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An Exploration of the Nanoworld with LEGO Bricks Dean J. Campbell,* Josiah D. Miller, Stephen J. Bannon, and Lauren M. Obermaier Department of Chemistry, Bradley University, Peoria, Illinois 61625, United States ABSTRACT: LEGO bricks can be used for a number of demonstrations of chemical structures and properties, especially at the nanoscale level. These bricks can also be used to model instrumentation that probes these structures and properties. Detailed resources about many of these demonstrations are located on the extensive Web site “Exploring the Nanoworld with LEGO Bricks” at http://mrsec.wisc.edu/Edetc/LEGO. This article describes the major features of the Web site, some of the site history and recent additions, and some related efforts that have had origins in this site. KEYWORDS: General Public, High School/Introductory Chemistry, Public Understanding/ Outreach, Demonstrations, Hands-On Learning/Manipulatives, Crystals/Crystallography, Laboratory Equipment/Apparatus, Molecular Properties/Structure, Solids he resources available on the Web site “Exploring the Nanoworld with LEGO Bricks”1 show how physical and chemical principles related to molecular-scale science and technology can be demonstrated with LEGO building-brick models.1 These resources continue to be developed to educate the public regarding structures with nanoscale dimensions.2-4 There are a number of reasons to use LEGO bricks for nanoscale science education purposes: • Many people are familiar with LEGO bricks, which have been produced for over 50 years,5 and their properties, such as connectivity and color. The multitude of LEGO Web sites shows that many people think that LEGO bricks are fun! • LEGO bricks typically have many connection points, allowing flexibility in building three-dimensional models. These models are excellent tools for grasping concepts such as structure-function relationships. • LEGO bricks can be readily connected and disconnected, allowing for rapid construction and modification of models. • Many bricks have simple, abstract shapes and simple colors that enable the same bricks to mean different things in different models, whether they are of atomic-level structures of matter, or macroscopic instrumentation used to study that matter. Additionally, many models can be built without frustrating or intimidating the user. The bricks can also be used as a medium for artistic expression.6,7 This LEGO project began in 1997 with non-LEGO educational demonstrations of scanning probe microscopy (SPM) and associated techniques such as atomic force microscopy (AFM) and magnetic force microscopy (MFM).8 One of these demonstrations of MFM used flexible sheet “refrigerator magnets”.9,10 These sheets are typically magnetized so that alternating north and south poles are arranged in parallel stripes on the back of the sheets. A narrow strip of refrigerator magnet material, representing the cantilever of an MFM, is alternately attracted and repelled by those magnetic stripes, Figure 1 (inset). Both smoothsurfaced magnets have been sprinkled with iron powder to
illustrate their ridge-like pattern of magnetic fields. In an actual SPM, as the cantilever tip and a sample surface are moved relative to each other, their interactions cause the cantilever to deflect in various ways. The very small deflections of a real SPM tip must be observed by monitoring the displacement of laser beam reflected from the tip of the cantilever onto a photodiode array; by contrast, the magnetic strip deflection in the demonstration can be observed by the naked eye. It was realized that a reasonable approximation of the SPM cantilever could be achieved with thin LEGO bricks rather than the magnetic strip, Figure 1.10,11 The stable end of the cantilever is connected to stacked bricks. Mounted at the top of the brick stack is a light source such as a bright light-emitting diode or laser pointer. At the top of the free end of the cantilever is a reflective surface such as a mirror or a swatch of metalized Mylar film, and on the underside of the cantilever tip is a probe to interact with a model substrate. The cantilever is held in place and the surface is moved back and forth underneath the probe, similar to an actual SPM. The original LEGO SPM model used a magnet to interact with a magnetic substrate such as a refrigerator magnet, making it more specifically an MFM model. The model shown in Figure 1 more accurately resembles an AFM; here, the cantilever tip is in physical contact with the substrate, so the bricks on the LEGO substrate surface can be taken to represent raised features such as atoms on a flat surface. The interaction between the probe tip and the surface causes deflection of the cantilever. Light from the illumination source reflects from the reflector on the cantilever and shines onto a wall or screen. The farther the SPM is positioned from the wall, the more the cantilever deflection will shift the beam spot location on the screen. In the example shown in Figure 1, every time the AFM tip passes over the raised bricks on the flat plate, the cantilever and beam spot deflect upward, and the paper over which the moving plate slides is marked with a pencil. The pencil marks on the paper are a map of the brick
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sophisticated automated models seem to be best suited for a “look but do not touch” display setting. Bearing in mind the challenges of cost and difficulty of access to specialized components, the simplest models are often best suited to a hands-on classroom environment.
