Activity pubs.acs.org/jchemeduc
The Analog Atomic Force Microscope: Measuring, Modeling, and Graphing for Middle School Valerie Goss,† Sharon Brandt,‡ and Marya Lieberman*,† †
Department of Chemistry & Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, United States Science Department, LaSalle Intermediate Academy, South Bend, Indiana 46628, United States
‡
S Supporting Information *
ABSTRACT: In this hands-on activity, students map the topography of a hidden surface using an analog atomic force microscope (A-AFM) made from a cardboard box and mailing tubes. Varying numbers of ping pong balls inside the tubes mimic atoms on a surface. Students use a dowel to make macroscale measurements similar to those of a nanoscale AFM tip as it scans a surface during imaging, and then they build a three dimensional model of the hidden surface. This laboratory is targeted for middle school students, though it readily can be modified for grades K−12.
KEYWORDS: Elementary/Middle School Science, High School/Introductory Chemistry, Laboratory Instruction, Physical Chemistry, Analytical Chemistry, Hands-On Learning/Manipulatives, Analogies/Transfer, Atomic Spectroscopy, Laboratory Equipment/Apparatus, Nanotechnology
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Our tool provides a hands-on learning experience in a simple model, the analog AFM. The A-AFM demonstrates the physical concept of scanning and tactile feedback used in nanoimaging, and introduces the atomistic picture of matter, quantization, and graphing and mapping. The A-AFM is well suited for middle school students because it is tactile, reinforces math skills, incorporates the use of manipulatives, is a collaborative exercise, and allows students to use critical thinking and creative and imaginative skills. We describe our model and provide instructions on how to build it. Prelaboratory questions, as well as instructions for AAFM student operation during a 40 min class period, are provided. Finally, the A-AFM can be modified and tailored for students in various levels of K−12 science, and in the Supporting Information, we describe how to make this activity appropriate for students working below and above middle school grade levels.
o illustrate to middle school students how the scanning atomic force microscope (AFM) works, we designed and built an analog atomic force microscope (A-AFM) that allows students to tactilely “image” different sample surfaces. By probing the hidden surfaces, graphing numerical values, and building with LEGO blocks, students construct a threedimensional (3D) model of the surface topography. In this way, students perform tasks similar to research scientists who study and capture images of nanosized materials on a surface. The model AFM introduces nanotechnology as an engaging, collaborative activity that gives students a good intuitive understanding of how the AFM images a surface that cannot be seen by the naked eye. A series of activities focusing on math and science concepts aids teachers in integrating the A-AFM into the curriculum. This learning tool can be modified with activities for primary grade students or for high school students. The AFM classroom activity exposes young science students to a tool used in nanoscience and nanotechnology, newer scientific frontiers that are expected to have a broad impact on their future. The atomic force microscope1 is a scanning probe microscope (SPM) that works by moving a tip (or a probe) over a surface and measuring the surface topography. Several excellent laboratory exercises demonstrating the operation and principles behind atomic force microscopes and scanning tunneling microscopes are available for college students.2−5 However, there are no activities for grades 5−8. © 2013 American Chemical Society and Division of Chemical Education, Inc.
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EXPERIMENTAL SECTION
Materials
Students use a 0.75 in. × 18 in. wooden dowel as a probe (analogous to the AFM tip) to measure height variations on a concealed surface inside a cardboard box prefilled with ping pong balls arranged in the shape of a letter. A rubber band, wrapped around the dowel, is used to mark the measured heights. The 8 in. × 8 in. × 12 in. box contains a square array of Published: February 5, 2013 358
dx.doi.org/10.1021/ed200704j | J. Chem. Educ. 2013, 90, 358−360
Journal of Chemical Education
Activity
25 (1.5 in. × 12 in.) mailing tubes. Each tube is filled to variable heights with ping pong balls (table tennis), which represent atoms. Graphing can be accomplished with ruled graph paper or with any available graphing program. 3D models are built using a LEGO base and blocks. Each pair of students needs one setup (experimental box and dowel, see Figure 1). Other
For students in grades 1−4, the dowels were modified with marks every 3.8 cm (the diameter of one ping pong ball) that indicated the number of balls in the tube. However, for grade 5 and higher, the students had to perform simple math to determine the number of balls in each tube (Figure 2). Building the 3D Surface Model
necessary supplies are a ruler, pencil, rubber band, and graph paper. In the activities, calculators were used but are optional. A complete supply list with suppliers, details for box construction, and a preformatted data sheet are included in the Supporting Information.
After all 25 locations are probed, the 5 × 5 data sheet displays the number of ping pong balls at each location. 3D models are built by stacking corresponding numbers of LEGO blocks onto the base using the number of “atoms” obtained from the data sheet. The students built 3D models before graphing to help them to identify the letters on the surface. Because students are not able to “see” the surface, just as is the case for nanosurfaces, the height data is used to determine surface structure and build the model. As students determined the LEGO-shaped surface, classroom teachers tracked the responses on the classroom board, similar to the “Wheel of Fortune”, as letters or characters are identified. The bottom of each A-AFM box is numbered, and the corresponding letter or character is written on the board in the space for each numbered A-AFM box. Thus, by pooling their data, the class analyzed the sequentially placed letters to determine a phrase or word.
