Atomic Force Microscopy: Seeing on the Atomic Scale

By Ashley Blystone

Atomic force microscopy (AFM) is a way to investigate the surface features of some materials. It works by “feeling” or “touching” the surface with an extremely small probe. This provides a three-dimensional (3D) map of the sample surface that gives us information about the roughness of the surface, and the distance between its atoms.

In this activity, you and your adult partner can build your own model to explore how an AFM works!

Helpful tip: This activity is a little complicated, so check out this video to see how it’s done!

Safety Suggestions
  • Thoroughly wash hands after this activity
  • Do not look directly into the path of the laser pointer
  • Have an adult helper around to cut the CDs
  • Caution: warm liquids

Materials

  • Laser pointer
  • Tape (Scotch, mounting, or double-sided)
  • Hot water
  • Scissors
  • Lego or Duplo blocks
  • 2 or 3 blank compact diss (CDs)
  • Play-Doh — (a lump about as big as a golf ball)
  • 1 sheet of printer paper
  • Pen, pencil, or marker
  • Zip ties
  • Paperclip
  • Rubber band
  • Small household objects (such as erasers, buttons, coins, keys, etc.)

Procedure

Getting Started and Preparing Your Sample

Place two or three blank CDs in hot water for at least 10 minutes. This will make them easier to cut into strips.

  1. Using tape, attach a Lego or Duplo block on each end of the narrow cardboard strip so that the blocks are supporting the strip.
  2. Use tape to attach the small household objects along the length of the cardboard strip. This will be your “sample” to test with your AFM model.
  3. Use Lego or Duplo blocks to create a stand for the larger piece of cardboard.
  4. Secure your sample to the standby connecting it to the blocks.
Assembling the AFM

Loop a zip tie around the laser pointer so that it covers the pointer’s “on” button. Tighten the zip tie so that it turns the pointer’s light on. IMPORTANT: do not look directly into the path of the laser light!

  1. Cut a narrow strip (about 2 cm or 1.5" wide) out of one of the CDs; be careful when cutting the CD.
  2. Carefully cut a small slot out of one end of the CD strip. The slot should be just big enough to fit the paperclip. If you make the slot too big try making a new, .
  3. Bend the paperclip so that it is unfolded. Place it in the slot so that it is perpendicular to the CD
  4. Use the rubber band to secure the paper clip in its spot in the slot. This can be tricky!
  5. Assemble two or three Duplo blocks to act as the base for your AFM.
  6. Attach the CD strip to the Duplo blocks using tape, with the shiny side of the CD facing up.
  7. Attach the Play-Doh to the AFM base, then press the laser pointer into the Play-Doh. Line it up with the CD strip, with the laser pointing toward the paper clip.
  8. Tape a piece of paper onto the base you made with cardboard and Duplo blocks.
  9. Place the stand behind the strip of household objects.
Analyzing the Sample

Make sure the laser pointer is on. Dimming the lights in the room can help you see the laser’s light.

  1. Place the AFM so that the paper clip is above the cardboard strip.
  2. Very slowly, move the AFM along the cardboard strip of household objects.
  3. As the paperclip lightly touches each household object on the cardboard strip, the CD will bend a little, changing the position of the laser light shining on the paper.
  4. Use a pen to make marks on the paper where the laser light hits it as the AFM moves across the cardboard strip.

What did you observe?

What happens to the position of the laser light when the paper clip touches an object?

  1. Do you think an object's height changes how much the laser light is deflected?
  2. If you look at the strip with your materials from the side, does it resemble the marks you made on the paper?
  3. Does the paperclip interact with each object in the same way? Does it sometimes get stuck on an object, or have a difficult time going across others?

How does it work? / Where's the chemistry?

The way atoms are arranged inside a material affects that material’s properties, such as hardness, thermal and electrical conductivity (ability to allow electricity), and opaqueness (ability to see through). Understanding how the atoms are arranged, especially on a material’s surface, is necessary for learning about the material’s properties. But this is not easy, because atoms are very tiny!

So, how do we actually “see” atoms? An AFM can be used to “feel” the arrangement of items on a material’s surface. An AFM uses a tool with a very tiny needle on its end, which can either be repelled or attracted to the surface. The needle is dragged across the surface of a material, and when the needle touches an atom, it causes the tool to bend upward. A beam of laser light shows how much the tool has bent, and that tells us the height of the atom. The resulting image is a height map of the material’s surface, similar to a map that shows mountains and hills from above.

In our model, the sensor is composed of a paperclip attached to a CD, where laser light is reflected from the CD sensor onto a sheet of paper. A group of objects attached to cardboard acts as the atoms on a surface. When the device is the surface, the paperclip moves, and the laser light is deflected or resisted. The deflection of the laser light is recorded on a piece of paper with a pen or pencil, giving you a map of the surface.

Ashley Blystone is a Research Specialist at the University of Illinois at Urbana Champaign.

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