SEMED at MSU

A Scanning Electron Microscopy Educational Outreach Program at Michigan State University

Dr. Carl Boehlert: SEMED Program Director

Funded by the National Science Foundation

This document was prepared by:

Alfred University ASM/TMS Joint Student Chapter

Mr. Erik Pavlina: ASM/TMS Joint Student Chapter Member Dr. Alan Meier: ASM/TMS Joint Student Chapter Advisor

Spring 2003

Cover Photo: SEM Photomicrograph of the eye of a fly at 2000X. The whole eye:

~50x Magnification

Big fat hairy fly rump:

~25x Magnification

Introduction –Levels of Structure As we travel away from the surface of the Earth, objects we take for granted began to appear different. As we take off in an airplane, people, cars, and buildings become smaller and smaller. Eventually at high altitudes, we can see large fields and buildings but we can no longer see people. In photographs taken by astronauts from space, we can see the oceans and continents. The only major human structure visible becomes the Great Wall of China which appears as a thin line. Finally, photos sent back from the Voyager satellites show the Earth as a small dot. Depending on your point of view, you would have a very different description of an object. For example, you would describe the Grand Canyon very differently depending if you were hiking inside the canyon, flying over it in an airplane, flying over in the Space Shuttle, or looking at photographs from a Voyager spacecraft. By looking at an object at many levels, we can begin to truly understand it. By looking at our planet at these different levels, we have developed an understanding of how continents formed, where our planet fits into the universe, and we have also proved that the world is not flat (a major breakthrough which we now take for granted). In understanding materials, we also have to look at the material at many different levels. Instead of moving away from the object, we now move in closer and look at materials at a higher magnification. The Scanning Electron Microscope (SEM) is one of the tools that can be used to obtain magnified images to study the structure of materials. Once, we understand the structure of these materials, we can “engineer” these materials to obtain the properties we desire and we can create new materials whish have never been made before. Similar to the Earth, many materials look very different depending on the magnification of the sample. What we can see, and cannot see, is grouped according the size of the structure. In general, there are five levels of structure used when discussing materials. These levels are:

1. Macrostructure: Describes what we can see with the naked eye. This level of structure covers dimensions from 0.1 mm up to several kilometers. 2. Microstructure: Describes what we can typically see with a microscope. Dimensions as smaller than 1 micron (µm), or one ten -thousandth of a millimeter (0.0001 mm) , are associated with this level of structure. To put this in perspective, a human hair is approximately 100 µm or 0.1 mm in diameter. A distance of 100 µm is near the limit of the resolution of our eyes without a microscope. If we were to slice a human hair into 100 slices, they would be 1 µm thick. 3. Crystal structure: Describes the ordered, periodic arrangement of atoms in a crystalline or amorphous (non-crystalline) structure. This level of structure is associated with dimensions on the order of 1 nanometer (nm), or one millionth of a millimeter (0.000001 mm).

4. Atomic structure: Describes the level of structure concerned with the atom. Typically, dimensions of 1 angstrom (Å), or one ten millionth of a millimeter (0.0000001 mm), are used when describing the atomic structure. Atomic radii are associated with this level. 5. Electronic structure: Describes the structure of the electron and proton. This level is associated with dimensions of 1 femtometer (fm), one trillionth of a millimeter (0.000000000001 mm) and smaller. The SEM is one of the tools which allows us to study the microstructure of a material. There are other tools that can be used to study the crystal, atomic, and electronic structure.

The Interesting Stuff

Okay, enough factual information and preaching on the excitement of science and the joys of materials science and engineering. Let’s move on to the interesting stuff: the SEM pictures. Let’s start with some common items that you may think you are familiar with:

Mystery Item #1 What is this?

~1000x Magnification

Hint: You often see these in the spring.

Mystery Item #1 Let’s back off a little:

~350x Magnification

Let’s back off a little more:

~30x Magnification

Still not sure? Turn the page to find the answer.

Mystery Item #1

Let’s back off even more. Is it obvious yet?

~10x Magnification

Still haven’t guessed it? The picture is of a tomato seed. Here is what you see when you open your seed package:

Actual Size (2 seeds)

Mystery Item #2 Let’s look at another common item: What is this?

~3000x Magnification

Hint: Someone with some common “cents” should know.

