Atomic Force Microscope

ByVimal Kumar

Outline:

• History of AFM• Principle of AFM• Instrumentation of AFM• Modes of operation of AFM• Forces & Force Distance curve• Applications of AFM in Polymers

History of AFM• Development of Scanning tunneling

microscopy (STM) in 1981 earned its inventors, Gerd Binng and Heinrich Rohrer (at IBM Zürich), the Nobel Prize in Physics in 1986

• Based on the above work Binnig, Quate and Gerber invented the first AFM in 1986

http://en.wikipedia.org/wiki/AFMGerd Binnig

Heinrich Rohrer

Outline:

• History of AFM• Principle of AFM• Instrumentation of AFM• Modes of operation• Forces & Force Distance curve• Applications of AFM

Principle of AFM:

Outline:

• History of AFM• Principle of AFM• Instrumentation of AFM• Modes of operation• Forces & Force Distance curve• Applications of AFM

Block diagram of AFM:

http://www.farmfak.uu.se/farm/farmfyskem-web/instrumentation/images/afm.gif

Ref: Synthetic Polymeric Membranes Characterization by Atomic Force Microscopy Page.26

Piezoelectric Scanner:

http://nanohub.org/resources/520/play

The Beam Deflection method

Courtesy- J. Gomez-Herrero, UAM, Spain

Micro Cantilever of AFM

• Tip is made up of Silicon Nitride or Silicon

• Tip radius ranges from 10nm to 200nm,Normal radius is 50 nm

• Spring constant is 0.1 to 100 N/m• Nowadays CNT tips were used for

special applications. In this case radius will be 15nm to 10 nm

The Microcantilever – the force sensor

Needle AFM Tip• Needle is fabricated with Ag2Ga

material• It is manufactured by Nano

science Instruments• It is available in varying lengths,

diameters, and attachment angles• Needle AFM tips are available in

standard lengths of 1, 5, or 10 µm with a diameter of 50 nm.

• The simple geometry and high conductivity of the Needle probes provides a wide range of enhanced sensing and manipulation capabilities

http://www.nanoscience.com/news/2009-Mar24.html

MWCNT AFM Tip:

Ref: Appl. Phys. Lett., Vol. 82, No. 23, 9 June 2003

CNT V/S Conventional Image:

Thermocouple Tip:

• Here thermocouple probes were used for scanning the surface.

• It maps the local temperature and thermal conductivity of an interface.

• It can be used to detect phase changes in polymer blends

• Measuring material variations in Conducting Polymers.

• Hot-spots in integrated circuits

http://en.wikipedia.org/wiki/Scanning_thermal_microscopy

Outline:

• History of AFM• Principle of AFM• Instrumentation of AFM• Modes of operation• Forces & Force Distance curve• Applications of AFM

Modes of operation:

• AFM Can be operated in 3 modes

1)Contact Mode AFM 2)Non-Contact Mode AFM 3)Taping Mode AFM

Contact Mode Taping Mode Non Contact Mode

Force on Tip Constant Force

Oscillating frequency of 20 nm to 100 nm

Frequency < 10 nm

Rate of Scan High Less Very Less

Usage Limited Wide Usage Limited

Advantages & Disadvantages

Lateral forces will damage the surface of soft materials

It is good for soft materials

It is good in hydrophobic surfaces

Outline:

• History of AFM• Principle of AFM• Instrumentation of AFM• Modes of operation• Forces & Force Distance curve• Applications of AFM

Types of Forces: Long-range electrostatic and magnetic

forces (up to 100 nm)• Capillary forces (few nm)• Vander Waals forces (few nm) that are

fundamentally quantum mechanical (electrodynamic) in nature

• Casimir forces• Short-range chemical forces (fraction of nm)• Contact forces• Electrostatic double-layer forces• Salvation forces• Neoconservative forces

https://nanohub.org/resources/522/download/2005.11.28-raman.pdf

Force Distance Curve:

Other SPM Techniques:

• STM – Scanning Tunneling Microscopy• LFM – Lateral Force Microscopy• EFM – Electric Force Microscopy• MFM – Magnetic Force Microscopy• SCM – Scanning Capacitance Microscopy• FMM – Force Modulation Microscopy• SNOM – Scanning Near Field Optical

Microscopy

Outline:

• History of AFM• Principle of AFM• Instrumentation of AFM• Modes of operation• Forces & Force Distance curve• Applications of AFM in Polymer Science

AFM FOR MORPHOLOGY OF POLYMERS:

Dendrites of iPP:

Ref: Microsc Microanal 9 (Suppl 2).2003

Spherulites:

Ref: Microsc Microanal 9 (Suppl 2).2003

Crystallization(or)Spherulites formation:

• This AFM tapping/phase mode image series shows the crystallization of a polylactide spherulite, crystallized from the melt at 95°C

http://www.polymermicroscopy.com/eng_afm_lacti1.htm

0% Disperal 1% Disperal®

2% Disperal® 10% Disperal®

Nano fillers Nucleation:• Some nano fillers have a nucleation effect

on the crystallization of polymers, i.e. the number of nuclei is increased and the crystallization time of the sample reduced.

