ~ 0.8 nm
- 31. AFM images of the samples: a)Cotton topography and phase (5 μm × 5 μm), b) Cotton topography and phase (2 μm × 2 μm),
- 32. c)Wool topography and phase (5 μm × 5 μm) d)Wool topography and phase (2 μm × 2 μm).
- 33. AFM images of the samples: a) PET, b)Antistatic PET, c) Antibacterial PET.
- 34. AFM images of the cross sections of the fibers: a)Antibacterial PET friction, b)Antistatic PET friction.
- 36. In general
- 37. LOGO