Lights, Nano, Action! (10-12)
Purpose: The purpose of this lab is to learn a little bit about some of the new tools and
technologies that had to be developed in order to “see” and study the very small
nano world.
Materials: LED flashlight, diffraction slide, magnifying glass or jewelers’ loupe, AFM
model, object, Internet access
Procedures:
X-Ray Diffraction Model
1.X-ray diffraction has provided a great deal of information about crystalline
materials ranging from gold to table salt to DNA. Diffraction methods are used
when atoms or molecules are arranged in a repeating pattern. Diffraction occurs
because the wavelength of the X-rays and the spacing between the atoms in a
crystal are comparable. From
X-Ray Diffraction
the pattern of diffraction spots,
scientists work backward to
identify what atoms are present
in the crystal and how they are
arranged relative to one
another.
What follows is a scaled up version of using X-rays and the resulting diffraction
patterns to determine the arrangement of atoms. We will use red visible light
instead of X-rays and dots and marks on a piece of plastic instead of atoms.
Because the wavelength of the light and the spacing of the dots are comparable,
diffraction patterns will be observed.
2.Turn the slide so the word NANOWORLD on the right. Use a magnifying glass
to observe the dots on the slide. There are eight different arrangements of dots
on the slide for you to observe. Describe the similarities and differences between
the spacings of the dots on the top two arrangements.
Both show dots in straight rows, but the spacings are different.
3.Switch on the LED flashlight and hold it at arms length so that you can see the
red light. Hold the plastic piece by your eye and view the light through the top two
dot patterns. You need to adjust the location of both plastic piece and light until
you see the diffraction pattern produced. Describe the similarities and differences
between the two resulting diffraction patterns.
Both produce the same diffraction pattern but with different spacings (backward
from what students probably thought, the closer spaced dots produced the more
spread out diffraction pattern).
4.Explain how this demonstration models what we learn from X-ray diffraction.
A red light substitutes for the X-rays and dots for crystals. The light makes a
diffraction pattern with the dots, just like the smaller X-rays do with the smaller
crystal structure. Different structures result in different “pictures” for us to
study.
Atomic Force Microscope Model
1.An Atomic Force Microscope (AFM) uses a supersharp tip to move across a nanoscale surface. To
make an image, researchers move the tip of the AFM
back and forth across the sample many times. A
computer combines the data to create an image.
AFMs are very powerful. They can even detect and
make images of individual atoms! Some can also be
used to move tiny things around, allowing researchers
to make nano-sized structures. This activity models
how an AFM creates a scan.
2.The model scanner can be used to make an image of an object you cannot
see. Slowly slide the scanning mechanism and watch as the probes “feel” the
hidden object. Use the image to make several observations. List them below.
Answers will vary to both questions 2 and 3 and depend on the object in the
scanner.
3.Use your observations to make an inference about the object.
4.How does our model AFM allow us to “see” something that we cannot see?
Answers will probably include something about the height of the pins showing
something about the “topography” of the object that we try to make into an image
of the object.
5.Describe something our model AFM is unable to “see.”
Answers will vary but may include what the object really is, how many objects, or
if it is solid or hollow. The height of the pins show something about the
“topography” of the object but details may be sketchy.
Summing Up:
1.The smallest thing that can be “seen” is limited by the wavelength of visible
light. The shortest wavelength of visible light is about 450nm. What is the
frequency of this light?
6.67 x 1014Hz
2.This limit happens because of diffraction effects that occur when the
wavelength of the light is similar to the dimensions of the object being looked at.
Why can we “see” smaller things with x-rays than with visible light? What is the
frequency of an x-ray with a wavelength of 5nm?
The smaller wavelength of x-rays is closer to the size of the object allowing us to
“see” smaller objects. 6 x 1016Hz
3.Rosalind Franklin used x-ray diffraction. What did she discover using this
technique?
She worked on the structure of DNA (although Watson and Crick ended up with
the credit). This makes for some good reading and debate.
4.Do you believe x-ray diffraction could be used to determine the structure of an
amorphous substance? Why or why not? You may want to watch this video for
help with your answer: http://www.youtube.com/watch?v=A1mbgDXag7c
To get a sharp easy to interpret diffraction pattern you need the rigid structure of
a crystal structure. The more random arrangement of particles in an amorphous
substance will produce a diffraction pattern that requires more analysis to
understand.