Figure 1. Hand-driven LEGO model of a scanning probe microscope. The light from the pocket laser at left shines onto the square of transparent plastic at the top of the probe tip and reflects onto the vertical piece of paper at right. Inset shows a refrigerator magnet model of a magnetic force microscope.
locations on the flat plate. The LEGO SPM models have generated the most interest at workshops and from visitors to the Web site. Many variations of the LEGO SPM have been built over the years, reflecting some of the design flexibility associated with many of the other models. The model can be built with the simplest rectangular bricks and the surface can be moved by hand. The LEGO Group has produced a wide variety of sensors, actuators, and control systems over the years, enabling the development of partially automated models. Models featuring electronic components can be captivating to members of the public and can help to illustrate what sensors and actuators must be considered for real instrumentation. Each LEGO control system has had advantages and disadvantages. The Dacta system was designed more for educational circles rather than household use. The Dacta system LEGO SPM model interfaced with a computer, drove motors to move a model substrate in two dimensions, collected light intensity data from light reflected from the top of the cantilever tip, and finally graphed that data as a function of time. A surface containing a physical series of bumps or a magnetic series of alternating north and south poles could interact with the cantilever tip to produce a wavelike graph. The Dacta system was followed later by the RCX system, and finally the NXT system. These systems contained programmable control modules that were capable of directing operations and collecting data without the need to be connected to a computer at all times. This capability is interesting, but not strictly necessary for any of the models used in this project. The RCX system used the same sensors and actuators as the Dacta system. Although the RCX system was not really capable of collecting data for graphing, this can be done more readily with the more recent Mindstorms NXT system. The sensors and actuators in the new NXT system have been redesigned, with shapes that are less blocky in appearance than the older systems.12 These powerful components can be interfaced with the more traditional sensors, actuators, and passive bricks, but there are fewer points of attachment, which can make for challenging model design. Additionally, the automated components for these models are quite expensive. The highly
’ THE LEGO BOOK The success of the SPM model has led to the development of additional models. Descriptions and instructions associated with many of these models have been compiled into the book Exploring the Nanoworld with LEGO Bricks.1 The main book is divided into four parts. The first part, “Structures at the Nanoscale”, includes the concept of a unit cell as the fundamental repeating unit of a crystal. Most models of atomic-level structures represent atoms as spheres, which presents challenges when using modeling materials composed almost entirely of rectangular building blocks. As with the SPM models, these “atoms” can be built with varying degrees of complexity and cost, ranging from a single-peg brick to a four-layer brick cluster that has a nearly octahedral shape, Figure 2 (middle). No LEGO brick has its width equal to its height, so the bricks are not even cubes, let alone spheres. As a result, LEGO models of cubic unit cells are typically not perfect cubes. However, the atomic-level models are designed to focus on correct representations of contact between the atoms. The four-layer brick cluster has been used for many models because of its ability to interconnect with other four-layer clusters in many directions. LEGO brick clusters have an advantage over simple spheres in modeling atoms because they can be used to represent fractions of atoms, an important concept in discussions of unit cells. A single cluster can also be built with multiple brick colors, representing how one position in a structure can be randomly occupied by more than one element. Figure 2 shows a model of the unit cell of the high-temperature phase of copper mercury iodide, which features atoms of different sizes, combined-color atoms representing the random occupancy of copper and mercury, and fractional iodide atoms. Models of molecular compounds can also be made with LEGO bricks. The best approach to modeling a tetrahedral atomic arrangement is to treat the central atom bricks as a cube and place the peripheral atom bricks at four of the possible eight corners of the cube. The best approach to modeling a triangular planar atomic arrangement is to place two peripheral atom bricks at the possible eight corners of the cube and place the third atom brick at either the opposite edge or the face of the cube. The second part of the book, “Probing the Structure of Materials at the Nanoscale”, contains brief descriptions of techniques (including SPM) that are used to determine the structures of solid materials. The photometer devices described in this section incorporate a non-LEGO component (a plastic cuvette glued to a 2 peg by 2 peg brick) and a Dacta or RCX light sensor that is sensitive to far-red wavelengths of light, Figure 3. When incorporated into a model with the cuvette and a light source, light absorption of aqueous copper(II) ions can be measured.13 Others have also incorporated LEGO bricks into photometer models.14 These models illustrate the capabilities of the LEGO system as an optical bench, especially when using large base plates with square peg arrays. LEGO components lend themselves to such rapid prototyping that they have been integrated into home-built optical mounts for a Raman spectrometer at this university. 603
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Figure 4. A LEGO diffractometer. Light from the pocket laser shines from right to left through a blazed plastic diffraction grating (held by the blue stack of bricks). The light sensor at left is mounted on a motorized arm that can be moved up and down. The sensor is connected to the NXT control module and can detect the first-order diffracted light from the grating.
