how do we measure forces at the nanoscale level? 1 © 2009 mcrel physical science lesson 7 how do we...
TRANSCRIPT
How Do We Measure Forces at the Nanoscale Level?
1© 2009 McREL
Physical Science
Lesson 7
How Do We Measure Forces at the Nanoscale Level?
Investigating Static Forces in Nature:
The Mystery of the Gecko
How Do We Measure Forces at the Nanoscale Level?
2© 2009 McREL
Probes
What are some instruments (probes) you have used in previous science classes?
How Do We Measure Forces at the Nanoscale Level?
3© 2009 McREL
How to Measure the Height of an Object With a Probe
• Insert the probe in an area of the box with no object (9.0 cm)• Insert the probe in an area of the box with the object (8.6 cm)• The height of the object at that point is the difference
(9.0 cm - 8.6 cm = 0.4 cm)
Image 7.5
How Do We Measure Forces at the Nanoscale Level?
4© 2009 McREL
Making a 3-D Representation
Based on the height data gathered from your probing activity, use a spreadsheet program to make a 3-D representation of the unseen surface.
38
52
2 44
62
25
5 3 2 2
4 3 2 2
0
1
2
3
4
5
6
5-6
4-5
3-4
2-3
1-2
0-1
Image 7.6
How Do We Measure Forces at the Nanoscale Level?
5© 2009 McREL
Atomic Force Microscope
Image 7.8
AFM measures/images topography of surface: deflection of cantilever proportional to height of surface feature
sharp tipcantilever
Image 7.7
How Do We Measure Forces at the Nanoscale Level?
6© 2009 McREL
Comparison of AFM and Box Model
AFM Box Model
What characteristic is measured by the probe?
How is the characteristic measured by the probe?
How Do We Measure Forces at the Nanoscale Level?
7© 2009 McREL
Modeling a Gecko Seta
Question: How do gecko spatulas of a seta affect the amount of surface contact?
(d) spatula-shaped tips (~0.2m)
(d)
1 m
(d) spatula-shaped tips (~0.2m)
(d)
1 m
One gecko seta Many spatulas on the top of one gecko seta
Image 7.9 Image 7.10
How Do We Measure Forces at the Nanoscale Level?
8© 2009 McREL
Possible Setup
Image 7.11 Image 7.12 Image 7.13 Image 7.14
How Do We Measure Forces at the Nanoscale Level?
9© 2009 McREL
Compliant Surfaces
If one or both surfaces are compliant :
Image 7.15
Soft – Transparent Tape
Hard – Desk Top
apparent contact area real contact area
How Do We Measure Forces at the Nanoscale Level?
10© 2009 McREL
Spatulas on Surfaces
Image 7.16
Image 7.17
How Do We Measure Forces at the Nanoscale Level?
11© 2009 McREL
Journal Prompts
1. Look back at your previous methods (from lessons 5) as to how the gecko adheres to a wall. Are there some that you could eliminate because of the new information you now have? Are there any new interpretations you would add?
2. What new questions do you have about surface-to-surface interactions?
How Do We Measure Forces at the Nanoscale Level?
12© 2009 McREL
Measuring Tiny Forces
How could the force between one gecko seta and a surface be measured?
Micro-Electro-Mechanical System (MEMS) Probe
Single Gecko Seta
Cantilever
Seta slides on the surface and builds up larger adhesion forces
Pull Direction
Image 7.19Image 7.18
How Do We Measure Forces at the Nanoscale Level?
13© 2009 McREL
Typical Lateral Force Curve
Image 7.20
How Do We Measure Forces at the Nanoscale Level?
14© 2009 McREL
Adhesion Hypothesis Dense arrays of
“spatulas” conform to match topography of an opposing surface.
Tip of one gecko seta
Image 7.21
Image 7.22
How Do We Measure Forces at the Nanoscale Level?
15© 2009 McREL
Making Connections
1. How are AFM and the MEMS devices used to help understand gecko adhesion?
2. What do we now know about the amount of force between a single seta and a surface?
3. How does this new information help us understand the adhesion method for the gecko?
4. What should we explore next?
How Do We Measure Forces at the Nanoscale Level?
16© 2009 McREL
Flow Chart
7. How Do We Measure Forces at the Nano Level?
Scale: Visible and Invisible
Dominant Force: Extremely Small, Large in Number
Tools: Atomic Force Microscope
8. How Can a Gecko Walk on a Ceiling?
2. What Do We Mean When We Speak About Surfaces in Contact?
Scale: VisibleForce: GravityTools: Eyes
3. What Are Your Ideas About Small Sizes?
Scale: Visible/InvisibleDominant Force: VariesTools: Eyes, Instruments
1. How Can a Gecko Walk on a Ceiling?
Scale: VisibleDominant Force: GravityTools: Eye
5. What Types of Forces Can Hold Objects Together?
Scale: Visible/InvisibleDominant Force: GravityTools: Eyes and Hands
4. What Do We Learn When We Look More Closely?
Scale: InvisibleDominant Force:
Extremely Small, Large in Number
Tools: Special instruments (scanning tunneling microscope)
6. How MUCH Force Is Needed to Make an Object Stick? What Factors Affect the STRENGTH of Force Acting?