• Additionally the size of the crystalline superstructures, e.g. spherulites, decreases and the transparency of the sample might be improved.

• The example shows isotactic polypropylene with different amounts of the nano filler "Disperal® 20" (Sasol). With increasing filler content the size of the crystalline superstructures is clearly reduced.

Macromolecular Materials and Engineering (2008), 293(3), 218-227.

Block copolymer-Morphology

• The tapping/phase mode image shows the bulk-morphology of a poly(styrene-b-ethylene/butylene/styrene-b-styrene) tri-block-copolymer.

http://www.polymermicroscopy.com/eng_afm_block.htm

Polymer Blends:

Miscibility of Branched Ethene Homopolymers with Iso- and Syndiotactic Polypropenes. Jürgen Marquardt, Ralf Thomann, Yi Thomann, Johannes Heinemann and Rolf Mülhaupt Macromolecules, 2001, 34, (25), 8669-8674

Phase dispersion of ethylene propylene rubber (EPR) in impact

copolymers (ICP)

Ref: Microsc Microanal 9 (Suppl 2).2003

This AFM tapping/phase mode image shows the bulk-morphology of a partially miscible blend of isotactic polypropylene (matrix) and of a non-crystalline polyethylene copolymer. Within the polyethylene phases single i-PP lamellae are visible.

Phase dispersion in polymer blends

NANOFIBRE INVESTIGATIONRef: Microsc Microanal 10(Suppl 2), 2004

NANOFIBRE BLEND INVESTIGATIONRef: Microsc Microanal 10(Suppl 2), 2004

NANOINDENDATION BY AFM

NANOINDENDATION• Nanoindentation is used for measuring young's modulus(E) of material, stiffness, hardness of material.

Where:• Pmax = maximum presure applied• Ar = area of the bore• H= Harness

Where:•A(hc) - Area of the indentation• hc Depth of the residual indentation •Β Constant •Er Mdulus •S stiffness (The slope of the curve, dP / dh)

http://en.wikipedia.org/wiki/Nanoindentation

NANO INDENTATION-I• AFM is operated in force mode• a diamond-tipped stainless steel cantilever probe is used

and the dents from left to right were taken using compensation angles of 0, 10, 20, 30, 35, 40, 45, and 50 degrees

Ref : M. R. VanLandingham, "The Effect of Instrumental Uncertainties on AFM Indentation Measurements," Microscopy Today, Issue No. 97-10, December 1997, pp. 12-15.

NANO PULL OUT TECHNIQUE

Nano Pull Out Technique:• Carbon nanotube(MWCNT) is

used as tip for AFM• Here Polyethylene-butene thin

film(~300 nm)• In this Polymer CNT

interaction Force is found • In this single CNT is Introduced

then detached from the polymer .

• This test is very important when we reinforce CNT in the polymer in the process of Composite manufacturing.

MWCNT AFM Tip:

Ref: Appl. Phys. Lett., Vol. 82, No. 23, 9 June 2003

• Exit Hole • Exit hole length

Ref: Appl. Phys. Lett., Vol. 82, No. 23, 9 June 2003

• Pull out force is found to be 47 Mpa

• The normal force of conventional fibers is 10Mpa

• From it we can conclude that CNTs are better materials for composites then the fibers.

Ref: Appl. Phys. Lett., Vol. 82, No. 23, 9 June 2003

AFM FOR POLYMER MEMBRANES

AFM for Membranes• Pore size by TEM, SEM are very small when

compared to AFM• By Using AFM we can find the Pore Size,

Density, Size Distribution, Pore Connectivity, Surface Roughness can be calculated.

• From above data we can calculate the Mean pore size ,Median pore size…etc

• The above date is very impotent when we want to design a good filtration equipment.

• AFM is a good Quality Control tool for the membrane process engineers

References:• Polymer Microscopy By Linda C. Sawyer, David T.Grubb• Synthetic Polymeric Membranes By K.C.Khulbe, C.Y.Feng, T.Matsuura• Atomic Force Microscopy in Cell Biology By Bhanu P.Jena, J.K.heinrich Horber, American Society for

Cell Biology• Atomic Force Microscopy By Pier Carlo Braga, Davide Ricci• Ref: Appl. Phys. Lett., Vol. 82, No. 23, 9 June 2003• M. R. VanLandingham, J. S. Villarrubia, W. F. Guthrie, G. F. Meyers, " Nanoindentation

of Polymers: An Overview," in Macromolecular Symposia, 167,• Advances in Scanning Probe Microscopy of Polymers, V. V. Tsukruk

and N. D. Spencer, eds. (2001) 15-44. • Miscibility of Branched Ethene Homopolymers with Iso- and Syndiotactic Polypropenes. Jürgen

Marquardt, Ralf Thomann, Yi Thomann, Johannes Heinemann and Rolf Mülhaupt Macromolecules, 2001, 34, (25), 8669-8674

• Macromolecular Materials and Engineering (2008), 293(3), 218-227.• Microsc Microanal 10(Suppl 2), 2004• Appl. Phys. Lett., Vol. 82, No. 23, 9 June 2003• www.nanoscience.com/news• www.wikipedia.org• www.google.com• www.nanohub.com/online_onlinelectures

QUESTIONS?