mesoscale spontaneous assembly (a.k.a. self-assembly), which has been explored as an alternative to photolithography for construction of nanoscale structures.19,20 The ABS plastic of LEGO bricks is denser than water,21 but bricks can be floated peg-side down on water like little block-shaped boats. Capillary interactions between the bricks draw them together into organized two-dimensional arrays that can actually be solvent welded with a lightweight nonpolar solvent. A similar demonstration involves assembly of LEGO brick and magnet clusters on dry, smooth surfaces.19 If the clusters are made sufficiently large, the magnets will be prevented from attracting together. This can be used to model how surfactant layers on magnetite nanoparticles can prevent their aggregation in ferrofluid suspensions.22,23 This book section also describes models of photonic crystals, which contain repeating structures on a similar size scale as wavelengths of visible light. Because light striking these crystals can be scattered and diffracted in a number of directions, they are being studied for a number of applications in optics.24,25 The book closes with appendices that give extensive directions for some of the more sophisticated models of instrumentation, as well as models of selected unit cells.
Figure 2. Model of the unit cell of the high-temperature phase of copper mercury iodide (right). Fractional (1/8 and 1/2) iodide atoms are yellow (complete atom shown in middle of figure). Random occupancies of copper and mercury are represented by mixed red and blue bricks (left).
Figure 3. A LEGO photometer. Light from the flashlight shines from left to right through the window shutters (to control light intensity), through the plastic cuvette, and into the light sensor connected to the NXT control module.
“Structure-Property Relationships at the Nanoscale”, the third part, links the atomic and molecular arrangement of matter to physical properties. For example, polymer chains that are not cross-linked can be represented by long bricks or chains of bricks that can be manually slid past each other. These chains can be immobilized by other bricks, illustrating how cross-linking stiffens polymer structures.15 The concept of Poisson’s ratios can also be illustrated with LEGO bricks. As an object is stretched, it typically decreases in width, and this ratio of dimensional changes is a positive Poisson’s ratio. Structures can also be fabricated with negative Poissson’s ratios if they have a specially kinked framework structure.16 The LEGO structures can actually be stretched and exhibit both types of ratios. The fourth part of the book, “Building Structures at the Nanoscale”, describes methods and challenges of building nanoscale structures with macroscale equipment and includes a twodimensional model of the process of photolithography.17 A more recent collaboration with researchers at the University of Maryland has yielded a more sophisticated three-dimensional demonstration of photolithography.18 The small, regularly shaped structure of LEGO bricks lend themselves well to demonstrations of
’ OTHER FEATURES OF THE WEB SITE The Web site associated with the book contains many other features. An extensive collection of building instructions for atomic-scale models including solid-state crystal structures, discrete molecules, and polymer chains are available. An interactive periodic table built from LEGO bricks is featured. Clicking on a brick corresponding to an element opens building instructions for an atomic-scale model of a solid form of that element. Building directions for a LEGO diffractometer are available. This model can help teach the mathematics and mechanics involved in diffraction techniques by using visible light from a pocket laser to probe a transparent plastic two-dimensional diffraction grating, Figure 4. The NXT system can be programmed to detect and graph the first-order diffracted light intensity as a function of diffraction angle, which can then be used to calculate the spacing of features on the grating. Electronic energy diagrams can be built with LEGO bricks. Phenomena such as d orbital splitting diagrams, semiconductor band diagrams, electron spin, and light absorption can be represented with bricks on a flat LEGO board. ’ CLASSROOM AND NON-CLASSROOM IMPACTS The goal of this site is to provide a repository of demonstration ideas for educators to add to science classrooms and other educational venues. The classroom impacts of these demonstrations have not yet been fully quantified, though the Web site has been referenced in various Web sites and publications. The 604
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authors have received numerous inquiries regarding demonstrations, especially SPM models. Even without active inquiries, the Web site is being used; for example, one of the authors encountered an advanced SPM LEGO model built from instructions posted on the site during a visit to an unaffiliated nanotechnology exposition. Simple SPM models have been used both as a hands-off demonstration in the classroom and as an activity to be performed in small groups at the middle school level.2 The LEGO model of the photometer has been made available for viewing during college chemistry laboratories involving spectrophotometers to give students a simplified view of the sourcesample-detector layout of the instruments. Noninstrument demonstrations have also been used both in and out of classrooms. The photolithography demonstration was tested in small groups at the middle school level. Simple atomiclevel models have been displayed at various science events. One way to present this activity is to give students two different colors of 2 peg 2 peg bricks and a flat base board, then challenge them to build a three-dimensional structure in which any two bricks of the same color cannot touch faces but bricks of different colors must be as close as possible. The inevitable result is the structure of sodium chloride. This activity can be followed by floating one color of these bricks peg-side down on water in plastic tubs and observing their spontaneous assembly into square arrays to produce two-dimensional crystals of LEGO bricks.2 In 2010, the Lakeview Museum of Arts and Sciences in Peoria, IL, featured a LEGO art exhibit by Nathan Sawaya called “The Art of the Brick”.6 This exhibit led to a collaborative public education effort. A workshop held at the museum provided elementary and middle school children with kits of LEGO bricks and non-LEGO components such as light sources, as well as training on how to build models such as those of solid state structures, spontaneous assembly, SPM, and Poisson’s ratios. Additionally, the mineral display at the museum was renovated to include atomic-level models of the structures of various minerals alongside real examples of the minerals. The models for the display were constructed by undergraduate students at an event held by the Bradley University chapter of the American Chemical Society.
