NANO AT HOME: An Experiment That You Can Try
PLEASE NOTE: The Center for Nano- and Molecular Science and Technology (CNM) at The University of Texas at Austin (UT-Austin) cannot guarantee the accuracy or the safety of these activities. Some of these activities might pose safety hazards for young children, and all activities should be performed under the supervision of a responsible parent, teacher or adult. The CNM and UT-Austin do not assume any responsibility for these activities or their results. If you have questions, corrections, or comments please do not hesitate to contact the CNM.
CD diffraction patterns
CNM scientists often create copies of very small structures by making molds of very small patterns to produce devices such as microchannel arrays. At home, you can easily make a mold of the very small grooves and patterns found on a compact disk (CD) or digital video disk (DVD). These patterns are nearly nanoscale, with embedded tracks that are 1600 nanometers apart and that contain even smaller pits to encode digital data such as computer files.
The data tracks are sufficiently small and close together to be able to diffract visible light. White light that strikes these features is broken into its component colors, which produces the rainbow of colors that you see when you hold a CD under light. Light waves from a single laser beam (which is usually made of only one color of light) interfere with each other (diffract) to produce a pattern of multiple beams when a laser is shone on these patterns.
CAUTION: Always involve the assistance of a responsible adult when doing experiments. Make sure that laser light is not directed at anyone’s eyes.
writable compact disk, such as a CD-R or CD-RW (WARNING: this experiment will make the CD unusable)
clear packaging tape
white school glue
laser pointer (optional)
1.) The tiny features that do the diffracting need to be exposed by removing the metal layer from the top of the CD. Old writable CDs often start to lose this metal layer over time. The layer can also be weakened by scratching a line through the metal layer or by carefully heating it with a hairdryer or heat gun and allowing it to cool. The metal layer can be removed by applying the packaging tape, making sure it has good contact with the metal layer, and then peeling the tape off the CD. When the tape is removed, the metal should come with it, leaving behind the tiny diffracting features. Keep dirt and fingerprints away from the features – do not touch the CD in places where you removed the tape.
2.) Next, smear a very thin layer of white school glue over the features and let the glue dry. The thinner the layer of glue, the faster it will dry (but be careful not to let your finger directly contact the CD).
3.) After the glue has dried completely, apply more clear packaging tape to the glue layer, making sure it has good contact with the glue. Carefully remove the tape, peeling up the dried glue. The surface of the glue that was in contact with the tiny diffracting features of the CD is now a mold, or a copy of the pattern on the CD. This dried glue layer will also diffract light. You can hold the glue layer up to bright light, like direct sunlight, to see a rainbow diffraction pattern. Or, a laser beam directed through the glue layer and the clear tape onto a wall will be diffracted into a row of spots (see picture).
Many other objects found around the house can diffract light, and with some experimentation you might be able to create replica molds of their tiny features, too.
– fireworks/holiday glasses
– finely woven translucent fabric
– some bird feathers
– halftone dot patterns on transparencies
– the phosphor dot array inside television picture tubes