Atomic force microscopy

References
Atomic force Microscopy by Peter Eaton and Paul West

1. Atomic Force Microscopy Sonu 1411NT11 1

2. Atomic Force Microscopy AFM works by scanning a probe over the sample surface, building up a map of the height or topography of the surface as it goes along. 2

3. Background of AFM In 1929 S hmalz described Stylus Profiler. In 1950 Becker suggested oscillating the probe that approach contact with surface. In 1971 Young described non contact type Stylus Profiler. In 1981 Binning and Rohrer described STM. AFM Invented in 1986 by Binning. 3

4. Different From other Microscopy No need of focusing, illumination, Depth of field. It also have height information that make it simple to quickly measure the height, volume, width of any feature in the sample. It physically feels the sample’s surface with a sharp probe, building up a map of the height of samples surface. It provides single atomic level structure so provide high resolution. 4

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6. The first AFM instrument built by Binning , Quate and Gerber The STM with a lever made by carefully gluing a tiny diamond onto the end of a spring made of a thin strip of gold. This was the cantilever of the first AFM. 6

7. AFM Instrument The main components of an AFM are 1. Microscope stage – Moving AFM tip, Sample holder, Force Sensor 2.Control electronics - Optical Microscope, Vibration controller 3. Computer - The control electronics usually takes the form of a large box interfaced to both the microscope stage and the computer. 7

8. Basic concept of AFM Instrumentation The piezoelectric transducer moves the tip over the sample surface, the force transducer senses the force between the tip and the surface, and the feedback control feeds the signal from the force transducer back in to the piezoelectric, to maintain a fixed force between the tip and the sample. 8

9. Piezoelectric transducers Convert electrical potential into mechanical motion. amorphous lead barium titanate, PdBaTiO3 or lead zirconate titanate, Pb [ZrxTi1–x]O3,0<x<1 9

10. Force transducers It may be constructed that measure forces as low as 10 piconewtons. 10

11. Force Sensor Optical lever sensor the End of the cantilever bends the position of the laser spot on the detector changes. As the cantilever detector distance is large a small movement of the cantilever causes a large change in the laser spot position at the detector. 11

12. Feedback control Feedback control is used to maintain a set force between the probe and the sample. 12

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14. Challenges of AFM regarding Design Requirement of sharp probe for high resolution. The force between probe and sample should be 1nN or less than that. The feedback controller should have a rapid control so adjust topographic film can be formed. A high speed computer that can generate the images in real time. Vibration free stage. 14

15. Scanning Modes There are different imaging modes of AFM Contact Mode Non Contact Mode Tapping Mode 15

16. Modes of Operation in AFM Mode of Operation Force of Interaction Contact mode strong(repulsive) - constant force or constant Height Non-contact mode weak (attractive) - vibrating probe Tapping mode strong (repulsive) - vibrating probe 16

17. Contact Mode High Resolution Images. Tip of the probe always touching the sample. F astest of all the topographic modes. Because of repulsive forces tip and sample may damage. Sensitive to the nature of sample. Not good for soft samples. 17

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19. Non Contact Mode Signal-to-noise benefits associated with modulated signals. Oscillating modes can measure images with a small probe–sample force . 19

20. Tapping Mode No Capillary effect. Amplitude signals are used in feedback. Used for Imaging in Air. 20

21. Limitations AFM can only image a maximum height on the order of 10-20 micrometers and a maximum scanning area of about 150×150 micrometers. The scanning speed of an AFM is also a limitation. Highly Dependent on AFM probes. 22

22. Applications It can image far more biological processes, such as imaging of proteins. Any sample like ceramic material, human cells or individual molecules of DNA, Dispersion of metallic Nanoparticles can be imaged. 23

23. References Atomic force Microscopy by Peter Eatson and Paul West. http:// hansmalab.physics.ucsb.edu/afmapp.html Quazar Technologies Pvt., LTd. Guide section. 24

24. Thank you 25