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Atomic Force Microscopy (AFM)

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Ariel Ash-Shakoor

on 2 June 2014

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Transcript of Atomic Force Microscopy (AFM)

The
Hertz
equation is useful for collecting data. It is the theory governing data collection for Force mapping mode.
When the light beam hits the cantilever. It creates a FORCE that displaces the probe. The probe then interacts with the sample.

Hooke's law describes this spring like phenomena as
F = kx or Force = spring constant X displacement








The video below helps illustrate this concept (4).
atomic
FORCE
Microscopy
1. Contact mode
3. Force mapping mode
2. Tapping mode
The video was slightly dramatic and even anticlimactic.
In the following parts of the presentation, we will discuss the details of AFM.

After watching the video, you still need to know:
The main component of AFM and how it works?
The overall applications and limitations of AFM
In the video, 4 main components were mentioned:
specimen stage
a tapered probe
computer and accessories
other AFM hardware
Now that we have seen the overall system, we will focus on the components in more detail in order to know how AFM works.
AFM
3 modes
An Atomic Force Microscope (AFM) is an analytical tool used to observe single molecule-scale organisms and to measure forces and displacements (1).

Before we begin, let's see a real example of an atomic force microscope as you would see and use it in everyday life.
( Turn up the volume on your computer)
The tapered probe moves toward the specimen
The controller sends the information to the computer and to a sensor
The Light bounces off of the cantilever
to a detector
Turn on machine
The light signal is amplified and sent to a controller
Light hits the cantilever
1.
2.
3.
4.
5.
6.
7.
The sensor converts the cantilever deflection to an electrical output. The computer displays the data.
1.
2.
3.
4.
5.
6.
System Components
So that is how the system works together. Let's take a closer look at the most important part, the probe.
Now we know all the system components and how the main component drives the system, but
When would we use AFM?
When and Why do people use AFM? The applications
also called "AC Mode" or "Intermittent Contact Mode"
cantilever oscillates at the surface of the specimen
the oscillation is near the resonance frequency of the cantilever
this oscillation is controlled by a piezoelectric element mounted on the AFM tip holder (13)
The cantilever oscillates, lightly
tapping the surface. It only
touches the specimen at the bottom of each oscillation. This helps prevent damage to soft specimens and avoids pushing specimens around the glass slide (13) (14).
A sample for tapping mode of AFM is prepared as a simple smear on a glass slide.
Tapping mode can be
performed on both wet and
dry samples.
Team 1 Homework 3 9/21/12
Alexa - Monitor, Alyssa - Recorder, Ariel - Coordinator, Xinchi - Checker
This diagram explains each step to generate data (3).
The 3 modes of AFM

What is AFM?
AFM is an
analytical
tool that can be used to
measure forces
and
image
small (The A for ATOMIC in AFM) molecules.

How does AFM work?
It has several parts that work in a feedback system to create data.
The most
important
part is the tapered cantilever
probe
. The probe undergoes similar force characteristics as a spring.
F=kx
(The F for FORCE in AFM)

What are the limitations of AFM?
AFM should not be used with hard or brittle surfaces, organisms, and/or very viscous media
Small movements of particles created by thermal energy can be detected as data

What are the three modes of AFM?
(The M for MICROSCOPY in AFM)
Contact mode
Tapping mode
Force mapping mode
Let's review what we learned again.

Can you answer the following questions?
How does AFM work? More specifically, how does the main component create information for data?
When can you use AFM?
What are the 3 modes of AFM?
AFM is more than just a microscope that can create pretty pictures.
AFM can image live cells in aqueous media as shown above with a lung cancer cell in salt solution (8).
As mentioned earlier, AFM can measure forces and displacements such as cell stiffness and protein unfolding (right). The force detection range is 0.01 to 100 nN! (9 and 10)
Before we move on to the 3 modes of AFM, let's summarize what we learned so far.
AFM is an analytical tool that can be used to measure forces and image small molecules.
It has several parts that work in a feedback system to create data.
The main part is the tapered cantilever probe. The probe undergoes similar force characteristics as a spring. F=kx
It is also important to note that AFM can
NOT
be used with large, hard materials or viscous media. The specimen can damage the AFM probe. The probe can also damage or displace the specimen if not used properly (12).
If you cannot answer the previous questions, then you should review the information before moving to the concluding section.



