Surface chemical reactions are critically important to a number of high-impact technologies including catalysts for fuels production and pollution prevention, and fabrication of solar cells and microelectronics. One could control these reactions better if one understood how these energies correlate with surface structure. In this award, funded by the Chemical Structure, Dynamics, and Mechanisms and Chemical Measurement and Imaging Programs of the Division of Chemistry, Professor Campbell will measure the energies of surface chemical reactions. His laboratory has developed microcalorimetry tools that allow the study of single crystal surfaces, which will be employed to measure the energies of a variety of surface species of importance in the design of better catalysts, solar cells and microelectronics, and correlated with atomic-level structural details. This will provide a deeper understanding of the relationships between surface chemical reactivity and structure. These energies also will provide important benchmarks for testing the accuracy of new theoretical/computational methods.
This work will also provide strong interdisciplinary, research-based education for many graduate and undergraduate students and postdocs. They will get hands-on experience with state-of-the-art research instrumentation and its design, and ample opportunities for international collaborations and interactions at national laboratories. They will be mentored in scientific leadership, public speaking and responsible conduct of research.
Chemical reactions that occur on solid surfaces are critically important in the production of clean fuels and chemicals using solid catalysts, in the catalytic clean-up of the pollutants generated by their use, and in the fabrication of solar cells and microelectronics. Understanding how to control those reactions would enable improvements that would benefit these technologies immensely. This in turn would benefit the environmental and energy outlook for the future. Chemists know that to control such reactions, one must know how the energies of the chemical intermediates involved (in this case, the atoms and molecular fragments adsorbed on the solid surfaces) depend upon the solid material used and the atomic-level details of its surface’s structure. In this research project, the energies of these chemical intermediates have been measured on several well-defined surfaces, and the results have elucidated how these energies depend on the atomic-level details of surface structure. In particular, the energies of adsorbed reaction intermediates have been measured on model platinum catalysts to understand fuels- and environmental-related catalytic reactions, and the energies of key intermediates formed during solar cell fabrication have been measured at well-defined interfaces between semiconducting polymers and the metal films grown on these polymers, in order to model the processes that occur when producing polymer thin-film solar cells. Platinum-group metals are used in many important catalytic reactions for the production of fuels and bulk chemicals and for pollution clean-up (as in automotive catalytic converters). Some of the most common surface intermediates in these reactions fall into eight classes of molecular fragments: primary, secondary and tertiary alkyls, carbenes, carbynes, hydroxyl, alkoxyls, carbonates. The energies of the simplest examples of seven of these classes of adsorbates (namely -CH3, -C(CH3)3, -CH2, -CH, -OH, -OCH3, -OOCH) were measured on the most common surface of clean platinum, its hexagonal closest-packed face. This is the first time the energies of any of these species have been measured on any surface. These energies provide tremendous insights into catalysts by platinum, and the mechanisms of the reactions it catalyzes. In making solar cells and light-emitting panels based on thin films of semiconducting polymers, a crucial part of the process is growing the appropriate metal electrode film onto that polymer’s surface. This metal/polymer interface controls device efficiency and lifetime. The structure and bonding energetics of several such metal/polymer interfaces were studied in detail. It was found that vapor deposition of low work-function metals (Ca and Li) onto polymers that contain heteroatoms (i.e., S, O or N) at room temperature generally produces a chemically and structurally complex interface: metal atoms diffuse into the polymer and undergo chemical reactions with the heteroatoms in the polymer which completely destroy its electronic character down to a depth of ~3 nm. Only after this does it grow the desired metal film. Since these reactions affect the electronic properties of the interface, which in turn control device performance, it is desirable to suppress them, so that the interface is more abrupt. To this end, it was discovered that low-temperature deposition significantly reduces the thickness of the reaction zone between metal and polymer, limiting its thickness to a single atomic layer. This improves the ability to control device performance, or at least to measure device performance for well-defined interface structures, so that relationships between interface structure and device performance can be discovered. Under previous funding from the National Science Foundation, this research laboratory developed the most powerful capabilities in the world for measuring the energies of surface chemical reactions. This unique instrumentation has been applied in making these measurements, and the results are of the type that cannot be measured anywhere else in the world, yet are recognized as being highly important for research progress in these areas. As a consequence, the principal investigator was invited to give 34 talks at scientific meetings (including nine at international conferences) and sixteen seminars at universities. He was recognized for the importance of these research contributions by receiving the Gerhard Ertl Lecture Award for 2012 and the Robert Burwell Award of the North American Catalysis Society (2013-4) and by his appointment as Editor-in-Chief of Surface Science Reports (the highest-impact journal in the world that focuses on surfaces or interfaces) and to the Editorial Boards or Scientific Advisory Boards for six other journals. This grant also provided strong interdisciplinary, research-based education for nine graduate students (two females) and one postdoc (female), as well as intensive research experiences for seven undergraduate students (3 females). These students get hands-on experience with state-of-the-art research instrumentation and its development, and learn to apply the skills to solve exciting research problems. Three graduate students spent a total of twelve months in the labs of international collaborators and scientists at national laboratories. The grant also enabled extensive outreach and public speaking on science topics by the principal investigator and students involved.
