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AFM (Atomic Force Microscopy)

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AFM (Atomic Force Microscopy)

  1. 1. ATOMIC FORCE MICROSCOPY SUBMITTED TO DR. Shazia Abrar SUBMITTED BY Sohaib Hasnain PROGRAMME M.Phil SUBJECT : Instrumental Analysis for Process Industries
  2. 2. History  Atomic force microscopy (AFM) was developed when people tried to extend STM technique to investigate the electrically non-conductive materials, like proteins.  In 1986, Binnig and Quate demonstrated for the first time the ideas of AFM, which used an ultra- small probe tip at the end of a cantilever.
  3. 3. What isAFM  AFM is a type of scanning probe microscopy (SPM), with demonstrated resolution on the order of fractions of a nanometer, more than 1000 times better than the optical diffraction limit.  The information is gathered by "feeling" or "touching" the surface with a mechanical probe
  4. 4.  AFM provides a 3D profile of the surface on a nanoscale, by measuring forces between a sharp probe and the surface.  The AFM has three major abilities: force measurement, imaging, and manipulation.  It is powerful because an AFM can generate images at atomic resolution with angstrom scale resolution height information, with minimum sample preparation.
  5. 5. Principle Of AFM  Surface Sensing An AFM uses a cantilever with a very sharp tip to scan over a sample surface. As the tip approaches the surface, the close-range, attractive force between the surface and the tip cause the cantilever to deflect towards the surface. However, as the cantilever is brought even closer to the surface, such that the tip makes contact with it, increasingly repulsive force takes over and causes the cantilever to deflect away from the surface.
  6. 6.  Detection Method A laser beam is used to detect cantilever deflections towards or away from the surface. By reflecting an incident beam off the flat top of the cantilever, any cantilever deflection will cause slight changes in the direction of the reflected beam. A position-sensitive photo diode (PSPD) can be used to track these changes. Thus, if an AFM tip passes over a raised surface feature, the resulting cantilever deflection (and the subsequent change in direction of reflected beam) is recorded by the PSPD.
  7. 7.  Imaging An AFM images the topography of a sample surface by scanning the cantilever over a region of interest. The raised and lowered features on the sample surface influence the deflection of the cantilever, which is monitored by the PSPD. The AFM can generate an accurate topographic map of the surface features.
  8. 8. How Are Force Measured  The probe is placed on the end of a cantilever (which one can think of as a spring).  The amount of force between the probe and surface is dependant on the spring constant (stiffness of the cantilever and the distance between th probe and the sample surface.  This force can be described using Hooke’s Law: F= -k·x
  9. 9. F = Force k = spring constant x = cantilever deflection • If the spring constant of cantilever (typically ~ 0.1-1 N/m) is less than surface, the cantilever bends and the deflection is monitored. •This typically results in forces ranging from nN (10 ) to µN (10-6) in the open air.
  10. 10. What Are Probes Made Of? They are generally made up of Silicon or Si3N4. Probes may be coated with other materials for the addiontal SPM application such as CFM(Chemical force Microscopy) and MFM(Magnetic Force Microscopy)
  11. 11. Why is different from optical microscopy  No lenses are needed.  No need of light source to illuminate the sample.  No eyeplece to look through the sample.  Itself imaging device technique which is able to measure the very small forces b/w the atom or molecules
  12. 12. Why AFM is better than STM  It give information about the conducting and non-conducting surfaces.  3-D image of surfaces are obtained by this techniques.  Sample can be analyzed in open Air.
  13. 13. Application The AFM has been applied to problems in a wide range of disciplines of the natural sciences, including solid-state physics, semiconductor science and technology, molecular engineering, polymer chemistry and physics, surface chemistry, molecular biology, cell biology, and medicine. It gives information about the toughness, roughness and smoothness value of surface.
  14. 14.  Applications in the field of solid state physics include (a) the identification of atoms at a surface, (b) the evaluation of interactions between a specific atom and its neighboring atoms.  In molecular biology, AFM can be used to study the structure and mechanical properties of protein complexes and assemblies. For example, AFM has been used to image microtubules and measure their stiffness.
  15. 15.  In cellular biology, AFM can be used to attempt to distinguish cancer cells and normal cells based on a hardness of cells, and to evaluate interactions between a specific cell and its neighboring cells in a competitive culture system.  Soft surfaces are analyzed by this technique without damaging it like Lipids.  Covalent bond strength is measured by this Technique
  16. 16. References  http://www.parkafm.com  www.nanoscience.com  http://www.nanoscience.gatech.edu  MikroMasch http://www.spmtips.com/products/cantilevers/datashe ets/sc11/ (Accessed 11/06/06).  Nanosensors Homepage http://www.nanosensors.com (Accessed 11/06/06).  MikroMasch http://www.spmtips.com/products/cantilevers/datashe ets/hi-res- w/ (Accessed 1/26/07).  NanoWizard AFM Handbook
  17. 17.  The Hessian Blob Algorithm: Precise Particle Detection in Atomic Force Microscopy Imagery.  Atomic-resolution three-dimensional hydration structures on a heterogeneously charged surface