|
The U.S. Department of Commerce has identified a list of 12 "emerging technologies" projected to have a combined economic impact of $1 trillion by the year 2000 (1). Of these areas, eight are critically dependent on the ability to design and characterize the chemistry of surfaces: advanced materials, superconductors, semiconductor devices, high-density data storage media, optoelectronics, sensor technology, biotechnology, and biomedical devices. However, the modification and subsequent examination of surfaces is rarely attempted in undergraduate chemistry courses.
Our work involves using the technique of scanning tunneling microscopy (STM) to examine electrode surfaces before and after modification. Such experiments have now been implemented in three different areas of our teaching enterprise at Duke University: as an experiment in our upper-level analytical chemistry laboratory course, as part of a research project conducted by an undergraduate student as part of an NSF-sponsored summer REU program, and as an investigation undertaken by a local high school student over the course of two summers as a participant in the American Chemical Society Project SEED. The latter two projects will be discussed here, and it is our intention to submit a more detailed account of the undergraduate experiment for later puThe U.S. Department of Commerce has identified a list of 12 "emerging technologies" projected to have a combined economic impact of $1 trillion by the year 2000 (1). Of these areas, eight are critically dependent on the ability to design and characterize the chemistry of surfaces: advanced materials, superconductors, semiconductor devices, high-density data storage media, optoelectronics, sensor technology, biotechnology, and biomedical devices. However, the modification and subsequent examination of surfaces is rarely attempted in undergraduate chemistry courses.
Our work involves using the technique of scanning tunneling microscopy (STM) to examine electrode surfaces before and after modification. Such experiments have now been implemented in three different areas of our teaching enterprise at Duke University: as an experiment in our upper-level analytical chemistry laboratory course, as part of a research project conducted by an undergraduate student as part of an NSF-sponsored summer REU program, and as an investigation undertaken by a local high school student over the course of two summers as a participant in the American Chemical Society Project SEED. The latter two projects will be discussed here, and it is our intention to submit a more detailed account of the undergraduate experiment for later publication.
Procedure
In both student projects a Burleigh Instruments ARIS-2200E STM was employed to image polycrystalline gold electrodes before and after deposition of a second metal onto the surface. Students prepared their own tungsten STM tips using an A.C.-etching procedure in 5% NaNO2. The electrodes used were available commercailly (AAI-AbTech, Yardley, PA) and consisted of 1000 of Au over a 100 adhesion layer of Ti on electronics-grade borosilicate glass. Electrodes were affixed to the STM sample holder using conductive carbon tape (SPI, West Chester, PA) and imaged in air. Modified electrodes were prepared by sonochemical deposition of 300 nm-Cu particles onto the Au surface in a procedure described elsewhere (2) or by the electrolytic deposition of various metals used in dental amalgams from acidic media using a Cypress Systems CS-1087 potentiostat.
Results
In a typical image obtained for an unmodified Au surface (see image below), small crystallites (~500 to 1000 in diameter) of Au formed during the sputtering process during electrode fabrication are clearly visible. Images of modified electrodes (not shown) always show a markedly different morphology, with visible characteristic surface features ranging in size from hundreds of nanometers to several microns.
 Click here to see larger jpeg of figure
The concepts students learn in these studies include electron tunneling, electroplating, nucleation phenomena, and amalgam chemistry. Although primarily touted as a method for atomic resolution imaging, STM clearly has utility for examining surfaces with features in the 100-nm to 1-micrometer size regime. Because of the recent availability of inexpensive instruments with user-friendly software, we encourage others to consider incorporating STM into the undergraduate curriculum.
Acknowledgment
This project was supported partially by a grant, DUE-9351426, from the National Science Foundation Division of Undergraduate Education Instrumentation and Laboratory Improvement Program.
Literature Cited
- Lederman, L. Science 1991, 251, 1S--20S.
- Madigan, N. A.; Murphy, T. J.; Fortune, J. M.; Hagan, C. R. S.; Coury, L. A. submitted.
blication.
Procedure
In both student projects a Burleigh Instruments ARIS-2200E STM was employed to image polycrystalline gold electrodes before and after deposition of a second metal onto the surface. Students prepared their own tungsten STM tips using an A.C.-etching procedure in 5% NaNO2. The electrodes used were available commercailly (AAI-AbTech, Yardley, PA) and consisted of 1000 of Au over a 100 adhesion layer of Ti on electronics-grade borosilicate glass. Electrodes were affixed to the STM sample holder using conductive carbon tape (SPI, West Chester, PA) and imaged in air. Modified electrodes were prepared by sonochemical deposition of 300 nm-Cu particles onto the Au surface in a procedure described elsewhere (2) or by the electrolytic deposition of various metals used in dental amalgams from acidic media using a Cypress Systems CS-1087 potentiostat.
Results
In a typical image obtained for an unmodified Au surface (see image below), small crystallites (~500 to 1000 in diameter) of Au formed during the sputtering process during electrode fabrication are clearly visible. Images of modified electrodes (not shown) always show a markedly different morphology, with visible characteristic surface features ranging in size from hundreds of nanometers to several microns.
Click here to see larger jpeg of figure
The concepts students learn in these studies include electron tunneling, electroplating, nucleation phenomena, and amalgam chemistry. Although primarily touted as a method for atomic resolution imaging, STM clearly has utility for examining surfaces with features in the 100-nm to 1-micrometer size regime. Because of the recent availability of inexpensive instruments with user-friendly software, we encourage others to consider incorporating STM into the undergraduate curriculum.
Acknowledgment
This project was supported partially by a grant, DUE-9351426, from the National Science Foundation Division of Undergraduate Education Instrumentation and Laboratory Improvement Program.
Literature Cited
- Lederman, L. Science 1991, 251, 1S--20S.
- Madigan, N. A.; Murphy, T. J.; Fortune, J. M.; Hagan, C. R. S.; Coury, L. A. submitted.
|
Citation
