Micro worlds: high-tech microscopes allow scientists to view objects with never-before-seen detail.
Magnified 50 times, a strawberry's seedy surface appears as an alien mountain range. Zooming to 300 times magnification, a microchip looks like a city map. At 1,000 magnification, human red blood cells pass for smooshed jelly beans, while ragweed pollen resembles spiky volleyballs. Since the 1950s, scientists have been improving the high-tech microscopes they use to get an up-close view of the specimens in their labs. Not only do these tools allow them to see the samples in unprecedented detail, but they also lead to new discoveries.
Just this year, biologist Claire Rind at Newcastle University in the United Kingdom used a scanning electron microscope to help prove that several tarantula species produce silk with special bristles on their feet called setae. The silk helps the spiders cling to vertical surfaces. But biology isn't the only discipline in which microscopes are changing how we see and understand the world. Advanced microscopes are vital to the relatively new field of nanotechnology, in which engineers build materials and machines using the tiniest units of matter: atoms and molecules.
Biology labs in most schools are equipped with optical microscopes, which use pieces of curved glass called lenses to focus light waves. The light waves start at the bottom of the microscope and go up through a prepared slide that holds a thin slice of whatever you're examining.
Once the light passes through the sample, it heads up to the lenses, which focus the light so you can see the specimen in detail through the eyepiece. Professional optical microscopes work like the ones you use in class, but with bigger lenses and therefore greater magnification.
To see specimens in even more detail, scientists turn to scanning electron microscopes (SEMs). Instead of using light waves, SEMs direct beams of negatively charged particles called electrons over a sample (see A Modern Microscope, p. 20). When those electrons hit the sample, other electrons get knocked off the atoms on the object's surface. "The way that the electrons come off the sample mimics what you expect to see when light scatters off of an object," says Scott Chumbley, an engineering professor at Iowa State University.
SEEING 3-D DETAIL
Since you're looking at tiny electrons instead of light, you can see much smaller objects with an SEM. The best optical microscopes can focus on a single plant or animal cell. But the best SEM can zoom in 10,000 times closer, to show you the DNA in the nucleus of a plant cell!
Another advantage of SEMs is that they have a greater depth of field than an optical microscope. In an optical microscope, your sample is a flat slice squeezed between slides. "An SEM has the ability to focus electrons that come from different areas on the sample, so your image looks 3-dimensional," says Chumbley.
SEMs are the primary tools for the field of nanotechnology. Engineers are now working at the molecular scale to build structures and mini-robots that are only a few nanometers wide. This unit of measure is one billionth of a meter, or roughly 100,000 times thinner than a human hair!
Today's nanoengineers are building more-efficient solar cells, superfast computers, and even scaffolding for growing human tissue in the lab. "You may think a human cell is very small, but a human cell is huge compared with a lot of the materials that we're making these days," says Chumbley. Some of these machines and materials are made with chemicals that cause nanostructures to grow. Others are built with high-tech machinery that can move and measure single atoms. All of these engineers' work on the nanoscale would be impossible without SEMs. Extremely magnified images help scientists visualize their nanoscale creations and guide their work.
A MODERN MICROSCOPE
These are the basic components of an SEM.
ELECTRON GUN: produces beam of electrons
MAGNETIC LENSES: focus the electron beam
BACKSCATTERED ELECTRON DETECTOR: provides details about the specimen's composition
VACUUM CHAMBER: encloses apparatus because air molecules can interfere with the electron beam
ANODE: accelerates the electron beam
DETECTOR: provides images of specimen's surface
[WHAT DO YOU THINK?]
What are some of the biggest challenges to building materials on the atomic scale?
NATIONAL SCIENCE EDUCATION STANDARDS:
Grades 5-8: Understandings about science and technology
Grades 9-12: Understandings about science and technology
COMMON CORE STATE STANDARD:
READING INFORMATIONAL TEXT:
7. Integrate information from Several formats (photos, captions, text)
Learn about how scanning electron microscopes (SEMs) work and how they have led to scientific discoveries.
* What does a microscope do'? (It magnifies small objects.)
* What are some examples of things studied under microscopes? (cells, hair, insects, bacteria, etc.)
* How can microscopy be useful to scientists? (It allows them to study things they aren't able to see with the naked eye.)
[DIGITAL STICKY NOTES] 1. Ask your students the before-reading questions. Record their definitions on a digital sticky note. Engage them in a discussion about microscopes and their uses.
[MASK TOOL] 2. Open the digital edition to pages 18-19, and have students do the same in their magazines. Use the mask tool to highlight the image on page 18. Ask students to take a close look at the photo. What do they think the photo on page 18 looks like? Can they guess what object it is showing magnified?
3. Call on a volunteer to read the first paragraph. Ask students if they agree with the author's description of the SEM image of a strawberry on page 18, and have them discuss their responses. Then read the rest of the article together, allowing student volunteers to read paragraphs aloud.
4. Revisit the before-reading questions and answers. Discuss any additional information students want to include in their answers. Have them use supporting details from the article, photos, captions, and infographic.
[GAME] 5. Click on the game icon on page 20. Play the matching game as a class, matching the images of the full-size objects to what they look like under a scanning electron microscope.
Read the text in the box labeled "What Do You Think?" on page 19: "What do you think some of the biggest challenges of nanoengineering are?" Support your opinion with facts from the text. Discuss what your students think about this use of SEM technology.
Use this "SEMs vs. Optical Microscopes" skills sheet from the online database at www. scholastic.com/scienceworld to analyze what your students have learned from the article with a Venn diagram.
DON'T TEACH PHYSICS?
Go to www.scholastic.com/scienceworld to download these assessment skills sheets instead:
BIOLOGY: BUILDING A BETTER SCOPE
Microscopy has changed since its invention in the 1500s. Use this skills sheet to help your students track the microscope and its improvements through time.
EARTH: ASTRONOMICAL DISTANCES
Scanning electron microscopes can help scientists see tiny things that they've never been able to see before. Astronomers use similar optics to investigate the universe. Use this activity to help your students understand how far from Earth several astronomical objects are.
* VIDEO EXTRA: Watch a video about nanotechnology at: www.scholastic.com/scienceworld.
* Find more information about microscopes at the Nobel Prize's Web site: www.nobelprize.org/educational/physics /microscopes/1.html.
* Learn more about nanotechnology at the National Nanotechnology Initiative: www.nano.gov.
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|Title Annotation:||PHYSICS: OPTICS|
|Date:||Oct 17, 2011|
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