Atomic Force Microscopy

Sonu

1411NT11

1

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

2

Background of AFM In 1929 Shmalz 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

Different From other Microscopy

No need of focusing, illumination, Depth of field.

It also have height information that make it simple toquickly measure the height, volume, width of any featurein 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 highresolution.

4

5

The first AFM instrument built by Binning, Quate and Gerber

The STM with a levermade by carefully gluing atiny diamond onto the endof a spring made of a thinstrip of gold. This was thecantilever of the first AFM.

6

AFM InstrumentThe main components of an AFM are

1.Microscope stage – Moving AFM tip, Sample holder,Force Sensor

2.Control electronics - Optical Microscope, Vibrationcontroller

3.Computer - The control electronics usually takes the formof a large box interfaced to both the microscope stageand the computer.

7

Basic concept of AFM InstrumentationThe piezoelectric transducer moves the tip over thesample surface, the force transducer senses the forcebetween the tip and the surface, and the feedbackcontrol feeds the signal from the force transducer back into the piezoelectric, to maintain a fixed force between thetip and the sample.

8

Piezoelectric transducers

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

9

Force transducers

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

10

Force Sensor

Optical lever sensor theEnd of the cantileverbends the position ofthe laser spot on thedetector changes. As thecantilever detectordistance is large a smallmovement of thecantilever causes a largechange in the laser spotposition at the detector.

11

Feedback controlFeedback control is used to maintain a set force betweenthe probe and the sample.

12

13

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

Scanning ModesThere are different imaging modes of AFM

Contact Mode

Non Contact Mode

Tapping Mode

15

Modes of Operation in AFMMode of Operation Force of Interaction

Contact mode strong(repulsive) - constant force orconstant Height

Non-contact mode weak (attractive) - vibrating probe

Tapping mode strong (repulsive) - vibrating probe

16

Contact Mode

High Resolution Images.

Tip of the probe always touching the sample.

Fastest 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

18

Non Contact Mode Signal-to-noise benefits associated with modulated

signals.

Oscillating modes can measure images with a small probe–sample force.

19

Tapping Mode No Capillary effect.

Amplitude signals are used in feedback.

Used for Imaging in Air.

20

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

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

References Atomic force Microscopy by Peter Eatson and Paul West.

http://hansmalab.physics.ucsb.edu/afmapp.html

Quazar Technologies Pvt., LTd. Guide section.

24

Thank you

25