~1000x Magnification

Mystery Item #2

Here’s one last picture:

~100x Magnification

Have you figured it out yet? Turn the page to find out. That’s no lie.

Mystery Item #2

~12x Magnification

It’s a picture of Abe Lincoln on the face of a shiny new penny (it doesn’t look as smooth and shiny at the microstructural level).

Let’s look at some man-made or engineered materials. You may be surprised at how these materials look using the SEM.

Paper Have you ever wondered what paper looks like? If you look at this page close enough, this is what you might see:

~60x Magnification

Paper Looking even closer, the individual fibers become larger. The fibers shown in this picture are approximately 100 µm in diameter:

~500x Magnification

And where does paper come from? Wood of course. Wood also has an interesting microstructure that is different at different levels.

Balsa Wood

~100x Magnification

~500x Magnification

Balsa Wood

~1000x Magnification

Post-ItTM Notes

Has your mother ever left you a list of chores stuck on the refrigerator? Chances are she used a Post-ItTM Note. Did you know that Post-it Notes resulted from unsuccessful experiments in developing SuperglueTM at 3M. It took over a decade before the company realized the potential of the adhesive and began offering Post-it Notes for commercial sale in 1980. The adhesive does not completely cover the paper. You can still see some of the paper fibers underneath the adhesive.

Post-ItTM Notes

Adhesive on Post-ItTM Note (~100x)

Adhesive on Post-ItTM Note (~500x)

Space Shuttle Tiles

Have you ever wondered what keeps the space shuttle from burning up during re-entry through the Earth’s atmosphere? Ceramic tile shields the thin aluminum skin of the shuttle from the immense heat resulting from the friction of the atmosphere on the shuttle during re-entry. The ceramic tile is composed of fused silica (SiO2) fibers. The high insulating properties of the silica combined with the air pockets between fibers form an insulating layer against temperatures that can reach as high as 3000 °F. It is possible to hold a space shuttle tile by the edge and then heat up the center of the tile with a blow torch.

Shuttle Tile (~1000x). Courtesy of W. Votava at Alfred University.

Chalk Chalk is primarily composed of calcium carbonate (CaCO3). At relatively low magnifications, the surface does not reveal why the chalk is able to leave a mark on hard surfaces.

~50x Magnification

If we look closer at the structure of the chalk, we can see calcium carbonate particles that are not bonded to one another very well. This weak bonding allows for the particles to easily break off and mark a surface.

Chalk

~1000x Magnification

Two more mystery items:

Mystery Item #3 What is this?

~500x Magnification

Mystery Item #3

~250x Magnification

Hint: Given enough time, this might become taller than you are. Still need some help? It is not a piece of wood, although it might look like one:

~100x Magnification

Mystery Item #3

~10x Magnification

It’s a picture of a sunflower shell and seed.

Actual Size (1x)

Mystery Item #4 What is this?

~250x Magnification

~50x Magnification

Hint: It’s not a seed or a bug. Be careful with one of these or you might get hurt. Turn the page to find out what it is.

Mystery Item #4 Here are a few more pictures to help you:

~10x Magnification

~10x Magnification

What is it? It’s the protective hull of a chestnut.

More Seeds When we looked at the tomato and sunflower seeds, we saw that seeds can very different surface finishes. Bean seeds have a relatively smooth surface while parsley seeds are very rough.

Bean Seed (~10x)

Parsley Seeds (~17x)

More Seeds

The difference in surface texture are even more obvious at higher magnifications.

Bean Seed (~500x)

Parsley Seed (~500x)

Some Gross-Out Information

There are very strict limits on the number of bug parts which can be included in the can of nuts which you buy are the store (I always felt that one bug part was more than enough). However, they are a good source of protein.

Fly Leg (~25x Magnification)

Fly Head (~25 x Magnification)

Some Final Thoughts

We hope that you have enjoyed the SEMED program and that you see the world around you in a different way. Materials Science and Engineering is one of the career paths where you can learn more about the world we live in and you can apply this knowledge to make new and better materials.

“It’s a small world…………………….but I wouldn’t want to paint it” --Steven Wright, Comedian “Wow! Science is COOL!” --Connor Mancini to Professor Poopypants during the Gerbil Jogger 2000 demonstration (in “Captain Underpants and the Perilous Plot of Professor Poopypants” by Dav Pilkey)