AFM.pptx if you need to study this is very important

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1. STM invented by Gerd Binnig & Heinrich Roher in 1981…. IBM Research - Zurich Won Nobel Prize in Physics, 1986. Atomic scale probe mechanically scanned over sample surface. Invention of AFM by Gerd Binnig at Zurich …1982 First Experimental implementation at Stanford Univ. in 1986 in Prof. C. Quate’s Lab, By Binnig, Quate  and Gerber Won national Medal of Science, 1992. Non-conductors as well as conducting samples. : Scanning Probe Microscopy (AFM , STM)

2. E-book : by Bert Voigtländer Scanning Probe Microscopy Atomic Force Microscopy and Scanning Tunneling Microscopy [ © Springer-Verlag Berlin Heidelberg 2015] “Grandfather” of Nanoscience and Nanotechnology was R.P. Feynman. In a visionary talk in 1959 he postulated the possibility of nanotechnology down to the very atoms. His talk entitled “There is Plenty of Room at the Bottom”

3. Atomic force microscopy (AFM) or scanning force microscopy (SFM) …. very-high-resolution scanning probe microscopy (SPM)…… Resolution ~ fractions of a nanometer , more than 1000 times better than the optical diffraction limit . A Prelude (before SPM)

4. Image of puC19 plasmid DNA molecules acquired with a NanoScope IIIa AFM in tapping mode in air. The size of the image is 2 × 2 μ m 2 . DNA Studies Using Atomic Force Microscopy: Capabilities for Measurement of Short DNA Fragments …. Dalong Pang et.al ., Frontiers in Molecular Biosciences 2015, 2 , 1 [A plasmid is a small, circular, double-stranded DNA molecule, distinct from a cell's chromosomal DNA. Plasmids naturally exist in bacterial cells G enes carried in plasmids provide bacteria with genetic advantages, such as antibiotic resistance ]

5. Characteristics of Common Techniques for Imaging and Measuring Surface Morphology Profilometer Optical Microscope Confocal Microscope SEM AFM Resolution X, Y 1µm 0.5µm 170 nm 2 nm 0.1 nm Resolution Z 1 nm N/A 500 nm N/A 0.01 nm Operation environment air air, liquid, vacuum air vacuum air, liquid, vacuum Sample preparation little little little hard (freeze, drying, coating) None Sample damage 10 -6 N destroyed by sample preparation 10 -10 N Magnification 10 3 10 4 10 7 10 9 A COMPARISION

6. AFM measures the sample surface using atomic force between tip and sample. [   Van der Waals forces ,  dipole-dipole interactions ,  electrostatic  ] Atomic Force Potential changes depending on the distance between two atoms. Principle r V (r ) AFM (Atomic Force Microscopy) ∂V(r) ∂ r F = -

7. r

8. Cantilever is displaced upon its interaction with the surface Deflection of cantilever : measured by Laser beam Reflection of laser beam is displaced on surface of photodiode Intensity of electrical signal : proportional to displacement of cantilever …..surface structure Atomic force microscopy using beam deflection detection er r Force between Tip and Sample in Static Mode: Measured by Hook’s Law: Si Cantilever : Force Sensor F = - kz k: Spring Constant (stiffness of Cantilever spring) z: distance over which the spring bends w.r.t equilibrium position (no sample) Interaction between tip and sample, which can be an atomic scale phenomenon, is transduced into changes of the motion of cantilever X, Y, Z sample positioner

9. Requirements of a Force Sensor Typical vibrational frequency of atoms in solids : 𝒘 vib ~ 10 13 Hz Atomic mass ~ 10 -25 kg Harmonic Oscillator Model : 𝒘 vib = k: force constant / spring constant for bonds of atoms in solids = .m ~ 10 N/m = 10 -9 N/ Å Cantilever Si (FORCE SENSOR) with spring constant 10 -9 N/ Å measures forces in Nanonewton regime.  

10. Inter-Atomic Forces r Repulsive Attractive Total interaction Repulsive force: Contact AFM Attractive force : Non-Contact AFM Lennard Jones Potential V(r) : Distance, r V(r) +F -F ∂V(r) ∂ r F = - i . steep repulsive term: overlapping electron orbitals: Short Range Force ii. smoother attractive term : VDW , London dispersion forces: Long Range Force

11. V : intermolecular potential between 2 atoms ϵ   : well depth : a measure of how strongly the 2 particles attract each other. σ : the distance at which the intermolecular potential between 2 particles is zero. : gives a measurement of how close 2 nonbonding particles can get : referred as van der Waals   radius : equal to one-half of the internuclear distance between nonbonding particles.   r  : the distance of separation between both particles The Lennard-Jones Model The 12-6 Lennard-Jones model is not the most faithful representation of the potential energy surface; its use is widespread due to its computational expediency.

12. i . Find r m. ( r min ) ii. Using r min show that, Assignment: Given, V (r) At r m , what will be the value of V (r ) ? At r = What do you infer ?   NOTE : These parameters can be fitted to reproduce experimental data or accurate quantum chemistry calculations. Due to its computational simplicity, the Lennard-Jones potential is used extensively in computer simulations even though more accurate potentials exist.

13. Experimental setup for the AM detection scheme using a lock-in amplifier to detect the deviation of the oscillation amplitude from the set point value

14. FORCE – DISTANCE CURVES

15. FABRICATION OF Si CANTILEVER Fabrication of Si Cantilever using alternating Lithographic Patterning and Chemical Etching

16. Single polymer chains (0.4 nm thick) recorded in a tapping mode under aqueous media with different pH Topography of a glass surface. The micro and nano-scale features of the glass, portraying roughness The image space is (x,y,z) = (20 µm × 20 µm × 420 nm).

17. Imaging of atomic orbitals with the Atomic Force Microscope – experiments and simulations F. J. Giessibl *, H. Bielefeldt , S. Hembacher , and J. Mannhart Universita ¨ t Augsburg, Institute of Physics, Electronic Correlations and Magnetism, Experimental physikVI , 86135 Augsburg, Germany Ann. Phys. (Leipzig) 10 (2001) 11––12, 887––910 Chemical structure imaging of a single molecule by atomic force microscopy at room temperature Kota Iwata , ,  Shiro Yamazaki ,   Pingo Mutombo , ,  Prokop Hapala , ,  Martin Ondráček , ,  Pavel Jelínek ,  &  Yoshiaki Sugimoto Nature Communications   volume 6 , Article number: 7766 (2015)

18. PTCDA (3,4,9,10-perylene tetracarboxylic dianhydride) molecules evaporated on a reactive semiconductor surface, Si(111)-(7 × 7) surface at ultrahigh vacuum STM

19. Advantages over Existing Microscopes High Resolution : 2~3 Å lateral, 0.1 Å vertical. Quantitative 3-D information. Non-conductors as well as conductors and semiconductors . Operates in air, liquid, and vacuum . Can measure electrical, magnetic, optical, and physical properties. Atomic scale manipulations and lithography.