5.There are one billion nanometers in one meter. The shortest wavelength of
visible light is about 450nm. DNA is about 2nm across. Why can’t you see DNA
with a light microscope? Why did scientists need to develop new tools to work at
the nanolevel?
See the answers to questions 1 and 2. In order to see structures at the nanolevel we
need to use “light” that is of the appropriately sized wavelength. Visible light is too
big to be of any use in viewing the very small. That is why new tools needed to be
developed.
6.Does x-ray diffraction allow us to directly observe a crystalline structure?
Explain.
No, but we can still learn about the structure we cannot see by how the particles
interact with the x-rays.
Lights, Nano, Action!
Purpose: The purpose of this lab is to learn a little bit about some of the new tools and
technologies that had to be developed in order to “see” and study the very small
nano world.
Materials: LED flashlight, diffraction slide, magnifying glass or jewelers’ loupe, AFM
model, object, Internet access
Procedures:
X-Ray Diffraction Model
1.X-ray diffraction has provided a great deal of information about crystalline
materials ranging from gold to table salt to DNA. Diffraction methods are used
when atoms or molecules are arranged in a repeating pattern. Diffraction occurs
because the wavelength of the X-rays and the spacing between the atoms in a
crystal are comparable. From
X-Ray Diffraction
the pattern of diffraction spots,
scientists work backward to
identify what atoms are present
in the crystal and how they are
arranged relative to one
another.
What follows is a scaled up version of using X-rays and the resulting diffraction
patterns to determine the arrangement of atoms. We will use red visible light
instead of X-rays and dots and marks on a piece of plastic instead of atoms.
Because the wavelength of the light and the spacing of the dots are comparable,
diffraction patterns will be observed.
2.Turn the slide so the word NANOWORLD on the right. Use a magnifying glass
to observe the dots on the slide. There are eight different arrangements of dots
on the slide for you to observe. Describe the similarities and differences between
the spacings of the dots on the top two arrangements.
3.Switch on the LED flashlight and hold it at arms length so that you can see the
red light. Hold the plastic piece by your eye and view the light through the top two
dot patterns. You need to adjust the location of both plastic piece and light until
you see the diffraction pattern produced. Describe the similarities and differences
between the two resulting diffraction patterns.
4.Explain how this demonstration models what we learn from X-ray diffraction.
Atomic Force Microscope Model
1.An Atomic Force Microscope (AFM) uses a supersharp tip to move across a nanoscale surface. To
make an image, researchers move the tip of the AFM
back and forth across the sample many times. A
computer combines the data to create an image.
AFMs are very powerful. They can even detect and
make images of individual atoms! Some can also be
used to move tiny things around, allowing researchers
to make nano-sized structures. This activity models
how an AFM creates a scan.
2.The model scanner can be used to make an image of an object you cannot
see. Slowly slide the scanning mechanism and watch as the probes “feel” the
hidden object. Use the image to make several observations. List them below.
3.Use your observations to make an inference about the object.
4.How does our model AFM allow us to “see” something that we cannot see?
5.Describe something our model AFM is unable to “see.”
Summing Up:
1.The smallest thing that can be “seen” is limited by the wavelength of visible
light. The shortest wavelength of visible light is about 450nm. What is the
frequency of this light?
2.This limit happens because of diffraction effects that occur when the
wavelength of the light is similar to the dimensions of the object being looked at.
Why can we “see” smaller things with x-rays than with visible light? What is the
frequency of an x-ray with a wavelength of 5nm?
3.Rosalind Franklin used x-ray diffraction. What did she discover using this
technique?
4.Do you believe x-ray diffraction could be used to determine the structure of an
amorphous substance? Why or why not? You may want to watch this video for
help with your answer: http://www.youtube.com/watch?v=A1mbgDXag7c
5.There are one billion nanometers in one meter. The shortest wavelength of
visible light is about 450nm. DNA is about 2nm across. Why can’t you see DNA
with a light microscope? Why did scientists need to develop new tools to work at
the nanolevel?
6.Does x-ray diffraction allow us to directly observe a crystalline structure?
Explain.