Probing the Surface and Gathering Data
Making the Graphs
The initial task in this experiment involves measuring the height of the empty tube and the diameter of one ping pong ball. Working in pairs, students make measurements and record them in the corresponding location in the data table (provided in the Supporting Information). Surface probing is accomplished by placing the dowel inside one tube, and then rolling the rubber band along the dowel until it matches the height of the tube. The rubber band serves as a movable marker. The dowel is then removed from the tube, and the length from the rubber band (mark) to the end of the dowel is measured and then recorded in the data table. By subtracting this measured value (empty space) from the height of the tube, students determine the space inside the tube that is occupied by ping pong balls (Figure 2). Finally, students divide the occupied space by the diameter of one ping pong ball to determine the number of “atoms” on the surface at that location. Rounding is necessary in most calculations. Calculations are performed on the data sheet, and the number of atoms is recorded there as well.
Students prepared graphs by analyzing a single row of data. Figures 3A and 3B show a transparent schematic of the box
Figure 1. (A) Classroom with the A-AFM setup at each desk, and (B) a student building a model surface.
Figure 3. Analog AFM box: (A) transparent schematic of the A-AFM showing the 25 mailing tubes; (B and C) ping pong balls “atoms” prefilled into the mailing tubes to create the surface; only one row of prefilled atoms is shown in cross section (B) and top view (C); and (D) a bar graph showing the topographic profile.
with tubes, and an example of how one row of ping pong balls may be arranged. The top view of that row (Figure 3C), and the profile bar graph (Figure 3D) show the number of ping pong balls or atoms inside the tube at specific sites. Profile graphs were made by plotting the information from the completed data table using graph paper. Students defined a vertical, horizontal, and diagonal row. Using the values from their data table, students made graphs plotting the number of ping pong balls versus the position in the row, allowing them to see the spread graphically. For consistency, the horizontal axis can represent the position in the row, and the vertical axis the number of ping pong balls. Graphing (Figure 3D) using software, such as Microsoft Excel, can be substituted for advanced students, and details on how to use the software is provided in the Supporting Information. Students can prepare contour plots directly on the data sheets by coloring or shading in the locations where there are five or more ping pong balls. Contour plots are “topo” plots that allow students to see their data revealing height variations in the surface topography.
Figure 2. Making measurements. A sample measurement and calculation demonstrating how to determine the number of ping pong balls (atoms) in one prefilled tube. 359
dx.doi.org/10.1021/ed200704j | J. Chem. Educ. 2013, 90, 358−360
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HAZARDS There are no hazards involved in this laboratory.
Activity
ASSOCIATED CONTENT
S Supporting Information *
Description on how to make this activity appropriate for students working below and above middle school grade levels; supply list with suppliers, details for box construction, and a preformatted data sheet; information about prelab activities. This material is available via the Internet at http://pubs.acs.org.
RESULTS Each of the 25 tubes contains between 1 and 8 ping pong balls arranged to spell out various letters. We found it added to the challenge and interest of the task if we used some height variation so that the letters did not become apparent until the students colored the contour plots or built 3D representations of their surfaces (Figure 4). The sample 3D models of the letters show examples of our strategy, along with the shaded letters, A, F, M representing data for three different A-AFM boxes.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS We thank the University of Notre Dame Extended Research Community (NDeRC) for their continued support of our STEM education efforts and to the National Science Foundation, GK−12 Program for funding. In particular, we thank NDeRC alums Michael Crocker and Rebecca Quardokus. We acknowledge the generous help of Patrick J. Mooney in editing this manuscript.
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REFERENCES
(1) Binnig, G.; Quate, C. F.; Gerber, C. Phys. Rev. Lett. 1986, 56, 930−933. (2) Zhong, C. J.; Han, L.; Maye, M. M.; Luo, A.; Kariuki, N. N.; Jones, W. E. J. Chem. Educ. 2003, 80, 194−197. (3) Pullman, D.; Peterson, K. I. J. Chem. Educ. 2004, 81, 549−552. (4) Heinz, W. F.; Hoh, J. H. J. Chem. Educ. 2005, 82, 695−703. (5) Planinšič, G.; Kovač, J. Phys. Educ. 2008, 43, 37.
Figure 4. Students made 3D models of the surface using LEGOs to represent the surface inside the box, shown here as letters (A, F, M). Also shown are shaded contour plots of the corresponding boxes.
Building and interpreting LEGO surfaces offer students the opportunity to transform collected data into a visual representation. At the end of the hands-on collaborative effort, each class discovers that the surfaces they probed are the shapes of letters, which spell out a message such as “AFM NANOTECHNOLOGY!” or “AFM NANO”.
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DISCUSSION The A-AFM laboratory has been used by 1030 grade 2 to grade 10 students. In middle school classrooms, the A-AFM activity was usually completed in a 40−50 min class session. The prelab activities in the Supporting Information took about 30 min of class time (before the lab) and could be done a day or two ahead of the lab. Using a class period to introduce nanotechnology gives students the understanding about “why” they should care about the subject. Teachers at all grade levels can relate this activity to educational standards on scale and measurement, as well as science and technology. The A-AFM is designed to provide a tactile experience for K−12 students to allow them to acquire knowledge and understanding about a nanotechnology research tool. In the future, such analog instruments will continue to provide students with impactful connections to the nanoworld. 360
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