Finally we get into some true Nanoscience. The electron microscope is a workhorse instrument of nanoscience and all of high tech manufacturing. Its large depth of focus results in stunning three dimensional imaging as exhibited in the crystal "garden" found on the concrete sample shown here. The scanning electron microscope is covered first and the transmission electron microscope is covered in the next module.
I am currently using an excellent introductory electron microscope booklet produced by JEOL. It is available for download as a PDF from the JEOL's web site:
In this module reference is made to two earlier concepts. The calculations made for the photoelectric effect are very similar to those made here for the scanning electron microscope. I have the students calculate the velocity of an electron accelerated by a 30 kV electric potential, then determine the resolution of the electron to find the ultimate resolution of the SEM.
The laboratory consists of two parts. First the students do a simulation of the electron beam as it interacts with the sample. The die roll simulates the incoming electron beam. The students keep a tally of each event that happens. The grid of cells represents a sample consisting of partially aluminum and partially titanium. The electron beam is scanned across the sample from cell 1 to cell 16 and at each location the die is rolled to determine the event that happens. Each member of the group rolls the die 16 times. The possible events are a secondary electron, a backscattered electron, a characteristic X-ray or an Auger electron. For the secondary and backscattered electrons a tally is recorded in the appropriate grid. Finally the tallies are translated into a grayscale image. If there were 5 electrons detected the corresponding secondary electron image, SEI, cell is left white, if no electrons were detected in a cell then the corresponding SEI cell is colored black. The same is done for the backscattered electron image BEI. If an X-ray is detected then a X is added to the histogram associated with the particular element the beam is on at the time. A count of the number of Aluminum X-rays generated and the number of Titanium X-rays generated is recorded in the grid for the X-ray analysis. The same is done for Auger electrons.
The other thing that I use here is the atom game. The first time a different type of event occurs the students are supposed to demonstrate with the atom game model exactly what happens. For example when a characteristic X-ray occurs the students should move an incident electron in to knock out an inner shell electron and then show a outer shell electron falling down to take its place as a photon is given off.
For the second part of the lab the students bring in a sample of their choice, although it needs to be approved by the instructor. Some samples that have worked well are bugs, pollen, leaves, hair, butterfly wings, concrete, crystals, corroded metal. Biological samples such as cells require lengthy specimen preparation and so we do not do those until later classes although some students have done them as special projects in the past. The students are required to obtain an SEM image and post it to the course web site bulletin board.
Since I have only one SEM and about 16 students I do both lab activities at the same time. I divide them into groups of 3-4 students and bring 3-4 students into the SEM room at a time. If you are designing an SEM room you may want to consider a miniature set of bleachers for students to sit in while they watch the student running the SEM. I saw this used a t a school where they train students to operate a mixing board for music. Our SEM room does not have bleachers but I think it would be a good idea. This year I was able to get a student with prior SEM experience help operate the SEM while I was helping the other students with the other part of the lab and with sample preparation.
If you cannot afford a full SEM and dedicate a room to it you may want to consider sharing one of the new transportable SEMs with other schools. FEI, JEOL, Hitachi and other now offer a portable SEM which is about the size of a microwave oven.
We thought it would be neat to have one of these portable SEMs shared between several school districts so it would be at each school for 1-2 weeks and then go back for a maintenance check at a nanoscience center before going out to the next school. The same could be done with the portable AFMs that are available. The science teachers from the participating high schools could attend a separate training session on the SEM and AFM before they are allowed to request the tool.
Nasa also has a virtual SEM simulator available at the following web site.
You could use the simulator if you can not afford an SEM.