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Prepared by Amare Worku (MSC in Tex. Eng.)
November 2015
BAHIRDAR UNIVERSITY
Seminar Title on: Atomic Force Microscopy (AFM)
LOGO
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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