’ LOOKING TO THE FUTURE Although the LEGO Group has not provided direct funding for this project, it has provided hard-to-find bricks, such as 1 peg 2 peg translucent bricks and magnetic bricks, for distribution to the public at chemistry education meetings and to those who have directly contacted the authors. As the magnetic brick supply has dwindled, the home-built alternative of gluing ceramic disk magnets to LEGO bricks has been explored. The challenge has been to find an adhesive that keeps the magnets glued to the bricks. The Web site continues to grow. Recently, the building instructions for many atomic-level models have been upgraded to include lists of the numbers and types of bricks required. Many other atomic-level models still need to be designed, including solid phases of some elements (to complete the aforementioned LEGO periodic table) and compounds such as rutile and pyrite. A recent success has been modeling fullerenes such as C60 and C70, using only the most basic LEGO bricks, in contrast to other models.26 These structures, as well as carbon nanotubes,27 can be constructed by stacking circles of carbon atoms. Small spacer bricks maintain correct atom connectivity in the fullerene models, but there is stress within the models and their construction
Figure 5. Model of a Si-CH2-CH2-Si cross-link in polydimethylsiloxane. Silicon atoms are yellow; oxygen atoms are red; carbon atoms are black; and hydrogen atoms are white.
should be approached with patience. The related carbon structure graphene, which has recently generated considerable press,28 can be easily modeled by constructing a single carbon layer from the LEGO graphite model. Polymers ranging from polyethylene to polydimethylsiloxane have been another recent focus of molecular model building, Figure 5. The challenge to build a model of the double helix structure of DNA, featuring the proper number of base pairs per complete twist in the helices, has been met by other builders.29 A quick perusal around the Internet will now yield a variety of SPM and other nanorelated LEGO models30 and many other science-related applications of these bricks.21 Model-building challenges that remain include instrumentation such as electron microscopy and plasmon resonance.31 The authors welcome your ideas and suggestions and are interested in possible collaborations.
’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected].
’ ACKNOWLEDGMENT The authors are grateful to the National Science Foundation, through the University of Wisconsin-Madison Materials Research Science and Engineering Center (MRSEC) for Nanostructured Materials and Interfaces (DMR-96325227), Bradley University, and to the LEGO Group for support of this project. The workshop and display at the Lakeview Museum were supported by funding from the Peoria Academy of Science and the Illinois Heartland Section of the American Chemical Society. We are also grateful for the many minds and hands that have helped us over the years. ’ REFERENCES (1) Campbell, D.; Freidinger, E.; Querns, M.; Swanson, S.; Ellis, A.; Kuech, T.; Payne, A.; Socie, B.; Condren, S. M.; Lisensky, G.; Rassmussen, R.; Hollis, T.; Villarreal, R. Exploring the Nanoworld with LEGO 605
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(31) Campbell, D. J.; Xia, Y. J. Chem. Educ. 2007, 84, 91–96.
