42 www.microscopy-today.com • 2010 November doi:10.1017/S1551929510001112 An AFM Learning Module Employing Diffraction Gratings Tonya Coffey, 1 * Isaac Bryan, 1 Zachary Bryan, 1 Davidson Wicker, 1 Julia Drake, 1 Nicholas Pope, 1 and Donovan N. Leonard 2 1 Dept. of Physics & Astronomy, Appalachian State University, Boone, NC 28608 2 Dept. of Mat. Sci. & Eng., Univ. of Tennessee, Knoxville, TN 37996 * cofeyts@appstate.edu Note: Te Department of Physics and Astronomy at Appalachian State University recently acquired an Atomic Force Microscope (AFM) system for education and outreach activities. We developed a new learning module about difraction gratings that uses the AFM, which we are sharing with other educators who wish to introduce AFM in the classroom. Empirically, it appears that AFM excites students, in addition to giving them hands-on experience with an important tool used in physics and nanoscience research. Introduction Te Physics and Astronomy Department of Appalachian State University acquired a Nanosurf Easyscan 2 system [1] in the Fall of 2008 with funds from an NSF MRI award (DMR 0821124). We have used this AFM in over a dozen outreach activities for middle and high school students. We also have incorporated the AFM into several of our college courses, including an overview course on microscopy, a frst-year seminar course on nanotechnology, and a senior-level lab course for physics students. We have learned from our outreach and teaching experience that introducing AFM to students excites them about nanoscience and nanotechnology and provides an important opportunity for implementing experiential learning in the classroom. Several principles are reinforced by having the students learn to operate the microscope and acquire images themselves. When students take ownership of acquiring AFM data during sample analysis and are able to take with them a digital fle or print out the imaging results, it allows them to share what they learned with their peers and family. Tis learning cycle, from abstract conceptualization to concrete experience, has proven to be an efective pedagogy for students of all ages. To improve our outreach and teaching activities, we have developed several new learning modules for AFM, and we share one physics- based module here. DIFFRACTION GRATING LEARNING MODULE Below we show the difraction grating learning module in its entirety. Tis module was written for facilitators of the outreach or teaching activity. Purpose of Activity Tis activity draws on students’ knowledge of difraction gratings and the physics of electromagnetic radiation in the visible range interacting with a grating. Tis experiment teaches students how difraction gratings work and introduces them to an atomic force microscope (AFM). With this experiment, the students will learn how to use an AFM and see that it can be used to scan and image objects at a very small scale. At the same time, the students learn about the concept of the difraction of light. Materials Needed • Difraction gratings • Lasers (Te wavelength of light coming from the laser should be known. We used a He-Ne laser, which has a wavelength of 632.8 nm.) • Goggles (rated for specifc wavelength of light coming from the laser) • Meter sticks • Calculators • Atomic Force Microscope Information to Know Before the Experiment Difraction gratings. Difraction gratings are made up of a large number of equally spaced, parallel slits. Te slits cause difraction when light passes through them. Once the light is difracted, the light waves interfere with one another and produce a pattern. For a monochromatic light source, which will be used in this experiment, the pattern will consist of bright and dark spots of light. Te following grating equation defnes the path of the most intense beams of light: nλ = d(sin ϕ + sin θ ) where n is the difraction order, λ is a specifc wavelength of light, d is the distance between the slits or grooves of the difraction grating, ϕ is the angle of incidence, and θ is the angle of difraction. Atomic force microscopes (AFMs). Most AFMs use a combination of a tiny cantilever, a laser, and a photodiode to image a region at the micro or nanoscale. As the cantilever moves across the surface, the laser beam shines down onto the back of the cantilever and refects back to the photodiode as shown in Figure 1. Te information from the photodiode is then sent to the control electronics. Te feedback loop in the control electronics adjusts the vertical position of the tip to try Figure 1: Schematic diagram showing how the atomic force microscope signal is generated and collected. https://doi.org/10.1017/S1551929510001112 Published online by Cambridge University Press