If you can answer the questions, then you understand the basic concepts of AFM! The final sections will review all of the information.
Sources
1.Ethier, C. R. and C. A. Simmons (2007). Introductory biomechanics: from cells to organisms. Cambridge; New York, Cambridge University Press
2.2.Schematic illustration of the AFM system. Current protocols “Atomic Force Microscopy.” http://www.currentprotocols.com/WileyCDA/CPUnit/refId-mc02c02.html September 12, 2012.
3.Ethier, C. R. and C. A. Simmons (2007). Introductory biomechanics: from cells to organisms. Cambridge; New York, Cambridge University Press
4.Virus Nanoindentation by AFM video.
Introduction to AFM Picture. Sarkar Lab “Research” http://www.chbmeng.ohio-state.edu/~sarkara/research/research/methods/methods.html September, 12 2012.
5.Maximum length/force information. Ethier, C. R. and C. A. Simmons (2007). Introductory biomechanics: from cells to organisms. Cambridge; New York, Cambridge University Press
Hair Picture. Health and Beauty “Make healthy Hair your default hair.”http://grannymillerblog.blogspot.com/2012/02/make-healthy-hair-your-default-hair.html September 12, 2012.
6.Stained Chromosomes. Agilent Technologies “AFM Image Library.” http://nano.tm.agilent.com/index.php/image-library. September 12, 2012
7.Blue-Green algae Cells. Agilent Technologies “AFM Image Library.” http://nano.tm.agilent.com/index.php/image-library. September 12, 2012
8.Lung Caner Cell. Agilent Technologies “AFM Image Library.” http://nano.tm.agilent.com/index.php/image-library. September 12, 2012
9.Squishy cells picture from UCLA. Force Technology Review “The Feel of Cancer Cells”. http://www.technologyreview.com/news/409137/the-feel-of-cancer-cells/ September 12, 2012
10.Protein AFM picture. Rice University. Physics and Astronomy department. http://physics.rice.edu/Content.aspx?id=97 September, 12, 2012.
11.Fluoroalkane F12H8. Agilent Technologies “AFM Image Library.” http://nano.tm.agilent.com/index.php/image-library. September 12, 2012
12.Ethier, C. R. and C. A. Simmons (2007). Introductory biomechanics: from cells to organisms. Cambridge; New York, Cambridge University Press
13.Blanchard, Cheryl R. "Atomic Force Microscopy." The Chemical Educator 1.5 (1996). <http://alike.www.ifeaxejewelry.com/atomic%20force%20 microscopy,%20cr%20blanchard.pdf>.
14.Geisse, Nicholas A. "AFM and combined optical techniques." Materials Today 12.7 July (2009): 40-45. <http://www.sciencedirect.com/science/ article/pii/S1369702109702019>.
15.Nanoscal Measurements. <http://garnogroup.lsu.edu/Research3.html> September 17, 2012
16.3D Atomic force microscopy video <http://www.youtube.com/watch?v=veTskO7EWM8>
17. Department of Radiation Science Human Metaphase Chromosomes <http://www.helmholtz-muenchen.de/iss/strahlenbiophysik/research/atomic-force-microscopy/gtg-banding-pattern-on-human-metaphase-chromosomes/index.html>
18.Department of Energy Biological & Environmental Research Climate and Environmental Sciences "Microscope: Scanning Probe - AFM, Bioscope, Radiological" <http://www.emsl.pnl.gov/capabilities/viewInstrument.jsp?id=1039>
19. Agilent Technologies.. <http://nano.tm.agilent.com/index.php/image-library>.
20.Radmacher, M, Cleveland JP. Mapping Interaction Forces with the Atomic Force Microscope. 1994.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1275941/
21. Topography Picture. http://www.sciencedirect.com/science/article/pii/S0091679X07830159
22.Thermal Noise. https://docs.google.com/viewer?a=v&q=cache:u6WaXXqZwqsJ:www.physics.utoronto.ca/~phy225h/experiments/thermal-noise/Thermal-Noise.pdf+thermal+noise&hl=en&gl=us&pid=bl&srcid=ADGEESjFDaec3cRu-tY7g4dl8KKSBjq9mljOjtfmMEYmZanCYDHw8dPOyPJikW3awJt6SLPguVr7HhUb2cIOpXvi9A4e8Wkv2JKEzMkBZCKjH1wx3hrwWLVFycH4i7-_fvVAXxzq7nyx&sig=AHIEtbQRVCIsj-YPfZ6k4-CiirObv5BcDw
23.Carbon Nanotube. Agilent Technologies “AFM Image Library.” http://nano.tm.agilent.com/index.php/image-library. September 12, 2012
24.Fluoroalkanes F12H20. Agilent Technologies “AFM Image Library.” http://nano.tm.agilent.com/index.php/image-library. September 12, 2012
25. Image of glass slide "http://www.sciencephoto.com/media/360244/enlarge". September 19, 2012
Thank you
AFM is a versatile instrument. It can be used in different ways or modes to highlight different aspects of the sample. Force mapping is one of the modes as we will discuss next. Above is a picture of a chemical, Fluoroalkane F12H8 (11).
Contact mode
The tip scans the sample in close contact with the surface
The force between the tip and surface is constant during the scan
Tapping mode
cantilever oscillates at the surface of the specimen
the oscillation is near the resonance frequency of the cantilever
this is controlled by a piezoelectric element mounted on the AFM tip holder
Force mapping mode
force mapping works by dragging the cantilever tip across the cell surface at various forces
the displacement of the cantilever tip is recorded as it comes into contact with the cell surface
Hertz theory
is used to describe the interaction between the cantilever tip and the cell surface creates a force curve which gives insight into important cellular characteristics
AFM is a versatile instrument that can be used for various applications in several fields such as materials science, life science, and electrochemistry.
Carbon nanotubes (23)
Fluoroalkane (24)
force mapping mode works by dragging the cantilever tip across the cell surface at various forces

