ATOMIC FORCE MICROSCOPE

PRESENTED BY

ANAM RANA

Registration #: 2013-ag-689

MSc. CHEMISTRY 4TH SEMESTER

Layout of Presentation

Microscope

Atomic Force Microscope

Basic components of AFM

AFM Modes of Operation

AFM Applications

Learning through visualization

Optical

microscope

Electron

microscope

Scanning Probe

microscope

A person with 6/6 vision can resolve objects which are about 0.089mm ( under normal lightening conditions)

Light microscope

The optical microscope (1674)

Which uses visible light (400nm-700nm)and a system of lenses to magnify images of small samples.

Magnification about 1000-2000 times

Resolution 200 nm because of diffraction of light

Viruses, proteins, and molecules are smaller so they can not resolve

Resolution can enhance by using smaller wavelength

Image without use of visible light……how?Electron Microscopy

The electron microscope is a type of microscope that uses a beam of electrons to create an image of the specimen. It is capable of much higher magnifications and has a greater

resolving power than a light microscope, allowing it to see much smaller objects in finer detail.

* Low diffraction

* High resolution TEM(0.2nm) & SEM(5nm)

Limitations of SEM and TEM…………

SEM requires Gold or Silver coating & freezing to get good imagecontrast

TEM requires conductive sample. So fine cutting and fixation of sampleare basic requirement. Sample preparation is lengthy and also requiredexperience specialist

Living samples cannot be observedBoth require high vacuum ( 10-4 torr)and sample dehydration

Optical microscope and electronsmicroscopes are parallel……?

Both provide 2-D lateral information

The image appear flat

Difficult to obtain information in 3rd dimension

Scanning Probe microscope

Scanning probe microscope (SPM) is a type of microscope that forms images of surfaces by employing a physical probe that scans the specimen

Scanning Tunneling Microscope (STM)

1980

Atomic Force Microscope (AFM)

1986

Atomic Force Microscope Atomic force microscope(AFM) or scanning force microscope (SFM) is a very high-

resolution type of scanning probe microscope, with demonstrated resolution on the orderof fractions of a nanometre.

The AFM is one of the foremost tools for imaging, measuring, and manipulating matter atthe nanoscale.

Invented by Binning and coworker in 1986 as an advancement in Scanning tunnelingmicroscope

Let’s model an AFM…

Why AFM not SEM/TEM SEM/TEM AFM

Sample Must be conductive

Insulating/conductive

Magnification 2- Dimensional 3- Dimensional

Environment Vacuum Vacuum/air/liquid

Time for image 0.1-1minutes 1-5minutes

Horizontal resolution

0.2nm(TEM) & 5nm(SEM)

0.2nm

Vertical resolution

N/A 0.05nm

Contrast on flat surfaces

Poor Good

Working Principle of AFM

The information is

gathered by "feeling"

the surface with a

mechanical probe, A

sharpened probe drag

over surface

Force interaction

between tip and sample

give topographic

information of sample

“ A probing solution”

Basic setup of an AFM Atomic scale resolution of AFM is depends

upon following components.

Cantilever with Sharp tip

Scanner

Deflection detection

Cantilever & Tip• AFM consist a cantilever( length=3-6nm tall, radius=15-

40nm ) with Sharp tip.

• Cantilever is basically a spring with spring constant

(k=0.01N/m-1N/m)

• Si or Si3N4 are used for making tips. A thin gold

layer is deposited to upper side of Cantilever for

good reflectivity of laser

• Two types are common in use

• Beam Shape

• V-Shaped

Cantilever must have smaller spring constant and mass………….??????

• Smaller spring constant

• To deflect by smaller interaction forces

• Not to disturb atoms from their site

• Flexible cantilever exerts lower force to

sample thus less distortion and less damage.

• Low mass

• To obtain both low spring constant and high

frequency( >2KHz), the mass of cantilever

should be very small ~ 10-10

• Kg. Higher the resonance frequency of

cantilever, faster and better the imaging.

Cantilever come close to sample the interaction forces come into play

Cantilever deflection detection

• Electron tunneling

• Capacitance detection

• Optical lever detection

Scanner

AFM Schematics

Contact Mode Modes of AFM

Non Contact mode

Tapping/Intermittent mode

• Cantilever oscillate at resonant

frequency

• The oscillating tip then move

towards the sample until touch

• Eliminates frictional forces and

enables to image soft materials

AFM Applications

DATA WRITTINGForce + Heating at tip.

To write 1 , the tip is gently touching the surface causing a dent.

AFM thermo mechanical data Storage

Data Reading

Bit reading depends on the piezoresistivity ( deflection, change in resistance)of Si cantilever.

Cantilever deflection is measured as tip rides over pits. If there is a pit , probe is pushed inside it.

AFM For Macromolecular studies Macromolecules are everywhere:

from DNA / proteins in biologicalscience to polymers / detergents inmaterials science.

AFM can be used to study theconformation and interactionenergies of one macromoleculeat a time.

AFM is Space

“MARS MISSIOM 2016”

High resolution power.

Does not require sample preparation /special medium

REFRENCES: R,Wiesendanger. 2004.Scanning Probe

Microscopy and Spectroscopy, Cambridge University Press

www.nanoscience.com

www.wikipedia.com

Haugstad, G.2012. Atomic Force Microscopy: Understanding Basic Modes and Advanced Applications.Jhon Wiley and sons Inc., Publication

H,Samuel and Marcia. L. 2013.Atomic Force Microscopy and Scanning Tunneling Microscopy

Any Question………???

Any Question………???