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How do you know it’s there if you can’t even see it?

Purpose

Learn about how we can "see" the nano world. Well, "image" is the better term since nano-sized objects are smaller than the wavelength of light, which means we can't "see" them. You will model how nano-scientists and others use indirect observations and measurements to identify the surface features of material that cannot be seen directly.

Overview

Remember back to the 
We rely on sight to tell us much about the world around us, but what can we use to measure the nano world which is smaller than light? (Remember back to How do the sizes of small things compare to one another?.) We'll begin by drawing an object based on touch alone and then see how well we could represent the information we obtained through our fingers. Next, we will expand this idea to scanning a surface with our finger. Finally, we will relate our experience back to the actual process nano-scientists use.

Investigate

  • Seeing by touch
    • Select a paper bag from the front table.
    • Reach in and feel the object - resist the urge to look inside.
    • Draw a description of the object in your notebook.
    • Pull the object out and compare your drawing to the actual item.
  • Simulating Scanning Probe Microscopy (SPM)
    • Information
      • A scanning probe microscope gives images of the surface of a sample by using a physical probe that measures the surface features, instead of “looking” at the surface.
      • Use your sense of touch to determine the pattern of bumps on a piece of cardboard. You will also place a piece of tape over your finger to determine if that affects your ability to scan the surface. 
    • Creating a sample
      • Create a 5" by 5" grid on the cardboard.
      • Make a pattern of physical depressions in the cardboard using your pen/pencil. Your pattern can be random or you can create a picture. You can add more texture by making the depressions/bumps from both sides.
      • Work in private so no one sees your pattern. Turn your cardboard over when complete.
    • Get organized
      • Have a piece of paper and pencil ready, and a bandana for a blindfold if peeking is an issue for you. ; )
      • Cover your pointer finger with tape.
      • Trade your cardboard piece with another person in the class, without looking at their pattern.
    • Mapping of the sample
      • Close your eyes and trace out the pattern using your taped finger. Use your other hand to draw the pattern that you are feeling.
        • Label your drawing with stuff like:
          • Title
          • Legend/key
          • Outline of cardboard
          • Location of bumps / depressions
      • Remove the tape from your finger and create a new map
        • Label the new drawing (same stuff as before).
      • Look at the sample you were mapping and discuss with the person who created it: 
        • How did your scan of the bumps with your taped finger compare to the actual bump pattern?
        • Was there more detail seen with your finger uncovered?
        • How do these images compare with the images we have from the nanoworld?

Why this works

The activity that you just performed is very similar to the way a scanning probe microscope gives images of the surface of a sample by using a physical probe that measures the surface rather than "seeing" the surface based on the light that bounces off of it. We have to use SPMs to image nano-sized materials and atoms rather than a light microscope because because nano-sized materials and atoms (0.1-100 nm) are smaller than the wavelength of light (400-700 nm). This session focused on building your background knowledge about scanning probe microscopes so you are better able to understand the functioning of an atomic force microscope (AFM) that will be explored in later sessions.

Wrap Up

  • Form two lines, standing back-to-back with a person from the other line.
  • Think about advice or tips you have for making this model work.
  • After 30 seconds or so the facilitator will call "turn" and you will discuss your advice with the person standing directly behind you. 
  • Repeat and think about some of the problems or challenges that come from using touch to see.

Materials

  • 1 paper lunch bag per student
  • 1 tactally interesting object per student (such as cotton balls, seashells, a die, paperclip, ball)
  • Clear tape (1 roll per group of 20)
  • 1 5" x 5" piece of thin cardboard per person (left-over cereal boxes work well)

Tools

  • n/a

Extensions

Based on

  • NCLT Scanning Probe Microscopy Lesson
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