Prepared by Amare Worku (MSC in Tex. Eng.)

November 2015

BAHIRDAR UNIVERSITY

Seminar Title on: Atomic Force Microscopy (AFM)

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Atomic Force Microscopy

Contents/ Outlines

1. Background and History

2. General Applications

3. How Does AFM Work?

4. Parts of AFM

5. THREE Modes: Contact mode, Non-contact mode, Tapping Mode

Contents/ Outlines

6. What are the limitations of AFM?

7. Advantages and Disadvanteges of AFM

8. The future of AFM

1. Background and History

Scanning tunneling microscopy 1981 – Swiss scientists Gerd Binnig and Heinrich Rohrer Atomic resolution, simple 1986 – Nobel prize

2. General Applications

1

Materials Investigated: Thin

and thick film coatings, ceramics,

composites, glasses, synthetic

and biological membranes,

metals, polymers, and

semiconductors.

3

AFM can image surface of material in

atomic resolution and also measure force at the

nano-Newton scale.

2

Used to study phenomena of:

Abrasion, corrosion,

etching (scratch), friction,

lubricating, plating, and polishing.

Further Applications

3. How Does AFM Work?

Tip vibrates (105 Hz) close to specimen surface

(50-150 Å) with amplitude 10-100 nm, May at

times lightly contact surfaceTwo ways - 'constant force' ……. feedback system

moves tip in z direction to keep force

constant.

'constant height'……. no feedback system -

usually used when surface roughness small

higher scan speeds possible.

3. Continued…

Hooke’s Law

x= the vertical displacement of the end of the cantilever.

k = the cantilever spring constant

F = the force acting

On the cantilever

F = -kx

Hooke’s Law

3. 1 Experimental Procedures

Sample preparation

Thin layer of wax on steel disk Measuring3-D ImagingManipulating/Analyzing

Diagram

3-D Imaging

Measuring

3-D ImagingManipulating/Analyzing

Manipulating/Analyzing

Scanning the Sample/measure

Tip brought within nanometers of the sample (van der Waals)

Radius of tip limits the accuracy of analysis/ resolution

Stiffer cantilevers protect against sample damage because they deflect less in response to a small force This means a more

sensitive detection scheme is needed

Data Analysis

Morphology Characterization/ Sub microscopic level

Surface roughness quantification

Physical properties/ Swelling, cohesiveness, smoothness

Will be analyzed

AFM Tips

4. Parts of AFM

1. Laser – deflected off cantilever2. Mirror –reflects laser beam to photo detector3. Photo detector –dual element photodiode that measures differences in light intensity and converts to voltage4. Amplifier 5. Register 6. Sample 7. Probe –tip that scans sample made of Si8. Cantilever –moves as scanned over sample and deflects laser beam

1. Z-Piezo Calibration: by scanning a sample of known

height (calibration grating)

In contact mode

2. Cantilever deflection calibration

3. Cantilever stiffness, k, calibration

Calibration Every month

5. THREE Modes: Contact mode, Non-contact, mode, Tapping Mode

A.Contact Mode Mode; hard, stable samples in air or liquid

B. Non-Contact Mode: non-invasive sampling.

C. Tapping (Intermittent contact): No shear and damaging samples

A. Contact Mode

Measures repulsion between tip and sample

Force of tip against sample remains constant

Feedback regulation keeps cantilever deflection

constant

Voltage required indicates height of sample

Problems: excessive tracking forces applied by

probe to sample

B. Non-Contact Mode

Measures attractive forces between tip and sample

Tip doesn’t touch sample Van der Waals forces between tip and

sample detected Problems: Can’t use with samples in fluid Used to analyze semiconductors Doesn’t degrade or interfere with sample-

better for soft samples

C. Tapping (Intermittent-Contact) Mode Tip vertically oscillates between contacting sample

surface and lifting of at frequency of 50,000 to

500,000 cycles/sec.

Oscillation amplitude reduced as probe contacts

surface due to loss of energy caused by tip

contacting surface

Advantages: overcomes problems associated with

friction, adhesion, electrostatic forces

More effective for larger scan sizes

CONTACTNON CONTACT

6. What are the limitations of AFM? AFM imaging is not ideally sharp

7. Advantages and Disadvanteges of AFM

ADVANTAGES DISADVANTAGES

1. Easy sample preparation2. Works in vacuum, air, and liquids3. Accurate height information4. Living systems can be studied5. 3-D Imaging6. Dynamic environment7. Surface roughness quantification

1. Limited vertical range2. Limited magnification range3. Data not independent of tip4. Tip or sample can be damaged5. Limited scanning speed

Comparison b/n AFM vs. SEM

8. The future of AFM

Sharper tips by improved micro-fabrication

processes: (tip – sample interaction tends to

distort or destroy soft biological molecules )

development of more flexible cantilever

springs and less damaging and non-sticky

probes needed

Nano-Identification on Fiber surface

MMF

Viscose Rayon

Cotton

TYPES OF FIBER UNDER AFM

AFM topographical scan of a glass surface.

Clean glass surface: roughness ~ 0.8 nm

AFM images of the samples: a)Cotton topography and phase (5 μm × 5 μm), b) Cotton topography and phase (2 μm × 2 μm),

c)Wool topography and phase (5 μm × 5 μm)

d)Wool topography and phase (2 μm × 2 μm).

AFM images of the

samples:

a) PET,

b)Antistatic PET,

c) Antibacterial PET.

AFM images of the cross sections of the fibers:

a)Antibacterial PET friction,

b)Antistatic PET friction.

In general

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