the displacement of the cantilever tip is recorded as it comes into contact with the cell surface

the interaction between the cantilever tip and the cell surface creates a force curve which gives insight into important cellular characteristics (20)
By measuring the deflection of the cantilever arm we can learn various properties from the cell sample such as:
Force variations
Topography
Elasticity
Stiffness
These are topographic images that were constructed from data collected from force mapping. The images at low force correspond to the true topography of the cell while those at a higher contact force show the appearance of cells during contact mode (21).
The tip scans the sample in close contact with the surface
The most common and simple mode
How Does
It Work?
The force between the tip and surface is constant during the scan
This image shows a 2 micrometer scan of collagen.
This image shows healthy red blood cells compared to a sickle cell (yellow).
And this is an image of a 447nanometer
virus.
All of these images were created
using Atomic Force Microscopy in Tapping Mode!
How the probe interacts with the sample for Contact mode
Analyzing the data
Here are some images taken with contact mode
Pyramids of iron powder (18)
A modified version of this equation is used as a model for viscoelastic analysis.

This model uses known properties such as Poisson's ratio and Young's modulus to calculate the force as a function of displacement (1).
DNA chromosomes (17)
Thermal
Noise
What can we
learn from this?
For more amazing AFM pictures, go to http://nano.tm.agilent.com/index.php/image-library
This video shows AFM in contact mode
(16)
(19)
(19)
(19)
(21)
`
Specimen stage
AFM can depict 3D as well as 2D images as shown above with an Algae Cell (7).
This presentation will discuss:
•Definition and purpose of AFM
•System components
The main component and how it works
•Applications and limitations overall
•Three modes of AFM
Contact mode
Tapping mode
Force Mapping mode
The theory behind the data
A source of noise and data disturbance
Overview
(15)
This picture shows how the system works together to create data (2).
Thermal noise is the fluctuation in the cantilever arm caused by the energy in water molecules within the sample.

The thermal noise can be detected within the force range of AFM. It can be calculated from the temperature and the cantilever's spring constant. It is important to consider this noise disturbance when processing data (22).
An example of sample preparation (25)
Full transcript