1. Force Microscopy Principle of Operation

2. Force Microscopy Basic Principle of Operation: detecting forces between a mass attached to a spring (cantilever), that feels some force when it is brought very close to the surface. Ideally the mass (tip) would not damage the surface. Sensor that responds to a force and a detector that measures it. The sensor-a cantilever beam with an effective spring constant k, moves in accordance with the forces acting on its tip

3. Force Microscopy Frequency of atoms vibration, , at room temperature ~ 10 15 Hz The mass, m, of an atom ~ 10 -30 kg  The effective spring constant, k, between atoms is k=  2 m  1N/m

4. Materials Characterization

5. AFM -Principle

7. Materials Characterization Courtesy Dr. Z. Barkai

8. Materials Characterization

9. AFM Images 2. Carbon nanotube 3. Human chromosomes TappingMode AFM image of single carbon-nanotube molecule on electrodes. These images represent an important breakthrough where we measured electronic transport through a single nanotube molecule for the first time. 530nm x 300nm scan courtesy C. Dekker and Sander Tans, Delft University of Technology, Department of Applied Physics and DIMES, The Netherlands.

10. Materials Characterization Courtesy Dr. Z. Barkai

11. Materials Characterization

12. AFM Images 1. Au (111) High resolution scan of Au (111) surface, with reconstruction strips (inset) hexagonal atomic structure. Scan size: 5nm; inset: 20 nm

13. Contact - Atomic Force Microscopy All rights reserved @ Norbert Total Repulsi ve Total Atractive Fv FcFc Las er

14. a - “Snap into contact” Contact AFM : in “b” or “c” Vacuum “c”-soft samples Determination of k or sample elasticity d - “Snap back point” d 1,2 - “Multiple Snap back points” AFM -Force vs Distance Air Air + Contaminatio n layer

15. AFM -Cantilevers

17. Diamond-coated AFM tip FIB Sharp Tip AFM -Cantilevers Gold-coated Si 3 N 4 Tip l Pyramidal, tetrahedral, or conical tips are the most common tip shapes

18. AFM -Cantilevers l Depositing a Si 3 N 4 layer on an etch pit in Si l Tips are broader then Si conical tips, harder, and thinner (stress in the film) l not suitable for non-contact (small thickness, small  )

19. AFM -Resolution AFM STM-single atom interaction STM l AFM-several atoms on tip interact with several atoms on surface l In contact, not necessarily a single atom contact, radius of contact ~(Rd) 1/2 (d-penetration depth, R-radius of tip)

20. AFM -Resolution Interaction of atom 1 : t=0 different from interaction of atom 3,2 Each tip atom produces a signals with offset to each other Periodicity reproduced but no true atomic resolution

21. AFM -Scanner Hysteresis Hystersis can be as high as 20 %, in x-y can be observed by looking at opposite direction scans (advantage to scan in one direction) At z, if extension needs more voltage  erroneous step height

22. Scanner-Software Corrections By measuring a calibration grating, and producing a look-up table for voltage corrections; they are only accurate for scans identical to the ones used for the calibration. (~10% deviation)