Chemical Education Today edited by
NSF Highlights
Susan H. Hixson
Projects Supported by the NSF Division of Undergraduate Education
National Science Foundation Arlington, VA 22230
Incorporating Scanning Probe Microscopy into the Undergraduate Chemistry Curriculum
Richard F. Jones Sinclair Community College Dayton, OH 45402-1460
by David W. Lehmpuhl
Nanotechnology is a ubiquitous word used to describe many processes and discoveries occurring at an atomic, molecular, or nanometer scale. Recently, the National Science Foundation established the National Nanotechnology Initiative, which emphasizes the importance of nanotechnology (1). The chemistry department at the University of Southern Colorado (to be called Colorado State University–Pueblo, July 1, 2003) has initiated a project with funding from the NSFCCLI program to help undergraduates obtain a firm foundation in a key component of nanotechnology, that of scanning probe microscopy. Scanning probe microscopy has been incorporated into the curriculum in three specific areas through demonstrations at the beginning and general chemistry level, a hands-on instrumental analysis experiment, and through undergraduate student research projects. The department purchased a Molecular Imaging Picoscan SPM (Tucson, AZ) with the capability to perform scanning tunneling microscopy (STM) as well as contact and alternating contact atomic force microscopy (AFM). In addition to the basic imaging modes, a liquid cell, a vibration isolation, and a controlled environment chamber were also purchased that provides a wide range of imaging options. Beginning or General Chemistry We chose to introduce students to scanning probe microscopy through the use of 15–20 minute demonstrations given to small (8–10) groups of students. The demonstrations were accomplished through coordination with the laboratory instructors. Days on which the scheduled laboratory was anticipated to be shorter than the allotted time (for instance during check-in) enabled the demonstrations to proceed without robbing students or faculty of valuable class time. This also enabled small, highly interactive demonstration sessions. The demonstrations began with a brief explanation of scanning probe microscopy, including STM and AFM. The students were shown the various components of the system and were encouraged to handle some tips and view them with an eyepiece to get an idea of the size of the cantilever and tip. The length of the demonstration did not allow enough time to collect an image and it was thought that showing the components of the system was more important. To teach students the capability of the system, two large posters were posted in the room with both AFM and STM images. The STM poster consisted of a series of images of highly oriented pyrolytic graphite (HOPG) starting at 1 µm and zooming in to 12 Å at which point carbon atoms are easily visible. A calculation showing students the relative size of a human hair next to the images gave them 478
sense of the size of atoms (i.e., a hair would be about 16 miles wide next to the 12 Å image). In their coursework students learn that graphitic carbon is hexagonal in nature, but the poster images show carbon atoms in a square arrangement. When asked some leading questions, students usually come up with the correct explanation of seeing two graphite layers. The AFM poster consisted of images of various substances including gold, mica, and glass imaged in the 50–500 nm scale, with the actual samples available for students to handle. Student learning was evaluated through the use of a short questionnaire administered early in the semester and readministered as an addition to the final. Student learning was evidenced by a significant increase in the number of students who could correctly draw a picture of a surface at the atomic level, who knew what AFM was, and who knew which surface—gold, mica, or glass—was flatter at an atomic level. Instrumental Analysis After an initial exposure to SPM in the general chemistry curriculum, chemistry majors return to the instrument in a hands-on experiment for the instrumental analysis laboratory. Students were given instructions but were required to set the instrument up themselves, including installing the probe, aligning the laser, preparing the sample, setting the software parameters, engaging the tip, and collecting multiple images. Post-image data analysis was completed using a separate software package (Visual SPM) provided by Molecular Imaging. Three contact-mode experiments were conducted in the first year over two, 3-hour class periods: studying glass coverslips before and after exposure to 2 M NaOH, studying the crystal structures of different salts, and imaging the formatted and unformatted portion of a floppy disc. The first two experiments were successful, but formatted and unformatted portions of a floppy disc revealed no difference visible via AFM. The NaOH etching resulted in visible pits developing in the surface of the coverslips after a 40-hour exposure (less exposure time would also likely have worked). In the second experiment, about 50 µL of 10–6 M salts were placed onto mica and air-dried. Striking differences in crystal formation were found for KNO 3 , CoCl 2 , and (NH4)2SO4. After completing the experiment, students were required to prepare a formal write-up as a PowerPoint presentation that was submitted electronically. The quality of the presentations were excellent. In future semesters it is hoped that more of an inquirybased approach can be used, but time constraints will necessitate some creativity. Students generally spent one entire class period setting the instrument up and collecting an image.
Journal of Chemical Education • Vol. 80 No. 5 May 2003 • JChemEd.chem.wisc.edu
Chemical Education Today
Requiring the class to design a set of experiments that can be performed on a particular topic with the results of the class compiled afterward would be beneficial in that it would allow some chemistry to be explored in the limited time available. Taking the glass-etching experiment as an example, students could study temperature, concentration of base or other etching agent, type of etching agent, rate of stirring, type of glass, etc. Undergraduate Student Research Student research is the third area of the curriculum in which scanning probe microscopy has been incorporated. We currently have in progress four undergraduate research projects involving the instrument. AFM is being used to study the surface of the fungus Pennicillium fellutanum for which the preliminary work was incorporated into a NIH grant that was recently funded. Another project is theoretically based in which a student is modeling AFM tip-sample interactions with Mathematica. A third project is looking at carbon particles, and a fourth is in conjunction with a faculty member from an engineering department in which the students are building an STM and comparing their results with those from the Molecular Imaging STM. Conclusion Scanning probe microscopy has been successfully incorporated into many facets of the undergraduate
curriculum, including general chemistry, instrumental analysis, and undergraduate research. More than 150 undergraduate students have been given a demonstration of the instrument, and 13 upper-level students are proficient in using it after the first year of the project. Three faculty members have been trained and the instrument is now being used beyond the chemistry curriculum. Undergraduate research results have been used to successfully obtain funding and have been presented at national and regional meetings. An experiment to correlate protein size and shape with function and molecular weight is under development for incorporation into the biochemistry laboratory during the spring 2003 semester. Acknowledgment Partial support for this work was provided by the National Science Foundation’s Course, Curriculum and Laboratory Improvement Program under grant DUE 0087833. Literature Cited 1. National Science Foundation National Nanotechnology Initiative, http://www.nano.gov/start.htm (accessed Nov 2002).
David W. Lehmpuhl teaches at the University of Southern Colorado, 2200 Bonforte Boulevard, Pueblo, CO 81001-4901;
[email protected].
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