Bricks; available online for download at http://mrsec.wisc.edu/Edetc/ LEGO (accessed Jan 2011). (2) Mongillo, J. F. Nanotechnology 101; Greenwood Press: Westport, CT, 2007. (3) Schooley, C. Microscopy Today 2009, 6, 64. (4) Greenberg, A. Integrating Nanoscience into the Classroom: Perspectives on Nanoscience Education Projects. ACS Nano 2009, 3, 762. (5) Diaz, J. LEGO Brick Timeline: 50 Years of Building Frenzy and Curiosities. http://gizmodo.com/349509/lego-brick-timeline-50years-of-building-frenzy-and-curiosities (accessed Jan 2011). (6) Sawaya, N. The Art of the Brick. http://brickartist.com/ (accessed Jan 2011). (7) Eric Harshbarger’s LEGO Web site. http://www.ericharshbarger.org/lego/ (accessed Jan 2011). (8) Ellis, A. B.; Geselbracht, M. J.; Johnson, B. J.; Lisensky; G. C.; Robinson, W. R. Teaching General Chemistry: A Materials Science Companion; American Chemical Society: Washington, DC, 1993. (9) Lorenz, J. K.; Olson, J. A.; Campbell, D. J.; Lisensky, G. C.; Ellis, A. B. J. Chem. Educ. 1997, 74, 1032A–1032B. (10) Ellis, A. B.; Kuech, T. F.; Lisensky, G. C.; Campbell, D. J.; Condren, S. M.; Nordell, K. J. J. Nanopart. Res. 1999, 1, 147–150. (11) Campbell, D. J.; Olson, J. A.; Calderon, C. E.; Doolan, P. W.; Mengelt, E. A.; Ellis, A. B.; Lisensky, G. C. J. Chem. Educ. 1999, 76, 1205–1211. (12) Hogan, H. “Thanks to an Optical Sensor, a Fourth R: Robotics.” Photonics Spectra Jan, 2009, 91. (13) Campbell, D. J.; Freidinger, E. R. Chem. Educator posted online May 2, 2003. (14) Knagge, K.; Raftery, D. Chem. Educator 2002, 7, 371–375. (15) Campbell, D. J.; Beckman, K. J.; Calderon, C. E.; Doolan, P. W.; Ottosen, R. M.; Ellis, A. B.; Lisensky, G. C. J. Chem. Educ. 1999, 76, 537–541. (16) Campbell, D. J.; Querns, M. K. J. Chem. Educ. 2002, 79, 76. (17) Campbell, D. J.; Kuech, T. F.; Lisensky, G. C.; Lorenz, J. K.; Whittingham, M. S.; Ellis, A. B. J. Chem. Educ. 1998, 75, 297–312. (18) Garvey, C. J.; Hammer, D. M.; Prasertchoung, S.; GomarNadal, E.; Hines, D. R.; Miller, J. D.; Campbell, D. J. Chem. Educator 2008, 13, 348–350. (19) Campbell, D. J.; Freidinger, E. R.; Querns, M. K. Chem. Educator 2001, 6, 321–323. (20) Campbell, D. J.; Freidinger, E. R.; Hastings, J. M.; Querns, M. K. Chem13 News Sep, 2001, 8-9. (21) Campbell, D. J.; Bailey, R. A. Chem13 News Feb, 2003, 4-5. (22) Freidinger, E. R.; Denk, R.; Campbell, D. J. Chem. Educato 2003, 8, 330–331. (23) Berger, P.; Adelman, N. B.; Beckman, K. J.; Campbell, D. J.; Ellis, A. B.; Lisensky, G. C. J. Chem. Educ. 1999, 76, 943–948. (24) Campbell, D. J.; Korte, K. E.; Xia, Y. J. Chem. Educ. 2007, 84, 1824–1826. (25) Campbell, D. J. Exploring Materials Science With LEGO Brick Models. In Communicating Materials Science—Education for the 21st Century; Baker, S., Goodchild, F., Crone, W., Rosevear, S., Eds.; (Mater. Res. Soc. Symp. Proc. 861E); Warrendale, PA, 2005), PP2.5. (26) The Brothers Brick. How to make a Buckminsterfullerene (and other fun shapes) from LEGO. http://www.brothers-brick.com/2008/ 01/25/how-to-make-a-buckminsterfullerene-and-other-fun-shapesfrom-lego/ (accessed Jan 2011). (27) Robinson, K. F.; Nguyen, P. N.; Applegren, N.; Campbell, D. J. Chem. Educator 2007, 12, 163–166. (28) Nobelprize.org. The 2010 Nobel Prize in Physics - Press Release. http://nobelprize.org/nobel_prizes/physics/laureates/2010/ press.html (accessed Jan 2011). (29) National Center for Biotechnology Education. A LEGO Model of DNA. http://www.ncbe.reading.ac.uk/dna50/lego.html (accessed Jan 2011). (30) For example, Nathan Unterman and Michael Falvo have done work in this area. 606
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